Photomicrographs showing microglia in the brain. (A) Montage of a saggittal section showing the distribution of brain microglia in control mice. (a-d) Different types of brain microglial cells observed under confocal laser scanning microscopy. Brain microglial cells were classified as ramified (a), hypertrophied (b), mono-polarized (c) and bipolarized (d). Hypertrophied microglia were defined as having large soma, and short, thick and radially projecting processes. Ramified microglial cells were defined as possessing thin, slender, radially projecting processes with well-developed ramifications. Monopolarized microglial cells were defined as having one thick process with well developed ramifications extending toward one direction. Bipolarized microglial cells were defined as having two thick processes emanating from the opposing poles of the cell and projecting in the opposite directions. Bar = 1 mm in A, and 20 μm in a-d.