Place and matching-to-place spatial learning affected by rat inbreeding (Dark–Agouti, Fischer 344) and albinism (Wistar, Sprague–Dawley) but not domestication (wild rat vs. Long–Evans, Fischer–Norway)

Abstract

Domestication has been shown to produce a shift in both morphological and behavioral characteristics of animals. While changes in body weight, brain size, reproductive rates, and temperament are well documented, the effects of domestication on learning and memory are not as clearly understood. This issue is of particular importance to the use of rodent models in learning and memory where the domestication of Rattus norvegicus for research has resulted in the availability of numerous strains. To investigate cognitive effects resulting from domestication, we examined the spatial performance of a number of rat strains: wild, Long–Evans, Fischer–Norway, Dark–Agouti, Wistar, Fischer 344, Sprague–Dawley. The wild rats served as a baseline for comparing inbred and outbred domestic strains and pigmented and albino domestic strains. Place (a measure of nonspatial and procedural learning), matching-to-place (spatial working memory), and probe (retention) performance were measured in the Morris swimming pool task. The task is an ideal means for comparing different rat strains because place learning has not been selected for in the domestication of Rattus norvegicus and because the task is ethologically relevant. The results indicated that wild rats and Long–Evans rats did not differ on any measure, with Fischer–Norway rats being only slightly inferior. Larger impairments were found in Wistar>Fischer 344>Dark–Agouti>Sprague–Dawley strains. Impairments were more obvious on place acquisition but also occurred in matching-to-place performance. Platform crosses, but not quadrant preference was found to be correlated with place learning. In general, although nonspatial and spatial deficits were associated with both inbreeding and albinism, impaired spatial performance is not a necessary result of domestication.