Alcohol Action in the Brain Reward Circuit

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DESCRIPTION (provided by applicant): The mesolimbic dopaminergic system originating in the midbrain ventral tegmental area (VTA) is critically involved in the development of alcoholism. During the previous round of funding of this project, two types of neuroadaptive changes were identified in VTA dopamine neurons after repeated alcohol (ethanol) exposure: 1) enhanced synaptic plasticity of NMDA receptor-mediated glutamatergic transmission and 2) increased dopamine-induced autoinhibition of dopamine neuron activity mediated by somatodendritic D2 autoreceptors. These changes will promote the development of alcoholism by 1) facilitating the formation of powerful and enduring memories of ethanol-associated stimuli and 2) causing reduced dopaminergic output during withdrawal, which drives compulsive ethanol intake to compensate for dopamine deficits via ethanol stimulation of dopamine neuron activity. Clinical and preclinical evidence indicates that negative life experiences, such as prolonged social isolation or compulsive eating of calorie-dense palatable food, especially during early stages of life, increase an individual's risk of developing alcoholism both concurrently and in the future. However, the neurobiological mechanisms underlying the effects of these experiences are not well understood. The current proposal will investigate how VTA dopamine neurons are affected by prolonged social isolation (Aims 1 and 2) and extended access to high fat/carbohydrate palatable food ('cafeteria diet') (Aims 3 and 4) during early adolescence in rats. The overriding hypothesis is that these experiences will increase alcoholism vulnerability by enhancing NMDA receptor plasticity and dopamine-induced autoinhibition in the VTA. Brain slice experiments (Aims 1 and 3) will employ patch-clamp electrophysiology, confocal fluorescence imaging, and photolytic application of signaling molecules to determine the cellular and molecular mechanisms involved. These ex vivo methodologies will be combined with behavioral assays (Aims 2 and 4) to elucidate the neurobiological mechanisms underlying the vulnerability to develop alcoholism.