Dorsal Raphe to Basolateral Amygdala Corticotropin-Releasing Factor Circuit Regulates Cocaine-Memory Reconsolidation.

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.

Optogenetic inhibition of the dorsal hippocampus CA3 region during early-stage cocaine-memory reconsolidation disrupts subsequent context-induced cocaine seeking in rats.

The dorsal hippocampus (DH) is key to the maintenance of cocaine memories through reconsolidation into long-term memory stores after retrieval-induced memory destabilization. Here, we examined the time-dependent role of the cornu ammonis 3 DH subregion (dCA3) in cocaine-memory reconsolidation by utilizing the temporal and spatial specificity of optogenetics. eNpHR3.0-eYFP- or eYFP-expressing male Sprague-Dawley rats were trained to lever press for cocaine infusions in a distinct context and received extinction training in a different context. Rats were then re-exposed to the cocaine-paired context for 15 min to destabilize cocaine memories (memory reactivation) or remained in their home cages (no-reactivation). Optogenetic dCA3 inhibition for one hour immediately after memory reactivation reduced c-Fos expression (index of neuronal activation) in dCA3 stratum pyramidale (SP) glutamatergic and GABAergic neurons and in stratum lucidum (SL) GABAergic neurons during reconsolidation. Furthermore, dCA3 inhibition attenuated drug-seeking behavior (non-reinforced lever presses) selectively in the cocaine-paired context three days later (recall test), relative to no photoinhibition. This behavioral effect was eNpHR3.0-, memory-reactivation, and time-dependent, indicating a memory-reconsolidation deficit. Based on this observation and our previous finding that protein synthesis in the DH is not necessary for cocaine-memory reconsolidation, we postulate that recurrent pyramidal neuronal activity in the dCA3 may maintain labile cocaine memories prior to protein synthesis-dependent reconsolidation elsewhere, and SL/SP interneurons may facilitate this process by limiting extraneous neuronal activity. Interestingly, SL c-Fos expression was reduced at recall concomitant with impairment in cocaine-seeking behavior, suggesting that SL neurons may also facilitate cocaine-memory retrieval by inhibiting non-engram neuronal activity.

Basolateral amygdala corticotropin-releasing factor receptor type 1 regulates context-cocaine memory strength during reconsolidation in a sex-dependent manner.

The basolateral amygdala (BLA) is a critical brain region for cocaine-memory reconsolidation. Corticotropin-releasing factor receptor type 1 (CRFR1) is densely expressed in the BLA, and CRFR1 stimulation can activate intra-cellular signaling cascades that mediate memory reconsolidation. Hence, we tested the hypothesis that BLA CRFR1 stimulation is necessary and sufficient for cocaine-memory reconsolidation. Using an instrumental model of drug relapse, male and female Sprague-Dawley rats received cocaine self-administration training in a distinct environmental context over 10 days followed by extinction training in a different context over 7 days. Next, rats were re-exposed to the cocaine-paired context for 15 min to initiate cocaine-memory retrieval and destabilization. Immediately or 6 h after this session, the rats received bilateral vehicle, antalarmin (CRFR1 antagonist; 500 ng/hemisphere), or corticotropin-releasing factor (CRF; 0.2, 30 or 500 ng/hemisphere) infusions into the BLA. Resulting changes in drug context-induced cocaine seeking (index of context-cocaine memory strength) were assessed three days later. Female rats self-administered more cocaine infusions and exhibited more extinction responding than males. Intra-BLA antalarmin treatment immediately after memory retrieval (i.e., when cocaine memories were labile), but not 6 h later (i.e., after memory reconsolidation), attenuated drug context-induced cocaine seeking at test independent of sex, relative to vehicle. Conversely, intra-BLA CRF treatment increased this behavior selectively in females, in a U-shaped dose-dependent fashion. In control experiments, a high (behaviorally ineffective) dose of CRF treatment did not reduce BLA CRFR1 cell-surface expression in females. Thus, BLA CRFR1 signaling is necessary and sufficient, in a sex-dependent manner, for regulating cocaine-memory strength.

Basolateral amygdala CB1 receptors gate HPA axis activation and context-cocaine memory strength during reconsolidation.

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.