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BACKGROUND: Alcohol use disorder (AUD) is a leading preventable cause of death. The central amygdala (CeA) is a hub for stress and AUD, while dysfunction of the noradrenaline (NA) stress system is implicated in AUD relapse. METHODS: Here we investigated whether alcohol (ethanol) dependence and protracted withdrawal alter noradrenergic regulation of the amygdala in rodents and humans. Male adult rats were housed under control conditions, subjected to chronic intermittent ethanol vapor exposure (CIE) to induce dependence, or withdrawn from CIE for two weeks, and ex vivo electrophysiology, biochemistry (catecholamine quantification by HPLC), in situ hybridization and behavioral brain-site specific pharmacology studies were performed. We also used qRT-PCR to assess gene expression of the α1(B), β1, and β2 adrenergic receptor in human post-mortem brain tissue from men diagnosed with AUD and matched controls. RESULTS: We found that α1 receptors potentiate CeA GABAergic transmission and drive moderate alcohol intake in control rats. In dependent rats, β receptors disinhibit a subpopulation of CeA neurons, contributing to their excessive drinking. Withdrawal produces CeA functional recovery with no change in local noradrenaline tissue concentrations, though there are some long-lasting differences in the cellular patterns of adrenergic receptor mRNA expression. Additionally, post-mortem brain analyses reveal increased α1B receptor mRNA in the amygdala of humans with AUD. CONCLUSIONS: Thus, CeA adrenergic receptors are key neural substrates of AUD. Identification of these novel mechanisms that drive alcohol drinking, particularly during the alcohol-dependent state, support ongoing new medication development for AUD.

A major problem managing alcohol use disorder is the high vulnerability to relapse, even after long periods of abstinence. Chronic alcohol use dysregulates stress responsivity, rendering this system hyporesponsive and making individuals vulnerable to relapse. Orexin (Orx; also called hypocretin) plays a role in diverse physiological processes, including stress. Orexin neurons, exclusively produced in the hypothalamus, project to the infralimbic cortex (IL). This study tested the hypothesis that IL-Orx transmission plays a significant role in stress-induced reinstatement of alcohol-seeking behavior in alcohol dependent rats.Male and female rats were trained to self-administer 10% alcohol (3 weeks) and then made dependent via chronic intermittent alcohol vapor exposure. Following extinction (5 days/week at 8 h abstinence for 10 sessions), rats received an intra-IL microinfusion of the dual Orx receptor (OrxR) antagonist TCS1102 (15 μg/0.5 μl/side) and then tested for footshock stress-induced reinstatement of alcohol seeking. In a separate cohort, Orx regulation of IL neuronal activity at the time of reinstatement was investigated using ex vivo electrophysiology.TCS1102 prevented reinstatement in dependent animals only. Moreover, Hcrtr mRNA expression in the hypothalamus and Hcrtr1/2 in the IL increased in alcohol-dependent animals at the time of testing. Lastly, dependence dampened basal Orx/OrxR influence over IL GABAergic synapses (using TCS1102) allowing for greater stimulated Orx effects.These results implicate IL-Orx transmission during stress-induced reinstatement of alcohol-seeking behavior in subjects with a history of alcohol dependence and show maladaptive recruitment of IL-Orx transmission by alcohol dependence.

BACKGROUND: Ethanol (EtOH) self-administration is particularly sensitive to the modulation of CB(1) signaling in the nucleus accumbens (NAc) shell, and EtOH consumption increases extracellular levels of the endogenous cannabinoid CB(1) receptor agonist 2-arachidonoyl glycerol (2-AG) in this brain region. Stimulation of CB(1) receptor with agonists increases EtOH consumption, suggesting that EtOH-induced increases in 2-AG might sustain motivation for EtOH intake. METHODS: In order to further explore this hypothesis, we analyzed the alterations in operant EtOH self-administration induced by intra-NAc shell infusions of 2-AG itself, the CB(1) inverse agonist SR141716A, the 2-AG clearance inhibitor URB602, anandamide, and the cyclooxygenase-2 (COX-2) inhibitor nimesulide. RESULTS: Surprisingly, self-administration of 10% EtOH was dose-dependently reduced by either intra-NAc shell SR141716A or 2-AG infusions. Similar effects were found by intra-NAc shell infusions of URB602, suggesting again a role for accumbal 2-AG on the modulation of EtOH intake. Intra-NAc shell anandamide did not alter EtOH self-administration, pointing to a specific role for 2-AG in the modulation of EtOH self-administration. Finally, the inhibitory effect of intra-NAc shell 2-AG on EtOH intake was significantly reversed by pretreatment with nimesulide, suggesting that oxidative metabolites of 2-AG might mediate these inhibitory effects on operant self-administration. CONCLUSIONS: We propose that 2-AG signaling in the NAc exerts an inhibitory influence on EtOH consumption through a non–CB1 receptor mechanism involving the COX-2 pathway.

Alcohol use dysregulates responsivity to stress, which is mediated by corticotropin-releasing factor (CRF). With repeated cycles of alcohol use, the hypothalamic-pituitary-adrenal axis becomes hyporesponsive, rendering individuals vulnerable to the reinstatement of alcohol-seeking behavior during stressful episodes. Orexin (Orx; also called hypocretin) plays a well-established role in regulating diverse physiological processes, including stress, and interacts with CRF. The infralimbic cortex (IL) is a CRF-rich region. Anatomical evidence suggests that CRF and Orx interact in this area. To test the behavioral implication of CRF and Orx transmission in the IL during the stress-induced reinstatement of alcohol-seeking behavior, male Wistar rats were trained to self-administer 10% alcohol for 3 weeks. The rats then underwent two weeks of extinction training (identical to the alcohol self-administration sessions, but alcohol was withheld). The day after the last extinction session, the rats received a bilateral intra-IL injection of the CRF(1) receptor antagonist CP154,526 (0.6 μg/0.5 μl/side), the dual Orx receptor antagonist TCS1102 (15 μg/0.5 μl/side), or their combination and then were tested for the footshock stress-induced reinstatement of alcohol-seeking behavior. CP154,526 significantly prevented reinstatement, but TCS1102 did not produce such an effect. Interestingly, the co-administration of TCS1102 and CP154,526 reversed the effect of CP154,526 alone, and footshock stress induced a significant increase in Crhr1 and Hcrtr2 mRNA expression in the IL. These results demonstrate a functional interaction between Orx receptor and CRF(1) receptor signaling and suggest that CRF(1) receptor antagonism may ameliorate stress-induced alcohol-seeking behavior.

