The effect of stimulation and unloading of baroreceptors on cough in experimental conditions.

Cough, the main airway defensive process, is modulated by multiple sensory inputs from the respiratory system and outside of it. This modulation is one of the mechanisms that contributes to the sensitization of cough pathways at the peripheral and/or central level via neuroplasticity and it manifests most often as augmented coughing. Cardiorespiratory coupling is an important mechanism responsible for a match between oxygenation and cardiac output and bidirectional relationships exist between respiration and cardiovascular function. While the impact of cough with the robust swings of the intrathoracic pressure on haemodynamic parameters and heart electrophysiology are well characterized, little is known about the modulation of cough by haemodynamic parameters - mainly the blood pressure. Some circumstantial findings from older animal studies and more recent sophisticated analysis confirm that baroreceptor stimulation and unloading alters coughing evoked in experiments. Clinical relevance of such findings is not presently known.

Legacy of Prof. Juraj Korpás: International Impact of Slovak School of Experimental Respirology.

Human health is the main role of medical research. Scientists were always intrigued by disease prevention, their diagnostics and proper treatment. In fact, research in medicine is always directed towards the improvement of the health care and improvement of the quality of life of the target population. Nowadays, physiological research, which is the base stone for clinical research, progresses fast forward, providing new information about body functions in health and diseases. This obvious progress is associated with modern methods, such as neuronal tracing, patch-clamp methods, electrophysiology, molecular biology and many more, which supported by comprehensive information technology guarantees high quality and complex data. Our younger colleagues, young scientists, post-docs or PhD students are well-trained and qualified in utilizing these new methods.

Modulation of Cough Reflex by Gaba-Ergic Inhibition in Medullary Raphé of the Cat.

We studied the effects of GABA receptor agonists microinjections in medullary raphé on the mechanically induced tracheobronchial cough response in anesthetized, unparalyzed, spontaneously breathing cats. The results suggest that GABA-ergic inhibition significantly contributes to the regulation of cough reflex by action of both GABA(A) and GABA(B) receptors. The data are consistent with inhomogeneous occurrence of GABA-ergic neurons in medullary raphé and their different involvement in the cough reflex control. Cells within rostral nucleus raphéobscurus with dominant role of GABA(A) receptors and neurons of rostral nucleus raphépallidus and caudal nucleus raphémagnus with dominant role of GABA(B) receptors participate in regulation of cough expiratory efforts. These cough control elements are distinct from cough gating mechanism. GABA-ergic inhibition in the raphé caudal to obex had insignificant effect on cough. Contradictory findings for GABA, muscimol and baclofen administration in medullary raphé suggest involvement of coordinated activity of GABA on multiple receptors affecting raphé neurons and/or the local neuronal circuits in the raphé modulating cough motor drive.

GABA-ergic neurotransmission in the nucleus of the solitary tract modulates cough in the cat.

GABA, muscimol, and baclofen were microinjected into the rostral (rNTS) and caudal solitary tract nucleus (cNTS) in 24 anesthetized cats. Electromyograms (EMGs) of diaphragm (DIA) and abdominal muscles (ABD), blood pressure and esophageal pressure (EP) were recorded and analysed. Bilateral microinjections of 1 mM GABA (total 66 ±â€¯4 nl), 1 mM baclofen (64 ±â€¯4 nl) and unilateral microinjections of 0.5 mM muscimol (33 ±â€¯1 nl) in the rNTS significantly reduced cough number (CN), amplitudes of ABD EMGs, expiratory EP, and prolonged the duration of the cough inspiratory phase. GABA microinjections decreased the amplitudes of cough-related DIA EMGs and inspiratory EP; muscimol microinjections decreased the cough DIA EMG on the contralateral side. Only microinjections of GABA into the cNTS suppressed CN. In some cases, microinjections prolonged the inspiratory phase, lowered respiratory rate, changed the depth of breathing, and increased blood pressure and heart rate. Our results confirm that GABA-ergic inhibitory mechanisms in the rNTS can regulate coughing in the anesthetized cat.

Central administration of nicotine suppresses tracheobronchial cough in anesthetized cats.

