Vasoactive intestinal polypeptide precursor mRNA exhibits diurnal variation in the rat suprachiasmatic nuclei.

Vasoactive intestinal polypeptide (VIP), which is synthesized in the ventrolateral subdivision of the suprachiasmatic nucleus (SCN), the circadian pacemaker in the mammalian brain, is suggested to mediate information on environmental light. Diurnal rhythms of VIP precursor mRNA in the SCN was determined in the present study by Northern blot hybridization with an antisense RNA probe in rats kept under light-dark conditions. VIP precursor mRNA was found most abundant during the dark phase, as light exposure suppressed VIP precursor mRNA. This suppression, however, did not last throughout the light phase and VIP precursor mRNA returned to the level before the onset of light after 8 h in light, suggesting that VIP mRNA responds to photic cues and not to light per se. This is in contrast to the sustained suppression of VIP peptide level in the SCN. It indicates that VIP mRNA is acting at a stage of light information processing upstream to VIP peptide in the circadian pacemaker.