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 suprachiasmatic nuclei (SCN) produce stable 20 h release patterns of vasoactive intestinal 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 of 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 collected during 50 h. None of the vole SCN slices showed a circadian modulation in VIP release. Peaks in AVP occurred, 20 h apart from each other, in four of six vole SCN slices. These findings contrast with the concurrent release patterns of VIP and AVP in rat SCN slices. The results suggest an independent role of both neuropeptides in the oscillatory output pathways of the circadian pacemaker in the common vole.