CIRCADIAN-RHYTHM OF ARG-VASOPRESSIN CONTENTS IN THE SUPRACHIASMATIC NUCLEUS IN RELATION TO CORTICOSTERONE

Circadian rhythms of locomotor activity and adrenal glucocorticoid are controlled by the suprachiasmatic nucleus (SCN), the center of a biol ogical clock, in mammals. Arg-vasopressin (AVP) contents in the SCN pl ay a role in endogenous circadian rhythm during the absence of time cu es. The AVP-containing neurons in the SCN are considered to transmit a circadian signal to the other parts of the brain. The circadian rhyth ms of AVP in the SCN in relation to the plasma corticosterone and loco motor activity were investigated. Under the light-dark cycle, plasma c orticosterone levels were reciprocally correlated with the AVP content in the SCN. Under free-running conditions with constant dim light. AV P rhythms were reciprocally synchronized with the locomotor activity. The correlation of AVP with plasma corticosterone is different at diff erent times of the day both under the LD cycle and constant dim light. Dexamethasone (i.p., 0.1 mg/100) increased the AVP contents, and this tendency was significantly greater during the dark period. These resu lts indicate that corticosterone in the blood may regulate the circadi an rhythm through AVP variation in the SCN. (C) 1998 Elsevier Science B.V. All rights reserved.