Locomotor and exploratory activity in three inbred strains of mice from young adulthood to senescence

Nine variables measuring activity and exploratory behavior were collected for nine independent groups of three inbred strains of mice (BALB/c, C57BL/6, and DBA/2) at three ages (150, 400, and 750 days). An analysis of variance measuring differences of performances and a covariance analysis estimating the evolution of scores with age shows that (1) some variables are unaffected by age; (2) a strain-age interaction is observed for some variables; (3) some groups do not exhibit any age-related change for certain variables; and (4) the level of ability of age-related behavior varies across groups. These data argue for rejection of a general factor of aging and suggest that we are dealing with two distinct phenotypes: performance, and age-related modification of the performance, which therefore are not linked.