Day-night differences in the contents of vasoactive intestinal peptide, gastrin-releasing peptide and Arg-vasopressin in the suprachiasmatic nucleus of rat pups during postnatal development.

To investigate the developmental features of peptide levels in the suprachiasmatic nucleus (SCN), the contents of vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP) and Arg-vasopressin (AVP) were measured in punched-out SCN tissue from rat pups on postnatal days (PD) 4, 15 and 20 using a specific enzyme immunoassay. The VIP content was high at night, and the day-night difference was largest at PD4 throughout the developmental stage. GRP and AVP contents increased following the maturation. GRP levels were higher during the dark than the light period from PD4 to PD20. Subjective day-night differences were also observed in blinded pups. Our results indicate that VIP, GRP and AVP in the SCN already show a diurnal rhythm in the SCN during the nursing period.