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M受体(MAChR)拮抗剂苯海索，是第一个被接受的治疗帕金森病(PD)的药物，目前仍在临床上用于这种疾病，是可用于治疗肌张力障碍的最有效的药物之一。然而，这些化合物的临床应用受到严重的中枢和外周不良反应的限制，这些不良反应可能是由与这些疾病的治疗无关的mAChR亚型介导的。此外，抗胆碱药在治疗帕金森病和肌张力障碍中的作用部位还很不清楚。人们普遍认为帕金森病和肌张力障碍都是涉及基底节(BG)功能障碍的回路障碍，也被认为是高胆碱能障碍。有证据表明，M1和M4是最丰富的mAChR亚型，表达于纹状体的主投射神经元，纹状体是BG的主要输入结构。纹状体投射神经元(也称为中棘神经元，MSN)的过度活动被认为与帕金森病和肌张力障碍的运动障碍有关，纹状体胆碱能信号的增加也与帕金森病和某些形式的肌张力障碍有关。基于mAChR激活对MSN的净兴奋，选择性阻断介导纹状体MSN净兴奋的mAChR亚型，而对其他亚型缺乏活性的药物，可能对帕金森病和肌张力障碍有治疗作用，而不会出现不良反应。然而，由于缺乏高度选择性的mAChR配体，直到最近才有可能确定参与纹状体生理和病理生理功能的单个mAChR亚型。现在我们已经开发了一系列新的化合物，它们对M1或M4亚型表现出前所未有的选择性，而在任何其他mAChR亚型都没有检测到活性。在这个方案中，我们将利用这些新型的、高选择性的mAChR配体和缺失编码特定mAChR亚型基因的转基因小鼠，来明确地确定M1和M4在调节纹状体MSN的生理功能中的作用。具体地说，我们将严格检验以下假设：1)M1和M4马赫参与调节MSN神经元的兴奋性；2)M1 mAChR激活增强MSN中的NMDA受体电流；3)M1和M4 mAChR在MSN皮质纹状体突触的传递和长期可塑性调节中发挥重要作用。最后，我们将确定选择性M1拮抗剂和M4增强剂对帕金森病和肌张力障碍啮齿动物模型运动功能障碍的缓解能力。这些研究结果将为M1和M4mAChR亚型在纹状体生理和病理生理功能中的不同作用提供重要的新信息，并为开发改进的抗胆碱能疗法治疗帕金森病、肌张力障碍和其他可能没有严重不良反应的运动障碍提供基础。

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.