A neural basis for melanocortin-4 receptor-regulated appetite.

Pro-opiomelanocortin (POMC)- and agouti-related peptide (AgRP)-expressing neurons of the arcuate nucleus of the hypothalamus (ARC) are oppositely regulated by caloric depletion and coordinately stimulate and inhibit homeostatic satiety, respectively. This bimodality is principally underscored by the antagonistic actions of these ligands at downstream melanocortin-4 receptors (MC4R) in the paraventricular nucleus of the hypothalamus (PVH). Although this population is critical to energy balance, the underlying neural circuitry remains unknown. Using mice expressing Cre recombinase in MC4R neurons, we demonstrate bidirectional control of feeding following real-time activation and inhibition of PVH(MC4R) neurons and further identify these cells as a functional exponent of ARC(AgRP) neuron-driven hunger. Moreover, we reveal this function to be mediated by a PVH(MC4R)?lateral parabrachial nucleus (LPBN) pathway. Activation of this circuit encodes positive valence, but only in calorically depleted mice. Thus, the satiating and appetitive nature of PVH(MC4R)?LPBN neurons supports the principles of drive reduction and highlights this circuit as a promising target for antiobesity drug development. Overall design: Single-neuron mRNA-seq was performed on fluorescently-labeled or -unlabeled cells that were manually isolated from dissociated adult mouse paraventricular and arcuate hypothalamus: Mc4r-2a-Cre::L10-GFP+ or Mc4r-2a-Cre::AAV-XFP+ or Mc4r-2a-Cre::AAV-XFP-negative PVH neurons; Agrp-IRES-Cre::L10-GFP+ ARC neurons; Pomc-hrGFP+ ARC neurons; and vGLUT2-IRES-Cre::AAV-XFP+ ARC neurons Note: Raw files unavailable for samples GSM2413312 GSM2413313 GSM2413314 GSM2413346 GSM2413347

下丘脑弓状核（arcuate nucleus of the hypothalamus, ARC）中表达阿黑皮素原（Pro-opiomelanocortin, POMC）与刺鼠相关肽（agouti-related peptide, AgRP）的神经元，受热量剥夺的反向调控，并分别协同促进与抑制稳态饱腹感。这种双向调控特性主要由这两种配体在下丘脑室旁核（paraventricular nucleus of the hypothalamus, PVH）的下游黑皮质素-4受体（melanocortin-4 receptors, MC4R）上的拮抗作用所奠定。尽管该类神经元对机体能量平衡至关重要，但其背后的神经环路机制仍未明确。

本研究利用在MC4R神经元中表达Cre重组酶的小鼠，通过实时激活或抑制PVH(MC4R)神经元，实现了对摄食行为的双向调控，并进一步证实该类细胞是ARC(AgRP)神经元驱动饥饿感的功能性效应器。此外，本研究揭示该调控功能通过PVH(MC4R)→外侧臂旁核（lateral parabrachial nucleus, LPBN）通路介导。激活该环路可编码正性效价，但该现象仅见于经历热量剥夺的小鼠。因此，PVH(MC4R)→LPBN神经元兼具饱食与渴求特性，这一结果支持驱力降低理论，并将该环路确立为抗肥胖药物开发的潜在靶点。

总体实验设计：对从解离的成年小鼠下丘脑室旁核与弓状核中手动分离的荧光标记或未标记细胞开展单神经元mRNA测序，所涉细胞类型包括：Mc4r-2a-Cre::L10-GFP+、Mc4r-2a-Cre::AAV-XFP+ 或 Mc4r-2a-Cre::AAV-XFP阴性的PVH神经元；Agrp-IRES-Cre::L10-GFP+ ARC神经元；Pomc-hrGFP+ ARC神经元；以及vGLUT2-IRES-Cre::AAV-XFP+ ARC神经元。

注：样本GSM2413312、GSM2413313、GSM2413314、GSM2413346、GSM2413347的原始测序文件无法获取。