Neuropeptide neuronal efferents from the bed nucleus of the stria terminalis and central amygdaloid nucleus to the dorsal vagal complex in the rat

The lateral bed nucleus of the stria terminalis (BSTL) and central nucleus of the amygdala (Ce) are amygdaloid nuclei that have similar afferent and efferent connections within the brain. Previous studies have demonstrated that both regions send axonal projections to the dorsal vagal complex (dorsal motor nucleus and nucleus tractus solitarii). The present study used the combined retrograde fluorescence-immunofluorescence method to examine whether cells contributing to this pathway contained any of the following neuropeptides: corticotropin-releasing factor, neurotensin, somatostatin, substance P, enkephalin, or galanin. The inputs to the dorsal vagal complex originated mainly from ventral BSTL and medial Ce, although a significant number of neurons within the dorsal BSTL and lateral Ce also contributed. Corticotropin-releasing factor, neurotensin, and somatostatin neurons mainly located within the dorsal BSTL and the lateral Ce contained retrograde tracer after injections into the vagal complex. Substance P neurons in the ventral BSTL and medial Ce provide a sparse input to the dorsal vagal complex. Enkephalin and galanin neurons within the BSTL and Ce did not appear to project to the dorsal vagal complex. Corticotropin-releasing factor and neurotensin neurons within the lateral hypothalamus also project to the dorsal vagal complex. Approximately 22% of the Ce and 15% of the BSTL retrogradely labeled neurons were peptide immunoreactive. Thus, it is concluded the Ce and BSTL are sources of a significant peptidergic pathway to the dorsal vagal complex. However, it is also apparent that the majority of putative transmitter types within the amygdaloid vagal projection still are unknown. The results suggest that the dorsal and ventral BSTL and the lateral and medial Ce, respectively, are homologous zones with regard to chemoarchitecture and connections. The data is discussed considering the possible function of peptides within descending amygdaloid pathways to the brainstem.