Physiological and histochemical changes of the extensor digitorum longus and soleus muscles after lateral cordotomy in the albino rat

Lower extremity blood flow and responses to occlusion ischemia differ in exercise-trained and sedentary tetraplegic persons

OBJECTIVE

To test whether lower extremity blood flow and hyperemic responses to vascular occlusion differ among electrically stimulated exercise trained and sedentary tetraplegic persons and subjects without tetraplegia (control).

DESIGN

Blinded cross-sectional comparison, control group.

SETTING

Academic medical center.

PARTICIPANTS

Ten sedentary tetraplegic men, 10 tetraplegic persons previously habituated to electrically stimulated cycling exercise for 0.4 to 7 years, and 10 nondisabled controls.

OUTCOME MEASURES

Subjects underwent quantitative Doppler ultrasound examination of the common femoral artery (CFA). End-diastolic arterial images and arterial flow-velocity profiles obtained at rest and following five minutes of suprasystolic thigh occlusion were computer digitized for analysis of heart rate (HR), CFA peak systolic velocity (PSV), CFA cross-sectional area (CSA), flow velocity integral (FVI), and computed CFA inflow volume (IV).

RESULTS

No group main effects were observed for resting HR or FVI. At rest, trained tetraplegic men had 14.9% greater PSV, 29.8% larger CSA, and 51.3% greater IV (p values < .05) than sedentary tetraplegic subjects. Resting PSV and IV of the trained subjects did not differ from controls, although CSA was smaller than controls (p < .05). Following occlusion, PSV, CSA, and IV averaged 16.5%, 33.4%, and 65.1% greater for trained tetraplegics persons, respectively, than sedentary tetraplegic subjects (p values < .05). Only CSA differed between the control and the trained groups (p < .05).

CONCLUSION

Tetraplegic persons conditioned by electrically stimulated cycling have greater lower extremity blood flow and hyperemic responses to occlusion than do their sedentary counterparts.

Cordotomy-denervation interactions on contractile and myofibrillar properties of fast and slow muscles in the rat

Cordotomy-denervation interactions were studied on contractile and myofibrillar properties of slow (soleus) and fast (extensor digitorum longus) muscles of the rat. The spinal cord was transected midthoracically in neonatal (2-day-old) animals. Two months after birth, a unilateral transection of the sciatic nerve was carried out in both cordotomized and control animals. Five weeks after denervation, contractile properties were tested isometrically in vitro; myofibrillar properties were assessed by histochemical staining of the muscle fibers and by electrophoretic analysis of the myosin heavy chain composition. The following results were obtained: (i) In cordotomized animals the contraction time of the soleus was significantly shorter (-23.3% on average) than that in the control animals and this shortening was accompanied by a proportional slow-to-fast shift in myofibrillar properties. (ii) The extensor digitorum longus properties were not significantly different in the control and cordotomized animals. (iii) Denervation in control animals was followed by a marked increase of contraction and half-relaxation times in the extensor digitorum longus, whereas in the soleus only the half-relaxation time was significantly increased; myofibrillar properties in the soleus showed an appreciable slow-to-fast shift, whereas in the fast muscle the main change was an increase in type 2A fibers to the detriment of type 2B. (iv) In cordotomized animals, denervation caused the soleus contraction time to increase to control values, whereas myofibrillar properties shifted to an even faster pattern; in the extensor digitorum longus denervation caused the same changes seen in the control animals. The results showed that cordotomy at birth caused the soleus to develop as a faster muscle than in the control animals. The concurrent effects of cordotomy and denervation on the myofibrillar properties of the soleus suggest that the slow-to-fast change in these properties is a common consequence of the reduction in the level of motor activity. The opposite effects of the two experimental conditions in the soleus contraction time support the view that the contractile alterations that follow denervation mainly reflect alterations in the muscle activation process.

