Vagal innervation of guinea pig bronchial smooth muscle

We isolated the guinea pig right bronchus with the vagus nerves intact and evaluated the changes in isometric tension of the smooth muscle in response to nerve stimulation. Brief (10-s) trains of electrical field stimulation or vagus nerve stimulation caused a biphasic contraction: the "first phase" sensitive to atropine and the "second phase" sensitive to capsaicin. The two phases could be dissociated by adjusting the stimulus intensity; greater stimulus intensities (pulse durations or voltage) were required to evoke the capsaicin-sensitive phase. When stimulated at 30-min intervals, the magnitude of both phases of the contractions declined over a 2-h period of repeated stimulation; however, this was prevented by indomethacin. Stimulation of the left vagus nerve resulted in a monophasic contraction of the right bronchus, with little evidence of a capsaicin-sensitive phase. Blocking neurotransmission through the bronchial ganglion, as monitored by intracellular recording techniques, abolished the first-phase contraction but had no effect on the capsaicin-sensitive phase. Selective blockade of muscarinic M1 receptors had no effect on vagus nerve-mediated contractions. The results demonstrate that the left and right vagus nerves carry preganglionic fibers to the right bronchial ganglion. The right but not the left vagus nerve also carries capsaicin-sensitive afferent fibers that, when stimulated, result in a persistent contraction of the right bronchus. Finally, we provide functional and electrophysiological evidence supporting the hypothesis that capsaicin-sensitive afferent neurons communicate with postganglionic motoneurons within the bronchus.     

Adrenergic reactions of sheep rumen in vitro

The alpha and beta-adrenergic responses of the isolated muscle of sheep rumen were analysed by pharmacodynamic methods after administration of alpha and beta-adrenergic agonists and alpha and beta-adrenergic antagonists. It was found that phenylephrine, and in a lower degree propranolol, stimulated contractions of isolated muscle of sheep rumen while adrenaline, noradrenaline, isoprenaline, phenoxybenzamine and regitine inhibited these contractions. Propranolol abolished the dilating (atonic) effect of catecholamines on the isolated muscles of sheep rumen and previous blockade of beta-adrenergic receptors with propranolol reversed the dilating effects of catecholamines. It is concluded that noradrenaline has an ambiceptor effect (similar to that of adrenaline) on the isolated muscle of the rumen.     

Role of vagus nerve in postprandial antropyloric coordination in conscious dogs

It is generally believed that gastric emptying of solids is regulated by a coordinated motor pattern between the antrum and pylorus. We studied the role of the vagus nerve in mediating postprandial coordination between the antrum and pylorus. Force transducers were implanted on the serosal surface of the body, antrum, pylorus, and duodenum in seven dogs. Dogs were given either a solid or a liquid meal, and gastroduodenal motility was recorded over 10 h. Gastric emptying was evaluated with radiopaque markers mixed with a solid meal. Dogs were treated with hexamethonium, N(G)-nitro-l-arginine methyl ester (l-NAME), or transient vagal nerve blockade by cooling. A postprandial motility pattern showed three distinct phases: early, intermediate, and late. In the late phase, profound pyloric relaxations predominantly synchronized with giant antral contractions that were defined as postprandial antropyloric coordination. A gastric emptying study revealed that the time at which gastric contents entered into the duodenum occurred concomitantly with antropyloric coordination. Treatment by vagal blockade or hexamethonium significantly reduced postprandial antral contractions and pyloric relaxations of the late phase. l-NAME changed pyloric motor patterns from relaxation dominant to contraction dominant. Solid gastric emptying was significantly attenuated by treatment with hexamethonium, l-NAME, and vagal blockade. Postprandial antropyloric coordination was not seen after feeding a liquid meal. It is concluded that postprandial antropyloric coordination plays an important role to regulate gastric emptying of a solid food. Postprandial antropyloric coordination is regulated by the vagus nerve and nitrergic neurons in conscious dogs.     

