FLUORESCENT DYE PRELABELED MICROGLIAL CELLS MIGRATE INTO ORGANOTYPIC HIPPOCAMPAL SLICE CULTURES AND RAMIFY

Microglial cells with their characteristic ramified morphology are exc lusively found in healthy CNS tissue, whereas various pathologies are associated with the occurrence of amoeboid, macrophage-like cells. It is still a matter of discussion whether amoeboid cells are blood-deriv ed macrophages, or whether a characteristic change in morphology, refl ecting activation of previously ramified microglia, takes place. Cells in dissociated microglia culture obtained from healthy rat brains, in evitably developing this amoeboid morphology, were labelled with a flu orescent dye and transferred onto organotypic hippocampal slice cultur es. Prelabelled cells with amoeboid morphology invaded these slice cul tures and had, after 9 days in vitro, gradually transformed into highl y ramified cells. Our findings strengthen the hypothesis that the obse rved amoeboid and ramified cells belong to a single population of micr oglia, appearing with different morphologies depending on the presence of stimuli provided by the CNS microenvironment. Microglial cells obv iously appear in different shapes and can switch from immunologically resting to activated modes and vice verse.