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Corticostriatal projection neurons from prelimbic medial prefrontal cortex to the nucleus accumbens core critically regulate drug-seeking behaviors, yet the underlying encoding dynamics whereby these neurons contribute to drug seeking remain elusive. Here we use two-photon calcium imaging to visualize the activity of corticostriatal neurons in mice from the onset of heroin use to relapse. We find that the activity of these neurons is highly heterogeneous during heroin self-administration and seeking, with at least 8 distinct neuronal ensembles that display both excitatory and inhibitory encoding dynamics. These neuronal ensembles are particularly apparent during relapse, where excitatory responses are amplified compared to heroin self-administration. Moreover, we find that optogenetic inhibition of corticostriatal projection neurons attenuates heroin seeking regardless of the relapse trigger. Our results reveal the precise corticostriatal activity dynamics underlying drug-seeking behaviors and support a key role for this circuit in mediating relapse to drug seeking., Competing Interests: Competing Interests The authors have no competing interests to declare.

Drugs of abuse cause changes in the prefrontal cortex (PFC) and associated regions that impair inhibitory control over drug-seeking. Breaking the contingencies between drug-associated cues and the delivery of the reward during extinction learning reduces relapse. Vagus nerve stimulation (VNS) has previously been shown to enhance extinction learning and reduce drug-seeking. Here we determined the effects of VNS-mediated release of brain-derived neurotrophic factor (BDNF) on extinction and cue-induced reinstatement in male rats trained to self-administer cocaine. Pairing 10 d of extinction training with VNS facilitated extinction and reduced drug-seeking behavior during reinstatement. Rats that received a single extinction session with VNS showed elevated BDNF levels in the medial PFC as determined via an enzyme-linked immunosorbent assay. Systemic blockade of tropomyosin receptor kinase B (TrkB) receptors during extinction, via the TrkB antagonist ANA-12, decreased the effects of VNS on extinction and reinstatement. Whole-cell recordings in brain slices showed that cocaine self-administration induced alterations in the ratio of AMPA and NMDA receptor-mediated currents in Layer 5 pyramidal neurons of the infralimbic cortex (IL). Pairing extinction with VNS reversed cocaine-induced changes in glutamatergic transmission by enhancing AMPAR currents, and this effect was blocked by ANA-12. Our study suggests that VNS consolidates the extinction of drug-seeking behavior by reversing drug-induced changes in synaptic AMPA receptors in the IL, and this effect is abolished by blocking TrkB receptors during extinction, highlighting a potential mechanism for the therapeutic effects of VNS in addiction., Competing Interests: The authors declare no competing financial interests., (Copyright © 2024 the authors.)

Lack of behavioral suppression typifies substance use disorders, yet the neural circuit underpinnings of drug-induced behavioral disinhibition remain unclear. Here, we employ deep-brain two-photon calcium imaging in heroin self-administering mice, longitudinally tracking adaptations within a paraventricular thalamus to nucleus accumbens behavioral inhibition circuit from the onset of heroin use to reinstatement. We find that select thalamo-accumbal neuronal ensembles become profoundly hypoactive across the development of heroin seeking and use. Electrophysiological experiments further reveal persistent adaptations at thalamo-accumbal parvalbumin interneuronal synapses, whereas functional rescue of these synapses prevents multiple triggers from initiating reinstatement of heroin seeking. Finally, we find an enrichment of μ-opioid receptors in output- and cell-type-specific paraventricular thalamic neurons, which provide a mechanism for heroin-induced synaptic plasticity and behavioral disinhibition. These findings reveal key circuit adaptations that underlie behavioral disinhibition in opioid dependence and further suggest that recovery of this system would reduce relapse susceptibility., Competing Interests: Declaration of interests The authors have no competing interests to declare., (Copyright © 2023 Elsevier Inc. All rights reserved.)

There is a critical need to develop a capable and well-trained workforce dedicated to the systematic study of sex differences and examination of sex as a biological variable. Through the support of the Office of Research on Women's Health and partner National Institute of Health centers, the Specialized Centers of Research Excellence (SCORE) on Sex Differences Career Enhancement Cores (CECs) were established to help address this need. We describe the integration of the Medical University of South Carolina SCORE CEC with other National Institutes of Health (NIH)-funded and institutional training programs to promote training synergies, share resources, and enhance mentorship opportunities. Benefits of developing an intrainstitutional training platform have included facilitating cross-disciplinary interactions, encouragement of peer mentorship, and reduced burden on training program leadership.

Clinical and preclinical studies indicate that adaptations in corticostriatal neurotransmission significantly contribute to heroin relapse vulnerability. In animal models, heroin self-administration and extinction produce cellular adaptations in both neurons and astrocytes within the nucleus accumbens (NA) core that are required for cue-induced heroin seeking. Specifically, decreased glutamate clearance and reduced association of perisynaptic astrocytic processes with NAcore synapses allow glutamate release from prelimbic (PrL) cortical terminals to engage synaptic and structural plasticity in NAcore medium spiny neurons. Normalizing astrocyte glutamate homeostasis with drugs like the antioxidant N-acetylcysteine (NAC) prevents cue-induced heroin seeking. Surprisingly, little is known about heroin-induced alterations in astrocytes or pyramidal neurons projecting to the NAcore in the PrL cortex (PrL-NAcore). Here, we observe functional adaptations in the PrL cortical astrocyte following heroin self-administration (SA) and extinction as measured by the electrophysiologically evoked plasmalemmal glutamate transporter 1 (GLT-1)-dependent current. We likewise observed the increased complexity of the glial fibrillary acidic protein (GFAP) cytoskeletal arbor and increased association of the astrocytic plasma membrane with synaptic markers following heroin SA and extinction training in the PrL cortex. Repeated treatment with NAC during extinction reversed both the enhanced astrocytic complexity and synaptic association. In PrL-NAcore neurons, heroin SA and extinction decreased the apical tuft dendritic spine density and enlarged dendritic spine head diameter in male Sprague-Dawley rats. Repeated NAC treatment during extinction prevented decreases in spine density but not dendritic spine head expansion. Moreover, heroin SA and extinction increased the co-registry of the GluA1 subunit of AMPA receptors in both the dendrite shaft and spine heads of PrL-NAcore neurons. Interestingly, the accumulation of GluA1 immunoreactivity in spine heads was further potentiated by NAC treatment during extinction. Finally, we show that the NAC treatment and elimination of thrombospondin 2 (TSP-2) block cue-induced heroin relapse. Taken together, our data reveal circuit-level adaptations in cortical dendritic spine morphology potentially linked to heroin-induced alterations in astrocyte complexity and association at the synapses. Additionally, these data demonstrate that NAC reverses PrL cortical heroin SA-and-extinction-induced adaptations in both astrocytes and corticostriatal neurons.