Organization of reflex sympathetic influence on rate and force of cardiac contraction]

In acute experiments on 21 cats it was proved that the change of afferent impulse on vagus nerves by means of either freeze-block or electrostimulation of their central ends results in differential reflex influences on rhythm and force of the cardiac contractions caused by sympathetic nervous system. The cut of the lower cardiac nerves may cause 'break-up' of the observed reflex, removing or inverting its ino- or chronotropy component. The given phenomenon was revealed in the experiments with high arterial pressure and with absence of tonic chronotropy influences of the left lower cardiac nerve.     

Microbial diversity in the rumen,reticulum, omasum,and abomasum of yak on a rapid fattening regime in an agro-pastoral transition zone

The ruminant digestive system harbors a complex gut microbiome, which is poorly understood in the case of the four stomach compartments of yak. High-throughput sequencing and quantitative PCR were used to analyse microbial communities in the rumen, reticulum, omasum, and abomasum of six domesticated yak. The diversity of prokaryotes was higher in reticulum and omasum than in rumen and abomasum. Bacteroidetes predominated in the four stomach compartments, with abundance gradually decreasing in the trend rumen > reticulum > omasum > abomasum. Microorganism composition was different among the four compartments, all of which contained high levels of bacteria, methanogens, protozoa and anaerobic fungi. Some prokaryotic genera were associated with volatile fatty acids and pH. This study provides the first insights into the microorganism composition of four stomach compartments in yak, and may provide a foundation for future studies in this area.     

Augmentation of respiratory mast cell secretion of histamine caused by vagus nerve stimulation during antigen challenge

We studied the effect of vagus nerve stimulation on the mast cell secretion of histamine after intraarterial (i.a.) administration of Ascaris suum antigen (AA) into the bronchial circulation of 10 randomly selected, natively allergic dogs in vivo. Respiratory mast cell response was measured as the arteriovenous difference (AVd) in histamine concentration across the bronchus. Plasma histamine concentration was determined simultaneously from right atrium, right ventricle, and femoral artery 60 and 15 sec before and 15, 30, 45, 60, 75, and 90 sec after i.a. injection of sham (Kreb-Henseleit) diluent, 1:100, and 1:30 concentrations of AA. The mean AVd in plasma histamine for five parasympathetically blocked animals (neural blockade with hexamethonium and beta-adrenergic blockade with propranolol) was 1.28 +/- 0.61 ng/ml (sham), 5.16 +/- 19.7 ng/ml (1:100 AA), and 36.6 +/- 11.1 ng/ml (1:30 AA). Substantial augmentation was obtained when AA was administered during parasympathetic stimulation in five other animals (beta-adrenergic blockade, no neural blockade), which was caused by continuous bilateral electrical stimulation of the vagus nerves. A mean AVd in plasma histamine of 110 +/- 27.6 ng/ml was obtained after 1:100 AA (p less than 0.001 vs parasympathetic blockade) and 166 +/- 32.4 ng/ml for 1:30 AA (p less than 0.001 vs parasympathetic blockade). Parasympathetic stimulation alone did not cause secretion of histamine. In contrast to the AVd response, parasympathetic stimulation did not augment nonrespiratory mast cell secretion after AA challenge. We conclude that vagus nerve stimulation augments secretion of histamine from respiratory mast cells during antigen challenge. We demonstrate that parasympathetic stimulation may potentiate the response to antigen challenge in central airways through augmented mast cell secretion of mediator.     

