The number of pre-shock trials affects sex differences in passive avoidance behavior.

Different groups of male and female Wistar rats were exposed to a standard passive avoidance procedure in which the number of pre-shock trials was experimentally manipulated (1, 3 or 9 trials). Sexually dimorphic passive avoidance behavior was observed after 1 and 3 pre-shock trials. Entrance latencies on the pre-shock trials did not differ for males and females after 1 trial. In the 3 trial condition, latencies differed between the sexes and were also a function of repeated trials for male subjects, as their latencies increased over trials, while those of females did not. When 9 pre-shock trials were presented, the sex difference in entrance latencies was still observed, but latencies increased for both males and females. Although the results of the experiment suggest that sex differences in passive avoidance behavior might be attributable to sex differences in habituation processes to the stimuli associated with exposure to the platform, correlations between the latencies on the final pre-shock trial and behavior on the post-shock trial were not significant. The variables responsible for the occurrence of sexual dimorphism in passive avoidance behavior remain, therefore, largely unknown. The interpretation of this behavioral difference in terms of more general differences between males and females should proceed very cautiously.