Myelination and remyelination in the regenerating visual system of the goldfish

The remyelination of regenerated optic axons was investigated in goldfish following either optic nerve crush or ouabain retinal intoxication. Axons grown after nerve crushing acquire thinner myelin sheaths than axons originating from reconstituted ganglion cells. If axons of reconstituted ganglion cells are crushed and allowed to regenerate, the subsequent myelination is weaker than that of control axons not interrupted by crushing, but stronger than that of axons of preexisting retinal ganglion cells. The present results suggest that a neuron is capable of inducing a normally developed myelin sheath when its axon contacts an oligodendrocyte the first time, whereas a neuron whose axon contacts an oligodendrocyte and the second time is not capable of forming a normal myelin sheath in the adult animal. The present results also support the notion that the oligodendrocyte requires a neuronal signal for myelin sheath formation.