Mechanisms of Amphetamine Action on Dopaminergic Signaling

说明(申请人提供)：相当大的研究努力有理由地指向确定安非他明的作用机制。然而，安非他明是否像最近对另一种精神刺激剂可卡因所显示的那样，作用于相的多巴胺能信号，目前尚不清楚。考虑到这种多巴胺能神经传递模式在学习和动机行为中的作用，以及苯丙胺在治疗注意缺陷多动障碍及其高度成瘾性质中的使用，预计会有一些参与。另一方面，虽然这两种药物都能抑制多巴胺的摄取，但苯丙胺，而不是可卡因，会耗尽多巴胺的囊泡储存。因此，安非他明可能与可卡因没有共同的能力，增加伏隔核多巴胺浓度瞬变的幅度，推测是由相性或爆发式放电和胞吐释放引起的。研究苯丙胺和时相多巴胺能信号之间的联系意义重大，因为这种精神刺激作用的行为相关机制还没有完全阐明。特别是，文献记载的苯丙胺对行为的影响和透析液中的多巴胺之间的分离表明，除了紧张性多巴胺能信号外，还有其他靶点。与在终端场产生多巴胺浓度瞬变的时相性多巴胺能信号不同，紧张性多巴胺能信号维持脑细胞外多巴胺的低、稳定或环境水平。为了解决这些与苯丙胺作用相关的重要问题，本项目将研究苯丙胺对时相多巴胺能信号的影响。第一个目标是比较苯丙胺对大鼠和叙利亚仓鼠的兴奋作用。虽然单独的研究表明，叙利亚仓鼠比包括老鼠在内的其他啮齿动物对苯丙胺不那么敏感，但这种差异并未在相同的条件下得到证实。通过在随后的实验中比较这两个物种的神经化学测量，将唯一地评估苯丙胺对时相多巴胺能信号的行为相关性。第二个目的将确定苯丙胺对伏隔核多巴胺摄取和胞吐多巴胺释放的影响，这一效应尚未在体内得到证实。这些突触前机制调节多巴胺的瞬时幅度。第三个目标将直接使用相同的方法，即自由活动动物的快速扫描循环伏安法，表征苯丙胺对伏隔核多巴胺浓度瞬变的频率和幅度的影响，这一方法以前被用来建立可卡因对多巴胺能时相信号的影响。这项研究将调查苯丙胺是如何影响大脑的，苯丙胺既是一种治疗剂，也是一种滥用药物。新的微型传感器技术将在实验室动物身上应用，以表征苯丙胺对与学习和动机有关的大脑化学的影响。

DESCRIPTION (provided by applicant): Considerable research effort has justifiably been directed towards identifying the mechanisms of amphetamine action. However, whether amphetamine acts on phasic dopaminergic signaling, as has been shown recently for cocaine, another psychostimulant, is not known. Some involvement is anticipated, given the role proposed for this mode of dopaminergic neurotransmission in learning and motivated behavior and amphetamine's use in treating attention deficit hyperactivity disorder and its highly addictive nature. On the other hand, while both drugs inhibit dopamine uptake, amphetamine, but not cocaine, depletes vesicular stores of dopamine. Consequently, amphetamine may not share with cocaine the ability to increase the amplitude of dopamine concentration transients in the nucleus accumbens, presumably elicited by phasic or burst firing and exocytotic release. Examining the link between amphetamine and phasic dopaminergic signaling is significant, because the behaviorally relevant mechanisms by which this psychostimulant acts are not fully elucidated. In particular, documented dissociations between amphetamine's effects on behavior and dialysate dopamine suggest other targets besides tonic dopaminergic signaling. In contrast to phasic dopaminergic signaling, which generates dopamine concentration transients in terminal fields, tonic dopaminergic signaling maintains a low, steady-state or ambient level of brain extracellular dopamine. To address these important issues related to amphetamine action, the present project will investigate the effects of amphetamine on phasic dopaminergic signaling. The first aim will compare the stimulant effects of amphetamine in rats and Syrian hamsters. While separate studies suggest that Syrian hamsters are less sensitive to amphetamine than other rodents including rats, this difference has not been established under the same conditions. By comparing neurochemical measurements in these two species in the subsequent experiments, the behavioral relevance of amphetamine effects on phasic dopaminergic signaling will be uniquely assessed. The second aim will determine the effects of amphetamine on dopamine uptake and exocytotic dopamine release in the nucleus accumbens, which have not been established in vivo. These presynaptic mechanisms regulate dopamine transient amplitude. The third aim will characterize the effects of amphetamine on the frequency and amplitude of dopamine concentration transients in the nuclues accumbens directly using the same approach, fast-scan cyclic voltammetry in freely moving animals, that was previously used to establish cocaine effects on phasic dopaminergic signaling. This research will investigate how amphetamine, which is used both as a therapeutic agent and a drug of abuse, affects the brain. New microsensor technology will be employed in laboratory animals to characterize amphetamine's effect on brain chemistry related to learning and motivaton.