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Johns Hopkins Medical Institutions, Baltimore, Maryland 21224
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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The hypothesis that airway afferent nerve subtypes act synergistically to initiate reflex bronchospasm in guinea pigs was addressed. Laryngeal mucosal application of capsaicin or bradykinin or the epithelial lipoxygenase metabolite 15(S)-hydroxyeicosatetraenoic acid evoked slowly developing but pronounced and sustained increases in tracheal cholinergic tone in situ. These reflexes were reversed by atropine and prevented by vagotomy, trimethaphan, or laryngeal denervation. Central nervous system-acting neurokinin receptor antagonists also abolished the reflexes without altering baseline cholinergic tone. Baseline tone was, however, reversed by disrupting pulmonary afferent innervation while preserving the innervation of the trachea and larynx. Surprisingly, selective pulmonary denervation also prevented the laryngeal capsaicin-induced tracheal reflexes, suggesting that laryngeal C-fibers act synergistically with continuously active intrapulmonary mechanoreceptors to initiate reflex bronchospasm. Indeed, reflex bronchospasm evoked by histamine was markedly potentiated by bradykinin, an effect mimicked by intracerebroventricular, but not intravenous, substance P. These data, as well as anatomic evidence for afferent nerve subtype convergence in the commissural nucleus of the solitary tract, suggest that airway nociceptors and mechanoreceptors may act synergistically to regulate airway tone.
central sensitization; airway hyperreactivity; nucleus of the solitary tract; gastroesophageal reflux; 15(S)-hydroxyeicosatetraenoic acid
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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MULTIPLE AIRWAY AFFERENT NERVE subtypes have been identified on the basis of their neurochemistry, electrophysiological properties, and responsiveness to physical and chemical stimuli. Myelinated airway mechanoreceptors, of which there are at least two types, are sporadically active throughout the respiratory cycle (4, 36, 39). Mechanoreceptors respond to the dynamic and/or sustained physical effects of lung inflation and deflation and may also be activated indirectly by bronchoconstrictors such as histamine, cysteinyl leukotrienes, or acetylcholine (4, 7, 11, 38). The ongoing activity of these mechanoreceptors contributes to respiratory rhythm. A subset of these mechanoreceptors may also be a primary driving force behind the baseline parasympathetic tone measurable in the airways of all mammalian species (22, 23). When acutely activated, airway mechanoreceptors induce cough and parasympathetic reflexes such as bronchospasm, mucus secretion, and vasodilatation (42).
Unmyelinated afferent C-fibers also innervate the airways. Generally quiescent throughout the respiratory cycle but activated by inflammation and proinflammatory mediators such as bradykinin, these airway afferent nerves are physiologically similar to the nociceptors of the somatic nervous system. Activation of bronchopulmonary C-fibers can also precipitate cough and increased parasympathetic nerve activity and produce distinct effects on respiratory pattern and cardiovascular function (10, 28).
In the somatosensory nervous system, stimulation of nociceptors induces pain sensation, allodynia, and hyperalgesia by acting in synergy with mechanically sensitive sensory nerves in a process known as central sensitization (29, 45). This synergy is made possible by the convergent terminations of these sensory nerve subtypes on subsets of integrative relay neurons in the spinal cord. Neurons located in the integrative centers of the brain stem receive similar convergent inputs from visceral afferent nerves (20, 24, 34). Given the many physiological and morphological similarities of the somatosensory and visceral afferent nerves, we reasoned that synergistic interactions between airway afferent nerve subtypes might also precipitate airway parasympathetic reflexes.
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METHODS |
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Surgery and animal preparation. All experiments were approved by the Johns Hopkins Medical Institutions Animal Care and Use Committee. Male Hartley guinea pigs (300-400 g; n = 121; Hilltop, Scottdale, PA) were anesthetized with urethane (1 g/kg ip) and placed supine on a heated pad. This dose of urethane provides deep, stable anesthesia for up to 9 h, although experiments rarely lasted for >4 h. The adequacy of the anesthesia was assessed throughout the course of the experiments by monitoring cardiovascular responses to a sharp pinch of the hindlimb.
The caudalmost portion of the extrathoracic trachea was cannulated, and the animals were ventilated (60 breaths/min, 6 ml/kg, 2-3 cmH2O positive end-expiratory pressure) after induction of paralysis (succinylcholine chloride, 2 mg/kg sc). Reflex-mediated alterations in tracheal smooth muscle tone were monitored isometrically in the rostral extrathoracic trachea, as described previously (7, 22). Pulmonary insufflation pressure was monitored with a pressure transducer attached to a side port of the tracheal cannula. The abdominal aorta and vena cava were cannulated to monitor blood pressure and deliver intravenous drugs, respectively. Tracheal tone, pulmonary insufflation pressure, and arterial blood pressure were monitored and recorded on a Grass polygraph. Krebs bicarbonate buffer was perfused through the tracheal lumen via a small incision in the caudal extrathoracic trachea. The buffer was recovered using a gentle suction source positioned at the level of the larynx. The buffer (composition in mM: 118 NaCl, 5.4 KCl, 1 NaHPO4, 1.2 MgSO4, 1.9 CaCl2, 25 NaHCO3, 11.1 dextrose) contained 3 µM indomethacin, 2 µM propranolol, and 1 µM phentolamine. These drugs were used to block the local effects of prostaglandins and to block any effects of circulating and neurally released catecholamines on the tracheal segment studied. All animals were also pretreated with propranolol (1 mg/kg iv) at the beginning of each experiment. At the end of each experiment, animals were killed using carbon dioxide delivered through the inspiratory port of the ventilator.Experimental design.
The anatomy of the extrinsic vagal pathways projecting to the guinea
pig airways permits selective transections of the afferent nerve fibers
innervating the intrapulmonary airways or larynx while leaving the
preganglionic parasympathetic fibers innervating the trachea intact
(Fig. 1) (9, 22). Moreover,
the trachea provides a convenient window on the activity of airway
parasympathetic nerves throughout the airways (7, 22, 30).
In the present study, we exploited these attributes to study
interactions between airway afferent nerve subtypes on airway smooth
muscle tone.
