Histochemical localization of adrenergic nerves in the guinea-pig trachea

Regulation of Airway Smooth Muscle Contraction in Health and Disease

Airway smooth muscle (ASM) extends from the trachea throughout the bronchial tree to the terminal bronchioles. In utero, spontaneous phasic contraction of fetal ASM is critical for normal lung development by regulating intraluminal fluid movement, ASM differentiation, and release of key growth factors. In contrast, phasic contraction appears to be absent in the adult lung, and regulation of tonic contraction and airflow is under neuronal and humoral control. Accumulating evidence suggests that changes in ASM responsiveness contribute to the pathophysiology of lung diseases with lifelong health impacts.Functional assessments of fetal and adult ASM and airways have defined pharmacological responses and signaling pathways that drive airway contraction and relaxation. Studies using precision-cut lung slices, in which contraction of intrapulmonary airways and ASM calcium signaling can be assessed simultaneously in situ, have been particularly informative. These combined approaches have defined the relative importance of calcium entry into ASM and calcium release from intracellular stores as drivers of spontaneous phasic contraction in utero and excitation-contraction coupling.Increased contractility of ASM in asthma contributes to airway hyperresponsiveness. Studies using animal models and human ASM and airways have characterized inflammatory and other mechanisms underlying increased reactivity to contractile agonists and reduced bronchodilator efficacy of β₂-adrenoceptor agonists in severe diseases. Novel bronchodilators and the application of bronchial thermoplasty to ablate increased ASM within asthmatic airways have the potential to overcome limitations of current therapies. These approaches may directly limit excessive airway contraction to improve outcomes for difficult-to-control asthma and other chronic lung diseases.

Reflex regulation of airway sympathetic nerves in guinea-pigs

Sympathetic nerves innervate the airways of most species but their reflex regulation has been essentially unstudied. Here we demonstrate sympathetic nerve-mediated reflex relaxation of airway smooth muscle measured in situ in the guinea-pig trachea. Retrograde tracing, immunohistochemistry and electrophysiological analysis identified a population of substance P-containing capsaicin-sensitive spinal afferent neurones in the upper thoracic (T1-T4) dorsal root ganglia (DRG) that innervate the airways and lung. After bilateral vagotomy, atropine pretreatment and pre-contraction of the trachealis with histamine, nebulized capsaicin (10-60 microm) evoked a 63+/-7% reversal of the histamine-induced contraction of the trachealis. Either the beta-adrenoceptor antagonist propranolol (2 microm, administered directly to the trachea) or bilateral sympathetic nerve denervation of the trachea essentially abolished these reflexes (10+/-9% and 6+/-4% relaxations, respectively), suggesting that they were mediated primarily, if not exclusively, by sympathetic adrenergic nerve activation. Cutting the upper thoracic dorsal roots carrying the central processes of airway spinal afferents also markedly blocked the relaxations (9+/-5% relaxation). Comparable inhibitory effects were observed following intravenous pretreatment with neurokinin receptor antagonists (3+/-7% relaxations). These reflexes were not accompanied by consistent changes in heart rate or blood pressure. By contrast, stimulating the rostral cut ends of the cervical vagus nerves also evoked a sympathetic adrenergic nerve-mediated relaxation that were accompanied by marked alterations in blood pressure. The results indicate that the capsaicin-induced reflex-mediated relaxation of airway smooth muscle following vagotomy is mediated by sequential activation of tachykinin-containing spinal afferent and sympathetic efferent nerves innervating airways. This sympathetic nerve-mediated response may serve to oppose airway contraction induced by parasympathetic nerve activation in the airways.

Central control of the cardiovascular and respiratory systems and their interactions in vertebrates

This review explores the fundamental neuranatomical and functional bases for integration of the respiratory and cardiovascular systems in vertebrates and traces their evolution through the vertebrate groups, from primarily water-breathing fish and larval amphibians to facultative air-breathers such as lungfish and some adult amphibians and finally obligate air-breathers among the reptiles, birds, and mammals. A comparative account of respiratory rhythm generation leads to consideration of the changing roles in cardiorespiratory integration for central and peripheral chemoreceptors and mechanoreceptors and their central projections. We review evidence of a developing role in the control of cardiorespiratory interactions for the partial relocation from the dorsal motor nucleus of the vagus into the nucleus ambiguus of vagal preganglionic neurons, and in particular those innervating the heart, and for the existence of a functional topography of specific groups of sympathetic preganglionic neurons in the spinal cord. Finally, we consider the mechanisms generating temporal modulation of heart rate, vasomotor tone, and control of the airways in mammals; cardiorespiratory synchrony in fish; and integration of the cardiorespiratory system during intermittent breathing in amphibians, reptiles, and diving birds. Concluding comments suggest areas for further productive research.

Age and region-dependent contraction to alpha-adrenoceptor agonists in rat and guinea-pig isolated trachea

1. The influence of age and of region on alpha-adrenoceptor-mediated contraction to (-)-adrenaline and (-)-noradrenaline was examined in rat (4-136 weeks) and guinea-pig (2-156 weeks) isolated tracheal ring preparations with particular emphasis on the early (up to 12 weeks) maturation phase. 2. In rat tracheal rings, significant regional variation was observed with respect to maximal (-)-adrenaline-induced contraction, such that the greatest activity was seen in ring preparations from the laryngeal end of the trachea. Tracheal rings from the carinal end responded very poorly or were unresponsive to (-)-adrenaline, depending on animal age. These regional differences were seen across the age range. The potencies of (-)-adrenaline and (-)-noradrenaline remained unchanged with respect to animal age, but the maximum contractile tension that developed in response to these agonists increased with increasing animal age in all regions of the trachea. 3. In guinea-pig isolated tracheal tissue, maximum contractile responses (Emax) to (-)-adrenaline and (-)-noradrenaline remained unchanged with increasing animal age. In addition, there was no evidence for a region-dependence in the responsiveness of tracheal tissue to alpha-adrenoceptor-mediated contraction in this species. 4. In both guinea-pig and rat isolated tracheal tissue, alpha-adrenoceptor-mediated contraction appeared to involve the activation of alpha1-adrenoceptors.