We tested the hypothesis that nicotine, which acts peripherally to promote coughing, might inhibit reflex cough at a central site. Nicotine was administered via the vertebral artery [intra-arterial (ia)] to the brain stem circulation and by microinjections into a restricted area of the caudal ventral respiratory column in 33 pentobarbital anesthetized, spontaneously breathing cats. The number of coughs induced by mechanical stimulation of the tracheobronchial airways; amplitudes of the diaphragm, abdominal muscle, and laryngeal muscles EMGs; and several temporal characteristics of cough were analyzed after administration of nicotine and compared with those during control and recovery period. (-)Nicotine (ia) reduced cough number, cough expiratory efforts, blood pressure, and heart rate in a dose-dependent manner. (-)Nicotine did not alter temporal characteristics of the cough motor pattern. Pretreatment with mecamylamine prevented the effect of (-)nicotine on blood pressure and heart rate, but did not block the antitussive action of this drug. (+)Nicotine was less potent than (-)nicotine for inhibition of cough. Microinjections of (-)nicotine into the caudal ventral respiratory column produced similar inhibitory effects on cough as administration of this isomer by the ia route. Mecamylamine microinjected in the region just before nicotine did not significantly reduce the cough suppressant effect of nicotine. Nicotinic acetylcholine receptors significantly modulate functions of brain stem and in particular caudal ventral respiratory column neurons involved in expression of the tracheobronchial cough reflex by a mecamylamine-insensitive mechanism.

The effects of nasal irritant induced responses on breathing and cough in anaesthetized and conscious animal models.

There is little evidence to support the down-regulation of coughing from the nose. The cough response to citric acid (CA) was studied in anesthetized and conscious guinea pigs after nasal pretreatment with saline, 1% DMSO, allylisothiocyanate (TRPA1 agonist) and allylisothiocyanate +AP-18 (TRPA1 antagonist). Cough was induced by adding citric acid (CA) to the tracheal perfusion in anaesthetized animals, or by inhaling 0.4M CA in conscious animals. The cough response was counted from the dose response curves, airflow traces and cough sound analysis. In conscious animals, nasal allylisothiocyanate induced reproducible, dose dependent nasal symptoms and a significant drop in respiratory rate. Cough induced by CA was suppressed after nasal allylisothiocyanate (p<0.05), and this effect was prevented by AP-18 (1mM). In anaesthetized animals, nasal allylisothiocyanate induced a significant drop in respiratory rate. Cough induced subsequently by CA was suppressed when compared to baseline and vehicle responses (p<0.05). The reasons for the suppression of CA induced cough by TRPA1 agonist applied to the nose are not clear and remain to be elucidated.

Differential effects of kainic acid lesions in medullary raphe on cough and sneeze in anesthetized rabbits.

The effects of microinjections of the excitatory neurotoxin kainic acid (2 mg/ml; 49 ± 1 nl) on the mechanically induced tracheobronchial cough, sneeze, and solitary expulsions from the trachea were examined in 11 anesthetized rabbits. Kainic acid was injected into the medulla (1.6-2.8 mm rostral to the obex, 1.4-1.6 and 2.9-3.2 mm below the dorsal medullary surface). Blood pressure, esophageal pressure (EP), and electromyograms (EMGs) of the diaphragm (DIA) and abdominal muscles (ABD) were recorded. Kainic acid reduced the number of coughs (means ± SE) from 3.8 ± 2.0 to 0.9 ± 0.7 (p = 0.016), the amplitude of DIA cough from 90 ± 11 to 42 ± 13 % (p = 0.004), ABD EMG moving average from 103 ± 9 to 37 ± 15 % (p = 0.006), and inspiratory from 0.67 ± 0.13 to 0.36 ± 0.12 kPa (p = 0.013) and expiratory EP from 1.70 ± 0.54 to 0.89 ± 0.46 kPa (p = 0.008). Kainic acid had no effect on the number of sneeze reflexes nor did it affect solitary expulsions from the trachea. These effects were accompanied by significant increases in systemic blood pressure and respiratory rate. Spatiotemporal analysis of the cough and sneeze reflexes revealed increases in the duration of cough active expiratory phase, in the intervals between maxima of DIA and ABD EMG discharges, and in the active portion of total cough phase duration. Our findings suggest a diverse role of raphe neurons in the central control of motor airway responses such as coughing and sneezing. A complex function of raphe neurons in the generation of the cough motor pattern also is suggested.

Integration of simulated multipotential signals: the role of integration window width and of the number of spikes.

Electrical signals recorded from nerves/muscles represent the fundamentals for experimental data analysis including an assessment of respiratory motor output. The present work, based on theoretical model, is focused on the linearity and variability of rectified and integrated electroneurogram (ENG)/electromyogram (EMG) signals in relation to the frequency of spike incidence and moving average window width used for processing of signals. Our simulations of multipotential signals (multiunit action potentials) originating from an overlapping of four single units with phase shifts firing at two frequencies demonstrates that (1) integrated ENG/EMG signals are only approximately linearly proportional to the frequency of action potentials in the superposition - multipotential and (2) the width of the moving average window strongly influences the range (dispersion) of integrated values. Better quality of EMG recordings, a higher number of action potentials within the multipotential signals, and a wider width of the moving average window increase the accuracy of integrated ENG/EMG values during processing of motor output signals.

