Enzyme-histochemical and morphological characteristics of fast- and slow-twitch skeletal muscle after brain infarction in the rat

The right middle cerebral artery was permanently occluded in 12-week-old male spontaneously hypertensive rats. After the surgery the rats were subjected to repeated behavioural tests during the observation period. Fourteen weeks after surgery the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus muscle of both sides were removed and examined with regard to muscle fibre characteristics obtained by histochemical and morphometrical methods. Comparisons were made with age-matched controls. Limb placement and the ability to traverse a beam or a rotating pole were repeatedly tested 2-13 weeks after the operation. In spite of permanent sensorimotor deficits in limb placement and when traversing a rotating pole or beam, no increase in pathological changes was noted in either EDL or soleus. The number and proportion of fibre types remained unchanged in both muscles. There was no difference in muscle fibre size in either EDL or soleus. It is concluded that brain infarction in the rat, although causing marked impairment of contralateral motor function, does not have a major influence on the muscle-fibre morphology or fibre-type composition, irrespective of muscle type.