Spastic Hypertonia Following Middle Cerebral Artery Occlusion in Rats: Assessment of Behavioral, Electrophysiological, and Morphological Parameters in Dynamics.

Gradual changes in muscle resistance after ischemic stroke offer precious insights into the time-course development of spastic hypertonia, but quantitative data about temporal changes in muscle tension are insufficient, particularly about changes in muscle properties in post-stroke animal models. In male Sprague-Dawley rats, changes in the motor function, muscle tension, and spastic muscle structure over a 20-day period after permanent middle cerebral artery occlusion (MCAO) were examined using behavioral tests, electrophysiological recordings, and muscle fiber staining. Motor function evaluated by gait analysis and rotarod test performance were impaired from day 0 to day 10. Muscle tension assessed by Modified Modified Ashworth Scale (MMAS) dropped immediately after MCAO, began to rise on day 3, peaked on day 10, and then decreased somewhat, yet remained relatively high throughout the 20-day observation period. These alterations in muscle tension were also verified by H-reflex recording. On days 10 and 20 postoperatively, the percentage of type I muscle fibers in MCAO group was higher than in sham-operated animals. Our results verified a progressive increase in muscle tension and motor dysfunction on days 3-10 after cerebral ischemia, while changes in structural properties of spastic muscles also contributed to hypertonia. The findings may contribute to better understanding of the recovery process in spastic hypertonia quantitatively in animal model after stroke, and are useful for developing new therapeutic approaches.