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Reflex tracheal contractions evoked from the larynx. First, we determined whether brief (1-2 min) application of capsaicin (30 µM, 0.2 ml; n = 7) to the larynx evoked reflex-mediated increases in tracheal smooth muscle tension. Capsaicin was applied selectively to the laryngeal mucosa by means of a laryngeal cannula (27 gauge) inserted through the cricothyroid membrane, such that the distal end of the cannula was positioned on the laryngeal mucosa. The selectivity of this laryngeal stimulation was confirmed in vagotomized animals by comparing responses to laryngeal capsaicin with responses evoked by addition of capsaicin directly to the tracheal perfusate. The reflex nature of any contractions evoked by laryngeal capsaicin was assessed by attempting to reverse the contraction with tracheal instillation of atropine (1 µM; n = 7) or by preventing contractions with cervical vagotomy (n = 3) or systemic administration of the ganglionic blocker trimethaphan (5 mg/kg iv; n = 3). We attempted to determine the afferent nerve subpopulations mediating the reflex responses evoked by laryngeal application of capsaicin by severing the recurrent and/or superior laryngeal nerves bilaterally, adjacent to their termination in the larynx (n = 3-4; Fig. 1).
In similar experiments, we assessed the ability of laryngeal application of bradykinin (3 µM; n = 7) and the putative (18) vanilloid receptor (VR1) agonist 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE, 3 µM; n = 4] to mimic the effects of capsaicin on tracheal cholinergic tone. The VR1-dependent nature of the effects evoked by 15(S)-HETE were assessed by attempting to reverse or prevent any tracheal contractions evoked by the lipoxygenase product with tracheal instillation of the selective VR1 antagonist capsazepine (30 µM; n = 3-4). The adequacy of the capsazepine concentration was determined by assessing the ability of capsazepine to prevent the direct contractile effects of capsaicin (10 µM) when administered to the trachea (n = 4).Role of neurokinins in reflex tracheal contractions evoked from the larynx. The role and site of action of neurokinins in the reflex-mediated contractions evoked by capsaicin were determined first by studying the effects of neurokinin receptor antagonists on these responses. We employed potent and structurally unrelated antagonists throughout the studies (see below) to ensure the validity of experimental results. Neurokinin receptor antagonists were administered by one of three routes: 1) tracheal/laryngeal administration of SR-140333 [neurokinin type 1 (NK1) receptor], SR-48968 [neurokinin type 2 (NK2) receptor], and SB-223412 [neurokinin type 3 (NK3) receptor] at 0.3 µM each (n = 3), 2) intravenous administration of SR-140333 and SB-223412 at 1 mg/kg each (n = 7) or the nonselective neurokinin receptor antagonist ZD-6021 at 5 mg/kg (n = 5) (7, 41), or 3) intracerebroventricular infusion of ZD-6021 at 0.67-6.7 nmol/min (n = 4). For these latter studies, neurokinin receptor antagonists were administered centrally (intracerebroventricularly) via a stainless steel cannula, which was stereotaxically cemented into the right lateral cerebral ventricle (2 mm caudal and 1.8 mm lateral to bregma and 4.8 mm below the surface of the skull). The cannula was attached to a Hamilton microsyringe via polyethylene tubing, and drugs were infused using a syringe pump (model A-99, Razel) at a speed of 40 µl/h. Injection sites were confirmed with Evans blue dye at the end of the experiments. For all experiments, control studies were performed in parallel in which the appropriate vehicle (see Drugs) was administered instead of the antagonist.
Synergistic interactions between airway afferent subtypes. In previous studies, we presented evidence that baseline cholinergic tone in the trachea is absolutely dependent on the ongoing activation of intrathoracic airway mechanoreceptors (22). The very presence of this ongoing activity and the dependence of baseline tone on peripheral input suggest that reflex-mediated alterations in parasympathetic nerve actions might depend on alterations in the activity and/or synergistic interactions with these airway mechanoreceptors. To test the hypothesis that laryngeal (capsaicin-sensitive) nociceptors act synergistically with intrathoracic airway mechanoreceptors to evoke reflex bronchospasm, the effect of denervating the lower airways on the ability of laryngeal capsaicin to evoke reflex contractions of the trachea was assessed. In these studies, a bilateral (intrathoracic) vagotomy was performed in which the vagi were severed immediately caudal to the origin of the recurrent laryngeal nerves (n = 7; Fig. 1). In doing so, the intrapulmonary airways and lungs were denervated, thereby removing all central input from airway mechanoreceptors, while the afferent and efferent innervation of the trachea and larynx were left completely undisturbed (9, 22). The appropriateness and selectivity of all nerve cuts were confirmed at autopsy. Animals were excluded from subsequent statistical analyses if the transections were inappropriate or damage to the recurrent laryngeal nerves was evident.
