Abstract
One of us 1 described a temporary return of indirect excitability in the tongue of the curarized cat, following tetanization of the hypoglossal nerve. We have made some additional observations on the phenomenon, using the cat's peroneal nerve and tibialis anticus muscle. The experimental conditions were as described in our accompanying paper, 2 except that crude curare (1% solution) was administered instead of MgSO4.
Curarization was carried to the stage at which single stimuli, applied to the otherwise resting nerve, failed to elicit a muscular twitch. The nerve was then tetanized, for periods varying from 1 second to one minute, the frequency also being varied from 14 to 120 per second.
Comparing the results with those obtained on animals “curarized’ to the same stage with Mg 2 , certain similarities appear. In both conditions, (a) tetanization of the nerve is followed by a return of the response to single stimuli; (b) the degree of this recovery varies with the frequency of tetanic stimuli employed; (c) the duration of the recovery is about the same, following a given period of stimulation.
Under curare, however, the first twitches obtained during the recovery are relatively weak. The curve described by the successive twitches shows first a rising and then a longer falling phase. Following 5 seconds of stimulation of the nerve, at 120 per second, the maximum recovery is seen in 6 to 10 seconds. If the period of tetanization is lengthened to 20 seconds the entire recovery curve is stretched out, so that the rising phase lasts for half a minute or more.
It seems to have been proven earlier 1 that this recovery is produced through the motor innervation of the muscle, and not through other fibers in the mixed nerve.
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