EXCITATORY AMINO ACID TRANSMITTERS IN CNS

该项目利用大鼠大脑的海马结构， 研究谷氨酸传递的机制。现时的建议 重点是脯氨酸在调节谷氨酸的生理作用 的病理生理学后果的报告 脯氨酸浓度在遗传疾病称为高脯氨酸血症。 脯氨酸是一种兴奋性和兴奋毒性的亚氨基酸，可以阻断记忆 形成并诱发逆行性遗忘。此外，高脯氨酸血症是 与儿童期癫痫发作的正常发病率高得多有关 和智力迟钝。一种Na+/Cl-依赖性高亲和力转运蛋白 对脯氨酸特异的蛋白质仅由谷氨酸亚类表达 途径。脯氨酸，在典型的人脑脊液浓度下 流体，加强在一个这样的途径传输：谢弗 侧副连合投射到CA 1区。“脯氨酸诱导的 “增强作用”是NMDA受体依赖性的且持久的。这些 观察结果表明，在正常情况下，体内存在一些谷氨酸突触 在部分增强的状态下，由于持续占据一个 小部分NMDA受体被脯氨酸阻断。机制研究 脯氨酸诱导的增强将使用场 来自CA 1锥体细胞的电位和全细胞膜片钳记录。 具体目标包括确定脯氨酸诱导 增强作用利用与参与增强的那些机制重叠的机制。 电诱发的长时程增强，无论是低浓度的 脯氨酸实际上在这些细胞中引起可测量的NMDA电流， 脯氨酸诱导的增强作用涉及突触前和突触后 机制，无论是AMPA和NMDA组件的突触后 反应增强以及脯氨酸是否改变GABA抑制。 另一组研究将检查脯氨酸转运蛋白在 脯氨酸诱导的增强作用。目的是确定是否 脯氨酸必须被摄取才能发生增强作用， 仅用于调节局部细胞外脯氨酸浓度。 这些研究将利用四肽gly- gly-phe-leu有效地并选择性地抑制高亲和力脯氨酸 运输和海马的外侧和内侧分区 穿通途径吸收脯氨酸的能力明显不同。一 最后的研究将探讨脯氨酸抑制的机制， 谷氨酸盐释放。在脯氨酸浓度下观察到这种效应 存在于脑脊髓液中， II型高脯氨酸血症，但不伴有正常脯氨酸浓度。 拟议研究的结果将阐明一种新的调节机制， 谷氨酸传输可能是药物治疗的一个有吸引力的靶点 发展它们也可能被证明与记忆的突触机制有关 和学习

This project employs the hippocampal formation of the rat brain to investigate mechanisms of glutamate transmission. The present proposal focuses on the physiological role of proline in regulating glutamate transmission and on the pathophysiological consequences of elevated proline concentrations in the genetic disorders known as hyperprolinemia. Proline is an excitatory and excitotoxic imino acid that can block memory formation and induce retrograde amnesia. Moreover, hyperprolinemia is associated with a much higher than normal incidence of childhood seizures and mental retardation. A Na+/Cl--dependent, high affinity transporter specific for pro-line is expressed exclusively by a subset of glutamate pathways. Proline, at a concentration typical of human cerebrospinal fluid, potentiates transmission in one such pathway: the Schaffer collateral-commissural projection to area CA1. "Proline-induced potentiation" is NMDA receptor-dependent and long-lasting. These observations suggest that some glutamate synapses in vivo normally exist in a partially potentiated state due to the continuous occupation of a small fraction of NMDA receptors by proline. Mechanistic studies of proline-induced potentiation will be carried out with use of field potential and whole cell patch clamp recordings from CA1 pyramidal cells. Specific objectives include determining to what extent proline-induced potentiation utilizes mechanisms that overlap those involved in electrically-evoked long-term potentiation, whether low concentrations of proline actually evoke a measurable NMDA current in these cells, whether proline-induced potentiation involves presynaptic as well as postsynaptic mechanisms, whether both AMPA and NMDA components of the postsynaptic response are potentiated and whether proline modifies GABA inhibition. Another set of studies will examine the role of the proline transporter in proline-induced potentiation. The objective is to determine whether proline must be taken up for potentiation to occur or whether transport serves simply to regulate the local extracellular proline concentration. These studies will take advantage of findings that the tetrapeptide gly- gly-phe-leu potently and selectively inhibits high affinity proline transport and that the lateral and medial divisions of the hippocampal perforant path differ markedly in their ability to take up proline. A final study will investigate the mechanism by which proline depresses glutamate release. This effect is observed with concentrations of proline that are present in the cerebrospinal fluid of persons having hyperprolinemia type II, but not with normal proline concentrations. Findings from the proposed studies will elucidate a novel regulation of glutamate transmission that may be an attractive target for drug development. They may also prove relevant to synaptic mechanisms of memory and learning.