LONG-EVANS AND SPRAGUE-DAWLEY RATS DIFFER IN THEIR SPATIAL NAVIGATION PERFORMANCE DURING ONTOGENY AND AT MATURITY

The Morris maze has become a popular method for the assessment of spatial navigation. However, its use to study the development of spatial abilities has been limited to pigmented rats. Thus, the aim of the present study was to compare albino Sprague-Dawley and pigmented Long-Evans rats using this test during postnatal Days 20 through 27, and Day 90. It was found that Long-Evans rats showed significantly shorter escape latencies and swim distances than the Sprague-Dawley rats on Days 20-25 but not on Days 26-27. However, when tested at Day 90, the Long-Evans rats again showed more rapid location of the escape platform and shorter swim distances than the Sprague-Dawley rats. Probe trial analysis (platform removed) indicated that Long-Evans rats were generally more accurate in their localization of the former platform location than Sprague-Dawley rats. In a second experiment in which 21-day-old rats of both strains were tested in a proximal-cue version of the maze, the question of whether this performance difference might have related to visuo-perceptual differences was considered. Since no dissimilarity in performance was observed, a spatial-learning difference between the two strains would seem best able to explain the preceding data.