Central connections of the motor and sensory vagal systems innervating the trachea

Cholera toxin beta-subunit was used as both a transganglionic and retrograde cell body tracer to determine respectively the central sensory and motor systems innervating the trachea in three mammalian species, dog, ferret and rat. A basic pattern was found in all three animals. Sensory fibers terminated in three subnuclei of the nucleus tractus solitarius (NTS) with the densest concentration localized in a restricted part of the medial part of the rostral NTS. Weaker projections were identified in the ventrolateral NTS subnucleus and sparse labeling was seen in the commissural NTS subnucleus. No labeling was identified in the area postrema. The pattern of retrograde cell-body labeling was also similar in all three species. Two main sites were labeled: the rostralmost part of the dorsal vagal nucleus and the rostral nucleus ambiguus (NA). In the NA, cell labeling was found in mainly in the ventral (or external) portion of the nucleus, but some labeled neurons were consistently found in the compact NA as well. In addition, labeled neurons were also seen in the dorsomedial part of the C1-C2 ventral horn. In summary, the central sites of termination of the sensory fibers and cells of origin innervating the trachea were similar in all three species.