Seasonal morphological variations and age-related changes of the seminal vesicle of viscacha (Lagostomus maximus maximus): an ultrastructural and immunohistochemical study.

The viscacha is a seasonal rodent that exhibit an annual reproductive cycle with periods of maximum reproductive activity and gonadal regression. We studied seasonal variations in the morphology and cellular population of the seminal vesicles (SVs) during both periods and in impuber animals. Seminal vesicles were studied by light and electronic microscopy. Measurements of epithelial height, nuclear diameter, luminal diameter, and muscular layer were performed. Also, we studied the distribution of androgen receptors (AR) in this gland during the reproductive cycle and in impuber animal. During gonadal regression, principal and clear cells showed signs of reduced functional activity. These were characterized by an epithelium of smaller height, irregular nuclei, and cytoplasm with few organelles, dilated cisterns, and glycogen granules. In impuber animals, the principal cells showed large nuclei with chromatin lax and cytoplasm with small mitochondria, poorly developed Golgi apparatus, and granules of glycogen. On the other hand, the cells exhibited seasonal variations in the distribution and percentage of immunolabeled cells to AR throughout the annual reproductive cycle. During the gonadal regression period, glandular mucosa exhibited numerous epithelial cells with intense nuclear staining. However, fibromuscular stromal cells were weakly positive for AR in contrast to what was observed during the activity period. Considering that testosterone values are lower in adult animals during the period of gonadal regression and in impuber animals, our immunohistochemical results show a significant correlation with the percentage of AR-immunopositive cells. In conclusion, these results demonstrate that the structure of the SVs changes in the activity period of viscacha, probably because of elevated levels of testosterone leading to an increase in the secretory activity of epithelial cells.