THE INFLUENCE OF CERTAIN DRUGS ON THE CRUSTACEAN NERVE-MUSCLE SYSTEM

Abstract

The effects of a wide selection of drugs on the peripheral nerve-muscle preparations of the cheliped of the crayfish, Cambarus clarkii, were studied. Of all drugs used, the local anaesthetics were the only ones which, as a group, showed the customary vertebrate effects on crustacean preparations. In general, the effects of the drugs used in the investigation were limited to changes in the excitability of the nerve fiber. These effects were of two types; either the refractory period of the nerve was markedly lengthened, or the nerve fiber became so hypersensitive that excitatory stimuli set up multiple discharges in the nerve. The effects of the drugs on peripheral inhibition were studied, with the conclusion that the substances exert little effect on the mechanisms involved in these phenomena, especially on those responsible for supplementary inhibition. An investigation was made into certain "reversal" effects in which stimulation of the inhibitory axon showed an excitation, and in which stimulation of the excitatory axon showed an inhibitory effect. Of these, the former is ascribed to stimulation of the adjacent hypersensitive motor fiber upon stimulation of the inhibitor; the latter, to a Wedensky-block. The central effects appear to be quite different from the effects on the peripheral systems.