Dopamine Neurotransmission in Experimental Parkinsonism

描述（由申请人提供）：帕金森病（PD）是一种毁灭性的神经病理学，在美国折磨着近100万人，在世界范围内则有数百万人。典型的三种症状，静止性震颤，强直和运动障碍，通常发生在生命的第五和第六个十年。有趣的是，尽管PD与大脑中黑质纹状体多巴胺（DA）神经元的退化明显相关，但直到纹状体DA几乎完全丧失（bbb80 %）时才出现症状。事实上，在症状变得明显之前，需要超过90%的病变。尽管广泛的神经退行性变，但正常运动功能的维持表明存在强有力的代偿机制。在PD研究的早期，Hornykiewicz和他的同事创造了“适应能力”来描述这种现象。后来的工作，依靠动物模型，证明细胞外DA在纹状体中维持在正常水平，直到病变超过大约80%。Zigmond和他的同事们已经发展了一个令人信服的补偿假说，这个假说已经存在了好几年：DA从完整区域扩散到衰竭区域，DA释放和合成的适应性增加保持了功能性多巴胺能张力。最近的研究结果对该模型中DA释放、摄取和合成的假设作用提出了挑战。然而，由于矛盾的结果尚未形成连贯的画面，因此非常需要确定在部分去神经支配后，DA信号是如何在纹状体中保存的。该项目的总体目标是研究PD临床前或无症状期黑质纹状体DA神经元的代偿适应。为此，细胞外DA的调控将在6-羟多巴胺损伤大鼠中进行表征，6-羟多巴胺损伤是该病理广泛使用的动物模型。具有毫秒时间和微米空间分辨率的实时微传感器将监测由瞬态电刺激引起的细胞外DA动态。有两个具体目标。第一个目的是利用P.I.开发的新技术，在清醒的动物中评估由生理频率引起的细胞外DA，以及支持这些水平的DA释放和摄取率。这些实验将扩展他之前在麻醉动物中的分析。第二个目的是确定体内DA释放与合成之间的关系。尽管DA合成的代偿性变化可能是最成熟的适应性，但其与失神经纹状体中DA释放的关系目前仍存在争议。综上所述，所提出的实验将对纹状体中尽管DA神经元大量丧失，但功能性多巴胺能张力是如何维持的产生新的见解。

DESCRIPTION (provided by applicant): Parkinson's disease (PD) is a devastating neuropathology that afflicts nearly one million people in the United States along and millions more worldwide. The classic triad of symptoms, resting tremor, rigidity and akinesia, typically occur in the fifth and sixth decade of life. Interestingly, although PD is clearly associated with degeneration of nigrostriatal dopamine (DA) neurons in the brain, symptoms do not present until the loss of striatal DA is nearly complete (>80 percent). In fact lesions of greater than 90 percent are required before the symptoms become marked. The maintenance of normal motor function despite extensive neurodegeneration suggests the existence of potent compensatory mechanisms. Early in this study of PD, Hornykiewicz and co-workers coined "adaptive capacity" to describe this phenomenon. Later work, relying on animal models, demonstrated that extracellular DA is maintained at normal levels in the striatum until the lesion exceeds approximately 80 percent. Zigmond and co-workers have developed what appeared to be for several years a convincing hypothesis for compensation: diffusion of DA from intact into depleted regions and an adaptive increase in DA release and synthesis preserve a functional dopaminergic tone. More recent results have challenged the postulated roles played by DA release, uptake and synthesis in this model. Because a coherent picture has yet to emerge from the conflicting results however, there is a great need to establish how DA signaling is preserved in the striatum following partial denervation. The overall goal of the proposed project is to investigate compensatory adaptation in nigrostriatal DA neurons during the preclinical or asymptomatic phase of PD. To this end, the regulation of extracellular DA will be characterized in the 6-hydroxydopamine-lesioned rat, a widely used animal model of this pathology. Real-time microsensors with millisecond temporal and micron spatial resolution will monitor extracellular DA dynamics elicited by transient electrical stimulation. There are two specific aims. The first aim is to evaluate extracellular DA evoked by a physiological frequency, and the DA release and uptake rates that support these levels, in the awake animal using new technology developed by the P.I. These experiments will extend his previous analysis in the anesthetized animal. The second aim is to determine the relationship between DA release and synthesis in vivo. Although a compensatory change in DA synthesis is perhaps the best established adaptation, its relationship to DA release in the denervated striatum is currently debated. Taken together, the proposed experiments will yield new insight into how a functional dopaminergic tone is maintained in the striatum despite the extensive loss of DA neurons.