Brain plasticity after corpus callosum transection in the newborn rat.

The importance of afferent fibers in the final shaping of the central nervous system has been well established in several papers. In order to study how much one can influence cortical development by changing afferent input to the cortex cerebri, we transected corpus callosum in rats at 2 or 3 postnatal days. Equal numbers of lesioned and control animals were transcardially perfused with mixed aldehydes at postnatal day 6 (P-6) or P-14. Brain tissue was processed for Golgi impregnation, Nissl stain, and quantitative electron microscopic analysis. Morphometric image analysis (MOP 3) of the primary sensory area did not show significant differences with respect to cortical depth and total and apical dendritic length. The cross-sectional area and maximal diameter of neuronal cell bodies were smaller in P-14-lesioned animals. Ultrastructural analysis of the cortex revealed that synaptic density was not reduced in lesioned animals. In conclusion, early in development, rat brain can compensate for major changes in the commissural afferent system.