The state of the contralateral motor center of the rat gastrocnemius muscle after unilateral damage of sciatic nerve

Effects of unilateral damage of the rat sciatic nerve on the spinal motor centre of contralateral gastrocnemius muscle were investigated. The state of contralateral gastrocnemius muscle centre was assessed using the method of paired monosynaptic testings and posttetanic potentiation of reflex response on days 1, 5 and 10 after nerve damage. The obtained data indicate changes in reflex activity of contralateral motor centre in these conditions. The activation of contralateral reflex systems after nerve damage seems to provide regenerative reorganisation of the motor control in the conditions of traumatic influence.     

Effect of the sciatic nerve blockade on the function of the contralateral motor center in the rat gastrocnemius muscle

When the rat spinal motor centre was activated by fixing the animal in a supine posture, the motor units of intact gastrocnemius muscle fired more frequently in the high-frequency range. Under conditions of the ischiatic nerve blockade, a shift to an increase in the background firing frequency of the motor units related to intact gastrocnemius muscle seems to be related to increased motoneurone excitability occurring because of the contralateral denervation.     

Effect of sciatic nerve crush on enzyme activities of skeletal muscles of the rat.

Weight loss and reduction in specific activity of cytochrome oxidase of both red (soleus) and white muscles (gastrocnemius and plantaris) of the rat was greatest 5 days after sciatic nerve crush (p less than 0.001) and then became minimal. In neither was there a significant, concomitant loss of protein. By 19 days, the specific activity of cytochrome oxidase was the same in both muscle types. The specific activity of lactate dehydrogenase was reduced significantly (p less than 0.001) in the white muscles, to a value approaching that of the red soleus by 19 days postoperatively, but remained unaltered in the soleus. Nerve crush is proposed as a model experimental system for studying neural regulation of skeletal muscle metabolism.     

Effect of strength training on pressor reflex responses from receptors in exercising muscles

The effect of strength training on muscle pressor reflex responses was investigated. Ten young, healthy volunteers and eight arm wrestling athletes performed forearm exercises at 30% of maximal voluntary effort until exhaustion. The exercises were either static or rhythmic, with alternating 20-s periods of muscle contraction and relaxation, followed by postexercise forearm arterial occlusion (PEAO). Heart rate, blood pressure (BP), and sympathetic nerve activity directed to muscle blood vessels (MSNA) were continuously recorded during the exercises. MSNA recordings were obtained from the peroneal nerve using a microneurographic method. During static exercises followed by PEAO, there were no differences in BP or MSNA between athletes and nonathlets. In contrast, a significant decrease in muscle pressor reflex responses was observed in the athletes during rhythmic exercises followed by PEAO. The possible relationship between this effect and changes in muscle energy supply, increased wash-out of metabolites, and reduced sensitivity of the muscle receptors in athletes is discussed.     

Effect of vertical jumping on the medial gastrocnemius and soleus muscles of rats

Ten rats were trained to perform approximately 30 jumps/day, 5 days/wk for at least 8 wk, from a force platform that enabled the number and height of jumps to be quantified. There was considerable variation in height jumped during an activity session both within and between rats. The two highest-jumping rats attained a displacement of center of mass of approximately 30 cm, estimated to be approximately 67% of the maximum attainable. The two lowest-jumping rats jumped to approximately 30% of the estimated maximum. The activity was described as "habitual activity" rather than "training" because there were no significant increases in the height of jumping by any rat over the period of activity. The isometric properties of medial gastrocnemius (MG) and soleus muscles were studied in terminal experiments on anesthetised rats. Five significant effects on MG were evoked by this pattern of exercise ("habituation"): 1) a 15-18% increase in force at frequencies of stimulation between 60 and 150 Hz and a 15% increase in maximum tetanic tension to 14.9 N, 2) a 3% increase in the maximum rate of rise of tetanic force to 3.4% of maximum tetanic tension per millisecond, 3) an increase in fatigability expressed as a smaller fatigue index in active rats (33%) than in controls (58%), 4) a decrease of 4% in the percentage of type IIa muscle fibers, and 5) an increase of 6% in the percentage of type II fibers that could not be classified with certainty as IIa or IIb.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of local hyperthermia on the motor function of the rat sciatic nerve

The effect of local heat treatment of the sciatic nerve was assessed using the toe-spreading test, which mainly assesses the motor function of the sciatic nerve. A 5 mm long segment of the nerve was heated at temperatures from 42.0 to 45.0 degrees C in vivo using a brass thermode. Hyperthermia led to a decrease in spreading of the toes. Recovery from functional loss took place in all cases, and this recovery was completed in 4 weeks. A 50 per cent functional loss in 50 per cent of the treated animals was observed after 58, 32 and 12 min of heating at 43.0, 44.0 and 45.0 degrees C respectively.     

