Myelination of regenerated axons in goldfish optic nerve by Schwann cells

Summary This study uses immunohistochemistry and EM to examine the site of injury in goldfish optic nerve during axonal regeneration. Within seven days of nerve crush axons begin to regrow and a network of GFAP⁺ reactive astrocytes appears in the nerve on either side of the injury. However, the damaged area remains GFAP^–. By 42 days after nerve crush, the sheaths of new axons acquire myelin marker 6D2, and the crush area becomes populated by a mass of longitudinally-orientated S-100⁺ cells. Ultrastructurally, the predominant cells in the crush area bear a strong resemblance to peripheral nerve Schwann cells; they display a one-to-one association with myelinated axons, have a basal lamina and are surrounded by collagen fibres. It is proposed that these cells are Schwann cells which enter the optic nerve as a result of crush, where they become confined to the astrocyte-free crush area.