Effects of chronic stimulation on the size and speed of long-term denervated and innervated rat fast and slow skeletal muscles

This study seeks to identify the mechanisms which motoneurones use to control the contractile force and speed of skeletal muscles. We have stimulated directly slow soleus (SOL) and fast extensor digitorum longus (EDL) muscles of adult rats intermittently at 100 Hz for 1-9 months. The muscles were either chronically denervated, denervated and reinnervated, or normally innervated. The stimulation started either immediately, or more commonly, after 1-9 months of denervation. Stimulation starting several months after denervation increased the mean maximum tetanic tension 37 times in SOL and eight times in EDL. These values represented 40 and 12% of the increases obtained by reinnervation after comparable periods of time. In denervated SOL and EDL muscles stimulated directly for more than 2 months, the mean isometric twitch contraction times were 13 and 12.7 ms, as in normal EDL muscles (13 ms). In innervated SOL muscles stimulated directly for 1-4 months, the mean twitch contraction times were 23.6 ms (normally innervated) and 19.2 ms (reinnervated), which were considerably shorter than in normal control SOL muscles (39.2 ms). Single motor unit recordings revealed that the natural (background) nerve impulse activity was essentially unaffected by the stimulation. Twitch contraction time and percentage of type II fibres in SOL muscles were related. The fastest muscles (denervated and stimulated) consisted of 100% type II fibres (with one exception), the second fastest (reinnervated and stimulated) of 70-50%, the third fastest (normally innervated and stimulated) of 45-0%, the second slowest (reinnervated) of 15-0%, and the slowest muscles (innervated controls) of 5-0% type II fibres.

Fibre sizes and histochemical staining characteristics in normal and chronically stimulated fast muscle of cat

1. Normal and chronically stimulated peroneus longus muscles of the cat's hind limb were studied with respect to fibre size and staining properties for myofibrillar (myosin) adenosine triphosphatase (ATPase) and succinate dehydrogenase (SDH) activity. The intensity of staining for SDH activity was measured by microphotometry from the central portions of the muscle fibres ('core-SDH staining'). For comparison, histochemical properties were also studied in non-stimulated soleus muscles. 2. On account of the pH sensitivity of their myofibrillar ATPase, about 18% of the fibres in normal peroneus longus muscles were classified as type I, and about half of the remainder as II A and II B respectively. 3. In the normal peroneus longus muscles, the mean diameter of single muscle fibres generally varied between about 25 and 75 micron, whereby the average size of type I less than type II. 4. In the normal peroneus longus muscles the staining intensity for core SDH varied over a wide range. The average heaviness of staining was clearly ranked in the order type I greater than type II A greater than type II B. 5. Chronic stimulation was given to the deafferented common peroneal nerve by aid of a portable and remotely controlled mini-stimulator. The stimulation was delivered in 'tonic' patterns (greater than or equal to 50% of total time taken up by activity) of 'fast' (20 or 40 Hz) or 'slow' (5 or 10 Hz) rates. 6. Prior to the period of long-term stimulation, the cats had been subjected to a dorsal rhizotomy and hemispinalization on the ipsilateral (left) side. In the absence of chronic stimulation, these operations had no evident effects on the sizes or staining properties of peroneus longus fibres. 7. After 8 weeks of treatment with tonic patterns of stimulation, the fibres of peroneus longus muscles clearly became more similar to each other with respect to their diameter as well as their staining for ATPase and SDH activity. With respect to ATPase staining, however, the chronically stimulated peroneus longus fibres had become more similar to non-stimulated soleus fibres than to non-stimulated type I fibres of peroneus longus. With respect to the staining for core SDH, the chronically stimulated fibres all became similar to normal II A fibres of peroneus longus. The 'fast' and 'slow' patterns of chronic stimulation had the same effects on the staining properties. 8. Chronically stimulated peroneus longus muscles showed a decrease in fibre diameter which corresponded, roughly, to the concomitant decrease in muscle weight.(ABSTRACT TRUNCATED AT 400 WORDS)