Background: Orexin-A (OrxA) administration in the posterior paraventricular nucleus of the thalamus (pPVT) reinstates extinguished cocaine-seeking behaviour following extended access to the drug (a model of dependence). The pPVT receives and integrates information associated with emotionally salient events and sends excitatory inputs to brain regions involved in the expression of emotional states, such as those driving cocaine-seeking behaviour (i.e., the nucleus accumbens, the central nucleus of the amygdala [CeA], the basolateral amygdala, the bed nucleus of the stria terminalis [BNST] and the prefrontal cortex). Methods: We monitored the activation pattern of these regions (measured by Fos) during cocaine-seeking induced by OrxA administered to the pPVT. The BNST and CeA emerged as being selectively activated. To test whether the functionality of these regions was pivotal during OrxA-induced cocaine-seeking behaviour, we transiently inactivated these regions concomitantly with OrxA administration to the pPVT. We then tested the participation of corticotropin-releasing factor receptors (CRF1) in the CeA during OrxA-induced cocaine-seeking using the CRF1 antagonist CP154526. Results: We observed selective activation of the CeA and BNST during cocaine-seeking induced by OrxA administered to the pPVT, but only transient inactivation of the CeA prevented cocaine-seeking behaviour. Administration of CP154526 to the CeA prevented OrxA-induced cocaine-seeking behaviour. Limitations: The use of only male rats could have been a limitation. Other limitations could have been the use of an indirect approach to test the hypothesis that administration of OrxA to the pPVT drives cocaine-seeking via CRF1 signalling in the CeA, and a lack of analysis of the participation of CeA subregions. Conclusion: Cocaine-seeking behaviour induced by OrxA administered to the pPVT is driven by activation of the CeA via CRF1 signalling.

The endocannabinoid system is involved in the regulation of the stress response, but the relative contribution of N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) and their mechanisms have to be elucidated. In this study, we compared the effects of the pharmacological inhibition of the two major endocannabinoid-degrading enzymes [fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) for AEA and 2-AG, respectively] on stress-coping [forced swim test (FST) and tail suspension test (TST)] and anxiety-like [elevated-plus maze (EPM) and light-dark test (LDT)] behaviors in wild-type and FAAH knockout mice. In vivo microdialysis estimated the effects of FAAH and MAGL inhibition on dopamine (DA) and serotonin (5-HT) levels in the medial prefrontal cortex (mPFC) during an FST. Mice were treated with PF-3845 (FAAH inhibitor), JZL184 (MAGL inhibitor), JZL195 (dual FAAH/MAGL inhibitor) or vehicle. Our data showed that PF-3845 increased latency to immobility and decreased total immobility time in FST, but no effects were observed in TST compared with vehicle-treated wild-type mice. By contrast, JZL184 decreased latency and increased immobility in TST and FST. JZL195 in wild-type mice and JZL184 in FAAH knockout mice reproduced the same passive coping behaviors as JZL184 in wild-type mice in TST and FST. In the microdialysis experiment, FST was associated with increased DA and 5-HT levels in the mPFC. However, JZL184-treated wild-type mice displayed a significant attenuation of forced swim stress-induced DA release compared with vehicle-treated wild-type mice and PF-3845-treated wild-type mice. Finally, FAAH and/or MAGL inhibitors induced robust and consistent anxiolytic-like effects in EPM and LDT. These results suggested differences between FAAH and MAGL inhibition in stress-coping behaviors. Notably, MAGL inhibition induced a consistent avoidant coping behavior and attenuated the stress-induced mPFC DA response in FST. However, more investigation is needed to elucidate the functional association between DA and 2-AG signaling pathways, and the molecular mechanism in the regulation of passive coping strategies during inescapable stress., Highlights • FAAH and/or MAGL inhibition induce opposite changes in stress-coping behaviors. • MAGL inhibition increases passive stress-coping behaviors in mice. • Passive stress-coping behaviors are regulated by 2-AG rather than AEA signaling. • MAGL inhibition attenuates mPFC dopamine increase in the forced swim test. • FAAH and/or MAGL inhibitors are associated with anxiolytic-like effects.

Hypothalamic orexin (Orx) projections to the paraventricular nucleus of the thalamus (PVT) have received growing interest because of their role in drug-seeking behavior. Using an established model of cocaine dependence (i.e., long access [LgA] to cocaine), we previously showed that OrxA injections in the posterior PVT (pPVT) reinstated extinguished cocaine-seeking behavior in rats after an intermediate period of abstinence (2–3 weeks). Considering the long-lasting nature of drug-seeking behavior, the present study examined whether the priming effect of intra-pPVT OrxA administration was preserved after a period of protracted abstinence (4–5 weeks) in rats that self-administered cocaine under LgA conditions. Furthermore, to better understand whether a history of cocaine dependence affects the Orx system—particularly the hypothalamic Orx↔pPVT connection—the number of Orx-expressing cells in the lateral hypothalamus (LH), dorsomedial hypothalamus (DMH), and perifornical area (PFA) and number of orexin receptor 1 (OrxR1)- and OrxR2-expressing cells in the pPVT were quantified. Orexin A administration in the pPVT induced cocaine-seeking behavior after intermediate abstinence, as reported previously. At protracted abstinence, however, the priming effect of OrxA was absent. A higher number of cells that expressed Orx was observed in the LH/DMH/PFA at both intermediate and protracted abstinence. In the pPVT, the number of OrxR2-expressing cells was significantly higher only at intermediate abstinence, with no changes in the number of OrxR1-expressing cells. These data build on our previous findings that the hypothalamic Orx↔pPVT connection is strongly recruited shortly after cocaine abstinence and demonstrate that the priming effect of OrxA is not long lasting. Furthermore, these findings suggest that throughout abstinence, the Orx↔pPVT connection undergoes neuroadaptive changes, reflected by alterations of the number of OrxR2-expressing cells in the pPVT.

Neural systems involved in processing natural rewards and drugs of abuse overlap and exposure to drugs of abuse induce neuroadaptations that can cause compulsive-like behavior. For example, the recruitment of the orexin (Orx) system by drugs of abuse has been proposed to induce neuroadaptations that in turn alter its function, reflected by maladaptive, compulsive, and addictive behavior. Orexin neurons project to the paraventricular nucleus of the thalamus (PVT)-particularly the posterior part (pPVT), a structure that plays a key role in stress regulation. This study investigated whether Orx transmission in the pPVT plays a role in stress-induced reinstatement of reward-seeking behavior toward ethanol (EtOH) and a highly palatable food reward [sweetened condensed milk (SCM)] in rats and whether this role changes with EtOH dependence. After being trained to orally self-administer EtOH or SCM, the rats were made dependent (EtOHD and SCMD) by chronic intermittent EtOH vapor exposure. The control nondependent groups (EtOHND and SCMND) were exposed to air. Following extinction, the rats were tested for stress-induced reinstatement of EtOH- and SCM-seeking behavior. Stress reinstated EtOH- and SCM-seeking behavior in all groups (EtOHD/ND and SCMD/ND). Administration of the dual Orx receptor (OrxR) antagonist TCS1102 (15 μg) in the pPVT prevented stress-induced reinstatement only in dependent rats (EtOHD and SCMD). In parallel, the qPCR analysis showed that Orx mRNA expression in the hypothalamus and OrxR1/R2 mRNA expression in the pPVT were increased at the time of testing in the EtOHD and SCMD groups. These results are the first to implicate Orx transmission in the pPVT in the stress-induced reinstatement of reward-seeking behavior in EtOH dependent rats and indicate the maladaptive recruitment of Orx transmission in the pPVT by EtOH dependence.

