Ethanol and mesolimbic GABAergic neurons

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DESCRIPTION (provided by applicant): This is an exploratory (R21) grant to examine the role of GABAergic (GABA) neurons in alcohol addiction. The mesolimbic dopamine (DA) system, originating from the ventral tegmental area (VTA), is thought to mediate the reinforcing properties of drugs of abuse, including ethanol. How acute ethanol increases the activity of VTA-DA neurons has not been fully elucidated. The VTA-DA neurons are under the tonic inhibitory control of GAB A neurons. It is well established that some drugs of abuse, such as opioids, excite VTA-DA neurons by inhibiting the GAB A neurons-a mechanism of disinhibition. There is recent in vivo evidence that ethanol inhibits VTA-GABA neurons. Preliminary data indicate that ethanol inhibits VTA-GABA neurons. Importantly, ethanol inhibition of the GAB A neurons is more potent than the excitation of DA neurons. My long-term goal is to identify the cellular mechanisms of alcohol addiction. The objective of this application is to examine the mechanisms by which GAB A neurons mediate the effects of ethanol in the VTA. The central hypothesis is that acute ethanol increases VTA-DA release within the addiction circuit primarily through disinhibition, by suppression of the inhibitory tone of VTA-GABA neurons. The proposed work will combine patch-clamp electrophysiological techniques with pharmacological tests on VTA neurons of rats, either in acute brain slices or in acutely dissociated neurons. Specific aim 1 will test the hypothesis that ethanol inhibits VTA-GABA neurons: this will be done by examining the effects of ethanol on both the spontaneous firing of GABA neurons, and the spontaneous IPSCs (sIPSCs) recorded from DA neurons. Specific aim 2 will test the hypothesis that ethanol inhibition of GABAergic inhibitory tone is more potent than its direct excitatory effect on DA neurons by comparing ethanol's excitatory action on DA neurons with its inhibitory potency on GABA neurons, and by comparing the ethanol-induced increase in VTA-DA cell firing in the presence and absence of synaptic inputs. This aim will also explore whether the inhibition of GABA neurons affects the burst firing of DA neurons. Specific aim 3 will test the hypothesis that ethanol inhibits VTA-GABA inter-neurons by enhancing their K+ currents by comparing ethanol's potency on VTA-GABA cells in the absence and presence of K+ channel blocker(s). The results of this study will characterize a previously under-investigated effect of ethanol on VTA-GABA neurons, and its subsequent indirect effect on VTA-DA neurons. Such results will provide valuable information on novel mechanisms underlying the addictive properties of alcohol and a firm scientific foundation for future neurobiological studies.