The neural crest- and placodes-derived afferent innervation of the mouse esophagus

BACKGROUND

The mouse is an invaluable model for mechanistic studies of esophageal nerves, but the afferent innervation of the mouse esophagus is incompletely understood. Vagal afferent neurons are derived from two embryonic sources: neural crest and epibranchial placodes. We hypothesized that both neural crest and placodes contribute to the TRPV1-positive (potentially nociceptive) vagal innervation of the mouse esophagus.

METHODS

Vagal jugular/nodose ganglion (JNG) and spinal dorsal root ganglia (DRG) neurons were retrogradely labeled from the cervical esophagus. Single cell RT-PCR was performed on the labeled neurons.

KEY RESULTS

In the Wnt1Cre/R26R mice expressing a reporter in the neural crest-derived cells we found that both the neural crest- and the placodes-derived vagal JNG neurons innervate the mouse esophagus. In the wild-type mouse the esophageal vagal JNG TRPV1-positive neurons segregated into two subsets: putative neural crest-derived purinergic receptor P2X(2) -negative/preprotachykinin-A (PPT-A)-positive subset and putative placodes-derived P2X(2) -positive/PPTA-negative subset. These subsets also segregated by the expression of TrkA and GFRα(3) in the putative neural crest-derived subset, and TrkB in the putative placodes-derived subset. The TRPV1-positive esophageal DRG neurons had the phenotype similar to the vagal putative neural crest-derived subset.

CONCLUSIONS & INFERENCES

The TRPV1-positive (potentially nociceptive) vagal afferent neurons innervating the mouse esophagus originate from both neural crest and placodes. The expression profile of the receptors for neurotrophic factors is similar between the neural crest-derived vagal and spinal nociceptors, but distinct from the vagal placodes-derived nociceptors.

Workshop: tuning the 'cough center'

The Workshop considered the mechanisms whereby the 'cough center' could be tuned by various afferent inputs. There were particular presentations on the effects of inputs from the nose, mouth, respiratory tract and lungs, cerebral cortex, somatic tissues and the pharynx. From all these sites cough induced from the lungs could be increased or decreased in its strength or modified in its pattern. Thus 'tuning' of cough could be due to the interaction of afferent inputs, or to the sensitization or desensitization of brainstem neural pathways. The pattern of response depended on the 'type' of cough being studied and, in some instances, on the timing of the sensory input into the brainstem. Cough inputs could also affect various 'non-cough' motor outputs from the brain, although this was not the main theme of the Workshop. The main conclusion was that cough is not a stereotyped output from the medullary 'cough center', but that its pattern and strength depend on many afferent inputs acting on the 'cough center'.

Distinction of cough from other sounds produced by daily activities in the upper airways

OBJECTIVES

The aim of this study was to validate the successfulness of our developed system for distinction between cough and other sounds which are present in daily human activities from the upper airways.

BACKGROUND

To date, methods used for monitoring of cough sound were primarily subjective. A reliable measure of cough is needed so that the severity of cough in various patients and the effectiveness of treatment can be assessed.

METHODS

Sounds of induced cough and sneezing, voluntary throat and nasopharynx clearing, forced ventilation and laughing, snoring, eructation, loud swallowing, and nasal blowing were studied. Characteristics of the sound events in 20 volunteers were calculated using the time-domain, spectral and non-linear analysis. The classification tree was constructed for classification between cough and non-cough sounds. We have validated the usefulness of our developed algorithm against subjective cough counts, which were performed by two trained observers.

RESULTS

The value of sensitivity for distinction between cough and other sounds was 86% and the value of specificity was 91%. The value of sensitivity for distinction between voluntary and induced cough sounds was 96% and specificity was 43%. The value of sensitivity between cough sounds and voluntary throat clearing was 96% and specificity was 85%. The value of sensitivity between cough sounds and induced sneezing was 95% and specificity was 93%.

CONCLUSION

We have developed an algorithm for distinction between cough and other sounds with a relatively high degree of accuracy (Tab. 1, Fig. 5, Ref. 15).

