Anatomical and functional mapping of vagal nociceptive sensory nerve subsets innervating the mouse lower airways by intersectional genetics

Abstract

Most vagal sensory afferents innervating the lower airways are activated by noxious stimuli including irritants (e.g. TRPV1 agonist capsaicin) and inflammatory mediators, causing nociceptive cardiorespiratory reflexes (e.g. cough, bronchospasm, changes in respiratory drive and heart rate). Vagal ganglia are comprised of embryologically distinct nodose and jugular neurons, but little is known of their specific contribution to nociceptive reflexes. Using a novel TRPV1Flp mouse in combination with P2X2Cre, Tac1Cre, intersectional reporter mice and AAV we mapped and modulated distinct nociceptive afferents. TRPV1+P2X2+ neurons were found exclusively in the nodose ganglion and were activated by {beta}mATP and capsaicin but rarely expressed Tac1. TRPV1+P2X2+ fibers innervated the lungs (many projected into the alveoli) but not the trachea. Centrally they innervated the nucleus tractus solitarius (nTS). >90% of TRPV1+Tac1+ neurons were found in the jugular ganglion and were activated by capsaicin but not {beta}mATP. TRPV1+Tac1+ fibers innervated the lungs (although none projected into the alveoli) and the trachea submucosa. They terminated solely in the paratrigeminal complex (Pa5). Many TRPV1-Tac1+ neurons were found in both nodose and jugular ganglia that innervated the trachea and large pulmonary airways. These projected to both nTS and Pa5. Using intersectional chemogenetics we selectively stimulated lower airway afferent subsets using intravenous injections of clozapine-N-oxide (CNO). Activation of TRPV1+, TRPV1+P2X2+ or TRPV1+Tac1+ fibers evoked bradycardia and bradypnea. Activation of Tac1+ fibers evoked tachycardia and tachypnea. Activation of vagal TRPV1-Tac1+ neurons only evoked tachycardia. These data show the distinct innervation patterns and reflex function of multiple nociceptive vagal afferent subsets.