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

描述（申请者提供）：缰核是一对核，位于丘脑背侧。它由内侧和外侧亚核（MHb, LHb）组成，它们连接到中脑腹侧的不同目标。对动物整个缰带的损伤研究表明，该区域具有多种功能，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，但该核的功能在很大程度上仍不清楚。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，从而介导负奖励信号。相比之下，MHb几乎完全投射到与VTA相邻的脚间核（IP），后者又投射到中缝和背侧被盖区。MHb有背侧（dMHb）和腹侧（vMHb）亚核，分别与外侧和内侧IP有特定的连接。先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。我们新的光遗传学数据显示，与LHb相比，dMHb的刺激会产生积极的奖励信号，我们假设这是通过MHb-IP途径介导的。在这里，我们将使用dMHb和vMHb特异性的ccr驱动程序，结合允许诱导表达光遗传蛋白Channelrhodopsin和Halorhodopsin的转基因小鼠，激活和沉默MHb神经元，以检查MHb与GABA神经元在IP中的功能联系。通过神经解剖、电生理和行为读数，基因靶向方法也将用于检查中缝中与5HT神经元的IP连接。目的1。我们将使用cre介导的转基因、病毒和传统的通道追踪来确定从缰状核通过IP到介导奖励和恐惧反应的后脑中心的通路的解剖学连通性。我们将分配神经递质表型的神经元在这些途径，以确定他们是否传递兴奋或抑制信号。目标2。我们将通过光遗传激活特异性突触前神经元，结合突触后神经元的细胞内记录，以及用转基因标记物鉴定记录的神经元，来测试MHb-IP和IP-raphe在脑切片制备中的生理联系。目标3。我们将利用光遗传学技术激活和沉默dMHb和vMHb在开放场运动、颅内自我刺激、实时位置偏好/厌恶、条件位置偏好/厌恶和习得性无助等奖励和抑郁行为模型中的表达。在这些实验的结论中，我们将更好地了解特定的链带成分及其下游通路，以及链带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.