A Genetically Defined Lateral Septum Circuit for Contextual Calibration of Food Reward-Seeking

对于数百万患有饮食失调(EDs)的人来说，回避和寻找食物已经成为令人虚弱并可能危及生命的行为。如果我们要改进治疗方法并确定治疗EDS的新疗法，我们理解大脑回路来校准进食和解释与食物相关的背景线索是绝对关键的。海马体(HPC)参与动机行为的语境调节，包括摄食，但HPC的语境信号是如何整合并传递到皮质下系统以衡量动机行为的还不是很清楚。利用深入的分子和电路分析，包括单细胞测序、光遗传学和单突触神经追踪，我们发现了一个背部受限的LS神经元亚群，其特征是神经肽前强啡肽(Pdyn)的独特表达模式。关键的是，在雄性和雌性小鼠中，这些LS(Pdyn)神经元从背侧HPC(例如CA3/2)接受强大的单突触输入，并强烈投射到下丘脑外侧(LH)与摄食相关的区域。我们的初步数据表明，LS(Pdyn)神经元对摄食具有抑制作用。这些发现与寻找食物的模型一致，在该模型中，抑制性LS(Pdyn)神经元通过抑制寻找食物的GABA能黄体生成素(Vgat)神经元来减少进食和进食。因此，这项拟议的工作将检验这一中心假设，即自上而下的兴奋性背侧HPC-&GT；背侧LS(Pdyn)-&GT；LH(Vgat)环路介导了对食物奖励寻求行为的上下文相关调节。因此，在目标1(在K99阶段下的第一年训练)中，我们将在行为自由的小鼠中部署纵向1-p钙成像，以测试LS(Pdyn)神经活动与食物获取和消费负相关的假设，以及这一活动可以被破译以区分与食物相关的环境(促进进食)和不相关的环境。在目标2(在K99周期的最后阶段)，我们将表征兴奋性海马输入到LS(Pdyn)抑制神经元之间的功能性突触连接，并将利用电路特有的光遗传学测试依赖于海马输入到背外侧隔区[LS(Pdyn)神经元表达的区域]的上下文依赖的摄食。在最后的目标3中，以及在建立我自己的独立研究计划中(在R00阶段的第3-5年)，我将实施目标1和目标2中建立的技术，以测试LS(Pdyn)抑制神经元是否突触到抑制性黄体生成素(Vgat)神经元，以及该回路是否对食物奖励寻求(电路特异性光遗传学)的上下文相关表达至关重要。此外，Aim 3将测试在LS(Pdyn)激活(结合LS的特定细胞类型的光遗传学和LH中的纵向钙成像)后，促黄体生成素(Vgat)神经元是否在体内受到抑制，直接将LS(Pdyn)神经活动与促黄体生成素(Lh)联系起来，以调节上下文触发的喂养。总之，这些研究将确定背侧LS(Pdyn)活动模式如何编码和部署环境信号，以便对动机摄食行为进行上下文校准。

For the millions of individuals living with eating disorders (EDs), food-avoidance and -seeking have become debilitating and potentially life-threatening behaviors. If we are to improve treatments and identify novel therapeutics for EDs, it is absolutely critical that we understand brain circuits that calibrate feeding and interpret food-related contextual cues. The hippocampus (HPC) is critically involved in the contextual regulation of motivated behaviors, including feeding, but how contextual signals of the HPC are integrated and relayed to subcortical systems to scale motivated behaviors isn't well known. Leveraging deep molecular and circuit analyses, including single-cell sequencing, optogenetics, and monosynaptic neural tracing, we have uncovered a dorsally restricted subpopulation of LS neurons, characterized by its unique expression pattern of the neuropeptide, prodynorphin (Pdyn). Critically, and in male and female mice, these LS(Pdyn) neurons receive robust monosynaptic input from the dorsal HPC (e.g., CA3/2) and project strongly to feeding-related regions of the lateral hypothalamus (LH). Our preliminary data suggest that LS(Pdyn) neurons exhibit an inhibitory role on feeding. These findings concord with a food-seeking model in which inhibitory LS(Pdyn) neurons reduce food approach and eating by inhibiting food-seeking GABAergic LH(Vgat) neurons. As such, the proposed work will test the central hypothesis that a top-down excitatory dorsal HPC->dorsal LS(Pdyn)->LH(Vgat) circuit mediates context-dependent-regulation of food reward-seeking behavior. Accordingly, and in Aim 1 (spanning the first year of training under the K99 phase), we will deploy longitudinal 1-p calcium imaging in freely behaving mice to test the hypothesis that LS(Pdyn) neural activity negatively correlates with food approach and consumption, and that this activity can be deciphered to discriminate food-associated contexts (that promote feeding) from those that do not. In Aim 2 (in the final phase of the K99 period), we will characterize functional synaptic connectivity between excitatory hippocampal inputs to LS(Pdyn) inhibitory neurons, and we will test for the dependence of context-dependent feeding on hippocampal inputs to the dorsolateral septum [the region in which LS(Pdyn) neurons are expressed] using circuit-specific optogenetics. In the final Aim 3, and in the establishment of my own independent research program (in years 3-5 of the R00 stage), I will implement the techniques established in Aims 1 and 2 to test whether LS(Pdyn) inhibitory neurons synapse onto inhibitory LH(Vgat) neurons and whether this circuit is critical for the context-dependent expression of food reward-seeking (circuit-specific optogenetics). Moreover, Aim 3 will test whether LH(Vgat) neurons are inhibited in vivo following LS(Pdyn) activation (combining cell-type-specific optogenetics of the LS and longitudinal calcium imaging in the LH), directly linking LS(Pdyn) neural activity to the LH for regulation of context-triggered feeding. In total, these studies will identify how dorsal LS(Pdyn) activity patterns encode and deploy environmental signals for the contextual calibration of motivated feeding behaviors.