Inhibitory effects of d-nicotine on the responses evoked by 1-isomer in trachea and bronchus isolated from guinea-pig and rabbit

1. The effects of d-nicotine on the responses induced by 1-isomer were studied in tracheae and bronchi isolated from guinea-pigs and rabbits. In guinea-pigs trachea 1-nicotine produced a biphasic response consisting of initial contraction and following relaxation. In other airway preparations 1-nicotine produced only contraction. 2. d-Nicotine did not produce any responses except for the case of guinea-pig trachea. d-isomer produced only relaxation and relative potency was approximately 0.44 in guinea-pig trachea. 3. Pretreatment with d-nicotine (30-300 microM) reduced concentration response curves for 1-isomer in a non-competitive manner in all preparations used in this study. 4. 1-nicotine at the concentration of 3 microns, which did not produce any response itself, reduced the concentration response curve of 1-nicotine in guinea-pig trachea. 5. Inhibition by d-nicotine or 1-nicotine (3 microM) of the concentration-response curve of 1-nicotine may be due to desensitization of nicotine receptors.

Neuronal control of airways smooth muscle

Sensory afferent nerves relay impulses from the airways to the central nervous system so that appropriate changes in bronchomotor tone and breathing patterns may occur. The dominant efferent control of airways smooth muscle is exerted via bronchoconstrictor parasympathetic cholinergic nerves. In some species this is opposed by bronchodilator sympathetic noradrenergic nerves. In addition, there exist both excitatory bronchoconstrictor and inhibitory bronchodilator non-adrenergic, non-cholinergic pathways. This review examines the role of the different branches of the autonomic nervous system in the control of airways smooth muscle tone with particular reference to modulation of these branches and the interactions which may exist between them.

Relaxant innervation of the guinea-pig trachealis: demonstration of capsaicin-sensitive and -insensitive vagal pathways

1. The guinea-pig trachea was isolated with its extrinsic innervation intact and placed in a water-jacketed dissecting dish containing warmed, oxygenated Krebs solution. The trachea was not separated from the oesophagus. Two adjacent cartilage rings of the rostral portion of the trachea were cut open opposite the trachealis and prepared for isometric tension measurements. 2. Following the addition of atropine and contraction of the trachealis with prostaglandin F2 alpha (PGF2 alpha), stimulation of the cervical sympathetic trunks elicited relaxations that were abolished by propranolol or hexamethonium. Stimulation of the vagus nerves caudal to the nodose ganglia also elicited relaxations. These vagally mediated relaxations were unaffected by propranolol but were abolished by hexamethonium or by cutting the recurrent laryngeal nerves. 3. After cutting the vagi caudal to the nodose ganglia, stimulation of the vagi rostral to the nodose ganglia elicited relaxations of the trachealis that were not significantly affected by either propranolol or hexamethonium but were abolished by cutting the superior laryngeal nerves. Stimulation of right vagi which had undergone supranodose vagotomy 14 days prior to experimentation was without effect on the smooth muscle of the guinea-pig trachea while the response to stimulation of the left vagus was unchanged. 4. Acute capsaicin desensitization abolished relaxations of the guinea-pig trachealis elicited by stimulation of the vagal fibres carried by the superior laryngeal nerves. In contrast, capsaicin desensitization only modestly inhibited relaxations elicited by stimulation of the preganglionic parasympathetic fibres carried by the recurrent laryngeal nerves and had no effect on sympathetic nerve-induced relaxations. 5. Removing the oesophagus selectively abolished relaxations elicited by stimulation of both vagal pathways of non-adrenergic relaxant innervation. Non-adrenergic relaxations of the trachealis elicited by electrical field stimulation were unaffected by removing the oesophagus. Oesophagus removal also had no effect on the parasympathetic-cholinergic contractile innervation or the sympathetic relaxant innervation of the trachealis. 6. The results indicate that the guinea-pig trachealis receives non-adrenergic relaxant innervation from both parasympathetic and capsaicin-sensitive vagal pathways. The results also suggest that the neurones mediating non-adrenergic relaxations of the trachea are sensitive to oesophagus removal. The observation that oesophagus removal abolishes parasympathetic relaxations of the trachealis while having no effect on parasympathetic contractions supports the hypothesis that the guinea-pig trachealis receives excitatory and inhibitory innervation from distinct vagal parasympathetic pathways.

The sensory and sympathetic innervation of guinea-pig lung and trachea as studied by retrograde neuronal tracing and double-labelling immunohistochemistry

