FIBROBLASTS AT THE TRANSECTION SITE OF THE INJURED GOLDFISH OPTIC-NERVE AND THEIR POTENTIAL ROLE DURING RETINAL AXONAL REGENERATION

The region at and around the site of optic nerve transection (ONS) in goldfish, topologically the equivalent of the glial scar in mammals, i s reported to remain free of astrocytes over weeks, but its cellular c onstituents are unknown.To learn what type of cell occupies the site o f injury and thus provides support for the rapidly regenerating retina l growth cones, immunostaining experiments at the light microscopic le vel and electron microscopic examinations were undertaken. Between 2 a nd 30 days after ONS, an area up to 150 mu m wide at the transection s ite exhibits intense anti-fibronectin immunoreactivity. This site cont ained cells and processes with ultrastructural characteristics of fibr oblasts and abundant collagen fibrils. Moreover, on fibroblast culture s derived from regenerating optic nerves, retinal axons grew to consid erable density in vitro. Since fibroblasts are constituents of the int erfascicular spaces and outer nerve sheath of the normal goldfish opti c nerve, the present data imply that fibroblasts of either source migr ate into the lesion. Judging from fibronectin immunostaining they rema in there during the passage of regenerating axons, and thus may provid e physical and perhaps molecular support for axon growth. The fibrobla sts are again restricted to interfascicular spaces after restoration o f the astrocytic glia limitans around regenerated fascicles. (C) 1995 Wiley-Liss, Inc.