Properties of spreading depression during different phases of cyclic excitation of the cerebral cortex in the rat

Properties of cortical spreading depression (SD) were studied at different phases of cyclic excitation occurring in the rat neocortex under low-frequency electrostimulation. SD waves appeared in the cortex spontaneously or were elicited by KCL microinjection. It is shown that the state preventing penetration of SD waves into the stimulated area (blockade of SD) developed during each cycle of excitation. The spatial extent of the SD blockade depended on the degree of excitation generalization over cerebral cortex. After the end of excitation the ability of the stimulated cortical area to conduct SD waves restored. In the intervals between the excitation cycles the SD waves duration was on the average half as long as before stimulation. The development of SD blockade during active phase and restoration of SD waves in the intervals confirms a hypothesis that K+-Na+ pump activation prevents the propagation of SD.