NIH Swiss and Black Swiss mice have retinal degeneration and performance deficits in cognitive tests.

Swiss mice are among the most commonly used outbred strains in biomedical research. Because prior knowledge of the baseline phenotypes of mouse strains will allow informed selection of strains for particular experiments, we sought to characterize the behavior of two previously untested outbred Swiss strains--NIH Swiss and Black Swiss--in the two most widely used paradigms for evaluating the cognitive abilities of mice. Unlike the C57BL/6J and C57BL/6J-Tyr(c-2J) controls, animals of both outbred Swiss strains were unable to demonstrate learning in the Morris water maze and contextual fear conditioning paradigms. A polymerase chain reaction assay revealed that all of the NIH Swiss and Black Swiss mice tested were homozygous for the recessive retinal degeneration 1 mutation of the Pde6b gene. Histological examination of NIH Swiss and Black Swiss mouse eyes confirmed the presence of retinal degeneration, which causes visual image blindness. These findings indicate that NIH Swiss and Black Swiss mice are visually im paired and thus may be unsuitable for use in some experiments.