Microglia is activated in spinal segments of nerve injured mice but not control mice. Left column, sham-operated; right column, CPN ligated. Nerve injury evoked an ipsilateral increase of microglial cells in superficial layers of L2 to L4 spinal dorsal horns, and also in deep layers of L3 and L4 spinal segments. No visible change occurred in L5 spinal segment. Asterisks indicate intact side. Bar = 350 um.