MORPHOLOGY AND ELECTROPHYSIOLOGY OF GUINEA-PIG PARATRACHEAL NEURONS

Background: Although guinea-pig tracheal preparations are used as mode ls of asthma, the morphological and electrophysiological characteristi cs of its associated ganglion neurones (paratracheal neurones) have no t been characterized. Methods: Intracellular staining and electrophysi ological recording techniques have been applied to guinea-pig paratrac heal neurones in isolated preparations. Results: Most (32/35) neurones were multipolar, with many short (<70 mu m), finely tapering processe s and one or more long processes; the latter, which were traced for up to 400 mu m, travelled along the interconnecting nerve trunks, often in pairs, or over smooth muscle bundles, About 20% (6/32) of neurones had conspicuous somal extensions that gave rise to 3-8 processes, The soma morphology of neurones of the intrinsic ganglionated plexus close to the trachealis muscle were usually more complex than those in or a ssociated with recurrent or vagal nerve trunks. Two types of neurone w ere identified electrophysiologically; neurones with fast excitatory s ynaptic potentials were found only in ganglia located very close to th e smooth muscle, whereas >90% of neurones lacking synaptic inputs were associated with recurrent nerve trunks, Transmural or focal electrica l stimulation failed to evoke either slow inhibitory or slow excitator y (cholinergic or non-cholinergic) synaptic potentials in either elect rophysiological type. Conclusions: It is tentatively concluded that th e neurones of the intrinsic ganglionated plexus receiving synaptic inp ut probably provided the parasympathetic innervation to effector cells (such as trachealis muscle), Both these and the spiking neurones loca ted in or near nerve trunks showed little potential for synaptic modul ation of their excitability. (C) 1997 Wiley-Liss, Inc.