The role of trigeminal nasal TRPM8-expressing afferent neurons in the antitussive effects of menthol.

The cold-sensitive cation channel TRPM8 is a target for menthol, which is used routinely as a cough suppressant and as an additive to tobacco and food products. Given that cold temperatures and menthol activate neurons through gating of TRPM8, it is unclear how menthol actively suppresses cough. In this study we describe the antitussive effects of (-)-menthol in conscious and anesthetized guinea pigs. In anesthetized guinea pigs, cough evoked by citric acid applied topically to the tracheal mucosa was suppressed by menthol only when it was selectively administered as vapors to the upper airways. Menthol applied topically to the tracheal mucosa prior to and during citric acid application or administered continuously as vapors or as an aerosol to the lower airways was without effect on cough. These actions of upper airway menthol treatment were mimicked by cold air delivered to the upper airways but not by (+)-menthol, the inactive isomer of menthol, or by the TRPM8/TRPA1 agonist icilin administered directly to the trachea. Subsequent molecular analyses confirmed the expression of TRPM8 in a subset of nasal trigeminal afferent neurons that do not coincidently express TRPA1 or TRPV1. We conclude that menthol suppresses cough evoked in the lower airways primarily through a reflex initiated from the nose.

Antitussive effects of nasal thymol challenges in healthy volunteers.

Eighteen healthy volunteers with normal lung function were tested for cough. Before and after nasal administration of thymol (0.025 ml, 10(-3) M) into both nostrils, urge-to-cough, cough threshold, cumulative and total count of coughs per provocation were estimated during standardized and validated capsaicin cough challenge. Nasal thymol challenges induced pleasant olfactory sensation and in 6 out of the 18 subjects also mild cooling sensation. Cough threshold was not influenced when compared with intranasal saline and vehicle challenges (12.5 vs. 13.2 vs. 10.2 µM of capsaicin to induce two or more coughs (C2), respectively), but the total count of coughs after nasal thymol challenge was significantly lower than that obtained after saline or vehicle (19 vs. 20 vs. 14 coughs/provocation, respectively; p<0.05). Importantly, subjects did not report the urge to cough, which appeared to correspond to C2. We conclude that the modulation of cough by thymol is mostly of olfactory origin.

Naloxone blocks suppression of cough by codeine in anesthetized rabbits.

Opioid receptors which are involved in cough generation are abundantly expressed in the brainstem. Codeine is a potent µ-opioid receptor agonist. In the present study we examined the effects of naloxone, a µ-opioid receptor antagonist, on mechanically-induced tracheobronchial cough and on the cough suppressing effect of codeine in six pentobarbitone anesthetized spontaneously breathing rabbits. A single dose of naloxone (0.4 mg/kg) followed by a single dose of codeine (7 mg/kg) were administered intravenously. The number and amplitude of cough and sneeze reflexes were examined sequentially; before and after naloxone, and then after codeine. We found that neither did naloxone alone nor codeine given after prior naloxone pretreatment appreciably affect coughing or sneezing. Likewise, there were no significant differences in the diaphragm and abdominal muscles electromyographic moving averages, or the inspiratory and expiratory esophageal pressure amplitudes. However, we detected a tendency for the rise in expiratory motor drive during coughing and sneezing after injection of naloxone. The respiratory rate was significantly higher after naloxone in comparison with control (P < 0.001). No significant differences in arterial blood pressure were observed. We conclude that the failure of codeine to suppress the cough reflex on the background of naloxone pretreatment confirms the involvement of µ-opioid mechanism in the central antitussive effect of codeine.

Lung cancer incidence and survival in chromium exposed individuals with respect to expression of anti-apoptotic protein survivin and tumor suppressor P53 protein.