Dysregulation of the input from the prefrontal cortex (PFC) to the nucleus accumbens (NAc) contributes to cue-induced opioid seeking but the heterogeneity in, and regulation of, prelimbic (PL)-PFC to NAc (PL->NAc) neurons that are altered has not been comprehensively explored. Recently, baseline and opiate withdrawal-induced differences in intrinsic excitability of Drd1 + (D1 + ) versus Drd2 + (D2 + ) PFC neurons have been demonstrated. Thus, here we investigated physiological adaptations of PL->NAc D1 + versus D2 + neurons after heroin abstinence and cue-induced relapse. Drd1-Cre + and Drd2-Cre + transgenic male Long-Evans rats with virally labeled PL->NAc neurons were trained to self-administer heroin followed by 1 week of forced abstinence. Heroin abstinence significantly increased intrinsic excitability in D1 + and D2 + PL->NAc neurons and increased postsynaptic strength selectively in D1 + neurons. These changes were normalized by cue-induced relapse to heroin seeking. Based on protein kinase A (PKA)-dependent changes in the phosphorylation of plasticity-related proteins in the PL cortex during abstinence and cue-induced relapse to cocaine seeking, we assessed whether the electrophysiological changes in D1 + and D2 + PL->NAc neurons during heroin abstinence were regulated by PKA. In heroin-abstinent PL slices, application of the PKA antagonist (R)-adenosine, cyclic 3',5'-(hydrogenphosphorothioate) triethylammonium (RP-cAMPs) reversed intrinsic excitability in both D1 + and D2 + neurons and postsynaptic strength in only D1 + neurons. Additionally, in vivo bilateral intra-PL infusion of RP-cAMPs after abstinence from heroin inhibited cue-induced relapse to heroin seeking. These data reveal that PKA activity in D1 + and D2 + PL->NAc neurons is not only required for abstinence-induced physiological adaptations but is also required for cue-induced relapse to heroin seeking. SIGNIFICANCE STATEMENT Neuronal plasticity in the medial prefrontal cortex is thought to underlie relapse to drug seeking, yet the subpopulation of neurons that express this plasticity to functionally guide relapse is unclear. Here we show cell type-specific adaptations in Drd1-expressing versus Drd2-expressing prelimbic pyramidal neurons with efferent projections to nucleus accumbens. These adaptations are bidirectionally regulated during abstinence versus relapse and involve protein kinase A (PKA) activation. Furthermore, we show that disruption of the abstinence-associated adaptations via site-specific PKA inhibition abolishes relapse. These data reveal the promising therapeutic potential of PKA inhibition for preventing relapse to heroin seeking and suggest that cell type-specific pharmacologies that target subpopulations of prefrontal neurons would be ideal for future therapeutic developments., (Copyright © 2023 the authors.)

Suppression of dangerous or inappropriate reward-motivated behaviors is critical for survival, whereas therapeutic or recreational opioid use can unleash detrimental behavioral actions and addiction. Nevertheless, the neuronal systems that suppress maladaptive motivated behaviors remain unclear, and whether opioids disengage those systems is unknown. In a mouse model using two-photon calcium imaging in vivo, we identify paraventricular thalamostriatal neuronal ensembles that are inhibited upon sucrose self-administration and seeking, yet these neurons are tonically active when behavior is suppressed by a fear-provoking predator odor, a pharmacological stressor, or inhibitory learning. Electrophysiological, optogenetic, and chemogenetic experiments reveal that thalamostriatal neurons innervate accumbal parvalbumin interneurons through synapses enriched with calcium permeable AMPA receptors, and activity within this circuit is necessary and sufficient for the suppression of sucrose seeking regardless of the behavioral suppressor administered. Furthermore, systemic or intra-accumbal opioid injections rapidly dysregulate thalamostriatal ensemble dynamics, weaken thalamostriatal synaptic innervation of downstream neurons, and unleash reward-seeking behaviors in a manner that is reversed by genetic deletion of thalamic µ-opioid receptors. Overall, our findings reveal a thalamostriatal to parvalbumin interneuron circuit that is both required for the suppression of reward seeking and rapidly disengaged by opioids., (© 2022. The Author(s).)

Cocaine self-administration disturbs intracellular signaling in multiple reward circuitry neurons that underlie relapse to drug seeking. Cocaine-induced deficits in prelimbic (PL) prefrontal cortex change during abstinence, resulting in different neuroadaptations during early withdrawal from cocaine self-administration than after one or more weeks of abstinence. Infusion of brain-derived neurotrophic factor (BDNF) into the PL cortex immediately following a final session of cocaine self-administration attenuates relapse to cocaine seeking for an extended period. BDNF affects local (PL) and distal subcortical target areas that mediate cocaine-induced neuroadaptations that lead to cocaine seeking. Blocking synaptic activity selectively in the PL projection to the nucleus accumbens during early withdrawal prevents BDNF from decreasing subsequent relapse. In contrast, blocking synaptic activity selectively in the PL projection to the paraventricular thalamic nucleus by itself decreases subsequent relapse and prior intra-PL BDNF infusion prevents the decrease. Infusion of BDNF into other brain structures at different timepoints after cocaine self administration differentially alters cocaine seeking. Thus, the effects of BDNF on drug seeking are different depending on the brain region, the timepoint of intervention, and the specific pathway that is affected., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The paraventricular thalamic nucleus (PVT) is highly interconnected with brain areas that control reward-seeking behavior. Despite this known connectivity, broad manipulations of PVT often lead to mixed, and even opposing, behavioral effects, clouding our understanding of how PVT precisely contributes to reward processing. Although the function of PVT in influencing reward-seeking is poorly understood, recent studies show that forebrain and hypothalamic inputs to, and nucleus accumbens (NAc) and amygdalar outputs from, PVT are strongly implicated in PVT responses to conditioned and appetitive or aversive stimuli that determine whether an animal will approach or avoid specific rewards. These studies, which have used an array of chemogenetic, optogenetic, and calcium imaging technologies, have shown that activity in PVT input and output circuits is highly heterogeneous, with mixed activity patterns that contribute to behavior in highly distinct manners. Thus, it is important to perform experiments in precisely defined cell types to elucidate how the PVT network contributes to reward-seeking behaviors. In this review, we describe the complex heterogeneity within PVT circuitry that appears to influence the decision to seek or avoid a reward and point out gaps in our understanding that should be investigated in future studies., (Copyright © 2020 McGinty and Otis.)

Cocaine self-administration (SA) in rats dysregulates glutamatergic signaling in the prelimbic (PrL) cortex and glutamate release in the nucleus accumbens (NA) core, promoting cocaine seeking. PrL adaptations that affect relapse to drug seeking emerge during the first week of abstinence, switching from an early (2 h) hypoglutamatergic state to a later (7 days) hyperglutamatergic state. Different interventions that normalize glutamatergic signaling in PrL cortex at each timepoint are necessary to suppress relapse. We hypothesized that plasticity-related proteins that regulate glutamatergic neurotransmission as well as dendritic spine morphology would be biphasically regulated during these two phases of abstinence in PrL cortical neurons projecting to the NA core (PrL-NA core). A combinatorial viral approach was used to selectively label PrL-NA core neurons with an mCherry fluorescent reporter. Male rats underwent 2 weeks of cocaine SA or received yoked-saline infusions and were perfused either 2 h or 7 days after the final SA session. Confocal microscopy and 3D reconstruction analyses were performed for Fos and pCREB immunoreactivity (IR) in the nucleus of layer V PrL-NA core neurons and GluA1-IR and GluA2-IR in apical dendritic spines of the same neurons. Here, we show that cocaine SA decreased PrL-NA core spine head diameter, nuclear Fos-IR and pCREB-IR, and GluA1-IR and GluA2-IR in putative mushroom-type spines 2 h after the end of cocaine SA, whereas the opposite occurred following 1 week of abstinence. Our findings reveal biphasic, abstinence duration-dependent alterations in structural plasticity and relapse-related proteins in the PrL-NA core pathway after cocaine SA.

