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Aims: Previous investigations demonstrated that tramadol, as a painkiller, similar to morphine induces tolerance and dependence. Furthermore, the cannabinoid receptor 1 (CB1R) located in the nucleus accumbens (NAc) plays a critical role in morphine-induced conditioning. Therefore, the main objective of this study was to evaluate the role of NAc CB1R in tramadol induced conditioning and reinstatement., Main Methods: In the present experiment, the effect of NAc CB1 receptors on tramadol induced conditioning was tested by microinjecting of arachidonylcyclopropylamide (ACPA, CB1R agonist) and AM 251 (CB1R inverse agonist) in the NAc during tramadol-induced conditioning in the adult male Wistar rats. In addition, the role of NAc CB1R in the reinstatement was also evaluated by injecting ACPA and AM 251 after a 10-days extinction period., Key Findings: The obtained data revealed that the administration of tramadol (1,2, and 4 mg/kg, ip) dose-dependently produced conditioned place preference (CPP). Moreover, intra-NAc administration of ACPA (0.25, 0.5, and 1 μg/rat) dose-dependently induced conditioning, while the administration of AM-251 (30, 60, and 120 ng/rat) induced a significant aversion. In addition, the administration of a non-effective dose of AM251 during tramadol conditioning inhibited conditioning induced by tramadol. On the other hand, the administration of ACPA after extinction induced a significant reinstatement. Notably, the locomotor activity did not change among groups., Significance: Previous studies have shown that tramadol-induced CPP occurs through μ-opioid receptors. The data obtained in the current study indicated that CB1R located in the NAc is involved in mediating conditioning induced by tramadol. Besides, CB1R also plays a vital role in the reinstatement of tramadol-conditioned animals. It might be due to the effect of opioids on enhancing the level of CB1R., (Copyright © 2020. Published by Elsevier Inc.)

Accounts regarding the use of novel psychoactive substances continue to escalate annually. These include reports on substituted benzofurans (SBs), such as 1-(1-benzofuran-2-yl)-N-ethylpropan-2-amine (2-EAPB) and 1-(1-benzofuran-5-yl)-N-ethylpropan-2-amine (5-EAPB). Reports on the deaths and adverse consequences from the use of SBs warrant the investigation of their mechanism, possibly predicting the effects of similar compounds. Accordingly, we investigated the possible rewarding and reinforcing effects of 2-EAPB and 5-EAPB through conditioned place preference (CPP), self-administration, and locomotor sensitization tests. We also determined the possible influence of 2-EAPB and 5-EAPB administration on dopamine- and plasticity-related proteins in the nucleus accumbens and ventral tegmental area. 2-EAPB and 5-EAPB induced CPP at different doses and were self-administered by rats. Only 5-EAPB induced locomotor sensitization in mice. 2-EAPB and 5-EAPB did not alter the expressions of dopamine D1 and D2 receptors in the nucleus accumbens, nor changed tyrosine hydroxylase and dopamine transporter expressions in the ventral tegmental area. Both 2-EAPB and 5-EAPB enhanced deltaFosB, but not transcription factor cyclic AMP-response-element binding protein and brain-derived neurotrophic factor in the nucleus accumbens. Hence, the potential rewarding and reinforcing effects on rodents induced by 2-EAPB and 5-EAPB may possibly be associated with alterations in other neurotransmitter systems (besides mesolimbic) and/or neuro-plastic modifications., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Major depressive disorder is typically treated with selective serotonin reuptake inhibitors (SSRIs), however, SSRIs take approximately six weeks to produce therapeutic effects, if any. Not surprisingly, there has been great interest in findings that low doses of ketamine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, produce rapid and long-lasting antidepressant effects. Preclinical studies show that the antidepressant-like effects of ketamine are dependent upon availability of serotonin, and that ketamine increases extracellular serotonin, yet the mechanism by which this occurs is unknown. Here we examined the role of the high-affinity, low-capacity serotonin transporter (SERT), and the plasma membrane monoamine transporter (PMAT), a low-affinity, high-capacity transporter for serotonin, as mechanisms contributing to ketamine's ability to increase extracellular serotonin and produce antidepressant-like effects. Using high-speed chronoamperometry to measure real-time clearance of serotonin from CA3 region of hippocampus in vivo, we found ketamine robustly inhibited serotonin clearance in wild-type mice, an effect that was lost in mice constitutively lacking SERT or PMAT. As expected, in wild-type mice, ketamine produced antidepressant-like effects in the forced swim test. Mapping onto our neurochemical findings, the antidepressant-like effects of ketamine were lost in mice lacking SERT or PMAT. Future research is needed to understand how constitutive loss of either SERT or PMAT, and compensation that occurs in other systems, is sufficient to void ketamine of its ability to inhibit serotonin clearance and produce antidepressant-like effects. Taken together with existing literature, a critical role for serotonin, and its inhibition of uptake via SERT and PMAT, cannot be ruled out as important contributing factors to ketamine's antidepressant mechanism of action. Combined with what is already known about ketamine's action at NMDA receptors, these studies help lead the way to the development of drugs that lack ketamine's abuse potential but have superior efficacy in treating depression.

Rationale: The rate of cannabinoid intake by those with alcohol use disorder (AUD) exceeds that of the general public. The high prevalence of co-abuse of alcohol and cannabis has been postulated to be predicated upon both a common predisposing genetic factor and the interaction of the drugs within the organism. The current experiments examined the effects of cannabinoids in an animal model of AUD., Objectives: The present study assessed the reinforcing properties of a cannabinoid receptor 1 (CB1) agonist self-administered directly into the nucleus accumbens shell (AcbSh) in female Wistar and alcohol-preferring (P) rats., Methods: Following guide cannulae surgery aimed at AcbSh, subjects were placed in an operant box equipped with an 'active lever' (fixed ratio 1; FR1) that caused the delivery of the infusate and an 'inactive lever' that did not. Subjects were arbitrarily assigned to one of seven groups that self-administered either artificial cerebrospinal fluid (aCSF), or 3.125, 6.25, 12.5, or 25 pmol/100 nl of O-1057, a water-soluble CB1 agonist, dissolved in aCSF. The first four sessions of acquisition are followed by aCSF only infusates in sessions 5 and 6 during extinction, and finally the acquisition dose of infusate during session 7 as reinstatement., Results: The CB1 agonist was self-administered directly into the AcbSh. P rats self-administered the CB1 agonist at lower concentrations and at higher rates compared to Wistar rats., Conclusions: Overall, the data indicate selective breeding for high alcohol preference has produced rats divergent in response to cannabinoids within the brain reward pathway. The data support the hypothesis that there can be common genetic factors influencing drug addiction., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Cocaine-associated memories are critical drivers of relapse in cocaine-dependent individuals that can be evoked by exposure to cocaine or stress. Whether these environmental stimuli recruit similar molecular and circuit-level mechanisms to promote relapse remains largely unknown. Here, using cocaine- and stress-primed reinstatement of cocaine conditioned place preference to model drug-associated memories, we find that cocaine drives reinstatement by increasing the duration that mice spend in the previously cocaine-paired context whereas stress increases the number of entries into this context. Importantly, both forms of reinstatement require Ca v 1.2 L-type Ca 2+ channels (LTCCs) in cells of the prelimbic cortex that project to the nucleus accumbens core (PrL→NAcC). Utilizing fiber photometry to measure circuit activity in vivo in conjunction with the LTCC blocker, isradipine, we find that LTCCs drive differential recruitment of the PrL→ NAcC pathway during cocaine- and stress-primed reinstatement. While cocaine selectively activates PrL→NAcC cells prior to entry into the cocaine-paired chamber, a measure that is predictive of duration in that chamber, stress increases persistent activity of this projection, which correlates with entries into the cocaine-paired chamber. Using projection-specific chemogenetic manipulations, we show that PrL→NAcC activity is required for both cocaine- and stress-primed reinstatement, and that activation of this projection in Ca v 1.2-deficient mice restores reinstatement. These data indicate that LTCCs are a common mediator of cocaine- and stress-primed reinstatement. However, they engage different patterns of behavior and PrL→NAcC projection activity depending on the environmental stimuli. These findings establish a framework to further study how different environmental experiences can drive relapse, and supports further exploration of isradipine, an FDA-approved LTCC blocker, as a potential therapeutic for the prevention of relapse in cocaine-dependent individuals.

Substance abuse disorders are linked to alteration of circadian rhythms, although the molecular and neuronal pathways implicated have not been fully elucidated. Addictive drugs, such as cocaine, induce a rapid increase of dopamine levels in the brain. Here, we show that acute administration of cocaine triggers reprogramming in circadian gene expression in the striatum, an area involved in psychomotor and rewarding effects of drugs. This process involves the activation of peroxisome protein activator receptor gamma (PPARγ), a nuclear receptor involved in inflammatory responses. PPARγ reprogramming is altered in mice with cell-specific ablation of the dopamine D2 receptor (D2R) in the striatal medium spiny neurons (MSNs) (iMSN-D2RKO). Administration of a specific PPARγ agonist in iMSN-D2RKO mice elicits substantial rescue of cocaine-dependent control of circadian genes. These findings have potential implications for development of strategies to treat substance abuse disorders.

