Synaptic Defects in the Ca Channel Mutant Mouse

Ca 通道突变小鼠的突触缺陷

• 批准号: 6540405
• 负责人: Kathleen Dunlap
• 金额: $ 27.36万
• 依托单位: TUFTS UNIVERSITY BOSTON
• 依托单位国家: 美国
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-06-01 至 2005-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6540405
• 关键词: G protein; GABA receptor; calcium channel; calcium channel blockers; calcium flux; cerebellar ataxia /dyskinesia; cerebellum; electrophysiology; exocytosis; fluorescent dye /probe; genotype; laboratory mouse; mutant; nerve /myelin protein; nervous system disorder; neural transmission; neurons; neuroregulation; point mutation; pore forming protein; protein isoforms; synapses; synaptosomes; tissue /cell culture; voltage /patch clamp

DESCRIPTION:(adapted from applicant's abstract) Naturally-occurring mutations in the gene encoding class A (or P/Q-type) calcium channels are associated with multiple abnormalities, ranging from migraine headache to motor ataxias to absence epileptic seizures. These heterogeneous neurological phenotypes underscore the central importance of P/Q-type calcium channels-the dominant exocytotic channels in central nervous system. P/Q is not, however, the only type of calcium channel controlling synaptic transmission in the CNS. N-type (or class B) calcium channels usually co-exist with P/Q and, together, they jointly govern the release of many, if not all, transmitters. Whether P/Q and N channels play unique functional roles at the synapse is unclear. Experiments with one P/Q channel mutant mouse, tottering, suggest, however, that the two channels are not functionally redundant and that tottering offers an opportunity to explore their different roles in exocytosis. Homozygous tottering animals display a dramatic neurological phenotype, characterized by ataxia and frequent absence seizures. Our preliminary experiments on tottering demonstrate that a primary consequence of the P/Q channel mutation is a shift in the ratio of P/Q:N channels in some (but not all) nerve terminals. For example, release of the excitatory transmitter glutamate and glutamatergic synaptic transmission at the parallel fiber-Purkinje cell synapse in cerebellum are controlled largely by N-type calcium channels in the mutant, rather than P/Q-type as they are in wild-type animals. As a consequence of these changes in the presynaptic calcium channel complement, excitatory transmission is reduced and G protein-dependent inhibition is enhanced at mutant synapses. In contrast, GABA release from inhibitory nerve terminals appears to be unaffected in tottering animals. On the basis of these observations, we hypothesize that the selective effect of the tottering allele on excitatory transmission leads to an overall decreased excitation of Purkinje cells. Three interacting factors contribute: 1) glutamate release from excitatory inputs is impaired due to the decreased involvement of P/Q channels; 2) the relative increase in N channel-mediated release further enhances susceptibility of these inputs to presynaptic inhibition (because N channels are more effectively modulated by G proteins than are P/Q channels); and 3) unimpaired inhibitory, GABAergic inputs are relatively more efficacious in the face of reduced excitation. As Purkinje cells control cerebellar output via GABAergic inhibitory transmission onto output neurons in deep cerebellar nuclei, we predict that a reduction in Purkinje cell activity will enhance net cerebellar output. Ultimately, such changes would excite thalamus and motor cortex, providing a plausible mechanism for the ataxia and seizures observed in these animals. Experiments proposed here will stringently test this hypothesis through in-depth cellular and synaptic exploration of calcium channels and calcium-dependent exocytosis in tottering cerebellum. Results will provide essential information for understanding the consequences of the mutation on cerebellar circuit behavior and may, in the long term, offer suggestions for new therapeutic interventions into ataxia and other motor disorders.

描述：（改编自申请人的摘要） 编码 A 类（或 P/Q 型）的基因中自然发生的突变 钙通道与多种异常相关，包括 偏头痛、运动性共济失调、失神性癫痫发作。这些 异质的神经表型强调了核心重要性 P/Q型钙通道——中枢神经中主要的胞吐通道 系统。然而，P/Q 并不是钙通道控制的唯一类型 中枢神经系统中的突触传递。 N型（或B类）钙通道通常 与 P/Q 共存，并且它们共同管理许多的释放，如果 不是全部，发射器。 P/Q和N通道是否发挥独特的功能作用 突触处尚不清楚。用一只 P/Q 通道突变小鼠进行的实验， 然而，摇摇欲坠，表明这两个通道无法正常工作 多余的，摇摇欲坠提供了一个探索他们不同的机会 胞吐作用中的作用。 纯合的蹒跚动物表现出戏剧性的神经表型， 其特点是共济失调和频繁失神发作。我们的初步 摇摇晃晃的实验表明，P/Q 的主要结果 通道突变是某些通道中 P/Q:N 通道比例的变化（但不是 所有）神经末梢。例如，兴奋性递质的释放 谷氨酸和谷氨酸能突触传递平行 小脑纤维浦肯野细胞突触主要由N型控制 突变体中的钙通道，而不是野生型中的 P/Q 型 动物。由于突触前钙通道的这些变化 补体、兴奋性传递减少和 G 蛋白依赖性 突变突触的抑制作用增强。相比之下，GABA 释放自 在摇摇欲坠的动物中，抑制性神经末梢似乎不受影响。 基于这些观察，我们假设选择性效应 兴奋性传递上的摇摇欲坠的等位基因导致整体下降 浦肯野细胞的兴奋。三个相互作用的因素起作用：1) 由于兴奋性输入的谷氨酸释放减少，谷氨酸释放受到损害 P/Q 通道的参与； 2) N通道介导的相对增加 释放进一步增强了这些输入对突触前的敏感性 抑制（因为 G 蛋白更有效地调节 N 通道 比 P/Q 通道）； 3) 未受损的抑制性 GABA 能输入是 在兴奋减少的情况下相对更有效。正如浦肯野 细胞通过 GABA 能抑制性传输来控制小脑输出 小脑深部核团的输出神经元，我们预测 浦肯野细胞活性将增强小脑的净输出。最终，这样的 变化会兴奋丘脑和运动皮层，提供一个合理的机制 对于在这些动物中观察到的共济失调和癫痫发作。提议的实验 这里将通过深入的细胞和 钙通道的突触探索和钙依赖性胞吐作用 小脑摇摇欲坠。结果将提供重要信息 了解突变对小脑回路行为的影响 从长远来看，可能会为新的治疗干预措施提供建议 导致共济失调和其他运动障碍。