Increased lateralization in rotational side preference in male mice rendered acallosal by prenatal gamma irradiation.

In order to test the hypothesis that the ontogenetic development of the corpus callosum is related to the establishment of behavioral laterality, the rotatory behavior in the free-swimming test was studied in male Swiss mice with callosal defects induced by exposure to gamma irradiations at the 16th embryonic day (total dose of 3 Gy). At adulthood, 43 irradiated and 56 non-irradiated mice were submitted to 3 sessions of the free-swimming rotatory test (diameter of the recipient=21 cm; session duration=5 min; inter-test interval=48 h). The number and direction of 30 degrees and 360 degrees turns were recorded. Animals were classified as side-consistent turners (to the right or to the left) when they did not change their preferred side of rotation in all three sessions and in both turning units. In general our results suggested that irradiated animals present more pronounced laterality than non-irradiated ones. In the irradiated group, the percentage of consistent turners was significantly higher than that of non-consistent turners. In the first session, the percentage of animals that presented strong turning preferences in the acallosal group was higher than in the normal group. In first session, the acallosal group presented a higher average number of turns to preferred side than the normal group. Taken together, our results constitute an endorsement to the hypothesis that the normal development of the corpus callosum is related to the establishment of cerebral laterality.