The sympathetic and sensory innervation of guinea-pig trachea and lung were studied by means of retrograde neuronal tracing using fluorescent dyes, and double-labelling immunofluorescence. Sympathetic neurons supplying the lung were located in stellate ganglia and in thoracic sympathetic chain ganglia T2-T4; those supplying the trachea resided in the superior cervical and stellate ganglia. Retrogradely labelled sympathetic neurons were usually immunoreactive to tyrosine hydroxylase; the majority also contained neuropeptide Y immunoreactivity. However, a small number were non-catecholaminergic (i.e. tyrosine hydroxylase negative), but neuropeptide Y immunoreactive. Within the airways, tyrosine hydroxylase/neuropeptide Y-immunoreactive axons were found in the smooth muscle layer, around blood vessels including the pulmonary artery and vein, and to a lesser extent in the lamina propria. Periarterial axons contained in addition dynorphin immunoreactivity. Sensory neurons supplying the lung were located in jugular and nodose vagal ganglia as well as in upper thoracic dorsal root ganglia; those supplying the trachea were most frequently found bilaterally in the nodose ganglia and less frequently in the jugular ganglia. A spinal origin of tracheal sensory fibres could not be consistently demonstrated. With regard to their immunoreactivity to peptides, three types of sensory neurons projecting to the airways could be distinguished: (i) substance P/dynorphin immunoreactive; (ii) substance P immunoreactive but dynorphin negative; and (iii) negative to all peptides tested. Substance P-immunoreactive neurons innervating the airways invariably contained immunoreactivity to neurokinin A and calcitonin gene-related peptide. Retrogradely labelled neurons located in the nodose ganglia belonged almost exclusively (greater than or equal to 99%) to the peptide-negative group, whereas the three neuron types each represented about one-third of retrogradely labelled neurons in jugular and dorsal root ganglia. Within the airways, axons immunoreactive to substance P/neurokinin A and substance P/calcitonin gene-related peptide were distributed within the respiratory epithelium of trachea and large bronchi, in the lamina propria and smooth muscle from the trachea down to the smallest bronchioli (highest density at the bronchial level), in the alveolar walls, around systemic and pulmonary blood vessels, and within airway ganglia. Those axons also containing dynorphin immunoreactivity were restricted to the lamina propria and smooth muscle. The origin of nerve fibres immunoreactive for vasoactive intestinal polypeptide, of which a part were also neuropeptide Y immunoreactive, could not be determined by retrograde tracing experiments. Vasoactive intestinal polypeptide-immunoreactive fibres terminating within airway ganglia may be of preganglionic parasympathetic origin, whereas others (e.g. those found in smooth muscle) may arise from intrinsic ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)

Vasoactive intestinal peptide and neuropeptide Y coexist in non-noradrenergic sympathetic neurons to guinea pig trachea

Vasoactive intestinal peptide (VIP) has been suggested to be a mediator of vagal inhibition of airway tone and it has been assumed that VIP-containing nerve fibres in the airway arise from intrinsic ganglia. We have used a combination of double- and triple-labelling immunohistochemistry, retrograde axonal tracing, organotypic culture and nerve lesion studies, to identify the origin and distribution of neurons containing immunoreactivity (IR) to VIP in guinea pig airway smooth muscle. We also investigated whether immunoreactivity to other neuropeptides coexisted with VIP-IR within these neurons. We found that all VIP-IR nerve fibres in guinea pig tracheal smooth muscle also contained IR to neuropeptide Y (NPY) but not to tyrosine hydroxylase (TH), a marker for noradrenergic neurons. Both VIP-IR and NPY-IR were absent from nerve cell bodies in the tracheal plexus. After maintenance of isolated trachea in organotypic culture for 4 days, to allow degeneration of extrinsic nerve fibres, nerve fibres containing VIP-IR or NPY-IR were almost completely absent from tracheal smooth muscle. Of ganglia known to supply the trachea, coexistence of VIP-IR and NPY-IR was found only in cell bodies of the stellate ganglion. Retrograde tracing studies using the fluorescent tracer, DiI, confirmed that the stellate ganglion was the site of origin of neurons containing VIP-IR and NPY-IR supplying the airways. These neurons projected to the airways from the stellate ganglion both directly through the mediastinum, and via the cervical sympathetic trunk and vagus nerves. These results suggest that nerve fibres containing both VIP-IR and NPY-IR in the tracheal smooth muscle of the guinea pig are derived from non-noradrenergic cell bodies in the stellate ganglion. The absence of VIP-IR from vagal post-ganglionic neurons suggests that VIP cannot be a mediator of vagal inhibitory transmission in tracheal smooth muscle of this species.

Evidence for prejunctional inhibitory muscarinic receptors on sympathetic nerves innervating guinea-pig trachealis muscle

1 Relaxation responses induced by stimulation of the postganglionic sympathetic nerve trunk were studied in the isolated, fluid-filled, innervated tracheal tube preparation of the guinea-pig. 2 The thromboxane-mimetic U46619, prostaglandin F2 alpha and histamine each caused concentration-dependent increases in the intraluminal pressure (ILP) of the fluid-filled tracheal tube, reflecting contraction of the trachealis muscle. Sympathetic nerve stimulation in the presence of the spasmogens caused relaxations which increased with increasing ILP. Relaxant responses evoked in the presence of these three spasmogens were comparable at any given ILP. 3 Muscarinic agonists caused concentration-dependent increases in ILP, pilocarpine being more potent than acetylcholine. Sympathetic nerve-induced relaxations were reduced in the presence of pilocarpine and acetylcholine when compared to those obtained at the same ILP in the presence of U46619. This inhibitory effect of muscarinic agonists on sympathetic nerve-induced responses was concentration-dependent. 4 Exogenously applied noradrenaline opposed the contractile effect of U46619 and acetylcholine to a similar extent, indicating that a comparable degree of postjunctional functional antagonism exists between the sympathetic neurotransmitter noradrenaline and both spasmogens. 5 The selective M2 muscarinic antagonists, gallamine and methoctramine, altered neither the postjunctional contractile action of acetylcholine nor its inhibitory effect on sympathetic nerve-induced relaxations. In addition, the inhibitory effect of acetylcholine was not modified by concentrations of pirenzepine known to block M1 muscarinic receptors. 6 The postjunctional contractile action of acetylcholine and its inhibitory effect on sympathetic neuro-transmission were antagonized by atropine, by the M3 muscarinic antagonist hexahydrosiladiphenidol and by higher concentration of pirenzepine. 7. These results suggest that in the guinea-pig trachea, muscarinic cholinoreceptor agonists inhibit sympathetic neurotransmission via activation of muscarinic receptors located on the sympathetic nerve endings. These inhibitory prejunctional muscarinic heteroreceptors are of the M3 subtype.

