Chronically Implanted Polarographic Electrodes

Abstract

Insulated metal polarographic cathodes were permanently implanted in the brains of cats, allowing continuous recording of oxygen availability. A study was made of the current flow as related to applied potential, nature of the cathode and alterations in brain physiology. Mean oxygen availability increases about 2-fold on breathing oxygen, 3-fold on breathing air containing 14% carbon dioxide and decreases with hypoxic gas mixtures. The oxygen availability to the brain is only slightly altered by a wide variety of pharmacological agents, including anesthetics and pressor agents, but appears to parallel changes in carbon dioxide tension and to be increased by ethyl and vinyl ether. A day or two after implantation of a cathode, waves having a frequency of 6–12/min. and an amplitude of up to ±30% of the mean current are obtained. Their frequency and amplitude are temperature-dependent and can be altered by various chemical agents. The waves are asynchronous from cathodes spaced farther apart than a few millimeters. All the observations to date are consistent with the concept that these waves represent fluctuations in the amount of oxygen available at the cathode due to rhythmic variations in blood flow through the finer cerebral vessels. Submitted on February 19, 1958