Morphological features of spiking and nonspiking cells in the paratracheal ganglion of the ferret

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Abstract
The present series of experiments was designed to study details of the morphology and connectivity of functionally identified cells located in the paratracheal ganglia of the ferret. The morphology of 11 spiking (AH cells) and seven nonspiking (type B cells) ganglion cells was examined. Intraaxonally injected horseradish peroxidase (HRP) was used as the label. Each spiking and nonspiking cell was identified by intracellular recording prior to the HRP injection. “Whole mount preparations” were processed for HRP histochemistry with diaminobenzidine as the chromogen. HRP-labeled cell bodies of both the spiking AH and nonspiking type B neurons demonstrated similar morphological features. Both types of ganglion cells showed (1) axons arising from a small, ill-defined axon hillock which exited from the cell as single or multiple branches of equal diameter and coursed unidirectionally through the interganglionic nerve trunk to an adjacent ganglion; (2) short, fine, tapering processes (presumptive dendrites) in the immediate vicinity of the injected cell; and (3) processes extending out of the ganglion cell perpendicular to the interganglionic nerve trunk which could be followed into the smooth muscle. Extraperikaryal injections of HRP into a ganglion retrogradely labeled perikarya in the adjacent ganglia. These results demonstrate that in airway ganglia the morphology of spiking and nonspiking neurons is remarkably similar despite electrophysiological differences. In addition it appears that ganglion cells project to adjacent ganglia and to smooth muscle by means of independent axonal processes. These morphological features of the ganglion cells in airways and the trajectories of their axons correspond to known features of their physiology: i.e., (1) the axon of a ganglion cell travels unidirectionally toward the adjacent ganglion and arborizes there, providing anatomical evidence of communication between ganglia via the interganglionic nerve trunk; and (2) the spiking and nonspiking neurons possess similar morphological features that are typical of ganglion cells described in other systems, such as in the myenteric plexus.