DOPAMINE D1, D2, AND D3 RECEPTORS AS BIOMARKERS FOR IMAGING NIGROSTRIATAL NEURONS

描述（由申请人提供）：帕金森病（PD）是第二常见的神经退行性疾病，影响北美超过100万人，并且没有治疗被证明可以减缓进展。神经影像学生物标志物有可能提供PD进展的无偏倚测量。与黑质纹状体神经元损失相关的多巴胺受体的变化可能导致多巴胺D2和D3受体的“失调”，并改变D2：D3比率。D2：D3比值的变化可能在以D2样受体功能改变为特征的CNS综合征的行为后果中起关键作用。然而，D3在病理生理学和治疗中的确切作用仍有待确定。我们以前开发了一种新的程序来测量D2和D3受体的密度在体外，并发现D3受体在纹状体和黑质的变化与PD大脑中的D1和D2受体不同。我们以前评估了三种不同的突触前PET示踪剂，[11 C]DTBZ，[11 C]CFT和[18 F]fluoroDOPA在黑质纹状体神经元给予广泛剂量的选择性多巴胺能神经毒素MPTP的猴子。这些PET研究表明，纹状体摄取的每一个线性相关的黑质纹状体神经元的数量（使用无偏体视计数酪氨酸羟化酶[TH]免疫染色的神经元在黑质），但只有当黑质纹状体神经元的损失不超过50%。相反，这些示踪剂中的每一个与纹状体多巴胺的体外测量线性相关。体内PET测量相互之间以及与纹状体中VMAT 2和DAT的定量放射自显影相关性良好。有趣的是，运动评级与黑质细胞计数完全相关，而不是与纹状体多巴胺或其他终端领域的措施，这表明除了纹状体终端领域的损失以外的因素影响运动帕金森症。我们推测突触后多巴胺受体的变化可能是造成这种差异的原因。在这个项目中，我们建议进行定量放射自显影测量突触后多巴胺受体图1显示了来自41只猴子的脑组织的纹状体中的MPTP（D1、D2和D3）的分布，其中16只猴子用宽范围的单一颈内动脉MPTP剂量处理（0至0.31 mg/kg）;其中10只将在MPTP后的不同时间进行研究（10天5例，3周5例）; 3组，每组5人，将接受单剂量MPTP，然后用慢性左旋多巴、多巴胺受体激动剂普拉克索或安慰剂治疗2个月。这些额外的措施，预计将提供一个更完整的反映状态的黑质纹状体神经元比突触前的措施。这个为期2年的项目的总体目标是确定多巴胺去神经后突触后标记物的变化，以确定最有效的神经影像学措施，准确测量黑质纹状体损伤的严重程度。我们还将研究左旋多巴或普拉克索（多巴胺D3受体激动剂）对这些标志物的长期治疗效果。本研究计划中的研究对于扩展我们对多巴胺受体亚型在PD进展中的功能作用的理解具有巨大的潜力。

DESCRIPTION (provided by applicant): Parkinson Disease (PD), the second most common neurodegenerative disease, affects more than one million people in North America, and no treatment has been proven to slow progression. Neuroimaging biomarkers have the potential to provide unbiased measurements of PD progression. Changes in dopamine receptors related to loss of nigrostriatal neurons may lead to "dysregulation" of dopamine D2 and D3 receptors with a change in the D2:D3 ratio. A change in the D2:D3 ratio may play a key role in the behavioral consequences of CNS syndromes characterized by altered D2-like receptor function. However, the precise role of D3 in the pathophysiology and treatment remains to be determined. We previously developed a novel procedure to measure the density of D2 and D3 receptors in vitro and found that D3 receptors in striatum and substantia nigra change differently from D1 and D2 receptors in PD brains. We previously evaluated three different presynaptic PET tracers, [11C]DTBZ, [11C]CFT and [18F]fluoroDOPA for nigrostriatal neurons in monkeys given a wide range of doses of the selective dopaminergic neurotoxin MPTP. These PET studies demonstrated that striatal uptake of each of these linearly correlates with the number of nigrostriatal neurons (using unbiased stereologic counts of tyrosine hydroxylase [TH] immunostained neurons in nigra) but only when the loss of nigrostriatal neurons does not exceed 50%. In contrast, each of these tracers linearly correlates with in vitro measures of striatal dopamine. The in vivo PET measures correlated well with each other and with quantitative autoradiography of VMAT2 and DAT in striatum. Interestingly, motor ratings correlated fully with nigral cell counts and not with striatal dopamine or other terminal field measures, suggesting that factors other than just loss of striatal terminal fields influence motor parkinsonism. We hypothesize that changes in postsynaptic dopamine receptors may account for this discrepancy. In this project, we propose to conduct quantitative autoradiography measures of the postsynaptic dopamine receptors (D1, D2 and D3) in the striatum from brain tissues from 41 monkeys, 16 of them are treated with a wide range of single internal carotid MPTP doses (0 to 0.31 mg/kg); 10 of them will be studied at different times after a MPTP (5 at 10 days and 5 at 3 weeks); 3 groups of 5 will have a single dose of MPTP then treated for 2 months with chronic levodopa, a dopamine receptor agonist pramipexole or placebo. These additional measures are expected to provide a more complete reflection of the state of nigrostriatal neurons than presynaptic measures alone. The overall goal of this 2-year project is to determine how postsynaptic markers change after dopamine denervation to determine the most effective neuroimaging measures for accurate measurement of the severity of nigrostriatal injury. We also will investigate the effects chronic treatment with levodopa or pramipexole (a dopamine D3 receptor agonist) on these markers. The studies proposed in this grant have great potential for extending our understanding of the functional roles of dopamine receptor subtypes in PD progression.