Objectives and methods: A fluorescence and electron microscopical approach, 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 phagocytosis in the injured central nervous system. After survival times ranging between two days up to three months, retinal flat-mounts were inspected and photoconverted.
Results: Fluorescence microscopy revealed that within a few days microglia became transcellularly stained due to the phagocytosed 4Di-10ASP-labelled neuronal debris. Ultrastructural analysis confirmed that marked ganglion cell-derived material was incorporated into phagosomes of various sizes. Though immediate phagocytic intake was not observed, the nature of the detected phagosomes suggests that small fractions of degenerated neurons are incorporated.
Conclusions: The approach presented, utilizing function-dependent transcellular fluorescent labelling of phagocytic microglia, might enrich further experimental studies of glia-neuron interactions in the injured nervous system.