Tracheal parasympathetic neurons of rat, mouse and guinea pig: partial expression of noradrenergic phenotype and lack of innervation from noradrenergic nerve fibres

Noradrenergic nerves were studied in whole-mount preparations of the rat, mouse and guinea pig trachea by means of glyoxylic acid-induced catecholamine fluorescence and dopamine beta-hydroxylase immunoreactivity. In an effort to raise tissue levels of catecholamines, some specimens were also treated with the monoamine oxidase inhibitor pargyline, and with L-DOPA, a precursor of noradrenaline. Noradrenergic nerve fibres were detected around blood vessels, within the tracheal smooth muscle and in the mucosa, but never around or in the proximity of neurons of the tracheal ganglia, even after amine precursor loading. These parasympathetic ganglion cells did not show catecholamine fluorescence under control conditions. In the rat and mouse, but not in the guinea pig, some tracheal neurones were dopamine beta-hydroxylase immunoreactive and showed uptake and metabolism of amine precursors, thus expressing aspects of the catecholaminergic phenotype.

Neuronally released (-)-noradrenaline relaxes smooth muscle of calf trachea mainly through beta 1-adrenoceptors: comparison with (-)-adrenaline and relation to adenylate cyclase stimulation

The nature of the receptors that mediate the relaxation of smooth muscle by field stimulation, (-)-noradrenaline and (-)-adrenaline was investigated in calf tracheal smooth muscle. The relation between relaxation, stimulation of the adenylate cyclase and density of beta-adrenoceptor subtypes was studied with the help of antagonists of beta 1- and beta 2-adrenoceptors. The question of the existence of catecholamine-containing nerves was also investigated. (1) Nerves with varicosities exhibiting catecholaminergic fluorescence were observed between bundles of smooth muscle cells. (2) Consistent with the existence of adrenergic nerves (-)-noradrenaline was also found. The content of (-)-noradrenaline (1 microgram.g-1 w.w.) was the same in smooth muscle strips from the sublaryngeal region and from the region close to the bifurcation of the calf trachea. (-)-Adrenaline was not detected. (3) Smooth muscle relaxation by low (-)-noradrenaline concentration (0.6-2 nmol/l) was mediated through beta 1-adrenoceptors. Low concentrations of (-)-adrenaline (0.06-1 nmol/l) relaxed through beta 2-adrenoceptors. High concentrations of (-)-noradrenaline and (-)-adrenaline also caused relaxation through beta 2- and beta 1-adrenoceptors respectively. (4) Field stimulation caused relaxation which was half maximal at 0.2-0.8 Hz. Blockade of beta 1-adrenoceptors strongly attenuated the relaxant response to field stimulation and shifted the frequency-relaxation curves to 4 times higher frequencies. These results are consistent with a beta 1-adrenoceptor-mediated relaxation caused by (-)-noradrenaline released from sympathetic nerve endings at low stimulation frequencies. (5) Blockade of beta 2-adrenoceptors failed to reduce smooth muscle relaxation caused by field stimulation at low stimulation frequencies (0.1-1 Hz). However, after beta 1-adrenoceptor blockade, additional blockade of beta 2-adrenoceptors reduced the relaxant effects observed at high frequencies (2-400 Hz). The results suggest that high concentrations of endogenous (-)-noradrenaline cause relaxation through beta 2-adrenoceptors. (6) Binding experiments with 3H-(-)-bupranolol and 3H-ICI 118,551 revealed between 10,000 and 20,000 beta-adrenoceptors per smooth muscle cell of which 3/4 were beta 2 and 1/4 beta 1. The equilibrium dissociation constant of (-)-adrenaline for both beta 1- and beta 2-adrenoceptors and of (-)-noradrenaline for beta 1-adrenoceptors was 1 mumol/l. The affinity of (-)-noradrenaline for beta 2-adrenoceptors was 10 to 20 times lower than for beta 1-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of noradrenaline on the isolated human bronchus. Comparison with the isolated guinea pig trachea

The pharmacodynamic activity of noradrenaline was evaluated comparatively in vitro on isolated human bronchi and on guinea pig tracheal spirals. Noradrenaline exerted a contractile effect on both preparations under resting tone and in the presence of propranolol 10(-6) M; maximal noradrenaline-induced contraction was 15-20% of maximal acetylcholine (ACh)-induced contraction. Without propranolol, the contractile effect of noradrenaline was negligible when the preparations were under resting tone and absent when they were precontracted with ACh. In contrast, noradrenaline exerted a strongly relaxant effect on both human bronchi (-log ED50 5.24 +/- 0.17; N = 5) and guinea pig tracheae (-log ED50 6.15 +/- 0.29; N = 8). With maximal contraction induced by ACh 3.10(-3) M the -log ED50 of both preparations were shifted to the right by functional antagonism and became 4.72 +/- 0.17 and 5.31 +/- 0.11, respectively. The pKD values of noradrenaline, calculated according to Furchgott and Bursztyn (1967), were 4.79 +/- 0.04 in human bronchi (N = 5) and 4.77 +/- 0.16 in guinea-pig tracheae (N = 8). In the presence of cocaine plus phenoxybenzamine these values were not significantly modified in human bronchi and only slightly modified in guinea pig tracheae. It is concluded that noradrenaline induces a strong beta-adrenergic response and a negligible alpha-adrenergic response from both human bronchi and guinea pig tracheae in vitro.

