Combined effects of tenotomy and denervation on the dynamic properties of soleus muscle of the rat

Isometric contraction time (CT), half relaxation time (1/2 RT), tetanus fusion frequency (TFF) and tetanus: twitch ratio (T : t ratio) were measured in the denervated (D) and tenotomized-denervated (TD) Soleus muscle of the rat. In D muscle there was an apparent speeding effect at the 2nd day after denervation, with a significant decrease of CT, which was followed by the usual slowing process of denervated muscle. In TD muscle, denervation was performed a week after tenotomy. Tenotomy "per se" was ineffective in modifying dynamic properties of muscle, but it accentuated the early shortening of CT caused by denervation, while reducing and delaying the subsequent slowing process. The results are discussed in the light of the hypothesis that muscle disuse has a speeding effect which counteracts the slowing effect of denervation, and/or that tenotomy modifies the effects of denervation by changing the pattern of fibrillation development.     

Cell proliferation in skeletal muscle following denervation or tenotomy

Summary Autoradiographic experiments using ³H-thymidine were designed to analyse cell proliferation which occurs in skeletal muscle after denervation and after tenotomy. In mouse tibialis anterior and tongue muscles during the first 24 h after denervation or tenotomy labelling levels were low and did not differ significantly from sham operated control muscles. By 48 h after denervation and tenotomy of tibialis anterior muscles, increased levels of labelling occurred in both muscle and connective tissue nuclei. Daily pulse labelling for 7 days after denervation produced a labelling level which was 8 times that of sham operated controls, 25–30% of the total nuclear population being labelled. Denervated muscles had twice the level of labelling compared to tenotomised muscles. These results provide conclusive evidence that both denervation and tenotomy stimulate cell proliferation in skeletal muscle and it is suggested that the increased numbers of labelled muscle nuclei are likely to be the result of mitotic activity in muscle satellite cells.     

Influence of tenotomy on posttetanic responses of the rat fast and slow muscle

The effect of two weeks of tenotomy on posttetanic isometric contractile responses of the rat fast: Extensor digitorum longus and slow: soleus muscles was studied in experiments on isolated muscle preparations. Direct tetanic stimulation (100 impulses, 50 Hz) increased the force of contractions by 20-25% (p < 0.05) of both, control and tenotomized fast muscles. Identical to above tetanic stimulation of control, slow muscle resulted in posttetanic depression, a decrease in the amplitude of contractile responses. Tenotomized slow muscles did not develop posttetanic depression. Caffeine (4 mM) increased and dandrolene (10 microM) decreased the force of unitary and tetanic contractions of control and tenotomized muscles. Neither drug, however, affected development of posttetanic phenomena in ether fast or slow muscles. The fact that in extensor digitorum longus, posttetanic potentiation is preserved for at least forty days of tenotomy but disappears after only 2 weeks of denervation suggests important role of neurotrophic influences in regulation of posttetanic responses of fast muscles.     

The effects of electrical inactivity and denervation on the distribution of acetylcholine receptors in developing rat muscle

Explants of thoracic body wall from rat embryos, including intercostal muscles, ribs, and the adjacent segments of spinal cord, were maintained in organ culture. Nerve-muscle differentiation proceeded in culture with a pattern and time course similar to that of the same synapses developing in utero. To understand further the factors that regulate acetylcholine sensitivity in developing rat myotubes, we studied the effects of electrical inactivity and denervation on the distribution of acetylcholine receptors. When muscle and spinal cord were explanted at 15 days of gestation, prior to the appearance of junctional receptor clusters, intact nerve terminals were required to initiate receptor aggregation at the site of nerve-muscle junction. Electrical activity was not necessary for induction of these primary junctional clusters. Inactivity resulted, however, in the appearance of secondary multiple receptor clusters at random sites along the fibers. In the presence of tetrodotoxin, the electrically inactive nerve terminals sprouted; this was accompanied by the enlargement of the junctional receptor clusters, at the end plate, but there was no correlation between nerve sprouting and the location of extrajunctional receptor aggregates. Later in development, at a time when the junctional receptors are metabolically more stable, terminal sprouting failed to induce the increase in size of junctional receptor aggregates.     

