Response of Neuropeptides to Hunger Signals in Teleost

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Introduction: The perception of hunger is a complex physiological process that requires precise coordination between the central and peripheral tissues. Methods: In this study, tilapia fasted for 24 h was chosen to establish a hunger model to study the mechanism of homeostasis recovery under the joint regulation of the central nervous system (CNS) and peripheral tissues. Results: The gastric and intestinal contents of tilapia were predominantly depleted after a fasting period of 9 h and 24 h, respectively. The serum glucose level significantly decreased at the 9-h and 24-h fasting, respectively, and the glucokinase-dependent glucosensing mechanism in the liver was identified as well as the significant activation of phospho-AMPK. However, fasting for 24 h did not activate glucosensing mechanisms and AMPK signaling pathways in the hypothalamus. On the other hand, significant reductions were observed in the mRNA levels of the lipid synthesis-related genes fas and accα, and the serum triglyceride levels as well. The mRNA levels of npy, agrp, pomc, and cart in the hypothalamus fluctuated during the fasting period without significant differences. With in situ hybridization npy signals upregulated in the ventral zone of posterior periventricular nucleus after 24-h fasting, pomc signals enhanced in the lateral tuberal nucleus. Based on the serum metabolomic analysis, the levels of branched-chain amino acids, butyrate, and short-chain acylcarnitine decreased, while those of medium- and long-chain acylcarnitine increased. Conclusion: Fasting for 24 h resulted in changes in npy and pomc signals within the hypothalamus and triggered the glucosensing mechanism in the liver of tilapia. This study is beneficial for elucidating the response of neuropeptides in the CNS to the changes of nutritional factors when hungry.