Sexual behavior and testosterone in middle-aged male rats

Various components of sexual behavior were compared in middle-aged (13 months) and young adult (3 months) male rats to ascertain the nature of behavioral differences and the role of testosterone (T) in these differences. Behavioral procedures included: 1) tests of mating behavior; 2) tests of mounting behavior with genital anesthetization that focused on sexual arousal; 3) tests of spontaneous seminal emission that focused on ejaculatory mechanisms. In Exp 1, sexually experienced or inexperienced middle-aged males showed evidence of reduced sexual arousal, with the inexperienced middleaged group demonstrating the greatest reduction. The two middle- aged groups did not differ in plasma T levels, but both had levels significantly below those of the young group. In Exp 2, spontaneous seminal emission was found to occur more often in middle-aged retired breeders than in young sexually inexperienced males. In Exp 3, the dose-response relationship of behavior and T was evaluated in groups of castrated middle-aged and young males implanted with T-filled Silastic capsules of varying length. Before treatment, the middle-aged males evidenced lower sexual arousal (i.e. fewer positive tests and longer latency measures in mating tests and fewer mounts in mounting tests). After treatment, both age groups showed increased arousal with increasing T titer, but the middle-aged males remained lower than young males, even though T levels were equivalent between the age groups. Supraphysiological T titers did not increase the behavior of middleraged males above the performance of untreated intact males. The results show that: 1) middle-aged male rats evidence a decline in sexual arousal but a slight increase in ejaculatory response; 2) the middle-aged decrease in circulating T is not the major factor in the decline of sexual arousal.