[The influence of the light stimulus on VIP mRNA in VIP containing neurons of the rat suprachiasmatic nucleus].

In this study, an in situ hybridization technique combined with computed image analysis was performed to examine whether or not synthesis of vasoactive intestinal peptide (VIP) was influenced by a light stimulus from the retina and diurnal changes of messenger RNA (mRNA) of VIP in the rat suprachiasmatic nucleus (SCN) were measured. The amount of mRNA was largest at 2:00 am, second largest at 20:00 pm during the dark phase and smallest at 14:00 pm during the light phase. We also confirmed the onset of fluctuation of mRNA preceding the diurnal variation of the content of the VIP-like immunoreactivity established by semiquantitative immunocytochemistry and this fluctuation was abolished under constant dark conditions. The present finding strongly suggested that light stimulus from the retina primarily influenced the transcription of VIP mRNA and induced diurnal variation of VIP synthesis.