Measuring Striatal Neurotransmission in Behaving Rats after Experimental TBI

描述(申请人提供)：纹状体与皮质和皮质下结构相连，影响认知功能。以往的工作表明，在实验性创伤性脑损伤(TBI)的受控皮质撞击(CCI)模型中，空间记忆和在新环境中的探索行为受到损害。多巴胺(DA)激动剂在临床和实验脑损伤模型后的治疗益处表明，DA系统在调节损伤后的这些缺陷中发挥了作用。受这些观察的启发，我们使用了体内电化学监测和快速扫描循环伏安法(FSCV)来评估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清除量的减少与DAT表达的减少相对应。此外，神经刺激剂哌醋甲酯对DAT功能的影响受CCI的调节。在CCI后清醒的大鼠中，基础DA水平的调节似乎也受到了损害。当检查微透析探头直接放置在纹状体周围的组织损伤时，这种类型的创伤也抑制诱发的DA释放，并影响损伤部位周围基础DA水平的自动调节。尽管CCI和微透析探头的直接纹状体损伤(DSI)对刺激的DA释放和基础DA水平的影响是显著的，但扩大关于TBI对DA神经传递的研究是至关重要的。目前，我们可以使用FSCV监测清醒动物在药物处理后[DA]的紧张性变化。然而，马克·怀特曼最近改进了他的伏安记录技术的性能，现在他可以检测到自发的DA瞬变，推测这可能与中脑DA神经元的突然放电有关。怀特曼的方法已经得到改进，部分是通过实施主成分回归(PCR)来解析伏安示踪中观察到的其他干扰的DA信号。我们推测，采用这一技术将是客观地评估和改进测量DA在几分钟内的紧张性变化的一种可行的方法，因此，将提供一种额外的工具，不仅测量DA传递的阶段，而且还测量DA传递的紧张性方面。我们的中心假说是脑创伤后自发的纹状体DA瞬变和影响基础DA的调节机制受损。因此，我们有以下长期的科学目标：1)表征创伤对自然发生的细胞外DA的影响，而不是电诱发的细胞外DA；2)表征脑损伤后控制基础DA的调节机制的状态；3)表征DAT抑制剂对损伤后纹状体细胞外DA的影响；4)在时间上将认知任务中的行为表现与CCI后自发的DA联系起来。为了支持这些科学目标，R21的技术目标是将这种新的伏安系统，包括化学计量学和聚合酶链式反应，纳入我们自己在两种脑损伤模型中的相性和张力性DA传递的研究中。这些科学目标源于对CCI清醒大鼠的体内伏安监测，将为评估一些康复相关的、多巴胺能和其他治疗干预措施以及它们恢复损伤后DA神经传递和认知的机制奠定基础。首要目标是深入了解这些干预措施对脑外伤临床人群认知和康复的潜在作用机制和有效性。

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.