#5 Sex Differences in Exploratory Behaviour of Laboratory CD-1 Mice (Mus musculus)
Sex differences in exploratory behaviour were investigated in 120 litters of control CD-1 mice in two-generation toxicity studies over a 13-year period. Exploratory behaviour of F1-generation mice was investigated at 3 weeks of age during the lactation period and at 8 weeks of age after weaning. In the F1 generation, at 3 weeks of age, female offspring showed less activity in terms of the number of movements, movement time, number of vertical activities and vertical time than male offspring. Longitudinal analysis showed that these variables were parallel in males and females during the 10-minute observation period. At 8 weeks of age, female offspring in the F1 generation showed less activity with respect to the number of movements, movement time, average distance, number of vertical activities and vertical time but showed more horizontal activities than male offspring. The number of movements, movement time and vertical time were not parallel in longitudinal analysis; however, all other variables were parallel. Sex differences in exploratory behaviour of immature mice showed quantitative changes only. In adult mice, variables for rearing excluding vertical time showed quantitative changes only; however, variables for ambulation and vertical time showed quantitative and qualitative changes. From these results, it appears that female CD-1 mice display less exploratory behaviour than male CD-1 mice and that these sex differences in exploratory behaviour occur from the prepubertal period.
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