Substance P-containing nerves mediate nicotine-induced contractions of rabbit bronchial smooth muscle

1. A possible role of substance P-containing nerves in the contractile response to nicotine was investigated in isolated rabbit bronchial smooth muscle preparation. 2. Nicotine caused a contraction which was attributed to the release of acetylcholine in the rabbit bronchus. The response was reduced by capsaicin (10(-5) M) and a substance P antagonist, [D-Arg1, D-Pro2, D-Trp7.9, Leu11] substance P (10(-5) M). 3. Substance P (10(-7) M)-induced contraction was reduced by atropine (10(-6) M) and potentiated by physostigmine (10(-6) M). Furthermore, substance P (10-7 M) enhanced the release of tritium or acetylcholine from the [3H]choline labelled bronchi. 4. Results suggest that substance P-like tachykinin accelerates the nicotine-evoked prejunctional endogenous neural release of acetylcholine on the nervous cells in the rabbit bronchial preparation.

Evidence that tracheal smooth muscle tone in guinea-pig is unaffected by overflow of noradrenaline released by perivascular nerve fibres

1. Fluorescence histochemical techniques demonstrated that in the guinea-pig the cervical common carotid, cranial thyroid and caudal thyroid arteries were surrounded by a rich plexus of adrenergic nerve fibres. 2. The superior cervical ganglia were the source of the perivascular adrenergic fibres of the cranial thyroid arteries and the anterior half of the cervical common carotid arteries. These ganglia may also provide some of the perivascular adrenergic fibres of the caudal thyroid arteries. 3. Perivascular stimulation of the cranial thyroid and caudal thyroid arteries failed to elicit a response from isolated extrathoracic tracheal tube preparations. This suggests that it is unlikely that the guinea-pig extrathoracic trachealis muscle is innervated by adrenergic fibres arising from these perivascular plexuses or that overflow of noradrenaline from perivascular nerves causes dilatation of the trachealis muscle.

Inhibitory responses to nicotine and transmural stimulation in hyoscine-treated guinea-pig isolated trachealis: an electrical and mechanical study

Guinea-pig isolated trachealis muscle treated with hyoscine (1 microM) exhibited mechanical tone which could be suppressed by transmural stimulation and, in a concentration-dependent manner, by nicotine (10-1000 microM). Hexamethonium (500 microM) did not itself cause tone changes, antagonized effects of nicotine but did not antagonize those of isoprenaline. Tetrodotoxin (0.3 microM) did not itself cause tone changes, did not modify the action of isoprenaline but antagonized the effects of nicotine and very markedly reduced responses to transmural electrical stimulation. Guanethidine (50 microM) did not itself cause tone changes, potentiated the action of isoprenaline, antagonized effects of nicotine and reduced responses to transmural electrical stimulation. Propranolol (1 microM) did not itself cause tone changes, antagonized effects of both isoprenaline and nicotine and reduced responses to transmural electrical stimulation. Propranolol (10 microM) caused greater antagonism of isoprenaline but did not further antagonize nicotine or further reduce responses to electrical stimulation. Intracellular electrophysiological recording from hyoscine-treated trachealis showed that 10 microM nicotine caused little or no mechanical or electrical change. Higher concentrations (100 microM and 1 mM) evoked relaxation which was often though not invariably accompanied by transient hyperpolarization and transient inhibition of electrical slow waves in the impaled cell. Hexamethonium (500 microM), tetrodotoxin (0.3 microM), guanethidine (50 microM) and propranolol (1 microM) each suppressed the electrical or mechanical changes evoked by nicotine (100 microM). However, nicotine (1 mM) tested in the presence of propranolol (1 microM), caused relaxation which could be accompanied by slow wave suppression but not by change in resting membrane potential. Transmural stimulation of hyoscine-treated trachea with single pulses of supramaximal voltage and 0.5 ms duration evoked neither relaxation nor membrane potential changes. Stimulation with similar pulses in trains of 5 s duration evoked relaxation which was dependent on pulse frequency. In many cells this relaxation was not accompanied by membrane potential change. In other cells suppression of slow waves occurred. At high pulse frequencies (greater than 16 Hz) this was generally accompanied by membrane hyperpolarization. In tissue treated with hyoscine and propranolol (both 1 microM), transmural stimulation with pulse trains as described above always evoked relaxation but no membrane potential changes were observed. 10 It is concluded that nicotine and transmural stimulation can excite intramural noradrenergic nerves in guinea-pig trachea and thereby evoke relaxation. The membrane potential changes (slow wave suppression and hyperpolarization) are similar to those evoked by the administration of agonists at beta-adrenoceptors. Nicotine and transmural stimulation also excite non-adrenergic non-cholinergic inhibitory (NANCI) nerves. The relaxation evoked by the NANCI neurotransmitter is accompanied by little, if any, membrane potential change.

Innervation of airway smooth muscle. Efferent mechanisms

The classical view, with one excitatory (cholinergic) and one inhibitory (noradrenergic) component, of the innervation of airway smooth muscle is incomplete and at least two other, possibly peptidergic, types of innervation must be included when the innervation of airways is considered. A summary of these neuronal components is given in Fig. 1 and their possible origin is outlined. Besides the inhibitory noradrenergic innervation of the airways observed in some species, an inhibitory NANC (i-NANC) innervation has been demonstrated. The polypeptide, VIP, seems to be the most likely candidate for the neurotransmitter in the i-NANC innervation of the airways. The excitatory cholinergic innervation is present in the airways from the trachea down to the peripheral bronchi. In the guinea-pig bronchi an excitatory NANC (e-NANC) innervation has been demonstrated as well. The e-NANC nerves may correspond to chemosensitive primary afferent nerves with substance P or a related tachykinin as transmitter. When the innervation of airway smooth muscle of different mammalian species is compared it is evident that all nerve components except the cholinergic, show a considerable variability among species. The cholinergic innervation seems to be present in all mammalian species whereas the other components may be completely absent from some species. Distinct regional variations in the innervation of the airways may occur, which is exemplified by the distribution of the autonomic innervation in the guinea-pig tracheo-bronchial tree. Cholinergic neurotransmission in for example the guinea-pig and human airways can be modulated by NA via prejunctional inhibitory alpha 2-adrenoceptors. Furthermore, the e-NANC neurotransmission in the guinea-pig airways may be modulated by NA or by selective alpha 2-adrenoceptor agonists, acting via prejunctional inhibitory alpha 2-adrenoceptors. The clinical importance of the NANC innervation in relation to asthma is discussed. The i-NANC nerves may exert a modulating effect on bronchoconstriction, and a functional defect would presumably lead to an exaggerated response to constrictor stimuli. The e-NANC nerves in the airways may also be clinically relevant since the transmitter (tachykinins) from these nerves can produce bronchoconstriction and promote inflammation of the airway epithelium, either by direct mechanisms or indirectly by activation of mast cells, and thus contribute to the features of asthma.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination of extrinsic pathways of adrenergic nerves to the guinea-pig trachealis muscle using surgical denervation and organ-bath pharmacology