BACKGROUND: Despite considerable efforts, few drugs are available for the treatment of alcohol (ethanol [EtOH]) use disorder (AUD). Ethanol directly or indirectly modulates several aspects of the central nervous system, including neurotransmitter/neuromodulator systems. Relapse vulnerability is a challenge for the treatment of EtOH addiction. Ethanol withdrawal symptoms create motivational states that lead to compulsive EtOH drinking and relapse even after long periods of abstinence. Among the therapeutics to treat AUD, naltrexone (NTX) is a pharmacological treatment for relapse. The present study evaluated the effect of NTX on EtOH drinking in male and female EtOH-dependent rats during abstinence. METHODS: Wistar rats (males and females) were first trained to orally self-administer 10% EtOH. Half of the rats were then made dependent by chronic intermittent EtOH (CIE) vapor exposure, and the other half were exposed to air. Using this model, rats exhibit somatic and motivational signs of withdrawal. At the end of EtOH vapor (or air) exposure, the rats were tested for the effects of NTX (10 mg/kg, p.o.) on EtOH self-administration at three abstinence time points: acute abstinence (8 h, A-Abst), late abstinence (2 weeks, L-Abst), and protracted abstinence (6 weeks, P-Abst). RESULTS: Naltrexone decreased EtOH intake in nondependent rats, regardless of sex and abstinence time point. In post-dependent rats, NTX decreased EtOH intake only at a delayed abstinence time point (P-Abst) in males, whereas it similarly reduced EtOH drinking in females at all abstinence time points. CONCLUSIONS: The therapeutic efficacy of NTX depends on the time of intervention during abstinence and is different between males and females. The data further suggest that EtOH dependence causes different neuroadaptations in male and female rats, reflected by differential effects of NTX. The results underscore the significance of considering the duration of EtOH abstinence and sex as a biological variable as important factors when developing pharmacotherapies for AUD.

Cannabidiol (CBD), the major non-psychoactive constituent of Cannabis sativa, has received attention for therapeutic potential in treating neurologic and psychiatric disorders. Recently, CBD has also been explored for potential in treating drug addiction. Substance use disorders are chronically relapsing conditions and relapse risk persists for multiple reasons including craving induced by drug contexts, susceptibility to stress, elevated anxiety, and impaired impulse control. Here, we evaluated the “anti-relapse” potential of a transdermal CBD preparation in animal models of drug seeking, anxiety and impulsivity. Rats with alcohol or cocaine self-administration histories received transdermal CBD at 24 h intervals for 7 days and were tested for context and stress-induced reinstatement, as well as experimental anxiety on the elevated plus maze. Effects on impulsive behavior were established using a delay-discounting task following recovery from a 7-day dependence-inducing alcohol intoxication regimen. CBD attenuated context-induced and stress-induced drug seeking without tolerance, sedative effects, or interference with normal motivated behavior. Following treatment termination, reinstatement remained attenuated up to ≈5 months although plasma and brain CBD levels remained detectable only for 3 days. CBD also reduced experimental anxiety and prevented the development of high impulsivity in rats with an alcohol dependence history. The results provide proof of principle supporting potential of CBD in relapse prevention along two dimensions: beneficial actions across several vulnerability states and long-lasting effects with only brief treatment. The findings also inform the ongoing medical marijuana debate concerning medical benefits of non-psychoactive cannabinoids and their promise for development and use as therapeutics. Sin financiación 7.160 JCR (2018) Q1, 21/267 Neurosciences, 11/267 Pharmacology & Pharmacy, 11/146 Psychiatry 3.205 SJR (2018) Q1, 16/555 Psychiatry and Mental Health, 9/335 Pharmacology No data IDR 2018 UEM

The orexin (Orx) system is known to play a critical role in drug addiction and reward-related behaviors. The dynorphin (Dyn) system, conversely, promotes depressive-like behavior and plays a key role in the aversive effects of stress. Orexin and Dyn are co-released and have opposing functions in reward and motivation in the ventral tegmental area (VTA). Earlier studies showed that microinjections of OrxA in the posterior paraventricular nucleus of the thalamus (pPVT) exerted priming-like effects and reinstated cocaine-seeking behavior, suggesting that Orx transmission in the pPVT participates in cocaine-seeking behavior. The present study sought to determine whether Orx and Dyn interact in the pPVT. Using a cellular approach, brain slices were prepared for whole-cell recordings and to study excitatory transmission in pPVT neurons. The superfusion of OrxA increased spontaneous glutamatergic transmission by increasing glutamate release onto pPVT neurons, whereas DynA decreased glutamate release. Furthermore, the augmentation of OrxA-induced glutamate release was reversed by DynA. To corroborate the electrophysiological data, separate groups of male Wistar rats were trained to self-administer cocaine or sweetened condensed milk (SCM). After self-administration training, the rats underwent extinction training and were tested with intra-pPVT administration of OrxA±DynA under extinction conditions. OrxA reinstated cocaine-and SCM-seeking behavior, with a greater effect in cocaine animals. DynA selectively blocked OrxA-induced cocaine seekingvs. SCM seeking. The data indicate that DynA in the pPVT prevents OrxA-induced cocaine seeking, perhaps by reversing the OrxA-induced increase in glutamate release, identifying a novel therapeutic target to prevent cocaine relapse.

Repeated cycles of alcohol [ethanol (EtOH)] intoxication and withdrawal dysregulate excitatory glutamatergic systems in the brain and induce neuroadaptations in the medial prefrontal cortex (mPFC) that contribute to cognitive dysfunction. The mPFC is composed of subdivisions that are functionally distinct, with dorsal regions facilitating drug-cue associations and ventral regions modulating new learning in the absence of drug. A key modulator of glutamatergic activity is the holoenzyme calcium/calmodulin-dependent protein kinase II (CaMKII) that phosphorylates ionotropic glutamate receptors. Here, we examined the hypothesis that abstinence from chronic intermittent EtOH (CIE) exposure dysregulates CaMKII activity in the mPFC to impair cognitive flexibility. We used an operant model of strategy set shifting in male Long-Evans rats demonstrating reduced susceptibility to trial omissions during performance in a visual cue-guided task versus albino strains. Relative to naive controls, rats experiencing approximately 10 days of abstinence from CIE vapor exposure demonstrated impaired performance during a procedural shift from visual cue to spatial location discrimination. Phosphorylation of CaMKII subtype α was upregulated in the dorsal, but not ventral mPFC of CIE-exposed rats, and was positively correlated with perseverative-like responding during the set shift. The findings suggest that abstinence from CIE exposure induces an undercurrent of kinase activity (e.g. CaMKII), which may promote aberrant glutamatergic responses in select regions of the mPFC. Given the role of the mPFC in modulating executive control of behavior, we propose that increased CaMKII subtype α activity reflects a dysregulated 'top-down' circuit that interferes with adaptive behavioral performance under changing environmental demands.

