SEASONAL TESTICULAR FUNCTION IN MALE RHESUS-MONKEYS

Some studies report seasonal patterns of testicular function in male r hesus monkeys even when they are housed away from females, while other s suggest that exposure to sexually active females is essential for ma le seasonality. We conducted the present experiment (1) to test claims that seasonal testicular activation occurs in the absence of females and (2) to determine whether regular exposure to and copulation with f emales enhances, or is without effect upon, seasonal increases in test icular function. We studied two groups of male monkeys housed in a col ony room containing no females. Males in the Female Exposure group (n = 7) were paired twice weekly with estradiol-implanted females and cop ulated vigorously. Males in the second group (n = 7) were placed in th e same test chamber (at least 16 h after it had been scrubbed with dis infectant) but were never exposed to females. Serum testosterone level s and testis volume were monitored for both groups. Each group display ed a seasonal pattern of testosterone and of testis volume comparable in timing and magnitude to seasonal increases previously reported in g roup-housed males, but the two groups did not differ from each other. Our findings confirm that seasonal changes in testosterone and testis size occur in the absence of sexual interaction and demonstrate that m oderate levels of sexual activity do not enhance this response. (C) 19 96 Academic Press, Inc.