Dopamine D2 Receptor Splice Variants and Autoreceptor Function

多巴胺受体的五种亚型（D1-D5）是G蛋白偶联受体超家族的成员。 受体。D1和D2亚型是最丰富的，介导最典型的多巴胺依赖性 行为。本申请集中于D2受体，特别是D2受体的功能意义。 第三个细胞质环中的29个残基片段，其选择性剪接以产生短和长的 D2受体，D2S和D2L。大量证据表明，D2受体是主要的 D2S是调节DA神经元活性和DA释放的自身受体，并且广泛接受D2S是 D2L是自身受体，而D2L是在纹状体中等多刺神经元中表达的突触后受体。在 相反，我们的工作支持一个模型，其中啮齿动物多巴胺神经元表达两种剪接变体， 两者都作为自身感受器起作用，但有一些细微的差异。我们已经确定了一个区别 剪接变体之间的差异是它们的钙依赖性脱敏率，我们现在提出， 评估可卡因诱导的敏感性，奖励和厌恶的这种差异的意义， 还比较剪接变体的其它功能性质。在第一个具体目标中，我们将比较 D2L和D2S作为抑制多巴胺的突触前自身受体的功能的其他方面 释放、多巴胺神经元放电和自发活动。我们将使用病毒介导的D2L或 D2受体缺失突变（D2-KO）小鼠和局部D2受体敲除小鼠中脑中的D2S。 为了在评估D2的测量之前恢复多巴胺神经元中D2L或D2S的表达， 自体受体活性我们还将确定这两种变体是否调节纹状体中G蛋白介导的信号传导。 神经元这一目标将集中在受体定位和调节多巴胺的释放和再摄取， 将探讨可卡因改变变异体的分布或表达的假设。第二 具体目标是基于另一种假设，即可卡因诱导的体树突自身受体 从D2S到D2L的转换触发或反映了其他变化，这些变化产生了行为敏感化、条件化 位置偏好可卡因，厌恶减少，或者表型转换是一种补偿性的， 一种调节奖励减少和厌恶增加的机制。为此，我们将测试这些 假设通过测量可卡因诱导的行为敏感化，条件性位置偏好， 仅表达D2S或D2L自身受体的小鼠的条件性味觉厌恶。实验支持 这两种假设都将为D2受体选择性剪接与DA的相关性提供有价值的见解。 神经元功能

The five subtypes of dopamine receptors (D1-D5) are members of the superfamily of G protein-coupled receptors. The D1 and D2 subtypes are the most abundant and mediate most classic dopamine-dependent behaviors. This application is focused on the D2 receptor and, in particular, on the functional significance of a 29-residue fragment in the third cytoplasmic loop that is alternatively spliced to produce the short and long forms of the D2 receptor, D2S and D2L. Considerable evidence indicates that the D2 receptor is the primary autoreceptor that regulates DA neuron activity and DA release, and it is widely accepted that D2S is that autoreceptor, whereas D2L is the postsynaptic receptor expressed in striatal medium spiny neurons. In contrast, our work supports a model in which rodent dopamine neurons express both splice variants, and both function as autoreceptors with some subtle differences. We have determined that one difference between the splice variants is their rate of calcium-dependent desensitization and we now propose to evaluate the significance of this difference for cocaine-induced sensitization, reward, and aversion, while also comparing other functional properties of the splice variants. In the first specific aim we will compare additional aspects of the function of D2L and D2S as the presynaptic autoreceptor that inhibits dopamine release, dopamine neuron firing, and locomotor activity. We will use virus-mediated expression of D2L or D2S in the midbrain of D2 receptor null-mutant (D2-KO) mice and of mice with regional D2 receptor knock- out, to restore the expression of either D2L or D2S in dopamine neurons prior to assessing measures of D2 autoreceptor activity. We will also determine if both variants regulate G protein-mediated signaling in striatal neurons. This aim will focus on receptor localization and regulation of dopamine release and reuptake, and will explore the hypotheses that cocaine alters the distribution or expression of the variants. The second specific aim is based on alternative hypotheses that a cocaine-induced somatodendritic autoreceptor switch from D2S to D2L triggers or reflects other changes that produce behavioral sensitization, conditioned place preference to cocaine, and decreased aversion, or that the phenotype switch is a compensatory mechanism that mediates decreased reward and increased aversion. In this aim we will test these hypotheses by measuring cocaine-induced behavioral sensitization, conditioned place preference, and conditioned taste aversion in mice expressing only D2S or D2L autoreceptors. Experimental support for either hypothesis will provide valuable insight into the relevance of D2 receptor alternative splicing for DA neuron function.