Kainate Receptors on Hippocampal Interneurons

描述(申请人提供)：海马区抑制性中间神经元调节锥体细胞，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，海马区中间神经元表达海人酸型离子型谷氨酸受体，这些海藻氨酸受体(KARs)是通过突触激活的。中间神经元上的突触后KAR参与兴奋性突触后电位(EPSP)。中间神经元上的KARs也抑制了从中间神经元到锥体细胞的GABA释放，尽管这种作用的机制尚不清楚。这两种作用表明，神经元间KARs在控制海马区的抑制活性和输出方面发挥着重要作用，可能是限制癫痫时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批判性评估，因为关于神经元间KARs的功能、调节这些功能的机制或KARS调节GABA释放的机制还缺乏足够的信息。 这项提议将寻求解决我们对KARS关于中间神经元的理解中的这些差距。利用全细胞膜片钳技术，KARs在中间神经元上的活动将被记录下来，并使用药理学工具进行操作。将解决三个具体目标。(1)突触后KARs的功能将通过检验四个假设来确定：(A)KARs是钙通透性的，并可以启动钙依赖的信号；(B)KARs被分离到与AMPA受体不同的传入通路；(C)KARs允许神经元间在低传入放电频率下执行时间整合；以及(D)这三种功能在不同的神经元间亚类中有差异地分布。(2)通过检验两个假设来确定调节KAR介导的EPSP的机制：(A)KAR介导的EPSP是由持续的受体递送到突触和从突触移除来调节的；(B)KAR介导的EPSP受到活动依赖的突触可塑性的影响。(3)通过检验两个假设来确定神经元间KARs突触前活动的机制：(A)谷氨酸可以激活直接调节GABA释放的突触前KARs；以及(B)KARS诱导的抑制是神经元间尖峰放电的间接结果。这些实验将提供有关神经元间KARs在海马体中的作用的信息，并为未来评估操纵这些KARs来控制超兴奋性的可能性提供合理的基础。

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.