Direct reciprocal connections between the bed nucleus of the stria terminalis and dorsomedial medulla oblongata: evidence from immunohistochemical detection of tracer proteins.

Connections between the bed nucleus of the stria terminalis and the dorsomedial medulla oblongata have been examined by immunohistochemical detection of the tracer proteins horseradish peroxidase (HRP) or wheat germ agglutinin (WGA). Two sets of four rats received 0.2 or 0.4 microliter of either tracer injected into the dorsomedial medulla oblongata, were fixed by perfusion 48 hours later, and were processed for immunohistochemical detection of the tracers. Rats receiving HRP showed only a few single neurons retrogradely labelled in the ipsilateral bed nucleus, and some anterogradely labelled fibers. Rats receiving WGA showed a large number of retrogradely labelled neurons in the ipsilateral bed nucleus. Labelled neurons were most concentrated in a group in the central, dorsal, and lateral aspects of the nucleus at the level of the anterior commissure and just caudal to this. Just ventral to this group was a dense cluster of anterogradely labelled fibers. The retrogradely labelled neurons ranged from 12 to 20 microns in size and were multipolar. These findings indicate that there are direct reciprocal connections between the bed nucleus of the stria terminalis and the autonomic centers of the dorsomedial medulla oblongata and strengthen the concept that this nucleus is involved in forebrain integration of autonomic functions.