TRPC3 channel mediates 5-HT2C receptor excitation in substantia nigra reticulata

描述（由申请人提供）：黑质网状部（SNr）是基底神经节的关键输出核。帕金森病运动症状通常与SNr GABA神经元放电强度和/或模式的异常相关。这些神经元接受密集的5-羟色胺（5-HT）神经支配，可以调节它们的膜电位和放电。参与这一重要的5-HT调节的受体和离子通道尚未完全了解。 这个R 03的提议试图回答以下两个重要问题：（1）5-HT 2C受体（5-HT 2C-R）介导SNr GABA神经元中的大量5-HT兴奋吗？(2)由于HT 2C-R与Gq/11蛋白偶联，而不是任何离子通道，那么在SNr GABA神经元中，什么离子通道介导HT 2C-R诱导的兴奋效应？换句话说，改变这些神经元膜电位的HT 2C-R效应通道是什么？为了回答这些问题，我们进行了一系列初步的电生理和分子研究。我们的数据表明，SNr GABA神经元选择性表达TRPC 3通道。这些通道具有张力活性，并介导线性Na+依赖性内向电流，逆转电位约为-35 mV。HT 2C-R的激活也诱导几乎相同的线性Na+依赖性内向电流，其逆转电位约为-35 mV。TRPC 3通道的抑制阻断了HT 2C-R诱导的兴奋。 基于这些初步的数据，我们建议，HT 2C-R介导的SNr GABA神经元和TRPC 3通道作为效应器通道的G蛋白偶联5-HT 2C-R的大部分5-HT兴奋。内源性5-HT激活5-HT 2C-R增强紧张性活性TRPC 3通道，诱导内向电流和去极化，促进基底神经节输出神经元的规则放电模式和强度，这对运动控制至关重要。 从拟议的项目的结果将推进我们的理解基底神经节运动控制神经元回路。同样重要的是，由于帕金森病是由多巴胺神经元变性引起的，在5-羟色胺系统中存在额外的异常，我们的实验也将为帕金森病的病理神经生理学的细胞机制提供新的见解，并为更好的治疗提供科学依据。此外，我们的新概念也可能对G蛋白偶联神经递质受体如何影响其他大脑区域神经元的电活动产生广泛的影响。 公共卫生相关性：帕金森氏病是一种常见的衰弱性运动障碍，由基底神经节神经元回路异常引起。对运动控制至关重要的基底神经节输出神经元的电活动由G蛋白偶联的5-羟色胺5-HT 2C受体调节。该提议将验证我们的新假设/概念，即TRPC 3通道，一种紧张性活性阳离子通道，作为基底节输出神经元中5-HT 2C受体的效应通道，从而为理解基底节和帕金森病提供了一个新的概念框架。

DESCRIPTION (provided by applicant): The substantia nigra pars reticulata (SNr) is a key basal ganglia output nucleus. Parkinsonian motor symptoms are often associated with abnormalities in SNr GABA neuron firing intensity and/or pattern. These neurons receive a dense serotonin (5-HT) innervation that may regulate their membrane potential and firing. The receptors and ion channels involved in this important 5-HT regulation are not fully understood. This R03 proposal seeks to answer the following two important questions: (1) does 5-HT2C receptor (5-HT2C-R) mediates the bulk of 5-HT excitation in SNr GABA neurons? (2) Because HT2C-R is coupled to Gq/11 protein, not any ion channel, so what ion channel(s) mediates the effects of HT2C-R-induced excitation in SNr GABA neurons? In other word, what is the effector channel for HT2C-R that changes the membrane potential in these neurons? To answer these questions, we have performed a series of preliminary electrophysiological and molecular studies. Our data show that SNr GABA neurons selectively express TRPC3 channels. These channels are tonically active and mediate a linear Na+dependent inward current with a reversal potential around -35 mV. Activation of HT2C-R also induces a virtually identical linear Na+dependent inward current with a reversal potential around -35 mV. Inhibition of TRPC3 channels blocks HT2C-R-induced excitation. Based on these preliminary data, we propose that HT2C-R mediates the bulk of 5-HT excitation in SNr GABA neurons and TRPC3 channels serve as the effector channel for G protein-coupled 5-HT2C-R. 5-HT2C-R activation by endogenous 5-HT enhances the tonically active TRPC3 channel, induces an inward current and depolarization that facilitates the regular firing pattern and intensity in basal ganglia output neurons that are critical to movement control. Results from the proposed project will advance our understanding of the basal ganglia movement control neuronal circuitry. Equally important, since Parkinson's disease is caused by dopamine neuron degeneration with additional abnormalities in the serotonin system, our experiments will also provide novel insights into the cellular mechanisms of pathoneurophysiology of Parkinson's disease and provide scientific bases for better treatments. Additionally, our novel concept may also have broad implications on how G-protein-coupled neurotransmitter receptors affect the electrical activity in neurons in other brain areas. PUBLIC HEALTH RELEVANCE: Parkinson's disease is a common debilitating movement disorder arising from abnormalities in the basal ganglia neuronal circuitry. The electrical activity of basal ganglia output neurons, critical to movement control, is regulated by G protein-coupled serotonin 5-HT2C receptors. This proposal will test our novel hypothesis/concept that TRPC3 channels, a type of tonically active cation channel, serve as the effector channel for 5-HT2C receptor in basal ganglia output neurons, thus providing a novel conceptual framework important to understanding the basal ganglia and Parkinson's disease.