M1 and M4 mAChRs in striatum-implication in treatment of movement disorders

描述（由申请人提供）：抗胆碱能药物，如毒蕈碱乙酰胆碱受体（mAChR）拮抗剂苯海索，是帕金森病（PD）的第一种公认治疗方法，目前仍在临床上用于治疗这种疾病，是治疗肌张力障碍的最有效药物之一。然而，这些化合物的临床效用受到严重的中枢和外周不良反应的限制，这些不良反应可能由与这些疾病的治疗无关的mAChR亚型介导。此外，抗胆碱能药物治疗PD和肌张力障碍的作用部位在很大程度上尚不清楚。一般认为PD和肌张力障碍都是涉及基底神经节（BG）功能障碍的回路疾病，也被认为是高胆碱能疾病。有证据表明，M1和M4是最丰富的mAChR亚型表达的主要投射神经元在纹状体，在BG的主要输入结构。纹状体投射神经元（也称为中型多棘神经元，MSN）的过度活跃被假定与PD和肌张力障碍中的运动缺陷相关，并且纹状体中增加的胆碱能信号传导也与PD和某些形式的肌张力障碍有关。基于通过mAChR活化的MSN的净兴奋，选择性阻断介导纹状体MSN的净兴奋的mAChR亚型，但对其他亚型没有活性的药物可能预期对PD和肌张力障碍具有治疗作用，而没有不期望的副作用。然而，由于缺乏高选择性的mAChR配体，明确的确定个别mAChR亚型参与纹状体的生理和病理生理功能，直到最近才成为可能。现在，我们已经开发了一系列新的化合物，对M1或M4亚型显示出前所未有的选择性，对任何其他mAChR亚型都没有检测到活性。在本研究中，我们将利用这些新型的、高选择性的mAChR配体和缺失特定mAChR亚型基因的转基因小鼠，明确确定M1和M4在调节纹状体MSNs生理功能中的作用。具体来说，我们将严格测试的假设，1）M1和M4 mACh参与调制的神经元兴奋性的MSN; 2）M1 mAChR激活增强NMDA受体电流的MSN; 3）M1和M4 mAChR在调制的传输和长期可塑性在皮质纹状体突触的MSN中发挥重要作用。最后，我们将确定选择性M1拮抗剂和M4增效剂减轻PD和肌张力障碍啮齿动物模型的运动缺陷的能力。这些研究的结果将提供关于M1和M4 mAChR亚型在纹状体的生理和病理生理功能中的不同作用的关键新信息，并为开发针对PD、肌张力障碍和其他运动障碍的改进的抗胆碱能疗法提供基础，这些疗法可能没有严重的不良反应。

DESCRIPTION (provided by applicant): Anticholinergic drugs, such as the muscarinic acetylcholine receptor (mAChR) antagonist trihexyphenidyl, were the first accepted treatment for Parkinson's disease (PD) and are still in clinic use for this disorder and are among the most effective drugs available for treatment of dystonia. However, clinical utility of these compounds is limited by the severe central and peripheral adverse effects that are likely mediated by mAChR subtypes that are not related to the treatment of these disorders. In addition, the site of action of anticholinergics in the treatment of PD and dystonia is largely unknown. It is commonly believed that both PD and dystonia are circuit disorders involving the basal ganglia (BG) dysfunction and also considered as hypercholinergic disorders. Evidence suggests that M1 and M4 are the most abundant mAChR subtypes expressed in principal projection neurons in the striatum, a major input structure in the BG. Hyperactivity of striatal projection neurons (also termed medium spiny neurons, MSNs) is postulated to be associated with motor deficits in PD and dystonia and increased cholinergic signaling in the striatum has also been implicated in PD and certain forms of dystonia. Based on net excitation of MSNs by mAChR activation, drugs that selectively block mAChR subtypes that mediate the net excitation of striatal MSNs, but devoid of activity for other subtypes, might be expected to have therapeutic effects on PD and dystonia without undesired adverse effects. However, due to lack of highly selective mAChR ligands, definitive determination of the individual mAChR subtypes involved in physiological and pathophysiological functions in the striatum has not been possible until recently. Now we have developed a series of novel compounds that display unprecedented selectivity for either M1 or M4 subtype with no detectable activity at any other mAChR subtypes. In this proposal, we will take advantage of these novel, highly selective mAChR ligands and transgenic mice in which gene coding a specific mAChR subtype is deleted, to definitively determine the roles of M1 and M4 in regulating physiological functions of striatal MSNs. Specifically, we will rigorously test the hypothesis that 1) M1 and M4 mACh are involved in modulation of neuronal excitability in MSNs; 2) M1 mAChR activation potentiates NMDA receptor currents in MSNs; 3) M1 and M4 mAChR play important roles in modulation of transmission and long-term plasticity at corticostriatal synapses in MSNs. Finally we will determine the ability of selective M1 antagonist and M4 potentiator to alleviate motor deficits of rodent models of PD and dystonia. The results of these studies will provide critical new information regarding the different roles of M1 and M4 mAChR subtypes in physiological and pathophysiological functions in the striatum and provide the basis for the development of improved anticholinergic therapies for PD, dystonia and other movement disorders that could be devoid of the severe adverse effects.