Chronic ethanol exposure has been shown to increase NMDA receptor ligand binding and the levels of receptor subunit proteins in mouse and rat brain. The increase in hippocampal NMDA receptors has been suggested to be related to the occurrence of ethanol withdrawal seizures and to increased susceptibility to glutamate-induced excitotoxicity, and could also result in altered cognition and could contribute to changes in ethanol reinforcement and """"""""craving"""""""" for ethanol. In contrast to NMDA receptors, little attention has been given to ethanol-induced alterations in non-NMDA (AMPA) glutamate receptors, which could also contribute to long-term cognitive changes following ethanol exposure and withdrawal. Although the time course of changes in ligand binding to the hippocampal NMDA receptor parallels the time course for the occurrence and dissipation of ethanol withdrawal seizures, long-term adaptive changes in NMDA and/or non-NMDA glutamate receptors may involve not only increases in receptor subunit protein levels, but also altered cell surface expression and/or synaptic localization of the receptors. Changes in these properties, which have important functional consequences, could occur either in the absence or presence of increased receptor synthesis. We propose to assess adaptations in synaptic targeting of NMDA and AMPA receptors following chronic ethanol treatment that produces physical dependence and withdrawal. Such receptor changes may be long-lasting, and contribute to cognitive deficits as well as prolonged increases in susceptibility to neurotoxicity. Using both biochemical and immunohistochemical techniques, in Aim 1 we will investigate adaptations in glutamate receptor synaptic localization and cell surface expression in hippocampus of C57BL/6 mice that have ingested ethanol chronically in a liquid diet, and undergone withdrawal. Increases in NMDA receptor function and subunit protein levels have also been found in cultured mouse and rat neurons that have been exposed chronically to ethanol, and thus in Aim 2 we will investigate glutamate receptor localization in ethanol-treated/withdrawn hippocampal neurons, to determine parallels between effects of ethanol in this in vitro system and in vivo. These studies will then allow a detailed investigation in Aim 3 of the molecular mechanisms that lead to changes in NMDA and/or AMPA receptor properties as a result of chronic ethanol exposure. The proposed studies go beyond previous phenomenological observations to determine how ethanol exposure results in adaptations that affect synaptic plasticity and may contribute to the CNS changes associated with addiction. Understanding these mechanisms can provide novel therapeutic approaches to ameliorating the neuronal consequences of chronic ethanol ingestion and withdrawal.
