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

描述（申请人提供）：网状黑质（SNr）是基底神经节的关键输出核。帕金森运动症状通常与SNr - GABA神经元放电强度和/或模式异常有关。这些神经元接受密集的5-羟色胺（5-HT）神经支配，可能调节其膜电位和放电。参与这一重要的5-羟色胺调节的受体和离子通道尚未完全了解。本R03提案旨在回答以下两个重要问题：(1)5-HT2C受体（5-HT2C- r）是否介导SNr GABA神经元中的大部分5-HT兴奋？(2)由于HT2C-R与Gq/11蛋白偶联，而不是任何离子通道，那么是哪种离子通道介导了HT2C-R在SNr GABA神经元中诱导的兴奋作用？换句话说，改变这些神经元膜电位的HT2C-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神经元选择性地表达TRPC3通道。这些通道是tontonic active，并介导线性Na+依赖的内向电流，其反转电位约为-35 mV。HT2C-R的激活也诱导出几乎相同的线性依赖于Na+的内向电流，其反转电位约为-35 mV。抑制TRPC3通道阻断ht2c - r诱导的兴奋。基于这些初步数据，我们提出HT2C-R介导了SNr GABA神经元中大部分5-HT的兴奋，TRPC3通道是G蛋白偶联5-HT2C-R的效应通道。内源性5-HT激活5-HT2C-R可增强TRPC3通道的张力活性，诱导向内电流和去极化，促进对运动控制至关重要的基底节区输出神经元的规则放电模式和强度。该项目的结果将促进我们对基底神经节运动控制神经元回路的理解。同样重要的是，由于帕金森病是由多巴胺神经元变性和血清素系统的额外异常引起的，我们的实验也将为帕金森病的病理神经生理学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大脑其他区域神经元的电活动具有广泛的意义。

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.