Neural Basis for Leptin Control of Energy Balance

描述(申请人提供)：瘦素通过作用于大脑中的瘦素受体(LEPR)，发挥显著的减肥效果。由于影响大而具体，人们对了解它们的神经基础(涉及的神经元和神经递质)很感兴趣。为了确定启动瘦素抗肥胖效应的瘦素反应神经元，我们正在以神经元特有的方式从基因上删除瘦素受体，然后评估对能量平衡的影响。我们早期的研究证实POMC、AgRP和SF1神经元参与其中。然而，从这些研究中也可以清楚地看到，故事的一个主要部分被遗漏了--其他“一级”瘦素反应神经元肯定也在发挥重要作用。为了识别这些“其他”神经元，我们正在使用一种新的方法--基于它们释放的快速作用的神经递质(即谷氨酸(兴奋性)或GABA(抑制性))来测试瘦素反应的“一级”神经元。为此，我们培育了在谷氨酸能(VGLUT2-Ires-Cre小鼠)或GABA能神经元(VGAT-Ires-Cre小鼠)中表达cre-重组酶的小鼠。在此之后，我们创造了在谷氨酸或GABA能神经元上缺乏LEPR的小鼠。我们的初步研究表明，瘦素的减肥作用主要是通过GABA能神经元上的LEPR介导的。这一发现提出了一种新的逻辑，用于拼接瘦素调节的神经回路(即GABA能抑制神经元的关键作用)。具体地说，我们认为瘦素对“局部”GABA能中间神经元的作用“间接”控制了主要的体重调节投射神经元(POMC和可能的弓状核中的AgRP神经元)的活动。许多方法正在被用来探索这一新的假设。这些包括：1)LEPR对GABA能神经元(及其亚群)的遗传操作(目标一和目标二)，2)解剖和电生理分析，以确定相关瘦素反应的GABA能神经元的位置、身份和功能(目标二和目标三)，以及3)通道视紫红质辅助电路映射(CRACM)，以测试“上游”瘦素反应的GABA能神经元和“下游”体重调节的POMC神经元之间的功能连接(目标三)。我们的假设模型令人感兴趣，因为瘦素反应的GABA能神经元可能是营养编程和/或代谢可塑性的重要底物。 与公共健康相关：大脑中的神经回路控制着身体脂肪的储存。为了开发减肥疗法，我们必须首先破译支撑这些电路的“接线图”。我们正在使用以下方法来询问由减肥激素瘦素参与的神经电路：1)神经元特异性基因操作，2)光遗传学(光激活神经元刺激)，用于探测电路连接，以及3)神经功能的电评估。

DESCRIPTION (provided by applicant): Leptin, by acting on leptin receptors (LEPRs) in the brain, exerts marked anti-obesity effects. Since the effects are large and specific, there is great interest in understanding their neural basis (the neurons and neurotransmitters that are involved). To identify the leptin-responsive neurons that initiate leptin's anti-obesity effects, we are genetically deleting LEPRs, in a neuron-specific fashion, and then assessing effects on energy balance. Our earlier studies established that POMC, AgRP and SF1 neurons are involved. However, it is also clear from these studies that a major part of the story is missing - other "first-order", leptin-responding neurons must also be playing an important role. To identify these "other" neurons, we are employing a novel approach - testing leptin-responsive, "first-order" neurons based upon the fast-acting neurotransmitter that they release (i.e. glutamate (excitatory) or GABA (inhibitory)). Towards these ends, we have generated mice that express cre-recombinase in either glutamatergic (VGLUT2-ires-Cre mice) or GABAergic neurons (VGAT-ires-Cre mice). After this, we then created mice that lack LEPRs on glutamatergic or GABAergic neurons. Our preliminary studies indicate that leptin's anti-obesity effects are mediated predominantly by LEPRs on GABAergic neurons. This finding suggests a new logic for piecing together leptin-regulated neural circuits (i.e. a key role for GABAergic inhibitory neurons). Specifically, we propose that leptin action on "local" GABAergic interneurons "indirectly" controls the activity of principle body weight-regulating projection neurons (POMC and possibly AgRP neurons in the arcuate nucleus). A number of approaches are being used to probe this novel hypothesis. These include: 1) Genetic manipulation of LEPRs on GABAergic neurons (and subsets of GABAergic neurons) (in Aims One and Two), 2) Anatomic and electrophysiological analyses to determine the location, identity and function of the relevant leptin-responsive GABAergic neurons (in Aims Two and Three), and 3) Channelrhodopsin-assisted circuit mapping (CRACM) to test the functional connectivity between "upstream" leptin-responsive GABAergic neurons and "downstream" body weight-regulating POMC neurons (in Aim Three). Our hypothesized model is of interest because leptin-responsive GABAergic neurons could be important substrates for nutritional programming and/or metabolic plasticity. PUBLIC HEALTH RELEVANCE: Neurocircuits in the brain control body fat stores. To develop anti-obesity therapies, we must first decipher the "wiring-diagrams" that underpin these circuits. We are using the following approaches to interrogate neural circuits engaged by the anti-obesity hormone, leptin: 1) neuron-specific gene manipulations, 2) optogenetics (light-activated neuronal stimulation) for probing circuit connectivity, and 3) electrical assessments of neuronal function.