Aging is associated with a general decline of physiological functions, and those which depend on the central nervous system, such as sexual behavior are the most affected.The critical age at which an impairment of sexual behavior is most likely to occur strongly depends on a range of factors, including genetic background, ecological conditions, social status and stress loads.In this study we used Wistar and accelerated-senescent OXYS rat males.We found a reduction of sexual behavior in males of both strains with age, but in the OXYS rats a decrease in sexual motivation was observed earlier, at the age of 12 months as compared with Wistar rats of the same age and with younger animals of both strains.Early decrease in sexual motivation in OXYS males did not depend on their sexual experience.There were no interstrain or age differences in the basal luteinizing hormone and testosterone levels in male rats, but the inhibitory effect of aging on the endocrine response of the testes of rats both strains was shown under the conditions of sexual stimulation.Reduction of sexual motivation in 12-month-old OXYS males was accompanied by changes in the metabolism of norepinephrine, dopamine and serotonin in CNS.There was reduction ofdopamine and serotonin levels and increase in dopamine catabolism in the hypothalamus in males of both strains with age.However, the OXYS rats had no typical age-related changes in levels of norepinephrine in the hypothalamus or serotonin and 5-hydroxyindoleacetic acid in the midbrain compared to Wistar.An important result of this work was establishing the fact that under conditions of sexual arousal, hypothalamic catabolism of dopamine was significantly lower in 12-and 26-month-old OXYS rats than in Wistar rats.These findings suggest an essential role for neurochemical changes in the decline of sexually motivated behavior of male OXYS rats.