The kinematics of the Zagros Mountains (Iran)

We present a synthesis of recently conducted tectonic, global positioning system (GPS), geomorphological and seismic studies to describe the kinematics of the Zagros mountain belt, with a special focus on the transverse right-lateral strike-slip Kazerun Fault System (KFS). Both the seismicity and present-day deformation (as observed from tectonics, geomorphology and GPS) appear to concentrate near the 1000 m elevation contour, suggesting that basement and shallow deformation are related. This observation supports a thick-skinned model of southwestward propagation of deformation, starting from the Main Zagros Reverse Fault. The KFS distributes right-lateral strike-slip motion of the Main Recent Fault onto several segments located in an en echelon system to the east. We observe a marked difference in the kinematics of the Zagros across the Kazerun Fault System. To the NW, in the North Zagros, present-day deformation is partitioned between localized strike-slip motion on the Main Recent Fault and shortening located on the deformation front. To the SE, in the Central Zagros, strike-slip motion is distributed on several branches of the KFS. The decoupling of the Hormuz Salt layer, restricted to the east of the KFS and favouring the spreading of the sedimentary cover, cannot be the only cause of this distributed mechanism because seismicity (and therefore basement deformation) is associated with all active strike-slip faults, including those to the east of the Kazerun Fault System.

Influence of stimulation of nasal afferents on expiration reflex evoked from vocal folds

Cough and sneezing are upregulated during the upper airway diseases, most likely to enhance airway defense. The aim of this study was to assess the expiration reflex (ER), another expulsive defensive airway reflex, during allergic rhinitis (AR) and intranasal (i.n.) capsaicin challenge. Thirty male guinea pigs, sensitized to ovalbumin were used in the study. They were divided into 3 groups of 10 animals each: AR group (i.n. ovalbumin), capsaicin group (i.n. capsaicin 50 microM, 15 microl), and controls without any challenge. The animals were anesthetized with urethane (1.1 mg/kg) and allowed to breath spontaneously via tracheostomy. Metal canula was introduced into the right hemithorax to assess intrapleural pressure. ER was elicited by mechanical stimulation of the vocal folds using a thin nylon loop introduced upwards via tracheostomy. Maximal expiratory effort of ER (MEE) and the count of post-ER laryngeal coughs were evaluated. Mechanical stimulation of the vocal folds in controls produced isolated ER. They were followed by post-ER cough only in 11% of provocations. AR and capsaicin challenge increased MEE compared with that in controls (P<0.05). In these two groups of animals, the ER was followed by post ER-cough in 75% of provocations. The count of post-ER coughs in the group order control/AR/capsaicin was 0-2/2-4/1-3, respectively; P<0.05). The ER from the vocal folds is upregulated in a similar manner as is cough and sneeze. The central neuronal mechanisms are proposed to mediate this effect, but the spread of inflammation from upper airways to the larynx, verified histologically in the present study, may contribute as well.

Convergence of nasal and tracheal neural pathways in modulating the cough response in guinea pigs

In the present study we investigated the possibility of central convergence of neural pathways coming from distant anatomical regions in modulating the cough response. We addressed this issue by inducing cough from the tracheo-bronchial region on the background of capsaicin-stimulated and mesocain-blocked nasal mucosa in 14 anesthetized guinea pigs. The control group consisted of 6 guinea pigs in which the active agents, capsaicin and mesocain, were substituted for by inert physiological saline. All animals were tracheostomized, and the larynx was disconnected from the proximal part of the trachea with preserved innervations, and all were subjected to the same protocol. Cough, induced by mechanical irritation of the tracheo-bronchial mucosa, was elicited three times: in the control condition, after intranasal capsaicin challenge, and after another capsaicin challenge preceded by intranasal instillation of a local anesthetic, mesocain. The main finding of the study was that the number of cough efforts per bout, assessed from positive deflections on the intrapleural pressure recordings, was significantly enhanced by intranasal capsaicin challenge and this effect was reversed by intranasal pretreatment with the anesthetic mesocain [2.1 +/-0.2 (control) vs. 3.5 +/-0.4 (capsaicin) vs. 2.2 +/-0.2 (capsaicin after mesocain) (P<0.01)], with no appreciable changes in the magnitude of cough efforts. The cough response in the control group remained unchanged. We conclude that tracheo-bronchial cough may be modified by neural sensory input to the brain coming from nasal mucosa. Therefore, cough reflex is subject to central convergence of peripheral neural pathways originating at distant anatomical locations.

