Neurochemistry/Physiology of Proopiomelanocortin Neurons

 描述(由申请人提供)：肥胖是一个主要的健康问题，容易导致糖尿病、心血管疾病和癌症。过多的卡路里摄入与下丘脑自身平衡中心对外周反馈信号的抵抗有关，也与涉及边缘回路的享乐过程有关，这些过程调节了美味食物的强化价值。这些神经通路相互作用，但机制在很大程度上是未知的。我们的工作主要集中在下丘脑前阿片黑素皮质素(POMC)神经元，它与邻近的AGRP/NPY神经元一起，整合营养状态的相互感受信号，调节食物摄入量和能量消耗。我们已经建立了一种独特的下丘脑特异性POMC缺乏症小鼠模型，具有POMC重新表达的能力。这些小鼠表现出遗传上可逆的吞噬、肥胖、进食模式改变和运动活动减少，并被用来测试POMC神经元异质性的功能重要性以及调节能量平衡所需的POMC神经元的绝对数量。我们发现POMC神经元通过突触释放GABA和谷氨酸，并通过使用基因策略荧光标记POMC神经元中的突触素，我们发现了POMC多肽、GABA或谷氨酸免疫标记的离散突触素阳性突触素。POMC神经元被证明投射到大脑的多个区域，这些区域将能量状态与动机、奖励和运动行为结合在一起。因此，我们下一个竞争周期的目标是验证下丘脑POMC神经元与边缘回路神经元突触接触的假设，通过黑素皮质素多肽、β-内啡肽和氨基酸神经递质的差异释放来生理调节它们的活动，并影响与食物获取和消费相关的食欲行为和运动活动。我们将通过以下三个具体目标来实验性地解决这一总体假设。1)标记与弓状POMC神经元有单突触联系的传入和传出神经元的位置和神经化学性质，重点是伏隔核、终纹床核、丘脑室旁核和腹侧被盖区。2)直接测定组成边缘兴奋环路的POMC神经元产生的神经肽和氨基酸类神经递质的基础水平和刺激释放。这些实验将使用脑微透析直接在线耦合到一种新的毛细管液相色谱/质谱仪系统，该系统能够同时检测具有皮摩尔敏感性的多种神经肽。3)验证POMC神经元/黑素皮质素投射到中皮质边缘多巴胺通路调节运动活动和食欲动机的假设。总之，这些对下丘脑POMC神经元的研究将提供关于动态平衡和饮食享乐控制之间的复杂联系的新的机械性见解，这可能是现代世界肥胖流行的基础。

 DESCRIPTION (provided by applicant): Obesity is a major health problem that predisposes individuals to diabetes, cardiovascular disease and cancer. Excessive caloric intake is linked to resistance of hypothalamic homeostatic centers to peripheral feedback signals and to hedonic processes involving limbic circuits that mediate the reinforcing value of palatable food. These neural pathways interact with each other, but the mechanisms are largely unknown. Our work has focused on hypothalamic proopiomelanocortin (POMC) neurons that, together with adjacent AGRP/NPY neurons, integrate interoceptive signals of nutritional state and regulate food intake and energy expenditure. We have developed a unique mouse model of hypothalamus-specific POMC-deficiency with the capacity for POMC re-expression. These mice exhibit genetically reversible hyperphagia, obesity, meal pattern alterations and decreased locomotor activity, and were used to test the functional importance of POMC neuron heterogeneity and the absolute number of POMC neurons required to regulate energy balance. We discovered that POMC neurons synaptically release GABA and glutamate and, by using a genetic strategy to fluorescently tag synaptophysin in POMC neurons, we identified discrete synaptophysin-positive boutons that were immuno- labeled either for POMC peptides, GABA, or glutamate. POMC neurons were shown to project to multiple brain areas that integrate energy status with motivational, rewarding and locomotor behaviors. Therefore, our goal for the next competing cycle of this project is to test the hypothesis that hypothalamic POMC neurons are in synaptic contact with limbic circuit neurons, physiologically modulate their activity through the differentil release of melanocortin peptides, β-endorphin and amino acid neurotransmitters, and influence appetitive behaviors and locomotor activity related to food acquisition and consumption. We will experimentally address this overarching hypothesis through the following three specific aims. 1) Map the location and neurochemical properties of afferent and efferent neurons with monosynaptic connections to arcuate POMC neurons, focusing on the nucleus accumbens, bed nucleus of the stria terminalis, paraventricular nucleus of the thalamus, and the ventral tegmental area. 2) Directly measure basal levels and stimulated release of the neuropeptides and amino acid neurotransmitters produced by POMC neurons in the nuclei named above that comprise the limbic motivational circuit. These experiments will employ brain microdialysis directly coupled on-line to a novel capillary liquid chromatography/mass spectrometry system capable of simultaneously detecting multiple neuropeptides with picomolar sensitivity. 3) Test the hypothesis that POMC neuron/melanocortin projections to the mesocorticolimbic dopamine pathway modulate locomotor activity and appetitive motivation for food. Together, these investigations of hypothalamic POMC neurons will provide new mechanistic insights regarding the complex links between the homeostatic and hedonic control of feeding, dysregulation of which may underlie the obesity epidemic in the modern world.