Nicotine exerts its rewarding effects by promoting an increase in dopamine (DA) release in the nucleus accumbens (NAc), and this process is influenced by the endocannabinoid system. Fatty acid amide hydrolase (FAAH) is the main enzyme responsible for the degradation of the endocannabinoid anandamide and other non-cannabinoid N-acylethanolamines. Previous research has reported that both genetic deletion and pharmacological inhibition of FAAH enhance nicotine-induced conditioned place preference at low doses. We conducted a microdialysis study to characterize nicotine-induced changes in DA and serotonin (5-HT) levels in the NAc of FAAH knockout (KO) mice using a conditioned place preference-like paradigm with three nicotine doses (0.1, 1 and 10 mg/kg, s.c.). Additionally, the effects of the selective FAAH inhibitor PF-3845 (10 mg/kg, i.p.) were also examined. Our data indicated that compared with wild-type mice, genetic deletion of FAAH selectively enhanced the effect of low-dose nicotine on DA release (p

Alcohol use disorder (AUD) is a chronic, relapsing disorder that is characterized by the compulsive use of alcohol despite numerous health, social, and economic consequences. Initially, the use of alcohol is driven by positive reinforcement. Over time, however, alcohol use can take on a compulsive quality that is driven by the desire to avoid the negative consequences of abstinence, including negative affect and heightened stress/anxiety. This transition from positive reinforcement- to negative reinforcement-driven consumption involves the corticotropin-releasing factor (CRF) system, although mounting evidence now suggests that the CRF system interacts with other neural systems to ultimately produce behaviors that are symptomatic of compulsive alcohol use, such as the hypocretin (Hcrt) system. Hypocretins are produced exclusively in the hypothalamus, but Hcrt neurons project widely throughout the brain and reach regions that perform regulatory functions for numerous behavioral and physiological responses-including the infralimbic cortex (IL) of the medial prefrontal cortex (mPFC). Although the entire mPFC undergoes neuroadaptive changes following prolonged alcohol exposure, the IL appears to undergo more robust changes compared with other mPFC substructures. Evidence to date suggests that the IL is likely involved in EtOH-seeking behavior, but ambiguities with respect to the specific role of the IL in this regard make it difficult to draw definitive conclusions. Furthermore, the manner in which CRF interacts with Hcrt in this region as it pertains to alcohol-seeking behavior is largely unknown, although immunohistochemical and electrophysiological experiments have shown that CRF and Hcrt directly interact in the mPFC, suggesting that the interaction between CRF and Hcrt in the IL may be critically important for the development and subsequent maintenance of compulsive alcohol seeking. This review aims to consolidate recent literature regarding the role of the IL in alcohol-seeking behavior and to discuss evidence that supports a functional interaction between Hcrt and CRF in the IL.

Administration of selective serotonin reuptake inhibitors (SSRIs), typically used as antidepressants, induces long-lasting behavioral changes associated with alcohol use disorder (AUD). However, the contribution of SSRI (fluoxetine)-induced alterations in neurobiological processes underlying alcohol relapse such as endocannabinoid and glutamate signaling in the central amygdala (CeA) remains largely unknown. We utilized an integrative approach to study the effects of repeated fluoxetine administration during abstinence on ethanol drinking. Gene expression and biochemical and electrophysiological studies explored the hypothesis that dysregulation in glutamatergic and endocannabinoid mechanisms in the CeA underlie the susceptibility to alcohol relapse. Cessation of daily treatment with fluoxetine (10 mg/kg) during abstinence resulted in a marked increase in ethanol seeking during re-exposure periods. The increase in ethanol self-administration was associated with (a) reductions in levels of the endocannabinoids N-arachidonoylethanolomine and 2-arachidonoylglycerol in the CeA, (b) increased amygdalar gene expression of cannabinoid type-1 receptor (CB1), N-acyl phosphatidylethanolamine phospholipase D (Nape-pld), fatty acid amid hydrolase (Faah), (c) decreased amygdalar gene expression of ionotropic AMPA (GluA2 and GluA4) and metabotropic (mGlu3) glutamate receptors, and (d) increased glutamatergic receptor function. Overall, our data suggest that the administration of the antidepressant fluoxetine during abstinence dysregulates endocannabinoid signaling and glutamatergic receptor function in the amygdala, facts that likely facilitate alcohol drinking behavior during relapse.

Hypothalamic orexin/hypocretin (Orx/Hcrt) neurons are thought to mediate both food-reinforced behaviors and behavior motivated by drugs of abuse. However, the relative role of the Orx/Hcrt system in behavior motivated by food versus drugs of abuse remains unclear. This investigation addressed this question by contrasting hypothalamic Orx/Hcrt neuronal activation associated with reinstatement of reward seeking induced by stimuli conditioned to cocaine (COC) versus highly palatable food reward, sweetened condensed milk (SCM). Orx/Hcrt neuronal activation in the lateral hypothalamus, dorsomedial hypothalamus and perifornical area, determined by dual c-fos/orx immunocytochemistry, was quantified in rat brains, following reinstatement of reward seeking induced by a discriminative stimulus (S+ ) conditioned to COC or SCM. The COC S+ and SCM S+ initially produced the same magnitude of reward seeking. However, over four subsequent tests, behavior induced by the SCM S+ decreased to extinction levels, whereas reinstatement induced by the COC S+ perseverated at undiminished levels. Following both the first and fourth tests, the percentage of Orx/Hcrt cells expressing Fos was significantly increased in all hypothalamic subregions in rats tested with the COC S+ but not rats tested with the SCM S+ . These findings point toward a role for the Orx/Hcrt system in perseverating, compulsive-like COC seeking but not behavior motivated by palatable food. Moreover, analysis of the Orx/Hcrt recruitment patterns suggests that failure of Orx/Hcrt neurons in the lateral hypothalamus to respond to inhibitory inputs from Orx/Hcrt neurons in the dorsomedial hypothalamus/perifornical area may contribute to the perseverating nature of COC seeking.

