AGE-RELATED-CHANGES OF SOCIAL MEMORY RECOGNITION IN MALE FISCHER-344 RATS/

Two different habituation- dishabituation test paradigms were used to evaluate differences in social memory/recognition among 3-, 15- and 22 -month-old male Fischer 344 rats. For test 1, males received three 2-m in exposures to the same stimulus ovariectomized female, followed by t hree 2-min exposures to a different stimulus female with an inter-tria l interval of 6 min. All groups showed a habituation response with inv estigation times decreasing on trials 2 and 3. Introduction of a diffe rent stimulus female on trial 4 (dishabituation) resulted in significa nt differences with investigation times of the 3-month animals being s ignificantly greater than both the 15- and 22-month animals and those of the 15- being greater than the 22-month animals. Notably, the 22-mo nth-old animals failed to dishabituate on this task. For test 2, all a nimals received two trials with different stimulus females used in eac h trial. While investigation times of the 3-month animals remained ele vated in trial 2, indicative of an absence of habituation to these dif ferent stimuli, those of the 15- and 22-month-old animals decreased si gnificantly, suggesting that habituation had occurred to the task and these animals failed to recognize differences in the stimuli. Taken to gether, these results demonstrate that the 22-month-old rats show enha nced habituation, but markedly deficient dishabituation responses comp ared to the 3-month-old animals, while the performance of the 15-month animals was intermediate. These results suggest an age dependent decr ement in social memory/recognition processes in the male Fischer 344 r at.