Topography of corticopontine remodelling after cortical lesions in newborn rats.

Autoradiographic and axonal degeneration staining techniques were combined in individual animals to study the distribution of corticopontine fibers. In normal animals, forelimb and hindlimb motor cortical projections terminated somatotopically within the ipsilateral pontine nuclei. Sparse crossed projections also displayed a somatotopic pattern. After unilateral sensorimotor cortical lesions in newborn rats, an increase in the crossed corticopontine fibers arising from the opposite unablated motor cortex was observed at maturity. These fibers distributed in a topographic pattern similar to the normal ipsilateral corticopontine pattern; forelimb motor cortical projections terminated rostral to hindlimb motor cortical fibers. The specific distribution of the anomalous fibers suggests that they constitute a functional pathway.