Role of RMTg afferents in mechanisms of withdrawal from chronic ethanol exposure

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PROJECT SUMMARY A significant number of individuals struggle to maintain sobriety as a result of withdrawal symptoms that emerge during early abstinence from alcohol. Despite this, pharmacotherapeutics for the treatment of withdrawal are lacking, at least in part, due to poor understanding of the mechanisms underlying symptoms of withdrawal. The rostromedial tegmental nucleus (RMTg) is a GABAergic region that exerts inhibitory control over midbrain bioaminergic and cholinergic nuclei. Recently, work from our lab revealed significantly enhanced cFos expression, a marker of recent neuronal activity, in the RMTg of chronic intermittent ethanol (CIE) exposed rats 12 hours into acute withdrawal. In addition, we showed that pharmacological inhibition of the RMTg attenuates withdrawal-induced anxiety-like behavior. However, the precise neural circuits that drive this putative RMTg hyperactivity is unknown. The lateral habenula (LHb) provides dense glutamatergic input to the RMTg and exhibits significant functional overlap with the RMTg. In addition, our preliminary data reveals a significant increase in cFos expression in RMTg-projecting lateral habenula (LHb) neurons during acute withdrawal. Together, these data lead us to hypothesize that LHb inputs to the RMTg play a mechanistic role in regulating symptoms of withdrawal from chronic ethanol exposure. Experiments in the current proposal are designed to test this hypothesis by using in vivo chemogenetics to bidirectionally and selectively manipulate LHb-RMTg activity during behavioral tests of withdrawal symptoms including anxiety-like behavior, mechanical pain sensitivity, and impulsive choice. Additional work will use ex vivo slice electrophysiology to explore the physiological neuroadaptations that occur in this circuitry during withdrawal from chronic ethanol exposure. Findings from these experiments will shed new light onto the role of this neural circuit in regulating symptoms of withdrawal and by extension have the potential to uncover new neurobiological targets for the treatment of alcohol use disorder.