Acute heat stress up-regulates neuropeptide Y precursor mRNA expression and alters brain and plasma concentrations of free amino acids in chicks

Heat stress causes an increase in body temperature and reduced food intake in chickens. Several neuropeptides and amino acids play a vital role in the regulation of food intake. However, the responses of neuropeptides and amino acids to heat-stress-induced food-intake regulation are poorly understood. In the current study, the hypothalamic mRNA expression of some neuropeptides related to food intake and the content of free amino acids in the brain and plasma was examined in 14-day-old chicks exposed to a high ambient temperature (HT; 40 ± 1 °C for 2 or 5 h) or to a control thermoneutral temperature (CT; 30 ± 1 °C). HT significantly increased rectal temperature and plasma corticosterone level and suppressed food intake. HT also increased the expression of neuropeptide Y (NPY) and agouti-signaling protein (ASIP) precursor mRNA, while no change was observed in pro-opiomelanocortin, cholecystokinin, ghrelin, or corticotropin-releasing hormone precursor mRNA. It was further found that the diencephalic content of free amino acids – namely, tryptophan, leucine, isoleucine, valine and serine – was significantly higher in HT chicks with some alterations in their plasma amino acids in comparison with CT chicks. The induction of NPY and ASIP expression and the alteration of some free amino acids during HT suggest that these changes can be the results or causes the suppression of food intake.