The temporal changes in epididymal sperm numbers during the month after sexual contact were examined in 80 adult albino rats. The comparably sexually experienced males in 6 experimental groups were allowed 3 ejaculations with ovariectomized females in which oestrus was induced by hormone injections. Epididymides were removed from the experimental males 1 h, 1 day, 2 days, 3 days, 7 days or 30 days later. Control males were sexually inexperienced or sexually experienced and living with females. Epididymal sperm counts revealed a pattern that resembled an inverted V-shaped function with a peak at 48 h after copulation. We suggest that sexual activity provokes an acute attenuation of sperm disposal within the epididymis with the result that more spermatozoa are available for ejaculation during sexually active times.

The juvenile stage of ontogeny is often characterized as a time of inactivity and quiescence for the immature reproductive system. The principle social behaviour by juveniles of many mammalian species is a rough-and-tumble activity known as play-fighting. An experiment is reported in which play-fighting by male rats was observed after various manipulations of gonadal steroids. Rats were housed in groups and castrated either on day 1 or day 10, times which are respectively during and after the sensitive period for androgen-induced organization of neural tissues in rats. Animals were injected with either 40 micrograms testosterone propionate or vehicle between 21 and 45 days of age, and play-fighting with unoperated, unfamiliar rats was examined. Castration on days 1 and 10 suppressed play-fighting. The behaviours remained suppressed in rats castrated on day 1 and injected with testosterone propionate, but testosterone propionate restored play-fighting to near-normal levels until 35 days of age in rats castrated on day 10. Moreover, gonadally intact juvenile males exposed to the androgen antagonist flutamide play-fought less than intact control males, although their social activity increased appreciably after day 35. It is concluded that the juvenile is not experiencing endocrine quiescence. Behavioural and physiological data suggest a reproductive system which is active, although differently from that in the adult. Hypersensitivity to testosterone and surges of gonadotrophin-releasing factors and LH at 35 days of age may be the events responsible for changes in play-fighting resulting from manipulations of gonadal steroids in juvenile rats.

Epididymal sperm quantity and quality were examined throughout the reproductive lifespan of sexually experienced and inexperienced rats. Males were housed with gonadally intact or ovariectomized females for 2 weeks to 1 year, and epididymides were analysed 1 week to 9 months after the females were removed. Results for the virgin males suggest a peak in sperm numbers at 6 months of age followed by a gradual decline and then notable decrements in sperm numbers and motility by 24 months of age. The same general pattern emerged for sexually experienced males, with two exceptions. There was a chronic increase of sperm numbers relative to those of virgin males at every age examined, and the decline in spermatozoa with ageing was slowed by previous sexual contact. The implications of these data for the ontogeny of fertility are not readily apparent because the epididymis remained reproductively functional throughout the lifespan. We do, however, suggest that epididymides are sensitive to experiential and hormonal changes during adulthood and, most important, the effects of these changes are maintained chronically and into old age.