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Morphological differences in the commissural connections of the forebrain in white outbred mice and BALB/C mice

BACKGROUND: The study of the mechanisms of interaction of paired structures of the mammalian brain is a fundamental problem of modern neuroscience, which is of great applied importance. Even mild underdevelopment of the corpus callosum in humans can lead to autism. It is known that the intensity of intraspecific interactions in BALB/c mice is lower than in white outbred ones, while some BALB/c substrains are characterized by underdevelopment of the corpus callosum. 
AIM: To compare the morphological parameters of the large brain commissures in white outbred mice and BALB/c mice grown in the Rappolovo nursery (Leningrad region). 
MATERIALS AND METHODS: The morphology of the corpus callosum was studied in 13 male white outbred mice and 7 male BALB/c mice at the age of 8 months. 
RESULTS: In mice of both subpopulations, the area of the anterior commissure of the left hemisphere was smaller than that of the right hemisphere (p 0.05). There were no differences between subpopulations in this parameter. The area of the left section of the corpus callosum trunkus in outbred mice was larger than the right one (p 0.001), while in BALB/c mice the areas of the left and right slices did not differ. Despite the absence of significant differences in the area of the anterior part (rostrum et genu) of the corpus callosum the density of the location of oligodendrocytes in this brain structure in the mice of the two subpopulations was different. The number of oligodendrocytes in 0.01 mm2 on the left section of the anterior part of the corpus callosum in BALB/c mice was greater than in white outbred mice (p 0.05). A similar trend was revealed when comparing slices of the right hemisphere (p = 0.065). 
CONCLUSIONS: The large area of the right parasagittal slice of the anterior commissure suggests that some of its constituent fibers do not cross the midline, but end within the same hemisphere, which may be the morphological basis for the functional dominance of the temporal cortex of the left hemisphere in mice of both subpopulations. The corpus callosum in BALB/c mice is developed symmetrically, and in white outbred ones asymmetrically. This feature may be the morphological basis for the functional dominance of the parietal cortex of the right hemisphere in outbred animals.