MOSSY FIBER-GRANULE CELL SYNAPSES

海马齿状回中反复出现的苔藓状纤维是颞叶癫痫的一个独特特征。新的苔藓状纤维颗粒细胞突触的形成产生了复杂的电路，可能能够支持混响激励，从而降低齿状回通常对癫痫传播的高阻力。该项目的总体目标是表征苔藓纤维颗粒细胞突触调节电路功能的特性。匹罗卡品治疗的大鼠，癫痫发作后也会形成持续密集的复发性苔藓纤维通路，将用于研究复发性苔藓纤维回路的三个不同寻常的特征，目前关于这些特征的信息很少：即门部异位颗粒细胞、GABA和神经肽Y的表达以及锌的释放。匹罗卡平诱导的癫痫持续状态增加了新的齿状颗粒细胞的产生，其中一些在门部发现。Hilar异位颗粒细胞具有几个独特的特征，表明它们在触发同步颗粒细胞活动中起关键作用。这些特征包括与其他颗粒细胞的相互连接，兴奋性神经支配异常，抑制性神经支配明显缺乏，以及与CA3锥体细胞相关的自发破裂。全细胞膜片钳记录和电子显微镜将被用来描述这些细胞的神经支配特征，并验证肝门异位颗粒细胞和正常位置颗粒细胞的神经支配差异在很大程度上解释了它们的兴奋性差异的假设。GABA和NPY是抑制性递质，在癫痫发作后在苔藓纤维中强烈表达；在中间期，NPY继续强烈表达。研究将验证这些递质在苔藓纤维颗粒细胞突触释放的假设，并主要用于减少谷氨酸的进一步释放。通过这种方式，他们提出限制复发苔藓纤维通路增强癫痫发作传播的能力。从苔藓纤维钮扣中释放锌被认为可以增加颗粒细胞的兴奋性。然而，最近的数据表明，它可能通过反对突触后NMDA受体的激活而起到抑制混响兴奋的作用。为了研究这个问题，我们将测试锌螯合剂对颗粒细胞癫痫样活性的影响，这种活性至少部分取决于NMDA受体的激活。

Recurrent mossy fiber sprouting in the hippocampal dentate gyrus is a unique feature of temporal lobe epilepsy. The formation of new mossy fiber-granule cell synapses creates complex circuitry that is presumably capable of supporting reverberating excitation and thereby diminishing the normally high resistance of the dentate gyrus to seizure propagation. The overall objective of this project is to characterize properties of mossy fiber-granule cell synapses that regulate circuit function. Pilocarpine-treated rats, which become epileptic and also develop a consistently dense recurrent mossy fiber pathway, will be used to investigate three unusual features of recurrent mossy fiber circuitry about which little information is currently available: namely, hilar ectopic granule cells, expression of GABA and neuropeptide Y, and release of zinc. Pilocarpine- induced status epilepticus increases the production of new dentate granule cells, some of which are found in the hilus. Hilar ectopic granule cells possess several unique features that suggest they play a key role in triggering synchronous granule cell activity. These features include reciprocal connections with other granule cells, abnormal excitatory innervation, apparent paucity of inhibitory innervation, and spontaneous bursting in association with CA3 pyramidal cells. Whole cell patch clamp recording and electron microscopy will be used to characterize the innervation of these cells and test the hypothesis that differences between the innervation of hilar ectopic and normally-situated granule cells accounts in large part for their differences in excitability. GABA and NPY are inhibitory transmitters that are strongly expressed in mossy fibers after a seizure; NPY continues to be strongly expressed during the interictal period. Studies will test the hypothesis that these transmitters are released at mossy fiber-granule cell synapses and serve mainly to reduce the further release of glutamate. In this way, they are proposed to limit the ability of the recurrent mossy fiber pathway to enhance seizure propagation. Release of zinc from recurrent mossy fiber boutons has been proposed to increase granule cell excitability. However, recent data suggest that it may instead act as a brake on reverberating excitation by opposing the activation of postsynaptic NMDA receptors. To investigate this issue, the effects of zinc chelators will be tested on granule cell epileptiform activity that depends, at least in part, on NMDA receptor activation.