Velocity-Dependent Ankle Torque in Rats after Contusion Injury of the Midthoracic Spinal Cord: Time Course

Abstract

Progressive neurophysiological changes in the excitability of the pathways that subserved ankle extensor stretch reflexes were observed following midthoracic contusion. The purpose of the present study was to determine the nature and time course of velocity-dependent changes in the excitability of the ankle stretch reflex following T(8) contusion injury. These studies were conducted in adult Sprague-Dawley rats using a 10-g 2.5-cm weight drop onto the exposed thoracic spinal cord (using an NYU injury device and a MASCIS protocol). Velocity-dependent ankle torques and triceps surae EMGs were measured in awake animals over a broad range of rotation velocities (49-612 deg/sec) using instrumentation and protocol previously reported. EMGs and ankle torques were measured before and at weekly intervals following injury. Statistical tests of the data included within group repeated measures ANOVA and between group one-way ANOVA comparisons with time-matched control animals. An alternating pattern of significant increase followed by significant decrease in velocity-dependent ankle torque was observed during the first postinjury month. An increase of 33% in the peak torque and 24% in peak EMG magnitude at 612 deg/sec was observed in the first week. EMG burst amplitudes, that were timed-locked to the dynamic phase of the rotation, were observed to increase and decrease in a manner, which indicated that the changes in torque included stretch-evoked active contractions of the ankle extensors. During the second and third postinjury months, consistent 24-40% increases in the peak torques and 17-107% increases in the EMG magnitudes at the highest velocity were observed. No significant increases in torques were observed in the slowest rotation velocity in these periods.

Cellular transplantation strategies for spinal cord injury and translational neurobiology

“…Nevertheless, it was interesting that fetal spinal cord transplants into sites of midthoracic contusion injuries in rats mitigated lumbar motoneuron hyperexcitability seen after these injuries. This observation was not only important from a transplantation perspective, but also because it led to renewed interest in the neurophysiological principle of "rate modulation" of primary afferent transmission to motoneurons, which has been associated with spasticity in rats [302][303][304][305] and humans after SCI. 306,307 This finding provided an opportunity for neurophysiological protocols used in animal experiments to be translated to human studies as discussed in more detail below.…”

Trans-Spinal Direct Current Stimulation Alters Muscle Tone in Mice with and without Spinal Cord Injury with Spasticity

“…For example, hypotonia is commonly observed in cerebellar deficits (Gilman, 1969), spinocerebellar lesions (Subramony and Ashizawa, 1993), and developmentally delayed children (Shumway-Cook and Woollacott, 1985). Hypertonia is associated with many CNS disorders, including stroke (Burke et al, 2013) and spinal cord injury (SCI; Adams and Hicks, 2005). Hypertonia includes spasticity and rigidity, and is characterized by a velocity-dependent increase in tonic stretch reflexes (Lance, 1980) and increased muscle activity during passive stretch (Katz and Rymer, 1989).…”

Measurement of Peripheral Muscle Resistance in Rats with Chronic Ischemia-Induced Paraplegia or Morphine-Induced Rigidity Using a Semi-Automated Computer-Controlled Muscle Resistance Meter

“…Technically PMR in lower extremities has been measured in rats restrained in a plastic holder (Dickinson et al, 1982;Kolasiewicz et al, 1987), or by immobilizing the animals by hand (Fischer et al, 2002) and by a concomitant measurement of the paw muscle resistance during forced manually-induced or electromechanicallyinduced flexion/displacement of the ankle and with muscle tension measured using a mechanical strain-gauge system (Johnels and Steg, 1982a,b). A comparable technique to measure ankle torque in conjunction with the triceps surae EMG recordings in fully awake rats has been described (Bose et al, 2002). More recently a new technique for quantifying muscle tone in a rat model of spinal injury-induced tail spasticity was reported.…”