ANATOMICAL EVIDENCE FOR A BI-NEURONAL PATHWAY CONNECTING THE NUCLEUS-TRACTUS-SOLITARIUS TO CAUDAL VENTROLATERAL MEDULLA TO ROSTRAL VENTROLATERAL MEDULLA IN THE RAT

Using tract tracing techniques and dual-color histochemistry, this stu dy investigated connections between the nucleus tractus solitarius (NT S), caudal ventrolateral medulla (CVLM), and rostral ventrolateral med ulla (RVLM) in the rat. The anterograde tracer biotinylated dextran am ine (BDA) was deposited into the NTS. The retrograde tracer Fluoro-Gol d was deposited into the RVLM. In the CVLM, Fluoro-Gold-labeled cells were found intermingled with anterogradely labeled fibers coursing fro m the NTS. BDA-labeled axons, varicosities, and boutons were observed in close apposition to retrogradely labeled neurons in the CVLM. These data provide anatomical evidence for a bi-neuronal pathway from NTS t o CVLM to RVLM; and support the hypothesis that these connections may comprise the medullary baroreceptor reflex pathway.