Changes in segmental reflexes following chronic spinal cord hemisection in the cat. I. Increased monosynaptic and polysynaptic ventral root discharges.

The effect of a chronic spinal cord hemisection on segmental reflex transmission was studied in cats. Recordings of ventral root responses were made after a terminal transection below the initial lesion to eliminate descending influence through the intact spinal half. Procedures to ensure comparability between sides, that are lacking in earlier work on this experimental model, were introduced in the present work. It was demonstrated that there was an increase in reflex size on the lesioned (left) side, relative to the other side, of both mono- and polysynaptic reflexes. The reflex changes were found at all survival times studied (from 2 to 515 days). In control animals mono- and polysynaptic reflexes were found to be larger on the right side. It is discussed that side symmetry of reflex size is not to be presupposed even in a normal population. Detailed clinical examinations of lesioned animals were not performed, but a tendency for enhancement of the ipsilateral knee-jerk was found. There was no syndrome of spasticity and general motor recovery was very good.