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

描述(申请人提供)：黑质网状部(SNR)是一个关键的基底节输出核。帕金森氏症的运动症状通常与SNR-GABA神经元放电强度和/或模式的异常有关。这些神经元接受致密的5-羟色胺(5-HT)神经支配，可能调节它们的膜电位和放电。参与这一重要的5-羟色胺调节的受体和离子通道尚不完全清楚。这个R03提案试图回答以下两个重要问题：(1)5-HT2C受体(5-HT2C-R)是否介导了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，那么是什么离子通道(S)介导了HT2C-R诱导的SNR GABA神经元的兴奋效应？换句话说，HT2C-R的效应通道是什么改变了这些神经元的膜电位？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。这些通道在音调上是活跃的，并介导一种线性的Na+依赖的内向电流，其反转电位约为-35 mV。HT2C-R的激活也诱导了一个几乎完全相同的线性Na+依赖的内向电流，其反转电位约为-35 mV。抑制TRPC3通道可阻断HT2C-R诱导的兴奋。根据这些初步数据，我们认为HT2C-R介导了SNR GABA神经元的大部分5-HT兴奋，TRPC3通道可能是G蛋白偶联的5-HT2C-R的效应通道。由内源性5-羟色胺激活的5-HT2C-R增强了张力激活的TRPC3通道，诱导内向电流和去极化，促进了对运动控制至关重要的基底神经节输出神经元的规则放电模式和强度。该项目的研究结果将促进我们对基底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5-羟色胺系统的额外异常引起的，我们的实验也将为帕金森病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脑区神经元的电活动产生广泛的影响。

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.