The strychnine‐like action of curare and related compounds on the somatosensory evoked response of the rat cortex

Abstract

1 . Drugs were applied to the cerebral cortex of rats anaesthetized with pentobarbitone and changes measured in the somatosensory primary evoked response. 2 . Computer-derived averages of thirty-two consecutive responses yielded stable and consistent measurements of the potential changes comprising the evoked response, and comparable records from the opposite (non-drug treated) cortex provided an essential control for systemic actions of the drug. 3 . The modifications produced by curare and strychnine were indistinguishable. The first positive wave (peak latency 7 msec) was unaltered; the second positive wave (peak latency 11.5 msec) was variably enhanced, and the first and second negative waves (peak latencies 16 and 40 msec) were replaced by a much larger negative wave (peak latency 22 msec). 4 . The time of onset of the effect on the negative waves and the maximal amplitude attained by the abnormal negative wave were related to the log concentration of the drug used. Curare is approximately 10 times more potent than strychnine. 5 . Toxiferine I, di-allylnortoxiferine and atropine also produced this effect but were less potent than strychnine. 6 . Succinylcholine, dihydro-β-erythroidine and gallamine triethiodide did not produce this effect (in concentrations up to 10⁻³M). 7 . The observations are consistent with an action of curare and strychnine on an intracortical cholinergic inhibitory system, but other possibilities including a “non-specific excitatory action” cannot be excluded.