ASYMMETRICAL EFFECTS OF THE UNILATERAL IMPLANT OF PILOCARPINE ON THE PREOPTIC-ANTERIOR HYPOTHALAMIC AREA ON SPONTANEOUS OVULATION OF THE ADULT-RAT

The effects on ovulation at the next estrus after unilaterally implant ing pilocarpine in the preoptic-anterior hypothalamic area (POA-AHA) o f rats on each day of the estrous cycle were analyzed. Implantation on the left side of POA-ARA on the day of estrus blocked ovulation in al l animals, whereas implantation on the right side did not (0/5 vs. 4/4 , P<0.05). Implantation on diestrus 1 or 2 on either side of the POA-A HA blocked ovulation. Implantation on the right side of the POA-AHA at the day of proestrus blocked ovulation (1/6 animals ovulated), while 10/12 with pilocarpine on the left side ovulated (P<0.05). The adminis tration of 3.7 mu g of GnRH at 13:00 h on the expected day of proestru s induced ovulation in 36/42 treated animals. In rats with a pilocarpi ne implant, the injection of estradiol benzoate on diestrus 2 restored ovulation only in those animals with the pilocarpine implant placed i n the left side of the POA-ARA, performed on the day of estrus. The re sults support the previous statements that in the adult rat POA-AHA, t he cholinergic mechanism regulating preovulatory GnRH release, is late ralized. In addition, at the beginning of the estrous phase, the POA-A HA-cholinergic system needs to remain undisturbed for normal ovulation to take place at the next estrus.