Intraluminal pressure changes were recorded in an isolated tracheal tube during electrical stimulation of the recurrent laryngeal nerve or transmural stimulation of the extra-thoracic trachealis muscle. The recurrent laryngeal nerve contained adrenergic nerve fibres running both anteriorly and posteriorly along this nerve and they caused an adrenergic inhibitory response of the trachealis muscle. The superior cervical ganglion was the source of the majority of the adrenergic fibres running both anteriorly and posteriorly within the recurrent laryngeal nerve. The antero-posterior adrenergic fibres reached the recurrent laryngeal nerve via an anastomosis with the superior cervical ganglion. The postero-anterior adrenergic fibres reached the recurrent laryngeal nerve via the vagus nerve, as ipsilateral vagotomy markedly reduced the inhibitory response of the trachealis muscle which had been due to the postero-anterior adrenergic fibres. Superior cervical ganglionectomy caused a significant reduction in the adrenergic response as a percentage of the total inhibitory response of the extra-thoracic trachealis muscle following transmural stimulation. The remaining response was due to stimulation of non-adrenergic non-cholinergic fibres and adrenergic fibres from another source.

A physiological basis for subclassifying beta-adrenoceptors examined by chemical sympathectomy of guinea-pigs

Chemical sympathectomy of guinea-pigs was induced by chronic pretreatment with 6-hydroxydopamine over a 20 day period. Control animals were sham injected with vehicle at the same times. Isolated tissues were removed from the animals and beta-adrenoceptor sensitivity assessed from cumulative concentration-response curves for isoprenaline, followed after wash-out by a partial agonist (salbutamol, ritodrine or prenalterol). The following responses were measured: increases in force and rate of contraction of left and right atria respectively, inhibition of carbachol-induced ileal contractions, relaxation of intrinsic tone of lung strips and tracheal spirals, inhibition of contractions of vas deferens and soleus muscle induced by field stimulation. Left and right atria and ileum from 6-hydroxydopamine-pretreated guinea-pigs exhibited supersensitivity to beta-adrenoceptor stimulation. This was measured as a leftwards shift of the concentration-response curve for isoprenaline and as an elevation of the partial agonist maximum response (relative to isoprenaline), when compared with tissues from sham-injected controls. The supersensitivity was assumed to be due to the loss of endogenous neurotransmitter release by chemical sympathectomy and specific for the beta-adrenoceptor. In contrast, lung strips, vas deferens and soleus muscle were not supersensitive. The responses of these tissues are thought to be mediated via beta 2-adrenoceptors whereas cardiac and ileal responses are beta 1-adrenoceptor mediated. The latter receptor subtype would therefore appear to be under the influence of sympathetic innervation, but since no supersensitivity occurred at beta 2-adrenoceptors these were presumed to be non-innervated but stimulated by circulating adrenaline. These results obtained by use of chemical sympathectomy with 6-hydroxydopamine support the contention that the physiological basis of beta-adrenoceptor subclassification is that the beta 1-subtype are innervated whereas the beta 2-subtype are non-innervated.

Extrinsic pathways of the adrenergic innervation of the guinea-pig trachealis muscle

Origins and extrinsic pathways of the adrenergic innervation of the guinea-pig trachealis muscle were studied using fluorescence histochemical techniques. Bilateral superior cervical ganglionectomy caused a marked reduction in the adrenergic innervation of the extra-thoracic region, which suggests that these ganglia are a major source of adrenergic innervation to this muscle. Combined anterior and posterior transection of the recurrent laryngeal nerves also caused a marked reduction in the density of adrenergic fibres in the extra-thoracic trachealis muscle. Crushing of these nerves revealed adrenergic fibres running both anteriorly and posteriorly. The majority of these adrenergic nerves were lost after superior cervical ganglionectomy and thus the fibres running in both directions originate in the superior cervical ganglion. Antero-posteriorly directed fibres entered the recurrent laryngeal nerve from the superior cervical ganglion via an anastomosis at the level of the cricoid cartilage, while those running postero-anteriorly entered the recurrent laryngeal nerve posteriorly from the vagus nerve and these adrenergic fibres were lost after cervical vagotomy.

Action of nicotine on guinea-pig isolated bronchial smooth muscle preparation

In the isolated bronchial preparation of the guinea-pig, nicotine induced a contraction but not a relaxation. The contractile response of the bronchial preparation to nicotine was inhibited by hexamethonium and d-tubocurarine but not influenced by atropine and tetrodotoxin. In the isolated tracheal preparation of the guinea-pig where nicotine stimulated nicotinic receptor in nervous tissues, the contractile response to nicotine as considerably accelerated by the treatment of the guinea-pig with egg-albumin, while the contractile response of the bronchial preparation to nicotine was not influenced by the same treatment. These results suggest that a possible site of action of nicotine in the isolated bronchial preparation is not on the nervous cells but on the smooth muscle cells. However, we could not rule out a contribution by chemical mediators released by nicotine in the contractile mechanisms in the bronchial preparation.