OBJECTIVE: Workers chronically exposed to hexavalent chromium have elevated risk of lung cancer. Our study investigates the incidence of lung cancer types, age at onset of the disease, and survival time among chromium exposed workers with respect to the expression of anti-apoptotic p53 and pro-apoptotic survivin proteins. MATERIAL AND METHODS: 67 chromium exposed workers and 104 male controls diagnosed with lung cancer were analyzed. The mean exposure time among workers was 16.7 ±10.0(SD) years (range 1- 41 years). To investigate the possible regulation of survivin by p53 we examined the expression of both proteins using immohistochemical visualization. RESULTS: Chromium exposure significantly decreases the age of onset of the disease by 3.5 years (62.2 ±9.1 in the exposed group vs. 65.7 ±10.5 years in controls; P=0.018). Small cell lung carcinoma (SCLC) amounted for 25.4% of all cases in chromium exposed workers and for 16.3% in non-exposed individuals. The mean survival time in the exposed group was 9.0 ±12.7 vs. 12.1 ±21.9 months in controls, but this difference was not significant. Survivin was predominantly expressed in both cell nucleus and cytoplasm, whereas p53 was expressed in the nucleus. There was a negative correlation between survivin and p53 expression. A decreased intensity of expression and fewer cells positive for survivin was detected in SCLC compared with other types of lung cancer. p53 was expressed in 94.1% and survivin in 79.6% of the samples analyzed. CONCLUSION: The study calls attention to decreased expression of survivin, as opposed to p53, in small cell lung carcinoma.

Central antitussive effect of codeine in the anesthetized rabbit.

BACKGROUND: Codeine represents a commonly used drug to suppress cough. Central antitussive effect of codeine has been confirmed in a number of animal studies. However, available data related to antitussive activity of codeine in rabbits are very limited. OBJECTIVE: We investigated the effects of codeine on cough, single expiratory responses (expiration-like reflex) induced by mechanical tracheo-bronchial stimulation, and on the sneeze reflex in the anesthetized rabbit. MATERIAL AND METHODS: Twenty pentobarbitone anesthetized spontaneously breathing rabbits were used for the study. Increasing doses of codeine (codeinum dihydrogenphosphate, Interpharm) were injected intravenously (iv); 0, 0.15, 0.76, and 3.78 mg/kg of codeine dissolved in saline, 0.25 ml/kg) or intracerebroventricularly (icv); 0, 0.015, 0.076, and 0.378 mg/kg of codeine dissolved in artificial cerebrospinal fluid, 0.033 ml/kg. RESULTS: Both iv and icv injections of codeine led to a dose-dependent reduction of coughing provoked by tracheo-bronchial stimulation; however, the doses differed substantially. The effective cumulative dose for a 50% reduction in the number of coughs was 3.9 and 0.11 mg/kg after iv and icv administration of codeine, respectively; representing about 35-fold higher efficacy of the icv route. The numbers of expiration-like responses and sneeze reflex responses remained unchanged. CONCLUSIONS: The study confirmed the central antitussive effect of codeine, but showed a low sensitivity of sneeze and expiration reflex to codeine. We validated the experimental model of an anesthetized rabbit for studies on central antitussive action.

Intranasal TRPV1 agonist capsaicin challenge and its effect on c-fos expression in the guinea pig brainstem.

Central neuronal interaction seems to play a role in pathogenesis of upper airway cough syndrome. In the guinea pig model we used the method c-fos expression to identify neurons involved in processing of nociceptive nasal stimuli and their contribution to enhancement of cough. 21 spontaneously breathing, urethane anaesthetized animals were used. The controls received intranasal saline, stimulation group received capsaicin (15 microl, 50 microM), and not-treated group was free of nasal challenge. After 2 h animals were deeply anaesthetized, exsanguinated and transcardially perfused with saline and paraformaldehyde. The brainstems were removed, post-fixed, and slices were processed immunohistochemically for c-fos. In capsaicin group the FLI was detected in the nTs 0.5 mm caudal, 1.5 mm lateral to the obex, the area postrema, LRN and VRG. Intensive FLI was identified in trigeminal nuclear complex. Mean number of FOS positive neurons per section was significantly higher in capsaicin group than that in no-treatment controls or saline controls at the level of obex (p<0.01). Neurons of nTs and VRG clearly activated after nasal provocation may participate in enhancement of cough.

Distinct generators for aspiration and expiration reflexes: localization, mechanisms and effects.

