Determining the role of dopamine D2L versus D2S receptors in vivo

描述（由申请人提供）：多巴胺能系统是不同神经过程（如学习和记忆、奖励和成瘾、运动和催乳素分泌）的关键调节剂。因此，四种多巴胺能通路中的失调导致不可挽回的神经障碍和精神疾病如精神分裂症、帕金森病和药物成瘾的病理生理学。具体地，已知D2多巴胺受体是抗精神病药物的主要靶标;然而，常规治疗剂仍然表现出有限的功效并且通常引起不良副作用。大多数临床前和临床研究认为D2受体是一个单一的实体，但D2基因的选择性剪接产生两种异构体-长型（D2 L）和短型（D2 S）。了解D2受体的信号传导在对多巴胺的生理反应的调节中的相关性，以及D2受体激动剂和拮抗剂在治疗中的当前使用，探索D2 L和D2 S是否可以被认为在体内具有同等功能是至关重要的。我们实验室最近的研究表明D2 S和D2 L亚型之间存在明显的功能差异，其中D2 S和D2 L分别具有突触前和突触后作用。然而，如果没有异构体选择性配体，很难准确区分两种异构体的体内功能。相应地，我们的实验室已经产生了D2亚型特异性敲除，以比较生理反应和生化差异，以确定哪种受体亚型在突触前/突触后起作用，它们的激活在信号转导和对药物滥用的反应方面如何不同，最后，哪种受体亚型被特定的抗精神病药物靶向。提出了以下具体目标来表征D2亚型：在目标1中，我们将通过比较D2 S-/-和D2 L-/-与其各自的野生型（WT）响应于多巴胺能激动剂和拮抗剂的运动来分析每个D2亚型在体内黑质纹状体通路中的作用。我们还将分析基础条件下和响应药理学挑战的D2 L和D2 S特异性信号传导。在目标2中，我们将分析每种亚型在中脑边缘通路中的作用，在那里我们将检查对可卡因的运动、奖励和敏化反应，并剖析可卡因诱导的立即早期基因和转导通路的细胞特异性诱导。这些研究的成功完成将提供关于D2受体介导的多巴胺能系统控制的重要信息。从而扩展了我们对多巴胺介导的反应的科学知识，并为D2靶向药物的药理学设计提供了重要信息。

DESCRIPTION (provided by applicant): The dopaminergic system is a key regulator of distinct neural processes such as learning and memory, reward and addiction, locomotion, and prolactin secretion. Consequently, a dysregulation among the four dopaminergic pathways contributes to the pathophysiology of irrevocable neurological disorders and psychiatric illnesses such as Schizophrenia, Parkinson's disease, and drug addiction. Specifically, D2 dopamine receptor is known to be a primary target of antipsychotic drugs; however, conventional therapeutics still exhibit limited efficacy and typically cause adverse side-effects. Most preclinical and clinical studies consider D2 receptor as a single entity, but alternative splicing of the D2 gene generates two isoforms-a long form (D2L) and a short form (D2S). Knowing the relevance of D2 receptor's signaling in the regulation of physiological responses to dopamine, and the current use of D2 receptors agonists and antagonists in therapy, it is essential to explore whether D2L and D2S can be considered as equally functioning in vivo. Recent studies from our lab have indicated a distinct functional difference between D2S and D2L isoforms, where D2S and D2L have a presynaptic and postsynaptic role, respectively. However, without isoform-selective ligands, it is difficult to accurately discriminate the in vivo function of the two isoforms. Correspondingly, our lab has generated D2 isoform specific knockouts to compare physiological responses and biochemical differences to determine which receptor isoform is acting pre-/post-synaptically, how their activation is distinct in terms of sigal transduction and in response to drugs of abuse, and finally, which receptor isoform is targeted by specific antipsychotics. The following specific aims are proposed to characterize the D2 isoforms: In aim 1, we will analyze the role of each D2 isoform in the nigrostriatal pathway in vivo, by comparing the locomotion of D2S-/- and D2L-/- with its respective wild-type (WT) in response to dopaminergic agonists and antagonists. We will also analyze D2L- and D2S-specific signaling under basal conditions and in response to pharmacological challenges. In aim 2, we will analyze the role of each isoform in the mesolimbic pathway, where we will examine the motor, rewarding and sensitization responses to cocaine and dissect cell-specific induction of immediate-early-genes and transduction pathways induced by cocaine. Successful completion of these studies will give important information on the D2 receptor-mediated control of the dopaminergic system. Thus expanding our scientific knowledge of dopamine-mediated responses and providing crucial information for pharmacological designing of D2-targeted drugs.