Mice Reared With Rats: an Interstrain Comparison of Mother and "Aunt" Effects

Some effects of the maternal environment upon several behaviour patterns of weanling and adult C57BL/10J mice and Purdue Swiss-Albino mice were studied by comparing: i) mice reared by rat mothers, 2) mice reared by their natural mouse mothers in the presence of a rat aunt, and 3) cross-fostered control mice. The rat-mother and rat-aunt preparations both were found to produce measurable, and similar, effects upon the behaviour of weanling and adult mice. Experiment I: C57BL/10J Mice Infantile mortality. A higher mortality was recorded for rat-reared mice and mice reared in the presence of a rat aunt than for mouse-reared mice. Body weight. At weaning, rat-reared mice were heavier than mouse-reared mice or mice reared in the presence of a rat aunt. However, at 63 days of age, rat-reared mice weighed less than mice in either of the other two groups. Open-field behaviour. On the first day of open-field testing, both at 21 days and at 63 days of age, mouse-reared mice were more active than rat-reared mice or mice reared with rat aunts. On Days 2-4 in adulthood control mice defecated less than experimental mice in either of the two groups. Passive avoidance learning. At 21 and 63 days of age, control mice reached criterion sooner than rat-reared mice or mice reared with a rat aunt. Fighting behaviour. More fighting was found among mouse-reared mice than among rat-reared mice or mice reared in the presence of a rat aunt. Experiment 2: Swiss-Albino Mice Infantile mortality. A higher mortality rate was recorded for rat-reared mice and mice reared in the company of a rat aunt than for mouse-reared mice. Body weight. At weaning, subjects in the three treatment groups did not differ significantly from one another in body weight. However, at 63 days of age, rat-reared mice were heavier than mice in either of the other two groups. Open-field behaviour. On the first day of open-field testing, both at 21 days and at 63 days of age, mouse-reared mice were more active than rat-reared mice or mice reared with rat aunts. Control mice were also more active than rat-tended mice on Days 2-4 of open-field testing at weaning. Rat-reared mice defecated more than mouse-reared mice and rat-aunt tended mice on all four days of open-field testing at 21 days of age. However, rat-reared mice defecated less than mice in the other two groups during the four days of adult open-field testing. On Days 2-4 in adulthood, rat-reared mice had a longer latency to leave the starting square than mouse-reared mice or rat-aunt tended mice. Passive avoidance learning. At 21 days and at 63 days of age, control mice reached criterion sooner and achieved a greater number of correct trials than rat-reared mice or mice reared with a rat aunt. Fighting behaviour. No differences in fighting behaviour were found between the three groups of animals used in the experiment.