The anatomy of the ferret paratracheal parasympathetic nerve-ganglion plexus

Silver-impregnated preparations of the ferret paratracheal nerve-ganglion plexus were studied for description and quantitation of the general morphology of ganglia and nerve bundles and trunks. Most ganglia were found in one or two chains, separated by interganglionic nerve trunks, running the length of the trachea in close apposition to the trachealis muscle. Ganglia were flat, one cell deep, and characterized by irregular spacing and small and variable numbers of perikarya. Perifascicular, infrafascicular, and mixed types of ganglia were seen. The mean perikaryon density was 127 +/- 20/cm2 of trachealis muscle. In addition to connections to the interganglionic nerve trunk, more than 70% of ganglia were also apparently "connected" to nerve bundles running to the periphery and/or the center of the preparation, and the plexus seemed considerably more complex than originally described. There was no significant change in density, size or type, or connections of ganglia with nerve bundles in the cervical or thoracic trachea.

Discrimination by dipyridamole of two types of responses to adenosine and ATP of the carbachol-induced contraction of guinea-pig trachea

Two types of effect of purines on the carbachol-induced contraction of the guinea-pig trachea in the presence or absence of glucose were evaluated using dipyridamole, and adenosine uptake inhibitor. ATP exerted a greater relaxant effect on the carbachol (10(-6) M)-induced contraction than did adenosine in concentrations ranging from 10(-4) to 10(-3) M. These effects of purines were enhanced by pretreatment with dipyridamole (10(-5) M) but were virtually unaffected by the purine receptor antagonists theophylline (10(-5) M) and quinidine (10(-5) M). The contraction evoked by carbachol was gradually reduced and was almost abolished 4-5 h after exposure to the glucose-free solution. This reduction was almost eliminated by readmitting glucose, and was restored to a certain degree by introducing ATP or adenosine. ATP was less effective than adenosine. This effect of purines but not that of glucose, was markedly diminished by pretreatment with dipyridamole (3 X 10(-6) M to 10(-5) M). The restoration of the carbachol-induced contraction following introduction of purines or glucose was completely antagonized by atropine (10(-6) M). These results suggest that the extracellular effects of adenosine and ATP on the carbachol-induced contraction in normal solution are potentiated by dipyridamole, whereas the possible intracellular effects of these purines in the glucose-free solution are inhibited by this adenosine uptake inhibitor.

Bronchopulmonary effects of clonidine on the bronchomotor responses of the guinea-pig

In conscious guinea pigs, clonidine (10 and 100 micrograms/kg i.v.) lowered diastolic (-7.9 +/- 3.5 and -12.4 +/- 5.2%) and systolic (-8.6 +/- 3.0 and -11.9 +/- 4.2%) arterial pressure and reduced heart rate (-14.5 +/- 3.9 and -27.7 +/- 3.8%), but did not significantly modify pulmonary airway resistance. Hypotension was suppressed by yohimbine and bradycardia was partially suppressed by atropine and yohimbine, which demonstrates in this animal an alpha 2-adrenergic effect for hypotension and a mixed cholinergic and alpha 2-adrenergic effect for bradycardia. Clonidine (10 and 100 micrograms/kg i.v.) enhanced the bronchoconstrictor effects of histamine 20 micrograms/kg (+80.0 +/- 22.5 and 89.1 +/- 26.5%), acetylcholine 25 micrograms/kg (+66.4 +/- 19.8 and +95.4 +/- 25.4%) and serotonin 15 micrograms/kg (+68.5 +/- 23.2 and +81.4 +/- 34.1%). The duration of this effect was comparable to that of the hypotensive and cardiac effects of clonidine. The effects of clonidine were suppressed after pretreatment with propranolol, reserpine or pentobarbitone, all drugs which enhance the bronchoconstrictor effect of ACh. Yohimbine (1 mg/kg), piperoxan (0.3 mg/kg) or prazosin in high dosage (0.3 mg/kg) inhibited the potentiation by clonidine of ACh-induced bronchoconstriction, whereas prazosin in lower doses (0.03 mg/kg) or AR-C 239 (0.05 mg/kg) had no action. A specific involvement of alpha 2-adrenoceptors stimulated by clonidine with subsequent reduction of the adrenergic activity associated with bronchospasm could therefore be demonstrated in the conscious guinea-pig during bronchomotor reactions.

Adrenergic and non-adrenergic inhibitory nerves in mammalian airways

A study of the actions of adrenergic and non-adrenergic nerves which affect mammalian airways was carried out. The preparations studied included strips of lung from guinea-pig, rat, rabbit, monkey and human, tracheal strips from the first 4 animals and bronchial strips from the last 3. Relaxations to field stimulation of sympathetic nerves were found in the guinea-pig trachea only. Functional nonadrenergic inhibitory nerves were found in the larger airways of all species except rat. Lung strips from all the mammals failed to respond to sympathetic or nonadrenergic inhibitory nerve stimulation suggesting a lack of functional inhibitory nerves of either type in the fine airways. Studies on the distribution of adrenergic nerves showed that primary target of the nerves in all species appeared to be the vasculature, especially in lung. Occasional fibres were seen entering the smooth muscle of the fine airways in guinea-pig, rabbit, and rat, but not in monkey or human lung or in monkey trachea or bronchus or human bronchus. Guinea-pig and rabbit trachealis muscles received a significant innervation but only the guinea-pig tissue responded to sympathetic stimulation. Inhibitory beta-adrenoceptors were demonstrated in the proximal airways of all species except rabbit. The fine airways of rat, monkey and human contained a mixed population of alpha-excitatory and beta-inhibitory adrenoceptors only were found in guinea-pig lung and alpha-adrenoceptors only in rabbit lung.