Recreational drug use peaks during adolescence. Our research with adolescent vs adult male rats, however, shows that rats taking cocaine as adolescents have lower levels of cue-induced reinstatement of drug-seeking than adults, despite similar levels of intravenous (i.v.) cocaine self-administration. Lower rates of reinstatement in younger rats could be explained by higher levels of brain plasticity. Two neuroplasticity-related genes, activity-regulated cytoskeletal-associated gene (Arc) and brain-derived neurotrophic factor (Bdnf), influence cocaine self-administration and cue-induced reinstatement. We tested whether reinstatement of cocaine seeking correlates with expression of these genes in reinforcement-related brain regions. Adolescent and adult male rats (postnatal day 35 or 83-95 at start) were allowed to acquire lever-pressing maintained by i.v. infusions of cocaine in daily 2-h sessions over 13 days. At one of three experimental time points, rats were sacrificed and tissue collected to analyze Arc and Bdnf mRNA by in situ hybridization in the entire medial prefrontal cortex and entire nucleus accumbens, as well as relevant subregions: prelimbic cortex, infralimbic cortex, and nucleus accumbens core and shell. Despite taking similar amounts of cocaine, adolescents reinstated less than adults. Gene expression was most notable in the prelimbic cortex, was generally higher in adolescent-onset groups, and was higher with longer abstinence. These data partially support the hypothesis that higher levels of Arc and/or Bdnf gene expression in reinforcement-related brain regions of younger animals contribute to lower rates of extinction responding and/or reinstatement. Future studies should include mechanistic analysis of Arc, Bdnf, and their signaling pathways in age-dependent effects of cocaine., (© 2018 Society for the Study of Addiction.)

A single BDNF microinfusion into prelimbic (PrL) cortex immediately after the last cocaine self-administration session decreases relapse to cocaine-seeking. The BDNF effect is blocked by NMDAR antagonists. To determine whether synaptic activity in putative excitatory projection neurons in PrL cortex is sufficient for BDNF's effect on relapse, the PrL cortex of male rats was infused with an inhibitory Designer Receptor Exclusively Activated by Designer Drugs (DREADD) viral vector driven by an αCaMKII promoter. Immediately after the last cocaine self-administration session, rats were injected with clozapine-N-oxide 30 min before an intra-PrL BDNF microinfusion. DREADD-mediated inhibition of the PrL cortex blocked the BDNF-induced decrease in cocaine-seeking after abstinence and cue-induced reinstatement after extinction. Unexpectedly, DREADD inhibition of PrL neurons in PBS-infused rats also reduced cocaine-seeking, suggesting that divergent PrL pathways affect relapse. Next, using a cre-dependent retroviral approach, we tested the ability of DREADD inhibition of PrL projections to the NAc core or the paraventricular thalamic nucleus (PVT) to alter cocaine-seeking in BDNF- and PBS-infused rats. Selective inhibition of the PrL-NAc pathway at the end of cocaine self-administration blocked the BDNF-induced decrease in cocaine-seeking but had no effect in PBS-infused rats. In contrast, selective inhibition of the PrL-PVT pathway in PBS-infused rats decreased cocaine-seeking, and this effect was prevented in BDNF-infused rats. Thus, activity in the PrL-NAc pathway is responsible for the therapeutic effect of BDNF on cocaine-seeking whereas inhibition of activity in the PrL-pPVT pathway elicits a similar therapeutic effect in the absence of BDNF. SIGNIFICANCE STATEMENT The major issue in cocaine addiction is the high rate of relapse. However, the neuronal pathways governing relapse remain unclear. Using a pathway-specific chemogenetic approach, we found that BDNF differentially regulates two key prelimbic pathways to guide long-term relapse. Infusion of BDNF in the prelimbic cortex during early withdrawal from cocaine self-administration decreases relapse that is prevented when neurons projecting from the prelimbic cortex to the nucleus accumbens core are inhibited. In contrast, BDNF restores relapse when neurons projecting from the prelimbic cortex to the posterior paraventricular thalamic nucleus are inhibited. This study demonstrates that two divergent cortical outputs mediate relapse that is regulated in opposite directions by infusing BDNF in the prelimbic cortex during early withdrawal from cocaine., (Copyright © 2018 the authors 0270-6474/18/388956-11$15.00/0.)

The neurotrophin Brain-Derived Neurotrophic Factor (BDNF) has been implicated in a number of neuropsychiatric disorders, including alcohol use disorder. Studies have shown that BDNF activity in cortical regions, such as the medial prefrontal cortex (mPFC) mediates various ethanol-related behaviors. We previously reported a significant down-regulation in Bdnf mRNA in mPFC following chronic ethanol exposure compared to control mice. The present study was conducted to extend these findings by examining whether chronic ethanol treatment reduces BDNF protein expression in mPFC and whether reversing this deficit via direct injection of BDNF or viral-mediated overexpression of BDNF in mPFC alters voluntary ethanol consumption in dependent and nondependent mice. Repeated cycles of chronic intermittent ethanol (CIE) exposure was employed to model ethanol dependence, which produces robust escalation of ethanol intake. Results indicated that CIE treatment significantly increased ethanol intake and this was accompanied by a significant decrease in BDNF protein in mPFC that lasted at least 72 h after CIE exposure. In a separate study, once dependence-related increased drinking was established, bilateral infusion of BDNF (0, 0.25, 0.50 μg) into mPFC significantly decreased ethanol intake in a dose-related manner in dependent mice but did not affect moderate drinking in nondependent mice. In a third study, viral-mediated overexpression of BDNF in mPFC prevented escalation of drinking in dependent mice but did not alter intake in nondependent mice. Collectively, these results provide evidence that adaptations in cortical (mPFC) BDNF activity resulting from chronic ethanol exposure play a role in mediating excessive ethanol drinking associated with dependence., (Published by Elsevier Ltd.)

Cocaine self-administration in rats results in dysfunctional neuroadaptations in the prelimbic (PrL) cortex during early abstinence. Central to these adaptations is decreased phospho-extracellular signal-regulated kinase (p-ERK), which plays a key role in cocaine seeking. Normalizing ERK phosphorylation in the PrL cortex immediately after cocaine self-administration decreases subsequent cocaine seeking. The disturbance in ERK phosphorylation is accompanied by decreased phosphorylation of striatal-enriched protein tyrosine phosphatase (STEP), indicating increased STEP activity. STEP is a well-recognized ERK phosphatase but whether STEP activation during early abstinence mediates the decrease in p-ERK and is involved in relapse is unknown. Here, we show that a single intra-PrL cortical microinfusion of the selective STEP inhibitor, TC-2153, immediately after self-administration suppressed post-abstinence context-induced relapse under extinction conditions and cue-induced reinstatement, but not cocaine prime-induced drug seeking or sucrose seeking. Moreover, an intra-PrL cortical TC-2153 microinfusion immediately after self-administration prevented the cocaine-induced decrease in p-ERK within the PrL cortex during early abstinence. Interestingly, a systemic TC-2153 injection at the same timepoint failed to suppress post-abstinence context-induced relapse or cue-induced reinstatement, but did suppress cocaine prime-induced reinstatement. These data indicate that the STEP-induced ERK dephosphorylation in the PrL cortex during early abstinence is a critical neuroadaptation that promotes relapse to cocaine seeking and that systemic versus intra-PrL cortical inhibition of STEP during early abstinence differentially suppresses cocaine seeking., (© 2017 Society for the Study of Addiction.)

