Neuro-muscular transmission in insects.

Abstract

I. An investigation was made on the electrical and mechanical responses of the sound muscle of the cicada (Graptopsaltria nigrofuscata) as well as of the wing muscle of the locust (Oxya st.) following indirect stimulation, and also on the other phenomena relating to the neuro-muscular transmission.II. Observations on the sound muscle.(1) An extremely rapid twitch appeared by a single indirect stimulus, the duration of the twitch being about 10 msec. or less at 30°C.(2) When the records are obtained between an active electrode at various points along the muscle surface and an indifferent electrode, surface action potentials to single indirect stimulus are positive and monophasic, showing little variation in the latent period.(3) Neither electrical nor mechanical response show gradation with changes in the stimulus strength. Though the so-called direct stimulation is, in fact, accomplished, the lack of sensitivity to the electric current of the muscle fiber can not be denied in this insect.(4) Miniature discharges are often found in injured muscles, and they are supposed to be due to the dissociate activity evoked by the injury in the muscle fibers or of the small specialized membrane areas of the fiber related to the nerve ending.(5) The peak voltage of action potential to repetitive stimuli shows no gradation at any stinnilus frequency. At high frequency a fusion of action potentials occurs as in the case of the mechanical responses. No results showing evident facilitation are obtained.III. Observations on the wing muscle.(1) During excitation a potential gradient develops along the muscle, and the negativity before and after which there is positivity in the region near the nerve entrance.(2) The intra-cellular action potential does not exceed the value of the resting potential which ranges between 50-70 mV. By the repetitive stimutation the peak voltage of action potential is almost constant at all frequencies, and a fusion also occurs as in the case of the surface action potential of the sound muscle.It is concluded that in the electrical response of the insect muscle the local process plays much more important role than the conduction process.The author wishes to express his indebtness to Prof. Y. Katsuki for his kind advice and criticism, to Dr. and Mrs. I. Tasaki for their kind advice on the work with the capillary electrode., to Mr. H. Uchiyama for his kind criticism in preparing this paper and to Drs. A. Watanabe and H. Takeda for their kind assistance at every stage of the investigation.