The Effects of Nerve Growth Factor on Nicotinic Synaptic Transmission in Mouse Airway Parasympathetic Neurons

In autonomic ganglia, acetylcholine (ACh) is released from preganglionic nerve terminals and binds to nicotinic ACh receptors (nAChRs) on postganglionic neurons, resulting in a brief, short-lived synaptic potential (fast excitatory postsynaptic potential [fEPSP]). Although nerve growth factor (NGF) is known to affect sensory and sympathetic nerves, especially during development, little is known regarding its effect on parasympathetic nerves, especially on adult neurons. Elevated levels of NGF and NGF-mediated neural plasticity may have a role in airway diseases, such as asthma and chronic obstructive pulmonary disease. In this study, we characterize the composition and response of nAChRs in parasympathetic neurons located in lower airways of mice, and note the effects of NGF on fEPSPs and on nicotinic currents. Based on immunohistochemical staining, nAChRs are made up of alpha-3 and beta-4 subunits; in addition, tropomyosin-related kinase A, the receptor for NGF, is also expressed by the neurons. Vagus nerve evoked fEPSPs and inward currents evoked by a nicotinic receptor agonist (1,1-dimethyl-4-phenylpiperazinium) were increased by NGF. NGF also affected the action potential after hyperpolarization. These studies were done in mice, which are routinely used to study airway diseases, such as asthma, where the allergen-induced contraction of airway smooth muscle has a well-defined parasympathetic cholinergic component.