Central projections of the nodose ganglion and the origin of vagal efferents in the lamb.

Injections of WGA-HRP and CTB-HRP were made into the cervical vagus or the nodose ganglion in a series of lambs, in order to define the sensory projections and motor origins of the vagus nerve. Injections into the nodose ganglion were much more successful than injections into the cervical vagus in effecting the desired result. The former produced labelling of both descending and ascending components of the solitary tract (TS). The descending component terminated massively in all ipsilateral and certain contralateral subnuclei of the nucleus of the solitary tract (nTS) and in the upper cervical spinal cord. Patchy terminations were also observed within the interpolated subnucleus of the nucleus of the spinal trigeminal tract, and within Lamina I of the upper cervical cord. The ascending component of TS terminated in rostral regions of the nTS, and in specific portions of the principal sensory trigeminal nucleus and the lateral parabrachial and Kölliker-Fuse nuclei. The motor origins of the vagus nerve arose almost completely ipsilaterally in the dorsal motor nucleus of the vagus, the nucleus ambiguus, and the caudal portion of the nucleus retroambiguus situated in the lateral part of the intermediate grey at upper cervical spinal levels. Labelled neurons in the nucleus dorsomedialis of the upper spinal cord were thought not to project their axons into the cervical vagus.