APICAL DENDRITES AND PROPAGATION OF SPREADING DEPRESSION IN CEREBRAL CORTEX

Abstract

Propagation of spreading depression (SD) in the cerebral cortex was studied using the slow potential variation characteristic of SD at two points along its spread. Shallow cuts through the upper 2 or 3 cortical layers made between the recording points temporarily blocked passage while cuts through the upper one-half of the cortex produced permanent block. Molecular layer preparations are those in which only the superficial layer of the cortex was not cut. Passage remained via this layer in such a preparation. The inference from cut experiments was that apical dendrites are crucially involved in passage of SD. Gamma aminobutyric acid (GABA), 1.0%, and nicotine, 0.1%, placed over the line of cut of the molecular layer preparation each could reversibly block passage of SD. If GABA or nicotine were true synaptic blocking agents, synaptic mechanisms would be involved in SD transfer. Reasons are given for the contiguity hypothesis, where a release of substance from depressed dendrites is believed to initiate SD in the nearby dendrites.