Circulating monocytic cells infiltrate layers of anterograde axonal degeneration where they transform into microglia

SPECIFIC AIMSLesion-induced anterograde (Wallerian) degeneration of axons within the central nervous system (CNS) leads to rapid recruitment of cells that are immune-positive for markers of the monocyte lineage and which had been previously regarded to represent exclusively intrinsic microglia. We tested this view using entorhinal cortex lesion (ECL) to induce lamina-specific axonal degeneration in the dentate gyrus of mice grafted with GFP-transduced bone marrow and nonchimeric animals intrasplenically injected with the cell tracker CFDA, both allowing for clear-cut detection of blood-derived monocytic cells within the CNS.PRINCIPAL FINDINGS1. Blood-derived cells infiltrate deafferentiated layers and transform into microgliaStereotaxic lesioning of the medial portion of the perforant path by ECL induces lamina-specific degeneration in its termination zone, the middle molecular layer (MML) of the dentate gyrus, while the inner and outer molecular layers (IML/OML) are not affected. The contralateral hippoc...