EFFECT OF MEDIAL ZONA INCERTA LESIONS ON THE OVULATORY SURGE OF GONADOTROPINS AND PROLACTIN IN THE RAT

Bilateral electrolytic lesions of the incertohypothalamic A 1 3 dopamine (DA) system were made on the morning of proestrus in female rats with regular estrous cycles under ether anesthesia. Hourly blood samples were withdrawn, via a jugular catheter from conscious, freely moving rats, between 14.00 h and 18.00 h on the afternoon of proestrus. Plasma LH, FSH and prolactin levels were determined by RIA. The preovulatory surges of LH and prolactin were blocked in animals in which the A13 DA nucleus was destroyed by more than 70%. Levels of FSH were not significantly different from those of control or sham-lesioned groups. Lesions that were dorsal, ventral or caudal to the A13 DA systems did not affect the preovulatory surges of LH and prolactin whereas anterior lesions caused variable changes in the level of all three hormones. These data suggest that the A13 DA region may have a role in the control of the preovulatory surges of LH and prolactin.