DYE-INDUCED PHOTOLESION IN THE MAMMALIAN RETINA - GLIAL AND NEURONAL REACTIONS

Irradiation in the presence of a dye applied to the extracellular spac e is known to produce degenerative features in irradiated neurones and fibers. In the present study, we confirmed the potential use of this procedure as a lesion technique by showing the removal of degenerating elements as part of the glial reaction to the lesion. The dye Rose Be ngal was applied to the vitreous body of a rat eye and a T-shaped irra diation pattern was projected onto the retina within the absorption ba nd of the dye. Degenerative features were restricted to the irradiated area, which could be readily identified from its shape. Retinae exami ned after various survival times showed that macrophages invaded the d amaged area within 1 day, and that mitotic activity of reactive glial cells subsequently occurred in the vicinity of the wound. Both cell ty pes were identified by their structural features. Macrophages were als o revealed by a staining technique using the dye Nile Red, whereas rea ctive glial cells were immunolabeled with an antibody directed against the glial fibrillary acidic protein. Reactive glial cells helped the macrophages to gradually remove injured cells and damaged processes. T heir main task, however, appeared to be in scar formation, since their processes seemed to suture the lips of the wound together and restore the limiting membrane at the inner retina. After 2 months' survival t ime, the parent ganglion cells of most disrupted axon bundles had retr ogradely degenerated, but regenerating ganglion cell axons were also o bserved. These results provide some new data about healing processes i n the retina. They demonstrate that the dye-induced photolesion techni que can be used to either remove or axotomize selected neurones in neu ral networks which have been made optically accessible. (C) 1993 Wiley -Liss, Inc.