Respiratory Effects from the Passage of Polarizing Currents Through the Medulla Oblongata. ∗

Abstract

In a series of experiments now extending over several years we have been attempting to investigate the site and functioning of the central respiratory mechanism by exposing the posterior portion of the floor of the fourth ventricle and studying the effects of local cooling of that region and the effects of the application of certain drugs to it. It was felt that additional information might be gained by studying the effects of the passage of polarizing currents through this part of the brain stem for it seemed likely that if too great current density was avoided, it might be possible in this way to produce temporary depression of function without causing irreparable tissue damage.

Twenty experiments have been performed. In all these, dogs anesthetized either with morphine and urethane or with pentobarbital were used. As one electrode we used the instrument which had previously served as our applicator in the experiments on central cooling. The silver chloride plated silver tip of this electrode, triangular in shape, measuring about 3 mm on a side, was placed in light contact with the floor of the fourth ventricle in the calamus scriptorius. A large, indifferent electrode, also silver-silver chloride was wrapped in cotton soaked in saline and placed, in some experiments, in the mouth, in others beneath the skin over the occiput.

With the electrodes so placed, a current of only a few milliamperes resulted in profound changes in respiration. In some cases the effects were completely reversible while in other cases recovery did not occur, suggesting that permanent damage had been done. Inspection of the brain in these latter cases frequently revealed gross tissue destruction.

The results, somewhat variable, seem to fall into 2 groups. In the majority of the experiments, the effect of the passage of such a current was a decrease in amplitude of respiration proportional to the current strength and independent of the direction of current flow. When respiration ceased, it was with the chest in the expiratory position. These results we believe represent the effect of depression of the entire respiratory center—inspiratory as well as expiratory parts. Two examples of this type of response are illustrated in Fig. 1 A and B.