683. GHRELIN RECEPTOR SIGNALLING IN THE EDINGER-WESTPHAL NUCLEUS REGULATES BINGE DRINKING IN A SEX-SPECIFIC MANNER

Abstract Background Binge drinking is the greatest predictor of the future development of alcohol use disorder. However, neurobiological sex differences in binge drinking remain poorly understood due to sex as a biological variable being historically overlooked. The centrally projecting Edinger-Westphal nucleus (EWcp) comprises of distinct cell populations and is an intersection of alcohol, stress and sex-steroid hormone receptors, yet whether it influences binge drinking differently between sexes remains unknown. Aims & Objectives Aim: Investigate sex differences in the role of the EWcp in binge drinking. Hypothesis: The EWcp peptidergic cells mediate binge drinking, and this is influenced by sex. Method Mice were allocated to the binge drinking or alcohol-naïve group, and perfused following the final drinking session to assess EWcpCART (peptidergic) cell activation. A cre-dependent designer receptor exclusively activated by designer drug (DREADD) was used to inhibit EWcpCART cells during binge drinking. We assessed the interaction between EWcpCART cells and ghrelin using this approach, however administered ghrelin 20mins prior to alcohol presentation. The functional involvement of the ghrelin receptor (GHSR) was examined through knockdown in the EW using a GHSR short hairpin RNA (shRNA). EW GHSR expression was characterised through RNAscope, leading to targeted GHSR shRNA knockdown from glutamatergic or peptidergic cells to assess the effect on binge drinking. Finally, we implanted cannulas, microinjecting a GHSR antagonist or inverse agonist prior to binge drinking. Results Activation of EWcpCART cells was greater in female compared to male binge drinking mice, with inhibition of EWcpCART cells reducing alcohol intake specifically in females. Ghrelin administration increased female binge drinking only, with EWcpCART cell inhibition preventing this. EWGHSR knockdown reduced alcohol intake only in females. Ghsr was expressed in 99% of peptidergic and ~40% of glutamatergic EW cells. Ghsr knockdown from peptidergic, but not glutamatergic, EW cells reduced binge drinking in females. Finally, GHSR antagonism and inverse agonism reduced alcohol intake in females. Discussion & Conclusions Collectively, these results reveal ghrelin/Ghsr signalling on peptidergic EWcp cells as a novel circuit mediating binge drinking in a sex-specific manner in female mice. Continued research characterising sex differences in the contribution of the ghrelin system toward excessive alcohol intake may unveil promising therapeutic targets.