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An improved understanding of the molecular basis of alcohol seeking despite the catastrophic consequences of alcohol abuse is likely to enrich our treatments for Alcohol Use Disorders (AUD) and comorbidities. The compulsive seeking is characterized by an imbalance between the superior drive to substance and disruption in control of substance use. To model the development of compulsive engagement of alcohol seeking, we exploit two distinct behavioral programs of C. elegans in conflict, ethanol preference and avoidance of aversive stimulus, simultaneously. We demonstrate that C. elegans exhibited the recapitulation of the pivotal features of compulsive alcohol seeking in mammals, which are repeated attempts, endurance, and finally aversion-resistant ethanol seeking. We find that the neuropeptide signaling via SEB-3, CRF receptor-like GPCR, facilitates the development of ethanol preference and compels animals to seek ethanol compulsively. Furthermore, our functional genomic approach and behavioral elucidation suggest the interaction between neuropeptidergic signaling, SEB-3 and TKR-1, Neurokinin receptor orthologue, to progress compulsive ethanol seeking behavior.

BackgroundAccumulating clinical evidence suggests women with prior exposure to adverse childhood experiences are more susceptible to alcohol relapse and other health-related issues. Yet, preclinical studies investigating sex-dependent effects of adolescent adverse social experiences (ASEs) on later alcohol-seeking behavior are lacking. This is mainly due to a lack of valid animal models and a shortage of studies comparing sexes. Therefore, we sought to investigate the sex-dependent effects of ASE on adult alcohol-seeking behavior, locomotion and reward sensitivity in both male and female rats.MethodsWe recently developed a rat model for adolescent peer-rejection which allows us to study the long-term consequences of ASEs. Peer-rejection interferes with adolescent rats‘ability to engage in adequate and reciprocal play behaviors that result in persistent dysregulation of social and pain-related behavior. Adolescent Wistar rats were reared from postnatal day (pd) 21 to pd 50 either within a group of Fischer 344 rats (ASE) or with Wistar rats (control). Adult male and female rats were tested in the reinstatement paradigm for cue-induced alcohol-seeking behavior, circadian locomotor activity, and sucrose consumption in adulthood long-after the termination of the peer-rejection condition.ResultsPeer-rejection induced persistent sex-dependent changes to cue-induced reinstatement. Females showed an increased reinstatement effect while peer-rejected males demonstrated a decrease. No differences were observed in circadian locomotor activity or reward sensitivity to sucrose.ConclusionsPeer-rejection has lasting sex-dependent consequences on alcohol-seeking behavior without affecting locomotion or sweet reward sensitivity. Our results suggest that peer-rejected female rats represent a vulnerable population to study relapse-like behaviors similar to clinical findings. While males seem to buffer the peer-rejection effect and demonstrate resilience to later-life alcohol-seeking behaviors, measured by the reinstatement effect. Finally, we provide a novel approach to investigate the molecular and neurobiological underpinnings of ASEs on alcohol and other drug-seeking behaviors.

The mesolimbic dopamine system comprises distinct compartments supporting different functions in learning and motivation. Less well understood is how complex addiction-related behaviors emerge from activity patterns across these compartments. Here we show how different forms of relapse to alcohol-seeking are assembled from activity across the ventral tegmental area and the nucleus accumbens. Using gCaMP and dLight fibre photometry, we show that self-administration and two forms of relapse (renewal/context-induced reinstatement and reacquisition) are associated with recruitment across the mesolimbic dopamine system. Using a variety of interventions, we show that this activity is causal to both forms of relapse. Finally, we use dissimilarity matrices to identify mesolimbic dopamine signatures of self-administration, extinction, and relapse. We show that signatures of relapse can be identified from heterogeneous activity profiles across the mesolimbic dopamine system and that these signatures differ for different forms of relapse.

Relapse to alcohol abuse is often caused by exposure to potent alcohol-associated cues. Therefore, disruption of the cue-alcohol memory can prevent relapse. It is believed that memories destabilize and become prone for updating upon their reactivation through retrieval, and then re-stabilize within 6 h during a “reconsolidation” process. We recently showed that relapse to cocaine seeking could be prevented by counterconditioning the cocaine-cues with aversive outcomes following cocaine-memory retrieval, in a place conditioning paradigm. However, to better model addiction-related behaviors, self-administration models are necessary. Here, we demonstrate that relapse to alcohol seeking can be prevented by aversive counterconditioning conducted during alcohol-memory reconsolidation, in conditioned place preference (CPP) and operant self-administration paradigms, in mice and rats, respectively. We found that the reinstatement of alcohol-CPP was abolished only when aversive counterconditioning with water-flooding was given shortly after alcohol-memory retrieval. Furthermore, rats trained to lever-press for alcohol showed decreased context-induced renewal of alcohol-seeking responding when the lever-pressing was counterconditioned with foot-shocks, shortly, but not 6 h, after memory retrieval. These results 0suggest that aversive counterconditioning can prevent relapse to alcohol seeking only when performed during alcohol-memory reconsolidation, presumably by updating, or replacing, the alcohol memory with aversive information. Also, we found that aversive counterconditioning preceded by alcohol-memory retrieval was characterized by upregulation of brain-derived neurotrophic factor (Bdnf) mRNA expression in the medial prefrontal cortex, suggesting that Bdnf plays a role in the memory updating process.

A critical area of inquiry in the neurobiology of alcohol abuse is the neural mechanisms by which cues gain the ability to elicit alcohol use. We previously showed that cue-evoked activity in rat ventral pallidum (VP) robustly encodes the value of cues trained under both Pavlovian and instrumental contingencies, despite a stronger relationship between cue-evoked responses and behavioral latency after instrumental training. Here, we assessed VP neural representations of cue value in rats trained with a Pavlovian conditioned stimulus (CS+) that predicted alcohol delivery, and in rats trained with an instrumental discriminative stimulus (DS) that predicted alcohol availability if the rat entered the reward port during the cue. We also examined the impact of alcohol exposure itself on the integrity of this type of signaling in rats trained with sucrose. Decoding of cue value based on VP firing was blunted for an alcohol CS+ versus an alcohol DS, as well as in comparison to a sucrose DS or CS+. Further, homecage alcohol exposure had opposing effects on VP encoding of cue value for a sucrose DS versus a sucrose CS+, enhancing decoding accuracy for the DS and reducing decoding accuracy for the CS+. These findings suggest that problem alcohol seeking may result from biased engagement of specific reward-related processes via changes in VP signaling.

Discrete and contextual cues that predict alcohol trigger alcohol-seeking. However, the extent to which context influences alcohol-seeking triggered by discrete cues, and the neural mechanisms underlying these responses, are not well known. We show that, relative to a neutral context, a context associated with alcohol persistently elevated alcohol-seeking triggered by a discrete cue, and supported higher levels of priming-induced reinstatement. Alcohol-seeking triggered by a discrete cue in a neutral context was reduced by designer receptor-mediated inhibition of ventral tegmental area (VTA) dopamine neurons in TH::Cre rats. Inhibiting terminals of VTA dopamine neurons in the nucleus accumbens (NAc) core reduced alcohol-seeking triggered by a discrete cue, irrespective of context, whereas inhibiting VTA dopamine terminals in the NAc shell selectively reduced the elevation of alcohol-seeking triggered by a discrete cue in an alcohol context. This dissociation highlights unique roles for divergent mesolimbic dopamine circuits in alcohol-seeking driven by discrete and contextual environmental cues.