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Reconsolidation of a cocaine associated memory requires DNA methyltransferase activity in the basolateral amygdala.

ABSTRACT: Drug addiction is considered an aberrant form of learning, and drug-associated memories evoked by the presence of associated stimuli (drug context or drug-related cues) contribute to recurrent craving and reinstatement. Epigenetic changes mediated by DNA methyltransferase (DNMT) have been implicated in the reconsolidation of fear memory. Here, we investigated the role of DNMT activity in the reconsolidation of cocaine-associated memories. Rats were trained over 10 days to intravenously self-administer cocaine by nosepokes. Each injection was paired with a light/tone conditioned stimulus (CS). After acquisition of stable self-administration behaviour, rats underwent nosepoke extinction (10 d) followed by cue-induced reactivation and subsequent cue-induced and cocaine-priming + cue-induced reinstatement tests or subsequently tested to assess the strength of the cocaine-associated cue as a conditioned reinforcer to drive cocaine seeking behaviour. Bilateral intra-basolateral amygdala (BLA) infusion of the DNMT inhibitor5-azacytidine (5-AZA, 1 μg per side) immediately following reactivation decreased subsequent reinstatement induced by cues or cocaine priming as well as cue-maintained cocaine-seeking behaviour. In contrast, delayed intra-BLA infusion of 5-AZA 6 h after reactivation or 5-AZA infusion without reactivation had no effect on subsequent cue-induced reinstatement. These findings indicate that memory reconsolidation for a cocaine-paired stimulus depends critically on DNMT activity in the BLA.

SUBMITTER: Shi HS

PROVIDER: S-EPMC4542613 | biostudies-other | 2015

REPOSITORIES: biostudies-other

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Project description:Environmental stimuli elicit drug craving and relapse in cocaine users by triggering the retrieval of strong cocainerelated contextual memories. Retrieval can also destabilize drug memories, requiring reconsolidation, a protein synthesis-dependent storage process, to maintain memory strength. Corticotropin-releasing factor (CRF) signaling in the basolateral amygdala (BLA) is necessary for cocainememory reconsolidation. We have hypothesized that a critical source of CRF in the BLA is the dorsal raphe nucleus (DR) based on its neurochemistry, anatomical connectivity, and requisite involvement in cocaine-memory reconsolidation. To test this hypothesis, male and female Sprague-Dawley rats received adeno-associated viruses to express Gi-coupled designer receptors exclusively activated by designer drugs (DREADDs) selectively in CRF neurons of the DR and injection cannulae directed at the BLA. The rats were trained to self-administer cocaine in a distinct environmental context then received extinction training in a different context. They were then briefly reexposed to the cocaine-predictive context to destabilize (reactivate) cocaine memories. Intra-BLA infusions of the DREADD agonist deschloroclozapine (DCZ; 0.1 mM, 0.5 μL/hemisphere) after memory reactivation attenuated cocaine-memory strength, relative to vehicle infusion. This was indicated by a selective, DCZ-induced and memory reactivation-dependent decrease in drug-seeking behavior in the cocaine-predictive context in DREADD-expressing males and females at test compared to respective controls. Notably, BLA-projecting DR CRF neurons that exhibited increased c-Fos expression during memory reconsolidation co-expressed glutamatergic and serotonergic neuronal markers. Together, these findings suggest that the DRCRF → BLA circuit is engaged to maintain cocaine-memory strength after memory destabilization, and this phenomenon may be mediated by DR CRF, glutamate, and/or serotonin release in the BLA.

