ABSTRACT
A microglial cell is a resident cell of the central nervous system (CNS). The CNS represents an exceptional organ in that its capillaries are nonfenestrated and the endothelial cells form tight junctions which, in essence, constitute the blood-brain barrier. The immature CNS contains considerably more brain macrophages than the mature CNS because large numbers of cells undergoing developmentally regulated cell death are being eliminated. At the time of birth the CNS contains large numbers of microglial cells, most of which are of the intermediate type with stout cellular processes. One of the major functions of intermediate microglia in the developing CNS is the continuous removal of cell debris resulting from naturally occurring cell death. In light of the aforementioned close relationship between neurons and perineuronal microglial satellites, it would seem that any normally occurring communication between neurons and microglia is altered after CNS injury in such a fashion as to stimulate microglial activation.
