Projections of the lateral hypothalamus and bed nucleus of the stria terminalis to the dorsal vagal complex in the pigeon

Abstract

The dorsal vagal complex is composed of the nucleus tractus solitarii (Nts) and the dorsal motor nucleus of the vagus (DMN X). In the pigeon, these nuclei are composed of cytoarchitectonically well-defined subnuclear groups, which have connections that are partially segregated to specific organs (Katz and Karten: J. Comp. Neurol. 218:42-73, '83b, J. Comp. Neurol. 242:397-414, '85). The present study sought to determine whether forebrain afferents to Nts-DMN X are differentially distributed to specific subnuclei and thereby modulate the functions of specific organs. Forebrain afferents to the dorsal vagal complex were determined by retrograde tracing techniques. Labeled perikarya were found in the bed nucleus of the stria terminalis (BNST), ventral paleostriatum, and stratum cellulare externum (SCE) of the lateral hypothalamus, and in the medial hypothalamus, nucleus periventricularis magnocellularis (PVM), which is the avian homologue to a portion of the mammalian paraventricular nucleus. The pattern of axonal distribution to Nts-DMN X subnuclei from the BNST-ventral paleostriatum and SCE were investigated by anterograde tracing techniques. These experiments revealed axonal projections distributed to specific Nts-DMN X subnuclei. However, there is a high degree of overlap of the axonal projections to Nts-DMN X subnuclei from BNST-ventral paleostriatum and SCE, as well as from PVM (Berk and Finkelstein: J. Comp. Neurol. 220:127-136, '83). Labeled fibers from BNST-ventral paleostriatum and SCE project heavily to Nts subnuclei medialis superficialis, lateralis dorsalis, and medialis ventralis and to DMN X subnucleus ventralis parvicellularis. Fewer labeled fibers were found in Nts subnucleus medialis intermedius and extremely sparse labeling was found in Nts subnucleus medialis dorsalis. The Nts and DMN X subnuclei that receive forebrain projections also have peripheral connections with the aortic nerve, crop, esophagus, glandular stomach, and caudal abdominal organs. Thus, the forebrain could modulate the functions of these segments of the cardiovascular and digestive systems.