Influences of retrochiasmatic surgical transection on mating and serum ovarian hormone levels in the androgenized rat

In previous studies female rats were shown to increase mating after retrochiasmatic surgical transections prior to ovariectomy and after ovariectomy with and without hormone replacement. This study was designed to determine if retrochiasmatic surgical transections (FC) or sham-FC would produce similar increased mating in androgenized rats. Four of thirty-one (13%) testosterone propionate (TP)-treated rats showed minimal mating without surgery, and 27 (87%) failed to mate. Mating occurred up to 30 days following FC, whereas temporary mating resulting from sham-FC had declined to presurgical levels by 30 days after surgery. Mating after ovariectomy was not facilitated by daily injections of 0.2μg of estradiol cypionate, but was facilitated after daily injections of 1.6 μg. TP-treated rats with FC showed more mating after 1.6 μg estradiol cypionate injections than the sham-FC and non-TP-treated controls. Serum estradiol-17β and progesterone levels at autopsy did not differ between TP-treated rats mating without surgery and those failing to mate. TP-treated rats with sham-FC surgery showed levels of estradiol-17β and progesterone similar to those of nonsurgical TP-treated rats and were combined into a single control group for comparison to the FC group. Serum levels of estradiol-17β did not differ between the control and FC group, whereas serum progesterone levels were decreased in the FC group. Serum levels of estradiol-17β and progesterone in TP-treated rats without FC were similar to baseline levels observed in this colony during the 4-day estrous cycle, but were less than peak levels observed at similar times on proestrus and diestrus Day 2, respectively. One possible effect of early androgen treatment would be to initiate a sustained inhibitory input to the mediobasal hypothalamus from the septal-preoptic area regions, thus causing deficits in mating. The lordosis responding in the androgenized rat after surgical interruption of the preoptic area-anterior hypothalamic continuum suggests that an inhibitory input was disrupted. It was further suggested that the higher mating observed in the FC group compared to the sham-FC group was not the result of higher ovarian hormone levels.