Synaptic Defects in the Ca Channel Mutant Mouse

Ca 通道突变小鼠的突触缺陷

• 批准号: 6319484
• 负责人: Kathleen Dunlap
• 金额: $ 27.74万
• 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/6319484
• 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-Type）的基因中的天然突变突变 钙通道与多种异常有关，从 偏头痛出现运动性行日，缺乏癫痫发作。这些 异质神经表型强调了 P/Q-Type钙通道 - 中枢神经中的显性胞吐通道 系统。但是，P/Q不是唯一的钙通道控制的类型 中枢神经系统中的突触传播。 N型（或B类）钙通道通常 如果 并非全部，发射器。 P/Q和N通道是否扮演独特的功能角色 在突触时尚不清楚。使用一个P/Q通道突变小鼠实验， 但是，建议，这两个通道在功能上不是 多余的，那个摇摇欲坠为探索他们的不同的机会提供了机会 在胞吐作用中的作用。 纯合的动物表现出戏剧性的神经表型， 以共济失调和经常缺勤为特征。我们的初步 tottering的实验表明P/Q的主要结果 通道突变是p/q：n通道比率的变化（但不是 所有）神经终端。例如，释放兴奋性发射器 平行处的谷氨酸和谷氨酸能突触传播 小脑中的纤维 - 纯素细胞突触主要由N型控制 突变体中的钙通道，而不是野生型中的p/Q-type 动物。由于这些突触前钙通道的这些变化是由于这些变化 补体，兴奋性传播减少并依赖G蛋白 突变突触时的抑制作用得到了增强。相反，GABA从 抑制性神经末端似乎在蹒跚的动物中不受影响。 根据这些观察，我们假设 兴奋性传播上的摇摇欲坠的等位基因导致总体下降 purkinje细胞的激发。三个相互作用的因素贡献：1） 由于减少 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n通道被G蛋白更有效地调节 比P/Q通道）； 3）无抑制作用，GABA能输入是 面对减少兴奋，相对有效。作为浦肯野 细胞通过GABA能抑制性传播控制小脑输出 在深小脑核中输出神经元，我们预测 Purkinje细胞活性将增强小脑输出。最终，这样的 变化会激发丘脑和运动皮层，提供合理的机制 对于这些动物中观察到的共济失调和癫痫发作。提出了实验 这里将严格通过深入的细胞和 钙通道的突触探索和依赖钙的胞吐作用 小脑结果将为基本信息提供 了解突变对小脑电路行为的后果 从长远来看，可能会为新的治疗干预提供建议 进入共济失调和其他运动障碍。