Development of NMDA Synapses in Rat Dysplastic Neurons

在患有难治性癫痫的患者中，可以通过手术切除癫痫发作区域，以减少局灶性癫痫发作。局灶性癫痫皮质与切除的邻近皮质相比，有明显更多的神经元定向障碍或皮质发育不良。在人类癫痫灶发育不良的皮质组织中，谷氨酸-NMDA受体具有NR2B亚基和NR1亚基的物理组装，NR1亚基已知形成一种高度兴奋的NMDA受体复合体。对切除的癫痫发育不良皮质的研究表明，这些NMDA受体异常可归因于蛋白质复合体的显著增加，这些蛋白质复合体在整个NMDA膜受体长环路中相互作用。我们现在建议使用胚胎辐射的大鼠皮质发育不良模型来测试关于在这些过度兴奋的NMDA离子通道发展过程中的膜和突触机制的假设，这些离子通道会导致儿童和成人的局灶性皮质癫痫发作。人类研究受到以下因素的限制：没有正常的对照组织，不知道什么时候和什么类型的产前损伤发生，以及没有持续跟踪出生后的发育。相比之下，通过对胎儿辐射大鼠进行的良好控制的研究，我们将量化谷氨酸NMDA受体发展异常永久物理结合的“关键时期”，这是导致过度兴奋的原因。本研究的长期目标是研究大鼠大脑皮层NMDA受体复合体的正常发育，以及伽玛射线产前损伤如何改变预期的神经元板层、神经元方向和参与神经元超兴奋性的膜受体蛋白的发育。同时，我们将研究聚集在NMDA受体上并参与突触传递的突触后蛋白。这些发现可能有助于设计新的治疗药物，以阻断1)NMDA受体中特定的异常蛋白共组装，或2)膜相关突触后蛋白中。这些药物可以成功地减少癫痫的发生，而不会抑制或干扰大脑中正常的突触传递。

In patients with medically intractable epilepsy, the region of seizure onset can be surgically removed to reduce focal seizures. The focal epileptic cortex, compared to adjacent cortex included in the resection, has significantly more disoriented neurons or cortical dysplasia. In human dysplastic cortical tissue from the epileptic focus, glutamate-NMDA receptors have the NR2B subunit physically coassembled with the NR1 subunit, which has been known to form a hyperexcitable NMDA receptor complex. Studies of resected epileptic dysplastic cortices have revealed that these NMDA receptor abnormalities are attributable to significant increases in protein complexes, which interact throughout the long NMDA membrane receptor loops. We now propose to use the fetal radiated rat model of cortical dysplasia to test hypotheses regarding the membrane and synaptic mechanisms during development of these hyperexcitable NMDA ion channels that cause focal cortical seizures in both children and adults. Human studies are limited by not having normal control tissue, by not knowing when and what type of prenatal damage occurred, and by not following postnatal development consistently. By contrast, with the well-controlled studies in fetal radiated rats we will quantify the "critical periods" when the glutamate NMDA receptor develops anomalous permanent physical coassembly that contributes to hyperexcitability. The long term objectives of this research are to study the normal development of the NMDA receptor complex in the rat cerebral cortex and how prenatal insults by gamma irradiation alter the development of the expected neuronal laminations, neuron orientations, and membrane receptor proteins that contribute to neuronal hyperexcitability. Simultaneously, we will study the postsynaptic proteins that cluster at the NMDA receptors and contribute to synaptic transmission. These findings may aid in designing new therapeutic agents targeted for blocking 1) only specific aberrant protein coassemblies in the NMDA receptor, or 2) in the membrane-associated postsynaptic proteins. Such drugs could successfully decrease epileptogenesis without depressing or interfering with normal synaptic transmission in the brain.