Morphometric Examination for Development of Reproductive Organs in Male Cynomolgus Monkeys

We previously reported on a histological classification of cynomolgus monkey testis into six grades (1, immature; 2, prepuberty; 3, onset of puberty; 4, puberty; 5, early adult; 6, adult) based on spermatogenesis development. In this investigation, the accessory reproductive organs from the same animals underwent histomorphometric examination, in addition to being examined histologically and weighed, to evaluate relationships between these parameters and the six grades. Seminiferous tubule diameter increased corresponding to the testicular maturity grade and was notably increased at grade 6. Beginning from grade 3, increases in the areas of the ductus epididymis were noted, and reserved sperm was visible in the lumen. In the prostate, the glandular lumen area per unit area showed an increase beginning from grade 3 but no clear differences between grades 4 and 6; advanced development of epithelial height was observed at grade 6. In the seminal vesicle, development of the epithelial cell layer was markedly increased at grade 6. It was concluded that development of the male accessory reproductive organs began after reserved sperm was observed in the lumen of the ductus epididymis (grade 3) and that these organs were developed notably when the testis reached sexual maturity (grade 6).