Adolescent Binge Drinking Increases Adult Alcohol Intake: Glutamate Mechanisms

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DESCRIPTION (provided by applicant): Binge drinking, defined as drinking that brings blood alcohol levels to 80 mg% or above, has been increasing in adolescents and young adults, and this prior experience is a strong predictor of alcoholic dependence later in life. Evidence also indicates that binge drinking is a persistent problem in the military and is prevalent among young adults entering the military, and that alcohol use disorder or binge drinking are associated with impaired health status and chronic health problems in veterans. However, while alcoholism and alcohol use disorder contribute to health problems in the US veteran population, the physiological mechanisms underlying alcohol abuse remain poorly understood. This is due in part, to alcohol's actions at multiple receptors and ion channels. Relevant to the present proposal, increasing evidence implicates activity dependent changes in the efficacy of glutamatergic neurotransmission as a major underlying event in the addicted brain. These neuroadaptive mechanisms may reflect manifestations of aberrant brain plasticity, and it has been suggested that the enhanced plasticity of the adolescent brain temporally correlates with enhanced vulnerability to addiction. With this in mind, the present proposal is based on strong preliminary data suggesting that binge drinking produces alterations in the glutamatergic system that can interact with stress to augment subsequent ethanol drinking behavior, and that adolescent mice may be more susceptible than adult mice to the impact of these perturbations. We have developed a model of binge drinking (Scheduled High Alcohol Consumption, SHAC) and found that binge drinking experience in adolescent mice significantly increased ethanol intake during adulthood, with further increases following exposure to restraint stress. Importantly, adolescents were more sensitive than adults to the impact of binge drinking on subsequent intake. Binge drinking with the SHAC procedure was decreased by a metabotropic receptor subtype 5 (mGluR5) antagonist, and it upregulated nucleus accumbens (NAc) mGluR5-Homer2-phosphatidylinositol 3-kinase (PI3K) signaling. Consistent with the inverse relationship between extracellular glutamate levels (via microdialysis) and nerve terminal glutamate immunolabelling, repeated bouts of binge drinking significantly increased extracellular glutamate levels and decreased glutamate immunolabelling within nerve terminals making asymmetrical (excitatory) synaptic contacts. Based on this evidence, the goal of the proposed studies is to test the hypothesis that adaptations in glutamate neuroplasticity following binge drinking confer susceptibility for enhanced alcohol intake in adolescent mice during adulthood. A secondary hypothesis is that stress produces additional adaptations that bestow further vulnerability for increased alcohol consumption. The proposed studies will be conducted in male and female adolescent and adult C57BL/6 mice, since we predict that there will be sex (female > male) and age (adolescent > adult) differences in the glutamatergic neuroadaptations that occur following binge drinking and exposure to stress. The specific aims will use a multidisciplinary approach to determine whether physical or psychological stressors will have an additive effect with binge drinking on subsequent ethanol intake (Aim 1), and whether alterations in glutamate immunolabelling and dendritic spine size (Aim 2) as well as alterations in the expression of glutamatergic genes and signaling pathways (Aim 3) within the NAc correspond to the escalation in ethanol intake following stress and binge drinking. These studies will determine whether alterations in accumbal glutamate are an important neurobiological mechanism that confers increased susceptibility for alcohol dependence following binge drinking and exposure to stress. This information can guide pharmacological treatment strategies for alcohol use disorder or binge drinking, an important area of focus in the treatment of our veterans.