Synergistic interactions between airway afferent nerve subtypes were further assessed by determining the ability of the nociceptor stimulant bradykinin to augment the reflex actions evoked by activating airway rapidly adapting receptors (RARs) with histamine (3, 7). Increasing concentrations of bradykinin (starting at 0.01 nmol/kg) were injected intravenously as a bolus until the threshold for evoking reflex contractions of the trachea was reached (average threshold dose of bradykinin was 0.08 ± 0.01 nmol/kg, range 0.04-0.1 nmol/kg, n = 8). Histamine (0.5-10 µg/kg) was subsequently dissolved in the threshold dose of bradykinin and injected intravenously into the same animals (n = 8). In control animals, histamine was administered in the presence of vehicle (isotonic saline), rather than bradykinin. To determine the role of the parasympathetic nervous system in the synergistic responses evoked by simultaneous injections of bradykinin and histamine, we compared responses in control animals with those obtained in vagotomized animals (n = 5) or animals pretreated with the muscarinic receptor antagonist atropine (1 mg/kg iv; n = 5). In all studies employing intravenous histamine and bradykinin, the histamine H1 receptor antagonist pyrilamine (1 µM) and the bradykinin B2 receptor antagonist FR-173657 (0.3 µM) were added to the tracheal perfusate to prevent any direct effects (via the vasculature) of the autacoids on the tracheal segment under study (7, 30). We then attempted to determine the role of neurokinins in the synergistic responses evoked by combined histamine and bradykinin injections. Animals were pretreated with ZD-6021 [5 mg/kg iv (n = 5) or 6.7 nmol/min for up to 20 min intracerebroventricularly (icv; n = 5)] before the injection of the autacoids. To ensure that any observed effect of centrally (intracerebroventricularly) administered ZD-6021 was not due to a peripheral site of action, we compared tracheal tension and pulmonary insufflation responses to intravenously administered neurokinin A (NKA, 0.5 nmol/kg; n = 4-5) in control (vehicle-treated) animals and animals treated intravenously or centrally with ZD-6021. In parallel experiments, we also assessed the effect of a threshold dose of the neurokinin receptor agonist substance P (SP), rather than bradykinin, on histamine-evoked reflex alterations in airway smooth muscle tone. In these studies, histamine was dissolved in a threshold dose of SP (determined by injecting increasing doses of the neuropeptide, starting at 0.05 nmol/kg; n = 3) and injected intravenously. Neurokinin receptor antagonists (SR-140333, SR-48968, and SB-223412 at 0.3 µM each) were added to the tracheal perfusate to prevent the direct effects of SP on the trachealis. To further support a role for neurokinins in the synergistic response, we then assessed the ability of SP (13 pmol/min; n = 4) to increase tracheal cholinergic tone when administered centrally (into the fourth ventricle). In these studies, a stainless steel cannula (22 gauge) was stereotaxically cemented into the fourth ventricle (midline and 18.2 mm caudal to bregma and 8.8 mm below the surface of the skull). SP was infused for 10 min using a Razel syringe pump, and injection sites were marked as described above. SR-140333, SR-48968, and SB-223412 at 0.1 µM each were included in the tracheal perfusate in these experiments to prevent any potential peripheral actions of SP on the tracheal segment under study. The appropriateness of the neurokinin receptor antagonist concentrations was determined by comparing atropine-insensitive tracheal contractions evoked by 10 µM capsaicin (added to the tracheal perfusate) in the absence and presence of the neurokinin antagonists. The selectivity of SP for central neurokinin receptors was further assessed by injection of ZD-6021 (25 nmol in 5 µl over 1-2 min; n = 3) into the lateral ventricle at the peak of the SP-evoked tracheal contraction. At the end of each experiment, the level of baseline cholinergic tone was determined by adding 1 µM atropine to the tracheal perfusate and subsequently evoking a maximum contraction by adding 300 mM barium chloride to the perfusate. The amount of tone (in g) reversed by adding atropine to the tracheal perfusate divided by the grams of contraction subsequently evoked by barium chloride was the baseline cholinergic tone. Reflex-mediated effects are expressed as a percent increase in baseline cholinergic tone or as a percentage of the maximum contraction.Neuronal tracing and immunohistochemistry. An anatomic basis for airway afferent nerve convergence in the brain stem was assessed by neuronal tracing with retrograde fluorescent tracers. Animals were anesthetized with pentobarbital sodium (50 mg/kg ip) and mounted in a Kopf stereotaxic frame. The brain stem was exposed between the occipital bone and first cervical vertebra by careful dissection of the dorsal neck muscles and overlying atlantooccipital membrane and dura mata. Rhodamine-coated latex microspheres (200 nl; LumaFluor, Naples, FL) were injected unilaterally into the commissural subnucleus of the nucleus of the solitary tract (nTS, 0.5-1 mm caudal, 0.5 mm lateral to obex, 0.8 mm deep; n = 4). The incisions were sutured, and the animals were removed from the frame and positioned ventral side up on a heated pad. The extrathoracic trachea was then exposed, and a second tracer (15 µl of 2.5% fast blue) was injected into the tracheal lumen. These incisions were also sutured, and the animals were allowed to recover under close supervision (sterile techniques were used for all surgeries).
Seven days after the injections, animals were deeply anesthetized with pentobarbital (100 mg/kg) and then transcardially perfused, first with 10 mM heparinized PBS containing 0.1% procaine and then with 4% paraformaldehyde in PBS. After perfusion, the brain stem, nodose ganglia, and jugular ganglia were removed, fixed (4% paraformaldehyde at 4°C for 2 h), and cryoprotected (18% sucrose at 4°C overnight) before they were frozen in OCT medium and cut. Frozen sections (12 µm) were stained for SP and neurofilament immunoreactivity as described previously (39). Briefly, sections were placed in 0.01 M PBS and covered in blocking solution (10% goat serum, 1% BSA, 0.5% Tween 20 in PBS) for 1 h. Sections were then incubated overnight (4°C) with a polyclonal rabbit anti-SP antibody (Oncogene Research Products, Boston, MA; diluted 1:200) or a monoclonal mouse antineurofilament antibody (160 kDa; clone NN18, Boehringer Mannheim, Indianapolis, IN; diluted 1:30), each diluted in PBS containing 0.3% Triton X-100 and 1% BSA. After several PBS washes, labeled sections were incubated (1 h at room temperature) with fluorescein-conjugated goat anti-rabbit or goat anti-mouse secondary antibody (1:40 dilution; Calbiochem, San Diego, CA) and rinsed in PBS, and coverslips were applied using a commercially available antifade kit (Slow Fade, Molecular Probes, Eugene, OR). Cells labeled with either tracer (fast blue and/or rhodamine) or stained for SP or neurofilament were visualized using an Olympus BX60 fluorescent microscope. The number of cells labeled with fast blue and/or rhodamine was manually counted per animal in a 1-mm2 area using 6-10 representative sections of each nodose and jugular ganglion. The sum of these representative sections (from a single animal) was used to calculate the total number of labeled cells in each ganglion. The total number of labeled cells was subsequently used to generate the mean ± SE for the group.Statistics. Values are means ± SE. Differences between group means were assessed using analysis of variance on Statview for Macintosh (Berkeley, CA). P < 0.05 was considered significant. When significant variation between groups was detected, treatment group means were compared using Scheffé's F test for unplanned comparisons.
