CHOLINERGIC MODULATION OF NIGRAL DOPAMINE NEURONS

目前，对DA神经元中调节放电模式的生理过程的了解还不完全。多巴胺(DA)能神经元在体内表现出自发的、起搏样的、规律性的放电和不规则的爆发式放电活动。从规则放电模式到爆发放电模式的变化与运动以及黑质纹状体靶点多巴胺释放的大小有关。尽管兴奋性突触传入在DA爆发活动中的作用已被推测，但从规则放电转变为爆发放电的机制尚不清楚。本研究的主要目的是阐明胆碱能受体激活调控谷氨酸诱导的SNC-DA神经元爆发放电的可能离子机制。我们的假设是，来自脚桥被盖核的胆碱能输入使SNC-DA神经元去极化并增加其放电频率，从而导致丘脑底核(STN)、扣带回和前额内侧区的谷氨酸能输入导致爆发放电诱导的倾向。关于乙酰胆碱对DA神经元离子电流的影响以及胆碱能调节DA神经元离子电流促进爆发式放电的机制，缺乏直接的信息。在这项研究中，细胞内电流钳和全细胞膜片钳记录将用于大鼠脑片和急性分离的SNC神经元。将评估突触后M受体和烟碱受体激活对神经细胞膜电位、分离离子电流、放电行为以及与刺激STN的相互作用的影响。1.研究胆碱能受体激活对起搏器样除极和后超极化过程中钙内流的影响；2.研究M受体激活引起静息膜电位去极化的离子机制(S)；3.确定胆碱能受体介导的膜电位变化和后超极化是否对谷氨酸诱发的猝发放电有调节作用。更好地了解乙酰胆碱在调节SNC-DA神经元放电行为中的作用，进而影响SNC靶结构中的多巴胺释放，这一点很重要。拟议的研究结果可能会对帕金森氏症等运动和行为障碍的症状表达和药物操作产生临床影响。

Currently there is an incomplete understanding of the physiological processes which regulate firing patterns in DA neurons. Dopaminergic (DA) neurons in vivo characteristically exhibit spontaneous, pacemaker-like, regular spiking as well as irregular burst-firing activity. The change from regular to burst-firing mode has been associated with movement as well as with the magnitude of dopamine release at nigrostriatal target sites. Although a role for excitatory synaptic inputs in DA bursting activity has been postulated, the mechanisms underlying the change from regular to burst-firing are not clearly understood The main goal of this research proposal is to elucidate possible ionic mechanisms by which cholinergic receptor activation can modulate glutamate-induced burst-firing in SNc-DA neurons. It is our hypothesis that cholinergic input from the peduncular pontine tegmental nucleus depolarizes SNc-DA neurons and increases their firing rate, thereby contributing to the tendency for burst-firing induction in response to glutamatergic input from the subthalamic nucleus (STN), cingulate gyrus, and medial prefrontal area. There is a paucity of direct information regarding the effects of acetylcholine on ion currents in DA neurons and mechanisms by which cholinergic modulation of ion currents in DA neurons may facilitate burst-firing. In this study, intracellular current clamp and whole-cell patch clamp recordings will be utilized in rat brain slices and acutely dissociated SNc neurons. The effects of postsynaptic muscarinic and nicotinic receptor activation on neuronal membrane potential, isolated ion currents, firing behavior, and interactions with STN stimulation will be assessed. The following specific aims will be addressed: 1. To examine the effect of cholinergic receptor activation on Ca2+ entry during the pacemaker-like depolarization and afterhyperpolarization (AHP); 2. To examine the ionic mechanism(s) underlying the depolarization of the resting membrane potential induced by muscarinic receptor activation; 3. To determine if cholinergic receptor-mediated changes in membrane potential and AHP can modulate burst-firing induced by glutamate. It is important to better understand the role of acetylcholine in the modulation of SNc-DA neuronal firing behavior which subsequently influences dopamine release in SNc target structures. Results from the proposed studies may have clinical consequences relevant to symptomatic expression and pharmacological manipulations in motor and behavioral disorders such as Parkinson's disease.