Circadian regulation of per repeat mRNA in the suprachiasmatic nucleus of rat brain.

We have recently reported fluctuations in the expression of the period repeat sequence (pp2.5) during light-dark cycles in the suprachiasmatic nucleus (SCN) of rat [Neurosci. Lett., 122 (1991) 113-116]. Presently, we performed in situ hybridization which shows that the fluctuation of pp2.5 expression continues during constant darkness conditions in the SCN of rat. The light exposure during subjective night but not subjective day triggered its elevated expression in a time-dependent manner which is parallel to that of c-fos expression. The results suggest the involvement of pp2.5 in the entrainment pathway of the circadian rhythm in rodent SCN.