Occasionally (<10% of experiments), animals exhibited little (<10% of the maximum contraction) or no baseline cholinergic tone or baseline tone that approximated the maximum cholinergic tone (>50% of the maximum contraction) attainable in this preparation (22). Such preparations rarely exhibited any reflex effects in response to any stimulus and were thus excluded from subsequent statistical analyses.Drugs. Atropine sulfate, barium chloride, capsaicin, heparin sulfate, indomethacin, histamine, urethane (ethyl carbamate), succinylcholine chloride, pentabarbital sodium, pyrilamine, phentolamine hydrochloride, and dl-propranolol hydrochloride were purchased from Sigma (St. Louis, MO). 15S-hydroxy-5Z,8Z,11Z,13E-eicosatetetraenoic acid [15(S)-HETE] was purchased as a solution (100 µg/ml) in ethanol from Cayman Chemicals (Ann Arbor, MI). Capsazepine was purchased from Tocris (Ellisville, MO); SP and NKA from Peninsula Laboratories (Belmont, CA); trimethaphan camsylate from Roche Laboratories (Nutley, NJ); and Tissue-Tek OCT embedding medium from VWR (Bridgeport, NJ). Bradykinin, SR-140333, and ZD-6021 were kindly provided by AstraZeneca (Wilmington, DE), FR-173657 by Fujisawa (Osaka, Japan), and SR-48968 and SB-223412 by Schering Plough (Kenilworth, NJ) and Glaxo SmithKline (King of Prussia, PA), respectively. Stock solutions (10-20 mM) of all drugs added to the tracheal perfusate were made in distilled water, except indomethacin (30 mM) and capsaicin (0.1 M), which were dissolved in absolute ethanol, and SR-140333, SR-48968, SB-223412, and FR-173657 (1 mM), which were dissolved in dimethyl sulfoxide (DMSO). For laryngeal application, capsaicin was dissolved in absolute ethanol (0.1 M) and diluted (30 µM) using Krebs buffer. For 15(S)-HETE, the supplied solution in 100% ethanol was evaporated under a constant stream of nitrogen and resuspended with 2% ethanol in Krebs buffer. ZD-6021 (5 nmol/µl icv) was dissolved in DMSO (41). Drugs administered intravenously or subcutaneously (1-50 mg/ml) were dissolved in saline, except SR-48968 and SR-140333, which were dissolved in DMSO (10 mg/ml) and diluted (1 mg/ml) in saline; ZD-6021 (5 mg/ml), which was dissolved in saline containing 15% Tween 20; and SB-223412, which was dissolved in DMSO (10 mg/ml) and diluted (1 mg/ml) with acid in saline.
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RESULTS |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Effect of laryngeal application of capsaicin on tracheal
cholinergic tone.
Baseline cholinergic tone in all experiments (excluding those in which
a manipulation was performed to abolish tone, e.g., vagotomy) averaged
32 ± 1% of the maximum attainable contraction of the trachealis
(n = 89). Brief (1-2 min) laryngeal challenge with
30 µM capsaicin produced a biphasic effect on baseline tracheal cholinergic tone. Tone initially fell on application of capsaicin to
the laryngeal mucosa (55 ± 18% decrease in cholinergic tone), a
response that was consistently followed by a pronounced and sustained
increase in tone (61 ± 14% increase in baseline cholinergic tone; Fig. 2). This latter effect
developed slowly (10-30 min) but showed no signs of reversal for
the duration of all control experiments, lasting long after the brief
capsaicin challenge (up to 60 min). The effects of laryngeal
application of capsaicin on tracheal smooth muscle tone were not
accompanied by any detectable increases in insufflation pressure or any
consistent effects on arterial blood pressure.
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Role of laryngeal C-fibers in contractions of the trachealis evoked
by laryngeal application of capsaicin.
The sustained increases in tracheal cholinergic tone evoked by
capsaicin were also evoked by other stimulants of airway C-fibers. Bradykinin (3 µM) applied to the laryngeal mucosa evoked a comparable increase in tracheal tension (52 ± 19% of the peak increase in tracheal cholinergic tone, n = 7). As previously
reported (23) and similar to the reflexes initiated by
laryngeal capsaicin, these effects of bradykinin developed slowly
(20-30 min) after an initial transient fall in tone and were
reversed entirely by atropine. The epithelial lipoxygenase product and
putative VR1 agonist 15(S)-HETE (3 µM) also evoked
gradually developing (20-30 min) but sustained and pronounced
increases in tracheal cholinergic tone, which generally
followed an initial relaxant response (Fig. 4). We confirmed the role of VR1 in this response to
15(S)-HETE by blocking these reflexes with the VR1
antagonist capsazepine (30 µM; Fig. 4; P < 0.01).
Interestingly, capsazepine was utterly ineffective at reversing the
15(S)-HETE-induced cholinergic reflexes, which were
nevertheless reversed entirely by atropine (n = 4; Fig.
4). The VR1 antagonist did, however, nearly abolish the
atropine-insensitive contractions evoked subsequently when 10 µM
capsaicin was administered intratracheally (51 ± 4 and 8 ± 5% of the maximum contraction in the absence and presence of 30 µM
capsazepine, respectively, n = 3-4,
P < 0.01).
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Synergistic interactions between airway afferent nerve subtypes.
In the airways, RARs are sporadically active throughout the respiratory
cycle, responding to the dynamic mechanical effects of lung inflation
and deflation (4, 37). We have presented evidence that
baseline cholinergic tone is absolutely dependent on the ongoing
activity of intrapulmonary airway mechanoreceptors (most likely RARs)
(22). We hypothesized that stimulation of capsaicin-sensitive laryngeal afferent nerves evokes reflex tracheal contractions at least in part by acting in synergy with the cyclically active airway mechanoreceptors. We addressed this hypothesis by studying the effects of laryngeal capsaicin challenge after bilateral transection of the vagi just caudal to the recurrent laryngeal nerves
(which preserved the preganglionic parasympathetic innervation of the
trachea). In animals where autopsy confirmed complete transection of
the vagi just caudal to the recurrent laryngeal nerves, baseline tone
was essentially abolished (3 ± 2% of the maximum contraction, n = 7, P < 0.01; Fig.
6A). Moreover, bilateral
intrathoracic vagotomy abolished reflex tracheal contractions evoked by
laryngeal capsaicin application (Fig. 6B).
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Anatomic evidence for central convergence of afferent nerve subtypes. A necessary prerequisite for central synergistic interactions between airway afferent nerve subtypes is convergence of these neural inputs at an integrative site along the parasympathetic-cholinergic reflex arc, most likely in the nTS (20, 24, 34). We tested this hypothesis by simultaneous retrograde neuronal tracing of afferent nerves after microinjections of fluorescent tracers into the trachea and brain stem.
