Sperm structural and motility changes during aging in the Brown Norway rat

The Brown Norway rat provides a useful model to study aging of the male rep roductive tract because of the selective age-dependent pathological changes that are found in the testis, epididymis, and prostate. In the testis, the re is a clear age-dependent decrease in both steroidogenesis and spermatoge nesis. In the epididymis, some striking segment-specific changes occur at t he histological and biochemical levels prior to the major loss of spermatog enesis. We hypothesized that formation of spermatozoa in the testis and mat uration of spermatozoa in the epididymis (ie, acquisition of motility and l oss of the cytoplasmic droplet) may be altered during aging. Changes in the morphology of spermatozoa were assessed by light and electron microscopy. Using computer-assisted sperm analysis, the motility parameters of spermato zoa obtained from the caput and cauda epididymidis of young and old Brown N orway rats were compared. In old animals, we also compared the motility of spermatozoa from epididymides adjacent to regressed testes with those from epididymides adjacent to nonregressed testes. There was a marked increase w ith age in the number of spermatozoa with abnormal flagellar midpieces; the nature of these defects did not change with age. In caput epididymidis, th e percentage of motile sperm was similar in young and old rats. In contrast , the percentage of motile spermatozoa was significantly decreased in cauda epididymidis of old rats; spermatozoa from the regressed testis side had a ltered motility characteristics. Furthermore, in the cauda epididymidis on the regressed testis side of aged Brown Norway rats, the proportion of sper matozoa that retained their cytoplasmic droplet was markedly elevated. Some of these effects are likely due to changes taking place in spermatozoa dur ing the process of spermatogenesis in the testis (eg, formation of the flag ellum), whereas others could occur during sperm maturation in the epididymi s (eg, acquisition of motility). The multiple effects of aging on sperm mor phology, the acquisition of motility, and the shedding of the cytoplasmic d roplet clearly indicate that the quality of spermatozoa is affected by agin g.