Synaptic regeneration in identified neurons of the lamprey spinal cords.

Identified reticulospinal neurons whose giant axons were severed after spinal cord transection were filled with horseradish peroxidase. Whole mounts and serial-section light and electron micrographs show axon regeneration across the spinal lesion and the formation of new synapses. Normal swimming activity returns in the spinally transected animals, although the regenerated synapses are in atypical regions of the spinal cord.