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The region at and around the site of optic nerve transeetion (ONS) in goldfish, topologically the equivalent of the glial seal' in mammals, is reported to remain free of astrocytes over weeks, but its cellular constituents are unknown.To leam what type of cell occupies the site of injury and thus provides support for the rapidly regenerating retinal growth cones, immunostaining experiments at the light micro scopic level and electron microscopic examinations were undertaken. Between 2 and 30 days after ONS, an area up to 150 f1m wide at the transection site exhibits intense anti-fibronectin immunoreactivity. This site contained cells and processes with ultrastructural characteristics of fibroblasts and abundant collagen fibrils. Moreover, on fibroblast cultures derived from regenerating optic nerves, retinal axons grew to considerable density in vitro. Since fibroblasts are constituents of the interfascicular spaces and outer nerve sheath of the normal goldfish optic nerve, the present data imply that fibroblasts of either source migrate into the.lesion. Judging from fibronectin immunostaining they remain there during the passage of regenerat ing axons, and thus may provide physical and perhaps molecular support for axon growth. The fibroblasts are again restricted to interfascicular spaces after restoration of the astrocytic glia limitans around regenerated fascicles. .

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