Characteristics of the functional state of rat tracheal and bronchial smooth muscle at different stages of alveolitis

In isolated tracheal smooth muscle preparations in normal rats and in rats with experimental fibrotic alveolitis, responses to electrical field stimulation of nervous and muscle fibers were studied. At stimulation of muscles or nerves of tracheal preparations without intramural ganglia in rats with acute alveolitis, parameters of smooth muscle contractions did not practically differ from those in normal rats. In rats with fibrotic alveolitis the amplitude and rate of muscle contraction decreased, while the response latent period (LP) increased. At stimulation of preganglionic nerve fibers of the tracheal preparations with intramural ganglia in rats with acute alveolitis, the value and rate of smooth muscle contraction decreased, while the response LP increased. After transition into chronic phase of the disease (fibrotic alveolitis), a partial restoration of the response parameters took place. In rats with acute alveolitis, the repeated stimulation of the nerve fibers led to an increase of amplitude and a decrease of rate of tracheal smooth muscle contractions. In rats with fibrotic alveolitis, the repeated stimulation caused a decrease of amplitude and rate of contractions and an increase of the response LP.     

Functional disturbances in the nervous structures of the respiratory tract in rats following nitrogen dioxide inhalation

The functional state of rat's airway smooth muscle was not changed after nitrogen dioxide inhalation for 30 days. The smooth muscle contraction increased only at second stimulation of preganglionic nervous fibers. Removal of mucosa or Novocain blockade of receptors decreased control smooth contraction at nerve and muscle fiber stimulation but the repeated stimulation of nerve increased the muscle contraction. The processing of trachea and bronchus preparations by prednisolon (1-10 microg/ml) decreased muscle reactions to 12% only at nerve stimulation. Prednisolon didn't change reactions of preparations with removed or blockaded receptors induced by nerve stimulation, but prednisolon (10 microg/ml) increased contraction at muscle stimulation. The relax effect of prednisolon on airway smooth muscle realizes via tracheobronchial receptors. High doses of prednisolon may direct effect on muscle increasing its contraction.     

Regeneration of reinnervated rat soleus muscle is accompanied by fiber transition toward a faster phenotype.

The functional recovery of skeletal muscles after peripheral nerve transection and microsurgical repair is generally incomplete. Several reinnervation abnormalities have been described even after nerve reconstruction surgery. Less is known, however, about the regenerative capacity of reinnervated muscles. Previously, we detected remarkable morphological and motor endplate alterations after inducing muscle necrosis and subsequent regeneration in the reinnervated rat soleus muscle. In the present study, we comparatively analyzed the morphometric properties of different fiber populations, as well as the expression pattern of myosin heavy chain isoforms at both immunohistochemical and mRNA levels in reinnervated versus reinnervated-regenerated muscles. A dramatic slow-to-fast fiber type transition was found in reinnervated soleus, and a further change toward the fast phenotype was observed in reinnervated-regenerated muscles. These findings suggest that the (fast) pattern of reinnervation plays a dominant role in the specification of fiber phenotype during regeneration, which can contribute to the long-lasting functional impairment of the reinnervated muscle. Moreover, because the fast II fibers (and selectively, a certain population of the fast IIB fibers) showed better recovery than did the slow type I fibers, the faster phenotype of the reinnervated-regenerated muscle seems to be actively maintained by selective yet undefined cues.     

Lack of fiber type selectivity during reinnervation of neonatal rabbit soleus muscle

Fast and slow contracting fibers in neonatal mammalian skeletal muscle are each innervated in a highly specific manner by motor neurons of the corresponding type, even at an age when polyinnervation is widespread. Chemospecific recognition is a possible mechanism by which this pattern of innervation could be established. We have investigated this possibility by studying the degree of specificity during reinnervation of rabbit soleus muscle following nerve crush on Postnatal Day 1 or 4. We assayed fiber type composition by measuring the twitch rise times of motor units within 2 days of the onset of functional reinnervation (5-6 days after nerve crush). In contrast to the broad, bimodal distribution of single motor unit twitch rise times seen in normal muscles, motor units in reinnervated muscles yielded a narrower, unimodal distribution of rise times. Rise times of reinnervated units were intermediate to those of normal fast and slow units, suggesting that reinnervated units were composed of a mixture of fast and slow contracting fibers. An alternative possibility, that specific reinnervation was masked by contractile dedifferentiation of muscle fibers, was examined by maintaining a transmission blockade induced by botulinum toxin poisoning for an equivalent interval. Twitch rise times of treated motor units exhibited the distinctly bimodal distribution characteristic of normal muscles, suggesting that muscle fibers can retain contractile diversity during a transient period of denervation. We carried out computer simulations to estimate the amount of rise time diversity induced by varying degrees of specificity during reinnervation. Based on this analysis, we conclude that there is little if any selective reinnervation of muscle fiber types at the ages studied.     

