PREFEEDING INCREASE IN PARAVENTRICULAR NE RELEASE IS REGULATED BY A FEEDING-ASSOCIATED RHYTHM IN RATS

Extracellular norepinephrine (NE) in the vicinity of the paraventricul ar nucleus was continuously measured over 24 h by means of in vivo mic rodialysis in rats under restricted daily feeding and ad libitum feedi ng. A 24-h rhythm in plasma corticosterone was monitored in separate r ats under identical conditions. Under ad libitum feeding, the paravent ricular NE showed a 24-h rhythm with lower levels in the light period and higher levels in the dark period. The temporal pattern was not aff ected by food deprivation for 3 days. The circadian peak of paraventri cular NE lagged slightly behind that of plasma corticosterone under ad libitum feeding. On the other hand, when rats were fed for 2 h at a f ixed time of day for 3 wk, the NE rhythm was changed and showed a majo r peak just before daily meals. To examine the nature of the prefeedin g NE peak, a 24-hour variation of paraventricular NE was measured in r ats under food deprivation that had been subjected to restricted daily feeding for 3 wk and subsequently to ad libitum feeding for 7 days. T he paraventricular NE was high around the time when meal had been supp lied under restricted daily feeding and low in the dark period. Simila r changes were observed in plasma corticosterone. The findings indicat e that the prefeeding increase in the paraventricular NE release is re gulated by a feeding-associated circadian rhythm manifest in rats unde r restricted daily feeding.