Abstract
Chronic irritating cough in patients with allergic disorders may reflect behavioral or reflex response that is inappropriately matched to the stimulus present in the respiratory tract. Such dysregulated response is likely caused by sensory nerve damage driven by allergic mediators leading to cough hypersensitivity. Some indirect findings suggest that even acid-sensitive, capsaicin-insensitive A-δ fibers called "cough receptors" that are likely responsible for protective reflex cough may be modulated through immune driven inflammation. The aim of this study was to find out whether protective reflex cough is altered during acute allergic airway inflammation in rabbits sensitized to ovalbumin. In order to evaluate the effect of such inflammation exclusively on protective reflex cough, C-fiber mediated cough was silenced using general anesthesia. Cough provocation using citric acid inhalation and mechanical stimulation of trachea was realized in 16 ovalbumin (OVA) sensitized, anesthetized and tracheotomised rabbits 24h after OVA (OVA group, n = 9) or saline challenge (control group, n = 7). Number of coughs provoked by citric acid inhalation did not differ between OVA and control group (12,2 ±6,1 vs. 17,9 ± 6,9; p = 0.5). Allergic airway inflammation induced significant modulation of cough threshold (CT) to mechanical stimulus. Mechanically induced cough reflex in OVA group was either up-regulated (subgroup named "responders" CT: 50 msec (50-50); n = 5 p = 0.003) or down-regulated (subgroup named "non responders", CT: 1200 msec (1200-1200); n = 4 p = 0.001) when compared to control group (CT: 150 msec (75-525)). These results advocate that allergen may induce longer lasting changes of reflex cough pathway, leading to its up- or down-regulation. These findings may be of interest as they suggest that effective therapies for chronic cough in allergic patients should target sensitized component of both, reflex and behavioral cough.
Highlights
A common feature to all allergic and atopic disorders is the presence of strong sensations, and/ or reflexes that are primary aimed to get rid of allergen [1]
Induced cough reflex in OVA group was either up-regulated (subgroup named “responders” cough threshold (CT): 50 msec (50–50); n = 5 p = 0.003) or down-regulated (subgroup named “non responders”, CT: 1200 msec (1200–1200); n = 4 p = 0.001) when compared to control group (CT: 150 msec (75–525)). These results advocate that allergen may induce longer lasting changes of reflex cough pathway, leading to its up- or down-regulation. These findings may be of interest as they suggest that effective therapies for chronic cough in allergic patients should target sensitized component of both, reflex and behavioral cough
Rabbits exposed to OVA aerosols showed a significant increase of eosinophil counts in Bronchoalveolar lavage (BAL) as compared to those exposed to Saline (11.6±1.92.0% vs. 2.2±0.6%; p = 0.001) (Fig 4.)
Summary
A common feature to all allergic and atopic disorders is the presence of strong sensations, and/ or reflexes that are primary aimed to get rid of allergen [1]. [1,2] This concept is in keeping with a hypothesis of neuropathic origin of chronic cough that have been raised recently highlighting the possible cause-effect link between exposure to infectious, irritant or allergic diseases and sensory nerve damage resulting in cough hypersensitivity [3]. Behavioral cough occurs as a result of subcortical and cortical processing of afferent information from airways. It is associated with conscious perception of the sensation of irritation (urge to cough) and serves in fine to reduce such sensation. It is associated with conscious perception of the sensation of irritation (urge to cough) and serves in fine to reduce such sensation. [7,10,12]
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