Synergistic interactions between airway afferent nerve subtypes mediating reflex bronchospasm in guinea pigs

Abstract

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.

Selective Expression of a Sodium Pump Isozyme by Cough Receptors and Evidence for Its Essential Role in Regulating Cough

“…1 A, B). Confirming previous studies (Ricco et al, 1996;Mazzone and Canning, 2002), about half of the labeled jugular ganglia neurons stained positively for substance P (Fig. 1 B).…”

“…The matrix appears uncoupled from the underlying smooth muscle, as muscle contraction does not activate the cough receptors or alter their excitability. Epithelial cells (including neuroendocrine cells) and epithelial-derived signaling molecules also appear to play no role in transducing cough receptor reflexes [based on the physical dissociation of the cough receptors from the epithelium, the lack of effect of epithelium removal on cough receptor activation and evoked cough, and cough receptor insensitivity to 5-HT, ATP, 15-HETE, and adenosine (Canning et al, 2006a;Carr et al, 2001;Chou et al;2008;Hwang et al, 2000;Kwong et al, 2008;Mazzone and Canning, 2002;Undem et al, 2004)]. …”

“…Note that the sodium pump-labeled fibers terminate between the epithelium and smooth muscle (abbreviated E and SM) layers. The substance P and ␣ 3 containing terminals likely arise from the jugular and nodose ganglia, respectively (Mazzone and Canning, 2002;Mazzone and McGovern, 2008). Scale bars, 50 m. E, Ouabain dosedependently reduces FM2-10 labeling.…”

“…Anesthetized (50 mg/kg ketamine and 2.5 mg/kg, i.m. xylazine) guinea pigs (n ϭ 9) or rats (n ϭ 3) received 5 l of 3% fast blue (Sigma) into the lumen of the extrathoracic trachea via a small incision in the neck (Mazzone and Canning, 2002). In other experiments, unilateral (left or right) sectioning of a superior (SLN) or recurrent (RLN) laryngeal nerve was performed before tracer injection (n ϭ 3 each).…”

“…For immunohistochemical staining of fast blue labeled nodose and jugular ganglia neurons (Mazzone and Canning, 2002), sections were incubated overnight (at 4°C) with monoclonal rat anti-substance P (1:400, Millipore Bioscience Research Reagents), washed, and incubated (1 h, room temperature) with fluorescein-conjugated goat anti-rat IgG (1:200 dilution). Labeling in a minimum of 5 sections/ganglia was analyzed.…”