Effects of the unilateral implant of haloperidol at the preoptic-anterior hypothalamic area, on ovulation.

In order to analyse whether the participation of the dopaminergic system of the preoptic-anterior hypothalamic area (POA-AHA) in the regulation of ovulation is asymmetric and varies during the estrous cycle of the rat, as it occurs with the cholinergic system, the effects of a unilateral implant of haloperidol were studied. Cyclic fourth-day rats with a permanent cannula directed to the right or left side of the POA-AHA, at 13:00 h of estrous (E), diestrous 1 or 2 (D1, D2) or proestrus (P), received an implant of haloperidol (10.0±3.0 μg) or cholesterol (8.0±2.0 μg). The animals were killed at the morning of the next expected day of estrous. In comparison with cholesterolimplanted animals, the ovulation rate was reduced by haloperidol implantation made on E or D1 on either side of POA-AHA (Cholesterol: 26/50vs Haloperidol: 1/35,P<0.05). The implantation of haloperidol on D2 or P did not affect ovulation (Cholesterol: 30/37vs Haloperidol: 23/34, ns). The injection of gonadotropin-releasing hormone (3.7 μg/kg) sc on the afternoon of P to rats with an implant of haloperidol made on E or D1 on either side of POA-AHA, restored ovulation (19/22vs 1/35,P<0.01). The injection of estradiol benzoate (10 μg) at 13:00 h on D2, to D1-haloperidol-implanted rats restored ovulation. The same treatment to E-haloperidol-implanted animals restored ovulation when the haloperidol was placed into the left side of POA-AHA (5/6), and it was ineffective when haloperidol was in the right side (0/8). These results suggest that the participation of the POA-AHA-dopaminergic system on the neuroendocrine mechanisms controlling the release of GnRH on the afternoon of proestrus and ovulation, varies during the estrous cycle, and is necessary at the beginning of the estrous cycle for normal ovulation. The positive feedback of estrogens on D2 needs the integrity of the right side of POA-AHA.