Kainate Receptors on Hippocampal Interneurons

描述（由申请人提供）：海马中的抑制性中间神经元调节锥体细胞并防止导致癫痫样活动的过度兴奋。谷氨酸能传递到中间神经元激活这些细胞来驱动这些功能。最近的研究表明，海马中间神经元表达离子型谷氨酸受体的红藻氨酸亚型，并且这些红藻氨酸受体（KARs）被突触激活。中间神经元上的突触后KAR有助于兴奋性突触后电位（EPSP）。中间神经元上的KAR也抑制GABA从中间神经元到锥体细胞的释放，尽管这种作用的机制尚不清楚。这两个动作表明，神经元间的KAR在控制海马的抑制活性和输出中起着重要作用，并且可能代表了限制癫痫期间过度兴奋的治疗靶点。然而，目前还不可能对这种可能性进行严格的评估，因为关于神经元间KARs的功能、这些功能的调节机制或KARs调节GABA释放的机制的信息不足。 该提案将寻求解决我们对中间神经元上的KAR的理解中的这些差距。使用全细胞膜片钳技术，将记录KAR对中间神经元的活性，并使用药理学工具进行操作。将讨论三个具体目标。(1)通过测试四个假设来鉴定突触后KAR的功能：（a）KAR是钙可渗透的并且可以启动钙依赖性信号传导;（B）KAR被分离到与AMPA受体不同的传入通路;（c）KAR允许中间神经元在低传入放电频率下进行时间整合;以及（d）这三种功能在不同的中间神经元亚类中分布不同。(2)调节KAR介导的EPSP的机制将通过测试两个假设来鉴定：（a）KAR介导的EPSP通过连续的受体递送到突触和从突触移除来调节;和（B）KAR介导的EPSP受到活性依赖性突触可塑性的影响。(3)神经元间KAR的突触前作用的潜在机制将被确定，通过测试两个假设：（a）谷氨酸可以激活突触前KAR，直接调节GABA的释放;（B）KAR诱导的抑郁症是神经元间尖峰的间接结果。这些实验将提供有关海马神经元间KARs作用的信息，并为未来的实验提供合理的基础，以评估操纵这些KARs来控制过度兴奋的可能性。

DESCRIPTION (provided by applicant): Inhibitory interneurons in the hippocampus regulate pyramidal cells and prevent hyperexcitability that leads to epileptiform activity. Glutamatergic transmission onto interneurons activates these cells to drive these functions. Recently, it has been shown that hippocampal interneurons express the kainate subtype of ionotropic glutamate receptor, and these kainate receptors (KARs) are synaptically activated. Postsynaptic KARs on interneurons contribute to the excitatory postsynaptic potential (EPSP). KARs on interneurons also depress the release of GABA from interneurons onto pyramidal cells, although the mechanisms underlying this effect remain unclear. These two actions suggest that interneuronal KARs play a major role in the control of inhibitory activity and output in the hippocampus, and possibly represent a therapeutic target to limit hyperexcitability during epilepsy. However, at present it is not possible to critically evaluate this possibility, because insufficient information is available about the functions of interneuronal KARs, the mechanisms by which these functions can be regulated, or the mechanisms by which KARs regulate GABA release. This proposal will seek to address these gaps in our understanding of KARs on interneurons. Using whole-cell patch clamp techniques, the activity of KARs on interneurons will be recorded and manipulated using pharmacological tools. Three specific aims will be addressed. (1) Functions for postsynaptic KARs will be identified, by testing four hypotheses: (a) that KARs are calcium-permeable and can initiate calcium-dependent signaling; (b) that KARs are segregated to different afferent pathways than AMPA receptors; (c) that KARs allow interneurons to perform temporal integration at low afferent firing frequencies; and (d) that these three functions are differentially distributed among different interneuronal subclasses. (2) Mechanisms of regulating the KAR-mediated EPSP will be identified, by testing two hypotheses: (a) that the KAR-mediated EPSP is regulated by continuous receptor delivery to, and removal from, the synapse; and (b) that the KAR-mediated EPSP is subject to activity-dependent synaptic plasticity. (3) Mechanisms underlying the presynaptic actions of interneuronal KARs will be identified, by testing two hypotheses: (a) that glutamate can activate presynaptic KARs that directly regulate GABA release; and (b) that the depression induced by KARs is an indirect consequence of interneuronal spiking. These experiments will provide information about the role of interneuronal KARs in the hippocampus, and provide a rational basis for future experiments to assess the possibility of manipulating these KARs to control hyperexcitability.