The effects of chronic unpredictable stress on male rats in the water maze.

Exposure to chronic stress can affect cognitive processes in a complex manner depending upon the intensity and duration of the stressors. The current study investigated the effects of chronic unpredictable stress (CUS), a procedure thought to use moderate stressors, on acquisition of and performance in the Morris Water Maze (MWM). Separate behavioral tests were also used to determine whether the stress-induced changes in MWM were due to general changes in locomotor activity or preference for a rewarding stimulus. Adult male rats were exposed to 10 days of different stressors applied at various times. Following the last stressor, stressed and non-stressed rats began training in the MWM, were tested in an open field box, or were tested for sucrose preference. In the MWM, rats exposed to stress had shorter latencies to reach the hidden platform during training. The path lengths on day 2 of training, trials 2 and 4, were shorter in CUS rats compared to controls, with the stressed rats traveling less in the outer portion of the maze. During the probe trial, CUS rats also traveled less overall and less in the outer portion of the maze, although all other measures were the same. The facilitation in learning the platform location was not due to a change in other behavioral components that could contribute to the measures, such as general activity, sensorimotor processing or the preference for a 2% sucrose solution. Thus, chronic unpredictable stress selectively appears to affect the search strategies in the water maze.