The role of brainstem norepinephrine in binge alcohol drinking and taste aversion

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Project Summary/Abstract Frequent binge drinking has been linked to numerous negative consequences, include and increased risk of developing ethanol dependence. Thus, it is of paramount importance to identify neuronal mechanisms that modulate binge drinking as such knowledge will provide insight into novel pharmaceutical treatments that will protect against this dangerous behavior and the transition to ethanol dependence. Considerable attention has been paid to the reinforcing effects of ethanol and how these effects motivate ethanol intake. There is strong evidence that ethanol also entails aversive effects and that these effects, because they are clearly dose related, can act as a deterrent to overconsumption. One pre-clinical behavioral assay for the aversive effects of ethanol is the development of a conditioned taste aversion (CTA). When a taste is paired with a treatment which produces aversive internal symptoms, a strong aversion to the taste develops. Studies comparing different rodent strains suggest a link between sensitivity to the aversive effects of ethanol and the propensity to voluntarily ingest ethanol. Importantly, recent data show that mice selectively bred to achieve high blood ethanol concentrations (BECs) while binge drinking exhibit reduced sensitivity to the aversive properties of ethanol without alterations in sensitivity to ethanol’s reinforcing properties. Thus, binge-like ethanol drinking in these mice may be driven by reduced sensitivity to ethanol’s aversive effects. Because the neurocircuitry underlying the aversive effects of ethanol is still poorly understood, we propose to combine cutting-edged chemogenetic, molecular, and behavioral tools to characterize the neurocircuitry modulating aversive reactions to ethanol and binge-like ethanol consumption. Based on previous studies and compelling pilot data, we will test the novel hypothesis that brainstem norepinephrine (NE) nuclei, specifically the locus coeruleus (LC) and A2 region (caudal nucleus of the solitary tract; NTS), are activated during binge-like ethanol drinking and serve as protective mechanisms to “break” ethanol drinking by promoting aversive responses. Specific Aim 1 will use Designer Receptors Exclusively Activated by Designer Drugs (DREADD) viral vectors to study the role of a NE circuit from the LC to the rostromedial tegmental nucleus (RMTg) in the modulation of ethanol-induced CTA and binge-like ethanol consumption, and Aim 2 will use DREADD viral vectors to study the role of a NE circuit from the A2 region to the lateral parabrachial nucleus (PBN) in the modulation of ethanol-induced CTA and binge-like ethanol consumption. Aim 3 will use immunohistochemistry and real-time PCR approaches to test the hypothesis that binge-like ethanol drinking increases NE signaling in the LC and A2, and that this signaling will become blunted after repeated binge-like drinking episodes, a mechanism that may contribute to the transition to dependence. As the mechanisms underlying the aversive effects of ethanol are not well understood, and the roles of the NE circuits under investigation have never been studies with respect to neurobiological response to ethanol, the proposed studies are highly novel and innovative.