Gonadotropin-releasing hormone exhibits circadian rhythm in phase with arginine-vasopressin in co-cultures of the female rat preoptic area and suprachiasmatic nucleus

To determine whether the suprachiasmatic nucleus can drive a circadian rele ase of gonadotropin-releasing hormone (GnRH) in the preoptic area, we measu red the release of GnRH, arginine-vasopressin and vasoactive intestinal pol ypeptide (VIP) in cocultures of the preoptic area and the suprachiasmatic n ucleus at 2-h intervals over a period of 120 h. The release of GnRH in cocu ltures exhibited a significant circadian rhythm in the presence of oestroge n but not in the absence of oestrogen, The period of the GnRH circadian rhy thm was the same as that of the arginine-vasopressin circadian rhythm, and different from the VIP circadian rhythm in each coculture. Furthermore, the peak phase of the GnRH rhythm occurred at the time same as that of the arg inine-vasopressin rhythm in each coculture, However, the peak phase of the GnRH rhythm was not always the same as that of the VIP rhythm. Administrati on of arginine-vasopressin significantly increased GnRH release in single p reoptic area cultures in the presence of oestrogen, but VIP did not. The re sult suggests that, in cocultures of the suprachiasmatic nucleus and the pr eoptic area, arginine-vasopressin neurones drive the circadian release of G nRH in the presence of oestrogen. We suggest that arginine-vasopressin neur ones in the suprachiasmatic nucleus mediate the clock information to GnRH n eurones in vivo as well.