[Effects of extrahypothalamic brain lesions on testicular function in rats--with special emphasis on asymmetry]

The aim of our studies was to investigate the involvement of extrahypothalamic brain structures in the control of testicular functions with special emphasis on the effect of right- and left-sided structures.

We performed lesion of the insular cortex, the amygdala, interrupted part of nerve fibers to and from the insular cortex, and cut the major commissural pathway of the brain the corpus callosum in adult male rats and studied the effect of the interventions on testicular steroidogenesis, serum testosterone and gonadotrop hormone concentrations.

Following lesion of the insular cortex on the right side serum testosterone level and steroidogenesis of the testes decreased (in the case of the left testis the difference was significant). Similar lesion on the left side did not change the parameters studied. Both right- and left-sided lesion induced a significant increase in serum LH concentration. The effect was more pronounced after right-sided lesion. Interruption of nerve fibers above the amygdala by a paramedian sagittal knife cut on the right or on the left side resulted in opposite effect on testicular steroidogenesis: right-sided intervention increased while left-sided one reduced testosterone secretion. Only left-sided cut influenced (decreased) serum testosterone level. There was no changes in LH concentration. Both right- and left-sided lesion of the amygdala induced a significant decrease in basal testosterone secretion in vitro of both testes and in serum testosterone level. However, serum LH concentration decreased only after left-sided surgery. Interruption of the corpus callosum in animals with left-sided orchidectomy induced a significant rise in steroidogenesis of the remaining (right) testis. Both sham surgery and callosotomy combined with left orchidectomy resulted in a significant increase in serum FSH level.

Results of our studies suggest that extrahypothalamic brain structures and interventions influence endocrine functions of the testis through the hypothalamo-hypophyseal-testicular axis and by a direct neural route. Certain components of the regulatory system exhibit functional asymmetry.