Effect of ozone on breathing in dogs: vagal and nonvagal mechanisms

We exposed two awake dogs with a chronic tracheostomy and the cervical vagus nerves exteriorized in skin loops to 1.0 ppm of ozone (O3) for 2 h at intervals of 4 wk. We measured ventilatory variables before and after O3 exposure during rest and exercise before and after vagal block. We compared the effects of vagal blockade, exercise, and O3 on the primary determinants of breathing pattern (VT/TI, VT/TE, TI, and TE) in each of three conditions: base line (steady state), during hypercapnia, and after inhalation of 1% histamine. Under base-line conditions, O3 increased respiratory rate and decreased tidal volume (VT) by shortening time of expiration (TE) and time of inspiration (TI) without affecting VT/TI, an indicator of the neural drive to breathing. During progressive hypercapnia, O3 shortened TE and TI by effects both on tonic (nonvolume-related) and on phasic (volume-related) vagal inputs, and only the latter were prevented completely by cooling of the vagus nerves. Histamine-induced tachypnea was increased by O3 and was totally blocked by cooling the vagus nerves. We conclude that O3 shortens the timing of respiration without increasing ventilatory drive, shortens TI and TE through vagal and nonvagal pathways, increases tonic nonvagal and phasic vagal inputs, and stimulates more than one vagal fiber type.     

Paradoxical Cardiac Rhythm in Rat Pups as a Possible Analog of the Sick Sinus Syndrome

Experiments with simultaneous recordings of ECG, electrogram of myocardial fibers of the right ventricle and neurogram of the right branch of vagus or sympathetic nerves were carried out on 3–18-day old rat pups. The electric activity recordings were performed under both in vivo and in situ conditions at unilateral or bilateral pneumothorax. It is established that the change in the cholinergic system activation level produced prior to pneumothorax decelerates the rhythm of cardiac contractions (CC) and induces periods of more frequent CC. After pneumothorax, this syndrome becomes more pronounced. The periods of alternation of the slow and fast rhythms may last for up to 1–2 min. The development of the pathological process leads to development of the sino-auricular and atrio-ventricular blocks. There appears a pattern of CC changes and complexes of the ventricular electric potentials that occur in decasecond and then in minute rhythms and are separated by periods of total asystole or preserved potentials of atrial excitation. When the electrograms of myocardium were recorded in rat pups under conditions of bilateral pneumothorax without any pharmacological intervention, it was possible to see a distortion of the sinus rhythm of CC developing for 2–2.5 h after respiration arrest and similar to the above-described distortion. The appearance and development of the phenomenon of the atypical cardiac rhythm is not directly related to the firing patterns of vagus and sympathetic nerves. At the same time, a correlation is clearly seen between the amplitude–frequency modulation of CC and discharges of vagus. A contraction of groups of respiratory muscles lasts for up to 30 min after pneumothorax, with occasional discharges seen in neurogram even after the complete immobilization of the animal. The development of the pathological process reveals a certain similarity with the phenomenon described in literature as the sinus node syndrome (tachy–bradycardia syndrome, TBS). Based on analysis of the cardiac rhythm transformation, it is suggested that the clinical TBS is a consequence of recapitulation, i.e., a successive release of ancient rhythms of excitation due to an impair of regulatory mechanisms.     

Comparative studies on the distribution of rhodanese and beta-mercaptopyruvate sulfurtransferase in different organs of sheep (Ovis aries) and cattle (Bos taurus)

1. The activities of rhodanese and beta-mercaptopyruvate sulfurtransferase (MST) in different organs of sheep and cattle were measured. 2. Liver, kidney, omasum, and rumen were the richest sources of both enzymes. The activities of both enzymes in other organs of the sheep and the cattle decreased in the order of lung, brain, heart, abomasum, lymph node, urinary bladder, spleen, and the skeletal muscle. 3. The activities of both enzymes in most organs of the sheep were higher than the cattle. 4. Both enzymes showed higher activities in the epithelial layers than the muscular layers of rumen, omasum and reticulum. 5. In most of the tissues of both species the level of rhodanese activity was greater than MST.     

Histological and histochemical observations on the forestomach of goat during pre-natal life.

