抄録
Orexins (A and B) expressed in specific neurons of the lateral hypothalamic area, have been implicated in feeding and sleep regulation. To determine the mechanism of age-associated decrease in appetite and food intake, the stimulatory effect of intracerebroventricular administration of orexin-A on food intake was compared between young and old male rats. Different doses (0 = vehicle, 0.25, 1, and 3 nmol) of orexin-A were injected into the left lateral ventricle and food consumption during 1, 2, and 4 h after injection was measured. Orexin-A stimulated food intake in a dose-dependent manner in young rats. However, no effects were observed at any dose in old rats. To examine the mechanism, young and old rats, the hypothalamus was removed and the protein levels of orexin receptors (OX1R = a specific receptor for orexin-A, OX2R = a receptor for both orexin-A and -B) were determined by Western blotting. The protein level of OX1R in the hypothalamus of old rats was significantly lower than that of young rats, although the protein level of OX2R was rather higher in old rats. The present result indicates that the decline in appetite and food intake in old rats was caused by decreased function of orexin system. The decrease in protein level of OX1R in the hypothalamus could be responsible for the lack of stimulatory effect of orexin-A on food intake in old rats. [Jpn J Physiol 54 Suppl:S226 (2004)]