Regeneration of motorneurones to a cricket muscle after partial or complete denervation

The metathoracic extensor tibiae muscle of the cricket Teleogryllus oceanicus is innervated by two excitatory axons; one of which leaves the metathoracic ganglion through nerve 5, the other through nerve 3. Axons in nerve 5 frequently regenerate to reinnervate the extensor tibiae if the nerve is sectioned in a late nymphal stage; functional reinnervation is rare if the nerve is sectioned in young adults. The muscle may become reinnervated by several axons regenerating through nerve 5, and individual muscle fibres may receive inputs from two regenerated axons. Axons regrowing through nerve 5 to a partially-denervated extensor tibiae preferentially innervate fibres in the central portion of the muscle, which is the normal innervation field of nerve 5. If the muscle is totally denervated by transection of both nerve 5 and nerve 3b, reinnervation is less specific and fibres throughout the muscle may be reinnervated by axons in either nerve. Reinnervation by regenerating axons is progressive. The proportion of muscles which are functionally reinnervated by regenerated axons increases with survival time as does the proportion of fibres within a muscle with reinnervation. The amplitude of excitatory junctional potentials and of muscle contraction evoked by regenerated axons both increase with survival time.     

Motor endplates in fast and slow muscles of the rat: what determines their difference?

Motor endplates in fast and slow skeletal muscles have different functional and morphological characteristics, and for brevity, are termed fast and slow respectively. We have examined the terminal arborization patterns of fast fibular and slow soleus axons 3-4 and 6 months after they reinnervated old preformed endplates or formed new ectopic endplates with denervated rat soleus muscles. Ectopic endplates formed by transplanted fibular and soleus nerves were fast and slow in appearance respectively. Both the fibular and the soleus nerves formed endplates of slow appearance when they reinnervated the original endplates. The fast appearance of ectopic fibular nerve endplates was unaffected by reinnervation of the original endplates by the slow soleus nerve. Dually innervated fibres had intermediate contraction speed compared to the fast fibres reinnervated only by the fibular nerve and the slow fibres reinnervated only by the soleus nerve. Continuous stimulation of the transplanted fibular nerve at 10 Hz for 3-4 months, starting just before the onset of ectopic endplate formation, prevented the increase in contraction speed seen without stimulation. The ectopic endplates of the stimulated axons were much smaller than usual and showed some signs of fast to slow transformation, but the transformation was incomplete and varied in degree between preparations. Transplanted soleus axons were less prone to growing along foreign pathways and to forming ectopic endplates than fibular axons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transplantation and transposition of skeletal muscles into the faces of monkeys

Restoration of normal facial movement after long-term facial paralysis with muscle atrophy has not yet been achieved reliably by either free grafts, in which fibers degenerate and regenerate, or by grafts made with microneurovascular repair, in which most fibers survive. Our purpose was to compare the structural and functional properties of free muscle grafts and continuously perfused muscle flaps transplanted into the faces of monkeys. In adult monkeys, the facial muscles were replaced by either a free graft of a donor muscle from the lower limb or a denervated flap of ipsilateral temporalis muscle. Each graft or flap was reinnervated with the preserved buccal branch of the facial nerve. The control muscles, grafts, and flaps were examined 90 days later for gross appearance, contractile properties, and fiber areas. Compared with muscle flaps, free grafts showed greater adaptability to the new location and innervation and a closer approximation to the structural and functional properties of the original facial musculature.     

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.     

Neuropeptide Y inhibits sympathetic neurotransmission in ipsilaterally innervated but not contralaterally reinnervated superior tarsal smooth muscle of the rat.

