Graded Hypoxia-Oligemia in Rat Brain

Neuropathological examination was done in normotensive rats immediately and 30 minutes after unilateral carotid artery clamping combined with 30 minutes of graded hypoxemia. No abnormalities were found in any hemisphere contralateral to the clamp, and they were absent or rare even in the ipsilateral hemisphere immediately after hypoxic exposure. However, after 30 minutes reoxygenation, ischemic neuronal alterations were present in the ipsilateral hemisphere of most animals exposed to arterial oxygen tension (Pao2) 28 mm Hg, and were more pronounced after Pao221 mm Hg. The distribution of ischemic neurons conformed to well-established patterns of selective vulnerability to hypoxia and was unaccompanied by vascular abnormality. Neuropathological study with the light microscope may be more sensitive than biochemical assay of the hemispheres for detecting small numbers of neurons undergoing ischemic cell change.