Project description:Re-exposure to a cocaine-associated context triggers craving and relapse through the retrieval of salient context-drug memories. Upon retrieval, context-drug memories become labile and temporarily sensitive to modification before they are reconsolidated into long-term memory stores. The effects of systemic cannabinoid type 1 receptor (CB1R) antagonism indicate that CB1R signaling is necessary for cocaine-memory reconsolidation and associated glutamatergic plasticity in the basolateral amygdala (BLA); however, the contribution of BLA CB1R signaling to cocaine-memory reconsolidation is unknown. Here, we assessed whether intra-BLA CB1R manipulations immediately after cocaine-memory retrieval alter cocaine-memory strength indexed by subsequent drug context-induced cocaine-seeking behavior in an instrumental rodent model of drug relapse. Administration of the CB1R antagonist, AM251 (0.3 µg/hemisphere) into the BLA increased subsequent drug context-induced cocaine-seeking behavior in a memory retrieval-dependent and anatomically selective manner. Conversely, the CB1R agonist, WIN55,212-2 (0.5 or 5 µg/hemisphere) failed to alter this behavior. In follow-up experiments, cocaine-memory retrieval elicited robust hypothalamic-pituitary-adrenal axis activation, as indicated by a rise in serum corticosterone concentrations. Intra-BLA AM251 administration during memory reconsolidation selectively increased this cocaine-memory retrieval-induced corticosterone response. Intra-BLA corticosterone administration (3 or 10 ng/hemisphere) during memory reconsolidation did not augment subsequent cocaine-seeking behavior, suggesting that CB1R-dependent effects of corticosterone on memory strength, if any, are mediated outside of the BLA. Together, these findings suggest that CB1R signaling in the BLA gates cocaine-memory strength, possibly by diminishing the impact of cue-induced arousal on the integrity of the reconsolidating memory trace or on the efficacy of the memory reconsolidation process.

Project description:The dynorphin (DYN)/kappa-opioid receptor (KOR) system plays a conserved role in stress-induced reinstatement of drug seeking for prototypical substances of abuse. Due to nicotine's high propensity for stress-induced relapse, we hypothesized that stress would induce reinstatement of nicotine seeking-like behavior in a KOR-dependent manner. Using a conditioned place preference (CPP) reinstatement procedure in mice, we show that both foot-shock stress and the pharmacological stressor yohimbine (2 mg/kg, i.p.) induce reinstatement of nicotine CPP in a norbinaltorphimine (norBNI, a KOR antagonist)-sensitive manner, indicating that KOR activity is necessary for stress-induced nicotine CPP reinstatement. After reinstatement testing, we visualized robust c-fos expression in the basolateral amygdala (BLA), which was reduced in mice pretreated with norBNI. We then used several distinct but complementary approaches of locally disrupting BLA KOR activity to assess the role of KORs and KOR-coupled intracellular signaling cascades on reinstatement of nicotine CPP. norBNI injected locally into the BLA prevented yohimbine-induced nicotine CPP reinstatement without affecting CPP acquisition. Similarly, selective deletion of BLA KORs in KOR conditional knock-out mice prevented foot-shock-induced CPP reinstatement. Together, these findings strongly implicate BLA KORs in stress-induced nicotine seeking-like behavior. In addition, we found that chemogenetic activation of G?i signaling within CaMKII? BLA neurons was sufficient to induce nicotine CPP reinstatement, identifying an anatomically specific intracellular mechanism by which stress leads to reinstatement. Considered together, our findings suggest that activation of the DYN/KOR system and G?i signaling within the BLA is both necessary and sufficient to produce reinstatement of nicotine preference.Considering the major impact of nicotine use on human health, understanding the mechanisms by which stress triggers reinstatement of drug-seeking behaviors is particularly pertinent to nicotine. The dynorphin (DYN)/kappa-opioid receptor (KOR) system has been implicated in stress-induced reinstatement of drug seeking for other commonly abused drugs. However, the specific role, brain region, and mechanisms that this system plays in reinstatement of nicotine seeking has not been characterized. Here, we report region-specific engagement of the DYN/KOR system and subsequent activation of inhibitory (Gi-linked) intracellular signaling pathways within the basolateral amygdala during stress-induced reinstatement of nicotine preference. We show that the DYN/KOR system is necessary to produce this behavioral state. This work may provide novel insight for the development of therapeutic approaches to prevent stress-related nicotine relapse.

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Reconsolidation of a cocaine associated memory requires DNA methyltransferase activity in the basolateral amygdala.

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