Functionally selective D2Rs, striatal circuit function and motivation

脑成像研究发现几种精神障碍患者纹状体多巴胺D2R结合的改变 与动机改变有关，包括精神分裂症、多动症和吸毒成瘾。尽管如此， 观察仍不清楚D2R水平的变化如何改变纹状体回路功能和动机。 在这个RO1项目的前4.5年中，我们发现D2R在腹侧纹状体中过度表达 小鼠的伏隔核(NAcc)增强了动力。我们进一步确定了一种新的机制 D2Rs调节动机：与多巴胺神经元中突触前D2Rs一样，D2Rs抑制多巴胺 释放后，我们发现D2Rs抑制了从间接通路到直接通路神经元的侧枝传递。直接式 通路是纹状体两条功能相反的输出通路之一。它促进丘脑皮质 而间接途径则抑制丘脑皮质的活动，因此 转播“不能走”的信号。我们假设减少侧枝抑制会增强直接通路 活动，从而促进有动机的行为。调节突触传递的相同机制在 纹状体内侧支也应该影响腹侧的主要间接输出终端的传递 苍白球(VP)。因此，我们假设NAcc中的D2Rs通过两种机制增强动机： 直接途径活性抑制和间接途径输出抑制。 要开发新的治疗动机障碍的策略，关键是要了解 腹侧纹状体D2Rs在分子水平上调节动机。通过两个下游的D2Rs信号 途径一条依赖于G蛋白，另一条不依赖于G蛋白，涉及arrestin。在这里，我们 将比较功能选择性D2R在增强动力和抑制能力方面的效率 间接途径传播。由于D2R介导的多巴胺抑制需要G蛋白信号转导 我们假设G蛋白而不是arrestin信号是抑制间接途径所必需的 传播带来更强的动力。 间接通路传递减少是否抑制直接通路和下游VP活性 未知，但对于理解D2Rs如何调节动机是必不可少的。因此，我们将测量神经元 在有动机的行为中，有选择地在VP以及直接或间接通路中活动。我们会 使用Cre/loxP系统结合依赖Cre的病毒选择性过表达野生型或 NAcc间接通路功能选择性D2Rs突变及膜片钳技术的应用 生理学、活体钙成像和行为分析，以解决以下目标： 目的1：确定NAcc D2Rs在VP抑制和动机中的作用 目的2：确定NAcc D2Rs调节动机的信号通路(S

Brain imaging studies have found alterations in striatal dopamine D2R binding in several mental disorders associated with altered motivation including schizophrenia, ADHD and drug addiction. In spite of these observations it is still unclear how changes in D2R levels alter striatal circuit function and motivation. In the first 4.5 years of this RO1 project we have found that D2R overexpression in the ventral striatum (Nucleus accumbens core; NAcc) of the mouse enhances motivation. We further identified a new mechanism by which D2Rs could regulate motivation: Like presynaptic D2Rs in dopamine neurons inhibit dopamine release, we found that D2Rs inhibit collateral transmission from indirect to direct pathway neurons. The direct pathway is one of the two functionally opposing output pathways of the striatum. It promotes thalamo-cortical activity, thereby relaying a “go” signal, whereas the indirect pathway inhibits thalamo-cortical activity, thus relaying a “no go” signal. We hypothesize that decreased collateral inhibition will enhance direct pathway activity thereby promoting motivated behavior. The same mechanism that regulates synaptic transmission at intrastriatal collaterals should also affect transmission at the main indirect output terminals in the ventral pallidum (VP). We therefore hypothesize that D2Rs in the NAcc enhance motivation via two mechanisms, dis- inhibition of direct pathway activity and inhibition of indirect pathway output. To develop new therapeutic strategies for disorders of motivation it will be crucial to understand how ventral-striatal D2Rs regulate motivation at the molecular level. D2Rs signal via two downstream pathways one that is G-protein dependent and one is G-protein independent and involves arrestin. Here, we will compare the efficiencies of functionally selective D2Rs in their ability to enhance motivation and to inhibit indirect pathway transmission. Since G-protein signaling is required for D2R-mediated inhibition of dopamine release we hypothesize that G-protein but not arrestin signaling is necessary for inhibiting indirect pathway transmission leading to enhanced motivation. Whether decreased indirect pathway transmission disinhibits direct pathway and downstream VP activity is unknown but essential for understanding how D2Rs regulate motivation. We will therefore measure neuronal activity selectively in the VP as well as in the direct or the indirect pathway during motivated behavior. We will use the Cre/loxP system in combination with Cre-dependent viruses to selectively overexpress wild-type or mutated functionally selective D2Rs in the indirect-pathway of the NAcc and employ patch clamp slice physiology, in vivo calcium imaging and a behavioral analysis to address the following aims: Aim 1: To determine the function of NAcc D2Rs in VP inhibition and motivation Aim 2: To identify the signaling pathway(s) by which NAcc D2Rs regulate motivation