Effects of Acute and Chronic Alcohol on Brain Reward in Mice

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DESCRIPTION (provided by applicant): Alcohol use disorders and alcoholism are complex behavioral and biological endpoints that begin with the pleasurable, rewarding effects of initial alcohol use. Although many overlapping brain mechanisms contribute to addiction, mechanisms of reward and motivation are among the most salient targets of all addictive or compulsive disorders. To better understand what motivates excessive alcohol consumption, and thereby develop more effective strategies for intervention, a more thorough understanding of the relationship between alcohol and biological mechanisms of reward is important. This proposal will focus on the rewarding properties of alcohol in mouse models. Intracranial self-stimulation (ICSS) is a behavioral method used in animal studies that has made major contributions to our understanding of cocaine, amphetamine, opiate and nicotine reward. However, the application of ICSS to the study of alcohol reward has been comparatively limited, and the effects of alcohol on brain stimulation-reward (BSR) have not been studied in mouse models where genetic differences can more easily be evaluated. The main advantage of ICSS over other operant behavioral methods in which the animal must perform a task in order to receive a drug reinforcer (action->outcome) is that the rewarding effect of a drug is measured independent of the motivation of the animal to seek or consume the drug. Alcohol self-administration in rodent models may be complicated by factors such as taste aversion and thirst that are avoided with ICSS, which allows a unique and novel approach to investigate the genetic and pharmacological regulation of alcohol reward. Preliminary studies in our laboratory have shown that alcohol potentiates the rewarding value of BSR after acute administration by oral gavage in both C57BL6/J and DBA/2 mice. Genetic factors represent about half of the risk for alcohol dependence, and our preliminary data have established clear genetic differences in alcohol reward between these two mouse strains: alcohol doses lower than 1 g/kg potentiate BSR while doses higher than 1 g/kg depreciate BSR in C57BL6/J mice, a strain that voluntarily consumes alcohol. In contrast, DBA/2 mice show a robust, dose-dependent potentiation of BSR at doses up to 2.4 g/kg but do not voluntarily consume alcohol. The rewarding effect of alcohol is greatest at early time points (15-30 minutes) and coincides with the peak blood alcohol concentration (BAC) after oral administration in both strains, supporting the idea that animals find the rising phase of the BAC curve more pleasurable or rewarding than the falling phase. Experiments are proposed to further elucidate the pharmacokinetics and pharmacological effects of acute alcohol administration; to investigate adaptations to alcohol reward with intermittent or chronic alcohol exposure; and to determine the contribution of dopaminergic mechanisms to alcohol reward. Understanding the role of reward in alcohol dependence will clarify mechanisms of increased drinking liability and lead to insights into novel therapeutic targets that modify consumption by changing alcohol reward.