The symptoms of obstructive lung diseases, which include reversible airways obstruction, airways hyperresponsiveness, chest tightness, dyspnea, mucus hypersecretion and cough, are in large part the result of an excessive and/ or inappropriate activation of the vagal afferent nerves innervating the airways and lungs. Understanding the mechanisms by which these sensory nerves are activated in health and disease and the reflexes and sensations evoked as a consequence of their activation have been longstanding goals of the research carried out in our laboratories. Studies of visceral afferent nerves in multiple organs including the airways and lung have revealed that many sensory nerve subtypes rely on specialized chemosensory signaling mechanisms at their nerve terminals to transduce mucosal irritation. We recently described a chemosensory transduction pathway originating in the airways mucosa that relies on the transmitter acetylcholine and the nicotinic subclass of acetylcholine receptors to initiate changes in breathing pattern in response to mucosal irritation. The involvement of nicotinic receptors is noteworthy, as their activity is inappropriately and excessively recruited in the airways of patients exposed to cigarette smoke or the nicotine-containing vapors of eCigarettes. The central hypothesis of this research proposal is that nicotinic receptors play essential roles in transducing reflexes initiated by subsets of vagal sensory nerves and modulate airway defensive reflexes both peripherally and centrally. We also hypothesize that the regulatory functions of nicotinic receptors are altered by chronic mucosal irritation associated with asthma and COPD, and by smoking. Studies proposed herein aim to: 1) characterize the vagal afferent nerve subtypes responsible for nicotine-induced exacerbations of obstructive lung diseases and the nicotinic receptor subtypes involved; 2a) determine the transduction mechanisms for nicotine-induced coughing and other airway defensive reflexes both at the peripheral nerve terminals and centrally at the termination sites of the neural crest C-fibers that are selectively stimulated through nicotinic receptor activation; 2b) once the mechanisms for nicotine-induced coughing are established in healthy animals, we will evaluate changes in transduction mechanisms using an allergen-induced cough hypersensitivity model; and 3) building upon our intriguing recent discovery of ?7 nicotinic receptor subtype dependent inhibition of evoked coughing through central sites of action, we will determine the CNS effects of nicotinic receptor activation on airway defensive reflexes, and how these central regulatory pathways are altered by chronic nicotine administration. For all of these studies, we will utilize techniques that are unique to our laboratories, including single cell recording and molecular approaches, reflex physiological recordings and in vivo imaging of nicotinic receptor occupancy. We anticipate that the results of these proposed studies will reveal the novel and essential roles of nicotinic receptors in transducing mucosal irritation in the airways of patients with chronic diseases of the airways and lungs.
The overall goal of the research outlined in this grant application is to better define the mechanisms by which airway mucosal irritation is transduced into airway defensive reflexes such as cough and bronchospasm. We will focus specifically on the role of the nicotinic subclass of acetylcholine receptors in these physiological processes.
