Involvement of a direct neural mechanism in the control of gonadal functions.

Much time has been devoted to study of the hypothalamo-hypophyseal-gonadal axis. However, there is now evidence of a complementary control mechanism for the gonads, namely a pituitary-independent, direct neural link that exists between the central nervous system and the gonads. We investigated whether mediobasal temporal lobe structures could control gonadal functions by a purely neural mechanism or whether they acted through the classical hypothalamo-hypophyseal system. Right- or left-sided deafferentiation of the temporal lobe was combined with right- or left-sided hemicastration in adult and prepubertal male and female rats. In adult females right-sided deafferentiation, regardless of the side of hemiovariectomy significantly reduced the extent of compensatory ovarian hypertrophy. Similar lesions on the left side did not interfere with the usual compensatory ovarian growth. This difference in compensatory hypertrophy between right- and left-sided lesioned rats was observed even in the face of a significant drop in serum LH concentrations in both groups. In pre- and postpubertal females temporal lobe lesion in either side was unable to alter compensatory hypertrophy or serum LH or progesterone concentrations. In adult male rats only left-sided deafferentiation combined with left orchidectomy resulted in decreased T production, while in prepubertal male rats, only right-sided brain surgery plus left orchidectomy resulted in a significant decrease in basal testosterone secretion of the remaining testis. These findings indicate that mediobasal temporolimbic structures are involved in the neural control of gonadal functions. It appears that this lateralized mechanism is age- and sex-dependent.