Immunohistochemistry for Ym1-positive MG/MΦ in the cortex, corpus callosum and hippocampus of young and aged TBI mice. (A) Ym1-positive amoeboid MG/MΦ surrounded the lesion site and were dispersed throughout the cortex of aged TBI mice (ii), whereas there were fewer Ym1-positive MG/MΦ in the cortex of young TBI mice and some cells displayed a ramified/hypertrophic cellular morphology (i). Bar = 100μm. (B) In the corpus callosum there were numerous Ym1-positive ramified/hypertrophic MG/MΦ in young TBI mice (iii, iv), whereas Ym1-positive MG/MΦ in the aged TBI mice displayed heterogeneous cellular morphologies as both Ym1-positive amoeboid (v) and ramified/hypertrophic (vi) cellular morphologies were observed. Bar = 50μm. (C) In the hippocampus of young TBI mice there were numerous highly branched Ym1-positive ramified/hypertrophic MG/MΦ (vii). In contrast, there were fewer of these cells observed in the hippocampus of aged TBI mice. Bar = 50μm.