Spreading depression resulting from cortical punctures

In acute experiments on cats under deep Nembutal anesthesia punctures of the cortex caused a prolonged negative shift of its surface potential (up to 15 mv, 5.5 min), which was followed by a prolonged positive shift. During these shifts of the potential, both components of the direct response were depressed. The changes in potential and the depression of electric activity spread over the cortex at a mean rate of 65 micrometers/s. The phenomenon arised when the punctures are made with a pipet 20 micrometers and above in diameter. A puncture of the surface structures was critical; passage of the pipet through the middle and deep layers was ineffective. It is assumed that when cortical punctures are made the SD is caused by K(+) ions which leak out of the destroyed glial structures.