Intermittent swim stress causes Morris water maze performance deficits in a massed-learning trial procedure that are exacerbated by reboxetine.

Various animal models of depression have been used to seek a greater understanding of stress-related disorders. However, there is still a great need for research in this area, as many unanswered questions remain. Therefore, we sought to employ a novel animal model of depression known as intermittent swim stress (ISS). In this model, the animal experiences 100 trials of cold water swim stress. ISS has already shown subsequent immobility in the forced swim test (FST), deficits in instrumental and spatial (spaced-trial procedure), and responsiveness to norepinephrine. We are now examining how this will translate in the Morris water maze for rats in a massed-learning trial procedure, and further assessing ISS sensitivity toward norepinephrine selective anti-depressant drugs. The results indicated no difference in cued learning when the platform was visible in the water maze, but a hidden platform task revealed poorer spatial learning for ISS-exposed rats versus controls. In terms of spatial memory, there was a notable ISS-induced deficit 1h after the learning trials, regardless of performance on the previous platform task. Interestingly, the administration of reboxetine interfered with the spatial learning and memory trials for both ISS and CC groups. As a result, ISS exposure compromised spatial learning and memory in the Morris water maze, and norepinephrine does not appear to be a mediator of this deficit. The results demonstrate a key difference in the effects of reboxetine in a massed- vs. spaced-learning trial procedure in the Morris water maze following ISS exposure.