Models of relapse have demonstrated that neuroadaptations in reward circuits following cocaine self-administration (SA) underlie reinstatement of drug-seeking. Dysregulation of the pathway from the prelimbic (PrL) cortex to the nucleus accumbens is implicated in reinstatement. A single BDNF infusion into the PrL cortex following a final cocaine SA session results in attenuation of reinstatement of cocaine-seeking. Inhibiting BDNF's receptor, TrkB, ERK/MAP kinase activation, or NMDA receptors blocks this attenuating effect, indicating that the interaction between glutamate-mediated synaptic activity and TrkB signaling is imperative to BDNF's suppressive effect on drug-seeking. Src family kinases (SFKs) are involved in both NMDA-mediated activation of TrkB- and TrkB-mediated tyrosine phosphorylation of NMDA receptors. We hypothesized that infusion of the SFK inhibitor, PP2, into the PrL cortex prior to a BDNF infusion, immediately after the end of the last cocaine SA session, would block BDNF's ability to suppress reinstatement of cocaine-seeking in rats with a cocaine SA history. PP2, but not the negative control, PP3, blocked BDNF's suppressive effect on context-induced relapse after 1 week of abstinence and cue-induced reinstatement after extinction. As previously reported, infusion of BDNF into the PrL cortex blocked cocaine SA-induced dephosphorylation of ERK, GluN2A, and GluN2B-containing receptors. Inhibition of SFKs using PP2 blocked BDNF-mediated phosphorylation of GluN2A, GluN2B, and ERK. These data indicate that SFK activity is necessary for BDNF-mediated suppression of cocaine-seeking and reversal of cocaine-induced dephosphorylation of key phosphoproteins in the prefrontal cortex related to synaptic plasticity.

Background: Excessive ethanol (EtOH) consumption remains an important health concern and effective treatments are lacking. The central oxytocin system has emerged as a potentially important therapeutic target for alcohol and drug addiction. These studies tested the hypothesis that oxytocin reduces EtOH consumption., Methods: Male C57BL/6J mice were given access to EtOH (20% v/v) using a model of binge-like drinking ("drinking in the dark") that also included the use of lickometer circuits to evaluate the temporal pattern of intake as well as 2-bottle choice drinking in the home cage. In addition, EtOH (12% v/v) and sucrose (5% w/v) self-administration on fixed- and progressive-ratio schedules were also evaluated. A wide range of systemically administered oxytocin doses were tested (0 to 10 mg/kg) in these models., Results: Oxytocin (0, 0.3, 1, 3, or 10 mg/kg) dose dependently reduced EtOH consumption (maximal 45% reduction) in the binge drinking model, with lower effective doses having minimal effects on general locomotor activity. Oxytocin's effect was blocked by pretreatment with an oxytocin receptor antagonist, and the pattern of contacts (licks) at the EtOH bottle suggested a reduction in motivation to drink EtOH. Oxytocin decreased 2-bottle choice drinking without altering general fluid intake. Oxytocin also reduced operant responding for EtOH and sucrose in a dose-related manner. However, oxytocin decreased responding and motivation (breakpoint values) for EtOH at doses that did not alter responding for sucrose., Conclusions: These results indicate that oxytocin reduces EtOH consumption in different models of self-administration. The effects are not likely due to a general sedative effect of the neuropeptide. Further, oxytocin reduces motivation for EtOH at doses that do not alter responding for a natural reward (sucrose). While some evidence supports a role for oxytocin receptors in mediating these effects, additional studies are needed to further elucidate underlying mechanisms. Nevertheless, these results support the therapeutic potential of oxytocin as a treatment for alcohol use disorder., (Copyright © 2017 by the Research Society on Alcoholism.)

Cocaine self-administration induces dysfunctional neuroadaptations in the prefrontal cortex that underlie relapse to cocaine-seeking. Cocaine self-administration disturbs glutamatergic transmission in the nucleus accumbens that is prevented by infusion of brain-derived neurotrophic factor (BDNF) into the prelimbic area of the prefrontal cortex. Intra-prelimbic infusion of BDNF decreases cocaine-seeking in a TrkB-ERK MAP kinase-dependent manner. Neuronal activity triggers an interaction between TrkB receptors and NMDA receptors, leading to ERK activation. In the present study, infusion of the GluN2A-containing NMDA receptor antagonist, TCN-201, or the GluN2B-containing NMDA receptor antagonist, Ro-25-6981, into the prelimbic cortex of rats blocked the suppressive effect of BDNF on cocaine-seeking. During early withdrawal from cocaine self-administration, tyrosine phosphorylation of ERK, GluN2A, and GluN2B in the prelimbic cortex was reduced and this reduction of phospho-proteins was prevented by intra-prelimbic BDNF infusion. TCN-201 infusion into the prelimbic cortex inhibited the BDNF-mediated increase in pERK and pGluN2A whereas Ro-25-6981 infusion into the prelimbic cortex blocked BDNF-induced elevation of pERK and pGluN2B, indicating that both GluN2A- and GluN2B-containing NMDA receptors underlie BDNF-induced ERK activation. These data demonstrate that BDNF-mediated activation of GluN2A- and GluN2B-containing NMDA receptors underlies ERK activation in the prelimbic cortex during early withdrawal, preventing subsequent relapse to cocaine-seeking., Competing Interests: The authors report no conflicts of interest., (Copyright © 2016 Elsevier B.V. and ECNP. All rights reserved.)

Rationale: The endogenous oxytocin system has emerged as an inhibitor of drug-seeking and stress in preclinical models., Objectives: The goal of this study was to examine whether systemic oxytocin administration attenuated methamphetamine (METH)-seeking in rats pre-exposed to a predator odor threat., Methods: In Experiment 1, rats were exposed for 5 days to the predator odor, 2,5-dihydro-2,4,5-trimethylthiazoline (TMT), or saline before METH self-administration began. After extinction training, rats were injected with 1 mg/kg, ip oxytocin (OXT) or saline 30 min before a cue-induced reinstatement test followed by re-extinction and a TMT-induced reinstatement test. In Experiment 2, TMT pre-exposure was followed by 10 days of 1 mg/kg OXT or saline injections before METH self-administration, extinction, and a TMT-induced reinstatement test., Results: In Experiment 1, TMT pre-exposed rats that were injected with saline 30 min before reinstatement exhibited greater drug-seeking induced by conditioned cues or TMT than that exhibited by saline pre-exposed rats. A single injection of OXT 30 min before reinstatement suppressed METH-seeking in both saline- and TMT pre-exposed rats. In Experiment 2, TMT pre-exposed rats that received saline injections for 10 days prior to METH self-administration exhibited enhanced drug-seeking induced by TMT during stress-induced reinstatement. OXT injections for 10 days prior to METH self-administration blocked only the stress-induced exacerbation of drug-seeking in TMT pre-exposed rats., Conclusions: These results support further research on the development of oxytocin as a novel therapeutic drug that has enduring effects on drug-seeking exacerbated by stress.