Consistent with previous studies, neuronal tracing from the airways with fast blue revealed the bilateral origin of three subpopulations of airway vagal afferent neurons (39). Airway afferent neurons with cell bodies in the nodose ganglia had a relatively large somal diameter and stained positively for neurofilament (a marker for myelinated axons) but lacked immunoreactivity to SP (Fig. 8, a, c, and d). In jugular ganglia, airway afferent neurons with large and small somal diameters were also labeled when fast blue was injected into the airways. Similar to the nodose neurons projecting to the airways, airway jugular ganglia neurons with large somal diameters stained positively for neurofilament. Only the labeled jugular neurons with small soma expressed SP (Fig. 8, e, g, and h).
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DISCUSSION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Airway smooth muscle possesses a baseline level of cholinergic contraction that is dependent on the activity of airway parasympathetic nerves. This cholinergic tone in the airways is subject to reflex adjustments in response to multiple afferent nerve inputs (6, 7, 10, 31, 42). We previously showed that disrupting the afferent innervation of the guinea pig lungs (while leaving the parasympathetic innervation of the trachea intact) abolishes baseline cholinergic tone in the trachealis (22, 23). Similar observations have been made in cats (19). We confirmed this observation in the present study and propose that cholinergic nerve activity in the airways is absolutely dependent on ongoing input from afferent (presumably mechanically sensitive) nerve fibers innervating the intrapulmonary airways and lungs. The presence of this baseline cholinergic tone and its likely dependence on ongoing activity of airway mechanoreceptors have important implications in the study of reflex-mediated alterations in airway caliber.
We have presented compelling evidence that laryngeal C-fiber-mediated parasympathetic reflexes are absolutely dependent on the ongoing afferent input arising from the intrapulmonary airways and lungs. No other interpretation is compatible with the observation that these reflexes are completely abolished by selective denervation of the larynx or the intrapulmonary airways and lungs. The implication of this observation is of potentially fundamental importance to understanding mechanisms of C-fiber-mediated reflexes and perhaps mechanisms of airway responsiveness. In effect, the stimulus for the parasympathetic reflexes evoked by laryngeal C-fiber activation is not only the capsaicin, bradykinin, or 15(S)-HETE applied to the mucosa, the stimulus is also the dynamic mechanical force delivered to the lung (and thus the pulmonary mechanoreceptors) during the respiratory cycle.
The laryngeal capsaicin-sensitive nerve-mediated parasympathetic reflexes described in the present study share many physiological attributes with inflammation-induced allodynia and hyperalgesia described in the somatic nervous system. Typically innocuous stimuli such as joint flexions or tidal lung stretches, which normally fail to evoke noxious sensation or defensive reflexes, produce pain in somatic tissues or reflex bronchospasm when initiated subsequent to or coincident with nociceptor stimulation (45). In animals, allodynia and hyperalgesia are initiated by neurokinins released in the CNS that sensitize central integrative neurons receiving convergent input from nociceptors and mechanoreceptors (17, 29). Central sensitization therefore reduces the threshold for reflex activation by subsequent mechanoreceptor input (36). A comparable role for neurokinins in mediating the reflexes initiated from the larynx in the present study is also apparent. We speculate, therefore, that laryngeal C-fibers evoke reflex bronchospasm by facilitating ongoing synaptic transmission through relay neurons of airway mechanoreceptors in the CNS, perhaps in the nTS.
The necessity of the laryngeal and the intrapulmonary afferent nerve inputs for mediating reflexes evoked from the larynx described here all but requires convergence of these separate reflex pathways at some level in the brain stem. Ultimately, this convergent input must lead to heightened activity in the preganglionic parasympathetic nerves regulating airway cholinergic tone. Although this convergence can occur at any number of brain stem locations along the reflex arc, we provide anatomic evidence that the interaction between airway nociceptors (jugular ganglia) and the mechanoreceptors (nodose ganglia) is likely to occur in the commissural nTS. Previous studies are consistent with this scenario (20, 24, 34).
The synergistic interactions between nociceptors and pulmonary mechanoreceptors might not be unique to laryngeal nociceptor-dependent reflexes. The potentiating effects of bradykinin on histamine-induced reflex bronchospasm suggest that pulmonary mechanoreceptors and nociceptors may also act synergistically to evoke reflex bronchospasm. In addition to the precedent set in our studies of the laryngeal reflexes as well as the anatomic evidence for afferent nerve convergence, several additional lines of evidence are consistent with this notion. Thus bradykinin-induced hyperresponsiveness to histamine is reversed entirely by centrally acting neurokinin receptor antagonists and mimicked by centrally, but not peripherally, administered SP. The ability of intracerebroventricular ZD-6021 to prevent the bradykinin-induced hyperresponsiveness while having no effect on the histamine-induced reflexes seems to rule out the possibility that bradykinin sensitizes airway afferent nerve endings to histamine. Of course, the inclusion of pyrilamine and FR-173657 in the tracheal perfusate rules out entirely any modulatory effects of bradykinin or histamine on the postganglionic parasympathetic nerves of the trachea. It is possible, however, that histamine might sensitize airway nociceptors to bradykinin (27). This issue awaits a systematic electrophysiological analysis. It is nevertheless indisputable that a central sensitizing effect produced by nociceptor stimulation is supported by the data presented above.
Identity of the afferent nerve fibers mediating reflex bronchospasm evoked from the larynx. In healthy guinea pigs, C-fibers are responsive to capsaicin and bradykinin, express VR1, and are the only nerve fibers expressing neurokinins in the airways (7, 14, 21, 26, 39). 15(S)-HETE, a lipoxygenase product synthesized in large quantities by the airway epithelium, may activate C-fibers via VR1 stimulation (18, 25). We observed that centrally acting neurokinin receptor antagonists prevented or reversed the reflexes evoked by laryngeal stimulation with capsaicin, while the VR1 antagonist capsazepine prevented reflexes initiated by 15(S)-HETE. The laryngeal mucosal afferent nerves mediating the capsaicin-, bradykinin-, and 15(S)-HETE-induced reflexes are thus likely to be neurokinin-containing C-fibers carried primarily by the superior laryngeal nerves (8). This is in agreement with our previous studies showing that pulmonary C-fiber-evoked, but not mechanoreceptor-evoked, reflex bronchospasm is abolished by centrally administered neurokinin receptor antagonists (7).
