New models of lateral habenula function in pathways regulating anxiety and mood

 描述(申请人提供)：缰核是位于丘脑背侧的一对核。它由内侧亚核和外侧亚核(MHb、LHb)组成，通过共同的神经束与脑干相连，但支配不同的脑干靶点。在最初的三年 在本项目中，我们使用转基因小鼠来确定MHb和LHb的基因表达模式和输出途径。最近的工作表明，一些LHb神经元通过局部GABA能中间神经元抑制腹侧被盖区(VTA)的多巴胺(DA)信号。这条通路被认为介导了奖赏预测错误和惩罚，这些信号可能在抑郁症中过度活跃，一些初步的人类研究已经将缰核与抑郁症的机制联系起来。虽然LHb对DA活动的调节显然很重要，但我们发现LHb的90%的输出投射到中脑/桥中缝核和背侧被盖(DTG)区，包括富含5-羟色胺(5HT)神经元的区域。关于LHb和中缝/DTG通路的具体联系或行为功能，我们知之甚少。鉴于5-羟色胺在睡眠、情绪和压力调节中的已知作用，LHb-中缝通路可能具有重要的临床意义。因此，除了了解LHb对DA活性的调节外，还需要更多的LHb功能模型。在这个项目的第4-8年，我们将使用光遗传辅助电路映射来定义从LHb到中缝和DTG中特定神经元的功能通路。我们还将在运动、焦虑、强化和应激的行为模型中测试这些LHb通路的功能。目的1：确定LHb是否与脑干GABA能神经元有直接突触联系。我们假设LHb与中缝和DTG中的GABA能神经元突触，就像在VTA中一样。我们将使用光遗传辅助电路映射，结合Cre重组酶驱动的特定神经元中ChR2的表达，利用脑片制备中的细胞内“视觉斑块”记录，评估LHb与中缝和DTG中基因标记的GABA能神经元之间的联系。目的2：确定LHb与5-羟色胺系统的直接和多突触联系。在这个目的中，我们将使用光遗传回路作图来确定在接受LHb输入的中缝核团中，LHb和5HT神经元之间是否存在单突触联系。我们还将使用电生理学和特定神经递质系统的抑制剂来确定中缝LHb和5HT神经元之间是否存在通过GABA能中间神经元的多突触联系，类似于LHb-RMTg-VTA系统。目的3：研究LHb输入对中缝系统的行为作用。在这里，我们将在LHb中表达光激活离子通道ChR2，然后刺激自由活动小鼠中缝核中的LHb纤维终末，以确定LHb-中缝通路在运动、焦虑模型、自我刺激强化和应激行为反应中的作用。

 DESCRIPTION (provided by applicant): The habenula is a paired nucleus residing in the dorsal thalamus. It consists of medial and lateral subnuclei (MHb, LHb), which connect to the brainstem via a common tract, yet innervate different brainstem targets. In the initial three years of this project, we have used transgenic mice to define the gene expression patterns and output pathways of the MHb and LHb. Recent work has shown that some LHb neurons inhibit dopamine (DA) signaling in the ventral tegmental area (VTA) via local GABAergic interneurons. This pathway is thought to mediate reward prediction error and punishment, signals which could be overactive in depression, and a few preliminary human studies have linked the habenula to mechanisms of depression. Although LHb regulation of DA activity is clearly important, we find that >90% of LHb outputs project instead to the midbrain/pontine raphe nuclei and dorsal tegmental (DTg) area, including regions rich in serotonergic (5HT) neurons. Little is known about the specific connections or the behavioral function of the pathway from the LHb and the raphe/DTg. Given the known roles of 5HT in the regulation of sleep, mood, and stress, the LHb-raphe pathway may be of great clinical significance. Thus in addition to understanding LHb regulation of DA activity, additional models of LHb function are needed. In years 4-8 of this project, we will use optogenetically assisted circuit mapping to define functional pathways from the LHb to specific neurons in the raphe and DTg. We will also test the function of these LHb pathways in behavioral models of locomotion, anxiety, reinforcement and stress. Aim 1: Determine if the LHb makes direct synaptic connections with brainstem GABAergic neurons. We hypothesize that the LHb synapses with GABAergic neurons in the raphe and DTg, as it does in the VTA. We will use optogenetically-assisted circuit mapping, with Cre recombinase-driven expression of ChR2 in specific neurons, to assess the connection between the LHb and genetically-labeled GABAergic neurons in the raphe and DTg, using intracellular "visual patch" recording in brain slice preparations. Aim 2: Determine the direct and polysynaptic connections of the LHb with the 5HT system. In this aim we will use optogenetic circuit mapping to determine if there is a monosynaptic connection between the LHb and 5HT neurons in the raphe nuclei receiving LHb inputs. We will also use electrophysiology and inhibitors of specific neurotransmitter systems to determine if there is a polysynaptic link between the LHb and 5HT neurons in the raphe via GABAergic interneurons, analogous to the LHb-RMTg-VTA system. Aim 3: Examine the behavioral role of LHb inputs to the raphe system. Here we will express the light-activated ion channel ChR2 in the LHb, then stimulate LHb fiber terminals in the raphe nuclei in freely moving mice to determine the role of the LHb-raphe pathway in locomotion, models of anxiety, self- stimulation reinforcement, and behavioral responses to stress.