ELECTROMYOGRAPHIC STUDY ON DENERVATED MUSCLES IN THE DOG

Abstract

Denervated muscles of dogs were studied in situ with needle electrodes from the beginning to the 21st day of denervation. 1. Scattered electrical activity began to appear on the fifth day after denervation but their perisistency was of low order. Electrical activity showed a peak at about the end of the first week and decreased gradually thereafter, but it was elicitable throughout the observation period. Stabilized activity developed about 3 minutes following the needling. 2. Tapping increased the electrical activity after the fifth day, and the most conspicuous response appeared at about the end of the first week of denervation. 3. Acetylcholine and neostigmine enhanced the electrial activity. Repetitive outbursts of spike potentials and regularly discharging potentials were recorded after a single injection of acetylcholine, and the peak response was shown at about the end of the first week. Neostigmine also produced rhythmically repeating discharges. While acetylcholine failed to evoke any recordable response during the first 4 days after denervation, neostigmine could evoke electrical activity even on the 2nd day. 4. d-tubocurarine cancelled all electrical activity before the respiratory paralysis by curarization began. 5. The common type of spike potentials observed in the denervated muscle were di-or triphasic with an amplitude ranging from 100μV to 1.3mV and a duration varying from 1.9 msec. to 4.1 msec. In contrast to the motor unit potential, these potentials did not show marked differences in amplitude but their duration was obviously shortened. 6. The discharge-interval-time-series of the common type of single spike potentials observed in the denervated muscle were divided into three types. Partial series of the same type did not always produce a long series. 7. Polyphasic potentials, indicative of early reinnervation, were never observed throughout the experiment period. 8. On histopathological examination, marked thinning of muscle fibers was demonstrated but no degenerative changes were observed. Fundamental electromyographic features of the denervated muscle in a dog, were presented, although the experimental results obtained were not available for the explanation of the genesis of electrical activity in the denervated muscle.