Neurohormones, Rikkunshito and Hypothalamic Neurons Interactively Control Appetite and Anorexia

Ghrelin is the orexigenic peptide produced in the periphery, and its plasma level shows remarkable pre/postprandial changes. Ghrelin is considered a pivotal signal to the brain to stimulate feeding. Hence, characterizing the target neurons for ghrelin in the hypothalamic feeding center and the signaling cascade in the target neurons are essential for understanding the mechanisms regulating appetite. Anorexia and cachexia associated with gastric surgery, stress-related diseases, and use of anti-cancer drugs cause the health problems, markedly deteriorating the quality of life. The anorexia involves several neurotransmitters and neuropeptides in the hypothalamic feeding center, in which corticotropin-releasing hormone (CRH), urocortine, serotonin (5HT) and brain-derived neurotrophic factor (BDNF) play a pivotal role. A Japanese herbal medicine, rikkunshito, has been reported to ameliorate the anorexia by promoting the appetite. This review describes 1) the interaction of ghrelin with the orexigenic neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus (ARC) and underlying signaling cascade in NPY neurons, 2) the anorectic pathway driven by BDNF-CRH/urocortine and 5HT-CRH/urocortine pathways, 3) the effect of rikkunshito on the interaction of ghrelin and NPY neurons in ARC, and 4) the effect of rikkunshito on the interaction of 5HT on CRH neurons in paraventricular nucleus (PVN).