Silver impregnability of ischemia-sensitive neocortical neurons after 15 minutes of cardiac arrest in the dog.

The development of postischemic neuronal argyrophilia and the subsequent fate of argyrophilic neurons were studied in dogs after 15 min of complete cerebral ischemia and survival varying from 1 h to 7 days. Histopathological examination of the vulnerable neocortical region was performed using the Nauta degeneration method, and the time course of cellular changes was described. Clear-cut neuronal argyrophilia was found to precede cell body shrinkage and gradual disintegration corresponding to selective neuronal death. To clarify this initial stage of neuronal impregnability, the samples from the animals surviving 8 h postarrest were stained with toluidine blue or processed for electron microscopy, and the distribution of argyrophilic cells was confirmed to be identical with that of hyperchromatic or electron-dense cells. On the other hand, infrequently observed "tissue infarctions" exhibited no silver affinity in spite of apparent cellular damage. These findings indicate that enhanced impregnability is related to cytochemical processes incidental to the phenomenon of "selective neuronal death", which can be readily detected by the Nauta method.