[Neuromotor apparatus in the condition of gravitational unloading: central and peripheral effects].

The functioning of central and peripheral structures of the gastrocnemius m. neuromotor apparatus was studied in rats exposed to simulated gravitational unloading. Gastrocnemius reflex (H) and motor (M) responses evoked by electrical stimulation of the sciatic nerve were measured after 7, 14, 21 and 35 days of tail-suspension. It was shown that thresholds of registered potentials went down on all days of testing; the H-amplitude rose during every testing and M-amplitude rose after 35 days of the gravitational unloading. Results of the experiments indicate changes in the functioning of motor centers that modulate properties and characteristics of peripheral neuromotor structures. The observed rearrangements can be caused by reduction of the afferent inflow.

Motor function disturbances: contralateral effects.

Electromyography methods were employed to examine the mechanisms underlying changes in the functional state of the contralateral neuromotor apparatus of rat gastrocnemius muscle during unilateral limitation of the hind leg motor function. Elimination of one hind leg from the total pattern of motor activity affected the state of contralateral neuromotor apparatus via changing the properties of motoneurons in the corresponding spinal motor center resulting mostly from activation of the bilaterally acting spinal mechanism.

[Effect of vibrostimulation of foot and supporting afferentation on functional state of shin muscles in rats during hindlimb unloading].

The goal of this work was to study the influence of daily 3-hr vibrostimulation of the supporting zones of the foot and 3-hr of usual locomotion on the functional state of the soleus, gastrocnemius, and tibial anterior muscles in rats after 7 and 14 days of hindlimb unloading. After 7 days of unloading the soleus weight decreased, while the weight of gastrocnemius and tibial anterior remained unchanged. After 14 days of hindlimb unloading a weight reduction was observed in all studied muscles. Vibrostimulation of the foot and supporting afferentation prevented the loss of weight in gastrocnemius and tibial anterior during the first week of unloading and reduced the negative effect of hindlimb unloading in 14 days. Our results demonstrate that the amplitude of the M-response after 7 days of hindlimb unloading was decreased predominantly in soleus as compared to gastrocnemius and tibial anterior. By the 14 day we observed restoration of the amplitude of the M-response in gastrocnemius and tibial anterior, and the increased amplitude of the M-response in soleus. Different techniques for foot stimulation in rats during hindlimb unloading demonstrated the positive effect in regard to M-response restoration--the amplitude of the M-response was increased in all studied muscles. Thus, our results demonstrate that foot vibrostimulation or supporting afferentation can completely prevent atrophy caused by hindlimb unloading in gastrocnemius and tibial anterior and decrease atrophy in soleus in rats.

[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.

[About possible specialization of different compartments of a motoneuron axon for synthesis of specific proteins].

The spontaneous quantum secretion of neurotransmitter and its regulation through the system of presynaptic acetylcholine receptors have been studied on a neuromuscular preparation of rat m. soleus of intact animals and animals in which the axonal transport was blocked via the application of colchicine to the sciatic nerve. It was shown that, after six days of colchicine application, the spontaneous quantum secretion, the reaction of presynaptic membrane, and the reaction of neurosecretory apparatus to the depolarization of nerve endings via increase of the content of potassium ions in the environment and to the activation of presynaptic receptors by carbachol are not disturbed. Keeping in mind a rather short half-life of proteins that take part in the exocytosis and its regulation, it may be concluded that their functioning does not depend on the state of the axonal transport. These data correspond to the hypothesis put forward earlier that the synthesis of some proteins performing their function in nerve terminals occurs directly at the site of their utilization but not in the perikaryon, as it has been traditionally assumed.

The state of the contralateral neuromotor apparatus of the rat in conditions of unilateral tenotomy.

The effects of unilateral transection of the Achilles tendon (tenotomy) on the electromyographic characteristics of the gastrocnemius muscle on the contralateral side were studied in rats. Motor responses, reflex responses, and motor unit spike activity in the contralateral gastrocnemius muscle were studied in baseline conditions and on afferent stimulation before and 10 days after tenotomy. Changes in the nature of motor unit spike activity and responses to afferent stimulation were observed. The results obtained here demonstrate increases in the excitability of individual motoneurons in the contralateral motor center of the gastrocnemius muscle after exclusion of the symmetrical gastrocnemius muscle from the overall pattern of movement activity.

[Contralateral neuro-motor apparatus under unilateral restriction of motor activity in rat].

Electromyographic recordings of contralateral m. gastrocnemius of the rat after unilateral section of Achilles' tendon (tenotomy) were studied. Motor reflex, Hoffman reflex and firing of motor units of contralateral m. gastrocnemius were recorded in control and in 10 days after tendotomy. Motor units changed their firing in the background and in reaction to sciatic nerve stimulation. The results of study showed that unilateral section of Achilles' tendon increased the excitability of single motoneurons of contralateral spinal senters.

[Effect of unilateral trauma of the sciatic nerve on characteristics of motor and reflex responses of paired gastrocnemius muscles]. / Vliianie odnostoronnei travmy sedalishchnogo nerva na kharakteristiki motornykh i reflektornykh otvetov parnykh ikronozhnykh myshts krysy.

The influence of unilateral n. ischiadicus lesion of conductivity on the electromyographic characteristics of the rat gastrocnemius muscles was investigated. The lesion was made by n. ischiadicus crashing. Motor and reflex gastrocnemius muscles' responses caused by n. ischiadicus stimulation (single impulses of various intensity and 0.3 ms duration) were estimated on broken and symmetric hind-limb before and 1, 5, 10, 20 and 30 days after the nerve crashing. Considerable changes of threshold and amplitude of the registered gastrocnemius muscle responses were observed ipsi- and contralaterally. It is suggested that the central dependence of processes arising in the motor centres of symmetric gastrocnemius muscles, follows unilateral n. ischiadicus lesion.

[Effect of the sciatic nerve blockade on the function of the contralateral motor center in the rat gastrocnemius muscle]. / Prekrashcheniie provedeniia v sedalishchnom nerve vliiaet na sostoianie kontralateral'nogo dvigatel'nogo tsentra ikronozhnoi myshtsy krysy.

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.