Stretch Hyperreflexia of Triceps Surae Muscles in the Conscious Cat after Dorsolateral Spinal Lesions

Abstract

Resistive force and electromyograms from triceps surae muscles were measured during dorsiflexion of both ankles of awake cats before and after interruption of one dorsolateral funiculus (DLF). DLF lesions produced ipsilateral increases in dynamic and static reflex force that persisted over 66 weeks. The increase in dynamic reflex force was velocity sensitive, as demonstrated by a greater effect for 60°/sec than for 10°/sec dorsiflexion. Also, the lesions increased dynamic force to a greater extent than static force (increased dynamic index). Background force (recorded immediately before each reflex response) was elevated ipsilaterally. However, increases in reflex force were observed when preoperative and postoperative background forces were matched within 10% and were associated with equivalent resting levels of electromyographic (EMG) activity. Resistive reflex force was significantly correlated with EMG responses to dorsiflexion and was not determined by nonreflexive mechanical stiffness of the muscles. Contralateral background and reflex force and associated EMG activity were decreased slightly, comparing preoperative and postoperative records.Clinical testing revealed ipsilateral postoperative increases in extensor tone, increased resistance to hindlimb flexion, hypermetria during positive support responses, and appearance of the Babinski reflex. However, the most reliable tests of DLF lesion effects were the quantitative measures of dynamic and static reflex amplitude. The enhancement of stretch reflexes is suggestive of spasticity. However, hyperactive stretch reflexes, hypertonicity, and the Babinski reflex were observed soon after interruption of the ipsilateral DLF, in contrast to a gradual development of positive signs that is characteristic of a more broadly defined spastic syndrome from large spinal lesions. Also, other signs that often are included in the spastic syndrome, including clonus, increased flexor reflex activity, and flexor spasms, did not result from DLF lesions. Thus, unilateral DLF lesions provide a model of spasticity but produce only several components of a more inclusive spastic syndrome.

Effect of cold air therapy in relieving spasticity: applied to spinalized rabbits

“…Although Ashworth scale has not been utilized in an animal model, other clinical parameters such as muscle stretch re¯ex, ankle clonus have been used as a measurement method for spasticity. 20,21 Electrophysiologic parameters are objective but there is some controversy regarding the usefulness of these parameters in evaluating spasticity. Although both H/M ratio and F/M ratio have been reported to assess either the spinal segmental re¯ex or excitability of the anterior horn cells, 22,23 there are studies reporting that they were increased in subjects with decreased muscle stretch re¯ex.…”

Common animal models for spasticity and pain

“…Following spinal cord injury (SCI), spasticity is a common problem in both the nonveteran [30] and veteran [31] populations, but robust spasticity has been difficult to reproduce in animal models, such as the SCI cat [32][33][34] or rat [35][36][37]. Without complete spinal transections, animals recover most motor function, a situation not seen in humans, where even partial spinal lesions often lead to chronic spasticity [38].…”

Spastic Tail Muscles Recover From Myofiber Atrophy and Myosin Heavy Chain Transformations in Chronic Spinal Rats

“…However, in humans and in some animal models, considerable neuromuscular activity sometimes develops after SCI in the form of spasticity, a syndrome that includes hyperreflexia, hypertonus, and long-lasting spasms (Bennett et al 2004;Fujimori et al 1968;Heckman 1994;Kuhn and Macht 1948;Lance and Burke 1974;Ritz et al 1992;Taylor et al 1997). Furthermore, preservation of slow (Hidler et al 2002;Thomas and Ross 1997;Zijdewind and Thomas 2003) and fatigue-resistant (Hartkopp et al 2003) muscle contractile properties has been observed in conjunction with spasticity after SCI in humans.…”