Not only vasopressin, but also the intracellular messenger protein kinase Calpha in the suprachiasmatic nucleus correlates with expression of circadian rhythmicity in voles.

The suprachiasmatic nucleus (SCN) is the locus of the main pacemaker for circadian behavioral rhythms. In common voles, variation in circadian behavioral rhythmicity correlates with vasopressin (AVP) immunoreactive cells in the SCN. Here we studied the immunostaining of four AVP linked Ca(2+)-dependent protein kinase C (PKC) isoforms (PKCalpha, PKCbeta1, PKCbeta2, and PKCgamma) at the beginning of the light period, and conclude that PKCalpha is highly expressed in the vole SCN compared to the other isozymes. Voles, characterized as strongly circadian rhythmic showed circadian variation in numbers of PKCalpha immunoreactive SCN neurons, while voles with weak or no circadian rhythmicity did not reveal such a circadian profile. PKCalpha immunoreactivity in acute SCN slices that were treated with a physiological dose of AVP was significantly lowered when compared with control slices. The intracellular messenger PKCalpha may reflect variation in locomotor behavior via the AVP system in the vole SCN. This system could play a key role in the vole SCN by mediating output of its circadian clock.