Non-keratinized, stratified squamous epithelium lined the mucosa of the fore-stomach. The mucosal appendages in the form of ruminal papillae did not develop in the rumen during this study, however, omasal laminae and reticular ribs were evident in groups I and II, respectively. Cytoplasmic accumulations were evident in the middle layer of the epithelium, which is characteristic of this region. The thickness of the epithelium increased constantly in the rumen and reticulum, but in the omasum it remained constant with the increase in the size of the fetus. The corial papillae in the rumen, reticulum and omasum appeared at the 12.7-, 11.5-and 14.6-cm CVR stage, respectively. The muscularis mucosae appeared in the omasum at the 14.6-cm CVR stage in the first-order laminae. The tunica muscularis consisted of spirally arranged muscle fibre bundles. Cross-cut muscle fibre bundles below the tip of the omasal laminae descended downward with the increase in the size of the fetus and continued with the inner circular layer. Acid and alkaline phosphatases and fat could not be observed. The concentration of glycogen in the epithelium was maximum in group III and minimum in group II.     

Axonal effects of capsaicin: an electrophysiological study

The effects of axonally applied capsaicin on the discharge activity and compound action potential of the cat vagus, saphenous and phrenic nerves and the cervical sympathetic trunk were studied under in vivo and in vitro conditions. Application of capsaicin (10(-4) M) to the vagus, saphenous and phrenic nerves resulted in the appearance of intense discharge activity which reached its maximum after 3-4 min and lasted for 15-20 min. Parallel with the increase in discharge activity, elicited by orthodromic activation induced by capsaicin, the amplitudes of the A delta and C components of an antidromically evoked compound action potential were significantly reduced. After the excitatory action of capsaicin vanished, an increase in the latency and duration and a decrease in the amplitudes of the components of the compound action potential were observed which might have led to the development of a local block of impulse propagation. These changes proved to be reversible after the removal of capsaicin from the nerve. Compound action potentials recorded from the saphenous or vagus nerves pretreated with capsaicin 3-5 days before the experiments failed to show any significant changes. It is concluded that upon direct axonal application capsaicin results in the excitation of both A delta and C fibres which is followed by a nonspecific but reversible blockade of impulse propagation. The possible significance of these transient effects of axonally applied capsaicin in term of the development of the highly specific functional impairment occurring a few days after perineural capsaicin treatment remains to be elucidated.     

Effect of cervical sympathetic trunk transection on renal sympathetic nerve activity in rats

Stellate ganglion blockade (SGB) with a local anesthetic increases muscle sympathetic nerve activity in the tibial nerve in humans. However, whether this sympathetic excitation in the tibial nerve is due to a sympathetic blockade in the neck itself, or due to infiltration of a local anesthetic to adjacent nerves including the vagus nerve remains unknown. To rule out one mechanism, we examined the effects of cervical sympathetic trunk transection on renal sympathetic nerve activity (RSNA) in anesthetized rats. Seven rats were anesthetized with intraperitoneal urethane. RSNA together with arterial blood pressure and heart rate were recorded for 15 min before and 30 min after left cervical sympathetic trunk transection. The baroreceptor unloading RSNA obtained by decreasing arterial blood pressure with administration of sodium nitroprusside was also measured. Left cervical sympathetic trunk transection did not have any significant effects on RSNA, baroreceptor unloading RSNA, arterial blood pressure, and heart rate. These data suggest that there was no compensatory increase in RSNA when cervical sympathetic trunk was transected and that the increase in sympathetic nerve activity in the tibial nerve during SGB in humans may result from infiltration of a local anesthetic to adjacent nerves rather than a sympathetic blockade in the neck itself.     

Increase of cardiodepressant activity in medium incubating the posterior pituitary lobe in situ during vagal nerve stimulation in rat.

Previous studies have indicated that there is a cardiodepressant factor in the medium incubating the posterior pituitary lobe in situ. The cardiodepressant activity of the medium incubating the posterior pituitary lobe before and during stimulation of the vagus nerves was tested on isolated auricles of the right heart atrium of a two-day-old rat. It was found that the medium incubating the posterior pituitary lobe collected before stimulation decreased the contraction rate of the auricle by 34%, while that collected during the intermittent stimulation of the central ends of the cut vagus nerves caused a decrease of the auricle contractions frequency by 52%. The addition of cholinergic, serotoninergic, histaminergic receptor blockers or prostaglandin synthetase into Ringer-Lock's solution bathing the auricle has no effect on the changes of the contraction rate caused by the incubation medium.     

