DEVELOPMENTAL-CHANGES IN THE GONADOTROPIN-RELEASING-HORMONE NEURON OFTHE FEMALE RABBIT - EFFECTS OF TAMOXIFEN CITRATE AND PREGNANT MARE SERUM GONADOTROPIN

Developmental changes in immunostained gonadotropin releasing hormone neurons were demonstrated in female rabbits assigned to the following treatment groups: (i) tamoxifen citrate, 10 mg.kg(-1).day(-1), in sesa me seed oil (vehicle) (n = 24) or (ii) vehicle alone (control, n = 24) for 108 days; and (iii) 50 IU of pregnant mare serum gonadotropin on postnatal days 22 and 25 (n = 24) or vehicle on nontreatment days. Tre atments had no effect on the total number of immunostained cells, but there was a significant (p = 0.0160) developmental shift from cells wi th smooth processes to rough. Group comparisons revealed that there wa s a significant (p < 0.001) age-related increase in the number of roug h cells in pregnant mare serum treated rabbits between days 25 and 75, indicating an advancement in the shift from smooth to rough cells. Pl asma gonadotropin levels, ovarian follicular development, and the deve lopmental shift from smooth to rough cells were markedly suppressed by tamoxifen treatment compared with rabbits of the control group, while no difference in estradiol levels were found. Our results suggest tha t a developmental shift in gonadotropin releasing hormone cell morphol ogy from smooth to rough precedes sexual maturity in the female rabbit .