Kisspeptin (Kiss) neurons in the antero-periventricular region of the preoptic area (POA) are the major source of stimulatory input to the gonadrotropin-releasing hormone to trigger the preovulatory surge of the luteinizing hormone (LH). Alpha-1-adrenergic receptor antagonist (Prazosin, Praz) blocks the LH surge by the reduction of Kiss synthesis in the POA in a time-of-day dependent manner, suggesting a role for the biological clock. Here we evaluated the expression of clock genes in the POA and arcuate nucleus of ovariectomized estradiol-primed rats treated with (OVX+E Praz) or vehicle (OVX+E Veh) at 11 h and 13 h. Rats were decapitated at 12 h, 14 h, 16 h, 17 h and 18 h and brains were removed to punch out the POA and the arcuate nucleus for Bmal1 and Per1 mRNA measurement by real time-PCR. In the POA of OVX+E Veh rats, Bmal1 expression was higher at 14 h, when Per1 mRNA levels were lower. Conversely, when high levels of Per1 were found (at 18 h), Bmal1 expression was lower. This reflects the functioning of the auto-regulatory clock protein loop: dimmers of CLOCK-BMAL1 stimulate the transcription of Per1, 2 and 3 as well as Cry 1-6 genes, which, once translated, inhibit Clock and Bmal1 transcriptions. Praz treatment completely abolished this relationship, which suggests a disruption in the biological clock. In the arcuate nucleus, neither temporal nor Praz effects were found. These data point to a role of the CLOCK proteins in triggering LH surge through modulation of Kiss synthesis.

Financial support: FAPEMIG, FAPESP, PRPq-UFMG, CAPES