OFC Astrocytes and Ethanol

PROJECT SUMMARY Alcohol use disorder (AUD) is characterized by the progression from recreational drinking to uncontrollable and excessive consumption resulting in myriad of social and neurobiological complications. While the mechanisms underlying the dependence-induced escalation in drinking are not completely understood, a key brain region disrupted in individuals with AUD is the orbitofrontal cortex (OFC). Previous studies from the Woodward laboratory showed that acute ethanol inhibits action potential firing of lateral orbitofrontal (lOFC) cortex pyramidal neurons via activation of astrocytic D1/D5 dopamine receptors, depolarization of the astrocyte membrane potential and the release of glycine via reversal of the astrocytic GlyT1 glycine transporter. Following chronic intermittent exposure (CIE) to alcohol, lOFC neurons become hyperexcitable and are tolerant to acute ethanol. Although our work has defined how acute and chronic ethanol alter lOFC neuron excitability, there is virtually nothing known about the effects of CIE exposure on lOFC astrocytes and how this contributes to changes in lOFC neuronal excitability. The overarching goal of this proposal is to address this major shortcoming in our knowledge by identifying CIE-induced changes in lOFC astrocyte physiology, structure and gene expression and test whether these changes contribute to the excessive drinking observed in alcohol-dependence. To accomplish this goal, studies in Aim 1 of this proposal use ex vivo slice electrophysiology and calcium imaging approaches complemented by in vivo fiber photometry measures of astrocyte calcium signaling following repeated cycles of CIE exposure. Aim 2 studies use super-resolution confocal imaging to measure CIE induced changes in lOFC astrocyte morphology and synaptic proximity and single nuclei RNAseq approaches to reveal changes in lOFC astrocyte and neuron gene expression. Aim 3 studies use a calcium exporter to blunt lOFC astrocyte calcium signaling and determine how this affects CIE induced alterations in lOFC astrocyte physiology, morphology, gene expression and voluntary ethanol consumption. Results from these studies will fill an important gap in our understanding of the role of lOFC astrocytes in alcohol action and will generate novel and testable hypotheses to support future studies.