Deficiency of corpus callosum varies with strain and supplier of the mice.

Six inbred strains of adult mice either obtained from commercial suppliers or bred in the author's laboratory at Waterloo were assessed for size of body, brain and corpus callosum (CC) at a wide range of ages. Because almost all measures varied significantly with age, a simple regression procedure was used to minimize age effects statistically. The strains A/J, C57BL/6J and DBA/2J differed substantially in brain size and size of CC, but none of these animals ever showed severe deficits of CC fibres crossing the midsagittal plane. For these 3 strains the sizes of body, brain and CC were larger when bred at the Jackson Laboratory than at Waterloo. Two BALB/c strains obtained from different suppliers had over 30% of mice with defective CC, ranging continuously from total absence of transcortical fibres to slightly reduced CC size. For these two strains bred at Waterloo, brain sizes were larger and CC defects were much less frequent than when bred by commercial suppliers. The strain 129/J had a 71% frequency of CC defects when reared at the Jackson Laboratory but 38% defects when bred and reared at Waterloo. However, bodies of 129/J mice bred at Jackson were larger than those bred at Waterloo. These results show that relatively small differences in rearing conditions can have relatively large effects on certain aspects of brain development.