Cocaine self-administration disturbs intracellular signaling in prefrontal cortical neurons that regulate neurotransmission in the nucleus accumbens. The deficits in dorsomedial prefrontal cortex (dmPFC) signaling change over time, resulting in different neuroadaptations during early withdrawal from cocaine self-administration than after one or more weeks of abstinence. Within the first few hours of withdrawal, there is a marked decrease in tyrosine phosphorylation of critical intracellular and membrane-bound proteins in the dmPFC that include ERK/MAP kinase and the NMDA receptor subunits, GluN1 and GluN2B. These changes are accompanied by a marked increase in STEP tyrosine phosphatase activation. Simultaneously, ERK and PKA-dependent synapsin phosphorylation in presynaptic terminals of the nucleus accumbens is increased that may have a destabilizing impact on glutamatergic transmission. Infusion of brain-derived neurotrophic factor (BDNF) into the dmPFC immediately following a final session of cocaine self-administration blocks the cocaine-induced changes in phosphorylation and attenuates relapse to cocaine seeking for as long as three weeks. The intra-dmPFC BDNF infusion also prevents cocaine-induced deficits in prefronto-accumbens glutamatergic transmission that are implicated in cocaine seeking. Thus, intervention with BDNF in the dmPFC during early withdrawal has local and distal effects in target areas that are critical to mediating cocaine-induced neuroadaptations that lead to cocaine seeking., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Background: Dysregulation in the prefrontal cortex-nucleus accumbens pathway has been implicated in cocaine addiction. We have previously demonstrated that one intra-dorsomedial prefrontal cortex brain-derived neurotrophic factor (BDNF) infusion immediately following the last cocaine self-administration session caused a long-lasting inhibition of cocaine-seeking and normalized the cocaine-induced disturbance of glutamate transmission in the nucleus accumbens after extinction and a cocaine prime. However, the molecular mechanism mediating the brain-derived neurotrophic factor effect on cocaine-induced alterations in extracellular glutamate levels is unknown., Methods: In the present study, we determined the effects of brain-derived neurotrophic factor on cocaine-induced changes in the phosphorylation of synapsin (p-synapsin), a family of presynaptic proteins that mediate synaptic vesicle mobilization, in the nucleus accumbens during early withdrawal., Results: Two hours after cocaine self-administration, p-synapsin Ser9 and p-synapsin Ser62/67, but not p-synapsin Ser603, were increased in the nucleus accumbens. At 22 hours, only p-synapsin Ser9 was still elevated. Elevations at both time points were attenuated by an intra-dorsomedial prefrontal cortex brain-derived neurotrophic factor infusion immediately after the end of cocaine self-administration. Brain-derived neurotrophic factor also reduced cocaine self-administration withdrawal-induced phosphorylation of the protein phosphatase 2A C-subunit, suggesting that brain-derived neurotrophic factor disinhibits protein phosphatase 2A C-subunit, consistent with p-synapsin Ser9 dephosphorylation. Further, co-immunoprecipitation demonstrated that protein phosphatase 2A C-subunit and synapsin are associated in a protein-protein complex that was reduced after 2 hours of withdrawal from cocaine self-administration and reversed by brain-derived neurotrophic factor., Conclusions: Taken together, these findings demonstrate that brain-derived neurotrophic factor normalizes the cocaine self-administration-induced elevation of p-synapsin in nucleus accumbens that may underlie a disturbance in the probability of neurotransmitter release or represent a compensatory neuroadaptation in response to the hypofunction within the prefrontal cortex-nucleus accumbens pathway during cocaine withdrawal., (© The Author 2015. Published by Oxford University Press on behalf of CINP.)

Background: Oxytocin, a neurohypophyseal neuropeptide, is a potential mediator and regulator of drug addiction. However, the cellular mechanisms of oxytocin in drug seeking remain unknown., Methods: In the present study, we used a self-administration/reinstatement model to study the effects of oxytocin on cocaine seeking and its potential interaction with glutamate function at the receptor level., Results: Systemic oxytocin dose-dependently reduced cocaine self-administration during various schedules of reinforcement, including fixed ratio 1, fixed ratio 5, and progressive ratio. Oxytocin also attenuated reinstatement to cocaine seeking induced by cocaine prime or conditioned cues. Western-blot analysis indicated that oxytocin increased phosphorylation of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptor GluA1 subunit at the Ser 845 site with or without accompanying increases in phosphorylation of extracellular signal-regulated kinase, in several brain regions, including the prefrontal cortex, bed nucleus of the stria terminalis, amygdala, and dorsal hippocampus. Immunoprecipitation of oxytocin receptor and GluA1 subunit receptors further demonstrated a physical interaction between these 2 receptors, although the interaction was not influenced by chronic cocaine or oxytocin treatment. Oxytocin also attenuated sucrose seeking in a GluA1- or extracellular-signal-regulated kinase-independent manner., Conclusions: These findings suggest that oxytocin mediates cocaine seeking through interacting with glutamate receptor systems via second messenger cascades in mesocorticolimbic regions., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Abstinence from cocaine self-administration (SA) is associated with neuroadaptations in the prefrontal cortex (PFC) and nucleus accumbens (NAc) that are implicated in cocaine-induced neuronal plasticity and relapse to drug-seeking. Alterations in cAMP-dependent protein kinase A (PKA) signaling are prominent in medium spiny neurons in the NAc after repeated cocaine exposure but it is unknown whether similar changes occur in the PFC. Because cocaine SA induces disturbances in glutamatergic transmission in the PFC-NAc pathway, we examined whether dysregulation of PKA-mediated molecular targets in PFC-NAc neurons occurs during abstinence and, if so, whether it contributes to cocaine-seeking. We measured the phosphorylation of cAMP response element binding protein (Ser133) and GluA1 (Ser845) in the dorsomedial (dm) PFC and the presynaptic marker, synapsin I (Ser9, Ser62/67, Ser603), in the NAc after 7 days of abstinence from cocaine SA with or without cue-induced cocaine-seeking. We also evaluated whether infusion of the PKA inhibitor, 8-bromo-Rp-cyclic adenosine 3', 5'-monophosphorothioate (Rp-cAMPs), into the dmPFC after abstinence would affect cue-induced cocaine-seeking and PKA-regulated phosphoprotein levels. Seven days of forced abstinence increased the phosphorylation of cAMP response element binding protein and GluA1 in the dmPFC and synapsin I (Ser9) in the NAc. Induction of these phosphoproteins was reversed by a cue-induced relapse test of cocaine-seeking. Bilateral intra-dmPFC Rp-cAMPs rescued abstinence-elevated PKA-mediated phosphoprotein levels in the dmPFC and NAc and suppressed cue-induced relapse. Thus, by inhibiting abstinence-induced PKA molecular targets, relapse reverses abstinence-induced neuroadaptations in the dmPFC that are responsible, in part, for the expression of cue-induced cocaine-seeking., (© 2013 The Authors, Addiction Biology © 2013 Society for the Study of Addiction.)

Rationale: Dephosphorylation of extracellular signal-regulated kinase (ERK) and cyclic AMP response element binding protein (CREB) in the dorsomedial prefrontal cortex (dmPFC) at the end of short access (ShA) cocaine self-administration is implicated in cocaine seeking. However, what receptors and phosphatases mediate this effect and whether ERK/CREB and related phospho-proteins in the dmPFC react similarly during early withdrawal from long access (LgA) cocaine self-administration are unknown., Objectives: The effects of ShA vs. LgA cocaine self-administration on the phosphorylation of protein phosphatase 2A (PP2A) and striatal-enriched protein tyrosine phosphatase (STEP), as well as GluN and GluA receptor subtype expression in the dmPFC during early withdrawal, were compared., Methods: Rats self-administered cocaine or received saline during 2- or 6-h daily sessions for 10-11 days. Two hours after the final session, the dmPFC was dissected out and processed for immunoblotting., Results: Similar to previous findings after ShA cocaine, phospho-ERK and phospho-CREB in the dmPFC were decreased after LgA cocaine. Cocaine elevated phospho-PP2A (deactivation) and decreased phospho-STEP (activation) in both ShA and LgA cocaine rats. GluN1, GluN2B, and phospho-GluN2B Tyr1472 in the dmPFC were decreased after ShA and LgA cocaine. Further, a significant reduction of GluA2, GluA1, and phospho-GluA1 Ser845 was found only in LgA rats., Conclusions: Activation of phospho-STEP may underlie ERK and CREB dephosphorylation in the dmPFC as well as internalization and degradation of GluN complexes during early withdrawal from both ShA and LgA cocaine self-administration, whereas differential alteration of AMPA receptor subunits after ShA and LgA cocaine self-administration depends on cocaine intake.

