Contractions dynamic of "fast" and "slow" rat muscle under spinal shock and modulators of contraction

Aim. To study the dynamics of neuromotor regulation of the contractile function of "fast" and "slow" muscles in rodents during spinal shock by spinal cord transection at the level Th11-Th12. Methods. The experiments were carried out on laboratory rats weighing 140-180 g. The animals were divided into two groups: "Control" (8 rats) and "Spinal shock" (6 rats). The lower leg muscles, m. soleus and m. extensor digitorum longus (m. EDL), were dissected by partially isolating without disrupting the connection with the body's circulatory system. The sciatic nerve was stimulated with single electrical impulses (10 V, 0.5 ms). Contractions of both muscles caused by electrical stimulation of the sciatic nerve before and after the injection of the substances into the femoral artery - tubocurarine (1 mM) or norepinephrine (10 mM) - were recorded in animals of both groups. After spinalization, muscle contractions were re-recorded during electrical stimulation of the sciatic nerve before and 10 minutes after the injection of tubocurarine or noradrenaline into the femoral artery in the same concentrations. Results. After spinalization of the animal, the contraction force of the muscle m. EDL fibers increased to 0.43±0.03 g (p=0.040), but the temporal parameters remained unchanged. M. soleus, on the contrary, showed a decrease in the contraction time to 0.053±0.005 s (p=0.045), and no change in the contraction force was observed under these conditions. Intra-arterial administration of norepinephrine in the control group resulted in an increase of m. soleus contractions up to 1.21±0.17 g (p=0.048), and m. EDL - up to 0.57±0.07 g (p=0.043). The administration of norepinephrine in spinalized animals caused an increase in the contraction of m. soleus up to 1.21±0.09 g (p=0.047), and m. EDL up to 0.66±0.05 g (p=0.043). The blocker of postsynaptic cholinergic receptors tubocurarine administration reduced the force of contraction of both muscle types in both control [m. soleus up to 0.39±0.03 g (p=0.039), m. EDL up to 0.11±0.02 g (p=0.042)] and spinalized [m. soleus up to 0.34±0.05 g (p=0.039), m. EDL up to 0.15±0.04 g (p=0.040)] animals. Conclusion. The data obtained demonstrate the presence of significant differences in the mechanisms of control of contractile activity in the "fast" and "slow" skeletal muscles of warm-blooded animals; the persistence of the similar effect of the basic modulators on the contraction of both muscles with such a striking reaction to spinalization highlights the contribution of neurotrophic control to the functioning of "fast" and "slow" motor units

Adaptive mechanisms of a mouse locomotor muscles "m.soleus" and "m.edl" the conditions of the allergic modification of the organism

The relevance of the problem discussed in the article is connected to the fact that mandatory athletes’ vaccination before competitions leads to the change in the function of the muscular system, the mechanisms of which have not yet been fully clarified. The purpose of the article is to determine the mechanism of a mouse skeletal muscles adaptation (SM) ("fast" (in case of m.edl) and "slow" (in case of m.soleus) in case of allergic alteration. The following research methods were used in the presented work: registration of the constrictive function of the abovementioned muscles in vitro to the humoral constriction initiators (carbacholinum and KCI) and determination of malonyldialdehyde (MDA) level in them, just as the indicators of the oxidant and antioxidant equilibrium. It has been demonstrated that the change in the “slow” muscle strength correlates with the MDA level dynamics, evidently, reflects the adaptation processes during the allergic modification. "Fast" muscles turn out to be more sustainable to oxidative stress which is most probably achieved by the work of compensatory mechanisms and is expressed in quite minor changes in the MDA dynamics. The article can be used in the search of the new possibilities for the correction of the locomotor muscles function in the conditions of the allergy, аnd also while the therapeutic impact strategy is determined, taking into account their fiber composition. © 2020 North Atlantic University Union NAUN. All rights reserved