Although we provide compelling evidence that the sustained increase in tracheal tone after laryngeal capsaicin application is mediated by C-fiber-evoked increases in cholinergic nerve activity, the nature of the initial relaxant response is less clear. The relaxant response may be a result of a coincidental noncholinergic relaxant reflex evoked by capsaicin. In support of this, we previously showed that laryngeal application of capsaicin evokes vagally mediated relaxations with kinetics comparable to those of the initial relaxant response observed in the present study (31). Alternatively, laryngeal capsaicin application in spontaneously breathing guinea pigs evokes an apnea followed by a period of rapid shallow breathing, suggesting that the relaxation observed in the trachea may also reflect a removal of cholinergic drive to the airways correlating with the apneic episode. Regardless of the underlying mechanism, the relaxant response was also observed after bradykinin and 15(S)-HETE application and was reduced by intravenous pretreatment with neurokinin receptor antagonists, suggesting that it is a common feature of laryngeal C-fiber activation. The pulmonary afferent nerves regulating baseline cholinergic tone and the pulmonary afferent nerves also necessary for coregulating the laryngeal capsaicin-induced reflex are unknown. We speculate, however, that these intrapulmonary afferent nerves are one and the same and are probably RARs. RARs, much like baseline tone, are highly sensitive to changes in dynamic lung compliance and the rate and volume of lung inflation (4, 37). By contrast, sustained lung inflation or positive end-expiratory pressure, stimuli that activate slowly adapting receptors, inhibit reflex tracheal contractions evoked by histamine and reduce baseline cholinergic tone in the airways (6, 40). It is unlikely, therefore, that slowly adapting receptors are responsible for mediating baseline tone or the capsaicin reflex. Bronchopulmonary C-fibers are also unlikely to be the afferent nerves responsible for driving baseline tone or the laryngeal reflex. C-fiber-mediated airway reflexes are abolished by neurokinin receptor antagonists (1, 7), yet these antagonists have no effect on baseline cholinergic tone (7, 22; present study). C-fibers are also generally quiescent throughout the respiratory cycle.Role of neurokinins in mediating reflex bronchospasm. It is interesting that centrally acting neurokinin receptor antagonists not only prevent the airway parasympathetic reflex evoked by laryngeal C-fiber stimulation, they also reverse the response when administered long after the challenge is terminated. The long-lasting effects of laryngeal C-fiber activation may thus not be due to an irreversible (agonist-independent) enhancement (or plasticity) of synaptic transmission in the brain stem but may be due to the persistent effects of the neurotransmitters. The duration of action of the neurokinins released in the brain stem may be exceedingly high. Hyperalgesia can be sustained by continuous activation of NK3 receptors, perhaps NK3 receptors localized to extrasynaptic sites (2, 17). Alternatively, once activated by capsaicin, bradykinin, or 15(S)-HETE, laryngeal C-fibers may remain active long after the brief (1-2 min) challenges. We observed, however, that although capsazepine prevented the reflexes initiated by 15(S)-HETE, the VR1 antagonist failed to reverse the effects. In vitro studies of capsaicin- and bradykinin-induced activation of tracheal and laryngeal C-fibers are also inconsistent with a prolonged activation of these afferent nerves (14, 21). These observations seem consistent with the notion of a long duration of action of the neurokinins in the brain stem once released, but alternative hypotheses are equally likely and await systematic evaluation (15).
Neurokinins released from the peripheral nerve terminals of C-fibers may initiate airway responses through axonal reflex effects or perhaps through peripheral sensitization of airway RARs (5). The failure of topically applied neurokinin receptor antagonists in the trachea and larynx against the capsaicin-induced reflexes, along with efficacy and selectivity of intracerebroventricular administration of the antagonists, seems to rule out a role for such peripheral effects of the neurokinins in the present study. Rather, the data indicate that neurokinins are acting in the brain. The specific neurokinin receptors mediating these responses are unknown. Previous studies have shown that all three neurokinin receptors are present and functional in regions of the nTS likely containing vagal afferent nerve terminals (32, 33, 35). We observed that systemic pretreatment with a combination of NK1 and NK3 receptor antagonists was equally effective at reducing the laryngeal capsaicin-induced reflex and blockade of all neurokinin receptor subtypes. We thus speculate that NK1 and NK3 receptors in the brain stem mediate the C-fiber-induced parasympathetic reflexes described in the present study and elsewhere (7).Physiological implications. The data presented in this study have important implications for the mechanisms of airway defensive reflexes. The ongoing activity of airway mechanoreceptors should always be considered a major factor influencing any reflexes initiated by C-fiber activation. The data may also have important implications for mechanisms of pulmonary disease. For example, diseases such as allergic rhinitis, gastroesophageal reflux disease, and upper respiratory tract infection can precipitate airway hyperresponsiveness and cough through vagal mechanisms (6, 12, 13, 16, 44). These inflammatory diseases may not directly affect the lower airways, indicating that they initiate pulmonary symptoms via extrapulmonary effects. Synergistic interactions between extrapulmonary afferent nerves and the spontaneously active airway mechanoreceptors might contribute to the pulmonary consequences of these extrapulmonary disorders. Finally, the results presented here have potentially important implications for therapeutic interventions targeted at visceral hyperreflexia, such as asthma and chronic obstructive pulmonary disease and perhaps gastroesophageal reflux disease and rhinitis. Drugs that selectively target the afferent pathways, by blocking the actions of their neurotransmitters in the CNS or by selectively preventing their activation peripherally, might prove superior to anticholinergics in the treatment of reactive airway diseases.
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ACKNOWLEDGEMENTS |
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This study was funded by grants from the National Institutes of Health (Bethesda, MD). S. B. Mazzone is a National Health and Medical Research Council of Australia C. J. Martin Fellow.
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FOOTNOTES |
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Address for reprint requests and other correspondence: S. B. Mazzone, Johns Hopkins Medical Institutions, 5501 Hopkins Bayview Circle, Baltimore, MD 21224 (E-mail: smazzone{at}jhmi.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
First published March 22, 2002;10.1152/ajpregu.00007.2002
Received 7 January 2002; accepted in final form 14 March 2002.
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REFERENCES |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Advenier, C,
Lagente V,
and
Boichot E.
