The Role of 5-HT6 Receptors in Primary Neuronal Cilia

描述（由申请人提供）：虽然近年来我们对成瘾的神经药理学有了很多了解，但我们仍然没有生物治疗方法可以阻止或逆转大脑功能中的适应，这些适应“劫持”了正常动机行为中涉及的机制。像纹状体这样的大脑区域是开发新的成瘾治疗方法的关键目标，但重要的是，这些治疗方法不破坏涉及日常动机行为的正常信息处理。这是多巴胺类药物的一个特殊问题，但其他神经递质，如血清素，也在成瘾的生物学中起着重要作用。一个潜在的靶点是5-HT6血清素受体，它在纹状体中大量表达，并影响涉及药物奖励和习惯形成的程序性学习。此外，5-HT6受体是唯一一种定位于初级神经元纤毛的5-羟色胺受体，这是一种存在于大多数神经元上的细胞器，在大脑发育和正常认知功能中起着关键作用，但尚未完全表征。由于纤毛包含许多调节基因转录和可塑性而不直接干扰突触功能的细胞信号系统，这表明探索5-HT6定位在纤毛中的意义是至关重要的下一步。纤毛定位被认为是由gpcr细胞内第三环的离散一致序列控制的，包括5-HT6和一小部分其他蛋白质。这个R21项目有两个目的。第一个目标将集中在5-HT6受体的直接位点突变上

DESCRIPTION (provided by applicant): While a great deal has been learned about the neuropharmacology of addiction in recent years, we still have no biological treatments that can prevent or reverse the adaptations in brain function that "highjack" the mechanisms involved in normal motivated behavior. Brain regions such as the striatum are key targets for developing novel treatments for addiction, but it is important that these treatments do not disrupt normal information processing involved in routine motivated behaviors. This has been a particular problem with dopaminergic drugs, but other neurotransmitters such as serotonin are also centrally involved in the biology of addiction. One potential target is the 5-HT6 serotonin receptor, which is heavily expressed in striatum and affects procedural learning that is involved in drug reward and habit formation. Additionally, the 5-HT6 receptor is the only serotonin receptor localized to the primary neuronal cilium, a cellular organelle present on most neurons that has a critical role in brain development and normal cognitive function that has not yet been thoroughly characterized. Since cilia contain a number of cellular signaling systems that modulate gene transcription and plasticity without interfering with synaptic function directly, thi suggests that exploring the significance of 5-HT6 localization in cilia is a crucial next step. Ciliary localization is thought to be governed by a discrete consensus sequence in the third intracellular loop of GPCRs including 5-HT6 and a small set of other proteins. This R21 project has two aims. The first aim will focus on making site direct mutations in 5-HT6 receptors that will prevent them from localizing to cilia without perturbing their molecular functions otherwise; we will then investigate the signaling consequences of activating 5-HT6 receptors that are or are not localized in cilia. We will perform most of these experiments in primary cultured striatal neurons prepared from 5-HT6 knockout mice, providing a strong basis for reaching conclusions about their function. We will examine the effects of 5-HT6 receptors on cilia and dendritic morphology, cyclic AMP production, DARPP32 hosphorylation, and gene expression using PCR arrays focusing on key pathways predicted to be sensitive to 5-HT6 and cilia function. In the second aim we will test whether ciliary localization of 5-HT6R receptors is critical to the well- established behavioral effects of expressing 5-HT6 receptors in dorsomedial striatum using instrumental learning as the key behavioral outcome. We will perform these experiments both in rats (where the effect is well established) and in wild-type and 5-HT6 knockout mice, where the effects of normal or mutant 5-HT6 receptors can be studied in the presence and absence of endogenous 5-HT6 receptors. These experiments will create a platform for determining whether targeting cell signaling mechanisms in the cilia will offer new opportunities for developing therapeutics for addiction and other compulsive disorders.