Pharmacologic differences of similarly electrogenic neuraxial sites of the bullfrog

¹ Department of Neurology, College of Physicians and Surgeons, Columbia University, New York City

Surface-negative potentials of long duration were evoked in the spinal cord, optic tectum, olfactory bulb and olfactory epithelium of frogs by appropriate stimuli. These responses were differently sensitive to the differently acting amino acid drugs and to d-tubocurarine. The spinal cord negativity was reversibly eliminated by topical application of -aminobutyric acid (C₄). It was not affected by the longer-chain -amino acids (C₆ or C₈) nor by d-tubocurarine. The negativity of the optic tectum was eliminated by all these drugs, but early spike activity remained. Transient ‘spontaneous’ activity occurred after C₆ or C₈ were topically applied to the tectum. The tectal response to stimulating the retina with light was not affected by applying the drugs to the retinal surface itself. The responses recorded in the olfactory bulb by stimulating the nerve, and the responses of the olfactory epithelium to odoriferous stimuli were not affected by any of the testing drugs. Pharmacologic specificity of potentials which have similar appearances is thus demonstrated.