CHOLINERGIC MECHANISMS AT EFFERENT SYNAPSES

传出突触的胆碱能机制

• 批准号: 3732225
• 负责人: BARBARA J MORLEY
• 金额: --
• 依托单位: FATHER FLANAGAN'S BOYS' HOME
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/3732225
• 关键词: antireceptor antibody; aziridines; chinchilla; cholinergic receptors; cochlea; ear hair cell; efferent nerve; electron microscopy; evoked potentials; fluorescent dye /probe; immunocytochemistry; ion transport; light microscopy; nerve endings; neural degeneration; neurotoxins; nicotinic receptors; olivocochlear bundle; organ of Corti; synapses

Our knowledge of cochlear efferent function is derived almost exclusively from studies of the medial olivocochlear neurons to the outer hair cells in the organ of Corti. There is a second, less well-understood efferent pathway which arises from lateral olivocochlear neurons which are the source of the efferent synapses which typically contact each spiral ganglion cell dendrite close to its synaptic junction with an inner hair cell. Lateral olivocochlear neurons have proven difficult to access with current physiological and neurochemical techniques. Pilot data in this laboratory indicate that, despite the fact that both lateral and medial efferent terminals contain cholinergic enzymes, only efferent fibers belonging to the lateral efferent system degenerate following intracochlear infusion of 1 microM of the cholinergic neurotoxin, ethylcholine aziridinium ion (AF64A). The first set of experiments proposed in this application are directed at extending this observation. We will investigate the ultrastructural changes in the organ of Corti in chinchillas following the intracochlear infusion of AF64A at several survival times. Sound-evoked cochlear potentials will be used to monitor the functional integrity of the cochlea before, during and after micro- perfusion with the AF64A solution. As a test of the specificity of AF64A on the lateral afferent system, we will monitor the integrity of the medial efferent system by measuring the effect of its activity on cochlear potentials. The observation that medial efferent terminals appear to survive AF64A treatment could reflect a low rate of uptake of the toxin resulting from the low discharge rates found in these neurons. In order to test this hypothesis, we will infuse 1 microM AF64A while simultaneously stimulating the ears with a broadband acoustic signal. We hypothesize that under these conditions of stimulation, the medial efferents will be activated and may accumulate the toxin and degenerate. The cholinergic receptor(s) in the medial and the lateral efferent systems have not been characterized. Increased sensitivity to AF64A suggests that there may be differences in the two systems that are reflected in the neurotransmitter receptor type. In this application we propose to investigate the kind of cholinergic receptor on outer hair cells (OHCs). We will test the hypothesis that the cholinergic receptor on OHCs is a nicotinic cholinergic receptor with similarity to the receptor at skeletal muscle. We will test this hypothesis by studying the cross-reactivity of antibodies specific to nicotinic receptors with OHCs and by investigating sodium flux in OHCs following exposure to cholinergic agonists and antagonists.

我们对耳蜗传出功能的了解几乎完全来自 从内侧橄榄耳蜗神经元到外毛细胞的研究 柯蒂氏器官。 还有第二个不太为人所知的传出神经 产生于外侧橄榄耳蜗神经元的通路 通常接触每个螺旋的传出突触的来源 神经节细胞树突靠近其与内毛的突触连接处 细胞。 已证明很难访问外侧橄榄耳蜗神经元 当前的生理学和神经化学技术。 试点数据在此 实验室表明，尽管外侧和内侧 传出末梢含有胆碱能酶，仅传出纤维 属于外侧传出系统，在耳蜗内退化后 输注 1 µM 胆碱能神经毒素、乙基胆碱 氮丙啶鎓离子 (AF64A)。 本文提出的第一组实验 应用程序旨在扩展这一观察结果。 我们将 研究柯蒂氏器的超微结构变化 龙猫耳蜗内输注 AF64A 数次后 生存时间。 声诱发耳蜗电位将用于监测 微前、中、后耳蜗的功能完整性 用 AF64A 溶液灌注。 作为AF64A特异性的测试 在外侧传入系统上，我们将监测内侧传入系统的完整性 通过测量传出系统的活动对耳蜗的影响 潜力。 观察到内侧传出终端似乎 AF64A 治疗后存活下来可能反映出毒素的摄取率较低 这是由于这些神经元中发现的低放电率造成的。 为了 为了检验这个假设，我们将同时注入 1 microM AF64A 用宽带声信号刺激耳朵。 我们假设 在这些刺激条件下，内侧传出神经将 被激活并可能积累毒素并变质。 胆碱能的 内侧和外侧传出系统中的受体尚未被 特点。 对 AF64A 的敏感性增加表明可能存在 两个系统的差异反映在神经递质上 受体类型。 在此应用中，我们建议调查 外毛细胞 (OHC) 上的胆碱能受体。 我们将测试 假设 OHC 上的胆碱能受体是烟碱胆碱能受体 与骨骼肌受体相似的受体。 我们将测试 通过研究特定抗体的交叉反应性来提出这一假设 烟碱受体与 OHC 并通过研究 OHC 中的钠通量 接触胆碱能激动剂和拮抗剂后。