Morphological and behavioural variation in CNS innate defence cell microglia is development and age sensitive

Aim:Microglia,the innate defence cells in central nervous system(CNS),alters their shapes and function with age.We observed and identified these morphological changes and functional association throughout the developmental gradient until adulthood in rat brain.Methods:Early and late embryonic stages,neonates and adult brains of albino rats were sectioned for routine Haematoxylin Eosin(HE)staining and specialized silver-gold staining to show distribution and morphological variation in situ.Isolated microglia from different age groups was subjected to scanning electron microscopy(SEM)for observing ultrastructural shapes of microglial cells.The Viability of isolated cells was measured by trypan blue staining and their cellular identity by immuno-staining for CD11b.Finally,phagocytic limitations of the cells in normally developing brain were assessed by carbon particle ingestion and oxidative burst through nitroblue tetrazolium assay to investigate microglial age-sensitivity behavioural response.Results:HE staining spotted overall cellular distribution in the brain and cells with monocytic appearance among the other CNS cells.On contrary,silver-gold staining showed variable morphologies of microglia in various age groups and also showed the appearance of ramified microglia in adult.Nearly 90%of isolated cells were viable and positive for CD11b.SEM showed variable shapes of amoeboid and ramified forms.Immunofluoresence confirms microglial identity.Functionally,microglia showed an age dependent baseline phagocytic capacity in normal condition which changes with developmental phase and age with most active phagocytic behaviour around perinatal phase.Conclusion:In normally developing brains,microglia shows variability in morphology and baseline phagocytic activity that changes with age.These results may represent the normal physiology of CNS development and function.