Ingestion of non-caloric liquid diet is sufficient to restore plasma corticosterone level, but not to induce the hypothalamic c-Fos expression in food-deprived rats

Male Sprague-Dawley rats were subjected to four different conditions; free fed control (FC), 48 h of food deprivation (FD), 1 h of refeeding with chow (RF/CW) or with a non-caloric liquid diet following FD (RF/NC) and then sacrificed for c-Fos immunohistochemistry in the hypothalamic paraventricular nucleus (PVN) and the nucleus tractus of solitarius (NTS). Plasma corticosterone level and the postmortem weight of gastric contents were measured. Plasma level of corticosterone significantly increased during FD, and then decreased within 1 h after ad libitum access to chow or non-caloric liquid diet. c-Fos-ir in the brain regions was not changed by FD; however, significantly increased by chow refeeding, but not by non-caloric diet. Chow, but not the non-caloric, refeeding significantly increased gastric contents. Results suggest that caloric load and/or gastric distension may require for the postprandial activation of neurons in the PVN and NTS, but ingestion of non-caloric palatable mixture may be sufficient to normalize the fasting-induced increase of plasma corticosterone. In conclusion, feeding-related changes in the HPA axis activity may not be related with meal-induced c-Fos expression in the PVN and NTS.