The superior tarsal smooth muscle (STM), which elevates the upper eyelid, normally is innervated by sympathetic neurons from the ipsilateral superior cervical ganglion that are not neuropeptide Y-immunoreactive (NPY-ir). Following neonatal ganglionectomy, this target is reinnervated by sympathetic nerves from the contralateral superior cervical ganglion that are strongly NPY-ir. We examined the effects of exogenously administered NPY on STM tone, response to norepinephrine, and sympathetic neurotransmission in ipsilaterally innervated and contralaterally reinnervated STMs. NPY (2-10 micrograms/kg iv) increased blood pressure but did not alter STM tone. Similarly, contractile responses to co-administered norepinephrine were not affected. These findings imply an absence of direct and indirect postjunctional actions of NPY on STM. Contractions elicited by stimulation of the cervical sympathetic nerve (1.5 Hz) were not affected by NPY on the contralaterally reinnervated side; however, ipsilateral contractions were decreased in a dose-dependent fashion, with an inhibition of about 40% at 10 micrograms/kg. We conclude that while the STM is unresponsive to exogenously administered NPY, this peptide exerts selective inhibitory effects on the ipsilateral NPY-ir-negative but not the contralateral NPY-ir-positive innervation. This suggests that the neonatally denervated STM is reinnervated by contralateral fibers that are functionally different from the normal ipsilateral innervation in being devoid of functional prejunctional NPY receptors.     

Muscle Plasticity During Sprouting and Reinnervation

SYNOPSIS. When peripheral nerves are cut, the axotomized nervesand denervated muscles undergo atrophic changes which are reversedonly when functional connections are remade in the periphery.The restored interaction completely reverses the effects ofaxotomy and denervation and leads to rematching of the sizeof the motoneuron, muscle unit force, speed and histochemicalproperties, according to the size principle. Differences inunit force and fatigue characteristics between motor unit typesare not fully restored in reinnervated muscles but do not obscuresize relationships between the motoneurons and their muscleunits. Although intact motoneurons will supply increased numbers ofmuscle fibers after partial nerve injuries, regenerating axonsappear to be limited in their ability to enlarge their muscleunits. Increased motor unit force in reinnervated slow motorunits is accounted for primarily by an increase in fiber diameter;fast motor units do not increase their mean force output. As a result of the rematching of muscle unit properties withthe size of the motoneurons that reinnervate them, motor unitproperties are appropriate for fine control of movement aftercomplete or partial nerve injuries. However, regenerating axonsdo not reinnervate their original muscle fibers and unless thefibers are injured close to the muscles, they often fail toreinnervate their original muscles. The mismatching of motorpools with inappropriate target muscles is probably the mainfactor responsible for poor recovery of motor function aftercomplete nerve injuries.     

Cholinergic nature of the primary afferent vagus synapsed in cross anastomosed superior cervical ganglia.

The superior cervical ganglion was reinnervated by vagal afferent fibers following heterologous cross anastomosis between the superior cervical preganglionic trunk and the vagal trunk at the level of the supranodose ganglion in cats. The contractions of the nictitating membrane and the postganglionic action potentials from the external carotid sinus nerve in response to electrical stimulation of the vagal artificial preganglionic trunk in these operated cats were inhibited by treatment with tetraethylammonium and atropine. The choline acetyltransferase activities were measured by the radiometric method. The activities in cross anastomosed superior cervical ganglion were lower than those of normal superior cervical ganglion, but higher than those of chronically decentralized superior cervical ganglion. The activities in cross anastomosed nodose ganglion were lower than those of normal nodose ganglion, but higher than those of chronically decentralized superior cervical ganglion. These results further support the view that the primary afferent vagus artificially synapsed in the superior cervical ganglion is cholinergic.     

Classification of muscle fiber types based on succinic dehydrogenase and myofibrillar ATPase reactions in normal and randomly reinnervated rat skeletal muscles.

In the normal and randomly reinnervated plantaris muscle of rat staining for succinic dehydrogenase (SDH) activity differentiates three fiber types (A, B and C), staining for myofibrillar adenosine triphosphatase (ATPase) differentiates three fiber types (alpha, beta and alpha beta). Here we present our finding type A corresponds to alpha beta fibers, B to beta or alpha beta, C to alpha or alpha beta. In normal soleus muscle both classifications were found to be compatible and B fibers correspond to beta and C to alpha fibers. An exception is the small percent of alpha beta fibers which correspond to B type. In randomly reinnervated soleus muscle changes in ATPase activity are not followed by changes in SDH staining and B fibers correspond to alpha, beta or alpha beta types.     

Sprouting of aberrant neuropeptide Y-immunoreactive sympathetic nerves into neonatally denervated smooth muscle.

