The overall goals of this proposal are to establish the mechanisms of parasympathetic and nonadrenergic noncholinergic (NANC) neural control of bronchoconstriction and to determine the extent to which alterations in the neural control are responsible for bronchial hyperresponsiveness in an established model of asthma. We hypothesize that (1) subtypes of muscarinic and neuropeptide receptors play important roles in neural regulation of airway smooth muscle tone, (2) airway parasympathetic ganglia function as integrative centers in which muscarinic receptors play a role to regulate airway smooth muscle tone, (3) mediators released during the allergic response induce alterations in neurotransmission through airway ganglia or in postsynaptic neurons either by direct action or indirectly by release of tachykinins from afferent C-fibers, and (4) alterations in neurotransmission produce the bronchial hyperresponsiveness of asthma. The normal rabbit, an IgE-producing rabbit model of bronchial hyperresponsiveness, and postmortem human tissues will be utilized in these studies. Neurotransmission in airway parasympathetic ganglia will be characterized at the tissue level by using an in vitro vagus nerve-bronchial ring preparation. In this preparation, ganglionic neurotransmission will be characterized by comparing the effects of field stimulation and vagal stimulation on the contractile response of bronchial muscle in the presence and absence of selected muscarinic agonists and antagonists. Functional studies also will be performed to establish the involvement of muscarinic receptor subtypes at the parasympathetic nerve-smooth muscle junctions in the airways. Location of the muscarinic receptor subtypes on the various cell types present in the lung will be determined by in situ hybridization techniques to demonstrate the presence of mRNA for each of the subtypes of muscarinic receptors. Once muscarinic receptor subtypes have been identified and functionally characterized in normal rabbit tissues, tissues from the hyperresponsive rabbits will be examined for evidence of differences from normal animals. The inhibitory NANC response will be characterized in rabbit airways and examined for alterations in hyperresponsive rabbits. Tachykinin receptor types will be localized using receptor-ligand autoradiography and in situ hybridization techniques as well as functionally characterized in vitro in tissue bath. Comparison of differences between normal and sensitized tissues in respect to in vivo alterations in neuronal function will be determined. Finally, the capacity of allergic and inflammatory mediators, released as a result of allergen- IgE interaction, to alter cholinergic regulation will be characterized, and the mechanisms by which these mediators affect neural regulation will be defined. Completion of these aims should further define the interaction of cholinergic and NANC mechanisms in the airways and establish the role of neural mechanisms in this bronchially hyperresponsive model of human asthma.
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