Lack of circadian patterns in vasoactive intestinal polypeptide release and variability in vasopressin release in vole suprachiasmatic nuclei in vitro

Organotypic hypothalamic cultures of neonatal rats comprising the suprachia smatic nuclei (SCN) produce stable 20 h release patterns of vasoactive inte stinal polypeptide (VIP) and arginine-vasopressin (AVP). Compared with rats , voles show variably expressed circadian activity patterns. In this study we measured neuropeptidergic release patterns in organotypic SCN cultures o f neonatal common voles (Microtus arvalis, n = 6). Slices were prepared at postnatal day 6. After 14 days of incubation, 2 h samples of medium were co llected during 50 h. None of the vole SCN slices showed a circadian modulat ion in VIP release, Peaks in AVP occurred, 20 h apart from each other, in f our of six vole SCN slices. These findings contrast with the concurrent rel ease patterns of VIP and AVP in rat SCN slices. The results suggest an inde pendent role of both neuropeptides in the oscillatory output pathways of th e circadian pacemaker in the common vole. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.