Smoking during adolescence may increase the likelihood to develop nicotine dependence and to abuse other drugs such as cocaine. Despite great efforts to understand underlying neurobiological mechanisms of this progression, less attention has been paid to the role of genetic factors. Here, we investigated the influence of both genetic background and age at first nicotine exposure in the long-lasting effects on mesolimbic dopamine transmission including the increased cocaine-rewarding effect. Mid-adolescent and adult rats of inbred strains Lewis (addiction prone) and Fischer 344 (addiction resistant) were administered nicotine (0.4 mg/kg) or vehicle once daily for 5 days. Changes in dopamine transmission were investigated by in vivo microdialysis and electrophysiology after 30 days of withdrawal, whereas changes in cocaine-rewarding effect were assessed via conditioned place preference paradigm. Nicotine pre-exposure differentially changed mesolimbic dopamine transmission depending on strain and age of pre-exposure. A potentiation of dopamine response to nicotine was observed in nucleus accumbens (NAc) core of both strains and age groups, whereas dopamine response in NAc shell was enhanced exclusively in Lewis rats exposed to nicotine during adolescence. A similar response was observed following cocaine challenge at adulthood. Changes in VTA dopamine cell population and activity were observed only in adolescent nicotine-pretreated Lewis rats, which also showed an increased cocaine-rewarding effect at adulthood. These results highlight the influence of genetic background in the long-lasting effects of nicotine exposure and suggest that exposure during adolescence might increase nicotine and cocaine-rewarding properties in genetically vulnerable individuals, thereby facilitating progression toward dependence., (© 2019 Society for the Study of Addiction.)

Cocaine addiction is a chronic relapsing brain disorder characterized by compulsive drug seeking. Preliminary study suggested that bromodomain-containing protein 4 (BRD4), an epigenetic reader protein, participates in cocaine-induced reward and neuroplasticity. However, the exact role of BRD4 in cocaine addiction, particularly cocaine relapse, remains elusive. In this study, we found that BRD4 phosphorylation in the nucleus accumbens (NAc) was closely related to the maintenance of cocaine reinforcement and relapse in different cocaine exposure paradigms. Cocaine significantly increased the binding of phosphorylated BRD4 (pBRD4) at the promoter of Gria2 and Bdnf genes in the NAc. (+)JQ1, a selective BRD4 inhibitor, markedly reduced the reinforcement and reinstatement of cocaine-seeking behaviors, which was accompanied by the decreased expressions of GRIA2 and BDNF. Furthermore, chromatin immunoprecipitation assay showed that (+)JQ1 clearly attenuated cocaine-enhanced binding of pBRD4 at the promotor of Gria2 and Bdnf genes. Blockade of casein kinase II significantly attenuated BRD4 phosphorylation and cocaine relapse-like behaviors, suggesting the important role of pBRD4 in modulating cocaine effect. Together, our findings suggest that BRD4 phosphorylation in the NAc modulates multiple addiction-related behaviors of cocaine and particularly relapse to cocaine-seeking behaviors. Inhibition of BRD4 activity may be a novel target against cocaine addiction and relapse., (© 2019 Society for the Study of Addiction.)

Ultrasound stimulation is an emerging noninvasive option in treating neuropsychiatric disorders. The present study investigates the behavioral alterations resulting from ultrasound stimulation on the nucleus accumbens (NAc) in freely moving mice. Our results show that an acute ultrasound stimulation on the NAc, rather than the visual cortex or auditory cortex, led to a pronounced avoidance behavior, while repeated NAc ultrasound stimulation resulted in an obvious conditioned place aversion with changes in synaptic protein (GluA1/2 subunit) expression. Notably, NAc ultrasound stimulation suppressed the morphine-induced conditioned place preference. The results provide evidence that NAc ultrasound stimulation can be applied as a potential noninvasive therapeutic option in treating psychiatric disorders.

Carisoprodol (Soma®) is a centrally-acting skeletal-muscle relaxant frequently prescribed for treatment of acute musculoskeletal conditions. Carisoprodol's mechanism of action is unclear and is often ascribed to that of its active metabolite, meprobamate. The purpose of this study was to ascertain whether carisoprodol directly produces behavioral effects, or whether metabolism to meprobamate via cytochrome P450 (CYP450) enzymatic reaction is necessary. Rats were trained to discriminate carisoprodol (100 mg/kg) to assess time course and whether a CYP450 inhibitor (cimetidine) administered for 4 days would alter the discriminative effects of carisoprodol. Additionally, pharmacokinetics of carisoprodol and meprobamate with and without co-administration of cimetidine were assessed via in vivo microdialysis combined with liquid-chromatography-tandem mass spectrometry from blood and nucleus accumbens (NAc). The time course of the discriminative-stimulus effects of carisoprodol closely matched the time course of the levels of carisoprodol in blood and NAc, but did not match the time course of meprobamate. Administration of cimetidine increased levels of carisoprodol and decreased levels of meprobamate consistent with its interfering with metabolism of carisoprodol to meprobamate. However, cimetidine failed to alter the discriminative-stimulus effects of carisoprodol. Carisoprodol penetrated into brain tissue and directly produced behavioral effects without being metabolized to meprobamate. These findings indicate that understanding the mechanism of action of carisoprodol independently of meprobamate will be necessary to determine the validity of its clinical uses., Competing Interests: Declaration of conflicting interests The authors declare no potential conflicts of interest with respect to the research, authorship, or publication of this article., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Alcohol use disorder (AUD) is detrimental to health and causes preterm death. Unfortunately, available pharmacological and nonpharmacological treatments have small effect sizes, and improved treatments are needed. Smoking and AUD share heritability and are pharmacologically associated, since drug-induced dopamine (DA) output in nucleus accumbens (nAc) involves nicotinic acetylcholine receptors (nAChRs) in both cases. Smoking therapy agents, such as the partial nAChR agonist varenicline or the DA/noradrenaline transporter inhibitor bupropion, could potentially also be used for AUD. To investigate this hypothesis, the effects of varenicline, bupropion, or a combination of the two on nAc DA levels, ethanol intake, and the alcohol deprivation effect (ADE) were examined. In vivo microdialysis showed that varenicline (1.5 mg/kg) and bupropion (2.5, 5, or 10 mg/kg) elevated nAc DA levels and that the combination produced additive effects. Five days treatment with varenicline, bupropion, or the combination did not suppress ethanol consumption, as compared with vehicle-treated control. However, combined administration of varenicline and bupropion completely blocked the ADE when readministering ethanol following 14 days of abstinence. Since ADE is considered highly predictive for the clinical outcome in man, our data suggest that the combination of varenicline and bupropion could be a promising treatment for AUD., (© 2019 Society for the Study of Addiction.)

Background: Recently, the recreational use of substituted phenethylamines has grown rapidly. Among these are 2-(3,5-dimethoxy-4-((2-methylallyl)oxy)phenyl)ethanamine (MAL) and 2-(2,5-dimethoxy-4-methylphenyl)-2-methoxyethan-1-amine (BOD). However, studies characterizing their abuse potential are still lacking., Aim: The purpose of this study was to investigate the abuse potential of MAL and BOD., Methods: The psychostimulant, reinforcing, and rewarding properties of MAL and BOD were analyzed using locomotor sensitization, self-administration, and conditioned place preference tests. Dopamine antagonists (i.e. SCH23390, haloperidol) were administered during conditioned place preference to evaluate the involvement of the mesolimbic dopamine system. Furthermore, dopamine-related protein expression in the nucleus accumbens and the ventral tegmental area was measured along with dopamine concentrations in the nucleus accumbens. Electroencephalography was conducted to determine effects of MAL and BOD on brain wave activity., Results: MAL induced psychostimulant effects and sensitization, while BOD induced locomotor depression in mice. Only MAL was self-administered by rats. Both drugs induced conditioned place preference in mice at different doses; dopamine receptor antagonists blocked MAL- and BOD-induced conditioned place preference. Both the compounds altered the expression of dopamine receptor D 1 and D 2 proteins in the nucleus accumbens and tyrosine hydroxylase (TH) and dopamine transporter in the ventral tegmental area, enhanced dopamine levels in the nucleus accumbens, and increased delta and gamma wave activities in the brain., Conclusions: MAL may induce abuse potential via the mesolimbic dopaminergic system and possibly accompanied by alterations in brain wave activity. Moreover, the lack of rewarding and reinforcing effects in BOD suggest that this drug may have little to no capability to engender compulsive behavior, though having found to induce alterations in dopaminergic system and brain wave activities.

Rationale: Cancer patients receiving the antineoplastic drug paclitaxel report higher incidences and longer duration of treatment-resistant depression than patients receiving other classes of chemotherapeutics. Rodents treated with paclitaxel exhibit a suite of changes in affect-like behaviors. Further, paclitaxel causes chemotherapy-induced peripheral neuropathy (CIPN) in humans and rodents. Kappa opioid receptors (KOR) have a well-established role in depression and neuropathy. The contributions of KOR signaling to paclitaxel-induced aversive-like state and CIPN in rodents remain to be explored., Objectives: We aimed to investigate whether dysregulation of the KOR/dynorphin system is associated with paclitaxel-mediated pain-like behavior and depression-like behavior., Methods: Cancer-free male C57BL/6J mice were treated with four injections of vehicle or paclitaxel (32 mg/kg cumulative). The effects of the selective KOR antagonist norbinaltorphimine (norBNI) on paclitaxel-induced sucrose preference deficits and mechanical hypersensitivity were measured. Prodynorphin mRNA and receptor-mediated G protein activation were measured at two time points following the last paclitaxel injection using quantitative real-time polymerase chain reaction and agonist-stimulated [ 35 S]guanosine-5'-O'-(γ-thio)-triphosphate ([ 35 S]GTPγS) binding, respectively, in the nucleus accumbens (NAc), caudate-putamen, amygdala, and spinal cord., Results: Paclitaxel produced a norBNI-reversible sucrose preference deficit, whereas mechanical hypersensitivity was not reversed by norBNI. Paclitaxel treatment increased the levels of mRNA for prodynorphin, a precursor for endogenous KOR agonists, in the NAc. Paclitaxel also had time-dependent effects on KOR-mediated G protein activation in the NAc., Conclusions: These results suggest that KOR signaling mediates an initial aversive component of paclitaxel, but not necessarily paclitaxel-induced mechanical hypersensitivity.

