Topography of hypoxic injury proved by argyrophilia in postnatal rat brain

The argyrophil III method, a new esterification-silver staining approach, was used to elucidate regional differences in the susceptibility of developing brain to hypoxic-ischemic (H-I) injury. We created a unilateral common carotid artery-ligation model with hypoxia (8% oxygen) in postnatal day (P) 7, P14 and P21 rats. The argyrophil (i.e., deteriorated) neurons were apparent in the ipsilateral hippocampus, cortex, and striatum in each age group. Argyrophil neurons exhibited some morphological signs of the "early phase" of injury preceding the loss of structure and/or cell death in the "late phase," as indicated by hematoxylin-eosin (H-E) staining. The argyrophil neurons were apparent as early as 12 hours after the insult, whereas the histological changes revealed by H-E staining were subtle. The early phase and late phase histological changes had a stereotyped pattern of appearance in all ages studied. However, the duration of H-I situation required to produce argyrophil cells differed according to age. The most resistive age was P14 (P14 > P7 > P21) in this observation. Therefore, argyrophil III staining is feasible for H-I brain damage model in neonates. The results suggest that both the early phase and the late phase pathological processes after H-I injury have a characteristic topographical vulnerability that does not change during development but have a differing susceptibility according to age.