Behavioral asymmetry in BALB/cCF mice with corpus callosum abnormalities]

The possible homology between anomalies of the corpus callosum in mice and in humans remains questionable. The small number of existing behavioural studies in mice have not shown effects, at the behavioural level, of the absence or reduction in size of the corpus callosum. We therefore examined the development, during the first 3 weeks of postnatal life, of a number of simple reflex and integrative responses in the members of a sample of 101 BALB/cCF mice; at autopsy carried out at 50 days of age, 29 mice showed anomalies of the corpus callosum (total absence or an area less than 0.75 mm2). Asymmetry of the development of these responses was measured either as the proportion of animals showing asymmetrical appearance of responses on the left and right sides, and as the delay between appearances on the left and right sides in "asymmetrical" mice. Both measures decreased over the first 15 postnatal days, at the same rate in normal and abnormal mice; in each case the decrease is better described by a second-order, quadratic, function than by a simple linear function. We therefore conclude that the integrity of the corpus callosum is not necessary for the normal maturation of sensorimotor behaviour in mice, and suggest that this conclusion may possibly be explained by the relatively recent appearance of mice in the mammalian radiation.