Dopamine neurotransmission in a model of DOPA-responsive dystonia

 描述（由申请人提供）：肌张力障碍的特征是不自主的肌肉收缩，导致虚弱的扭转运动和姿势。异常多巴胺（DA）神经传递在许多不同形式的肌张力障碍中被一致地观察到，但是引起肌张力障碍的DA缺陷知之甚少。左旋多巴反应性肌张力障碍（DRD）被认为是了解异常DA神经传递如何引起肌张力障碍的原型障碍。DRD的特征是儿童期发作的肌张力障碍，具有昼夜波动，由此症状在一天中恶化。DRD的显著特征是用L-DOPA或DA激动剂恢复DA信号传导后症状的显著改善。事实上，DRD是由DA合成关键基因突变引起的，包括酪氨酸羟化酶（TH）。引起DRD的TH突变与一些残留TH活性相关，而消除TH活性的突变引起儿童帕金森病，表明TH活性和[DA]是肌张力障碍发展的关键决定因素。然而，引起肌张力障碍的DA信号传导功能障碍的性质尚不清楚。为了解决我们知识中的这一空白，我们产生了在TH中携带引起人DRD的Q381 K突变的敲入小鼠（DRD小鼠）。与人类疾病一样，DRD小鼠表现出TH活性降低、[DA]减少、在整个活动期过程中恶化的肌张力障碍运动以及响应于L-DOPA的肌张力障碍改善。因此，DRD小鼠表现出人类DRD的核心神经化学和症状特征，从而为我们提供了从基因到行为剖析DRD潜在机制的前所未有的机会。我们的初步数据表明，肌张力障碍是由<1%的正常[DA]介导的。成年人突触前DA的类似减少会导致帕金森综合征。因此，不同的突触后反应可能解释了帕金森病（PD）和肌张力障碍之间DA传递减少的神经学后果的差异。事实上，我们的初步数据表明D1 R超敏感性，超兴奋性的中型棘神经元（MSN），MSN树突数量减少和异常皮质纹状体神经支配。因此，我们将测试的假设，即早期生活DA缺乏症结合（错误）适应性突触后反应引起肌张力障碍，通过使用多学科的方法来检查前和突触后的后果减少DA传输与肌张力障碍。具体目标是：1。探讨单胺代谢与肌张力障碍严重程度的关系。2.确定导致肌张力障碍的DA受体亚型和信号传导缺陷。3.描述表达D1和D2 R的MSN的内在和突触特性的改变。4.研究DRD小鼠早期DA剥夺对表达D1 R和D2 R的MSN的皮质纹状体突触树突形态和超微结构的影响。

 DESCRIPTION (provided by applicant): Dystonia is characterized by involuntary muscle contractions that cause debilitating twisting movements and postures. Abnormal dopamine (DA) neurotransmission is consistently observed across many different forms of dystonia, but the DA defects that give rise to dystonia are poorly understood. L-DOPA-responsive dystonia (DRD) is considered a prototype disorder for understanding how abnormal DA neurotransmission evokes dystonia. DRD is characterized by childhood onset dystonia with diurnal fluctuation whereby symptoms worsen throughout the course of the day. The distinguishing feature of DRD is the dramatic improvement in symptoms after restoration of DA signaling with L-DOPA or DA agonists. Indeed, DRD is caused by mutations in genes critical for DA synthesis, including tyrosine hydroxylase (TH). DRD-causing TH mutations are associated with some residual TH activity whereas mutations that abolish TH activity cause childhood parkinsonism suggesting that TH activity and [DA] are critical determinants in the development of dystonia. However, the nature of the DA signaling dysfunction that gives rise to dystonia is unknown. To address this gap in our knowledge, we generated a knockin mouse bearing the human DRD-causing Q381K mutation in TH (DRD mice). Like the human disorder, DRD mice display reduced TH activity, a reduction in [DA], dystonic movements that worsen throughout the course of the active period and improvement in the dystonia in response to L-DOPA. Thus, DRD mice exhibit the core neurochemical and symptomatic features of human DRD, thereby providing us with the unprecedented opportunity to dissect the mechanisms underlying DRD from gene to behavior. Our preliminary data demonstrate that the dystonia is mediated by [DA] that is <1% of normal. A similar reduction in presynaptic DA in adults would cause parkinsonism. Therefore, divergent postsynaptic responses likely account for the differences in the neurological consequences of reduced DA transmission between Parkinson's disease (PD) and dystonia. Indeed, our preliminary data demonstrate D1R supersensitivity, hyperexcitability of medium spiny neurons (MSNs), a reduction in MSN dendrite number and abnormal corticostriatal innervation. Therefore, we will test the hypothesis that early life DA deficiency in combination with (mal)adaptive postsynaptic responses gives rise to dystonia by using a multidisciplinary approach to examine the pre- and postsynaptic consequences of reduced DA transmission associated with dystonia. The Specific Aims are: 1. To elucidate the relationship between monoamine metabolism and the severity of dystonia. 2. To determine the DA receptor subtype(s) and signaling defects that contribute to the dystonia. 3. To delineate alterations in th intrinsic and synaptic properties of D1 and D2R-expressing MSNs. 4. To examine the dendritic morphology and ultrastructural changes in corticostriatal synapses onto D1R and D2R-expressing MSNs in response to early-life DA deprivation in DRD mice.