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，使个人容易患糖尿病，心血管疾病和癌症。过量的热量摄入与下丘脑稳态中心对外周反馈信号的抵抗以及涉及边缘系统回路的享乐过程有关，边缘系统回路介导可口食物的强化价值。这些神经通路相互作用，但机制在很大程度上是未知的。我们的工作集中在下丘脑前阿黑皮素（POMC）神经元，连同相邻的AGRP/NPY神经元，整合营养状态的内感受信号，调节食物摄入和能量消耗。我们已经开发了一种独特的小鼠模型，下丘脑特异性POMC缺陷与POMC重新表达的能力。这些小鼠表现出遗传可逆的摄食过多、肥胖、进食模式改变和运动活性降低，并用于测试POMC神经元异质性的功能重要性和调节能量平衡所需的POMC神经元的绝对数量。我们发现POMC神经元突触释放GABA和谷氨酸，并且通过使用遗传策略来荧光标记POMC神经元中的突触体蛋白，我们鉴定了对于POMC肽、GABA或谷氨酸免疫标记的离散突触体蛋白阳性终扣。POMC神经元被证明投射到多个大脑区域，这些区域将能量状态与动机，奖励和运动行为相结合。因此，本项目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，通过不同释放黑皮质素肽、β-内啡肽和氨基酸神经递质生理调节其活性，并影响与食物获取和消耗相关的食欲行为和运动活动的假设。我们将通过以下三个具体目标来实验性地解决这个总体假设。1)绘制与弓状POMC神经元具有单突触连接的传入和传出神经元的位置和神经化学性质，重点是延髓核、终纹床核、丘脑室旁核和腹侧被盖区。2)直接测量由上述核团中的POMC神经元产生的神经肽和氨基酸神经递质的基础水平和刺激释放，所述核团包括边缘系统激励回路。这些实验将采用脑微透析直接耦合在线一种新的毛细管液相色谱/质谱系统，能够同时检测多种神经肽与皮摩尔的灵敏度。3)检验POMC神经元/黑皮质素投射到中皮质边缘多巴胺通路调节自发活动和对食物的食欲动机的假设。总之，下丘脑POMC神经元的这些调查将提供新的机制的见解之间的复杂联系的自我平衡和享乐控制的喂养，失调的基础可能是肥胖症的流行在现代世界。

 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.