Absence of population cerebral asymmetries in mice with callosal defects induced by prenatal gamma irradiation.

The development of the corpus callosum of 19 male Swiss mice was disturbed by exposure to a 60Co gamma source on embryonic day 16 with a total dose of 2 Gy (dose rate of 56 to 59 rads/min). At adulthood the animals were perfused with saline followed by formaldehyde and the cerebral hemispheres were weighed and photographed in dorsal, lateral and medial views. Brain asymmetries were evaluated by measurements of hemisphere weight, as well as dorsal and lateral areas. From the measurements of the midsagittal callosal areas, performed on the medial views, 2 subgroups could be identified: one with a small callosal remnant (N = 9) and another with a non-measurable callosal area (N = 10). In spite of a pronounced individual asymmetry, the irradiated mice (N = 19) did not show a populational asymmetry toward any side. A slight tendency favoring the left hemisphere was found in the small remnant subgroup. These results are consistent with our previous data for a strain of mice in which some animals present callosal defects. We conclude that the present data support the hypothesis that the corpus callosum may play a role in directing morphological hemispheric asymmetries.