MOSSY FIBER-GRANULE CELL SYNAPSES

复发性苔藓纤维在海马齿状回发芽是颞叶癫痫的一个独特特征。新苔藓状纤维颗粒细胞突触的形成创造了复杂的电路，推测该电路能够支持混响兴奋，从而降低齿状回对癫痫传播的正常高抵抗。这个项目的总体目标是描述苔藓状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成为癫痫患者，也发展出持续致密的复发性苔藓纤维通路，将被用来研究复发性苔藓纤维回路的三个不寻常的特征，目前关于这些特征的信息很少：即肺门异位颗粒细胞，GABA和神经肽Y的表达，以及锌的释放。匹罗卡品诱导的癫痫持续状态增加了新的齿状颗粒细胞的产生，其中一些在肺门被发现。肺门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发挥关键作用。这些特征包括与其他颗粒细胞的相互联系，异常的兴奋性神经支配，明显的抑制性神经支配的缺乏，以及与CA3锥体细胞相关的自发爆裂。全细胞膜片钳记录和电子显微镜将被用来表征这些细胞的神经支配，并检验这样的假说，即肺门异位颗粒细胞的神经支配的差异是它们兴奋性差异的主要原因。GABA和NPY是癫痫发作后在苔藓纤维中强烈表达的抑制性递质；NPY在癫痫发作间期继续强烈表达。研究将检验这一假设，即这些递质是在苔藓纤维颗粒细胞突触释放的，主要用于减少谷氨酸的进一步释放。通过这种方式，他们被建议限制复发苔藓纤维通路的能力，以促进癫痫的传播。从复发性苔藓纤维结节中释放锌可以增加颗粒细胞的兴奋性。然而，最近的数据表明，它可能通过对抗突触后NMDA受体的激活而起到抑制反射兴奋的作用。为了研究这个问题，将测试锌螯合剂对颗粒细胞癫痫样活动的影响，这种活动至少部分依赖于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.