Chronic drug exposure alters gene expression in the brain and produces long-term changes in neural networks that underlie compulsive drug taking and seeking. Exactly how drug-induced changes in synaptic plasticity and subsequent gene expression are translated into persistent neuroadaptations remains unclear. Emerging evidence suggests that complex drug-induced neuroadaptations in the brain are mediated by highly synchronized and dynamic patterns of gene regulation. Recently, it has become clear that epigenetic mechanisms contribute to drug-induced structural, synaptic, and behavioral plasticity by regulating expression of gene networks. Here we review how alterations in histone modifications, DNA methylation, and microRNAs regulate gene expression and contribute to psychostimulant addiction with a focus on the epigenetic mechanisms that regulate brain-derived neurotrophic factor (BDNF) expression following chronic cocaine exposure. Identifying epigenetic signatures that define psychostimulant addiction may lead to novel, efficacious treatments for drug craving and relapse.

Rationale: Regulator of G-protein signaling 4 (RGS4) is a brain-enriched negative modulator of G-protein-coupled receptor signaling. Decreased availability of RGS4 in the frontal cortex and striatum has been described in animal models of schizophrenia and drug addiction. However, cellular and behavioral consequences of dysregulated RGS4-dependent receptor signaling in the brain remain poorly understood., Objective: This study aims to investigate whether RGS4, through inhibiting the function of mGluR5 receptors in the dorsal striatum (dSTR), regulates cellular and behavioral responses to acute amphetamine., Methods: After herpes simplex virus-RGS4 was infused into the dSTR, RGS4 overexpression as well as binding of recombinant RGS4 to mGluR5 was assessed. The effect of RGS4 overexpression on behavioral activity induced by the intrastriatal mGluR5 agonist, DHPG, or amphetamine was recorded. Activation of extracellular signal-regulated kinase (ERK) and Akt (protein kinase B) was measured in the dSTR tissue at the end of each behavioral experiment., Results: RGS4 overexpressed in the dSTR coimmunoprecipitated with mGluR5 receptors and suppressed both behavioral activity and phospho-ERK levels induced by DHPG. RGS4 overexpression or the mGluR5 antagonist, 3-((2-methyl-4-thiazolyl)ethynyl)pyridine (MTEP), attenuated amphetamine-induced phospho-ERK (but not phospho-Akt) levels. RGS4 suppressed amphetamine-induced vertical activity and augmented horizontal activity over 90 min. Similarly, MTEP augmented amphetamine-induced horizontal activity, but did not affect vertical activity., Conclusions: The present data demonstrate that RGS4 in the dSTR attenuates amphetamine-induced ERK signaling and decreases the behavioral efficacy of acute amphetamine likely by limiting mGluR5 function.

Neuroadaptations that participate in the ontogeny of alcohol dependence are likely a result of altered gene expression in various brain regions. The present study investigated brain region-specific changes in the pattern and magnitude of gene expression immediately following chronic intermittent ethanol (CIE) exposure and 8 hours following final ethanol exposure [i.e. early withdrawal (EWD)]. High-density oligonucleotide microarrays (Affymetrix 430A 2.0, Affymetrix, Santa Clara, CA, USA) and bioinformatics analysis were used to characterize gene expression and function in the prefrontal cortex (PFC), hippocampus (HPC) and nucleus accumbens (NAc) of C57BL/6J mice (Jackson Laboratories, Bar Harbor, ME, USA). Gene expression levels were determined using gene chip robust multi-array average followed by statistical analysis of microarrays and validated by quantitative real-time reverse transcription polymerase chain reaction and Western blot analysis. Results indicated that immediately following CIE exposure, changes in gene expression were strikingly greater in the PFC (284 genes) compared with the HPC (16 genes) and NAc (32 genes). Bioinformatics analysis revealed that most of the transcriptionally responsive genes in the PFC were involved in Ras/MAPK signaling, notch signaling or ubiquitination. In contrast, during EWD, changes in gene expression were greatest in the HPC (139 genes) compared with the PFC (four genes) and NAc (eight genes). The most transcriptionally responsive genes in the HPC were involved in mRNA processing or actin dynamics. Of the few genes detected in the NAc, the most representatives were involved in circadian rhythms. Overall, these findings indicate that brain region-specific and time-dependent neuroadaptive alterations in gene expression play an integral role in the development of alcohol dependence and withdrawal., (© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction.)

Chronic methamphetamine (meth) can lead to persisting cognitive deficits in human addicts and animal models of meth addiction. Here, we examined the impact of either contingent or non-contingent meth on memory performance using an object-in-place (OIP) task, which measures the ability to detect an object relative to its location and surrounding objects. Further, we quantified monoamine transporter levels and markers of neurotoxicity within the OIP circuitry and striatum. Male Long-Evans rats received an acute meth binge (4 × 4 mg/kg i.p., 2 h intervals) or self-administered meth (0.02 mg/infusion, i.v.; 7 days for 1 h/day, followed by 14 days for 6 h/day). Rats were tested for OIP recognition memory following one week of withdrawal. Subsequently, transporters for serotonin (SERT) and norepinephrine (NET) were quantified using Western blot in tissue obtained from the hippocampus, perirhinal cortex, and prefrontal cortex. In addition, striatal dopamine transporters, tyrosine hydroxylase, and glial fibrillary acidic protein were measured to assess potential neurotoxicity. Control (saline-treated) rats spent more time interacting with the objects in the changed locations. In contrast, contingent or non-contingent meth resulted in disrupted OIP performance as seen by similar amounts of time spent with all objects, regardless of location. While only acute meth binge produced signs of neurotoxicity, both meth regimens decreased SERT in the perirhinal cortex and hippocampus. Only meth self-administration resulted in a selective decrease in NET. Meth-induced changes in SERT function in the OIP circuitry may underlie memory deficits independently of overt neurotoxic effects. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Glial cell line-derived neurotrophic factor (GDNF) supports the viability of midbrain dopamine (DA) neurons that degenerate in Parkinson's disease. Middle-aged, 12 month old, Gdnf heterozygous (Gdnf(+/-)) mice have diminished spontaneous locomotor activity and enhanced synaptosomal DA uptake compared with wild type mice. In this study, dopamine transporter (DAT) function in middle-aged, 12 month old Gdnf(+/-) mice was more thoroughly investigated using in vivo electrochemistry. Gdnf(+/-) mice injected with the DAT inhibitor, nomifensine, exhibited significantly more locomotor activity than wild type mice. In vivo electrochemistry with carbon fiber microelectrodes demonstrated enhanced clearance of DA in the striatum of Gdnf(+/-) mice, suggesting greater surface expression of DAT than in wild type littermates. Additionally, 12 month old Gdnf(+/-) mice expressed greater D(2) receptor mRNA and protein in the striatum than wild type mice. Neurochemical analyses of striatal tissue samples indicated significant reductions in DA and a faster DA metabolic rate in Gdnf(+/-) mice than in wild type mice. Altogether, these data support an important role for GDNF in the regulation of uptake, synthesis, and metabolism of DA during aging., (Published by Elsevier Inc.)