Orexin/hypocretin (Orx/Hcrt) projections from the lateral hypothalamus (LH) to the paraventricular nucleus of the thalamus (PVT) are implicated in drug addiction. Specifically, the posterior region of the PVT (pPVT) innervates brain structures that modulate motivated behavior. This study investigated the role of pPVT-Orx/Hcrt transmission in cocaine-seeking behavior. Because the effects of Orx/Hcrt are mediated by two Orx/Hcrt receptors (Hcrt-r1 and Hcrt-r2), we examined the extent to which Hcrt-r1 and Hcrt-r2 are involved in Orx/Hcrt-induced cocaine seeking. Male Wistar rats were made cocaine dependent by self-administering cocaine 6 h/day (long access [LgA]) for 21 days. Following self-administration training, the animals were subjected to daily extinction training, during which cocaine was withheld. Following extinction, the rats received intra-pPVT microinjections of Orx-A/Hcrt-1 (0-2 µg) alone or, using a single dose of 0.5 µg, in combination with an Hcrt-r1 antagonist (SB334867; 0-15 µg) or an Hcrt-r2 antagonist (TCSOX229; 0-15 µg). Orx-A/Hcrt-1 alone reinstated (primed) cocaine-seeking behavior. Unexpectedly, co-administration of Orx-A/Hcrt-1 with SB334867 did not have any effects on Orx-A/Hcrt-1-induced reinstatement, whereas co-administration of Orx-A/Hcrt-1 with TCSOX229 prevented cocaine-seeking behavior. These results suggest that Hcrt-r2 in the pPVT mediates the reinstating effect of Orx-A/Hcrt-1 in animals with a history of cocaine dependence and further identify Hcrt-r2 as a possible molecular target that can guide future therapeutic approaches for the prevention of drug seeking.

Cocaine addiction is a chronically relapsing disorder that is characterized by compulsive drug use and the loss of control over intake despite adverse consequences. The currently available therapeutic approaches fail to completely treat or address the compulsive nature of drug seeking and drug taking that are associated with addiction. This chronic relapsing disorder is believed to result from neurodysregulation and long-lasting neuroadaptations that are induced by prolonged drug use. An increasing body of evidence indicates the potential benefit of targeting the orexin system, which is known to participate in numerous physiological functions, to prevent some of the behavioral effects of drugs of abuse, such as their reinforcing and addictive actions, with minimal effects on behavior that is directed toward conventional reinforcers. This chapter discusses preclinical studies that suggest the key involvement of the orexin system in cocaine addiction.

Prescription opioids, such as oxycodone, are potent analgesics that are used to treat and manage pain. However, oxycodone is one of the most commonly abused prescription drugs. Finding an effective strategy to prevent prescription opioid use disorder is urgent. Orexin receptors (OrxR1 and OrxR2) have been implicated in the regulation of motivation, arousal, and stress, making them possible targets for the treatment of substance use disorder. To study the significance of environmental stimuli in maintaining the vulnerability to relapse to oxycodone use, resistance to the extinction of oxycodone-seeking behavior that was elicited by an oxycodone-related stimulus was examined. Rats were trained to self-administer oxycodone in the presence of a contextual/discriminative stimulus (SD). Using this procedure, the rats readily acquired oxycodone self-administration and exhibited increases in physical signs of opioid withdrawal. Following extinction, response-reinstating effects of re-exposure to the SD perseverated. We then tested whether OrxR blockade prevents oxycodone intake and relapse. The effects of the OrxR1 antagonist SB334867 and OrxR2 antagonist TCSOX229 on oxycodone self-administration were tested. SB334867 significantly decreased oxycodone self-administration, whereas TCSOX229 did not produce any effect. To investigate whether OrxR1 and OrxR2 blockade prevents oxycodone seeking, the rats were tested for the ability of SB334867 and TCSOX229 to prevent the SD-induced conditioned reinstatement of oxycodone-seeking behavior. SB334867 decreased oxycodone-seeking behavior, whereas TCSOX229 was ineffective. These results suggest that OrxR1 antagonism prevents excessive prescription opioid use and relapse and might be beneficial for the treatment of prescription opioid use disorder.

Deletion of fatty acid amide hydrolase (FAAH), enzyme responsible for degrading endocannabinoids, increases alcohol consumption and preference. However, there is a lack of data on neurochemical events in mice exposed to alcohol in the absence of FAAH. Extracellular levels of endocannabinoids and relevant neurotransmitters were measured by in vivo microdialysis in the nucleus accumbens (NAc) of FAAH knockout (KO) and wild-type (WT) mice during an ethanol (EtOH; 2 g/kg, ip) challenge in EtOH-naive and repeated (r) EtOH-treated mice. In both genotypes, EtOH treatment caused no changes in baseline endocannabinoid levels, although FAAH KO mice displayed higher baseline N-arachidonoylethanolamine levels than WT mice. EtOH challenge caused a sustained increase in 2-arachidonoylglycerol (2-AG) levels in EtOH-naive WT mice but not in FAAH KO mice. In contrast, 2-AG levels were decreased following EtOH challenge in (r)EtOH-treated mice in both genotypes. Whereas (r)EtOH-treated mice showed higher baseline dopamine and serotonin levels than EtOH-naive mice in WT mice, these differences were attenuated in FAAH KO mice. Significant differences in baseline γ-aminobutyric acid (GABA) and glutamate levels by EtOH history were observed in WT mice but not in FAAH KO mice. Moreover, opposed effects on glutamate response were observed after EtOH challenge in EtOH-naive and (r)EtOH-treated FAAH KO mice. Finally, FAAH deletion failed to show EtOH-induced locomotion sensitivity. These data provide evidence of a potential influence of 2-AG in the neurochemical response to EtOH exposure in the NAc.

BackgroundDespite considerable efforts, few drugs are available for the treatment of alcohol (ethanol [EtOH]) use disorders (AUDs). Ethanol directly or indirectly modulates several aspects of the central nervous system, including neurotransmitter/neuromodulator systems. Relapse vulnerability is a challenge for the treatment of EtOH addiction. Ethanol withdrawal symptoms create motivational states that lead to compulsive EtOH drinking and relapse even after long periods of abstinence. Among the therapeutics to treat AUDs, naltrexone (NTX) is a pharmacological treatment for relapse. The goal of the present study was to evaluate the effect of NTX on EtOH drinking in EtOH-dependent male and female rats during abstinence.MethodsWistar rats (males and females) were first trained to orally self-administer 10% EtOH. Half of them were then made dependent by chronic intermittent EtOH (CIE) vapor exposure, and the other half were exposed to air. Using this model, rats exhibit somatic and motivational signs of withdrawal. At the end of EtOH vapor (or air) exposure, the rats were tested for the effects of NTX (10 mg/kg, p.o.) on EtOH self-administration at three abstinence time points: acute abstinence (8 h, A-Abst), late abstinence (2 weeks, L-Abst), and protracted abstinence (6 weeks, P-Abst).ResultsNTX decreased EtOH intake in nondependent rats, regardless of sex and abstinence time point. In post-dependent rats, the effects of NTX improved with a longer abstinence time (i.e., L-Abst and P-Abst) in males, whereas it similarly reduced EtOH drinking in females at all abstinence points.ConclusionsThe data suggest that the therapeutic efficacy of NTX depends on the time of intervention during abstinence and sex. The data further suggest that EtOH dependence induces different neuroadaptations in male and female rats, reflected by differential effects of NTX. The results underscore the significance of considering the duration of EtOH abstinence and sex for the development of pharmacotherapeutic treatments for AUD.