Cough reflex sensitivity is increased in the guinea pig model of allergic rhinitis

Increased cough reflex sensitivity is found in patients with allergic rhinitis and may contribute to cough caused by rhinitis. We have reported that cough to citric acid is enhanced in the guinea pig model of allergic rhinitis. Here we address the hypothesis that the cough reflex sensitivity is increased in this model. The data from our previous studies were analyzed for the cough reflex sensitivity. The allergic inflammation in the nose was induced by repeated intranasal instillations of ovalbumin in the ovalbumin-sensitized guinea pigs. Cough was induced by inhalation of doubling concentrations of citric acid (0.05-1.6 M). Cough threshold was defined as the lowest concentration of citric acid causing two coughs (C2, expressed as geometric mean [95% confidence interval]). We found that the cough threshold was reduced in animals with allergic rhinitis. C2 was 0.5 M [0.36-0.71 M] and 0.15 M [0.1-0.23 M] prior and after repeated intranasal instillations of ovalbumin, respectively, P<0.01, n=36). C2 was not affected in control animals (n=29). We have reported that the selective leukotriene cys-LT1 receptor antagonist montelukast inhibited cough enhancement in this model. We found that this was accompanied by inhibition of the changes in cough reflex sensitivity. C2 was reduced in animals with allergic rhinitis treated orally with vehicle (0.57 M [0.28-1.1] vs. 0.09 M [0.04-0.2 M], P<0.05, n=8), but not in animals treated with montelukast (0.57 M [0.22-1.4 M] vs. 0.52 M [0.17-1.6 M], NS, n=8). We conclude that the cough reflex sensitivity is increased in the guinea pig model of allergic rhinitis. Our results suggest that guinea pig is a suitable model for mechanistic studies of increased cough reflex sensitivity in rhinitis.

Role of gender and pubertal stage on cough sensitivity in childhood and adolescence

Studies in healthy adult volunteers and patients with chronic cough have shown that women have increased cough sensitivity to inhaled tussigenic stimuli, including capsaicin. The explanation for this phenomenon remains unknown, although the influence of pubertal changes (dimensional, hormonal) may play a role. In the present study we set out to examine the effect of the pubertal status on cough reflex sensitivity in a population of male and female children and adolescents. The study consisted of cough reflex sensitivity (CRS) testing, spirometry, and a children-completed pubertal status questionnaire. The inclusion criteria were no current symptoms of respiratory disease, no respiratory infection in the preceding 2 weeks, no allergic disease, and no other disease that could modulate CRS. All children were non-smokers. For assessing the CRS we used a compressed air-driven nebuliser controlled by a dosimeter with an inspiratory flow regulator valve. Each subject inhaled up to 12 capsaicin aerosol concentrations (0.61-1250 micromol/l) during 400 ms at 1 min intervals. CRS was defined as the lowest capsaicin concentration that evoked minimally 2 coughs. 225 children (median age 13 yr, 103 girls/122 boys) were divided according to the pubertal status (prepubertal, early pubertal, and late pubertal) and gender. We found that CRS [geometric mean (95%CI)] was similar in prepubertal and early pubertal girls and boys. However, CRS was significantly higher in late pubertal girls (n=56) than in boys (n=26) [53.57 (35.62-80.64) micromol/l vs. 119.7 (70.74-208.55) micromol/l; respectively; P=0.017]. We conclude that puberty and gender have a significant influence on the cough threshold to capsaicin. It seems, however, hard to determine what factors are responsible for the observed gender differences in cough reactivity adolescents.

Differences in oxidative status, lung function, and pulmonary surfactant during long-term inhalation of medical oxygen and partially ionized oxygen in guinea pigs

Inhalation of partially ionized oxygen may have less adverse effects on lung functions than medical oxygen. Guinea pigs inhaled air, 100% molecular medical oxygen (O(2)mol), partially negatively (O(2)neg) or positively (O(2)posit) ionized oxygen during 17 and 60 h. After 17 h, dityrosines, markers of oxidative injury, in lung homogenate increased in O(2)neg and decreased in O(2)posit groups vs. controls. After 60 h, dityrosines rose after inhalation of O(2)mol and O(2)neg, but not in the O(2)posit group. Lysine-LPO products increased and lung wet/dry weight ratio decreased in O(2)mol and O(2)neg, and not in O(2)posit group. Relative neutrophil count in BALF was elevated in all oxygen-treated groups with lower numbers in O(2)posit vs.O(2)mol and O(2)neg groups. After 60 h, surfactant activity was better in O(2)posit vs. O(2)mol group. In conclusion, long-term inhalation of partially positively ionized oxygen is associated with less oxidative stress, milder lung inflammatory response, and better surfactant activity than molecular or negatively ionized oxygen.