Functional characteristics of rat gastrocnemius and tibialis anterior muscles during growth

Several morphological and functional characteristics of the rat gastrocnemius medialis and tibialis anterior muscle were studied in young, adult, and old rats to assess the influence of growth. Antagonist muscles were studied to determine how changes of muscle architecture and functional characteristics are influenced by the demands of increased body weight and by the specific roles of these muscles in locomotion. Both muscles change drastically, for instance, in muscle length, volume, physiological cross-sectional area aponeurosis length, and their muscular geometry changes allometrically for both muscles. The relationships between muscle length, distance between origin and insertion, tendon length, and tibial length also change with growth. Both muscles are rather pennate, so that the increase of physiological cross-sectional area is a major factor in the determination of muscle length. No significant difference could be shown for fundamental physiological characteristics (i.e., functional characteristics normalized for muscular dimensions such as maximal work per unit volume). The changes of morphological and functional variables of both muscles parallel each other as is apparent from the index of antagonist characteristics, which is constant for all variables studied with the exception of muscle volume and tendon length. Consequently, the considerable and similar changes of TA and GM morphology and functional characteristics that take place during growth from approximately four weeks postnatally is not caused by changes of muscular material but by changes of the amount and architectural arrangement of the material involved.     

Contractile responses of the rat gastrocnemius and soleus muscles to isotonic resistance exercise.

Male rats were divided into control and weight-trained (WT) groups. WT rats performed squat-type exercises twice daily, 5 days/wk, for 14 wk. They averaged 36 lifts/day, with an average weight of 555 g. Muscle-to-body weight ratio (mg/g) of the soleus (Sol) was not different from control, but it increased 11 and 6% in the gastrocnemius (Gast) and plantaris, respectively (P < 0.05). The normalized twitch tension of the in situ Sol was elevated by 21%, whereas single-skinned type I fibers from the Sol showed an increased rate constant of tension redevelopment (K(tr)) but no other contractile adaptations to WT. In contrast, the Gast type I fibers showed an increase (P < 0.05) in maximal velocity of shortening (25%), peak power (15%), K(tr) (18%), and normalized tension (7%). The K(tr) and normalized tension of the Gast type IIa fibers increased by 24% (P < 0.05) and 12% (P < 0.05), respectively, whereas velocity and power showed a tendency to increase. Fiber size, determined by myosin ATPase histochemistry, was not different for any fiber type from the Gast or Sol. These results indicate that isotonic resistance exercise of the calf targets the Gast (type I and type IIa fibers) and has little effect on the Sol.     

Aspects of segmental reflex after damage of the sciatic nerve in thyroxin-treated rats

In experiments on spinalized rats, in whom the sciatic nerve was severed three weeks before, and which were given thyroxin (100 µg/kg) for three days before the acute experiment, the amplitude of the reflex firing in the ventral horn (RFVH) of segment L₅ was recorded when the dorsal horn was stimulated before and 20 min after the intraperitoneal administration of obsidan, clofelin, and finoptin. It was found that obsidan did not alter, while clofelin and finoptin mainly reduced the amplitude of the monosynaptic component of the RFVH, which was restored under the influence of thyroxin on the side of the operation.Dnepropetrovsk Medical Institute, Ukrainian Ministry of Health. Translated from Neirofiziologiya, Vol. 24, No. 6, pp. 653–659, November–December, 1992.     

Effect of vitamin E-deficiency on regeneration of the sciatic nerve

The regeneration of the sciatic nerve fibres was studied in both normal and vitamin E-deficient rats at 30 and 60 days after crush. The vitamin E is involved in one of the most important mechanisms of protection against peroxidation of plasma membrane lipids; the plasma membrane plays certainly a role in nerve regeneration. Both the diameter and the total number of myelinated nerve fibres was calculated at different times. The number of myelinated fibres in the undenervated deficient animals was lower than that found in the undenervated normals animals. Following the nerve crush, in normal animals after two months the number of myelinated fibres exceeded the number found in undenervated normal animals, whereas in the deficient rat nerves it was significantly lower than in the corresponding controls and moreover it did not even reach the number found in the nerves of undenervated deficient rats. Finally, the caliber distribution of myelinated fibres in undenervated and denervated deficient rats shows a relative percent increase in the number of greatest axons and a decrease in smaller axons. This result confirm the vitamin E to be an important factor of the normal process of nerve regeneration.     

Motor responses of the facial muscles to local stimulation of the motor cortex and facial nerve nucleus in the white mouse

The character of motor responses of the facial muscles evoked by stimulation of various regions of the frontal neocortex and of the nucleus of the facial nerve was studied in outbred mice. Motor responses of the vibrissae, of the upper lip and the jaw to monopolar microstimulation in the frontal cortical areas in 55 per cent of the cases had the latencies from 5 to 15 ms. The latencies of the responses to the facial nucleus stimulation ranged from 3 to 12 ms with maximal expressed interval of 4-6 ms. Excitation conduction velocities of the facial nerve estimated on the basis of latencies measurements, were from 1.5 to 12 m/s.