THE ACTION OF CHLORPHENESIN CARBAMATE ON THE FROG SPINAL CORD

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Abstract
Studies were carried out to elucidate the mechanism of action of chlorphenesin carbamate (CPC) and to compare the effect of the drug with that of mephenesin on the isolated bullfrog spinal cord. Ventral and dorsal root potentials were recorded by the sucrose-gap method. CPC caused marked hyperpolarizations and depressed spontaneous activities in both of the primary afferent terminals (PAT) and motoneurons (MN). The hyperpolarizations were seen in high-Mg2+ and Ca2+-free Ringer''s solution, suggesting that CPC has direct actions on PAT and MN. Various reflex potentials (dorsal and ventral root potentials elicited by stimulating dorsal and ventral root, respectively) tended to be depressed by CPC and by mephenesin. Excitatory amino acids (L-aspartic acid and L-glutamic acid) caused marked depolarizations in PAT and MN, and increased the firing rate in MN. CPC did not modify the depolarization but abolished the MN firing induced by the amino acids. Mephenesin reduced both the depolarization and the MN firing. The dorsal and ventral root potentials evoked by tetanic stimulation (40 Hz) of the dorsal root were depressed by the drugs. CPC has an apparent depressing action on the spinal neuron, and this action may be ascribed to the slight hyperpolarization and/or the prolongation of refractory period.