[The central mechanism of feeding-associated circadian corticosterone rhythm in rats: analyses of paraventricular noradrenaline by in vivo microdialysis].

A prefeeding peak of plasma corticosterone level in rats under a periodic feeding schedule is controlled by a food-entrainable circadian rhythm, an oscillatory mechanism of which is located outside of the suprachiasmatic nucleus. A stimulatory role of the catecholaminergic neurons innervating the paraventricular nucleus (PVN), where the corticotropin releasing hormone (CRH) producing neurons are located, have been suggested in the expression of the hormone peak. A periodic feeding schedule with free-access to meal from 10 to 12 (14) hour was imposed on male Wistar rats for 2-3 weeks under the light-dark cycle. Prefeeding peaks of plasma corticosterone and wheel running activity that appear during a 3 day food deprivation after the periodic feeding schedule were suppressed by the intraventricular injection of 6-OHDA, a catecholamine deprivator. The release of endogenous noradrenaline in the vicinity of PVN was measured by means of in vivo microdialysis. A 24 hour variation of noradrenaline release was observed in rats under ad libitum feeding with a peak in the dark period. On the other hand, under periodic feeding noradrenaline release was significantly increased prior to daily meal, and decreased after meal intake. And the noradrenaline release was also enhanced during the time of previous meal feeding when food was deprived for 3 days after the periodic feeding schedule. The finding indicates that the central noradrenergic neurons innervating the PVN mediates the food-entrainable circadian oscillation to the hypothalamus-pituitary-adrenocortical axis as well as the locomotor activity.