Effect of ageing on the proliferation and apoptosis of testicular germ cells in the @entity329 XXXX .

@entity1603 @entity194 @entity329 @entity1167 @entity528
The cellular mechanisms implicated in the @entity194 of seminiferous epithelium in ageing are currently under debate, although recent reports suggest that apoptosis may be the primary mechanism implicated in aged germ cell loss. Other investigators have suggested that changes in spermatogonial proliferation are also involved. In the present work, the changes in proliferation and apoptosis in the seminiferous epithelium of aged (24 months) @entity329 were examined in concert and compared with those in young (6 months) animals. Proliferation of germ cells was studied by @entity1603 labelling and apoptosis was assessed by transmission electron microscopy and in situ TUNEL labelling. Aged animals showed a significant decrease in the numbers of total and proliferating spermatogonia plus preleptotene spermatocytes per unit volume and per testis and in the proliferative index (24.8 +/- 1.6%) compared with young animals (30.8 +/- 1.2%) (P < 0.05). The number of apoptotic spermatogonia plus spermatocytes per unit volume and the apoptotic index were significantly higher in aged animals (1.51 +/- 0.23% v. 0.77 +/- 0.04%; P < 0.05). Apoptosis was confirmed by morphological characteristics: condensation of the chromatin and nuclear fragmentation. In aged hamsters, @entity528 could be classified into several categories, showing an increase of apoptotic cells in tubular cross-sections characterized by @entity1167 in comparison with all other types. Spermatogonial proliferation was also diminished as seen in tubular cross-sections showing hypospermatogenesis, sloughing off of germ cells and @entity1167 . The results obtained in the present study suggest that the decrease in the proliferation of spermatogonia and the increase in apoptosis constitute two consecutive mechanisms correlated with the ageing of the seminiferous epithelium.
