STRESS-INDUCED DISTURBANCES IN MORRIS WATER-MAZE PERFORMANCE - INTERSTRAIN VARIABILITY

Marked differences were observed across strains of mice (i.e., DBA/2J, C57BL/6J, BALB/cByJ and CD-1 mice) in acquisition, performance and reversal of a place learning response in a Morris water-maze. While DBA/2J, C57BL/6J and CD-1 mice typically learned the response readily, only 20% of BALB/cByJ mice acquired the response. Commensurate with the effects of hippocampal disturbances, the performance deficits in BALB/cByJ mice were not evident when the position of the platform in the water-maze was cued. Exposure to uncontrollable foot shock did not affect the acquisition or performance of this response in the former three strains, but provoked a modest disruption of reversal performance in DBA/2J mice and markedly impaired reversal performance in BALB/cByJ mice. It seemed, however, that the response strategies adopted in these strains could be distinguished from one another. In the reversal paradigm BALB/cByJ mice initially persisted in returning to the original training quadrant rather than to the new goal quadrant. Following 2 days of training the perseveration was no longer apparent and animals seemed to adopt a random search strategy. In contrast, DBA/2J mice, which exhibited a smaller stress-induced disturbance, did not display a perseverative response style. These data suggest that inescapable shock does not disturb response-outcome associations, but may result from the induction of a perseverative response style. However, it appears that the mechanisms responsible for an interference of performance may not be uniform across strains. The mechanisms responsible for the poor performance of BALB/cByJ mice have not been determined, but the behavioral profile demonstrated is consistent with that associated with hippocampal disturbances and excessive glucocorticoid release in response to environmental stressors.