Nicotine self-administration is associated with decreased expression of the glial glutamate transporter (GLT-1) and the cystine-glutamate exchange protein xCT within the nucleus accumbens core (NAcore). N-acetylcysteine (NAC) has been shown to restore these proteins in a rodent model of drug addiction and relapse. However, the specific molecular mechanisms driving its inhibitory effects on cue-induced nicotine reinstatement are unknown. Here, we confirm that extinction of nicotine-seeking behavior is associated with impaired NAcore GLT-1 function and expression and demonstrates that reinstatement of nicotine seeking rapidly enhances membrane fraction GLT-1 expression. Extinction and cue-induced reinstatement of nicotine seeking was also associated with increased tumor necrosis factor alpha (TNFα) and decreased glial fibrillary acidic protein (GFAP) expression in the NAcore. NAC treatment (100 mg/kg/day, i.p., for 5 d) inhibited cue-induced nicotine seeking and suppressed AMPA to NMDA current ratios, suggesting that NAC reduces NAcore postsynaptic excitability. In separate experiments, rats received NAC and an antisense vivo-morpholino to selectively suppress GLT-1 expression in the NAcore during extinction and were subsequently tested for cue-induced reinstatement of nicotine seeking. NAC treatment rescued NAcore GLT-1 expression and attenuated cue-induced nicotine seeking, which was blocked by GLT-1 antisense. NAC also reduced TNFα expression in the NAcore. Viral manipulation of the NF-κB pathway, which is downstream of TNFα, revealed that cue-induced nicotine seeking is regulated by NF-κB pathway signaling in the NAcore independent of GLT-1 expression. Ultimately, these results are the first to show that immunomodulatory mechanisms may regulate known nicotine-induced alterations in glutamatergic plasticity that mediate cue-induced nicotine-seeking behavior., (© 2019 Society for the Study of Addiction.)

Rationale: Caveolin-1 (CAV1) is a structural protein critical for spatial organization of neuronal signaling molecules. Whether CAV1 is required for long-lasting neuronal plasticity remains unknown., Objective and Methods: We sought to examine the effects of CAV1 knockout (KO) on functional plasticity and hypothesized that CAV1 deficiency would impact drug-induced long-term plasticity in the nucleus accumbens (NAc). We first examined cell morphology of NAc medium spiny neurons in a striatal/cortical co-culture system before moving in vivo to study effects of CAV1 KO on cocaine-induced plasticity. Whole-cell patch-clamp recordings were performed to determine effects of chronic cocaine (15 mg/kg) on medium spiny neuron excitability. To test for deficits in behavioral plasticity, we examined the effect of CAV1 KO on locomotor sensitization., Results: Disruption of CAV1 expression leads to baseline differences in medium spiny neuron (MSN) structural morphology, such that MSNs derived from CAV1 KO animals have increased dendritic arborization when cultured with cortical neurons. The effect was dependent on phospholipase C and cell-type intrinsic loss of CAV1. Slice recordings of nucleus accumbens shell MSNs revealed that CAV1 deficiency produces a loss of neuronal plasticity. Specifically, cocaine-induced firing rate depression was absent in CAV1 KO animals, whereas baseline electrophysiological properties were similar. This was reflected by a loss of cocaine-mediated behavioral sensitization in CAV1 KO animals, with unaffected baseline locomotor responsiveness., Conclusions: This study highlights a critical role for nucleus accumbens CAV1 in plasticity related to the administration of drugs of abuse.

Rationale: Effort-based decision-making tasks allow animals to choose between preferred reinforcers that require high effort to obtain vs. low-effort/low reward options. Mesolimbic dopamine (DA) and related neural systems regulate effort-based choice. Tetrabenazine (TBZ) is a vesicular monoamine transport type-2 inhibitor that blocks DA storage and depletes DA. In humans, TBZ induces motivational dysfunction and depression. TBZ has been shown reliably to induce a low-effort bias in rats, but there are fewer mouse studies., Objectives: The present studies used touchscreen operant procedures (Bussey-Saksida chambers) to assess the effects of TBZ on effort-based choice in mice., Methods: C57BL6 mice were trained to press an elevated lit panel on the touchscreen on a fixed ratio 1 schedule reinforced by strawberry milkshake, vs. approaching and consuming a concurrently available but less preferred food pellets (Bio-serv)., Results: TBZ (2.0-8.0 mg/kg IP) shifted choice, producing a dose-related decrease in panel pressing but an increase in pellet intake. In contrast, reinforcer devaluation by pre-feeding substantially decreased both panel pressing and pellet intake. In free-feeding choice tests, mice strongly preferred the milkshake vs. the pellets, and TBZ had no effect on milkshake intake or preference, indicating that the TBZ-induced low-effort bias was not due to changes in primary food motivation or preference. TBZ significantly decreased tissue levels of nucleus accumbens DA., Conclusion: The DA depleting agent TBZ induced an effort-related motivational dysfunction in mice, which may have clinical relevance for assessing novel drug targets for their potential use as therapeutic agents in patients with motivation impairments.

Nicotine use disorder has been associated with glutamatergic alterations within the basal ganglia that might contribute to relapse. Specifically, initiation of cue-induced nicotine seeking produces rapid, transient synaptic potentiation (t-SP) in nucleus accumbens core (NAcore) medium spiny neurons (MSNs), defined as increases in spine head diameter and AMPA to NMDA current ratios (A/N). Ifenprodil, which inhibits nicotine reinstatement when administered systemically, antagonizes GluN2B-containing NMDA receptors, has affinity for serotonin receptors, and blocks serotonin transporters (SERT). The mechanisms underlying its therapeutic efficacy, however, remain unknown. Using pharmacological and genetic approaches, the current study examined the role of NAcore GluN2B receptors as well as SERT in mediating cue-induced nicotine seeking and associated MSN structure and physiology. Prior to reinstatement, rats received intra-NAcore injections of either ifenprodil, citalopram or artificial cerebral spinal fluid (15 min prior), or GluN2B or control siRNAs (3 consecutive days prior). Rats were sacrificed after a 15-min cue-induced reinstatement session for dendritic spine analysis, western blotting or whole-cell electrophysiology. Intra-NAcore ifenprodil blocked nicotine-seeking behavior and promoted a higher frequency of shorter spines on MSN dendrites. However, a decrease in membrane-bound GluN2B receptor expression did not prevent cue-induced nicotine seeking or associated MSN cell physiology. Interestingly, intra-NAcore citalopram, an SSRI, prevented cue-induced nicotine seeking. Together, these results indicate that the therapeutic effects of ifenprodil on cue-induced nicotine seeking may, in part, be due to its actions at SERT rather than GluN2B, which may be specific to nicotine-seeking as opposed to other drugs of abuse.

In this review, a series of experiments is presented, in which γ-amino butyric acid (GABA)ergic and glutamatergic effects on dopamine function in the rat nigrostriatal and mesolimbic system was systematically assessed after pharmacological challenge with GABAA receptor (R) and and N-methyl d-aspartate (NMDA)R agonists and antagonists. In these studies, [123I]iodobenzamide binding to the D2/3R was mesured in nucleus accumbens (NAC), caudateputamen (CP), substantia nigra/ventral tegmental area (SN/VTA), frontal (FC), motor (MC) and parietal cortex (PC) as well as anterior (aHIPP) and posterior hippocampus (pHIPP) with small animal SPECT in baseline and after injection of either the GABAAR agonist muscimol (1 mg/kg), the GABAAR antagonist bicuculline (1 mg/kg), the NMDAR agonist d-cycloserine (20 mg/kg) or the NMDAR antagonist amantadine (40 mg/kg). Muscimol reduced D2/3R binding in NAC, CP, SN/VTA, THAL and pHIPP, while, after amantadine, decreases were confined to NAC, CP and THAL. In contrast, d-cycloserine elevated D2/3R binding in NAC, SN/VTA, THAL, frontal cortex, motor cortex, PC, aHIPP and pHIPP, while, after bicuculline, increases were confined to CP and THAL. Taken together, similar actions on regional dopamine levels were exterted by the GABAAR agonist and the NMDAR antagonist on the one side and by the GABAAR antagonist and the NMDAR agonist on the other, with agonistic action, however, affecting more brain regions. Thereby, network analysis suggests different roles of GABAARs and NMDARs in the mediation of nigrostriatal, nigrothalamocortical and mesolimbocortical dopamine function.

The mesolimbic dopamine system comprises distinct compartments supporting different functions in learning and motivation. Less well understood is how complex addiction-related behaviors emerge from activity patterns across these compartments. Here we show how different forms of relapse to alcohol-seeking in male rats are assembled from activity across the VTA and the nucleus accumbens. First, we used chemogenetic approaches to show a causal role for VTA TH neurons in two forms of relapse to alcohol-seeking: renewal (context-induced reinstatement) and reacquisition. Then, using gCaMP fiber photometry of VTA TH neurons, we identified medial and lateral VTA TH neuron activity profiles during self-administration, renewal, and reacquisition. Next, we used optogenetic inhibition of VTA TH neurons to show distinct causal roles for VTA subregions in distinct forms of relapse. We then used dLight fiber photometry to measure dopamine binding across the ventral striatum (medial accumbens shell, accumbens core, lateral accumbens shell) and showed complex and heterogeneous profiles of dopamine binding during self-administration and relapse. Finally, we used representational similarity analysis to identify mesolimbic dopamine signatures of self-administration, extinction, and relapse. Our results show that signatures of relapse can be identified from heterogeneous activity profiles across the mesolimbic dopamine system and that these signatures are unique for different forms of relapse. SIGNIFICANCE STATEMENT It is axiomatic that the actions of dopamine are critical to drug addiction. Yet how relapse to drug-seeking is assembled from activity across the mesolimbic dopamine system is poorly understood. Here we show how relapse to alcohol-seeking relates to activity in specific VTA and accumbens compartments, how these change for different forms of relapse, and how relapse-associated activity relates to activity during self-administration and extinction. We report the mesolimbic dopamine activity signatures for relapse and show that these signatures are unique for different forms of relapse., (Copyright © 2020 the authors.)

