Bed nucleus of the stria terminalis: Cytoarchitecture, immunohistochemistry, and projection to the parabrachial nucleus in the rat

The bed nucleus of the stria terminalis (BST) sends a dense projection to the parabrachial nucleus (PB) in the pons. The BST contains many different types of neuropeptidelike immunoreactive cells and fibers, each of which exhibits its own characteristic distribution within cytoarchitecturally distinct BST subnuclei. Corticotropin releasing factor (CRF)‐, neurotensin (NT)‐, somatostatin (SS)‐, and enkephalin (ENK)‐like immunoreactive (ir) neurons are particularly numerous within areas of the BST that project to the PB. In this study, we use the combined retrograde fluorescence‐immunofluorescence method to determine whether neurons in the BST that project to the PB contain these immunoreactivities. After Fast Blue injections into PB, retrogradely labeled neurons were numerous throughout the lateral part of the BST, particularly in the dorsal lateral (DL) and posterior lateral subnuclei. Retrogradely labeled neurons were also present in the preoptic, ventral lateral, and supracapsular BST subnuclei and in the parastrial nucleus. Many of the CRF‐ir, NT‐ir, and SS‐ir neurons in DL were retrogradely labeled. A few double‐labeled cells of each type were also found in the posterior lateral, ventral lateral and supracapsular BST subnuclei ENK‐ir neurons were never retrogradely labeled. Our results show that BST neurons that project to the PB stain for the same neuropeptides as those in the central nucleus of the amygdala (CeA) that project to the PB, demonstrating further the close anatomical relations between these two structures.