Cough reflex sensitivity testing in in seasonal allergic rhinitis patients and healthy volunteers

Dysfunction of upper and lower airways frequently coexists, and they appear to share key elements of pathogenesis. The interrelationship between upper and lower airway manifestations of allergy remains still incompletely investigated. Little is known about the critical factors that determine airway afferent nerve endings reactivity (cough sensitivity) in patients with allergic rhinitis. Subclinical inflammatory changes within the lower airways and/or chronic upper airway cough syndrome (previously referred to as postnasal drip syndrome) are probably responsible for this effect. The aim of this study was to evaluate capsaicin cough sensitivity in pollen sensitive patients with seasonal allergic rhinitis without treatment out of a grass pollen season time using the European Respiratory Society (ERS) guidelines on the assessment of cough. Cough sensitivity was defined as the lowest capsaicin concentration which evoked two (C2) or five (C5) coughs. Capsaicin aerosol in doubling concentrations (from 0.49 to 1000 micromol/l) was inhaled by a single breath method (KoKo DigiDoser; nSpire heath Inc, Louisville, CO), modified by the addition of an inspiratory flow regulator valve (RIFR; nSpire heath Inc, Louisville, CO). The seasonal rhinitis subjects (5M, 7F; mean age 23 yr) had not been complaining primarily about coughing. Their pulmonary function was within normal range. Concentrations of capsaicin causing two (C2) and five coughs (C5) were reported. Volunteers' (5M, 7F, mean age 23 yr) cough sensitivity (geometric mean and 95 % CI) for C2 was 16.5 (4.1-67.0) micromol/l vs. allergic rhinitis patients' C2 3.5 (1.9 - 6.4) (P= 0.018). Volunteers' C5 was 132.4 (41.3 - 424.5) micromol/l vs. allergic rhinitis patients' C5 13.1 (6.0 - 28.6) micromol/l (P= 0.013). We conclude that airway afferent nerve endings reactivity in pollen sensitive subjects suffering from seasonal allergic rhinitis was significantly increased out of pollen season compared with healthy volunteers.

Distinction between voluntary cough sound and speech in volunteers by spectral and complexity analysis

Objective monitoring of cough sound for extended period is an important step toward a better understanding of this symptom. Because ambulatory cough monitoring systems are not commercially available, we prepared own monitoring system, which is able to distinguish between voluntary cough sound and speech in healthy volunteers. 20-min sound records were obtained using portable digital voice recorder. Characteristics of the sound events have been calculated in time and frequency domains and by a nonlinear analysis. Based on selected parameters, classification tree was constructed for the classification of cough and non-cough sound events. We validated the usefulness of our algorithm developed against manual counts of cough obtained by a trained observer. The median sensitivity value was 100% (the interquartile range was 98-100) and the median specificity was 95% (the interquartile range was 90-97). In conclusion, we developed an algorithm to distinguish between voluntary cough sound and speech with a high degree of accuracy.

Acidification of the oesophagus acutely increases the cough sensitivity in patients with gastro-oesophageal reflux and chronic cough

Gastro-oesophageal reflux disease (GORD) is one of the most common causes of chronic cough; however, the mechanisms by which GOR initiates coughing are incompletely understood. We address the hypothesis that acidification of oesophagus acutely increases the cough reflex sensitivity in patients with GORD and chronic cough. Nine patients with GORD with chronic cough and 16 patients with GORD without cough were recruited. In a randomized double blind study, saline and acid (HCl, 0.1 mol L(-1)) were separately infused into oesophagus via naso-oesophageal catheter. Cough reflex sensitivity to inhaled capsaicin was determined immediately after completion of each infusion. Infusion of acid into oesophagus increased capsaicin cough reflex sensitivity in patients with GORD and chronic cough. In contrast, acid had no effect on the cough sensitivity in patients with GORD without cough. In a separate study, acid infusion into oesophagus did not affect the cough sensitivity in 18 healthy subjects. We conclude that acid in the oesophagus acutely increases the cough reflex sensitivity to capsaicin in patients with GORD and chronic cough. This phenomenon may contribute to the pathogenesis of cough due to GORD.

