CHOLINERGIC MODULATION OF NIGRAL DOPAMINE NEURONS

目前对调节DA神经元放电模式的生理过程还不完全了解。多巴胺能（DA）神经元在体内表现出自发的、类似心脏起搏器的、有规律的尖峰和不规则的爆发活动。从常规模式到突发模式的变化与运动以及黑质纹状体靶部位多巴胺释放的大小有关。虽然兴奋性突触输入在DA爆发活动中的作用已被假设，但从常规到突然放电的变化机制尚不清楚。本研究的主要目的是阐明胆碱能受体激活调节谷氨酸诱导的SNc-DA神经元突然放电的可能离子机制。我们的假设是，来自桥状核被盖核的胆碱能输入使SNc-DA神经元去极化并增加其放电速率，从而有助于响应来自丘脑下核（STN）、扣带回和内侧前额叶区的谷氨酸能输入，诱发突发放电。关于乙酰胆碱对DA神经元中离子电流的影响以及胆碱能调节DA神经元中离子电流可能促进突发放电的机制缺乏直接信息。在本研究中，细胞内电流钳和全细胞膜片钳记录将用于大鼠脑切片和急性游离SNc神经元。将评估突触后毒蕈碱和烟碱受体激活对神经元膜电位、孤立离子电流、放电行为以及与STN刺激的相互作用的影响。将讨论以下具体目标：探讨胆碱能受体激活对起搏器样去极化和后超极化（AHP）过程中Ca2+进入的影响；2. 探讨毒蕈碱受体激活诱导静息膜电位去极化的离子机制；3. 目的探讨胆碱能受体介导的膜电位和AHP的变化是否能调节谷氨酸诱导的突发性放电。因此，更好地了解乙酰胆碱在SNc- da神经元放电行为的调节中的作用，进而影响SNc靶结构中多巴胺的释放。拟议研究的结果可能具有与帕金森病等运动和行为障碍的症状表达和药理操作相关的临床后果。

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.