Effects of distraction and stress on delayed matching-to-place performance in aged rats

The performance of male Long-Evans rats on the delayed match-to-place (DMP) version of the Morris water maze was assessed in two separate experiments; the first compared young (4 months) with middle-aged (16 months) rats, whereas the second compared middle-aged (14 months) with old (26 months) rats. Old rats continued to use a short-term memory strategy on the DMP task, but their performance on both search and recall trials was impaired relative to that of middle-aged animals. Rats of all ages habituated rapidly to visual distraction and the performance of old rats was not affected by exposure to a mild predator stress in the form of cat urine. The performance of the middle-aged rats did not differ significantly from that of young rats, even when they were challenged on recall trials by visual distraction or by exposure to predator odour. These results do not provide strong support for the prediction that visual distraction and psychological stress would interact with age in affecting spatial short-term memory in Long-Evans rats.