[Mechanism on formation of new ipsilateral corticospinal tract following neonatal unilateral cortical ablation in rats].

The corticospinal tract in the rat after neonatal ablation of the unilateral cerebral cortex was studied morphologically using the antegrade horse-radish peroxidase (HRP) tracing method. An aberrant ipsilateral tract was observed 7 days after the operation. Formation of the aberrant neuronal pathway has been confirmed to be contributed mainly by new axons, which ramified at the level of the pyramidal decussation from healthy corticospinal fibers. This ramified axon ran toward the ipsilateral dorsal funiculus. A few fibers also contributed to the aberrant pathway by changing their direction on the way of extension at the level of the pyramidal decussation. These results indicate that the ramification and change of the direction of extending axons play an important role for formation of a new ipsilateral corticospinal tract.