Changes in the local blood flows of the single kidney with partial impairment of the autonomic innervation

The changes of cortical and intramedullary blood flow of the remaining after nephrectomy kidney under the condition of guanethidine sympathectomy and continuous pharmacological blockade of parasympathetic mediation by atropine were studied in chronic experiments on Wistar line rats in dynamics at 4, 7, 15, 30, 60, 90 and 120 days. Decrease in cortical and increase of intramedullary peritubular blood flow were noted in both experimental series, that is both blockade of sympathetic and parasympathetic nerves after 15 days. The conclusion was made that blood flow redistribution is a universal mechanisms of single kidney adaptation to its neurogenic impairments.     

β2-Adrenergic Receptors on Peripheral Nerves

We report that peripheral nerves have a functional adenylate cyclase-coupled beta-adrenergic receptor. The pharmacological specificity of this receptor is shown to be of the beta 2 subtype. Two peripheral nerves, the sciatic from the frog and rat and the vagus from the rat, responded to beta 2-agonists with 10-50-fold increases in intracellular cyclic AMP level. This increase was inhibited by the beta-adrenergic antagonist propranolol. In contrast, a central nerve tract, the corpus callosum, responded to isoproterenol with only a minimal one- to twofold increase in cyclic AMP level. These studies demonstrate that peripheral nerves have beta 2-adrenergic receptors that are responsive to exogenously applied catecholamines and suggest a role for these ligands in the previously described modulation of axonal conduction.     

Effects of high-frequency artificial respiration on the rhythm of heart contraction in cats

High-frequency artificial hyperventilation of cat lung with a rate above the initial rhythm of the heart reconstructs the rhythm so that each breathing cycle coincides with one systole of the heart. Synchronization of breathing movements and heart systoles is easily removed by atropine, and cold blockade of vagus nerves by open artificial pneumothorax.     

Postnatal changes in vagal control of esophageal muscle contractions in rats

AimsReplacement of smooth muscles by striated muscles occurs in the esophagus during the early postnatal period. The aim of this study was to clarify postnatal changes in vagal control of esophageal muscle contractions in rats.Main methodsAn isolated segment of the neonatal rat esophagus was placed in an organ bath and the contractile responses were recorded using a force transducer.Key findingsElectrical stimulation of the vagus trunk evoked a biphasic contractile response in the neonatal esophageal segment. The first and second components of the contractions were inhibited by α-bungarotoxin and atropine, respectively. Ganglion blockers, hexamethonium and mecamylamine, did not affect vagally mediated contractions. The first component gradually enlarged with age in days, whereas the second component declined during the first week after birth. Application of d-tubocurarine or acetylcholine caused an apparent contraction in the esophageal striated muscle at postnatal day 0, but responses to these drugs were not observed at 1 week after birth. The neonatal esophagus expressed the γ-subunit of nicotinic acetylcholine receptors. In contrast, the ε-subunit was dominantly expressed in the adult esophagus.SignificanceThe vagus nerves directly innervate both the esophageal striated muscles and smooth muscles in the early neonatal period. During the process of muscle rearrangement, the property of the striated muscles is altered substantially. The specific features of striated muscles in the neonatal rat esophagus might compensate for immature formation of neuromuscular junctions. Unsuccessful conversion of the striated muscle property during postnatal muscle rearrangement would be related to disorders of esophageal motility.     

