Development of Leptin-Sensitive Hypothalamic Pathways

描述（由申请人提供）：导致肥胖的新生儿因素知之甚少。这项研究的长期目标是阐明脂肪细胞源性激素瘦素如何影响调节哺乳动物能量稳态的神经内分泌途径的发展。这一目标的核心是确定瘦素如何影响下丘脑弓状核（ARH）神经投射的发育，ARH是整合外周能量储存相关信息的关键部位。瘦素信号通过ARH传递到参与体重调节的其他大脑区域，例如下丘脑室旁核（PVH），这是调节能量代谢的最终共同途径的重要组成部分。在该提案的主体中提出的证据支持这样的概念，即瘦素在新生儿生命期间通过指导参与控制进食和能量平衡的神经回路的形成而作为发育因子发挥作用。在这一建议的总体假设是，瘦素直接作用于ARH在一个有限的新生儿的关键时期，以促进形成神经投射到PVH参与调节体重。我们建议，出生后的瘦素激增有一个持久的影响ARH的预测，并在瘦素信号的发展扰动引起永久性的变化，在成熟的动物传递瘦素信号的神经通路。生理学和体外实验方法将用于通过解决以下具体目标来测试这一假设。具体目标1。我们建议使用轴突标记的方法和组织化学技术来定义组织和发展的ARH预测肥胖小鼠缺乏瘦素（ob/ob小鼠）和糖尿病小鼠缺乏功能的长形式的受体（db/db小鼠）。具体目标2。我们还将通过检查用外源性瘦素处理的ob/ob和db/db小鼠中ARH-PVH通路的发展来测试瘦素的发育活性，并确定这种发育活性是否仅限于新生儿关键期。具体目标3。为了确定瘦素在指导ARH-PVH通路的发展中的作用位点，我们将利用一种新的外植体共培养试验，除了研究瘦素对体外分离的ARH外植体轴突生长的直接影响之外。具体目标4。此外，我们将研究如何营养操纵瘦素水平影响ARH-PVH途径的发展。具体目标5.最后，我们将确定是否改变模式的瘦素依赖下丘脑内信号伴随观察到的发展变化ARH-PVH途径。拟议的研究结果将扩大我们对瘦素的认识，包括促进瘦素反应性下丘脑神经通路形成的深刻的发育活动。这些研究还可能提供有关新生儿营养环境如何对整个生命中的喂养和能量平衡的中枢调节产生持久影响的重要线索。

DESCRIPTION (provided by applicant): Neonatal factors that contribute to obesity are poorly understood. The long-range goal of this research is to clarify how the adipocyte-derived hormone leptin influences development of neuroendocrine pathways that regulate mammalian energy homeostasis. Central to this goal is determining how leptin affects development of neural projections from the arcuate nucleus of the hypothalamus (ARH), a key site for integration of information related to peripheral energy stores. Leptin signals are conveyed via the ARH to other brain regions involved in the regulation of body weight, such as the paraventricular nucleus of the hypothalamus (PVH), an important component of the final common pathway for regulation of energy metabolism. Evidence presented in the body of this proposal supports the concept that leptin functions as a developmental factor during neonatal life by directing formation of neural circuits involved in the control of feeding and energy balance. The overall hypothesis addressed in this proposal is that leptin acts directly on the ARH during a restricted neonatal critical period to promote formation of neural projections to the PVH involved in the regulation of body weight. We propose that the postnatal leptin surge has an enduring effect on ARH projections, and that developmental perturbations in leptin signaling cause permanent changes in neural pathways that transmit leptin signals in mature animals. Both physiological and in vitro experimental approaches will be used to test this hypothesis by addressing the following specific aims. Specific Aim 1. We propose to use axonal labeling methods and histochemical techniques to define the organization and development of ARH projections in obese mice that lack leptin (ob/ob mice) and in diabetic mice that lack a functional long form of its receptor (db/db mice). Specific Aim 2. We will also test the developmental activity of leptin by examining development of the ARH-PVH pathway in ob/ob and db/db mice treated with exogenous leptin, and determine if this developmental activity is restricted to a neonatal critical period. Specific Aim 3. To determine the site of action for leptin in directing development of the ARH-PVH pathway, we will utilize a new explant coculture assay, in addition to examining the direct effects of leptin on axon outgrowth from isolated ARH explants in vitro. Specific Aim 4. In addition, we will examine how nutritional manipulation of leptin levels impacts development of the ARH-PVH pathway. Specific Aim 5. Finally, we will determine if altered patterns of leptin dependent intrahypothalamic signaling accompany observed developmental changes in the ARH-PVH pathway. The results of the proposed research will expand our appreciation of leptin to include a profound developmental activity that promotes formation of leptin-responsive hypothalamic neural pathways. These studies may also provide essential clues about how the neonatal nutritional environment imposes enduring consequences on central regulation of feeding and energy balance throughout life.