Synaptic Mechanisms of Dopaminergically Mediated MRI Signal Changes

这个项目的基本目标是了解驱动对多巴胺能刺激的血流动力学反应的分子和突触过程。这一知识对于正确解释在可卡因或安非他明等药物挑战后观察到的人类变化至关重要。首先，我们将研究多巴胺转运体(DAT)阻滞剂(如可卡因或安非他明)对大鼠脑内血流动力学反应的区域分布的影响，方法是使用药物磁共振(PhMRI)测量血氧水平依赖(BOLD)对比度或相对脑血容量(RCBV)。然后，我们将测试选择性多巴胺D1和D2拮抗剂阻断phMRI信号变化的能力。在这些实验之后，将研究多巴胺受体和腺苷受体之间的相互作用对血流动力学的影响，方法是选择性地拮抗腺苷系统，并使用DAT阻滞剂提供刺激。同时，我们将通过对纹状体和额叶皮质的多巴胺浓度进行微透析测量来检验血流动力学变化与多巴胺浓度成正比的假设。然后，我们将通过单侧黑质注射6-羟基多巴胺和使用喹啉酸注射选择性单侧损毁突触后纹状体神经元来预形成选择性突触前多巴胺纤维损伤。然后，我们将使用DAT阻滞剂在刺激后对这些动物进行rCBV测量，以测试phMRI信号的来源是突触前还是突触后。我们还将进行相关的正电子发射断层扫描(PET)测量DAT、D1R和D2R，以确定它们与phMRI的相关性。然后，我们将使用上面的损伤模型来研究受体超敏的作用，以确定阿朴吗啡或苯丙胺刺激后两个纹状体之间的数量差异，这两种化合物已知在这些基于多巴胺受体超敏的损伤模型中引起相反的行为效应。这些结果将与相同动物的多巴胺受体结合特性的定量PET测量相关联。最后，在这些研究之后，将对长期自我服用可卡因的大鼠进行PET定量测量，以确定长期服用可卡因后多巴胺受体结合特性的变化。这些研究应该导致对行为-代谢耦合的突触和分子基础的基本理解，这对于发展理解人类药物滥用的生物学基础至关重要。

The underlying goal of this project is to understand the molecular and synaptic processes that drive the hemodynamic response to a dopaminergic stimulus. This knowledge is crucial to proper interpretation of the changes observed in humans after pharmacologic challenges such as cocaine or amphetamine. First, we will study the effects of blockers of the dopamine transporter (DAT) (such as cocaine or amphetamine) on the regional distribution of hemodynamic responses in rat brains using pharmacological MRI (phMRI) measurements of blood oxygenation level dependent (BOLD) contrast or relative cerebral blood volume (rCBV). Then we will test the ability of selective dopamine D1 and D2 antagonists to block the phMRI signal changes. These experiments will be followed by study of the hemodynamic consequences of the interactions between dopamine receptors and adenosine receptors by selective antagonism of the adenosine system in combination with stimulus delivered using DAT blockers. Concurrently, we will test the hypothesis that hemodynamic changes are proportional to dopamine concentrations by making microdialysis measurements of dopamine concentrations in striatum and frontal cortex. Then we will preform selective pre-synaptic dopamine fiber lesions using unilateral injections of 6-hydroxydopamine in the substantia nigra, and selective unilateral lesioning of the post-synaptic striatal neurons using quinolinic acid injections. Then we will perform rCBV measurements in these animals After stimulus using DAT blockers to test whether the origins of the phMRI signals are pre-or post-synaptic. We will also perform correlative positron emission tomography (PET) measurements of DAT, and D1 and D2 receptors to determine their correlations with the phMRI. Then, we will examine the role of receptor supersensitivity using the lesion models above to determine the quantitative differences between the two striata after stimulation with apomorphine or amphetamine, two compounds known to elicit opposite behavioral effects in these lesion models based upon dopamine receptor supersensitivity. These results will be correlated with quantitative PET measurements in the same animals of dopamine receptor binding properties. Lastly, these studies will be followed by quantitative PET measurements in rats who chronically self administer cocaine to determine what changes in dopamine receptor binding properties accompany chronic cocaine administration. These studies should lead to a fundamental understanding of the synaptic and molecular underpinnings of behavioral-metabolic coupling which is crucial to developing a biological basis for understanding of human drug abuse.