Dopaminergic Modulation of Excitatory Transmission in BNST and Regulation by Ethanol

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Project Summary/Abstract Alcohol addiction is characterized by repeated relapses to alcohol abuse despite negative consequences. This counter-adaptive behavior is believed to result from adaptations in underlying neurocircuitry which occur in response to chronic alcohol abuse. These adaptations result in persistent negative affective states, during abstinence, which drive reinstatement of alcohol use as a means of negative reinforcement, or relief from negative conditions. The bed nucleus of the stria terminalis (BNST) is a key mediator of stress and anxiety states and behavioral responses to stressors. Models of stress-induced reinstatement of drug seeking have identified norepinephrine signaling in the BNST as critical to relapse behavior. Noradrenergic excitation of the BNST through β-adrenergic receptors promotes anxiety-like behaviors and drug reinstatement, whereas inhibition of BNST activity through α2-adrenergic receptors reduces anxiety-like behaviors. The BNST also receives prominent dopaminergic innervation from the ventral tegmental area (VTA). Investigations into the role of dopaminergic signaling in the BNST are relatively sparse and somewhat contradictory. For example, low doses of bath applied dopamine resulted in increased excitatory activity in the BNST, while high doses resulted in increased inhibitory actions. Further, the inhibitory actions are suggested to occur through dopamine cross-activation of α2-adrenergic receptors. In order to resolve these discrepancies, it is important to have a clear understanding of endogenous dopamine signals and how rapid changes in dopamine concentrations may selectively recruit post-synaptic receptor activation. Often, investigations of dopamine signaling use fast-scan cyclic voltammetry, which provides high temporal resolution of dopamine release and uptake in response to local electrical stimulation of terminals fields. However, in the BNST, dopamine and norepinephrine provide overlapping innervation, thus both catecholamines are released in response to local electrical stimulation, and cyclic voltammetry cannot distinguish between catecholamines. This hinders the use of this technique in assessing the potentially opposing roles of dopamine and norepinephrine signaling on BNST synaptic physiology. In this proposal we introduce a model in which we optogenetically target VTA dopamine neurons projecting to the BNST, such that we may use selective optical-stimulation of local dopamine release, measured with cyclic voltammetry, in BNST slices, ex vivo. Further, we propose to use optically-stimulated dopamine release in combination with whole cell electrophysiology to measure the cellular responses to endogenous dopamine signals. This ex vivo model allows us to employ various pharmacological manipulations to assess how dopamine signaling is integrated into synaptic physiology and to what degree endogenous dopamine signals recruit activation of α2-adrenergic receptors. Finally, we will examine how chronic intermittent ethanol vapor exposure alters the mechanisms of dopaminergic modulation of BNST synaptic function.