Tussigenic agents in the measurement of cough reflex sensitivity

Different inhalation methods are used for cough reflex sensitivity (CRS) measurement. The single-breath method of tussigenic agent aerosol inhalation is widely used now. Comparison of two tussigenic agents--citric acid and capsaicin--in cough reflex sensitivity measurement was used in healthy volunteers. In 17 healthy volunteers (7 M, 10 F; mean age 21 years) without respiratory tract infection in last 3 weeks, without cardiovascular, allergic, respiratory metabolic diseases, and with normal spirometry, cough reflex sensitivity was examined by nebuliser ProvoJet Ganshorn Medizin Elektronic, Germany) with doubled concentrations of capsaicin (SIGMA) from 0.49 to 1000 micromol/l and citric acid (LACHEMA) concentrations of 1, 3, 10, 30, 100, 300, 1000 micromol/l. Cough reflex sensitivity was defined as the lowest concentration of tussigenic agents which elicited 2 and 5 coughs (C2, C5). Geometric mean and 95% confidence interval (CI) of citric acid C2 was 454.5 (284.8-725.4) mmol/l in 88.2% of volunteers; citric acid C5 was 1000 micromol/l (0) in 47.1% of volunteers. Capsaicin C2 was 23.5 (8.2-67.5) micromol/l in 100% of volunteers and C5 was 263.7 (111.2-625.1) micromol/l in 76.5% of volunteers. We conclude that capsaicin single-breath test is more relevant for cough reflex sensitivity measurement in healthy volunteers than citric acid cough test.

Influence of chest gamma-irradiation on cough response in awake guinea pigs

Radiotherapy of tumors in the chest and neck regions may have serious pulmonary side effects. It is well known that inflammation is an essential manifestation of radiation-induced injury. This can heal spontaneously, by specific treatment, or it may progress to more intensive inflammation up to irreversible pulmonary fibrosis. To prevent such complications, it would be useful to have a simple non-invasive and sensitive method for monitoring the course of airway and lung post-irradiation inflammation. This study is devoted to search for such a method. We supposed that cough response intensity (CRI) could be one of the methods, which we are looking for. Guinea pigs (Trik strain, n=32) were used in the study. Animals were divided into two subgroups. Animals of a non-untreated (NT) group (n=14; M=7, F=7) were submitted to sham chest irradiation. The animals of a treated (XRT) group (n=18; M=9, F=9) were exposed to a single dose of gamma rays. Cough was provoked by exposure of animals to citric acid aerosol (CA) in gradually increasing concentrations (0.05-1.6M). CRI testing was performed two days before sham/real chest irradiation, than on 1st, 3rd, 10th, 15th, 21st, and 28th days following the day of irradiation. CRI was quantified in each animal by counting the number of coughs induced by all used concentration of CA. We found a significant increase of CRI in the animals of XRT group on 10th and 21st day compared with the NT animals. An increase of CRI also was found inside the XRT group on the 10th day after irradiation compared with the pre-irradiation value of CRI.

Oral N-acetylcysteine reverses hyperoxia-related cough suppression in guinea pigs

Hyperoxia-induced lung injury is well known in animal and human studies. We have previously shown that hyperoxic exposure of guinea pigs is associated with suppression of cough reflex. The goal of this study was to determine the effects of oral N-acetylcysteine (NAC) on hyperoxia-induced oxidative stress in lung tissue directed on cough reflex. The experimental group was pretreated with NAC daily for 7 days and subsequently exposed to 100% O2 for 60 h. Hyperoxic group inhaled 100% O2 only. The control group was exposed to normoxia. Cough was induced by inhalation of citric acid aerosol before and after exposure to oxygen. Cough was also induced by mechanical stimulation of airways in anesthetized animals just after the end of oxygen exposure. Our results showed a significant decrease (P=0.002) in citric acid-induced cough in hyperoxic animals and reversal of that effect in animals pretreated with NAC. In addition, there was a significant interaction between antioxidant therapy and hyperoxia (P=0.005). NAC also reversed the hyperoxia-induced inhibition of mechanically-induced cough. In conclusion, our results indicate that NAC attenuated hyperoxia-induced down-regulation of chemically and mechanically-induced cough.

Experimental allergic rhinitis-related cough and airway eosinophilia in sensitized guinea pigs

Allergic rhinitis is one of the most common causes of chronic cough. The characteristic feature of allergic rhinitis is eosinophilic nasal inflammation. This study was determined to find the relation between airway eosinophils and chemically-induced cough in guinea pigs with antigen-induced rhinitis at the early and late allergic phases. Forty animals were sensitized with ovalbumin (OVA) and divided into four separated groups. Four weeks later, the sensitized animals were either once or repeatedly (6 times at 7-day intervals) intranasally challenged with OVA to develop experimental allergic rhinitis. The control group was given saline. Cough was elicited by inhalation of citric acid aerosols and evaluated at 30 min (early phase) or 24 h (late phase) after the 1st or 6th nasal challenge (NC) in the sensitized animals. The citric acid-induced cough was significantly increased in the sensitized animals in the early allergic phase after the first and repeated NC compared with the control values [14(9-19) vs. 16(10-17) vs. 8(6-10); P=0.049], whereas there was no significant increase in the cough response tested in the late allergic phase. A correlation between the cough intensity and the number of eosinophils from nasal mucosa only (P=0.008) was found.

