Electroacupuncture activated pathway from caudal ventrolateral medulla to rostal ventrolateral medulla

Abstract

Our previous studies have shown that electroacupuncture (EA) at the Jianshi‐Neiguan acupoints (P5‐P6, overlying the median nerve) attenuates sympathoexcitatory responses through inhibition of neuronal activity in rostral ventrolateral medulla (rVLM). The caudal ventrolateral medulla (cVLM) modulates rVLM sympathetic nerve activity during baroreflex stimulation through a GABAergic mechanism. However, there is no information on the role of cVLM neurons in processing somatic nerve input during EA. Thus, the present study evaluated the potential for EA to activate cVLM neurons that project to the rVLM. Seven to ten days after unilateral microinjection of the retrograde tracer, rodamine‐conjugated microspheres (100 nl) into the rVLM, rats were subjected to 30 min of EA or control (needle placement without electrical stimulation) at P5‐P6 acupoints applied bilaterally. Perikarya containing the microsphere tracer were identified in the cVLM of both groups. Compared to three control animals, immunoreactivity of c‐Fos, an immediate early gene and neurons double‐labeled with c‐Fos and the tracer were more frequently found in the cVLM both rostrally and caudally (Bregma, −12.84 to −14.04 mm) in four EA‐treated rats. Neurons often colabeled with GAD67 mRNA detected with in situ hybridization and c‐Fos protein in the cVLM in two EA‐treated rats, but rarely in two controls. These results suggest that EA at P5‐P6 acupoints activates cVLM neurons, some of which are GABAergic. Furthermore, EA‐activated cVLM neurons frequently project directly to the rVLM (supported by NIH grants HL‐72125 and HL‐63313).