The role of tachykinin receptor antagonists in the prevention of bronchial hyperresponsiveness, airway inflammation and cough.
Eur Respir J
10:
1892-1906,
1997[Abstract].
2.
Baude, A,
and
Shigemoto R.
Cellular and subcellular distribution of substance P receptor immunoreactivity in the dorsal vagal complex of the rat and cat: a light and electron microscope study.
J Comp Neurol
402:
181-196,
1998[Web of Science][Medline].
3.
Bergren, DR.
Sensory receptor activation by mediators of defense reflexes in guinea-pig lungs.
Respir Physiol
108:
195-204,
1997[Web of Science][Medline].
4.
Bergren, DR,
and
Sampson SR.
Characterization of intrapulmonary, rapidly adapting receptors of guinea pigs.
Respir Physiol
47:
83-95,
1982[Web of Science][Medline].
5.
Bonham, AC,
Kott KS,
Ravi K,
Kappagoda CT,
and
Joad JP.
Substance P contributes to rapidly adapting receptor responses to pulmonary venous congestion in rabbits.
J Physiol
493:
229-238,
1996
6.
Canning, BJ,
and
Fischer A.
Neural regulation of airway smooth muscle tone.
Respir Physiol
125:
113-127,
2001[Web of Science][Medline].
7.
Canning, BJ,
Reynolds S,
and
Mazzone SB.
Multiple mechanisms of reflex bronchospasm in guinea pigs.
J Appl Physiol
91:
2642-2653,
2001
8.
Canning, BJ,
Reynolds S,
Meeker SM,
and
Undem BJ.
Electrophysiological identification of tracheal (T) and laryngeal (LX) vagal afferents mediating cough in guinea pigs (Abstract).
Am J Respir Crit Care Med
161:
A434,
2000.
9.
Canning, BJ,
and
Undem BJ.
Relaxant innervation of the guinea pig trachealis: demonstration of capsaicin-sensitive and -insensitive vagal pathways.
J Physiol
460:
719-739,
1993
10.
Coleridge, HM,
Coleridge JCG,
and
Schultz HD.
Afferent pathways involved in reflex regulation of airway smooth muscle.
Pharmacol Ther
42:
1-63,
1989[Web of Science][Medline].
11.
Dixon, M,
Jackson DM,
and
Richards IM.
The effects of 5-hydroxytryptamine, histamine and acetylcholine on the reactivity of the lung of the anesthetized dog.
J Physiol
307:
85-96,
1980
12.
Empey, DW,
Laitinen LA,
Jacobs L,
Gold WM,
and
Nadel JA.
Mechanisms of bronchial hyperreactivity in normal subjects after upper respiratory tract infection.
Am Rev Respir Dis
113:
131-139,
1976[Web of Science][Medline].
13.
Folkerts, G,
Westra-de V,
de Vries A,
Faas S,
van der Linde H,
Engels F,
de Jong JC,
Verheyen FAKCP,
Van Heuven-Nolsen D,
and
Nijkamp FP.
Virus- and bradykinin-induced airway hyperresponsiveness in guinea pigs.
Am J Respir Crit Care Med
161:
1666-1671,
2000
14.
Fox, AJ,
Urban L,
Barnes PJ,
and
Dray A.
Effects of capsaicin- and proton-evoked excitation of single airway C-fibres and vagus nerve from the guinea-pig.
Neuroscience
67:
741-752,
1995[Web of Science][Medline].
15.
Grant, ER,
Dubin AE,
Zhang SP,
Zivin RA,
and
Zhong Z.
Simultaneous intracellular calcium and sodium flux imaging in human vanilloid receptor 1 (VR1)-transfected human embryonic kidney cells: a method to resolve ionic dependence of VR1-mediated cell death.
J Pharmacol Exp Ther
300:
9-17,
2002
16.
Harding, SM,
and
Richter JE.
The role of gastroesophageal reflux in chronic cough and asthma.
Chest
111:
1389-1402,
1997[Web of Science][Medline].
17.
Houghton, AK,
Ogilvie J,
and
Clarke RW.
The involvement of tachykinin NK2 and NK3 receptors in central sensitization of a spinal withdrawal reflex in the decerebrated, spinalized rabbit.
Neuropharmacology
39:
133-140,
2000[Web of Science][Medline].
18.
Hwang, SW,
Cho H,
Kwak J,
Lee SY,
Kang CJ,
Jung J,
Cho S,
Min KH,
Suh YG,
Kim D,
and
Oh U.
Direct activation of capsaicin receptors by products of lipoxygenases: endogenous capsaicin-like substances.
Proc Natl Acad Sci USA
97:
6155-6160,
2000
19.
Jammes, Y,
and
Mei N.
Assessment of the pulmonary origin of bronchoconstrictor vagal tone.
J Physiol
291:
305-316,
1979
20.
Jordan, D.
Central nervous pathways and control of the airways.
Respir Physiol
125:
67-81,
2001[Web of Science][Medline].
21.
Kajekar, R,
Proud D,
Myers AC,
Meeker SN,
and
Undem BJ.
Characterization of vagal afferent subtypes stimulated by bradykinin in guinea pig trachea.
J Pharmacol Exp Ther
289:
682-687,
1999
22.
Kesler, BS,
and
Canning BJ.
Regulation of baseline cholinergic tone in guinea-pig airway smooth muscle.
J Physiol
518:
843-855,
1999
23.
Kesler, BS,
Mazzone SB,
and
Canning BJ.
Nitric oxide-dependent modulation of smooth muscle tone by airway parasympathetic nerves.
Am J Respir Crit Care Med
165:
481-488,
2002
24.
Kubin, L,
and
Davies RO.
Central pathways of pulmonary and airway vagal afferents.
In: Regulation of Breathing, edited by Dempsey JA,
and Pack AI.. New York: Dekker, 1995, p. 219-284.
25.
Kumlin, M,
Hamberg M,
Granstrom E,
Bjorck T,
Dahlen B,
Matsuda H,
Zetterstrom O,
and
Dahlen SE.
15(S)-hydroxyeicosatetraenoic acid is the major arachidonic acid metabolite in human bronchi: association with airway epithelium.
Arch Biochem Biophys
282:
254-262,
1990[Web of Science][Medline].
26.
Kummer, W,
Fischer A,
Kurkowski R,
and
Heym C.
