ISCHEMIC NEURONS IN RAT BRAINS AFTER 6, 8, OR 10 MINUTES OF TRANSIENTHYPOXIC ISCHEMIA

The incidence and distribution of ischemic (necrotic) neurons in the b rains of rats 72 hr after hypoxic ischemia induced via asphyxiation is described and scored. Anesthetized Sprague-Dawley rats (10/group) wer e endotracheally intubated and had their airways occluded for 6, 8, or 10 min, which resulted, respectively, in approximately 3, 5, or 7 min of pulselessness (MABP < 10 mm Hg). Survival was 10/10, 9/10, and 6/1 0 in the 6-, 8-, and 10-min groups: deaths occurred within 1 hr after resuscitation. At 72 hr, rats were reanesthetized and their brains wer e perfusion-fixed with 3% buffered paraformaldehyde. Paraffin-embedded , 5-mu m-thick, H&E-stained sections at 5 coronal levels of the brain had shrunken, hypereosinophilic ischemic neurons in 12 anatomic region s. Ischemic neurons were most consistently found in the lateral reticu lar thalamic nucleus: lateral caudoputamen; CA1 region of the hippocam pus; subiculum; and, with longer asphyxia times, among cerebellar Purk inje neurons. Categorical histologic damage scores were assigned to af fected regions on the basis of manual counts of ischemic neurons and s ummed for the whole brain. Brain histologic damage scores were signifi cantly (p < 0.01) different for the 6-, 8-, and 10-min groups (means o f 8 +/- 2; 14 +/- 4; and 22 +/- 4). Brain regions where both the numbe r of rats affected and ranked categorical scores for ischemic neurons increased with asphyxia time were the lateral caudoputamen and cerebel lar Purkinje neurons.