Physical and metabolic correlates of sexual inactivity in aged male mice

The object of this study was to identify specific syndromes of sexual loss in aged male mice. Emphasis was placed on uncovering syndromes that involve physical as opposed to motivational deterioration. To this end, 30-mo-old CBF1 male mice were subjected to a large battery of tests, each of which was designed to detect sensory, neuromuscular, metabolic, or sexual deficits. Over 50 measures were obtained on each of 63 males. A group of 23 6-mo-old males were studied simultaneously to establish base lines of normal performance. Old males routinely showed evidence of deterioration in some tests but not in others. Some old males actually performed as well as young males in some tests, including an exhaustive test of sexual capacity. Ten nonsexual measures were significantly correlated with sexual activity. Further analyses then suggested seven distinct syndromes of reproductive loss, each with its own specific cause and unique manifestation. Six of these syndromes manifested themselves as behavioral deficits; one was related to a failure to eject sperm. Our data also suggest the possible existence of two more syndromes, but these remain to be verified more fully. Although additional syndromes undoubtedly will be found in male mice, the present testing paradigm can be exploited to isolate and study the functional bases of each of these specific facets of reproductive loss.