Fiber type and fiber size changes in selected thigh muscles six months after low thoracic spinal cord transection in adult cats: exercise effects

The effects of low thoracic spinal cord transection on muscle weights, fiber type compositions and, fiber cross-sectional areas of selected hind limb muscles were studied. Adult cats were spinalized at T12 and maintained for approximately 6 months. Some spinalized cats were exercised on a treadmill 30 min/day, 5 days/week to determine the role of weight support in maintaining the muscle properties. Spinalization resulted in a significant decrease in the weights of most extensors, whereas the flexors or those that act as both flexors and extensors were maintained near control values. All muscles showed a significant increase in the percentage of fast-twitch fibers and decrease in slow oxidative fibers following spinalization. In addition, the predominant fast fiber type in each muscle tended to have the largest decrease in cross-sectional area in the spinalized cats. The atrophic and fiber type adaptations were less pronounced in the exercised cats. In contrast, the relative cross-sectional area of high oxidative fibers generally was similar among the three groups. These results demonstrated that the muscles below the level of the lesion became more "fast-like" histochemically following spinal cord transection, whereas the oxidative properties were relatively unaffected. Further, daily exercise involving weight support appeared to be an important deterrent to these atrophic responses, particularly in the muscles that normally have a postural function (i.e., the slow extensors).

Fiber type and fiber size of cat ankle, knee, and hip extensors and flexors following low thoracic spinal cord transection at an early age

Effects of low thoracic spinal transection on muscle weights, fiber type distributions, and fiber cross-sectional areas (CSAs) of selected cat hind limb mixed-fast flexors and extensors and slow extensors were studied. Cats were spinalized at T12 at 2 weeks of age and maintained for 6 to 12 months. In general spinalization resulted in a decrease in muscle weights of extensors, while the weights of those muscles that function as either flexors or as both flexors and extensors were maintained. The percentages of fast-twitch [fast glycolytic (FG) and fast oxidative-glycolytic (FOG)] fibers increased and slow oxidative (SO) fibers decreased as a result of spinalization. However, FG fibers had a smaller CSA after spinal transection in both extensors and flexors. The total relative CSA of FG fibers per whole muscle was similar in spinalized and control cats. The relative muscle CSA occupied by SO fibers decreased in extensors and flexors as a result of a lower proportion of SO fibers and/or smaller SO fibers in spinalized cats. These findings suggest that muscles become more "fast-like" histochemically while little change occurs in the oxidative staining properties in either extensors or flexors in 6- to 12-month-old cats transected at 2 weeks of age. Further, these data suggest that the amount of muscle atrophy that occurs as a result of spinal transection is not closely related to the percentage reduction in SO fibers.

The adaptive response of skeletal muscle to increased use

Skeletal muscle undergoes profound changes in morphological, physiological, and biochemical character when subjected to prolonged periods of increased use. Although increased use may be brought about in a variety of ways, the results show consistent features. In particular, endurance exercise and chronic stimulation differ only in degree: the properties which change in response to exercise are also those which change at an early stage of stimulation; the properties which are resistant to change under exercise conditions change only after prolonged stimulation. There is therefore a hierarchy of stability in the properties of skeletal muscle which is revealed in its response to changing functional demands. The adaptive potential of muscle provides a logical framework for understanding neural influences on the emergence of fiber types during muscle development. It is also relevant to the study of pathological conditions which may involve a sustained departure from normal postural and locomotor patterns of activity.

Spinal transection and the postnatal differentiation of slow myosin isoenzymes

Newborn rats underwent cordotomy, and the myosin composition of individual muscles was investigated 3 months postoperatively. The results indicate that, after cordotomy, the myosin composition in the extensor digitorum longus and tibialis anterior muscles is normal, whereas in the soleus muscle the myosin has catalytic and molecular properties intermediate between those of adult fast and slow myosin. Together with histochemical data these results indicate that spinal transection causes a developmental arrest in the soleus muscle, at a stage corresponding to a mixed fiber population.