General physiology and pathophysiology of microglia

Microglial cells are of scions foetal monocytes that migrate into and disseminate within the central nervous system in early embryogenesis and in perinatal period. After invasion, microglial progenitors undergo specific metamorphosis and acquire a ramified morphological phenotype known as resting or surveillant microglia. These cells in the healthy brain have highly motile processes by which they scan their territorial domains. Microglial cells also acquire multiple receptors to neurotransmitters and neurohormones and retain receptors associated with their immune and defensive function. Insults to the central nervous system of diverse aetiology trigger a complex, multistage activation process that produce multiple activated microglia phenotypes, which have both neuroprotective and cytotoxic capabilities. These phenotypes are most likely disease/pathology context specific, and the balance between neurotoxicity and neuroprotection are critical for the resolution and outcome of neuropathological processes.