Individual Differences in Cocaine Activation/Reward and the Dopamine Transporter

描述(由申请人提供)：本申请要求将NIDA赞助的优秀奖续期为R01。总体目标是了解为什么个体在可卡因诱导的激活方面存在差异，具体地说，i)多巴胺(DA)转运体(DAT)如何有助于这种不同的反应，以及ii)这种个体变异性如何预测可卡因滥用的易感性。成年近交系雄性Spraogue-Dawley大鼠在注射低剂量可卡因后，根据其在开阔场地的不同运动活动，可分为低可卡因反应者或高可卡因反应者(分别为LCRs或Hcr)。可卡因激活的这些最初的差异部分是由于可卡因如何有效地抑制背侧纹状体(DSTR)和伏隔核(NAC)的DAT。这一分类还预测了与奖励和强化相关的重复可卡因诱导行为，因为LCR比HCR更表现出运动敏感化、条件性位置偏好和自我管理可卡因的动机。不同的LCR/HCR DAT抑制有望导致细胞外DA水平和DA受体(R)刺激的不同。目的1)在体微透析技术用于确定DSTR和NAC核心区内源性细胞外DA与可卡因诱导的LCRs和HCRS急性和重复运动激活之间的总体关系，以及ii)新的体内最先进的电化学记录技术，以实时评估自由行为LCRs和HCRS中可卡因诱导的DSTR和NAC亚区(核心区和壳区)内源性细胞外DA水平的变化。目的2探讨LCRs和Hcr在可卡因诱导的1)DSTR和NAC的快速DAT调节(贩运)以及2)有助于解释行为差异的长期DAT和DA R调节方面的潜在差异。这些实验将测量旷场活动、细胞表面DAT水平、[~3H]DA摄取动力学以及孤儿G蛋白偶联受体GPR37的水平。体外放射配基结合的定量放射自显影分析将用于评估DAT、D1Rs、D2Rs和激动剂刺激的G蛋白偶联的调节。目的3将确定LCR/HCR分类如何预测可卡因的成瘾相关效应，通过测量i)在获得可卡因自我给药和可卡因预暴露期间的敏感度，ii)在递进强化比率表下测量的可卡因对激励效应的敏感度，以及iii)在提示诱导恢复对可卡因的反应和在二级强化表下反应的激励性感觉化。同时在体电化学记录将被用来解决自我给药实验中的特定问题。总之，这些结果将为以下问题提供新的见解：为什么最初对可卡因运动激活的不敏感与更容易上瘾的表型有关，快速和长期的DAT适应及其后果如何导致这种个体差异，以及敏化如何影响可卡因的自我给药。了解可卡因滥用/成瘾的个体差异的生物学基础对于治疗这一疾病至关重要。每个人对可卡因滥用和上瘾的易感性差异很大。这个项目将使用一个动物模型来探索正常大脑化学成分的个体差异如何导致可卡因诱导的激活和成瘾样行为的变异性。了解可卡因滥用/成瘾的个体差异的生物学基础，对于开发治疗并最终预防这一毁灭性的脑部疾病和公共卫生问题的新方法至关重要。

DESCRIPTION (provided by applicant): This application requests renewal of a NIDA-sponsored MERIT Award as a R01. The overall goal is to under- stand why individuals differ in cocaine-induced activation and, specifically, i) how the dopamine (DA) trans- porter (DAT) contributes to this differential responsiveness and ii) how this individual variability is predictive of cocaine abuse liability. Adult outbred male Sprague-Dawley rats can be classified as either low or high cocaine responders (LCRs or HCRs, respectively) based on their differential open-field locomotor activity following a low dose cocaine injection. These initial differences in cocaine activation are explained, in part, by how effectively cocaine inhibits the DAT in dorsal striatum (dSTR) and nucleus accumbens (NAc). This classification also predicts repeated cocaine-induced behaviors associated with reward and reinforcement, in that LCRs, more than HCRs, exhibit locomotor sensitization, conditioned place preference and motivation to self- administer cocaine. Differential LCR/HCR DAT inhibition would be expected to result in differences in extra- cellular DA levels and DA receptor (R) stimulation. Aim 1 will use i) in vivo microdialysis to define the overall relationship between endogenous extracellular DA in dSTR and NAc core and acute and repeated cocaine- induced locomotor activation in LCRs and HCRs and ii) new state-of-the-art in vivo electrochemical recording technology to assess real-time changes in cocaine-induced endogenous extracellular DA levels in dSTR and subregions of NAc (core and shell) in freely-behaving LCRs and HCRs. Aim 2 will explore potential differences between LCRs and HCRs in cocaine-induced i) rapid DAT regulation (trafficking) in dSTR and NAc and ii) longer-term DAT and DA R regulation that could help to explain the behavioral differences. These experiments will measure open-field activity, cell surface DAT levels, [3H]DA uptake kinetics, and levels of the orphan G- protein-coupled receptor GPR37. Quantitative autoradiographic analysis of in vitro radioligand binding will be used to assess regulation of DATs, D1Rs, D2Rs and agonist-stimulated G-protein coupling. Aim 3 will deter- mine how LCR/HCR classification predicts addiction-related effects of cocaine by measuring i) sensitization during acquisition of cocaine self-administration and cocaine pre-exposure, ii) sensitization to motivational effects of cocaine measured under a progressive ratio schedule of reinforcement, and iii) incentive sensiti- zation in the context of cue-elicited reinstatement of responding for cocaine and responding under a second- order schedule of reinforcement. Concurrent in vivo electrochemical recording will be used to address particular questions in the self-administration experiments. Together, the results will provide novel insights as to why initial insensitivity to cocaine locomotor activation is associated with the more "addiction prone" pheno- type, how both rapid and longer-term DAT adaptations and their consequences contribute to this individual variability, and how sensitization impacts cocaine self-administration. Understanding the biological bases for individual differences in cocaine abuse/addiction is of fundamental importance for treating this disease. Individuals vary markedly in their vulnerability to cocaine abuse and addiction. This project will use an animal model to explore how individual differences in normal brain chemistry can contribute to variability in cocaine-induced activation and addiction-like behaviors. Understanding the biological bases for individual differences in cocaine abuse/addiction is of fundamental importance for developing new ways to treat, and ultimately prevent, this devastating brain disease and public health problem.