Microglia/macrophages are activated and recruited to the lesion site 7 days after H-I. Exposure to H-I at P7 resulted in increased CD11b – positive cells, as measured by OX-42 immunoreactivity, in ipsilateral somatosensory cortex (B) compared to contralateral control (A). CD11b – expressing cells were abundant in corpus striatum of both hemispheres but showed distinct morphology (C,D). Cells in the ipsilateral striatum displayed the activated amoeboid phenotype (D) similar to those in ipsilateral cortex (E) when compared to the ramified morphology in the contralateral hemisphere (C) that is associated with a less activated state. Scale bars = 100 μm (A,B), 50 μm (C-E).