Proteomic analysis of rat laryngeal muscle following denervation

Laryngeal muscle atrophy induced by nerve injury is a major factor contributing to the disabling symptoms associated with laryngeal paralysis. Alterations of global proteins in rat laryngeal muscle following denervation were, therefore, studied using proteomic techniques. Twenty-eight adult Sprague-Dawley rats were divided into normal control and denervated groups. The thyroarytenoid (TA) muscle was excised 60 days after right recurrent laryngeal nerve was resected. Protein separation and identification were preformed using 2-DE and MALDI-MS with database search. Forty-four proteins were found to have significant alteration in expression level after denervation. The majority of these proteins (57%), most of them associated with energy metabolism, cellular proliferation and differentiation, signal transduction and stress reaction, were decreased levels of expression in denervated TA muscle. The remaining 43% of the proteins, most of them involved with protein degradation, immunoreactivity, injury repair, contraction, and microtubular formation, were found to have increased levels of expression. The protein modification sites by phosphorylation were detected in 22% of the identified proteins that presented multiple-spot patterns on 2-D gel. Significant changes in protein expression in denervated laryngeal muscle may provide potential therapeutic strategies for the treatment of laryngeal paralysis.     

Effect of denervation and phentolamine on the thermogenic action of noradrenaline in rat skeletal muscle

Vascularly isolated skeletal muscle of the cold-acclimated (CA) rat was perfused with blood in situ or in vitro and the effect of denervation and an alpha-adrenolytic agent (phentolamine) on its oxygen consumption was studied in the resting state and after administering noradrenaline (NA). The resting metabolism of muscle in situ rose by 28% after denervation. The infusion of NA further raised the oxygen consumption of acutely denervated muscle perfused in situ of in vitro by 43%. The thermogenic effect of NA on muscle denervated two hours before the experiment was only transitory. Phentolamine raised the oxygen consumption of the innervated muscle in situ by 42%; the infusion of NA did not stimulate metabolism any further. Phentolamine reduced the vascular resistance of resting muscle, but did not inhibit the vasoconstriction during the infusion of NA. The results show that the thermogenic effect of infused NA in perfused muscle is inhibited not by acute denervation, but by a vasoconstriction, which cannot be prevented by the administration of an alpha-adrenolytic agent.     

Terminal sprouting in rat sternocostalis muscle following partial denervation

Summary The sternocostalis muscle of the rat was examined at one to five days after partial denervation and levels of terminal sprouting were assessed.The removal of one intercostal nerve caused localised degeneration which did not extend more than a few muscle fibres deep into the field of distribution of the adjacent nerve. Terminal sprouting was clearly seen at 24 h after operation and did not appear to develop further up to five days.There was no difference in the sprouting responses to section of either intercostal nerve 2, 4 or 5. There was, however, a decrease in the response with increasing distance from the cut nerve. No sprouting response was observed in the contralateral muscle.Comparison of sprouting levels of B and C type end plates revealed a greater percentage of C type end plates with sprouts. However, the response of B type end plates, considered in relation to the levels of spontaneous sprouting, was greater than that of C type end plates.     

Reinnervation of the rat levator ani muscle after neonatal denervation

After axonal injury on postnatal day 14 (P14), but not P21, motoneurons in the spinal nucleus of the bulbocavernosus (SNB) do not display their normal response to circulating testosterone levels. This could result from a permanent disruption of communication between motoneurons and their testosterone-sensitive target muscles. We assessed the extent of reinnervation of one of these target muscles, the levator ani (LA) muscle, 5 months after the pudendal nerve was cut either on P14 or P21. The number of motoneurons innervating the LA in control and nerve cut animals was determined using retrograde labeling procedures. Functional recovery of the LA muscle was determined via the testing of its in situ contractile properties. Compared to control muscles, reinnervated LA muscles were smaller, had fewer muscle fibers, generated a lower maximum tetanic tension, and were more fatigable. In spite of the fact that fewer motoneurons reinnervated the LA muscle after nerve cut on P14 than on P21, there were no differences in the weight or contractile properties of the LA muscle between these two groups. These data suggest that motoneurons that survived injury on P14 innervated more muscle fibers than normal and exhibited a similar ability to functionally reinnervate the target muscle as those motoneurons that survived injury on P21.     