Fipronil (FPN), a widely used pesticide for agricultural and non-agricultural pest control, is possibly neurotoxic for mammals. Brain monoaminergic systems, involved in virtually all brain functions, have been shown to be sensitive to numerous pesticides. Here, we addressed the hypothesis that chronic exposure to FPN could modify brain monoamine neurochemistry. FPN (10 mg/kg) was chronically administered for 21 days through oral gavage in rats. Thereafter, the tissue concentrations of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid; serotonin (5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA); and noradrenaline (NA) were measured in 30 distinct brain regions. FPN significantly decreased DA and its metabolite levels in most striatal territories, including the nucleus accumbens and the substantia nigra (SN). FPN also diminished 5-HT levels in some striatal regions and the SN. The indirect index of the turnovers, DOPAC/DA and 5-HIAA/5-HT ratios, was increased in numerous brain regions. FPN reduced the NA content only in the nucleus accumbens core. Using the Bravais-Pearson test to study the neurochemical organization of monoamines through multiple correlative analyses across the brain, we found fewer correlations for NA, DOPAC/DA, and 5-HIAA/5-HT ratios, and an altered pattern of correlations within and between monoamine systems. We therefore conclude that the chronic administration of FPN in rats induces massive and inhomogeneous changes in the DA and 5-HT systems in the brain.

One of the hallmarks of addiction is the enduring vulnerability to relapse. Following repeated use, cocaine (COC) induces neuroadaptations within the dopamine (DA) system, arguably underlying several aspects of COC-seeking behavior. Peripheral stimulation of D2, but not D1, receptors induces relapse. However, where in the brain these effects occur is still matter of debate. The D1 and D2 receptors (D1R; D2R) are highly expressed in the nucleus accumbens (NAcc) and the dorsolateral striatum (DLS), but their specific involvement in the reinstatement of COC-seeking remains elusive. We assessed the reinstating effects of intracerebral infusions of agonists of D1R (SKF82958) or D2R (quinelorane) within the NAcc or DLS of rats after extinction of COC self-administration (COC SA). To assess whether we could block peripheral D2 agonist (quinelorane) induced reinstatement, we simultaneously infused either a D1R (SCH23390) or a D2R (raclopride) antagonist within the NAcc or DLS. When infused into the NAcc, but not into the DLS, SKF82958 induced reinstatement of COC-seeking; conversely, quinelorane had no effect when injected into the NAcc, but induced reinstatement when infused into the DLS while the D1R agonist has no effect. While administration of raclopride into the NAcc or DLS impedes the reinstating effect of a systemic quinelorane injection, the infusion of SCH23390 into the NAcc or DLS surprisingly, blocks the reinstatement induced by the peripheral D2R stimulation. Our results point to a double dissociation between D1R and D2R of the NAcc and DLS, highlighting their complex interactions within both structures, in the reinstatement of COC-seeking behavior., (Copyright © 2020. Published by Elsevier Ltd.)

KOP-r agonist U50,488H produces strong aversion and anxiety/depression-like behaviors that enhance alcohol intake and promote alcohol seeking and relapse-like drinking in rodents. Mammalian target of rapamycin complex 1 (mTORC1) pathway in mouse striatum is highly involved in excessive alcohol intake and seeking, and in the U50,488H-induced conditioned place aversion. Therefore, we hypothesized that KOP-r activation increases alcohol consumption through the mTORC1 activation. This study focuses on: (1) how chronic excessive alcohol drinking (4-day drinking-in-the-dark paradigm followed by 3-week chronic intermittent access drinking paradigm [two-bottle choice, 24-h access every other day]) affected nuclear transcript levels of the mTORC1 pathway genes in mouse nucleus accumbens shell (NAcs), using transcriptome-wide RNA sequencing analysis; and (2) whether selective mTORC1 inhibitor rapamycin could alter excessive alcohol drinking and prevent U50,488H-promoted alcohol intake. Thirteen nuclear transcripts of mTORC1 pathway genes showed significant up-regulation in the NAcs, with two genes down-regulated, after excessive alcohol drinking, suggesting the mTORC1 pathway was profoundly disrupted. Single administration of rapamycin decreased alcohol drinking in a dose-dependent manner. U50,488H increased alcohol drinking, and pretreatment with rapamycin, at a dose lower than effective doses, blocked the U50,488H-promoted alcohol intake in a dose-dependent manner, indicating a mTORC1-mediated mechanism. Our results provide supportive and direct evidence relevant to the transcriptional profiling of the critical mTORC1 genes in mouse NAc shell: with functional and pharmacological effects of rapamycin, altered nuclear transcripts in the mTORC1 signaling pathway after excessive alcohol drinking may contribute to increased alcohol intake triggered by KOP-r activation., Competing Interests: Declaration of competing interest All authors declare that they have no conflicts of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Background: Drug addiction is a chronically relapsing disorder in humans yet the underlying mechanism remained unclear. Recent studies suggested that histidine triad nucleotide binding protein1 (HINT1) may play significant roles in diverse neuropsychiatric diseases including drug addiction., Methods: In the current study, we used different batches of mice to establish different stages of methamphetamine (METH)-induced behavioral sensitization (BS) to explore the dynamic changes throughout the process of addiction in different brain regions, including the prefrontal cortex (PFC), nucleus accumbens (NAc), caudate putamen (CPu), and hippocampus (Hip). In addition, we used HINT1 knockout (KO) mice to investigate the effect of HINT1 protein deletion on METH-induced BS., Results: We found that in PFC of the METH group mice, the HINT1 expression level initially increased after development phase, and then dropped to the normal level during expression phase. However, there was no statistical difference in the HINT1 expression level in the other three encephalic regions (NAc, CPu, and Hip). The absence of HINT1 could promote METH-mediated addictive behavior to a certain extent, while the significant difference between genotypes only occurred in the development phase., Conclusions: Using the new technique, hip fractures were correctly predicted in 78% of cases compared with 36% when using the T-score. The accuracy of the prediction was not greatly reduced when using SSM and SAM (78% and 74% correct, respectively). Various geometric and BMD distribution traits were identified in the fractured and non-fractured groups.

Besides reducing food intake and controlling energy balance, glucagon-like peptide-1 (GLP-1) suppresses the reinforcing properties of palatable foods and addictive drugs. This reduction in reward involves activation of GLP-1 receptors (GLP-1R) within areas processing natural and artificial rewards, including the laterodorsal tegmental area (LDTg), ventral tegmental area (VTA) and nucleus accumbens (NAc) shell. These areas are part of a neurocircuitry mediating reward from addictive drugs and natural rewards including sexual behaviors. The male sexual encounter with a female includes three different stages: a pre-sexual interaction phase with social behaviors, which is followed by a sexual interaction phase with mounting and intromission of the female, and ends with a post-sexual interaction phase characterized by self-grooming behaviors. Albeit GLP-1 modulates reward, the influence of GLP-1R activation on sexual interaction is unknown. Thus, we infused the GLP-1R agonist, exendin-4 (Ex4), into sub-regions of the reward neurocircuitry in sexually naïve male mice and recorded their novel interaction with an estrus female. We found that Ex4 into the LDTg, posterior VTA or NAc shell reduces pre-sexual interaction behaviors and activation of GLP-1R in the LDTg or posterior VTA decreases sexual interaction behaviors. Contrarily, Ex4 infusion into anterior VTA does not influence these behaviors. Furthermore, self-grooming behaviors are not influenced by activation of GLP-1R in the aforementioned areas. These data highlight that activation of GLP-1R in reward-related areas reduces different aspects of the sexual interaction chain and further supports a role of the GLP-1R in social behaviors., Competing Interests: Declaration of competing interest The authors do not declare any conflicts of interest., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Women and men can differ in their propensity to take risks and develop impulse control and addiction disorders. Sexual dimorphisms in behavioral control by the mesolimbic dopaminergic reward system may underlie these phenomena, given its sensitivity to gonadal hormones. However, this is hard to test experimentally using humans. Using the rat gambling task (rGT), we investigated what impact acute inhibition of accumbal dopamine had on decision-making and impulsivity in animals of both sexes. We expressed an inhibitory designer receptor exclusively activated by designer drugs (hM4D[Gi]) in the accumbal dopaminergic efferents of female and male transgenic (Tg) rats, engineered to selectively express cre recombinase in neurons synthesizing tyrosine hydroxylase. We then trained the rats to perform the rGT and assessed the effect of an acute clozapine-n-oxide (0-3 mg/kg) challenge. Chemogenetic inhibition of dopaminergic projections to the accumbens did not affect choice in females, perhaps due to low levels of risky choice in Tg+ animals at baseline, but induced a switch from risky to optimal decision-making in males performing the cued rGT. This manipulation also decreased motor impulsivity but only in females. These data support the hypothesis that cue-driven risky choice is mediated, at least in males, by activity of accumbal dopaminergic neurons. However, motor impulsivity is more sensitive to inhibition of accumbal dopamine neurons in female rats. These data may help explain differences in the manifestation of addictions across gender and reinforce the importance of examining both sexes when seeking to attribute control of behavior to specific monoaminergic pathways. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

