SEXUAL BEHAVIOR AND HORMONES IN AGING MALES

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We propose to extend our research to identify factors other than testosterone (T) that may account for the decline in sexual behavior of aging males. Because the old male primates (24 years and older) that will serve as subjects are nearing maximum life expectancy, and many have been under study for over 15 years, this is a unique research opportunity. Our aims are to determine (1) sexual behavior and serum hormone levels in very old rhesus males and the effects of increasing T levels on sexual behavior, (2) the extent to which failing health in very old males reduces sexual activity and its effect on serum hormone levels, (3) threshold levels of T that will induce levels of sexual behavior in old (24 years and older) long-term-castrated males that are comparable to those of intact males of the same age, (4) the extent to which penile reflexes correlate with sexual performance and serum T levels in old intact and castrated males, (5) whether differences in the sexual behaviors of young (mean of 12 years) and old males observed in laboratory pair tests also occur in a semi-naturalistic social environment, (6) the differences (physiological and behavioral) between the few preferred females who can arouse old rhesus males to copulate and most other females, who cannot, (7) whether sperm motility and fertility, like sexual behavior, decline in old rhesus males whose serum T levels are within the range for young males, (8) whether drugs that act on the dopaminergic and serotoninergic systems influence sexual behavior in old males, (9) whether living in isolation increases the rate of decline in sexual behavior and influences serum testosterone levels in old rats, and (10) whether the deterioration of penile papillae that we have observed in old rats reflects a decrease in tissue sensitivity or reflects a decrease in serum T levels. The research seeks answers to questions relevant to aging male mammals in general, but each experiment is relevant in varying degrees to the problems of sexual behavior confronting old men. The focus is on behavior, but answers must be drawn from a number of disciplines, including endocrinology, anatomy, physiology, and comparative psychology. Our findings should be of interest to practicing sex therapists as well as professors of geriatrics.