Functionally selective D2Rs, striatal circuit function and motivation

脑成像研究发现，在几种精神疾病中，纹状体多巴胺D2 R结合发生了变化 与动机改变有关，包括精神分裂症、多动症和药物成瘾。尽管有这些 然而，D2 R水平的变化如何改变纹状体回路功能和动机仍不清楚。 在RO 1项目的前4.5年中，我们发现腹侧纹状体中D2 R过表达 （NAcc）增强动机。我们进一步确定了一种新的机制 D2 Rs通过什么来调节动机：就像多巴胺神经元中的突触前D2 Rs抑制多巴胺 释放后，我们发现D2 Rs抑制了从间接通路神经元到直接通路神经元的侧支传递。直接 这条通路是纹状体的两条功能上相反的输出通路之一。它能促进丘脑皮层 活动，从而中继“去”的信号，而间接途径抑制丘脑皮层活动，因此， 发出“禁止通行”的信号我们假设侧支抑制的减少会增强直接通路 活动，从而促进动机行为。调节突触传递的相同机制， 纹状体内的侧支也会影响腹侧的主要间接输出终末的传递。 苍白球（VP）。因此，我们假设NAcc中的D2 R通过两种机制增强动机， 抑制直接途径活性和抑制间接途径输出。 为了开发新的治疗动机障碍的策略，关键是要了解如何 腹侧-纹状体D2 R在分子水平上调节动机。D2 R信号通过两个下游 一种是G蛋白依赖性的，另一种是G蛋白不依赖性的，涉及抑制蛋白。这里我们 将比较功能选择性D2 R在增强动机和抑制 间接途径传播。由于G蛋白信号传导是D2 R介导的多巴胺抑制所必需的， 我们假设G蛋白而不是arrestin信号是抑制间接途径所必需的， 传播导致动机增强。 间接途径传递减少是否会抑制直接途径和下游VP活性， 这对于理解D2 R如何调节动机是未知的，但却是必不可少的。因此，我们将测量神经元 活动选择性地在VP以及在直接或间接的途径在动机行为。我们将 使用Cre/loxP系统与Cre依赖性病毒组合，选择性过表达野生型或 在NAcc的间接途径中突变的功能选择性D2 Rs，并采用膜片钳切片 生理学、体内钙成像和行为分析，以解决以下目标： 目的1：探讨NAcc D2 Rs在VP抑制和激活中的作用 目的2：确定NAcc D2 Rs调节动机的信号通路

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