Sympathetic nerves normally project ipsilaterally to lateral cranial targets. Following unilateral superior cervical ganglionectomy in neonatal rats, however, neurons from the contralateral superior cervical ganglion sprout into the denervated region. In the present study we examined neuropeptide Y immunoreactivity (NPY-ir) of neurons comprising ipsilateral (control) and denervation-induced contralateral pathways to the superior tarsal smooth muscle of the eyelid. Fluoro-Gold injection of the control muscle retrogradely labelled 133 +/- 18 neurons in the ipsilateral superior cervical ganglion; of these, 21 +/- 3% displayed detectable NPY-ir. Fluoro-Gold injections of the reinnervated muscle labelled 20 +/- 4 neurons in the contralateral superior cervical ganglion, of which 85 +/- 3% contained detectable NPY-ir. Examination of the control tarsal muscle revealed DBH-ir noradrenergic nerves throughout the muscle and vasculature, while NPY-ir nerves were present primarily around blood vessels. In the reinnervated preparation, NPY-ir fibers innervated both blood vessels and tarsal muscle in a pattern similar to that of DBH-ir innervation. Acute excision of the remaining superior cervical ganglion eliminated all DBH-ir fibers bilaterally; NPY-ir was reduced markedly in the reinnervated preparations, though some fibers remained. We conclude that, following neonatal denervation, the tarsal muscle is reinnervated by a subpopulation of sympathetic neurons that differs in neuropeptide phenotype from that of the normal ipsilateral innervation.     

Étude par électrophorèse en gel de polyacrylamide de I'évolution enzymatique des tissus de Poire Passe-Crassane pendant la maturation du fruit cueilli

Evolution of different enzymes (glucose 6-phosphate dehydrogenase EC 1.1.1.49, fructose 1–6 diphosphate aldolase EC 4.1.2.1.3, malic enzyme EC 1.1.1.40, pyruvic decarboxylase EC 4.1.1.1) was followed by polyacrylamide gel electrophoresis and specific staining during the maturation of the pear (cv. Passe-Crassane) harvested and stored at +15°C. During the increase of the respiration rate, the glucose 6 P dehydrogenase activity declines while the three other enzymes activity increases. Results obtained are discussed.     

Effect of prednisolone on trachea smooth muscle of normal rats and rats with fibrosing alveolitis

Effect of prednisolone on isolated preparations of trachea of normal rats and rats with fibrosing alveolitis was studied. Prednisolone at a concentration of 0.4 μg/l decreased responses of smooth muscle on stimulation of preganglionic nerve fibers at trachea areas with intramural ganglia in rats with acute alveolitis by 48%, while in normal rats—by 19% of control. In trachea preparations without ganglia, prednisolone at a dose of 10 μg/l decreased responses of muscle to the nerve fiber stimulation by 21.3%. The higher prednisolone doses were less efficient: 0.1–10 μg/l glucocorticoid practically did not affect the smooth muscle responses produced by stimulation of muscle cells. In rats with fibrosing alveolitis, 10 μg/l prednisolone restored the smooth muscle responses to control values in preparations of trachea with intramural ganglia. After the prednisolone treatment, amplitude of the rat trachea muscle contraction in response to the nerve fiber electric stimulation did not differ statistically significantly from control and 0.1–10 μg/l prednisolone did not change the response value. The conclusion is made that prednisolone affected the diseased rats more efficiently than the healthy animals. The character of the glucocorticoid effect depends on the presence of intramural ganglia in the trachea wall.     

Réinnervation vagale sensitive et la composition du muscle sternocéphalique chez le lapin

The crossed nerve anastomosis between the peripheral end of the vagus nerve, cut above the nodose ganglion, and the peripheral end of the accessory nerve has demonstrated the capacity of some vagal afférents to reinnervate, via the accessory nerve stump, certain sternocephalicus muscle fibers in the rabbit. These results add to our understanding of the capacity of these afferents to counter the post-denervational atrophying process that occurs in the reinnervated muscles and to evaluate the changes induced in these muscles during reinnervation. Our work shows that within 3 months, the vagal sensory reinnervation of previously denervated sternocephalicus muscles induces their total weight recovery. This recovery is concomitant on the one hand with the hypertrophy of the four muscle fiber types (I, IIbd, IIc and IIa) identified histochemically in the normal muscles and, on the other, with the appearance of small newly formed myofibers, which are often underlined by characteristic central nuclei. The vagal sensory neurones induce important changes in the percentages and the muscle cross-sectional distribution of the fibers in reinnervated muscles. In these muscles we see also the disappearance of the fast myosin heavy chains MHCiib and MHCiid, the upholding of the fast MHCiia percentage and an increase in the slow MHCi isoform.     

