Effects of age and genotype on acquisition of an active avoidance response in mice

Two experiments were conducted in which inbred C57BL/6J and DBA/2J mice were trained in an active avoidance jump‐up task under distributed practice conditions at a variety of ages comprising a large part of their life‐span. DBA/2J mice were found to be basically an escaping strain and exhibited little change in behavior as a function of age. C57BL/6J mice developed consistent avoidance behavior when training was initiated at 31–36 days of age. Avoidance behavior appeared to reach a peak in the 45–day‐old group and progressively decreased in 145‐ and 560‐day‐old groups. Increased footshock intensity in old DBA/2J mice enhanced escape responding without increasing avoidance responding. Increased footshock intensity in old C57BL/6J mice enhanced avoidance responding.