In the last years, clinical and preclinical researchers have increased their interest in non-psychotomimetic cannabinoids, like cannabidiol (CBD), as a strategy for treating psychostimulant use disorders. However, there are discrepancies in the pharmacological effects and brain targets of CBD. We evaluated if CBD was able to prevent the locomotor sensitization elicited by cocaine and caffeine co-administration. The effect of CBD on putative alterations in the metabolic activity of the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc), and its respective subregions (cingulated, prelimbic, and infralimbic cortices, and NAc core and shell) associated to the behavioral response, was also investigated. Rats were intraperitoneally and repeatedly treated with CBD (20 mg/kg) or its vehicle, followed by the combination of cocaine and caffeine (Coc+Caf; 5 mg/kg and 2.5 mg/kg, respectively) or saline for 3 days. After 5 days of withdrawal, all animals were challenged with Coc+Caf (day 9). Locomotor activity was automatically recorded and analyzed by a video-tracking software. The metabolic activity was determined by measuring cytochrome oxidase-I (CO-I) staining. Locomotion was significantly and similarly increased both in Veh-Coc+Caf- and CBD-Coc+Caf-treated animals during the pretreatment period (3 days); however, on day 9, the expression of the sensitization was blunted in CBD-treated animals. A hypoactive metabolic response and a hyperactive metabolic response in mPFC and NAc subregions respectively were observed after the behavioral sensitization. CBD prevented almost all these changes. Our findings substantially contribute to the understanding of the functional changes associated with cocaine- and caffeine-induced sensitization and the effect of CBD on this process.

Rationale: The functional role of the endocannabinoid system (ECS) and Transient Receptor Potential Vanilloid type-1 (TRPV1) within the Nucleus Accumbens shell (NAc shell) remains unknown. Preclinical studies in rodents have reported that the ECS modulates emotional responses such as anxiety. The NAc shell has a high density of synaptically co-localized cannabinoid receptor type-1 (CB1R) and TRPV1, suggesting a potential involvement in the modulation of anxiety., Objectives: The present study aims to establish the role of ECS-TRPV1 interactions within the NAc shell and its effects on anxiety. It is hypothesized that the neurochemical regulation elicited by ECS within the NAc shell mediates anxiety-like behaviors in rodents., Methods: In this study, male Sprague Dawley rats were implanted with bilateral brain cannula targeting the NAc shell. Following recovery from surgery, animals received microinfusion pretreatments (0, 0.125, 0.5 nmol/0.4 μl) of N-arachidonoyl-serotonin (AA-5-HT), a dual blocker of the endocannabinoid-inactivating enzyme, fatty acid amide hydrolase (FAAH) and a TRPV1 antagonist in the NAc shell. Following treatment, animals were tested in an elevated plus maze (EPM) paradigm for a period of 5 minutes. At the end of the experiment, animals were sacrificed and their brains collected for histological and biochemical analysis., Results: Results showed that animals treated with AA-5-HT in a dose dependent manner spent significantly more time in the open arms than vehicle-treated animals. In addition, AA-5-HT administration induced a significant downregulation of CB1R expression in the NAc shell., Conclusions: The present findings suggest that the ECS within the NAc shell modulates anxiety-like behaviors via FAAH and CB1R activity., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: The social motivational theory of autism spectrum disorder (ASD) focuses on social anhedonia as key causal feature of the impaired peer relationships that characterize ASD patients. ASD prevalence is higher in boys, but increasing evidence suggests underdiagnosis and undertreatment in girls. We showed that stress-induced motivational anhedonia is relieved by repeated treatment with fenofibrate (FBR), a peroxisome proliferator-activated receptor α (PPARα) agonist. Here, we used the valproic acid (VPA) model of ASD in rats to examine male and female phenotypes and assess whether FBR administration from weaning to young adulthood relieved social impairments., Methods: Male and female rats exposed to saline or VPA at gestational day 12.5 received standard or FBR-enriched diet from postnatal day 21 to 48-53, when behavioral tests and ex vivo neurochemical analyses were performed. Phosphorylation levels of DARPP-32 in response to social and nonsocial cues, as index of dopamine D 1 receptor activation, levels of expression of PPARα, vesicular glutamatergic and GABAergic transporters, and postsynaptic density protein PSD-95 were analyzed by immunoblotting in selected brain regions., Results: FBR administration relieved social impairment and perseverative behavior in VPA-exposed male and female rats, but it was only effective on female stereotypies. Dopamine D 1 receptor signaling triggered by social interaction in the nucleus accumbens shell was blunted in VPA-exposed rats, and it was rescued by FBR treatment only in males. VPA-exposed rats of both sexes exhibited an increased ratio of striatal excitatory over inhibitory synaptic markers that was normalized by FBR treatment., Limitations: This study did not directly address the extent of motivational deficit in VPA-exposed rats and whether FBR administration restored the likely decreased motivation to operate for social reward. Future studies using operant behavior protocols will address this relevant issue., Conclusions: The results support the involvement of impaired motivational mechanisms in ASD-like social deficits and suggest the rationale for a possible pharmacological treatment. Moreover, the study highlights sex-related differences in the expression of ASD-like symptoms and their differential responses to FBR treatment.

Zeta inhibitory peptide (ZIP), a PKMζ inhibitor, is widely used to interfere with the maintenance of acquired memories. ZIP is able to erase memory even in the absence of PKMζ, via an unknown mechanism. We found that ZIP induces redistribution of the AMPARGluA1 in HEK293 cells and primary cortical neurons, and decreases AMPAR-mediated currents in the nucleus accumbens (NAc). These effects were mimicked by free arginine or by a modified ZIP in which all but the arginine residues were replaced by alanine. Redistribution was blocked by a peptidase-resistant version of ZIP and by treatment with the nitric oxide (NO)-synthase inhibitor L-NAME. ZIP increased GluA1-S831 phosphorylation and ZIP-induced redistribution was blocked by nitrosyl-mutant GluA1-C875S or serine-mutant GluA1-S831A. Introducing the cleavable arginine-alanine peptide into the NAc attenuated expression of cocaine-conditioned reward. Together, these results suggest that ZIP may act as an arginine donor, facilitating NO-dependent downregulation of AMPARs, thereby attenuating learning and memory.

Individuals who begin drug use during early adolescence experience more adverse consequences compared to those initiating later, especially if they are female. The mechanisms for these age and gender differences remain obscure, but studies in rodents suggest that psychostimulants may disrupt the normal ontogeny of dopamine and glutamate systems in the prefrontal cortex (PFC). Here, we studied Sprague-Dawley rats of both sexes who began methamphetamine (METH, i.v.) self-administration in adolescence (postnatal [P] day 41) or adulthood (P91). Rats received seven daily 2-h self-administration sessions with METH or saccharin as the reinforcer, followed by 14 daily long access (LgA; 6 h) sessions. After 7 and 14 days of abstinence, novel object (NOR) or object-in-place (OiP) recognition was assessed. PFC and nucleus accumbens were collected 7 days after the final cognitive test and NMDA receptor subunits and dopamine D 1 receptor expression was measured. We found that during LgA sessions, adolescent-onset rats escalated METH intake more rapidly than adult-onset rats, with adolescent-onset females earning the most infusions. Adolescent-onset rats with a history of METH self-administration exhibited modest deficits in OiP compared to their adult-onset counterparts, but there was no sex difference and self-administration groups did not differ from naïve control rats. All rats displayed intact novel object recognition memory. We found no group differences in D 1 and NMDA receptor expression, suggesting no long-lasting alteration of ontogenetic expression profiles. Our findings suggest that adolescent-onset drug use is more likely to lead to compulsive-like patterns of drug-taking and modest dysfunction in PFC-dependent cognition., Competing Interests: Declaration of Competing Interest All authors report they have no conflicts of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

MiR-124 is a highly expressed miRNA in the brain and regulates genes involved in neuronal function. We report that miR-124 post-transcriptionally regulates PARP-1. We have identified a highly conserved binding site of miR-124 in the 3'-untranslated region (3'UTR) of Parp-1 mRNA. We demonstrate that miR-124 directly binds to the Parp-1 3'UTR and mutations in the seed sequences abrogate binding between the two RNA molecules. Luciferase reporter assay revealed that miR-124 post-transcriptionally regulates Parp-1 3'UTR activity in a dopaminergic neuronal cell model. Interestingly, the binding region of miR-124 in Parp-1 3'UTR overlapped with the target sequence of miR-125b, another post-transcriptional regulator of Parp-1. Our results from titration and pull-down studies revealed that miR-124 binds to Parp-1 3'UTR with greater affinity and confers a dominant post-transcriptional inhibition compared to miR-125b. Interestingly, acute or chronic cocaine exposure downregulated miR-124 levels concomitant with upregulation of PARP-1 protein in dopaminergic-like neuronal cells in culture. Levels of miR-124 were also downregulated upon acute or chronic cocaine exposure in the mouse nucleus accumbens (NAc)-a key reward region of brain. Time-course studies revealed that cocaine treatment persistently downregulated miR-124 in NAc. Consistent with this finding, miR-124 expression was also significantly reduced in the NAc of animals conditioned for cocaine place preference. Collectively, these studies identify Parp-1 as a direct target of miR-124 in neuronal cells, establish miR-124 as a cocaine-regulated miRNA in the mouse NAc, and highlight a novel pathway underlying the molecular effects of cocaine.

