Regulation of NMDA Receptor Localization by Ethanol

研究表明，长期酒精暴露可增加小鼠和大鼠脑内NMDA受体配体结合和受体亚单位蛋白水平。海马区NMDA受体的增加被认为与乙醇戒断发作的发生有关，与谷氨酸诱导的兴奋性毒性的敏感性增加有关，还可能导致认知改变，并可能导致乙醇强化和对乙醇的渴望的改变。与NMDA受体相比，很少有人关注乙醇诱导的非NMDA(AMPA)谷氨酸受体的变化，这也可能有助于乙醇暴露和戒断后的长期认知变化。虽然与海马NMDA受体结合的配体变化的时间进程与乙醇戒断发作的发生和消退的时间进程平行，但NMDA和/或非NMDA谷氨酸受体的长期适应性变化可能不仅涉及受体亚单位蛋白水平的增加，而且还涉及受体的细胞表面表达和/或突触定位的改变。这些特性的变化具有重要的功能后果，在没有或存在受体合成增加的情况下都可能发生。我们建议评估在产生身体依赖和戒断的慢性乙醇治疗后，突触靶向NMDA和AMPA受体的适应性。这种受体的变化可能是长期的，并导致认知障碍以及对神经毒性的敏感性长期增加。在目标1中，我们将利用生化和免疫组织化学技术，研究C57BL/6小鼠在液体饮食中长期摄入乙醇并戒断后，海马区谷氨酸受体突触定位和细胞表面表达的适应性。在长期暴露于乙醇的培养的小鼠和大鼠神经元中，也发现NMDA受体功能和亚单位蛋白水平的增加，因此在目标2中，我们将研究乙醇处理/撤除的海马神经元中谷氨酸受体的定位，以确定乙醇在体外系统中的作用与体内的相似之处。然后，这些研究将允许在目标3中详细研究导致慢性酒精暴露导致NMDA和/或AMPA受体特性变化的分子机制。拟议的研究超越了以前的现象学观察，以确定酒精暴露如何导致影响突触可塑性的适应，并可能有助于与成瘾相关的中枢神经系统的变化。了解这些机制可以为改善慢性酒精摄入和戒断的神经元后果提供新的治疗方法。

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.