Effects of unilateral castration on the hypothalamic structures involved in the regulation of gonadal function in rat

This study was undertaken to evaluate the effects of unilateral gonadectomy on the hypothalamic structures involved in the regulation of gonadal function in adult rats of both sexes. Unilateral gonadectomy was performed; 15 days later stereological parameters of cell activity of both the halves of hypothalamic preoptico-suprachiasmatic area (PO-SC) and arcuate nucleus (NA) were analyzed. Under the same experimental conditions the activities of the FSH and LH immunoreactive cells were analyzed separately in both the halves of the adenohypophysis. The results showed that in the rats of both sexes subjected to unilateral gonadectomy the mean diameter of cell nuclei of the contralateral half of PO-SC was significantly greater than that of the ipsilateral half. However, in the control intact or bilaterally gonadectomized rats, there were no significant differences in the values of the same parameter between two halves of PO-SC. On the other hand, neither in the unilaterally gonadectomized nor in the controls, the values of the mean diameter of NA cell nuclei differed significantly between the two halves of this structure. The FSH and LH pituitary cells behaved like NA cells. Therefore, since in the experimental animals compensatory function was developed, and since nervous signaling was different from the sides of the removed and intact gland, the present results suggest involvement of a pure nervous mechanism, besides hormonal control, in the regulation of the compensatory gonadal function. This mechanism seems to be functional in the rats of both sexes. These results also indicate that PO-SC is the anatomical structure involved in this regulation.