Bilateral foci of necrosis (arrows)efface the architecture of the retrosplenial cortex of a mouse (A) exposed to 476 ppm carbonyl sulfide for 4 h on day 0 and for 1 h on day 1, with euthanasia on day 8. A higher-magnification photomicrograph (B) of the retrosplenial cortex in this mouse reveals degenerating (eosinophilic, “red, dead”) neurons (arrows), a glial scar with numerous reactive microglia (arrowheads), and vacuolar change (clear spaces) in the surrounding neuropil. In mice exposed to H2S by inhalation, similar foci of necrosis (arrows) were typically present in the inferior colliculus of the brainstem (C) and in the thalamus. Hematoxylin and eosin (H&E) stain; scale bar is 1000 microns in A and C and 100 microns in B.