The resilience of the size principle in the organization of motor unit properties in normal and reinnervated adult skeletal muscles

Henneman's size principle relates the input and output properties of motoneurons and their muscle fibers to size and is the basis for size-ordered activation or recruitment of motor units during movement. After nerve injury and surgical repair, the relationship between motoneuron size and the number and size of the muscle fibers that the motoneuron reinnervates is initially lost but returns with time, irrespective of whether the muscles are self- or cross-reinnervated by the regenerated axons. Although the return of the size relationships was initially attributed to the recovery of the cross-sectional area of the reinnervated muscle fibers and their force per fiber, direct enumeration of the innervation ratio and the number of muscle fibers per motoneuron demonstrated that a size-dependent branching of axons accounts for the size relationships in normal muscle, as suggested by Henneman and his colleagues. This same size-dependent branching accounts for the rematching of motoneuron size and muscle unit size in reinnervated muscles. Experiments were carried out to determine whether the daily amount of neuromuscular activation of motor units accounts for the size-dependent organization and reorganization of motor unit properties. The normal size-dependent matching of motoneurons and their muscle units with respect to the numbers of muscle fibers per motoneuron was unaltered by synchronous activation of all of the motor units with the same daily activity. Hence, the restored size relationships and rematching of motoneuron and muscle unit properties after nerve injuries and muscle reinnervation sustain the normal gradation of muscle force during movement by size-ordered recruitment of motor units and the process of rate coding of action potentials. Dynamic modulation of size of muscle fibers and their contractile speed and endurance by neuromuscular activity allows for neuromuscular adaptation in the context of the sustained organization of the neuromuscular system according to the size principle.     

The long-term influence of decentralisation or preganglionic hypogastric nerve stimulation in vivo on the reinnervation of minced vas deferens in the guinea-pig

Previous studies have shown that minced regenerating smooth muscle of the guinea-pig vas deferens becomes reinnervated by nerves growing in from the surrounding intact vas deferens. Using electron microscopy, we have examined the effect of altering activity in the preganglionic nerves, either by decentralisation, or by chronic stimulation of the hypogastric nerve, in vivo, on the reinnervation of regenerating smooth muscle cells. Chronic stimulation induced earlier reinnervation than that seen in unstimulated (sham-operated) or decentralised preparations; the number of nerve profiles present in four preparations stimulated for up to 7 days was approximately 10-20 times that seen in unstimulated or decentralised preparations. However, electron micrographs revealed that "empty" nerve terminals were a feature following stimulation for longer periods. Decentralised preparations showed little change of reinnervation, at least up to 7 weeks. Compensatory changes in the density of innervation were found in the unstimulated contralateral vas deferens.     

Contractile properties of reinnervated skeletal muscle and their relation to the degree of nerve damage

Experiments with 22 rats have shown that the anterior tibial muscle in the stage of incomplete reinnervation is marked by decreased force and retardation of the semi-relaxation of an isometric contraction. In completely reinnervated muscles, the changes in the contractility are determined by the degree of nerve damage. The group of animals with the sciatic nerve injury demonstrated the contractility characteristic of a slower muscle, in contrast to the group with the fibular nerve damage.     

Inhibitory innervation to the guinea pig trachealis muscle

The inhibitory innervation of the cervical trachea was studied in situ in anesthetized male guinea pigs. We measured effects of electrical stimulation of vagal motor and sympathetic trunk nerve fibers, during atropine, on trachealis muscle tension. Effects of direct transmural stimulation of trachealis muscle were also determined. We confirmed the dual nature of the inhibitory innervation to this muscle. Vagal motor inhibitory nerves are shown to be preganglionic. Neural transmission at the level of the ganglia is characterized by filtering of high frequency action potentials. The neurotransmitter at the myoneural junction is unidentified but is not norepinephrine. Maximal relaxation accounts for about 20-40% of maximal relaxations seen with transmural stimulation of trachealis muscle in the presence of atropine. Sympathetic trunk nerve fibers are also preganglionic. Neurotransmission at the level of the ganglia is apparently 1:1 at high-action potential frequencies. Norepinephrine released presynaptically has access to smooth muscle beta- but not alpha-receptors. Maximal adrenergic relaxations account for 60-80% of total transmural stimulation relaxations. Transmural stimulation relaxations appear to be accounted for by release of neurotransmitter from sympathetic adrenergic plus vagal nonadrenergic postganglionic nerve fibers.