Functional studies of the medial habenula in models of reward and mood disorders

描述(申请人提供)：缰核是位于丘脑背侧的一对核。它由内侧和外侧亚核(MHb、LHb)组成，与腹侧中脑的不同靶点相连。对动物整个缰核的损伤研究表明，该区域与多种功能有关，包括昼夜节律和睡眠、应激反应、颅内自我刺激奖励以及尼古丁和其他滥用药物的行为影响。在人类中，一些初步的临床研究已经将缰核奖赏通路与抑郁症的可能机制联系起来，但这个核团的功能在很大程度上仍然不清楚。最近的研究表明，一些LHb神经元抑制腹侧被盖区(VTA)的多巴胺(DA)信号，从而介导负奖赏信号。相反，MHB几乎只投射到毗邻VTA的脚间核(IP)，后者又投射到中缝和被盖背侧区域。MHb有背侧亚核(DMHb)和腹侧亚核(VMHb)，分别与外侧IP和内侧IP有特定的联系。以前的研究没有区分这些亚核的作用，但几乎没有理由相信它们具有相同的功能。我们的新的光遗传学数据表明，与LHb相反，刺激dMHb产生了一个积极的奖励信号，我们假设这是通过MHb-IP通路调节到脑干的。在这里，我们将使用针对dMHb和vMHb的CRE驱动程序，与允许光遗传蛋白Channel视紫质和卤视紫红质诱导表达的转基因小鼠相结合，激活和沉默MHb神经元，以检查IP中MHb和GABA神经元之间的功能联系。利用神经解剖学、电生理学和行为学读数，还将使用基因定向方法来检查IP与中缝5HT神经元的联系。目的1.我们将使用Cre介导的转基因、病毒和传统的束追踪来确定从缰核到后脑中枢的解剖学连接，这些通路介导奖赏和恐惧反应。我们将把神经递质表型分配给这些通路中的神经元，以确定它们是传递兴奋性信号还是抑制性信号。目的2.通过对特定突触前神经元的光基因激活和突触后神经元的细胞内记录，并用转基因标记鉴定记录的神经元，我们将在脑片制备中检测MHB-IP和IP-中缝之间的生理联系。目的3.利用光遗传学技术激活和沉默奖赏和抑郁行为模型中的dMHb和vMHb，包括旷场运动、脑内自我刺激、实时地点偏爱/厌恶、条件性地点偏爱/厌恶和习得性无助。在这些实验的结论中，我们将更好地了解特定的缰核成分及其下游通路，以及缰核在情绪障碍中的潜在作用。

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 distinct targets in the ventral midbrain. Lesion studies of the entire habenula in animals have implicated this area in diverse functions, including circadian rhythms and sleep, stress responses, intracranial self-stimulation reward, and the behavioral effects of nicotine and other drugs of abuse. In humans, a few preliminary clinical studies have linked habenula reward pathways to possible mechanisms of depression, but the function of this nucleus remains largely unclear. Recent work has shown that some LHb neurons inhibit dopamine (DA) signaling in the ventral tegmental area (VTA), and thus mediate a negative reward signal. In contrast, the MHb projects almost exclusively to the interpeduncular nucleus (IP), adjacent to the VTA, which projects in turn to the raphe and dorsal tegmental areas. The MHb has dorsal (dMHb) and ventral (vMHb) subnuclei, which make specific connections to the lateral and medial IP, respectively. Prior studies have not distinguished the roles of these subnuclei, yet there is littl reason to believe they have the same function. Our new optogenetic data show that, in contrast to the LHb, stimulation of the dMHb generates a positive reward signal, and we hypothesize that this is mediated via a MHb-IP pathway to the brainstem. Here we will use Cre-drivers specific for the dMHb and vMHb, combined with transgenic mice that allow inducible expression of the optogenetic proteins Channelrhodopsin and Halorhodopsin, to activate and silence MHb neurons in order to examine the functional link from the MHb to GABA neurons in the IP. Genetically targeted approaches will also be used to examine the IP connection to 5HT neurons in the raphe, using neuroanatomical, electrophysiological, and behavioral readouts. Aim 1. We will use Cre-mediated transgenic, viral, and conventional tract-tracing to determine the anatomical connectivity of pathways from the habenula, via the IP, to hindbrain centers mediating reward and fear responses. We will assign neurotransmitter phenotypes to the neurons in these pathways to determine whether they transmit excitatory or inhibitory signals. Aim 2. We will test the physiological connections between the MHb-IP and the IP-raphe in brain slice preparations, using optogenetic activation of specific presynaptic neurons combined with intracellular recording of postsynaptic neurons, and identification of the recorded neurons with transgenic markers. Aim 3. We will use optogenetics to activate and silence the dMHb and vMHb in behavioral models of reward and depression, including open field locomotion, intracranial self-stimulation, real-time place preference/aversion, conditioned place preference/aversion, and learned helplessness. At the conclusion of these experiments we will better understand the specific habenula components and their downstream pathways, and the potential role of the habenula in mood disorders.