LEPTIN ACTION ON HYPOTHALAMIC PEPTIDES GOVERNING FEEDING

该项目的目标是了解食物摄入和体重调节的神经生物学基础。瘦素是脂肪细胞中肥胖基因的产物，是最重要的外周饱腹感因子之一，通过在大脑中起作用来抑制食物摄入和体重。由于肥胖的人和通过饮食控制而肥胖的老鼠，循环瘦素水平升高，但维持正常的食物摄入量，因此人们认为肥胖个体对内源性瘦素相对不敏感。在啮齿类动物中，慢性瘦素输注产生对瘦素饱腹作用的抵抗。下丘脑对瘦素饱腹作用产生抵抗的机制尚不清楚。这个问题将在慢性瘦素输注的大鼠中得到解决。一个简单的假设是，一种模型促氧神经肽Y （NPY）和厌食神经紧张素（NT）肽的分泌和作用的改变是对瘦素饱腹作用的抵抗的基础。以下具体目标将被处理。特异性目的1：确定弓状核(ARC)-室旁核（PVN）通路中NPY分泌（合成和释放）的减少和/或NT分泌的增加是否可以解释瘦素引起的急性食物摄入减少；以及对NPY和NT作用的反应性变化是否也参与其中；特异性目的2：确定NPY和NT的分泌和作用的变化是否在瘦素的急性作用基础上被慢性瘦素暴露逆转，并导致对瘦素饱腹作用的抵抗；特异性目的3：研究瘦素诱导急性下食及对瘦素饱腹作用产生抵抗过程中瘦素受体活性和基因表达的变化；具体目标4：描述NPY和NT系统活性的逆转以及瘦素受体功能的逆转，这些逆转可能与暴饮暴食相关，并在退出慢性瘦素输注后恢复到控制状态。肽神经分泌将通过评估合成电位（mRNA）、释放可用性（肽含量）和输出（体内和体外释放）来评估。多肽和激素将通过RIA测定。神经肽及其受体和瘦素受体的前mrna将通过原位杂交技术测量。NPY和NT受体活性将通过配体结合试验评估。这些研究将进一步加深我们对下丘脑中与进食有关的瘦素信号的理解，因此将与饮食失调治疗方法的发展有关。

The goal of this project is to understand the neurobiological basis of food intake and body weight regulation. Leptin, a product of the obese gene in fat cells, is one of the most important peripheral satiety factors that inhibits food intake and body weight by acting in the brain. Since obese humans, and mice made obese by dietary manipulation, have elevated levels of circulating leptin but maintain a normal food intake, it is thought that obese individuals are relatively insensitive to endogenous leptin. In rodents, chronic leptin infusion produces resistance to the satiety action of leptin. The hypothalamic mechanisms for the development of resistance to leptin's satiety action are unknown. This problem will be addressed here in a chronic leptin infused rat. A simple hypothesis that alterations in the secretion and actions of a model orexigenic, neuropeptide Y (NPY), and anorectic, neurotensin (NT), peptide underlies the resistance to leptin's satiety action will be tested. The following Specific Aims will be addressed. Specific Aim 1: To determine whether decreased NPY secretion (synthesis and release) and/or increased NT secretion in the arcuate nucleus (ARC)- paraventricular nucleus (PVN) pathway can account for the acute leptin induced decrease in food intake; and whether changes in responsiveness to the actions of NPY and NT are also involved; Specific Aim 2: To determine whether the changes in secretion and action of NPY and NT that are established to underlie the acute effects of leptin are reversed with chronic leptin exposure and lead to the development of resistance to leptin's satiety action; Specific Aim 3: To determine the changes in leptin receptor activity and gene expression during the acute hypophagia induced by leptin and during the development of resistance to leptin's satiety action; Specific Aim 4: To describe the reversals in activities of the NPY and NT systems and in leptin receptor function that may be anticipated to occur in association with the hyperphagia and subsequent return to the control condition that follows withdrawl from chronic leptin infusion. Peptide neurosecretion will be evaluated by assessing synthetic potential (mRNA), availability for release (peptide content), and output (in vivo and in vitro release). Peptides and hormones will be measured by RIA. Prepro-mRNAs for neuropeptides and their receptors, and for leptin receptors will be measured by in situ hybridization technique. NPY and NT receptor activities will be assessed by ligand-binding assay. These studies will further our understanding of leptin signaling in the hypothalamus in relation to feeding, and therefore will be relevant to the development of therapeutic approaches to eating disorders.