FUNCTIONAL NEUROANATOMY OF LEPTIN RESPONSIVE NEURONS

下丘脑弓状核中两种不同的肽能神经元(POMC和NPY/AgRP)对瘦素等代谢信号做出反应。在前一个捐赠周期中所做的研究帮助确定了这些瘦素反应神经元的神经解剖学目标，包括交感节前神经元以及下丘脑外侧区(LHA)和下丘脑室旁核(LHA)的神经元。自上次提交以来，另一种关键的代谢激素Ghrelin已被确定可调节食物摄入量和体重。有证据表明，CMS神经元群是Ghrelin的靶点。这包括弓状核中的NPY/AgRP神经元。该项目将使用最先进的功能神经解剖学技术，包括轨迹追踪，利用原位Ghrelin诱导基因表达 杂交组织化学和神经元表型的化学鉴定(单独和联合)，以鉴定生长激素反应性神经元的解剖投射。我们将确定在表达NPY/AGRP和POMC/CART的弓状和交叉后神经元中，Ghrelin反应神经元群体投射到脊髓、迷走神经背侧运动核、下丘脑外侧区和室旁核等部位的程度，这些部位可能在激活Ghrelin激活的传出通路中发挥不同的作用。最后，我们将直接检验这一假设，即仅在NPY/AgRP神经元中表达的ghrelin受体足以调节ghrelin增加食物摄入量的作用。 并降低能源消耗。为了实现这一点，我们将使用一种新的小鼠模型，该模型对Ghrelin受体的表达为空。小鼠是这样制作的，Cre重组酶的作用将重新激活ghrelin受体的表达。我们将我们的小鼠交叉到AgRP-CRE小鼠，这将导致小鼠仅在NPY/AgRP神经元中表达Ghrelin受体。我们将评估野生型、Null和AgRP重新激活的小鼠对急性Ghrelin注射的反应和对饮食诱导肥胖的敏感性。这些研究将极大地扩展我们对Ghrelin参与的神经回路的了解。

Two distinct populations of peptidergic (POMC and NPY/AgRP) neurons in the arcuate nucleus of the hypothalamus respond to metabolic cues such as leptin. Studies done in the previous grant cycle helped define the neuroanatomical targets of these leptin-responsive neurons including sympathetic preganglionic neurons and neurons in the lateral hypothalamic area (LHA) and paraventricular hypothalamic nucleus. Since the previous submission, another critical metabolic hormone, ghrelin, has been identified to regulate food intake and body weight. Evidence suggests that CMS neuronal groups are targets of ghrelin. This includes NPY/AgRP neurons in the arcuate nucleus. This project will employ state of the art functional neuroanatomical techniques including tract tracing, ghrelin induced gene expression using in situ hybridization histochemistry, and chemical identification of neuronal phenotypes (alone and in combination) to identify the anatomical projections of ghrelin-responsive neurons. We will determine to what degree populations of ghrelin responsive neurons in the arcuate and retrochiasmatic neurons expressing NPY/AGRP and POMC/CART project to sites including spinal cord, dorsal motor nucleus of the vagus, the lateral hypothalamic area and the paraventricular nucleus, which are likely to play a distinct role in activating the efferent pathways activated by ghrelin. Finally, we will directly test the hypothesis that ghrelin receptor expression only in NPY/AgRP neurons is sufficient to mediate the effects of ghrelin to increase food intake and decrease energy expenditure. To accomplish this we will use a novel mouse model that is null for ghrelin receptor expression. The mouse is made such that the action of Cre-recombinase will reactivate ghrelin receptor expression. We will cross our mice to AgRP-Cre mice, which will result in mice with ghrelin receptor expression only in NPY/AgRP neurons. We will assess the responses to acute ghrelin administration and sensitivity to diet induced obesity in wild type, null, and AgRP reactivated mice. These studies will substantially expand our knowledge of the neural circuits engaged by ghrelin.