![]() We also summarize how neural, humoral, and other factors modulate efferent and afferent divisions of the ANS and their metabolic function. Here, we discuss key structures of the ANS, focusing on the role of ANS neurons in the regulation of feeding and metabolism. Therefore, both efferent and afferent divisions of the ANS can regulate energy balance and glucose homeostasis. In addition, recent studies have suggested that the gut microbiome stimulates vagal sensory neurons to affect many facets of metabolic function 14, 15. For instance, it was demonstrated that ingestion of food causes mechanical stretch of the stomach or intestinal walls, which is relayed by vagal sensory neurons to the CNS and stimulates anorexigenic neurons or inhibits orexigenic (appetite-promoting) neurons to stop feeding 12, 13. ![]() However, recent evidence has demonstrated that parasympathetic or vagal afferent (sensory) fibers inform the CNS of food in the gut. Together, these results demonstrate how the efferent (motor) divisions of the ANS regulate metabolism. Thus, it appears that neurons of the ANS translate neural and humoral signals into commands that directly regulate peripheral organs and metabolic function. In addition, peripheral hormones such as insulin and glucagon-like peptide-1 (GLP-1) were demonstrated to regulate the activity of autonomic neurons 9, 10, 11. As such, autonomic neurons are influenced by neuropeptides and neurotransmitters 5, 6, 7, 8. In these examples, the activity of autonomic neurons is affected by α-melanocyte-stimulating hormone (α-MSH), a neuropeptide released from POMC neurons in the ARH, which acts on the anorectic melanocortin-4 receptor (MC4R). In addition, POMC neurons in the ARH reportedly regulate parasympathetic preganglionic neurons in the brainstem, which decreases insulin secretion from pancreatic β-cells 3, 4. For instance, anorexigenic (appetite-suppressing) pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARH) activate sympathetic preganglionic neurons in the spinal cord, which in turn increases thermogenesis in brown adipose tissue (BAT) 1, 2. In particular, the hypothalamus utilizes the sympathetic and parasympathetic divisions of the ANS to innervate peripheral organs and to control the metabolic function of our body. The autonomic nervous system (ANS) serves as a key structure to mediate unconscious regulation of bodily function by the central nervous system (CNS).
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