Changes in the Diameter of Apical Dendrites During Spreading Depression

Abstract

One of the concomitants of spreading depression is a considerable increase in the cortical electrical resistance. After cortical asphyxiation a similar resistance increase has been observed. It was postulated that these resistance increases are due to a transport of ions from the extracellular compartment into the cortical cells and fibers. To maintain osmotic equilibrium this has to be accompanied by water transport causing a swelling of cortical elements. A swelling of nerve cells and apical dendrites has been found to accompany the asphyxial resistance increase. In the present paper the diameters of apical dendrites during spreading depression were compared with the dendritic diameters in the contralateral hemisphere where no spreading depression was in progress. A mean increase in diameter of 17% was observed during spreading depression. No swelling of the apical dendrites was observed in the retrosplenial area which is not normally invaded by spreading depression. These findings support the notion that the resistance change during spreading depression is due to the same mechanism as that after cortical asphyxiation, namely to an ion transport accompanied by a water movement from extra- into intracellular spaces.