Sex differences, or not, in spatial cognition in albino rats: acute stress is the key

Male rats, Rattus norvegicus, typically outperform females in tests of spatial cognition. However, as stress affects cognition differently in the two sexes, performance differences may be an artefact of stress. Rats face at least two sources of stress during an experiment: the test situation (acute) and housing conditions (chronic, e.g. isolation). We used a task (the Morris water maze, MWM) that allowed testing of both spatial working and reference memory to investigate whether chronic stress (isolation housing) and/or acute stress (the task) has a differential impact on spatial cognition in male and female albino rats. Irrespective of age at the onset of isolation housing, isolated rats were not spatially impaired relative to pair-housed rats. However, the acute stress of the task led to adult males apparently outperforming adult females: adult females took longer to reach the platform than did males because they spent more time in thigmotaxis (swimming close to the wall) during testing. In juvenile rats, the stress caused by swimming in the MWM resulted in both males and females being highly thigmotactic and no sex difference in performance. We conclude that stress can lead to apparent differences between the sexes in performance on a spatial cognition task.