Exposure to pyrethroids, a popular insecticide class that targets voltage-gated Na+ (Nav) channels, has been correlated to an increase in diagnosis of neurodevelopmental disorders, such as attention deficit hyperactive disorder (ADHD), in children. Dysregulation of medium spiny neurons (MSNs) firing in the nucleus accumbens (NAc) is thought to play a critical role in the pathophysiology of ADHD and other neurodevelopmental disorders. The Nav1.6 channel is the primary molecular determinant of MSN firing and is sensitive to modification by pyrethroids. Building on previous studies demonstrating that deltamethrin (DM), a commonly used pyrethroid, leads to use-dependent enhancement of sodium currents, we characterized the effect of the toxin on long-term inactivation (LTI) of the Nav1.6 channel, a parameter known to affect neuronal firing, and characterized changes in MSN intrinsic excitability. We employed whole-cell patch-clamp electrophysiology to measure sodium currents in HEK-293 cells stably expressing Nav1.6 channels and intrinsic excitability of MSNs in the brain slice preparation. We found that in response to repetitive stimulation acute exposure to 10 μM DM potentiated a build-up of residual sodium currents and modified availability of Nav1.6 by inducing LTI. In the NAc, DM modified MSN intrinsic excitability increasing evoked action potential firing frequency and inducing aberrant action potentials with low amplitude and depolarized voltage threshold, phenotypes that could be explained by DM induced changes on the Nav1.6 channel. These results provide a potential initial mechanism of toxicity of DM that could lead to disruption of the NAc circuitry overtime, increasing the risk of ADHD and other neurodevelopmental disorders., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Historically, the roots of alcoholism have been linked to either environment or heredity. However, the interaction between these factors is still largely unexplored. The evidence supports a link between alcohol consumption and the endogenous opioid system. We here studied the opioid genes expression in male and female Wistar rats derived from a short-term breeding program which selected -- at adolescence -- for high (ADHI line) or low (ADLO line) ethanol drinking. Specifically, in this work we analyzed central opioid gene expression in the rats of the second filial generation (S 2 -ADLO and S 2 -ADHI). Selective downregulation of pronociceptin (Pnoc) and its receptor (Oprl1) mRNA levels were observed in the prefrontal cortex of male S 2 -ADHI rats when compared to S 2 -ADLO, and for Oprl1 also in the nucleus accumbens. An increase in gene expression was instead observed for pro-opiomelanocortin (Pomc) in the nucleus accumbens of S 2 -ADHI males when compared to S 2 -ADLO, as well as for mu opioid receptor (Oprm1) but in females. The differences in mRNA levels may be due to the different alcohol consumption between the two groups of rats or may represent pre-existing differences between them. Moreover, we show a sex-specific modulation of the expression of these genes, thus pointing out the importance of sex on ethanol responses. The results might lead to more specific and effective pharmacological treatments for alcoholism., Competing Interests: Declaration of Competing Interest We declare having no conflict of interest related to our MS or its results., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Rationale: The nuclear receptor retinoid X receptor (RXR) belongs to a nuclear receptor superfamily that modulates diverse functions via homodimerization with itself or several other nuclear receptors, including PPARα. While the activation of PPARα by natural or synthetic agonists regulates the sleep-wake cycle, the role of RXR in the sleep modulation is unknown., Objectives: We investigated the effects of bexarotene (Bexa, a RXR agonist) or UVI 3003 (UVI, a RXR antagonist) on sleep, sleep homeostasis, levels of neurochemical related to sleep modulation, and c-Fos and NeuN expression., Methods: The sleep-wake cycle and sleep homeostasis were analyzed after application of Bexa or UVI. Moreover, we also evaluated whether Bexa or UVI could induce effects on dopamine, serotonin, norepinephrine epinephrine, adenosine, and acetylcholine contents, collected from either the nucleus accumbens or basal forebrain. In addition, c-Fos and NeuN expression in the hypothalamus was determined after Bexa or UVI treatments., Results: Systemic application of Bexa (1 mM, i.p.) attenuated slow-wave sleep and rapid eye movement sleep. In addition, Bexa increased the levels of dopamine, serotonin, norepinephrine epinephrine, adenosine, and acetylcholine sampled from either the nucleus accumbens or basal forebrain. Moreover, Bexa blocked the sleep rebound period after total sleep deprivation, increased in the hypothalamus the expression of c-Fos, and decreased NeuN activity. Remarkably, UVI 3003 (1 mM, i.p.) induced opposite effects in sleep, sleep homeostasis, neurochemicals levels, and c-Fos and NeuN activity., Conclusions: The administration of RXR agonist or antagonist significantly impaired the sleep-wake cycle and exerted effects on the levels of neurochemicals related to sleep modulation. Moreover, Bexa or UVI administration significantly affected c-Fos and NeuN expression in the hypothalamus. Our findings highlight the neurobiological role of RXR on sleep modulation.

Combined use of nicotine and alcohol constitute a significant public health risk. An important aspect of drug use and dependence are the various cues, both external (contextual) and internal (interoceptive) that influence drug-seeking and drug-taking behavior. The present experiments employed the use of Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) and complementary Pavlovian drug discrimination procedures (feature-positive and feature-negative training conditions) in order to examine whether medial prefrontal cortex (prelimbic; mPFC-PL) projections to the nucleus accumbens core (AcbC) modulate sensitivity to a nicotine + alcohol (N + A) interoceptive cue. First, we show neuronal activation in mPFC-PL and AcbC following treatment with N + A. Next, we demonstrate that chemogenetic silencing of projections from mPFC-PL to nucleus accumbens core decrease sensitivity to the N + A interoceptive cue, while enhancing sensitivity to the individual components, suggesting an important role for this specific projection. Furthermore, we demonstrate that clozapine-N-oxide (CNO), the ligand used to activate the DREADDs, had no effect in parallel mCherry controls. These findings contribute important information regarding our understanding of the cortical-striatal circuitry that regulates sensitivity to the interoceptive effects of a compound N + A cue., (© 2019 Society for the Study of Addiction.)

Nicotine-associated cues can trigger reinstatement in humans as well as in animal models of drug addiction. To date, no behavioral intervention or pharmacological treatment has been effective in preventing relapse in the long term. A large body of evidence indicates that N-acetylcysteine (N-AC) blunts the activation of glutamatergic (GLUergic) neurons in the nucleus accumbens (Nacc) associated with reinstatement. We evaluated the effect of an experimental cue exposure therapy (eCET) alone or in combination with N-AC to verify whether restoring GLU homeostasis enhances extinction of nicotine-associated cues. Rats were trained to associate discriminative stimuli with intravenous nicotine or saline self-administration. Reinforced response was followed by cue signals. After rats met the self-administration criteria, the lasting anti-relapse activity of i.p. N-AC or vehicle was assessed in three different experimental conditions after 14 days of treatment: treatment + eCET; treatment + lever-presses extinction (LP-EXT); and treatment + abstinence. N-AC 100 mg/kg, but not 60 mg/kg, induced anti-relapse activity that persisted 50 days after treatment only when paired with either LP-EXT or eCET with the greater activity found in the latter condition. To identify potential mechanisms for behavioral results, separate groups of rats that received either N-AC or vehicle + eCET were killed at different time points for Nacc Western-blot analysis. Seven days after treatment, chronic N-AC restored the expression of proteins crucial for GLU homeostasis, while at 50 days, it increased the expression of type II metabotropic GLU receptors. These results suggest that N-AC treatment in combination with eCET may offer a novel strategy to prevent relapse in nicotine addiction., (© 2019 Society for the Study of Addiction.)

