Fate of oligodendrocytes during retinal axon degeneration and regenerationin the goldfish visual pathway

Retinal axons in goldfish regenerate after optic nerve lesion, restore syna ptic connections, and become myelinated by oligodendrocytes. The fate of ol igodendrocytes during these events is not known and mag require generation of new oligodendrocytes or dedifferentiation and redifferentiation of the e xisting ones, To determine the reaction of oligodendrocytes to optic nerve lesion, we used the terminal transferase technique to detect apoptosis, bro modeoxyuridine incorporation to reveal mitosis, antibodies to identify myel in and oligodendrocytes and Lucifer yellow injections to reveal cell morpho logy, Along with the reappearance of the myelin molecules 36K protein, gala ctocerebroside, and myelin basic protein, myelinating oligodendrocytes (ide ntified by Lucifer yellow injections) reappear 21 days postlesion. Prior to this time, the dye-filled cells had fen processes oriented along the regen erating axons. They resembled oligodendrocytes seen both in vitro and in vi vo which express the L1-related E587 antigen and synthesize the 36K myelin protein in coculture with axons. No signs of oligodendrocyte apoptosis were detected after lesion and only felv of the oligodendrocytes present had re cently arisen. 36K/E587 double-labeled oligodendrocytes which were most lik ely dedifferentiating oligodendrocytes were identified in 8-day postlesion nerves among E587-positive elongate cells whose numbers increased until 14 days postlesion, These findings suggest that oligodendrocytes dedifferentia te-like Schwann cells-from cells which express myelin molecules to elongate cells which express the L1/E587 antigen, They rcdifferentiate to myelinate axons from roughly 3 weeks onward. These findings suggest an adaptive plas ticity of goldfish oligodendrocytes beneficial to the repair of the visual pathway. (C) 1999 John Wiley & Sons, Inc.