Dye-induced photolesion in the mammalian retina: glial and neuronal reactions.

Irradiation in the presence of a dye applied to the extracellular space 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 Bengal was applied to the vitreous body of a rat eye and a T-shaped irradiation pattern was projected onto the retina within the absorption band of the dye. Degenerative features were restricted to the irradiated area, which could be readily identified from its shape. Retinae examined after various survival times showed that macrophages invaded the damaged area within 1 day, and that mitotic activity of reactive glial cells subsequently occurred in the vicinity of the wound. Both cell types were identified by their structural features. Macrophages were also revealed by a staining technique using the dye Nile Red, whereas reactive 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. Their 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 time, the parent ganglion cells of most disrupted axon bundles had retrogradely degenerated, but regenerating ganglion cell axons were also observed. These results provide some new data about healing processes in the retina. They demonstrate that the dye-induced photolesion technique can be used to either remove or axotomize selected neurones in neural networks which have been made optically accessible.