Daily profiles of arginine vasopressin mRNA in the suprachiasmatic, supraoptic and paraventricular nuclei of the rat hypothalamus under various photoperiods.

Daily rhythm of arginine vasopressin (AVP) mRNA levels in the suprachiasmatic nucleus (SCN) of rats maintained under a short, LD 8:16 photoperiod differed from that of rats maintained under a long, LD 16:8 photoperiod: under the short photoperiod the morning AVP rise occurred significantly later than under the long one. Daily profiles of AVP mRNA in the supraoptic and paraventricular nuclei were not rhythmic and AVP mRNA levels under LD 8:16 did not differ from those under LD 16:8. The data indicate that photoperiod affects selectively the clock driven AVP gene expression in the SCN.