Retinal ganglion cell and nonneuronal cell responses to a microcrush lesion of adult rat optic nerve

Injury of the optic nerve has served as an important model for the study of cell death and axon regeneration in the CNS, Analysis of axon sprouting an d regeneration after injury by anatomical tracing are aided by lesion model s that produce a well-defined injury site. We report here the characterizat ion of a microcrush lesion of the optic nerve made with 10-0 sutures to com pletely transect RGC axons. Following microcrush lesion, 62% of RGCs remain ed alive 1 week later, and 28% of RGCs, at 2 weeks. Optic nerve sections st ained by hematoxylin-based methods showed a thin line of intensely stained cells that invaded the lesion site at 24 h after microcrush lesion. The les ion site became increasingly disorganized by 2 weeks after injury, and both macrophages and blood vessels invaded the lesion site. The microcrush lesi on was immunoreactive for chondroitin sulfate proteoglycans (CSPG), and an adjacent GFAP-negative zone developed early after the lesion, disappearing by 1 week. Luxol fast blue staining showed a myelin-free zone at the lesion site, and myelin remained distal to the lesion at 8 weeks. To study the ax onal response to microcrush lesion, anterograde tracing was used. Within 6 h after injury all RGC axone retracted back from the site of lesion. By 1 w eek after injury, axone regrew toward the lesion, but most stopped abruptly at the injury scar. The few axons that were able to cross the injury site did not extend further in the optic nerve white matter by 8 weeks postlesio n, Our observations suggest that both the CSPG-positive scar and the myelin -derived growth inhibitory proteins contribute to the failure of RGC regene ration after injury. (C) 2001 Academic Press.