Morphological brain asymmetries in male mice with callosal defects due to prenatal gamma irradiation.

We have previously suggested a relationship between the development of the corpus callosum and the direction of cerebral asymmetries (Schmidt and Caparelli-Daquer, 1989; Schmidt et al., 1991). Here we report a study on morphological brain asymmetries using a distinct experimental approach. At embryonic day 16, mice were exposed to a gamma source, receiving a total dose of 2 Gy. At adulthood 32 irradiated and 28 normal male Swiss mice were evaluated for individual and populational interhemispheric asymmetries of weight, dorsal area, and neocortical volume. All irradiated mice showed callosal defects ranging from total absence to a partial reduction of the midsagittal callosal area. The normal and irradiated groups displayed a pronounced individual asymmetry in all measurements. In contrast, populational asymmetry could be identified only in the normal group. These results are consistent with our previous data in acallosal mutant mice and support the hypothesis that the corpus callosum may play a role in directing interhemispheric morphological brain asymmetries.