Effect of sympathetic denervation on the rate of protein synthesis in rat skeletal muscle

Rates of protein synthesis were investigated in skeletal muscles from rats submitted to chemical and surgical sympathectomy. Three models of sympathetic denervation were used: 1) treatment with guanethidine (100 mg.kg(-1).day(-1) sc); 2) lumbar sympathetic denervation (surgical excision of the second and third lumbar ganglia of the sympathetic chain, from which arises the postganglionic fibers to the skeletal muscles of rat hindlimb); and 3) adrenodemedullation. Protein synthesis was estimated in isolated soleus muscle by the rate of incorporation of [(14)C]tyrosine (0.1 mM, 0.05 microCi/ml) into total protein. Soleus isolated after 2 and 4 days of chemical sympathectomy or after 3 days of lumbar denervation showed a 17-20% statistically significant decrease in in vitro rates of protein synthesis. These effects were reverted by addition of 10(-5) M isoproterenol or epinephrine in vitro. Neither clenbuterol nor isoproterenol (10(-7), 10(-6), or 10(-5) M) in vitro affected the rate of protein synthesis in soleus from normal rats. On the other hand, clenbuterol or epinephrine (10(-5) M) increased by 20% the rate of protein synthesis in soleus muscles from adrenodemedullated rats and prevented its decrease in muscles from fasted rats. The data suggest that the sympathetic nervous system stimulates protein synthesis in oxidative muscles, probably through the activation of beta(2)-adrenoceptors, especially in situations of hormonal or nutritional deficiency.     

Effect of denervation on the synthesis of ribonucleic acid and deoxyribonucleic acid in rat diaphragm muscle

1. The effect of unilateral denervation of rat diaphragm muscle on its content of nucleic acids and their incorporation of precursors was investigated. 2. After denervation the paralysed hemidiaphragm hypertrophies and within 3 days its content of RNA increases considerably. The concentration of DNA/unit mass remains fairly constant. 3. During this period there is some increase in the rate of incorporation of [(14)C]adenine into RNA, whereas there is some diminution in the rate of incorporation of [(14)C]orotic acid. 4. Incorporation of [(14)C]adenine and [(3)H]thymidine into DNA is much increased in the paralysed tissue, reaching its maximum by about the third day, but returning to normal by the tenth. 5. The significance of these results in relation to the hypertrophy after denervation is discussed.     

Effect of olivomycin on denervation changes in the membrane of frog tonic muscle fibers]

Membrane properties of frog denervated tonic muscle fibers were investigated after the action of olivomycin, which is an inhibitor of protein synthesis. Olivomycin injected as a single dose (7.5 mg) during 1--2 days after the denervation of m. pyriformis decreases the regenerative action potentials. This action is decreased three weeks after denervation. After denervation, olivomycin failed to prevent the appearance of extrajunctional cholinoergic receptors, but blocked the increase of junctional ones. The data support the view that some neuronal factor may influence the synthesis of functional membrane proteins.     

The effects of sympathetic denervation on spontaneous ventricular defibrillation in the rat.

Ventricular tachycardia or ventricular fibrillation was electrically induced in 38 normal rats (group 1) and 24 sympathetically denervated rats (6-hydroxydopamine) (group 2). The time for spontaneous reversion to sinus rhythm was measured during (1) control, (2) isoproterenol, and (3) the combination of isoproterenol and phenylephrine. The time for spontaneous reversion was the same in both groups in the three states. The reversion time was prolonged threefold by isoproterenol, and restored to control values when phenylephrine was added to the infusion of isoproterenol. The tachycardia duration and the refractory period were inversely related: log10 (tachycardia duration) = 3.466-0.091 (refractory period). Ventricular tachycardia/fibrillation induction was examined as follows: (i) Ventricular tachycardia/fibrillation was induced in 100% of normal rats (group 1), but only 42% of the denervated rats (group 2, p less than 0.001); (ii) during isoproterenol, ventricular tachycardia/fibrillation was induced in 100% of rats of both groups; and (iii) when phenylephrine was added to isoproterenol, ventricular tachycardia/fibrillation was induced in 100% of group 1 rats versus 82% of group 2 rats, (p = NS). These observations suggest (1) the induction of ventricular tachycardia/fibrillation is highly dependent on intact sympathetic innervation, and (2) exogenous adrenergic agonists modulate the duration of ventricular fibrillation through their effects on ventricular refractory period, independent of sympathetic innervation.