TRANSCELLULAR LABELING OF ACTIVATED RETINAL MICROGLIA FOLLOWING TRANSECTION OF THE OPTIC-NERVE

Objectives and Methods: A fluorescence and electron microscopical appr oach, based on the transection of the rat optic nerve and the axotomy- induced transcellular labelling of activated retinal microglial cells, using the carbocyanine dye 4Di-10ASP, was employed to monitor phagocy tosis in the injured central nervous system. After survival limes rang ing between two days up to three months, retinal Aat-mounts were inspe cted and photoconverted. Results: Fluorescence microscopy revealed tha t within a few days microglia became transcellularly stained due to th e phagocytosed 4Di-10ASP-labelled neuronal debris. Ultrastructural ana lysis confirmed that marked ganglion cell-derived material was incorpo rated into phagosomes of various sizes. Though immediate phagocytic in take was not observed, the nature of the detected phagosomes suggests that small fractions of degenerated neurons are incorporated. Conclusi ons: The approach presented, utilizing function-dependent transcellula r fluorescent labelling of phagocytic microglia, might enrich further experimental studies of glia-neuron interactions in the injured nervou s system.