The gut-brain peptide glucagon-like peptide-1 (GLP-1) reduces reward from palatable food and drugs of abuse. Recent rodent studies show that activation of GLP-1 receptors (GLP-1R) within the nucleus of the solitary tract (NTS) not only suppresses the motivation and intake of palatable food, but also reduces alcohol-related behaviors. As reward induced by addictive drugs and sexual behaviors involve similar neurocircuits, we hypothesized that activation of GLP-1R suppresses sexual behavior in sexually naïve male mice. We initially identified that systemic administration of the GLP-1R agonist, exendin-4 (Ex4), decreased the frequency and duration of mounting behaviors, but did not alter the preference for females or female bedding. Thereafter infusion of Ex4 into the NTS decreased various behaviors of the sexual interaction chain, namely social, mounting and self-grooming behaviors. In male mice tested in the sexual interaction test, NTS-Ex4 increased dopamine turnover and enhanced serotonin levels in the nucleus accumbens (NAc). In addition, these mice displayed higher corticosterone, but not testosterone, levels in plasma. Finally, GLP-1R antagonist, exendin-3 (9-39) amide (Ex9), infused into the NTS differentially altered the ability of systemic-Ex4 to suppress the various behaviors of the sexual interaction chain, indicating that GLP-1R within the NTS is one of many sub-regions contributing to the GLP-1 dependent sexual behavior link. In these mice NTS-Ex9 partly blocked the systemic-Ex4 enhancement of corticosterone levels. Collectively, these data highlight that activation of GLP-1R, specifically those in the NTS, reduces sexual interaction behaviors in sexually naïve male mice and further provide a link between NTS-GLP-1R activation and reward-related behaviors., (Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The ability to choose goals based on decision usefulness or the time required to reach the goals chosen are important aspects of decision making. There is considerable evidence in the literature indicating the fact that drug abuse affects different aspects of cognition. In the current study, we assessed the effects of morphine dependence and its withdrawal on cost-benefit decision making and furthermore the involvement of BDNF and p-CREB in the nucleus accumbens, a key brain area involved in decision making was measured. Different groups of male Wistar rats were trained in an effort-based and/or delay-based form of cost-benefit T-maze decision-making task. Thereafter, the animals were morphine dependent and the percentage of the high reward preference was evaluated. After behavioral tests, the BDNF level, and p-CREB/CREB ratio were measured by Western blot analysis. The results showed that during effort-based but not delay-based decision making, BDNF and p-CREB levels increased. During effort-based decision making in morphine dependent rats, BDNF decreased but there was no significant change in p-CREB. Besides, during delay-based decision making in the morphine dependent group, both BDNF and p-CREB did not show any significant change. These findings revealed that BDNF and p-CREB/CREB ratio in the NAc are essential factors for effort-based but not delay-based decision making. In addition, impairment of effort-based decision making in morphine dependent rats is related to the decrease of BDNF level but not p-CREB/CREB ratio in the NAc. However, delay-based decision making defects in morphine dependent rats did not associate with the change in BDNF and p-CREB levels in the NAc., Competing Interests: Declaration of competing interest The authors had no conflicts of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The guidance cue receptor DCC controls mesocortical dopamine development in adolescence. Repeated exposure to an amphetamine regimen of 4 mg/kg during early adolescence induces, in male mice, downregulation of DCC expression in dopamine neurons by recruiting the Dcc microRNA repressor, microRNA-218 (miR-218). This adolescent amphetamine regimen also disrupts mesocortical dopamine connectivity and behavioral control in adulthood. Whether low doses of amphetamine in adolescence induce similar molecular and developmental effects needs to be established. Here, we quantified plasma amphetamine concentrations in early adolescent mice following a 4 or 0.5 mg/kg dose and found peak levels corresponding to those seen in humans following recreational and therapeutic settings, respectively. In contrast to the high doses, the low amphetamine regimen does not alter Dcc mRNA or miR-218 expression; instead, it upregulates DCC protein levels. Furthermore, high, but not low, drug doses downregulate the expression of the DCC receptor ligand, Netrin-1, in the nucleus accumbens and prefrontal cortex. Exposure to the low-dose regimen did not alter the expanse of mesocortical dopamine axons or their number/density of presynaptic sites in adulthood. Strikingly, adolescent exposure to the low-dose drug regimen does not impair behavioral inhibition in adulthood; instead, it induces an overall increase in performance in a go/no-go task. These results show that developmental consequences of exposure to therapeutic- versus abused-like doses of amphetamine in adolescence have dissimilar molecular signatures and opposite behavioral effects. These findings have important clinical relevance since amphetamines are widely used for therapeutic purposes in youth., (© 2019 Society for the Study of Addiction.)

Rationale: The beta-lactam antibiotic ceftriaxone reliably attenuates the reinstatement of cocaine seeking. While the restoration of nucleus accumbens core (NA core) GLT-1 expression is necessary for ceftriaxone to attenuate reinstatement, AAV-mediated GLT-1 overexpression is not sufficient to attenuate reinstatement and does not prevent glutamate efflux during reinstatement., Aims: Here, we test the hypothesis that ceftriaxone attenuates reinstatement through interactions with glutamate autoreceptors mGlu2 and mGlu3 in the NA core., Methods: Male and female rats self-administered cocaine for 12 days followed by 2-3 weeks of extinction training. During the last 6-10 days of extinction, rats received ceftriaxone (200 mg/kg IP) or vehicle. In experiment 1, rats were killed, and NA core tissue was biotinylated for assessment of total and surface expression of mGlu2 and mGlu3 via western blotting. In experiment 2, we tested the hypothesis that mGlu2/3 signaling is necessary for ceftriaxone to attenuate cue- and cocaine-primed reinstatement by administering bilateral intra-NA core infusion of mGlu2/3 antagonist LY341495 or vehicle immediately prior to reinstatement testing., Results: mGlu2 expression was reduced by cocaine and restored by ceftriaxone. There were no effects of cocaine or ceftriaxone on mGlu3 expression. We observed no effects of estrus on expression of either protein. The antagonism of mGlu2/3 in the NA core during both cue- and cocaine-primed reinstatement tests prevented ceftriaxone from attenuating reinstatement., Conclusions: These results indicate that ceftriaxone's effects depend on mGlu2/3 function and possibly mGlu2 receptor expression. Future work will test this hypothesis by manipulating mGlu2 expression in pathways that project to the NA core.

The addictive properties of opioids may be mediated to some extent by cocaine-and amphetamine-regulated transcript (CART) in the reward pathway. Moreover, some claims CART interacts with the glutamate system. Here, we evaluated whether intra-nucleus accumbens (NAc) shell infusions of CART induces Conditioned Place Preference (CPP) or Conditioned Place Aversion (CPA) and affects morphine reward. We also measured NR1 subunit expressions of the N-methyl-d-aspartate (NMDA) receptor in various parts of the reward pathway (NAc, prefrontal cortex and hippocampus) after conditioning tests. Animals with bilateral intra-NAc shell cannulas were place-conditioned with several doses of subcutaneous morphine prior to intra-NAc shell infusions of artificial cerebrospinal fluid (aCSF). Immunohistochemistry (IHC) showed a dose-dependent increase in the NR1 expression in all examined parts. When rats were conditioned with intra-NAc shell infusions of CART, CPP and CPA induced with 2.5 and 5 μg/side respectively and IHC showed NR1elevation with 2.5 and reduction with 5 μg/side in all areas. Sub-rewarding dose of CART administration (1.25 μg/side) prior to sub-rewarding dose of morphine (2.5 mg/kg) induced CPP and NR1 increased in all examined tissues in IHC. However, infusion of an aversive dose of CART (5 μg/side) prior to the rewarding dose of morphine (5 mg/kg) produced neither CPP nor CPA and NR1 in the NAc and hippocampus decreased significantly. It seems that the rewarding or aversive effects of intra-NAc shell CART and its facilitating or inhibiting effects on morphine reward are dose-dependent. Additionally, NMDA may be closely involved in the affective properties of opioids and CART in the reward pathway., (Copyright © 2020 Elsevier Inc. All rights reserved.)

For almost two decades schizophrenia has been considered to be a functional disconnection disorder. This functional disconnectivity between several brain regions could have a neurodevelopmental origin. Various approaches suggest the ventral subiculum (SUB) is a particular target region for neurodevelopemental disturbances in schizophrenia. It is also commonly acknowledged that there is a striatal dopaminergic (DA) dysregulation in schizophrenia which may depend on a subiculo-striatal disconnection involving glutamatergic NMDA receptors. The present study was designed to investigate, in adult rats, the effects of the non-competitive NMDA receptor antagonist ketamine on DA responses in the ventral striatum, or, more specifically, the core part of the nucleus accumbens (Nacc), following postnatal functional inactivation of the SUB. Functional inactivation of the left SUB was carried out by local tetrodotoxin (TTX) microinjection at postnatal day 8 (PND8), i.e. at a critical point in the neurodevelopmental period. DA variations were recorded using in vivo voltammetry in freely moving adult rats (11 weeks). Locomotor activity was recorded simultaneously with the extracellular levels of DA in the core part of the Nacc. Data obtained during the present study showed that after administration of ketamine, the two indexes were higher in TTX animals than PBS animals, the suggestion being that animals microinjected with TTX in the left SUB at PND8 present greater reactivity to ketamine than animals microinjected with PBS. These findings could provide new information regarding the involvement of NMDA glutamatergic receptors in the core part of the Nacc in the pathophysiology of schizophrenia., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Synchronization and desynchronization of neuronal oscillatory activities between different brain areas play an important role in effective information communication. The hippocampus-mPFC circuit is well recognized as an important neural circuit pathway involved in drug addiction. We aimed to examine cocaine-related changes in oscillation synchronization in the hippocampus-mPFC circuit and to explore the role of the NAc in oscillation synchronization between the hippocampus and the mPFC during intravenous cocaine administration. In our experiment, adult male Sprague-Dawley rats were divided into the Saline group, Cocaine group and Lesion group by the random number table method. Using an electrophysiological method, we continuously recorded the local field potentials (LFPs) of the hippocampus and the mPFC after pulse intravenous cocaine or saline. Our results showed that theta coherence occurred in the hippocampus-mPFC circuit during intravenous cocaine administration (Coherence θ, Pre-drug  = 0.2212 ± 0.0126, Coherence θ, Post-drug  = 0.3118 ± 0.0149, t = 4.894, P < 0.001), and the NAc Lesions could disrupt hippocampus-mPFC theta coherence (Coherence θ, Pre-drug  = 0.3164 ± 0.0188, Coherence θ, Post-drug  = 0.2628 ± 0.0248, t = 2.408, P < 0.05). These findings indicated that the NAc could influence oscillation synchronization between the hippocampus and mPFC during intravenous cocaine administration, which might help to elucidate the neurophysiological mechanisms of the neural circuits that underlie the function of the NAc during the strengthening of drug addiction., Competing Interests: Declaration of Competing Interest The authors have no conflicts of interest to declare., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: Individual differences in behavioural traits influence susceptibility to addictive disorders. Drug addiction involves changes in gene expression, proposed to occur via DNA methylation (DNAm)., Aims: To investigate DNAm changes in reward-related brain structures (nucleus accumbens (NAc), lateral habenula (LHb)) in response to cocaine exposure in rats differing in spontaneous exploratory activity., Methods: Rats were observed in the exploration box and categorised as high- (HE) or low explorers (LE). Rats were administered vehicle or cocaine (12 mg/kg, i.p.) for 7 days, followed by a 14-day withdrawal period and cocaine challenge (7 mg/kg); horizontal locomotor activity was recorded. Brain tissue was dissected after 24 h; we analysed messenger RNA (mRNA) and activity levels of epigenetic DNA modifiers (DNMTs and TETs) as well as mRNA and promoter methylation levels at selected genes previously linked to addictive behaviours., Results: The cocaine challenge dose stimulated locomotor activity in both LE- and HE rats only when administered after a repeated cocaine schedule, suggesting development of behavioural sensitisation. Quantitative polymerase chain reaction analyses demonstrated higher basal expression of Dnmt3a, Tet2 and Tet3 in the LHb of HE- vs. LE rats, and we observed differential effects of cocaine exposure on the expression and activity of epigenetic DNA modifiers in the NAc and LHb of HE- and LE rats. Furthermore, cocaine exposure differentially altered promoter methylation levels of A 2A R, Ppp1cc , and Taar7b in the NAc and LHb of HE- and LE rats., Conclusions: DNAm might play a role in the HE- and LE phenotypes as well as mediate behavioural effects of LE- and HE rats in response to drugs of abuse.

