The alpha3 subtype of the nicotinic acetylcholine receptor is expressed in airway-related neurons of the nucleus tractus solitarius, but is not essential for reflex bronchoconstriction in ferrets.

To assess the role of nicotinic acetylcholine receptors (nACh-R) in the transmission of afferent constricting inputs from bronchopulmonary receptors to the nucleus tractus solitarius (nTS) and in the mediation of reflex airway constriction, we performed a combined immunohistological and functional study. In ferrets, the expression of nAch-R on the nTS neurons activated by histamine stimulation of airway sensory receptors was studied using laser scanning confocal microscopy to co-immunolocalize c-fos encoded protein (cFos) and nACh-R alpha3 subunit. We observed that activation of airway sensory receptors by inhalation of aerosolized histamine, induced cFos expression in a subset of nTS neurons that also expressed the nAch-R alpha3 subtype. Furthermore, activation of nACh-R within the commissural subnucleus by nicotine, increased cholinergic outflow to the airways. These effects were diminished by prior administration of hexamethonium (nACh-R blocker) within the commissural subnucleus of the nTS. However, hexamethonium had no significant effects on airway reflex constrictions induced by lung deflation. These findings indicate that nACh-R are expressed by the nTS neurons receiving inputs from airway sensory receptors, activation of which by nicotine increases cholinergic outflow to the airways, but the nACh-R pathways are not required for reflex bronchoconstriction.