Arg-vasopressin content in the suprachiasmatic nucleus of rat pups: circadian rhythm and its development

Abstract

To investigate the development of Arg-vasopressin (AVP) content and its diurnal rhythm in the suprachiasmatic nucleus (SCN), AVP was measured by enzyme immunoassay in the rat pup SCN punched out from tissue slices obtained at postnatal day (PD) 1, 5, 10, 12 and 20 from animals maintained under a light-dark cycle (LD). The AVP levels, measured at a restricted time of day, increased from PD1 reaching the adult level at PD10–12. Diurnal rhythm similar to that in adults was evident at PD10–12 under the LD conditions used. The peak value of AVP was observed at the earlier light period, and its trough occurred at the end of the light period. The circadian rhythm remained for 7 days under constant dark (DD) or constant light (LL) conditions. These results indicate that the AVP, one of the output signals from the SCN, starts to oscillate after PD10–12, and shows a free-running rhythm during the nursing period.