Single fiber electromyography. A method for the evaluation of motor axonopathy during toxicity studies in dogs.

In man, single fiber electromyography is used as a very sensitive indicator for the assessment of functional changes in motor nerves. The purpose of the present study was to adapt the above testing procedure to allow repeated investigations of dogs used in subchronic toxicity tests. Experiments were performed on anesthetized pure-bred beagle dogs. Action potentials from single muscle fibers in response to electrical stimulation of motor nerves were recorded with Medelec microelectrodes, amplified with a Medelec system and monitored on a Tektronic oscilloscope. Repeated electrical stimulation with pulses of 0.03 msec and 1 p.p.s. produced characteristic action potentials of single muscle fibers consisting of a positive, followed by a negative, deflection having a duration of from 500 to 800 microseconds altogether. Successive potentials occurred with a variable latency (the jitter) ranging from +/- 5 to 15 microseconds. Quantitative evaluation of the jitter will allow the clinical evaluation of motor axonopathies in dogs.