DIFFERENCES IN THE SENSITIVITY OF THE RIGHT AND LEFT SIDE OF THE PREOPTIC-ANTERIOR HYPOTHALAMIC AREA TO THE EFFECTS OF A UNILATERAL IMPLANTATION OF HALOPERIDOL, PERFORMED ON THE DAY OF ESTRUS, ON SPONTANEOUS OVULATION

There is evidence that the preoptic anterior hypothalamic area (POA-AH A) dopaminergic system modulates, in an asymmetric way, the neuroendoc rine events regulating ovulation. We analysed the possibility that on the day of oestrus, the sensitivity of the right and left side of the POA-AHA to haloperidol implantation is different. Unilateral implantat ion of a mixture of haloperidol: cholesterol on the right side of the POA-AHA blocked ovulation (0/8 vs 8/14 with cholesterol implant, ovula ted, p < 0.05). When the implants were made on the left side, there we re no differences between haloperidol-cholesterol and cholesterol-impl anted animals, (7/15 vs 5/8). Injection of gonadotropin releasing horm one (GnRH) on the afternoon of the expected day of proestrus restored ovulation (5/6 ovulated), while the administration of oestradiol benzo ate at 13.00 h on the second day of diestrus did not do so (0/4 ovulat ed). These results suggest that the dopaminergic system on the right s ide of the POA-AHA is more sensitive to haloperidol than the left one.