Originally studied for its role in energy homeostasis, the paraventricular nucleus of the thalamus (PVT) has recently gained attention because of its involvement in the modulation of drug-directed behavior. The posterior part of the PVT (pPVT) is connected with brain structures that modulate motivated behavior, and we tested whether the pPVT plays a pivotal role in cocaine seeking. The aim of the present study was to investigate whether transient inactivation of the pPVT prevents cue-induced reinstatement of cocaine seeking but not natural reward seeking. Male Wistar rats were trained to associate a discriminative stimulus (S(+)) with the availability of cocaine or a highly palatable conventional reinforcer, sweetened condensed milk (SCM). Following extinction, the cocaine S(+) and SCM S(+) elicited comparable levels of reinstatement. Intra-pPVT administration of the γ-aminobutyric acid-A (GABAA) and GABAB receptor agonists muscimol and baclofen (0.06 and 0.6mM, respectively) prior to the presentation of the cocaine or SCM S(+) completely prevented the reinstatement of cocaine seeking, with no statistically significant effects on SCM seeking. These data show that the pPVT plays an important role in neuronal mechanisms that drive cocaine-seeking behavior.

The paraventricular nucleus of the thalamus (PVT) is not traditionally considered part of the brain addiction neurocircuitry but has received growing attention with regard to a role in the modulation of drug-seeking behavior. This study sought to establish the pattern of neural activation induced by a response-reinstating discriminative stimulus (SD ) conditioned to either cocaine (COC) or a conventional reinforcer using a palatable food substance, sweetened condensed milk (SCM). Male Wistar rats were trained to associate one SD (S+ ; COC or SCM availability) and a distinctly different SD (S- ; non-reward; i.e. the availability of saline or the absence of SCM). Following extinction of COC- and SCM-reinforced responding, rats were presented with the respective S+ or S- alone and tested for the reinstatement of reward seeking. The COC S+ and SCM S+ elicited identical reinstatement, whereas the non-reward S- was behaviorally ineffective. PVT sections were obtained following completion of the reinstatement tests and labeled for Fos. The number of Fos+ neurons was compared among rats that were presented with the COC S+ , SCM S+ or S- . Rats that were presented with the COC S+ exhibited a significant increase in Fos expression compared with rats that were presented with the S- . Moreover, Fos expression was significantly correlated with the number of reinstatement responses that were induced by the COC S+ . In contrast, the SCM S+ and S- produced identical increases in Fos expression, without behaviorally relevant correlations. The findings implicate the PVT as an important site that is selectively recruited during COC-seeking behavior.

The hypocretin/orexin (HCRT) neuropeptide system regulates feeding, arousal state, stress responses, and reward, especially under conditions of enhanced motivational relevance. In particular, HCRT neurotransmission facilitates drug-seeking behavior in circumstances that demand increased effort and/or motivation to take the drug. The present study used a shRNA-encoding adeno-associated viral vector to knockdown Hcrt expression throughout the dorsal hypothalamus in adult rats and determine the role of HCRT in cocaine self-administration. Chronic Hcrt silencing did not impact cocaine self-administration under short-access conditions, but robustly attenuated cocaine intake under extended access conditions, a model that mimics key features of compulsive cocaine taking. In addition, Hcrt silencing decreased motivation for both cocaine and a highly palatable food reward (i.e., sweetened condensed milk; SCM) under a progressive ratio schedule of reinforcement, but did not alter responding for SCM under a fixed ratio schedule. Importantly, Hcrt silencing did not affect food or water consumption, and had no consequence for general measures of arousal and stress reactivity. At the molecular level, chronic Hcrt knockdown reduced the number of neurons expressing dynorphin (DYN), and to a smaller extent melanin-concentrating hormone (MCH), in the dorsal hypothalamus. These original findings support the hypothesis that HCRT neurotransmission promotes operant responding for both drug and non-drug rewards, preferentially under conditions requiring a high degree of motivation. Furthermore, the current study provides compelling evidence for the involvement of the HCRT system in cocaine self-administration also under low-effort conditions in rats allowed extended access, possibly via functional interactions with DYN and MCH signaling.

The hypocretin/orexin (HCRT) neuropeptide system regulates feeding, arousal state, stress responses, and reward, especially under conditions of enhanced motivational relevance. In particular, HCRT neurotransmission facilitates drug-seeking behavior in circumstances that demand increased effort and/or motivation to take the drug. The present study used a shRNA-encoding adeno-associated viral vector to knockdownHcrtexpression throughout the dorsal hypothalamus in adult rats and determine the role of HCRT in cocaine self-administration. LongtermHcrtsilencing did not impact cocaine self-administration under short-access conditions, but robustly attenuated cocaine intake during extended self-administration access, a model that mimics key features of compulsive cocaine-taking. In addition,Hcrtsilencing decreased motivation for both cocaine and palatable food (i.e., sweetened condensed milk; SCM) under a progressive ratio schedule of reinforcement, but did not alter responding for SCM under a fixed ratio schedule. Importantly,Hcrtsilencing did not affect food or water consumption, and had no consequence to general measures of arousal-dependent behaviors.At the molecular level, longtermHcrtknockdown moderately reduced the downstream expression of dynorphin (DYN) and melanin-concentrating hormone (MCH) in the dorsal hypothalamus.These original findings support the hypothesis that HCRT neurotransmission promotes operant responding for both drug and non-drug rewards, preferentially under conditions requiring a high degree of motivation. Furthermore, the current study provides compelling evidence for the involvement of the HCRT system in cocaine self-administration also under low-effort conditions in rats allowed extended access,possibly via functional interactions with DYN and MCH signaling.

