Measuring Striatal Neurotransmission in Behaving Rats after Experimental TBI

描述（由申请人提供）：纹状体与皮层和皮层下结构相连接，影响认知功能。先前的研究表明，在实验性创伤性脑损伤（TBI）的控制性皮质冲击（CCI）模型中，空间记忆和新环境中的探索行为受到损害。在TBI的临床和实验模型中，多巴胺（DA）激动剂的治疗效果表明，DA系统在介导这些损伤后的缺陷中发挥了作用。基于这些观察结果，我们使用快速扫描循环伏安法（FSCV）进行体内电化学监测，以评估CCI后电诱发的细胞外DA水平的变化。CCI后，体内诱发的DA溢出受损。此外，CCI后DA清除率的降低与DAT表达的减少相对应。此外，神经兴奋剂哌醋甲酯对DAT功能的影响可通过CCI调节。在CCI后清醒的大鼠中，基础DA水平的调节似乎也受到损害。当检查纹状体周围直接放置微透析探针的组织损伤时，这种类型的创伤也会抑制诱发的DA释放并影响损伤部位周围基础DA水平的自动调节。虽然CCI和微透析探针直接纹状体损伤（DSI）对刺激DA释放和基础DA水平的影响是显著的，但扩展这些关于TBI对DA神经传递的研究是至关重要的。目前，我们可以监测清醒动物在FSCV药理学操作后[DA]的张力变化。然而，Mark Wightman最近改进了他的伏安记录技术的性能，这样他现在可以检测自发的DA瞬变，可能与中脑DA神经元的突发放电有关。Wightman的方法在一定程度上得到了改进，通过实施主成分回归（PCR）来解决伏安痕量中观察到的其他干扰的DA信号。我们推测，采用这种技术将是一种可行的方法，可以客观地评估和改进几分钟内测量的DA的强音变化，因此，将为测量DA传递的相位和强音方面提供一个额外的工具。我们的中心假设是，创伤后脑损伤后，自发纹状体记忆障碍瞬时和影响基础记忆障碍的调节机制受损。因此，我们有以下的长期科学目标：1)表征创伤对自然发生的影响，而不是电诱发的细胞外DA；2)表征脑外伤后基底DA的调控机制状态3)表征DAT抑制剂对损伤后纹状体细胞外DA的影响；4)认知任务中的行为表现与CCI后自发性DA瞬间的时间联系。为了支持这些科学目标，本R21的技术目标是将这种新的伏安系统，包括PCR的化学计量学，纳入我们自己在两种TBI模型中的阶段性和强直性DA传输的研究中。这些科学目标来源于适应体内伏安法监测清醒的CCI大鼠，将为评估一些康复相关、多巴胺能和其他治疗干预措施以及它们在损伤后恢复DA神经传递和认知的机制奠定基础。总体目标是深入了解这些干预措施对TBI临床人群认知和恢复的潜在作用机制和疗效。

DESCRIPTION (provided by applicant): The striatum interfaces with cortical and subcortical structures to affect cognitive function. Previous work suggests that in the controlled cortical impact (CCI) model of experimental traumatic brain injury (TBI), spatial memory and exploratory behavior in novel environments is impaired. The therapeutic benefits of dopamine (DA) agonists following clinical and experimental models of TBI suggest a role for DA systems in mediating these deficits post-injury. Motivated by these observations, we have used in vivo electrochemical monitoring with fast scan cyclic voltammetry (FSCV) to assess alterations in electrically evoked extracellular DA levels after CCI. After CCI, in vivo evoked overflow of DA is impaired. Additionally there are decrements in DA clearance that correspond to decreased DAT expression after CCI. Additionally, the effects of the neurostimulant, methylphenidate, on DAT function are moderated by CCI. In awake rats after CCI, it also appears that regulation of basal DA levels is impaired. When examining tissue damage sustained directly around striatal placement of microdialysis probes, this type of trauma also suppresses evoked DA release and affects autoregulation of basal DA levels around the injury site. While the effects of CCI and direct striatal injury (DSI) from microdialysis probes on stimulated DA release and basal DA levels is significant, it is critically important to extend these investigations regarding TBI on DA neurotransmission. Currently, we can monitor tonic changes in [DA] in awake animals after pharmacological manipulation using FSCV. However, Mark Wightman has recently improved the performance of his voltammetric recording techniques such that he can now detect spontaneous DA transients, presumably associated with the burst firing of midbrain DA neurons. Wightman's approach has been refined, in part, through the implementation of principle components regression (PCR) to resolve DA signals from other interferents observed in the voltammetric trace. We speculate that adapting this technique would be a viable approach for objectively assessing and refining measurement of tonic changes in DA measured over several minutes, and thus, would provide an additional tool for measuring not only phasic, but also, tonic aspects of DA transmission. Our central hypothesis is that spontaneous striatal DA transients and regulatory mechanisms affecting basal DA are impaired after TBI. Hence, we have the following long-range scientific objectives: 1) to characterize the effects of trauma on naturally occurring, as opposed to electrically evoked, extracellular DA; 2) to characterize the state of regulatory mechanisms governing basal DA after TBI 3) to characterize the effects of DAT inhibitors on striatal extracellular DA post-injury; 4) to temporally link behavioral performance in cognitive tasks with spontaneous DA transients after CCI. In support of these scientific objectives, the technical aim of this R21, is to incorporate this new voltammetric system, including chemometrics with PCR, in to our own studies of phasic and tonic DA transmission in two models of TBI. These scientific objectives derived from adapting in vivo voltammetry monitoring to awake rats with CCI will lay the ground-work for evaluating a number of rehabilitation relevant, dopaminergic, and other therapeutic interventions and the mechanisms by which they restore DA neurotransmission and cognition after injury. The overarching goal is to gain insight into potential mechanisms of action and efficacy of these interventions on cognition and recovery for the clinical population with TBI.