Distribution of the cortico-spinal fibres in the cervical and lumbar enlargements of the rat spinal cord.

We examined the distribution pattern of the corticospinal fibres in cervical and lumbar enlargements of the rat spinal cord with the Fink-Heimer silver impregnation method, after extensive cortical ablation. Corticospinal fibres are bilateral and run in the lateral and anterior funiculi. The distribution at the cervical and lumbar levels does not differ. The main area of termination are: 1) the lateral part of the ventral horn basis; 2) an area surrounding the motoneurons group posteriorly. At the electron microscope we were unable to find degenerating boutons of the corticospinal projections contacting HRP labelled motoneurons retrogradely. This indicates that at both levels few monosynaptic corticospinal fibres or none at all end on the motoneurons. Our study does not support the suggestion of differences in the termination pattern of the corticospinal tract of the rat between cervical and lumbar enlargements made on the basis of electrophysiological studies.