Cebranopadol is a novel agonist of nociceptin/orphanin FQ peptide (NOP) and opioid receptors with analgesic properties that is being evaluated in clinical Phase 2 and Phase 3 trials for the treatment of chronic and acute pain. Recent evidence indicates that the combination of opioid and NOP receptor agonism may be a new treatment strategy for cocaine addiction. We sought to extend these findings by examining the effects of cebranopadol on cocaine self-administration (0.5 mg/kg/infusion) and cocaine conditioned reinstatement in rats with extended access to cocaine. Oral administration of cebranopadol (0, 25, and 50 μg/kg) reversed the escalation of cocaine self-administration in rats that were given extended (6 h) access to cocaine, whereas it did not affect the self-administration of sweetened condensed milk (SCM). Cebranopadol induced conditioned place preference but did not affect locomotor activity during the conditioning sessions. Finally, cebranopadol blocked the conditioned reinstatement of cocaine seeking. These results show that oral cebranopadol treatment prevented addiction-like behaviors (i.e., the escalation of intake and reinstatement), suggesting that it may be a novel strategy for the treatment of cocaine use disorder. However, the conditioned place preference that was observed after cebranopadol administration suggests that this compound may have some intrinsic rewarding effects.

Dysregulation of the nociceptin (N/OFQ) system has been implicated in alcohol abuse and alcoholism and growing evidence suggests that targeting this system may be beneficial for treating alcoholism. To further explore the treatment target potential of the N/OFQ system, the novel non-peptide, small-molecule N/OFQ (NOP) agonist MT-7716, (R)-2-{3-[1-(Acenaphthen-1-yl)piperidin-4-yl]-2-oxo-2,3-dihydro-1H-benzimidazol-1-yl}-N-methylacetamide hydrochloride hydrate, was examined for its effects on ethanol self-administration and stress induced reinstatement of alcohol seeking in non-dependent and post-dependent rats. Male Wistar rats were trained to self-administer ethanol and then made ethanol dependent via repeated intragastric ethanol intubation. The effects of MT-7716 (0.3 and 1 mg/kg; PO) on alcohol self-administration were determined two weeks following dependence induction, when baseline self-administration was restored. Effects of MT-7716 on stress-induced reinstatement were tested in separate cohorts of rats, one and three weeks post-withdrawal. MT-7716 reduced alcohol self-administration and stress-induced reinstatement of alcohol seeking in post-dependent rats, but was ineffective in non-dependent animals. Moreover, the prevention of stress-induced reinstatement by MT-7716 was more pronounced at 3 weeks post-dependence. The results further confirm treatment target potential for the NOP receptor and identify non-peptide NOP agonists as promising potential treatment drugs for alcohol abuse and relapse prevention. The findings also support dysregulation of the N/OFQ system as a factor in alcohol seeking and reinforcement.

Hypothalamic orexin/hypocretin (Orx/Hcrt) peptides participate in the regulation of a wide range of physiological processes and are recruited by drugs of abuse. To advance our understanding of the potential of the Orx/Hcrt receptor-1 (Hcrt-r1) as a treatment target for cocaine addiction, the effect of SB334867 [N-(2-methyl-6-benzoxazolyl)-N'-1,5-n-aphthyridin-4-yl urea], a specific Hcrt-r1 antagonist, on reinstatement elicited by cocaine-associated stimuli versus stimuli associated with a highly palatable conventional reinforcer [sweetened condensed milk (SCM)] was tested. Two separate groups of male Wistar rats were trained to associate a discriminative stimulus (S⁺) with the response-contingent availability of cocaine (0.25 mg/0.1 ml/infusion) or SCM [2/1 (v/v)] and subjected to reinstatement tests following extinction of cocaine-reinforced or SCM-reinforced behavior, during which the reinforcers and S⁺ were withheld. Following extinction, presentation of the cocaine or SCM S⁺ produced comparable recovery of responding. Hcrt-r1 blockade by SB334867 (1-10 mg/kg, intraperitoneal) dose-dependently and selectively reversed conditioned reinstatement induced by cocaine-related stimuli, without interfering with reward seeking produced by the same stimulus when conditioned to SCM. The findings suggest an important role for Hcrt-r1 in appetitive behavior controlled by reward-related stimuli with selectivity for cocaine seeking and identify Hcrt-r1 as a potential treatment target for cocaine relapse prevention.

Hypothalamic orexin/hypocretin (Orx/Hcrt) neurons are thought to mediate both food-reinforced behaviors and behavior motivated by drugs of abuse. However, the relative role of the Orx/Hcrt system in behavior motivated by food vs. drugs of abuse remains unclear. This investigation addressed this question by contrasting hypothalamic Orx/Hcrt neuronal activation associated with reinstatement of reward seeking induced by stimuli conditioned to cocaine (COC) vs. highly palatable food reward, sweetened condensed milk (SCM). Orx/Hcrt neuronal activation in the lateral hypothalamus (LH), dorsomedial hypothalamus (DMH), and perifornical area (PFA), determined by dual c-fos/orx immunocytochemistry, was quantified in rat brains following reinstatement of reward seeking induced by a discriminative stimulus (S+) conditioned to COC or SCM. The COC S+ and SCM S+ initially produced the same magnitude of reward seeking. However, over four subsequent tests, behavior induced by the SCM S+ decreased to extinction levels, whereas reinstatement induced by the COC S+ perseverated at undiminished levels. Following both the first and fourth tests, the percentage of Orx/Hcrt cells expressing Fos was significantly increased in all hypothalamic subregions in rats tested with the COC S+, but not rats tested with the SCM S+. These findings point toward a role for the Orx/Hcrt system in perseverating, compulsive-like cocaine seeking but not behavior motivated by palatable food. Moreover, analysis of the Orx/Hcrt recruitment patterns suggests that failure of Orx/Hcrt neurons in the LH to respond to inhibitory inputs from Orx/Hcrt neurons in the DMH/PFA may contribute to the perseverating nature of cocaine seeking.

σ₁ Receptors have been implicated in cognitive function, anxiety, depression, and the regulation of stress responses. In addition, σ₁ receptors have been shown to participate in the behavioral and motivational effects of psychostimulants. Recent studies have shown that σ₁ receptor antagonism prevents ethanol-induced conditioned place preference in mice and excessive drinking in alcohol-dependent or alcohol-preferring rats. Therefore, this study was designed to determine whether this role for σ₁ receptors extends to ethanol-seeking behavior using an animal model of relapse and tested whether the suppressant effect of a potent σ₁ receptor antagonist, BD1047, generalizes to natural reward-seeking behavior. Two separate groups of rats were trained to orally self-administer 10% (w/v) ethanol or a highly palatable reinforcer, 3%/0.125% (w/v) glucose/saccharin (SuperSac), in the presence of a discriminative stimulus (S). Following extinction, during which the reinforcers and S were withheld, the presentation of the ethanol or SuperSac S produced comparable recovery of responding. BD1047 (1-20 mg/kg) exerted similar behavioral effects on both ethanol S-induced and SuperSac S-induced reinstatement, with the prevention of conditioned reinstatement only at the highest BD1047 dose. The present results show that σ₁ receptor blockade under the present conditions exerts similar effects on conditioned reinstatement induced by ethanol-related and SuperSac-related stimuli, suggestive of overlapping neural mechanisms that control ethanol and natural reward seeking.

