Extravagal innervation of canine tracheal stretch receptors.

In dogs an extravagal pathway consisting of the pararecurrent nerve, the ramus anastomoticus, the internal branch of the superior laryngeal nerve, and the superior laryngeal nerve carries nerve fibres from the upper trachea. A segment of the upper trachea innervated by fibres in this pathway was isolated in situ and ventilated separately from the rest of the respiratory tract. Single unit and whole nerve neurograms recorded from the pararecurrent nerve, the ramus anastomoticus, and the interior branch of the superior laryngeal nerve demonstrated discharge patterns characteristic of airway stretch receptors. The discharge was strongly modulated by ventilatory manoeuvres of the isolated tracheal segment but not the rest of the respiratory tract. The number of tracheal stretch receptors with fibres in this non-vagal pathway was found to be similar to the number innervated by vagal pathways. A search for the presence of extravagal fibres innervating rapidly adapting receptors, however, was unsuccessful. A non-vagal pathway exists between tracheal stretch receptors and the nodose ganglion. The functional significance of this pathway was not determined.