Re-evaluation of our earlier c-Fos-like immuno-reactive studies and brainstem transection/lesion experiments in over 40 anaesthetized, non-paralyzed cats allowed comparison of two distinct airway defensive reflexes with the distinct generators for inspiration (I) and expiration (E), described recently in juvenile rats. The spiration reflex (AspR) is characterized by solitary rapid and strong inspiratory effort with a reciprocal inhibition, preventing a subsequent active expiration, while the expiration reflex (ExpR) manifests by rapid and strong expiratory effort, starting without a preceding, inspiration, or reciprocal inhibition of occasional spontaneous inspiration. The retro-trapezoid nucleus/parafacial respiratory group neurones described as the distinct generator for active E in rats, are activated also during the ExpR in adult cats. Brainstem transection 5 mm above the obex eliminates the E generator and the ExpR, but preserves the I generator located in the pre-Bötzinger Complex, and also the AspR. This suggests the existence of a distinct I generator in cats as well as rats, and its contribution to the generation of the AspR. Persistence of the AspR in adult cats during asphyxic gasping, their similar character and the strong activation of I neurones at many places in the medulla and pons, suggest a common brainstem neuronal circuit contributing to generation of both the gasping and the gasp-like AspR. That the AspR and ExpR have distinct multilevel brainstem control mechanisms supports the dual theory of control and provides unique models for testing respiratory rhythm and pattern generation. The AspR may be compared with the powerful "auto-resuscitation effects of asphyxic gasping"; the ExpR may underly the effectiveness of the laryngeal chemoreflexes in prevention of lung diseases.

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.

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.

Provocation of aspiration reflexes and their effects on the pattern of cough and reflex apnea in cats.

Aspiration reflexes (AspRs) manifesting as reflex spasmodic inspirations and their effects on motor pattern of tracheobronchial cough and reflex apnea were studied on 22 spontaneously breathing pentobarbitone-anesthetized cats. AspRs induced during cough inspiration enhanced peak inspiratory (P<0.01) and expiratory (P<0.02) esophageal pressures, amplitudes of diaphragm (P<0.01) and abdominal muscles (P<0.05) EMG activity, and prolonged the entire expiratory period (P<0.01) and total cycle duration (P<0.05) of cough. Transient inhibitions and splits of cough expiration frequently occurred with AspR within active cough expiratory period; however, cough spatiotemporal characteristics were not altered significantly. Sub-threshold nasopharyngeal stimulation failing to provoke AspR had no significant effects on coughing. Hering-Breuer inflation apnea was moderately prolonged by AspRs (20%; P<0.05), unlike the apnea produced by continual mechanical laryngeal stimulation. AspRs are inducible during tested behaviors interacting with their motor pattern. Central mechanisms involving pulmonary stretch receptor stimulation is suggested for modulation of cough and inflation apnea by AspR.

Excitability and rhythmicity of tracheobronchial cough is altered by aspiration reflex in cats.

Effects of nasopharyngeal stimulation on excitability and rhythmicity of mechanically induced tracheobronchial cough were examined on 18 pentobarbitone anesthetized cats. After the 17.2+/-2.4 aspiration reflexes (AspRs), tracheobronchial stimulation evoked lower number of coughs (P<0.05) with longer latency to the diaphragm activation (P<0.02), compared to control. AspRs induced within "inter-cough" periods (motor quiescence between individual coughs; 3.3 AspRs per period) reduced cough number by 50% (P<0.01), shortened cough-related abdominal activity (P<0.02), prolonged inter-cough period (P<0.02), and the total cough cycle duration (P<0.05). Cough efforts occurred irregularly with very variable "inter-cough" distances and total cough cycle durations. The subthreshold nasopharyngeal stimulation (failing to evoke AspR) did not affect rhythmic coughing. AspRs induced during persisting post-stimulation coughs did not significantly reduce their number. Excitability and rhythmicity of mechanically induced tracheobronchial cough can be reduced by AspRs, but not by subthreshold nasopharyngeal stimulation. The suppressive effect of spasmodic inspirations on chronic cough is suggested.

Influence of microinjections of D,L-homocysteic acid into the Botzinger complex area on the cough reflex in the cat.

Microinjections of D,L-homocysteic acid (DLH) were used to test the hypothesis that neuronal activation within the Botzinger complex area can modify the spatiotemporal characteristics of the cough reflex in 17 spontaneously breathing pentobarbitone anesthetized cats. DLH (50 mM, 1.25-1.75 nmol, 9 cats) reduced the number (P<0.01) of coughs and expiratory amplitude of abdominal electromyographic activity (P<0.01), and also esophageal pressure (P<0.001) during mechanically induced tracheobronchial cough. The duration of cough abdominal activity was shortened by 48% (P<0.05). DLH microinjections also temporarily reduced the respiratory rate (P<0.01) and increased the mean arterial blood pressure (P<0.001), baseline of esophageal pressure (P<0.01), and end tidal CO(2) concentrations (P<0.01). Lower doses of DLH (0.27-0.35 nmol, 7 cats) or vehicle (25-35 nl, 8 cats) induced few alterations in cardiorespiratory or cough characteristics. The results support predominantly inhibitory effects of neurons in the region of the Bötzinger complex on cough abdominal activity and cough number.