Mice of two strains bred for large and small relative brain weight (BB and SB) were tested for hyponeophagy, responses in the unavoidable slippery funnel test and the test for understanding object permanence (as per J. Piaget), in which they had to find an underpass to a comfortable shelter when hidden (a cognitive test). Between-strain differences were evaluated in control mice and in groups after 2 h of restraint, which provokes the development of a stress reaction. In the hyponeophagy test, reactions to a novel foodstuff in a novel environment were significantly greater in SB mice (but not BB mice) after restraint than in controls. In the unavoidable slippery funnel test, BB mice showed significantly longer adaptive escape reactions after restraint, while this change was insignificant in SB mice. BB mice transferred from one type of response to another more frequently than SB mice. In SB mice the pattern of the ratio of the amounts of time spent in the three types of reaction in the funnel test in controls and after restraint were different from those in BB, which is evidence of between-strain differences. BB mice (total control and experimental) solved the cognitive test better than SB mice. Stress had no significant influence on measures of solving this test. These data show that differences in behavior exist between the BB and SB strains (including in the state of stress), despite cessation of selection for relative brain weight.
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