Different morphological phenotypes of spinal microglial cells observed with confocal laser scanning microscopy. Four types of spinal microglial cells were detected in control mice. (A, B) Ramified microglial cells have radially projecting processes which are long, thin with fine ramifications. (C) Hypertrophied cell has large soma and thick, short and radially projecting processes with fewer ramifications. (D) Mono-polarized microglia (arrow) has one main process (arrowhead) which is thick and projects toward one direction. (E, F) Bipolarized microglia (arrow) usually has spindle-like cell body and two main processes emanating from the opposing poles of the cell body and projecting in opposite directions. Bar = 10 μm in A-C, 20 μm in D-F.