Sexual Activity of Aged Male Mice: Correlation with Level of Arousal, Physical Endurance, Pathological Status, and Ejaculatory Capacity1

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Abstract
CBF1 male mice of either 6 or 25 months of age were given a variety of tests to 1) identify specific deficits in the sexual performance of the aged individuals, and 2) determine the extent to which any such deficits might reflect general debilitation, pathological interference, an inability to arouse, or age-dependent changes in the reproductive system itself. Aged CBF1 males exhibited marked individual variation in their sexual capacity. Some old males exhibited copulatory behavior that was similar in all regards to that of young males. Other individuals showed a specific loss of one or more of the major components of copulatory behavior: mounting, intromission, or ejaculation. Still other old males displayed the entire copulatory sequence, but they did so less frequently than young males. Old and young males also differed in the following parameters: level of arousal in response to a novel environment, treadmill performance, extra-gonadal sperm reserves, sperm concentration in their ejaculates, and the occurrence of gross lesions in several organ systems. The individual variation displayed in these parameters, however, failed to correlate well with any of the individual variation observed in the sexual behavior of old males. Urogenital pathologies proved an exception; their occurrence provoked specific aberrations in the ejaculatory process. Our data, when viewed in toto, suggest that mounting, intromission, and ejaculatory behavior deteriorate independently with age in male mice. Furthermore, our data suggest that such deteriorations are not normally associated with a general failure in the muscular supports for all physical activity, nor are they routinely a result either of indirect pathological interference, of a general failure to arouse, or of some generalized lesion affecting all aspects of the reproductive system.