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）对瘦素等代谢信号作出反应。在上一个资助周期完成的研究有助于定义这些瘦素反应神经元的神经解剖学靶点，包括交感神经节前神经元和下丘脑外侧区（LHA）和室旁核的神经元。自上次提交以来，另一种重要的代谢激素ghrelin已被确定用于调节食物摄入和体重。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。本项目将采用最先进的功能性神经解剖学技术，包括神经束追踪、生长激素释放肽诱导的基因表达， 杂交组织化学和神经元表型的化学鉴定（单独和组合），以鉴定生长素释放肽反应性神经元的解剖学投射。我们将确定表达NPY/AGRP和POMC/CART的弓状神经元和视交叉后神经元中的ghrelin反应神经元群体投射到包括脊髓、迷走神经背侧运动核、下丘脑外侧区和室旁核在内的部位的程度，这些部位可能在激活ghrelin激活的传出通路中发挥独特的作用。最后，我们将直接检验仅在NPY/AgRP神经元中的ghrelin受体表达足以介导ghrelin增加食物摄入的作用的假设 减少能量消耗。为了实现这一点，我们将使用一种新的小鼠模型，是空的生长激素释放肽受体表达。制备小鼠，使得Cre重组酶的作用将重新激活生长素释放肽受体表达。我们将我们的小鼠与AgRP-Cre小鼠杂交，这将导致仅在NPY/AgRP神经元中表达ghrelin受体的小鼠。我们将评估野生型、无效和AgRP再激活小鼠对急性胃饥饿素给药的反应和对饮食诱导的肥胖的敏感性。这些研究将大大扩展我们对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.