Expression of vasoactive intestinal peptide mRNA in the suprachiasmatic nuclei of the circadian tau mutant hamster.

The tau mutation of the Syrian hamster is one of only two mutations currently known to affect the circadian system in mammals. In order to investigate the molecular mechanisms associated with this mutation, we have compared the level of expression of the mRNA for vasoactive intestinal peptide (VIP) in the suprachiasmatic nuclei (SCN) and cerebral cortex of homozygous tau mutant and wild-type animals using in situ hybridization histochemistry. We observed no significant circadian variation in this message within the SCN, cingulate cortex or parietal cortex of either genotype. Comparison between genotypes indicated a significantly higher signal for VIP mRNA in the SCN of tau animals. This phenotypic effect within the SCN raises the possibility that some of the circadian consequences of the tau mutation are associated with an increased expression of the VIP gene.