A twitch tension method to assess motor nerve function in rat.

A simple and quantitative method is described which assesses the motor function of the rat tibial nerve by recording the twitch tension developed by the digital flexors. Stimulating electrodes are placed at the proximal end of the sciatic nerve of anesthetized rats, and the associated foot is immobilized on a sliding stage. The middle digit is connected via a thread to a force-displacement transducer and the sciatic nerve is stimulated supramaximally. The resulting twitch tension curve is recorded on an oscilloscope and/or signal averager. Measurement of the area and amplitude of the twitch tension curve provides an estimate of the recovery of motor function. The method is illustrated by examining the return of motor function following either sciatic nerve crush, or sciatic transection and repair. The results obtained are compared with other assessments of sciatic nerve function, such as the toe-spreading reflex and the analysis of walking tracks. The results from the twitch tension method are more sensitive, unaffected by changes in sensory function, and less prone to variation than the other assessments.