Non-adrenergic, non-cholinergic nerves in mammalian airways: their function and the role of purines

1. Relaxations to field stimulation of sympathetic nerves were found in the guinea-pig trachea only. 2. Relaxations to field stimulation of non-adrenergic inhibitory nerves were found in the larger airways of human, monkey, guinea-pig and rabbit, but not rat. 3. Lung strips from all the mammals failed to respond to sympathetic or non-adrenergic inhibitory nerve stimulation. 4. Inhibitory beta-adrenoceptors were demonstrated in the proximal airways of all species except rabbit. 5. Of the fine airways examined, beta-adrenoceptors only were found in guinea-pig and alpha-adrenoceptors only in rabbit while rat, monkey and human tissues contained mixed populations of both receptors. 6. Adenosine is a likely candidate for the neurotransmitter in the non-adrenergic inhibitory nerves. Inhibitory receptors for adenosine were present in guinea-pig trachea although receptors for ATP are probably lacking.

Innervation of the trachealis muscle in the guinea-pig: a quantitative ultrastructural study

The fine structure and composition of the nerve plexuses associated with the cervical and the thoracic parts of the trachealis muscle were studied in two groups of six guinea-pigs. One group of animals was perfused with fixative before removal of the specimens. In the second, the specimens were incubated in 5-hydroxydopamine before cold immersion fixation. In both the cervical and the thoracic trachea, plexuses of nerves were found within and between the fascicles of muscle cells. The number of intrafascicular nerves/1000 micrometer 2 was low, and only a small proportion of the nerves contained more than five axons. Interfascicular nerves were more numerous and the mean number of axons/nerve was significantly higher than within the muscle. The number of efferent terminal profiles/100 axonal profiles was higher in the intrafascicular than in the interfascicular plexus, but in neither case was there evidence of a very close approximation of exposed terminal membranes to the membranes of adjacent muscle cells. Terminals classified as those of autonomic efferent axons were present in much greater numbers in the nerves than any other type of terminal. Examination of 5-hydroxydopamine-incubated specimens showed that less than half of these terminals were the terminals of adrenergic axons. Terminals of the type considered to represent the terminals of purinergic axons were also found in the nerves but were present in much smaller numbers than in the nerves of the submucous plexuses. The presence in the nerves of mitochondria-containing terminals with features similar to those of mechanosensitive nerve endings was related to physiological evidence of the location of stretch receptors in the muscle.

Tne density of adrenergic nerves at various levels in the guinea-pig lung

1. Gunea-pig tracheal and lung segments were systematically examined for adrenergic nerves using the fluorescence histochemical technique. Fluorescence in nerves was enhanced with alpha-methylnoradrenaline or by pretreating animals with nialamide. 2. There was a progressive decrese in density of fluorescent fibres in airway smooth muscle from the laryngeal end of the trachea, which was densely innervated, to the bronchioles, which contained only occasional fibres. This was despite obvious fluorescence in blood vessels in the lung. 3. It is suggested that, if adrenergic nerves are involved in reflex bronchodilatation in this species, they directly control larger airways and other factors, e.g. non-adrenergic inhibitory nerves, may be important in the control of smaller airways.

The uptake kinetics and metabolism of extraneuronal noradrenaline in guinea-pig trachea as studied with quantitative fluorescence microphotometry

1 Extraneuronal uptake of noradrenaline and alpha-methylnoradrenaline into single cells of guinea-pig tracheal smooth muscle have been studied by means of quantitative fluorescence microphotometry. 2 Fluorescence brightness due to accumulation of alpha-methylnoradrenaline was dose-dependent and was increased by the catechol-O-methyltransferase inhibitor drugs, tropolone or beta-thujaplicin (200 micrometer) but not by 3,4-dimethoxy-5-hydroxybenzoic acid (200 microgram). 3 Fluorescence brightness due to accumulation of noradrenaline was increased if animals were pretreated with the monoamine oxidase inhibitor drug, nialamide. 4 The study suggests that metabolism of amines by catechol-O-methyltransferase and monoamine oxidase can occur subsequent to extraneuronal uptake is guinea-pig tracheal smooth muscle. 5 The uptake of noradrenaline into tracheal smooth muscle was concentration-dependent, saturable, and had a Km of 156 micrometer.

A histochemical study of extraneuronal accumulation of noradrenaline in the guinea-pig trachea

1. Accumulation of noradrenaline in extraneuronal tissue of the guinea-pig trachea has been studied by the use of the fluorescence histochemical technique of Falck and Hillarp.2. After incubation in solutions of noradrenaline, fluorescence developed in cellular structures (tracheal smooth muscle, vascular smooth muscle and endothelium, fibroblasts and chondroblasts), in the intercellular matrix of the cartilage and throughout the loose connective tissue of the adventitia and submucosa.3. The effect of various experimental procedures on the development of this fluorescence has been examined i.e. incubation with noradrenaline at reduced temperature (0 degrees C), removal of fluorescence by washing with Krebs solution at 37 degrees C or 0 degrees C, incubation with phenoxybenzamine (10(-4)M) or metanephrine (10(-4)M).4. From these observations it has been concluded that noradrenaline accumulates in the trachea:(a) in cellular structures where it is firmly bound, i.e. not easily removed by washing at 0 degrees C, and where the accumulation is prevented by phenoxybenzamine, metanephrine or cold.(b) in the intercellular matrix of the cartilage where it is also firmly bound, but where the accumulation is not prevented by phenoxybenzamine, metanephrine or cold. This probably represents binding to sulphated mucopolysaccharides.(c) in the adventitia and submucosa where it is loosely bound and easily removed by washing.5. Some implications of these findings in pharmacological experiments with guinea-pig trachea are discussed.