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MERIT奖续期为R 01。总体目标是理解为什么个体在可卡因诱导的激活方面存在差异，具体而言，i）多巴胺（DA）转运体（DAT）如何促成这种差异性反应，以及ii）这种个体差异性如何预测可卡因滥用倾向。成年远交雄性Sprague-Dawley大鼠可根据其在低剂量可卡因注射后的差异性旷场运动活性分为低或高可卡因应答者（分别为LCR或HCR）。可卡因激活中的这些初始差异部分地由可卡因如何有效地抑制背侧纹状体（dSTR）和背侧核（NAc）中的DAT来解释。这种分类还预测了与奖励和强化相关的重复可卡因诱导的行为，因为LCR比HCR更表现出运动敏感化、条件性位置偏好和自我施用可卡因的动机。预期差异性LCR/HCR DAT抑制将导致细胞外DA水平和DA受体（R）刺激的差异。目的1将使用i）体内微透析来确定dSTR和NAc核心中内源性细胞外DA与LCR和HCR中急性和重复可卡因诱导的运动激活之间的总体关系，以及ii）最先进的体内电化学记录技术来评估dSTR和NAc亚区中可卡因诱导的内源性细胞外DA水平的实时变化（核和壳）在自由行为的LCR和HCR中。目的2将探讨可卡因诱导的LCR和HCR之间的潜在差异：i）dSTR和NAc中的快速DAT调节（运输），以及ii）可能有助于解释行为差异的长期DAT和DA R调节。这些实验将测量旷场活性、细胞表面DAT水平、[3 H]DA摄取动力学和孤儿G蛋白偶联受体GPR 37的水平。体外放射性配体结合的定量放射自显影分析将用于评估DAT、D1 R、D2 R和激动剂刺激的G蛋白偶联的调节。目标3将确定LCR/HCR分类如何通过测量i）可卡因自我给药和可卡因预暴露获得期间的致敏性，ii）在强化的渐进比率计划下测量的对可卡因的动机效应的致敏性，和iii）在线索诱发的可卡因反应恢复和在二阶强化时间表下的反应的背景下的激励敏化。将使用同步体内电化学记录来解决自我给药实验中的特定问题。总之，这些结果将提供新的见解，为什么最初对可卡因运动激活的不敏感性与更“成瘾倾向”的表型相关，快速和长期DAT适应及其后果如何促成这种个体变异性，以及敏化如何影响可卡因自我给药。了解可卡因滥用/成瘾个体差异的生物学基础对于治疗这种疾病至关重要。个人对可卡因滥用和成瘾的脆弱性差异很大。该项目将使用动物模型来探索正常脑化学的个体差异如何有助于可卡因诱导的激活和成瘾行为的变化。了解可卡因滥用/成瘾个体差异的生物学基础对于开发治疗并最终预防这种毁灭性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.