Morphological and quantitative study of the intrinsic nerve plexuses of the canine trachea as revealed by immunohistochemical staining of protein gene product 9.5.

BACKGROUND

The ganglionated nervous plexuses in the trachea play an important role in the regulation of respiration. Although the tracheal tissue of the dog has frequently been used in physiological and pharmacological studies, little is known about the morphology of the intrinsic nervous plexuses in the dog trachea and quantitative data about the ganglia and nerve cell bodies are lacking. The structure of the nervous plexuses and detailed morphometric data about the intrinsic neurons of the dog have not previously been reported.

METHODS

The structure of the intrinsic nerves in the dog trachea was examined by a combination method of digestion with KOH and immunohistochemical attaining of protein gene product 9.5. In addition, areas of nerve cell profiles, numbers of nerve cell bodies per ganglion and densities of nerve cell bodies per ganglion were estimated in preparations from five dogs.

RESULTS

In the dog trachea, the peritracheal plexus, outer submucosal plexus, inner submucosal plexus, and mucosal plexus were identified from adventitia to epithelium in that order. The peritracheal plexus, situated in the lamina adventitia of the trachea, consisted of thick nerve bundles that were densely distributed in the membranous wall. The peritracheal plexus contained ganglia with round or oval nerve cell bodies. In the trachealis muscle, the intramuscular plexus, which was a well-developed, three-dimensional nervous network, was observed. It did not include ganglia and consisted of inter- and intrafascicular networks. The outer submucosal plexus was observed as small clusters in the inside of the trachealis muscle. A few round nerve cells were observed in the outer submucosal plexus as small clusters. The ganglionated inner submucosal plexus was identified in the superficial layer of the submucosal layer. A finer meshwork, namely, the mucosal plexus, was observed in the lamina propria. Among the entire length of the trachea, we counted 2,134-2,873 ganglia (average, 2,389) and 13,902-24,232 nerve cell bodies (average,18,461) were counted in the peritracheal plexuses of five dogs. The densities of ganglia and nerve cell bodies were high near the carina and low near the thoracic inlet. The number of nerve cell bodies per ganglion was estimated as 6.5-8.8 (average, 7.7). The average maximum area of nerve cell profiles was 522 +/- 223 microm2.

CONCLUSIONS

The structure of the tracheal plexuses in the dog is more complex than those in other smaller animals. The constitution of the plexuses seems to be that of the intestine. The numerous nerve cells in the peritracheal plexus in the adventitia can be expected to play important roles in airway regulation and in the pathogenesis of tracheal collapse.