Binge eating behavior (BEB) is the most common condition among eating disorders. In animal models, binge eating behavior is defined as overconsumption in a brief time interval and it develops as a progressive increase in food intake along time. It is triggered by restricting food access to regular chow or to palatable food and is associated with dopamine release from the ventral tegmental area to the nucleus accumbens. The dopamine system, exhibits day-night patterns, suggesting regulation by the circadian system. This study explored in rats the differential contribution of restricted food access to chow and sucrose for developing BEB, it explored whether BEB exhibits a day-night pattern, and whether behavioral changes are associated with the number of tyrosine hydroxylase (TH) positive cells in the ventral tegmental area, with the expression of dopamine 1 receptors (D1) and glutamate receptor subunit 1 receptors (GLUR1) in the nucleus accumbens. Present data indicate that under conditions of restricted access binge eating is developed for chow or sucrose. Both types of binge eating were independent of each other and exhibited a day-night pattern with increased intensity during the active phase (night). Binge eating was preceded by anticipatory activation, except when restricted food access was given during the day. Increased optical density for D1 receptors was found after exposure to the combination of restricted food access and sucrose. No association was observed between binge eating and the number of positive cells to TH in the ventral tegmental area, nor for GLUR1 in the nucleus accumbens. Present results point out the importance of time schedules to eat, highlighting an increased vulnerability to develop binge eating during the active phase. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Cue-induced reinstatement of cocaine seeking after self-administration (SA) and extinction relies on glutamate release in the nucleus accumbens core (NAcore), which activates neuronal nitric oxide synthase interneurons. Nitric oxide (NO) is required for structural plasticity in NAcore medium spiny neurons, as well as cued cocaine seeking. However, NO release in the NAcore during reinstatement has yet to be directly measured. Furthermore, the temporal relationship between glutamate release and the induction of an NO response also remains unknown. Using wireless amperometric recordings in awake behaving rats, we quantified the magnitude and temporal dynamics of novel context- and cue-induced reinstatement-evoked glutamate and NO release in the NAcore. We found that re-exposure to cocaine-conditioned stimuli following SA and extinction increased extracellular glutamate, leading to release of NO in the NAcore. In contrast, exposing drug-naïve rats to a novel context led to a lower magnitude rise in glutamate in the NAcore relative to cue-induced reinstatement. Interestingly, novel context exposure evoked a higher magnitude NO response relative to cue-induced reinstatement. Despite differences in magnitude, novel context evoked-NO release in the NAcore was also temporally delayed when compared to glutamate. These results demonstrate a dissociation between the magnitude of cocaine cue- and novel context-evoked glutamate and NO release in the NAcore, yet similarity in the temporal dynamics of their release. Together, these data contribute to a greater understanding of the relationship between glutamate and NO, two neurotransmitters implicated in encoding the valence of distinct contextual stimuli., (© 2020 International Society for Neurochemistry.)

We recently showed that the mesolimbic dopaminergic system was tonically suppressed during chronic pain by enhanced corticotropin releasing factor (CRF) signaling within the dorsolateral bed nucleus of the stria terminalis (dlBNST), and that inhibition of intra-dlBNST CRF signaling restored the mesolimbic dopaminergic system function. Specifically, bilateral intra-dlBNST injections of the CRF type 1 receptor antagonist NBI27914 increased intra-nucleus accumbens dopamine release and induced reward-related behaviors in rats with chronic pain. Here, we used a conditioned place preference (CPP) test to explore whether intra-dlBNST injections of neuropeptide Y (NPY) restored the mesolimbic reward system function in chronic pain rats, because we previously showed that NPY had an effect opposite to that of CRF in dlBNST neurons. Specifically, CRF depolarized type II dlBNST neurons whereas NPY hyperpolarized them. However, unexpectedly, intra-dlBNST NPY injections had no effect on CPP test outcomes. Then, we compared the effects of NPY on the membrane potentials of type II dlBNST neurons of sham-operated control rats and those of chronic pain animals. Whole-cell patch-clamp electrophysiology revealed that NPY hyperpolarized type II dlBNST neurons in the sham-operated group. By contrast, in the chronic pain group, NPY did not hyperpolarize, but rather depolarized, type II dlBNST neurons. These results indicate that NPY no longer hyperpolarizes type II dlBNST neurons in rats with chronic pain, therefore it does not reverse the excitatory effects of CRF. This may be why intra-dlBNST injections of NPY into chronic pain rats did not exhibit a rewarding effect in the CPP test, whereas intra-dlBNST injections of NBI27914 did. This is the first study to demonstrate a chronic pain-induced neuroplastic change in NPY signaling in the dlBNST. Such a change may be involved in the dysfunction of the mesolimbic reward system under the chronic pain condition., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Cocaine-cue extinction training combined with brief interventions of environmental enrichment (EE) was shown previously to facilitate extinction and attenuate reacquisition of cocaine self-administration in rats. It is unknown whether or not the usefulness of this approach would be undermined if extinction training took place in a novel rather than familiar context. Drawing on previous studies involving pharmacological interventions, we hypothesized that the facilitative effects of EE for cocaine relapse prevention would be independent of the context used for extinction training. Rats trained to self-administer cocaine underwent cocaine-cue extinction training in either the familiar self-administration context or a novel context, with or without EE. Rats then were tested for reacquisition of cocaine self-administration in the familiar context. Target brain regions were lysed and probed for memory-related changes in receptors for glutamate and BDNF by western blotting. Contrary to our hypothesis, the facilitative effects of EE for cocaine relapse prevention were dependent on the context used for extinction training. While EE facilitated extinction regardless of context used, it inhibited cocaine relapse only after extinction training in the familiar context. EE was associated with increased GluA2 in nucleus accumbens, TrkB in dorsal hippocampus and activated TrkB in ventromedial prefrontal cortex. Of these, the changes in dorsal hippocampus and ventromedial prefrontal cortex mirrored outcomes of the cocaine relapse tests in that these changes were specific to rats receiving EE plus extinction training in the familiar context. These findings support a role for hippocampal-prefrontal BDNF-TrkB signaling in extinction-based relapse prevention strategies involving EE., Competing Interests: Declaration of Competing Interest All authors declare no competing financial interests., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Although several studies have been performed in rodents, non-human primates and humans, the biological basis of vulnerability to develop cocaine addiction remains largely unknown. Exposure to critical early events (as Repeated Cross Fostering (RCF)) has been reported to increase sensitivity to cocaine effects in adult C57BL/6J female mice. Using a microarray approach, here we report data showing a strong engagement of X-linked lymphocyte-regulated 4a and 4b (Xlr4) genes in cocaine effects. The expression of Xlr4, a gene involved in chromatin remodeling and dendritic spine morphology, was reduced into the Nucleus Accumbens (NAc) of adult RCF C57BL/6J female. We used virally mediated accumbal Xlr4 down-modulation (AAVXlr4-KD) to investigate the role of this gene in vulnerability to cocaine effects. AAVXlr4-KD animals show a potentiated behavioral and neurochemical response to cocaine, reinstatement following cocaine withdrawal and cocaine-induced spine density alterations in the Medium-Sized Spiny Neurons of NAc. We propose Xlr4 as a new candidate gene mediating the cocaine effects., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The ability to learn the reward-value and action-outcome contingencies in dynamic environment is critical for flexible adaptive behavior and development of effective pharmacological control of goal-directed behaviors represents an important challenge for improving the deficits in goal-directed behavior which may underlie seemingly disparate symptoms across psychiatric disorders. Adenosine A 2A receptor (A 2A R) is emerging as a novel neuromodulatory target for controlling goal-directed behavior for its unique neuromodulatory features: the ability to integrate dopamine and glutamate signaling, the "brake" constraint of various cognitive processes and the balanced control of goal-directed and habit actions. However, the contribution and circuit mechanisms of the striatopallidal A 2A Rs in nucleus accumbens (NAc) to control of goal-directed behavior remain to be determined. Here, we employed newly developed opto-A 2A R and the focal A 2A R knockdown strategies to demonstrate the causal role of NAc A 2A R in control of goal-directed behavior. Furthermore, we dissected out multiple distinct behavioral mechanisms underlying which NAc A 2A Rs control goal-directed behavior: (i) NAc A 2A Rs preferentially control goal-directed behavior at the expense of habit formation. (ii) NAc A 2A Rs modify the animals' sensitivity to the value of the reward without affecting the action-outcome contingency. (iii) A 2A R antagonist KW6002 promotes instrumental actions by invigorating motivation. (iv) NAc A 2A Rs facilitate Pavlovian incentive value transferring to instrumental action. (v) NAc A 2A Rs control goal-directed behavior probably not through NAc-VP pathway. These insights into the behavioral and circuit mechanisms for NAc A 2A R control of goal-directed behavior facilitate translational potential for A 2A R antagonists in reversal of deficits in goal-directed decision-making associated with multiple neuropsychiatric disorders., (Copyright © 2020. Published by Elsevier Ltd.)