Hormone release during computer-monitored sexual behavior in mature and aged male rats

Sexual behavior and the increase in plasma hormone levels of LH, prolactin, and testosterone associated with sexual behavior were examined in three age groups of sexually naive male rats. The two younger groups (5- and 11-month-old) mated normally and their behavioral latencies decreased significantly following sexual experience. Both plasma testosterone and LH concentrations increased significantly following entrance of a receptive female into the mating arena. Plasma prolactin levels rose but not significantly. However, the 27-month-old rats neither mated nor showed an increase in the three plasma hormone concentrations during exposure to a receptive female. Only basal testosterone levels were significantly lower than those of the younger animals. Low testosterone levels possibly contributed to deficiencies in both behavior and its associated hormone release. The monitoring of sexual behavior was facilitated by a computer, programmed to record, store, and analyze behavioral events.