The alpha 3 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 tra nsmission of afferent constricting inputs from bronchopulmonary receptors t o the nucleus tractus solitarius (nTS) and in the mediation of reflex airwa y constriction, we performed a combined immunohistological and functional s tudy. In ferrets, the expression of nAch-R on the nTS neurons activated by histamine stimulation of airway sensory receptors was studied using laser s canning confocal microscopy to co-immunolocalize c-fos encoded protein (cFo s) and nACh-R alpha 3 subunit. We observed that activation of airway sensor y receptors by inhalation of aerosolized histamine, induced cFos expression in a subset of nTS neurons that also expressed the nAch-R a3 subtype. Furt hermore, activation of nACh-R within the commissural subnucleus by nicotine , increased cholinergic outflow to the airways. These effects were diminish ed by prior administration of hexamethonium (nACh-R blocker) within the com missural subnucleus of the nTS. However, hexamethonium had no significant e ffects on airway reflex constrictions induced by lung deflation. These find ings indicate that nACh-R are expressed by the nTS neurons receiving inputs from airway sensory receptors, activation of which by nicotine increases c holinergic outflow to the airways, but the nACh-R pathways are not required for reflex bronchoconstriction. (C) 2000 Published by Elsevier Science Ire land Ltd.