Sever its spinal cord, and the eel-shaped lamprey will soon be undulating through the water as usual.﻿

A jawless fish called the lamprey is known for its resilience: after its spinal cord is severed, it can regrow part of its central nervous system and resume swimming normally. Now, scientists have discovered that the sea lamprey (Petromyzon marinus) can repeat the feat even if the same site is re-injured.

Jennifer Morgan at the Marine Biological Laboratory in Woods Hole, Massachusetts, and her colleagues cut lampreys’ upper spinal cords. At first, the animals could only move their heads. But over 11 weeks, the lampreys gradually regained their undulating swimming movements. During this period, a subset of the nerve fibres running from the brain down the spinal cord regenerated, bridging the injury. When the researchers then cut the spinal cord in the same place, the lampreys again regenerated some of their nerve fibres and recovered mobility.

Further studies might reveal why lampreys seem to be capable of greater regeneration than are many species. They could also help to uncover the factors that prevent the mammalian central nervous system from regenerating.