Effects of inescapable shock on maze performance as a function of age in mice

The hypothesis was investigated that aged animals receiving an experimental treatment of inescapable shock would suffer greater deficits in swim T-maze performance than either their younger shocked counterparts or their age-matched nonshocked controls. Three age groups of male C57BL/6J mice were studied: (a) young-mature (8-9 mo); (b) middle-aged (15-16 mo); and (c) aged (26-27 mo). Equal numbers (n = 16) from each age group were assigned to either a treatment group, which received 3 days of inescapable shock (6 sec, 200 microA) during a 60-min session on a variable time schedule (VI-60 sec), or a control group, which was placed inside the apparatus for an equal amount of time. Beginning 24 hr after the last shock session, swim maze training consisted of 10 daily trials over 5 consecutive sessions. The hypothesis was partially confirmed with respect to the latency to swim to the choice-point of the T-maze. Only the aged treatment group demonstrated significantly impaired performance. With respect to the measure of learning (percent correct responses) in the alternation task, inescapable shock significantly impaired performance; however, the effect was a weak one and there was no evidence of differential impairment across age.