Dietary intake of flavonoids and hyperoxia-induced oxidative stress related cough in guinea pigs

There is many evidence that inhalation of high oxygen concentration has a toxic influence on pulmonary function and structures. Hyperoxia-induced oxidative stress is well characterized in rodents and has been used as a valuable model of human respiratory distress syndrome. We have previously shown that hyperoxic exposure of guinea pigs is associated with suppression of cough reflex. The goal of this study was to determine the effects of dietary intake of antioxidant flavonoids (Flavin7, Vita Crystal Slovakia Ltd., 2 ml/kg b.w.) on hyperoxia-induced oxidative stress in lung tissue directed on cough reflex. The experimental group (n = 8) was pretreated with Flavin7 as a single daily dose for 14 days and subsequently exposed to 100% 02 for 60 h. Hyperoxic group (n = 8) inhaled 100% Oz only. Control group (n = 8) was exposed to normoxia. Cough was induced by inhalation of citric acid aerosol at time before and after exposure to hyperoxia. Cough was also induced by mechanical stimulation of airways in anaesthetized animals just after the end of oxygen exposition. When to compare animal groups before and after hyperoxia, our results have shown a significant decrease 2 (1-6) vs 6 (4-6) p = 0.041 in citric acid-induced cough in hyperoxic animals and no significant changes 8 (5.5-8.5) vs 5 (4-6.5) p = 0.055 in animals with antioxidant therapy. Mechanically-induced cough after hyperoxia was not influenced by substitution with flavonoids. In conclusion, our results indicate that flavonoids attenuated hyperoxia-induced down-regulation especially of chemically-induced cough (Tab. 2, Fig. 2, Ref. 30). Full Text (Free, PDF) www.bmj.sk.

Changes of cough reflex sensitivity induced by cancer radiotherapy of chest and neck regions

It is reasonable to suppose that airway mucosa can be damaged by irradiation applied to chest and neck regions. The inflammatory process is a consequence of an injury. Airway inflammation is one mechanism responsible for cough induction. So, one can suppose that radiotherapy (RT) focused on the patients' chest or neck may injure airway mucosa, which might change sensitivity of the nerve-endings mediating the cough reflex. The purpose of this study was to examine cough reflex sensitivity (CRS) in patients who underwent RT in the chest and neck regions. CRS test using capsaicin was performed in patients with breast cancer (Group A, n=19), and with lung or neck cancer in (Group B, n=14) who underwent RT. Capsaicin aerosol in doubled concentrations (0.49-1000 microM) was inhaled by a single breath. CRS was defined as the lowest capsaicin concentration that evoked 2 or more coughs (C2). Radiation doses ranged from 40 to 70 Gy. Capsaicin cough challenge was performed before and then in the 2(nd) and 5(th) week of RT. We observed a significantly reduced value of C2, i.e., increased cough reflex sensitivity, in Group B in the 2(nd) week of RT (P= 0.04). We conclude that CRS in the lung or neck cancer patients undergoing RT is significantly enhanced, which could result from injury to the nerve endings in airway mucosa.

Effects of thorax irradiation on citric acid-induced cough in guinea pigs

Thoracic irradiation may cause an acute lymphocytic alveolitis or hypersensitivity pneumonitis. It is well known that cough reflex is sensitized by a number of inflammatory mediators. The purpose of the present study was to investigate the effect of the thoracic irradiation on the cough response in awake guinea pigs. Guinea pigs (Trik strain) were exposed to sham irradiation (n=16), a single irradiation dose of 10 Gy (n=12), and a fractionated irradiation dose (in five fractions) of 15 Gy (n=12) delivered to the thorax. Cough was induced by citric acid aerosol inhalation in gradually increasing concentrations (0.05-1.6 M) during the first week after thoracic irradiation. The cough response was expressed as a total number of coughs induced during all citric acid challenges. Irradiated animals with single dose of 10 Gy exhibited a time- dependent significant increase of citric acid-induced cough in the 6th day after irradiation compared with control animals (P=0.005), whereas cough was not altered significantly in irradiated animals with fractionated dose of 15 Gy. This study demonstrates that the increased cough response may be a determinant of the functional changes of airway nerve-endings mediating cough in the early phase after thoracic irradiation.