Development and use of competitive PCR assays for the rumen cellulolytic bacteria: Fibrobacter succinogenes, Ruminococcus albus and Ruminococcus flavefaciens

Competitive PCR assays were developed for the enumeration of the rumen cellulolytic bacterial species: Fibrobacter succinogenes, Ruminococcus albus and Ruminococcus flavefaciens. The assays, targeting species-specific regions of 16S rDNA, were evaluated using DNA from pure culture and rumen digesta spiked with the relevant cellulolytic species. Minimum detection levels for F. succinogenes, R. albus and R. flavefaciens were 1-10 cells in pure culture and 10(3-4) cells per ml in mixed culture. The assays were reproducible and 11-13% inter- and intra-assay variations were observed. Enumeration of the cellulolytic species in the rumen and alimentary tract of sheep found F. succinogenes dominant (10(7) per ml of rumen digesta) compared to the Ruminococcus spp. (10(4-6) per ml). The population size of the three species did not change after the proportion of dietary alfalfa hay was increased. All three species were detected in the rumen, omasum, caecum, colon and rectum. Numbers of the cellulolytic species at these sites varied within and between animals.     

Potentiation of vagal contractile response by thromboxane mimetic U-46619

We studied the effect of the thromboxane mimetic U-46619 on tracheal smooth muscle contraction caused by bilateral stimulation of the vagus nerves in 14 mongrel dogs in situ. The parasympathetic contractile response was studied isometrically after beta-adrenergic blockade with 2 mg/kg iv propranolol plus 20 micrograms X kg-1 X min-1 continuous intravenous infusion and blockade of endogenous prostaglandin synthesis with 5 mg/kg iv indomethacin. An initial frequency-response curve was generated by electrical stimulation of the caudal ends of cut cervical vagi over the range of frequencies 2-25 Hz (constant 25 V) at 15-s intervals. In five dogs, 10(-10) to 10(-8) mol of the thromboxane mimetic (15S)-hydroxyl-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U-46619) was injected selectively into the tracheal arterial circulation, causing a transient contractile response (less than or equal to 10 g/cm). Additional frequency response studies were generated 7 min before and 1, 15, 30, 45, and 60 min after U-46619. Substantial augmentation of tracheal contraction to efferent vagal stimulation was observed after U-46619 for all frequencies greater than 4 Hz (P less than 0.02). Augmentation of vagally mediated contraction was not observed in four other dogs after equivalent tracheal contraction was elicited without U-46619. Similarly, in four separate dogs, augmentation of tracheal contraction was not observed when acetylcholine was given instead of vagal stimulation after U-46619. We conclude that the thromboxane analogue, U-46619, causes augmentation of tracheal contractile response induced by efferent vagus nerve stimulation. Potentiation is caused by a prejunctional action of U-46619 and is not induced by nonspecific precontraction with another agonist.     

Motor effects of gastrin releasing peptide (GRP) and bombesin in the canine stomach and small intestine

Close intraarterial injections of synthetic porcine gastrin releasing peptide (GRP) or bombesin stimulated contractions in the stomach and inhibited ongoing contractile activity in the small intestine of anaesthetized dogs. Contractile activity of the circular muscle was recorded by serosal strain gauges and phasic activity when desired was elicited by local field stimulation or intraarterial motilin injections. In the stomach (corpus and antrum) following tetrodotoxin blockade of field-stimulated contractions, the contractile response to either peptide was not present, suggesting that stimulation of receptors on nerves initiated contractions in the stomach. Similarly, in the small intestine, the inhibitory response was eliminated by tetrodotoxin suggesting a neural receptor. Pre-treatment with reserpine did not alter the inhibitory response, either in the presence or absence of atropine, therefore, adrenergic inhibitory mechanisms did not appear to be involved. The concentration of bombesin producing 50% inhibition of field stimulation (ED50) was increased following treatment with the putative M1 muscarinic antagonist, pirenzipine suggesting activation of M1 cholinergic inhibitory receptors by bombesin. After blockade by atropine of field-stimulated contractions and the contractile response to intraarterial acetylcholine, the ED50 for bombesin inhibition of motilin contractions was increased. After muscarinic blockade, the residual inhibitory response of GRP/bombesin may involve activation of a neural non-cholinergic non-adrenergic inhibitory mechanism. These results suggest that GRP and bombesin act to alter motility in the dog in vivo by affecting neural activity.