The Sea Lamprey: What This Primitive Animal Can Teach Us About the Potential for Repair of the Injured Spinal Cord

The lamprey is a primitive vertebrate that recovers functionally after spinal cord transection. Research over the past quarter of a century has shown that this recovery is based on regeneration of descending axons from the brain as well as axons of propriospinal relay neurons that connect the locomotor pattern-generating circuitry above and below the lesion. Although not all neurons regenerate and the distance of regeneration is limited, the regenerating axons grow selectively in their correct paths and make synapses specifically with correct target neurons. Morphological and molecular biological data suggest that the mechanisms that drive the regeneration may be different from those that underlie the original development of axon pathways during embryonic development. Nevertheless, recent data suggest that some of the molecules that guide axons during embryonic development may modulate the regeneration of mature axons after injury. These findings in the lamprey contribute to an understanding of the potential and limits of axonal regeneration in the treatment of spinal cord injuries.