DIURNAL OSCILLATION IN VASOACTIVE-INTESTINAL-PEPTIDE GENE-EXPRESSION INDEPENDENT OF ENVIRONMENTAL LIGHT ENTRAINING

Vasoactive intestinal peptide (VIP) is a neuromodulator and secretagog ue for neuronal survival factors. Moreover, in the suprachiasmatic nuc leus (SCN) of mature animals, where the circadian clock resides, day-n ight cycles are paralleled by rhythmical alteration in the levels of t he mRNA encoding VIP. We now show, for the first time, that diurnal os cillation in VIP mRNA occurred in animals reared in the dark and also preceded eye opening. Thus, by Northern blot hybridization elevated le vels of VIP mRNA were measured at night time as compared to day time. Furthermore, diurnal oscillation in VIP mRNA were more pronounced in r ats reared in the dark. These observations suggested an endogenous as well as exogenous (environmental) control of VIP gene expression in th e SCN and implicated VIP as an integral part of the circadian clock.