On April 24-27, 2010, the Motivational Neuronal Networks meeting took place in Wrightsville Beach, North Carolina. The conference was devoted to "Emerging, re-emerging, and forgotten brain areas" of the reward circuit. A central feature of the conference was four scholarly discussions of cutting-edge topics related to the conference's theme. These discussions form the basis of the present review, which summarizes areas of consensus and controversy, and serves as a roadmap for the next several years of research., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Exposure to psychostimulants increases brain-derived neurotrophic factor (BDNF) mRNA and protein levels in the cerebral cortex and subcortical structures. Because BDNF is co-localized with dopamine and glutamate in afferents to the striatum of rats, it may be co-released with those neurotransmitters upon stimulation. Further, there may be an interaction between the intracellular signaling cascades activated by dopamine, glutamate, and TrkB receptors in medium spiny striatal neurons. In the present study, the effect of acute amphetamine administration on TrkB phosphorylation, as an indirect indicator of activation, and striatal gene expression, was evaluated. In Experiment 1, 15 min or 2 h after a single saline or amphetamine (2.5 mg/kg, i.p.) injection, the caudate-putamen (CPu), nucleus accumbens (NAc), and dorsomedial prefrontal cortex (dmPFC) were extracted and processed for phospho (p)-TrkB immunoreactivity. Immunoprecipitation analyses indicated that neither the tyrosine phosphorylation (p-Tyr) or autophosphorylation sites of TrkB (706) were changed in NAc, CPu, or dmPFC 15 min after amphetamine administration. In contrast, p-Tyr and the PLCγ phosphorylation site of TrkB (816) were increased in the NAc and CPu 2 h after amphetamine. In Experiment 2, intra-striatal infusion of the tyrosine kinase inhibitor, K252a, increased amphetamine-induced vertical activity but not total distance traveled. In addition, K252a inhibited amphetamine-induced preprodynorphin, but not preproenkephalin, mRNA expression in the striatum. These data indicate that acute amphetamine administration induces p-TrkB activation and signaling in a time- and brain region-dependent manner and that TrkB/BDNF signaling plays an important role in amphetamine-induced behavior and striatal gene expression.

The caudate putamen (CPu) has been implicated in habit learning and neuroadaptive changes that mediate the compulsive nature of drug-seeking following chronic cocaine self-administration. Re-exposure to an operant chamber previously associated with cocaine, but not yoked-saline, increases activity-regulated cytoskeleton-associated (Arc) gene mRNA expression within the dorsolateral (dl) CPu following prolonged abstinence. In this study, we tested the hypothesis that antisense gene knockdown of Arc within the dlCPu would alter cocaine-seeking. Initial studies showed that a single infusion of Arc antisense oligodeoxynucleotide (ODN) into the dlCPu significantly attenuated the induction of Arc mRNA and Arc protein by a single cocaine exposure (20 mg/kg i.p.) compared to scrambled-ODN-infused controls. In cocaine self-administering rats, infusion of Arc antisense ODN into the dlCPu 3 h prior to a test of context-driven drug-seeking significantly attenuated Arc protein induction, but failed to alter responding during testing, suggesting striatal Arc does not facilitate context-induced drug-seeking following prolonged abstinence. However, Arc antisense ODN infusion blunted the decrease in responding during subsequent 1-h extinction tests 24 and 48 h later. Following re-exposure to a cocaine-paired context, surface expression of the AMPA-type glutamate receptor GluR1 was significantly reduced whereas GluR2 was significantly increased in the dlCPu, independent of Arc antisense ODN infusion. Together, these findings indicate an important role for Arc in neuroadaptations within brain regions responsible for drug-seeking after abstinence and direct attention to changes occurring within striatal circuitry that are necessary to break down the habitual behaviour that leads to relapse.

Rationale: Extracellular signal-regulated kinase (ERK), cAMP response element binding protein (CREB), and protein kinase B (PKB or Akt) in the striatum are differentially activated by acute and repeated amphetamine (AMPH) administration. However, the dopamine receptor subtypes that mediate transient vs. prolonged phosphorylation changes in these proteins induced by AMPH challenge in AMPH-sensitized rats are unknown., Objectives: The role of the D1 and D2 class of dopamine receptors in the differential phosphorylation of striatal ERK, CREB, Thr308-Akt and Ser473-Akt and the expression of behavioral sensitization induced by AMPH challenge in AMPH-pretreated rats were determined., Methods: D1 or D2 dopamine receptor antagonists were injected before an AMPH challenge in AMPH-sensitized rats. After behavioral activity was recorded, rats were euthanized either 15 min or 2 h after AMPH challenge and striatal phosphoprotein status was analyzed by Western blotting., Results: The D1 receptor antagonist (SCH23390) decreased stereotypical behavior whereas the D2 receptor antagonist (eticlopride) decreased all behavioral activity induced by an AMPH challenge in AMPH-sensitized rats. SCH23390, but not eticlopride, significantly decreased ERK, CREB, and Thr308-Akt phosphorylation in the striatum 15 min, and ERK and CREB phosphorylation 2 h, after AMPH challenge in AMPH-sensitized rats. In contrast, eticlopride, but not SCH23390, prevented a decrease in Akt phosphorylation 2 h after AMPH challenge., Conclusions: These data indicate that the time course of phosphoprotein signaling is differentially regulated by D1 and D2 receptors in the striatum of AMPH-sensitized rats, suggesting that complex regulatory interactions are activated by repeated AMPH exposure.

Chronic methamphetamine (meth) abuse can lead to persisting cognitive deficits. Here, we utilized a long-access meth self-administration (SA) protocol to assess recognition memory and metabotropic glutamate receptor (mGluR) expression, and the possible reversal of cognitive impairments with the mGluR5 allosteric modulator, 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl) benzamide (CDPPB). Male, Long-Evans rats self-administered i.v. meth (0.02 mg/infusion) on an FR1 schedule of reinforcement or received yoked-saline infusions. After seven daily 1-h sessions, rats were switched to 6-h daily sessions for 14 days, and then underwent drug abstinence. Rats were tested for object recognition memory at 1 week after meth SA at 90 min and 24 h retention intervals. In a separate experiment, rats underwent the same protocol, but received either vehicle or CDPPB (30 mg/kg) after familiarization. Rats were killed on day 8 or 14 post-SA and brain tissue was obtained. Meth intake escalated over the extended access period. Additionally, meth-experienced rats showed deficits in both short- and long-term recognition memory, demonstrated by a lack of novel object exploration. The deficit at 90 min was reversed by CDPPB treatment. On day 8, meth intake during SA negatively correlated with mGluR expression in the perirhinal and prefrontal cortex, and mGluR5 receptor expression was decreased 14 days after discontinuation of meth. This effect was specific to mGluR5 levels in the perirhinal cortex, as no differences were identified in the hippocampus or in mGluR2/3 receptors. These results from a clinically-relevant animal model of addiction suggest that mGluR5 receptor modulation may be a potential treatment of cognitive dysfunction in meth addiction.

Brain-derived neurotrophic factor (BDNF) is critical in synaptic plasticity and in the survival and function of midbrain dopamine neurons. In this study, we assessed the effects of a partial genetic deletion of BDNF on motor function and dopamine (DA) neurotransmitter measures by comparing Bdnf(+/-) with wildtype mice (WT) at different ages. Bdnf(+/-) and WT mice had similar body weights until 12 months of age; however, at 21 months, Bdnf(+/-) mice were significantly heavier than WT mice. Horizontal and vertical motor activity was reduced for Bdnf(+/-) compared to WT mice, but was not influenced by age. Performance on an accelerating rotarod declined with age for both genotypes and was exacerbated for Bdnf(+/-) mice. Body weight did not correlate with any of the three behavioral measures studied. Dopamine neurotransmitter markers indicated no genotypic difference in striatal tyrosine hydroxylase, DA transporter (DAT) or vesicular monoamine transporter 2 (VMAT2) immunoreactivity at any age. However, DA transport via DAT (starting at 12 months) and VMAT2 (starting at 3 months) as well as KCl-stimulated DA release were reduced in Bdnf(+/-) mice and declined with age suggesting an increasingly important role for BDNF in the release and uptake of DA with the aging process. These findings suggest that a BDNF expression deficit becomes more critical to dopaminergic dynamics and related behavioral activities with increasing age., (© 2010 The Authors. Genes, Brain and Behavior © 2010 Blackwell Publishing Ltd and International Behavioural and Neural Genetics Society.)

