Morphology and electrophysiology of guinea‐pig paratracheal neurones

Background Although guinea‐pig tracheal preparations are used as models of asthma, the morphological and electrophysiological characteristics of its associated ganglion neurones (paratracheal neurones) have not been characterized. Methods Intracellular staining and electrophysiological recording techniques have been applied to guinea‐pig paratracheal neurones in isolated preparations. Results Most (32/35) neurones were multipolar, with many short (<70 μm), finely tapering processes and one or more long processes; the latter, which were traced for up to 400 μm, 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 associated with recurrent or vagal nerve trunks. Two types of neurone were identified electrophysiologically; neurones with fast excitatory synaptic potentials were found only in ganglia located very close to the smooth muscle, whereas <90% of neurones lacking synaptic inputs were associated with recurrent nerve trunks. Transmural or focal electrical stimulation failed to evoke either slow inhibitory or slow excitatory (cholinergic or non‐cholinergic) synaptic potentials in either electrophysiological type. Conclusions It is tentatively concluded that the neurones of the intrinsic ganglionated plexus receiving synaptic input probably provided the parasymathetic innervation to effector cells (such as trachealis muscle). Both these and the spiking neurones located in or near nerve trunks showed little potential for synaptic modulation of their excitability. Anat. Rec. 247:261–270, 1997. © 1997 Wiley‐Liss, Inc.