Metabotropic glutamate receptors (mGluRs) have been implicated in the regulation of anxiety, stress responses and the neurobehavioral effects of psychostimulants. The present study was designed to examine whether antagonizing mGluR5 or activating mGluR2/3 prevents stress-induced reinstatement of cocaine seeking. Male Wistar rats were trained to self-administer cocaine and then subjected to daily extinction training for 2 weeks. Subsequent exposure to 15 minutes of intermittent footshock elicited robust reinstatement of responding at the previously active lever. Both the selective mGluR5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]piperidine (MTEP) (0-3 mg/kg, intraperitoneally) and the selective mGluR2/3 agonist (-)-2-oxa-4-aminobicylco[3.1.0]hexane-4,6-dicarboxylic acid (LY379268) (0-3 mg/kg, subcutaneously) prevented cocaine seeking induced by footshock stress following the same dose-response function. The data show that although mGluR2/3 and mGluR5 are differentially located on synaptic compartments, both LY379268 and MTEP produced the same behavioral effects in reducing stress-induced reinstatement. These results are important because they demonstrate that a reduction in glutamate-mediated neural excitability (albeit via different mechanisms of action) reverses footshock-induced reinstatement and suggest that pharmacological manipulations of mGluR2/3 and mGluR5 can prevent the effects of stress, a major precipitating factor for relapse. These findings further confirm that mGluR2/3 or mGluR5 are promising targets for relapse prevention.

Background: Alcohol withdrawal refers to a cluster of symptoms that may occur from suddenly ceasing the use of alcohol after chronic or prolonged ingestion. These symptoms make alcohol abstinence difficult and increase the risk of relapse in recovering alcoholics. In previous studies, we demonstrated that treatment with Nociceptin/orphanin FQ (N/OFQ) significantly reduces alcohol consumption and attenuates alcohol-seeking behavior induced by environmental conditioning factors or by stress in rats. In this study, we evaluated whether activation of brain NOP receptors may also attenuate alcohol withdrawal signs in rats. Methods: For this purpose, animals were subjected to a 6-day chronic alcohol intoxication (by intragastric administration), and at 8, 10, and 12 hours following cessation of alcohol exposure, they were treated intracerebroventricularly (ICV) with N/OFQ (0.0, 1.0, and 3.0 μg/rat). Somatic withdrawal signs were scored after ICV treatment. In a subsequent experiment, to evaluate N/OFQ effects on alcohol withdrawal-induced anxiety, another group of rats was subjected to ethanol intoxication and after 1 week was tested for anxiety behavior in the elevated plus maze (EPM). In the last experiment, an additional group of rats was tested for anxiety elicited by acute ethanol intoxication (hangover anxiety). For this purpose, animals received an acute dose (3.0 g/kg) of 20% alcohol and 12 hour later were tested in the EPM following ICV N/OFQ (0.0, 1.0, and 2.0 μg/rat). Results: Results showed that N/OFQ significantly reduced the expression of somatic withdrawal signs and reversed anxiety-like behaviors associated with both chronic and acute alcohol intoxication. N/OFQ did not affect anxiety scores in nondependent animals. Conclusions: These findings suggest that the N/OFQ-NOP receptor system may represent a promising target for the development of new treatments to ameliorate alcohol withdrawal symptoms.

Background Rats with extended daily cocaine access show escalating cocaine self-administration and behavioral signs of dependence. Regulation of glutamatergic transmission by metabotropic glutamate receptors has emerged as a mechanism in the addictive actions of drugs of abuse. We examined here whether neuroadaptive dysregulation of metabotropic glutamate receptor function is a factor in escalating cocaine self-administration. Methods Rats with 1 hour daily cocaine access (short access [ShA]) versus 6-hour access (long access [LgA]) were tested for differences in the effects of the metabotropic glutamate receptor 2/3 (mGluR2/3) agonist (−)-2-oxa-4-aminobicylco(3.1.0)hexane-4,6-dicarboxylic acid (LY379268) and the metabotropic glutamate receptor 5 (mGluR5) antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]-pyridine (MTEP) on cocaine-reinforced progressive-ratio responding and differences in expression levels and functional activity of mGluR2/3 and mGluR5. Results The LgA groups showed higher progressive-ratio breakpoints than ShA groups. LY379268 (0–3 mg/kg subcutaneous) dose-dependently lowered breakpoints in the LgA group but reduced breakpoints only at 3 mg/kg in the ShA group. Consistent with this behavioral effect, functional mGluR2/3 activity was significantly elevated following LgA cocaine exposure. MTEP (0–3 mg/kg intraperitoneal) reduced breakpoints in the ShA group only. Long access cocaine exposure was associated with decreased mGluR5 expression, accompanied by reduced functional mGluR5 activity in the nucleus accumbens. A downward trend developed in mGluR5 protein expression in the medial prefrontal cortex and hippocampus. Conclusions Functional upregulation of mGluR2/3 and downregulation of mGluR5 are likely factors in the transition to cocaine dependence. The differential behavioral effects of LY379268 and MTEP in rats with a history of long access to cocaine have implications for the treatment target potential of mGluR2/3 and mGluR5.

Background Growing evidence supports a role of metabotropic glutamate receptors (mGluRs) in ethanol reinforcement, ethanol seeking, and ethanol withdrawal. To extend the understanding of the role of mGluRs in the addiction-relevant effects of ethanol as well as of the treatment target potential of these receptors for alcohol abuse, the effects of a selective mGlu2/3 agonist (LY379268) and a selective mGlu5 antagonist (MTEP) were tested on two processes central to alcohol addiction: ethanol reinforcement and stress-induced reinstatement of ethanol seeking in rats with a history of ethanol dependence. Methods Following operant ethanol self-administration training, male Wistar rats were made dependent by intragastric ethanol intubations. Ethanol dependence was confirmed by the presence of somatic withdrawal signs. Following 2 weeks of withdrawal, stable ethanol self-administration was reestablished, and the effects of LY379268 (0–3 mg/kg subcutaneous) and MTEP (0–3 mg/kg, intraperitoneal) on ethanol self-administration were determined in both nondependent and postdependent rats. A second set of rats underwent extinction training and then was tested for the effects of LY379268 or MTEP on reinstatement of ethanol seeking induced by footshock stress. Results LY379268 and MTEP dose-dependently reduced both ethanol self-administration and reinstatement of ethanol seeking induced by footshock stress. Additionally, LY379268 was more effective than MTEP in inhibiting both behaviors in postdependent than in nondependent animals. Conclusions These findings suggest that neuroadaptation associated with chronic ethanol exposure or withdrawal alters the sensitivity of mGlu2/3 receptors, with implications for the understanding of the neural basis of alcohol dependence and the treatment target potential of these receptors.