Changes in Volume of Cortical Neuronal Elements During Asphyxiation

Abstract

Cortical electrical resistance increases considerably after cortical asphyxiation. After a latent period of about 3 minutes a sudden resistance change occurs during which one-third of the cortical conductivity may be lost. It was postulated that this drop in conductance is due to a transport of ions, accompanied by water, from the extracellular spaces into the cortical cells and fibers. A swelling of cortical elements must thus be expected. The cortex was quickly frozen either before or after the sudden conductivity drop. The frozen cortex was kept in alcohol for 1 week during which the alcohol dissolves the ice in the cortex and fixes the tissue. Histological preparations stained with gallocyanin and with silver for the investigation of cells and fibers respectively were made. In rabbit cortex the mean diameter of nerve cells after the sudden conductivity drop was more than 11% greater than before the resistance change, which represents a volume increase of about 40%. The apical dendrites increased in diameter about 30% implying a volume increase of about 70%. If one assumes that the combined perikaryal and dendritic volume is 30% of the total cortical volume, then the amount of fluid stored by the cortical neurons during the sudden resistance change would amount to about 16% of the cortical volume. Such fluid and ionic movements are ample to explain the resistance changes observed.