Immunohistological Assessment of Male Germ Cell Apoptosis, and Histological Observation of Seminiferous Tubules and Epididymides According to Temporal Testicular Regulation in the Large Japanese Field Mouse <i>(Apodemus speciosus )</i>

The large Japanese field mouse (Apodemus speciosus) is a seasonal breeder, and its spermatogenic activity changes throughout the year.In some mammal species, testicular regression results from increased apoptosis of the male germ cell.However, no study has investigated the association between apoptosis and temporal testicular regression using closely classified spermatogenic phases in seasonal breeders.Using terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining, we immunohistochemically investigated male germ cell apoptosis and its relation to temporal testicular regulation and circannual cycles of activation and regression in this species.Furthermore, we classified spermatogenic activity into 9 phases (pre-increase, early-increasing, mid-increasing, late-increasing, peak, early-decreasing, mid-decreasing, late-decreasing, and post-decreasing) using testicular weight and the histological observation of spermatogenesis, and investigated the morphological temporal changes of seminiferous tubules and epididymides.Germ cell apoptosis occurred at low levels around the peak phase, but was observed at high rates during the pre-increase, mid to late-decreasing, and post-decreasing phases.It should be noted that relatively many apoptotic cells were observed even in the early to mid-increasing phases.The primary type of apoptotic germ cell observed during all phases (except the mid-decreasing phase) was the spermatocyte.It is considered that apoptosis would be the main cause of cell loss, and live cell desquamation would accelerate testicular regression.The histological description of seminiferous tubules and epididymides will support future testicular histological evaluations of A. speciosus and provide guidelines for comparison with other species.