The sensory and sympathetic innervation of guinea pig lung and trachea as studied by retrograde neuronal tracing and double-labeling immunohistochemistry.
Neuroscience
49:
715-737,
1992[Web of Science][Medline].
27.
Lee, LY,
and
Morton RF.
Histamine enhances vagal pulmonary C-fiber responses to capsaicin and lung inflation.
Respir Physiol
93:
83-96,
1993[Web of Science][Medline].
28.
Lee, LY,
and
Pisarri TE.
Afferent properties and reflex functions of bronchopulmonary C-fibres.
Respir Physiol
125:
47-65,
2001[Web of Science][Medline].
29.
Ma, QP,
and
Woolf CJ.
Involvement of neurokinin receptors in the induction but not the maintenance of mechanical allodynia in rat flexor motoneurones.
J Physiol
486:
769-777,
1995
30.
Mazzone SB and Canning BJ. An in vivo guinea pig preparation for
studying the autonomic regulation of airway smooth muscle tone.
Auton Neurosci. In press.
31.
Mazzone, SB,
and
Canning BJ.
Evidence for differential reflex regulation of cholinergic and noncholinergic nerves innervating the airways.
Am J Respir Crit Care Med
165:
1076-1083,
2002
32.
Mazzone, SB,
and
Geraghty DP.
Respiratory action of capsaicin microinjected into the nucleus of the solitary tract: involvement of vanilloid and tachykinin receptors.
Br J Pharmacol
127:
473-481,
1999[Web of Science][Medline].
33.
Mazzone, SB,
and
Geraghty DP.
Respiratory actions of tachykinins in the nucleus of the solitary tract: characterization of receptors using selective agonists and antagonists.
Br J Pharmacol
129:
1121-1131,
2000[Web of Science][Medline].
34.
Mifflin, SW.
Convergent carotid sinus nerve and superior laryngeal nerve afferent inputs to neurons in the NTS.
Am J Physiol Regulatory Integrative Comp Physiol
271:
R870-R880,
1996
35.
Mutoh, T,
Bonham AC,
and
Joad JP.
Substance P in the nucleus of the solitary tract augments bronchopulmonary C fiber reflex output.
Am J Physiol Regulatory Integrative Comp Physiol
279:
R1215-R1223,
2000
36.
Nagy, I,
Miller BA,
and
Woolf CJ.
NK1 and NK2 receptors contribute to C-fibre-evoked slow potentials in the rat spinal cord.
Neuroreport
5:
2105-2108,
1994[Web of Science][Medline].
37.
Pack, AI,
and
DeLaney RG.
Response of pulmonary rapidly adapting receptors during lung inflation.
J Appl Physiol
55:
955-963,
1983
38.
Pisarri, TE,
Jonzen A,
Coleridge JC,
and
Coleridge HM.
Rapidly adapting receptors monitor lung compliance in spontaneously breathing dogs.
J Appl Physiol
68:
1997-2005,
1990
39.
Riccio, MM,
Kummer W,
Biglari B,
Myers AC,
and
Undem BJ.
Interganglionic segregation of distinct vagal afferent fibre phenotypes in guinea-pig airways.
J Physiol
496:
521-530,
1996
40.
Richardson, CA,
Herbert DA,
and
Mitchell RA.
Modulation of pulmonary stretch receptors and airway resistance by parasympathetic efferents.
J Appl Physiol
57:
1842-1849,
1984
41.
Rumsey, HL,
Aharony D,
Bialecki RA,
Lengel D,
Barthlow HG,
Abbott BM,
McCarthy M,
Wenrich B,
Cacesse R,
Undem B,
Ohnmahct C,
Shenvi A,
Albert J,
Brown F,
Bernstein P,
and
Russel K.
Pharmacological characterization of ZD6021, a novel, orally active antagonist of the tachykinin receptors.
J Pharmacol Exp Ther
298:
307-315,
2001
42.
Sant'Ambrogio, G,
and
Widdicombe J.
Reflexes from airway rapidly adapting receptors.
Respir Physiol
125:
33-45,
2001[Web of Science][Medline].
43.
Schelegle, ES,
and
Green JF.
An overview of the anatomy and physiology of slowly adapting pulmonary stretch receptors.
Respir Physiol
125:
17-31,
2001[Web of Science][Medline].
44.
Togias, A.
Unique mechanistic features of allergic rhinitis.
J Allergy Clin Immunol
105:
S599-S604,
2000[Web of Science][Medline].
45.
Yaksh, TL,
Hua XY,
Kalcheva I,
Nozaki-Taguchi N,
and
Marsala M.
The spinal biology in humans and animals of pain states generated by persistent small afferent input.
Proc Natl Acad Sci USA
96:
7680-7686,
1999
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;
n = 4) and animals in which 30 µM capsazepine (CPZ)
was added to the tracheal perfusate 15 min before laryngeal stimulation
(
; n = 4). Pretreatment with
capsazepine (
; n = 1), and 6.7 nmol/min
(
; n = 2)]. C and
D: effects of neurokinin antagonists on baseline cholinergic
tone and peak increase in cholinergic tone evoked by laryngeal
capsaicin, respectively. SR-140333, SR-48968, and SB-223412 were
applied topically, directly to the tracheal and laryngeal mucosa (0.3 µM each; n = 3). ZD-6021 was administered
systemically (5 mg/ kg iv; n = 5) or centrally
(0.67-6.7 nmol/min icv; n = 4). Vehicle animals
(n = 10) were pooled, since neither baseline
cholinergic tone nor reflex tracheal contractions evoked by capsaicin
differed among vehicle treatment groups. Systemic injections of the
NK1 and NK3 receptor-selective antagonists
SR-140333 and SB-223412, respectively (1 mg/kg iv each), also
significantly attenuated reflex tracheal contractions evoked by
laryngeal capsaicin administration. These antagonists abolished
responses to laryngeal capsaicin in 3 of 7 guinea pigs and
substantially reduced responses in the remaining 4 animals: 67 ± 19% (n = 7) and 29 ± 10% (n = 7) mean percent increase in tracheal cholinergic tone in vehicle- and
antagonist-pretreated animals, respectively (P < 0.05). * P < 0.05 vs. vehicle.
P < 0.05, significant reduction in synergistic response.
