RECEPTOR POPULATIONS UNDERLYING TONIC GABA CURRENTS IN HIPPOCAMPUS

描述（由申请人提供）：GABAA受体（GABAARs）介导快速抑制和慢速强直抑制。GABAARs是临床上重要的抗焦虑药、抗惊厥药和麻醉剂的作用靶点。过去的工作涉及强直电流中高亲和力的突触外GABAAR亚基组合和相位IPSCs中低亲和力的突触群体。过去的工作支持了低GABA亲和力阻止突触受体在强直电流中发挥主要作用的流行观点。然而，考虑到海马神经元中大量的突触受体，就会产生这样的问题：尽管突触受体对GABA的敏感性很低，但它们为什么不促进强直电流。为了解释主流观点与我们的计算和初步观察之间的差异，我们假设GABA转运体的一个主要被忽视的作用是保护突触受体免受环境GABA积累的影响，并防止突触受体对紧张电流的贡献。对这一假设的支持将显著改变对强直电流的主流解释，并表明仅靠受体特性无法解释高亲和的突触外受体对强直电流的几乎唯一贡献。为了验证我们的假设，我们将利用我们实验室最近描述的新型药理工具。目的1将测试GAT-1转运体在保护突触受体免受环境GABA影响中的作用。目的2将测试高亲和性突触外受体与低亲和性突触受体介导的紧张电流的兴奋性和正变构调节的生理意义。

DESCRIPTION (provided by applicant): GABAA receptors (GABAARs) mediate fast inhibition and slow, tonic inhibition. GABAARs are the target of clinically important anxiolytics, as well as anticonvulsants and anesthetics. Past work implicates high-affinity extrasynaptic GABAAR subunit combinations in tonic currents and low-affinity, synaptic populations in phasic IPSCs. This past work supports the prevailing view that low GABA affinity prevents a major role of synaptic receptors in tonic currents. However, consideration of the large number of synaptic receptors in hippocampal neurons raises questions about why synaptic receptors do not contribute to tonic currents in spite of their low GABA sensitivity. To explain discrepancies between prevailing views and our calculations and preliminary observations, we hypothesize that a major overlooked role of GABA transporters is to protect synaptic receptors from ambient GABA buildup and to prevent synaptic receptor contributions to tonic currents. Support for this hypothesis would significantly alter a prevailing explanation for tonic currents and would suggest that receptor properties alone cannot explain the nearly exclusive contribution of high-affinity extrasynaptic receptors to tonic currents. To test our hypothesis, we will leverage novel pharmacological tools that our laboratory has recently characterized. Aim 1 will test a role for GAT-1 transporters in shielding synaptic receptors from ambient GABA. Aim 2 will test the physiological implications for excitability and for positive allosteric modulation of tonic current mediated by high affinity extrasynaptic receptors versus low-affinity synaptic receptors.