Cocaine-mediated neuroadaptations in the prefrontal cortical-nucleus accumbens pathway underlie drug-seeking in animals with a cocaine self-administration (SA) history. Neuroplasticity in the cortico-accumbens pathway is regulated, in part, by the expression and availability of neurotrophic factors, such as BDNF. We have previously demonstrated that infusion of BDNF into the dorsomedial prefrontal cortex (dmPFC) immediately after the last of 10 cocaine SA sessions attenuates contextual, cue- and cocaine prime-induced reinstatement of cocaine-seeking (Berglind et al., 2007) and normalizes cocaine-induced disruption of glutamatergic transmission in the nucleus accumbens (Berglind et al., 2009). In the present study, the suppressive effect of intra-dmPFC BDNF on cocaine-seeking is shown to depend on Trk receptor-mediated activation of extracellular signal-regulated kinase (ERK) signaling in the dmPFC. The tyrosine kinase inhibitor, K252a, and the mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor, U0126 (1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene), prevented BDNF's suppressive effects on cocaine-seeking. Vehicle-infused rats with a cocaine SA history showed significant decreases in ERK and cyclic AMP response element binding protein (CREB), but not Akt, phosphorylation after the final cocaine SA session that were reversed by intra-dmPFC BDNF. Additionally, BDNF's ability to normalize cocaine-mediated decreases in ERK and CREB phosphorylation was blocked by U0126, demonstrating that ERK/MAPK activation mediated the behavioral effects. This study elucidates a mechanism whereby BDNF/TrkB (tropomyosin receptor kinase B) activates ERK-regulated CREB phosphorylation in the dmPFC to counteract the neuroadaptations induced by cocaine SA and subsequent relapse to cocaine-seeking.

In this study, the expression patterns of zif268 and activity-regulated cytoskeleton-associated gene (arc) were investigated in the basolateral amygdala (BLA) and dorsal hippocampal (dHPC) subregions during context-induced drug-seeking following 22 h or 15 d abstinence from cocaine self-administration. Arc and zif/268 mRNA in BLA and dHPC increased after re-exposure to the cocaine-paired chamber at both timepoints; however, only the BLA increases (with one exception-see below) were differentially affected by the presence or absence of the cocaine-paired lever in the chamber. Following 22 h of abstinence, arc mRNA was significantly increased in the BLA of cocaine-treated rats re-exposed to the chamber only with levers extended, whereas following 15 d of abstinence, arc mRNA in the BLA was increased in cocaine-treated rats returned to the chamber with or without levers extended. In contrast, zif268 mRNA in the BLA was greater in cocaine-treated rats returned to the chamber with levers extended vs. levers retracted only after 15 d of abstinence. In the dentate gyrus (DG) following 22 h of abstinence, zif268 mRNA was greater in rats returned to the chamber where levers were absent regardless of drug treatment whereas arc mRNA was increased in CA1 (cell bodies and dendrites) and CA3 only in cocaine-treated groups. Following 15 d of abstinence, arc mRNA was significantly greater in CA1 and CA3 of both cocaine-treated groups returned to the chamber than in those placed into a familiar, non-salient alternate environment; however, only in CA1 cell bodies the cocaine context-induced increases significantly greater than in yoked-saline controls. In contrast, zif/268 mRNA in all dHPC regions was significantly greater in both cocaine-treated groups returned to the cocaine context than in the cocaine-treated group returned to an alternative environment or saline-treated groups. These data suggest that the temporal dynamics of arc and zif268 gene expression in the BLA and dHPC encode different key elements of drug context-induced cocaine-seeking., (Copyright 2010 IBRO. Published by Elsevier Ltd. All rights reserved.)

Reduction in the amount of brain-derived neurotrophic factor (BDNF) in corticostriatal afferents is thought to contribute to the vulnerability of medium spiny striatal neurons in Huntington's disease. In young Bdnf heterozygous ((+/-)) mice, striatal medium spiny neurons (MSNs) express less preprodynorphin (PPD), preproenkephalin (PPE), and D(3) receptor mRNA than wildtype mice. Further, in aged Bdnf (+/-) mice, opioid, trkB receptor, and glutamic acid decarboxylase gene expression, and the number of dendritic spines on MSNs are more affected than in wildtype or younger Bdnf (+/-) mice. In this study, the possibility that intrastriatal infusions of BDNF would elevate gene expression in the striatum of Bdnf (+/-) mice was investigated. Wildtype and Bdnf (+/-) mice received a single, bilateral microinjection of BDNF or PBS into the dorsal striatum. Mice were killed 24 h later and semi-quantitative in situ hybridization histochemical analysis confirmed that PPD, PPE, and D(3) receptor mRNA was less in the caudate-putamen (CPu) and nucleus accumbens (NAc) core of Bdnf (+/-) mice than in wildtype mice. A BDNF infusion increased PPD mRNA in the CPu and NAc core of wildtype mice and restored PPD mRNA levels in the NAc core of Bdnf (+/-) mice. BDNF also restored the gene expression of PPE in the CPu of Bdnf (+/-) mice to wildtype levels; however, PPE mRNA in the NAc did not differ among groups. Furthermore, BDNF increased D(3) receptor mRNA in the NAc core of wildtype and Bdnf (+/-) mice. These results demonstrate that exogenous BDNF restores striatal opioid and D(3)R gene expression in mice with genetically reduced levels of endogenous BDNF.

Acute and chronic exposure to psychostimulants results in altered function of G-protein-coupled receptors in the forebrain. It is believed that neuroadaptations in G-protein signaling contribute to behavioral sensitivity to psychostimulants that persists over a prolonged drug-free period. Proteins termed activators of G-protein signaling (AGS) have been characterized as potent modulators of both receptor-dependent and receptor-independent G-protein signaling. Nevertheless, the regulation of AGS gene and protein expression by psychostimulants remains poorly understood. In the present study, we investigated amphetamine (AMPH)-induced changes in expression patterns of several forebrain-enriched AGS proteins. A single exposure to AMPH (2.5 mg/kg i.p.) selectively induced gene expression of AGS1, but not Rhes or AGS3 proteins, in the rat prefrontal cortex (PFC) as measured 3 h later. Induction of AGS1 mRNA in the PFC by acute AMPH was transient and dose-dependent. Even repeated treatment with AMPH for 5 days did not produce lasting changes in AGS1 mRNA and protein levels in the PFC as measured 3 weeks post treatment. However, at this time point, a low dose AMPH challenge (1 mg/kg i.p.) induced a robust behavioral response and upregulated AGS1 expression in the PFC selectively in animals with an AMPH history. The effects of AMPH on AGS1 expression in the PFC were blocked by a D2, but not D1, dopamine receptor antagonist and partially by a glucocorticoid receptor antagonist. Collectively, the present study suggests that (1) AGS1 represents a regulator of G-protein signaling that is rapidly inducible by AMPH in the frontal cortex, (2) AGS1 regulation in the PFC parallels behavioral activation by acute AMPH in drug-naive animals and hypersensitivity to AMPH challenge in sensitized animals, and (3) D2 dopamine and glucocorticoid receptors regulate AMPH effects on AGS1 in the PFC. Changes in AGS1 levels in the PFC may result in abnormal receptor-to-G-protein coupling that alters cortical sensitivity to psychostimulants., (2010 IBRO. Published by Elsevier Ltd. All rights reserved.)