The integrative membrane properties of human bronchial parasympathetic ganglia neurons

Parasympathetic ganglia neurons in the lower airway of laboratory animals have membrane properties associated with integration of signals from the central nervous system. In this study, intracellular recordings were made from parasympathetic ganglia located on bronchi from human lungs in order to determine the level of integration provided by human neurons. Ganglion neurons were characterized as either tonic or phasic: tonic neurons responded with repetitive action potentials sustained throughout a depolarizing current step whereas phasic neurons generated one action potential and accommodated. Phasic neurons could be further differentiated as having either short or long duration afterhyperpolarizing potentials following single action potentials. In phasic neurons, stimulation of preganglionic nerves elicited one or two populations of nicotinic fast excitatory postsynaptic potentials (fEPSPs) that were graded in amplitude, subthreshold for action potential generation, and decreased in amplitude during higher frequency stimulation. In tonic neurons, single preganglionic stimuli evoked two to five populations of fEPSPs, one to three of which were at threshold for action potential generation. Dye injection into the neurons revealed multiple, branching dendrites. These results provide evidence that human bronchial ganglion neurons have unique membrane properties and anatomical characteristics associated with integrating presynaptic stimuli. Changes in these properties may thus affect output from these ganglia and, consequently, autonomic tone in the lower airways.