ACTION CURRENT OF THE SINGLE LATERAL-LINE NERVE FIBER OF FISH

Abstract

The function of the lateral-line organ of Japanese eel has been examined precisely by means of recording the impulse discharges from a single nerve fiber supplying the organ, which was activated by various kinds of natural and artificial stimulations. The results obtained are summarised, as follows.1) Examinations by water flow.With a calm water flow only thin nerve fibers could be excited. Somewhat higher rates of flow first excite the thicker fibers. The aspect of discharges was not changed by the direction of the water flow. The number of discharges from a single nerve fiber increased with increase of the flow rate. The maximum discharge frequency attained was different in fibers with different diameters. The relation between the average number of spikes and the logarithm of the flow rate was nearly linear in every single fiber examined.2) Examinations by pressure and touch.Applying pressures of various grades on the skin surface along the lateralline, results were obtained, which were similar to those above mentioned qualitatively and quantitatively. However, some very thick fibers of phasic nature were' very sensitive to the impulse shock and had a relatively low thresholds. They showed sometimes inhibitory phenomena during stimulation, and facilitatoryeffect after the cessation of the stimulation. The lateral-line organ of fish has, too, a dual innervation of slow and phasic fibers, as many other sensory organs have.3) Examination by mechanical vibrations.In all fibers examined, the discharges were seen to appear in every cycle of mechanical vibrations, provided that the vibration frequency was relatively low. With very low frequencies we had generally a few spikes in each cycle, which changed into one-for-one relation in the middle range of frequency (20-50 cps.). When the stimulus frequency was further increased, there appeared the discharge deficit oftener, the more frequent the stimulus. The largest frequency producing one-for-one appearance of the spikes was different in different fibers, owing to the different diameters. The thicker the fiber the higher it was. The thinnest fiber could follow the vibrations of under 10 cps. only. On the contrary most of the thicker fibers could follow those of 50 cps., and the thickest one even to those near 100 cps.4) The D. C. stimulation of the receptor easily evokes the iterative firing of the nerve fiber. The average number of spikes had a linear relationship with the logarithm of the current strength. The threshold for repetitive discharges could not be determined precisely, but it was certain that weak currents made the thinner fibers discharge more easily than the thicker fibers. Many fibers were excited by the ingoing current and a few by the outgoing one.5) The A. C. stimulation of the receptor evoked, also, discharges in every stimulus cycle. For the low stimulus frequency there were a few spikes in the negative phase only. With the increase of the stimulus frequency the number of spikes in one stimulus cycle decreased gradually, to become the one-for-one appearance, to random falling out of the spikes, and finally to a stage where there resulted only one impulse in many stimulus cycles. The maximum frequency for one-for-one appearance of the spikes was related to the fiber diameter, the thicker fiber being able to follow a higher frequency. The upper limit could not be determined owing to the disturbances brought by the stimulus current itself.The strength of the stimulating current caused changes in the aspect of the discharges. Namely, an increase in strength brought more spikes to appear in the negative phase. With very low frequency it resulted in some spikes appearing in the positive phase, too. If the stimulus frequency is high, and if the current is sufficiently strong, then the one-for-one appearance of the spikes continued to follow much higher frequency, than when it is weak.