The central amygdaloid nucleus innervation of the dorsal vagal complex in rat: a Phaseolus vulgaris leucoagglutinin lectin anterograde tracing study.

The central nucleus of amygdala (Ce) participates in expression of autonomic responses associated with fear or stress-related behaviors. The Ce can alter autonomic activity through its direct projection to the dorsal vagal complex [i.e., nucleus of the solitary tract (nTS) and the dorsal vagal nucleus]. In order to more precisely define the anatomical organization of the neurons within the Ce and their terminal fields within the dorsal vagal complex, the Phaseolus vulgaris leucoagglutinin lectin (PHA-L) anterograde tracing method was employed in rats. In cases where injections of PHA-L were centered within the medial Ce, dense axon terminal labeling was observed within the medial nTS at rostral levels. Terminal boutons were also observed within the ventral part of the lateral nTS, the dorsal vagal nucleus and contralateral medial nTS. At and just rostral to the obex, numerous axonal boutons were seen within the medial and commissural parts of the nTS and adjacent parts of the dorsal vagal nucleus. Contralateral axon terminal labeling was present within the medial and commissural parts of the nTS. Caudal to the obex, PHA-L immunoreactive boutons were concentrated bilaterally within the medial and commissural nTS and dorsal vagal nucleus. In cases where injections of PHA-L were centered within the lateral Ce moderate axon terminal labeling was observed throughout the rostrocaudal extent of the medial and commissural part of the nTS. Very few PHA-L immunoreactive terminals were observed within the ventral part of the lateral nTS, dorsal vagal nucleus and contralateral medial nTS. The results demonstrate that the medial Ce projects bilaterally to the medial and commissural subnuclei of the nTS and the dorsal vagal nucleus. The lateral Ce projects mainly to the ipsilateral medial and commissural nTS. Thus, both the medial and lateral Ce can directly influence regions of the nTS where peripheral cardiovascular, cardiopulmonary and gastric afferents terminate. The medial Ce can also directly affect vagal nerve outflow through its projection to neurons within the dorsal motor nucleus.