Nucleus Raphe Pallidus in EA inhibition of rostral ventrolateral medulla and cardiovascular excitatory responses

Abstract

EA at P5‐6 acupoints (median nerve) excites the arcuate nucleus and ventrolateral periaqueductal gray (vlPAG), and inhibits sympathetic cardiovascular rostral ventrolateral medulla (rVLM) neurons and associated reflex responses. The present study investigated the role of the NRP in EA inhibition of rVLM neurons and whether EA and activity from the vlPAG to the rVLM passes through the NRP. In [alpha]‐chloralose anesthetized cats the splanchnic nerve (SN) was stimulated to induce cardiovascular sympathoexcitatory reflexes and EA was applied at P 5‐6 acupoints. A recording electrode was inserted into the NRP or rVLM. Microinjection of dl‐homocysteic acid (DLH), but not normal saline (NS), into vlPAG increased the NRP neuronal response to SN stimulation (5±1 to 12±1 spikes/30 stim). EA at P 5‐6 for 30 min increased the NRP response to SN stimulation (5±1 to 14±3 spikes/30 stim). EA excitation of the NRP response was blocked by microinjection of kynurenic acid (KYN) into the caudal vlPAG. Furthermore, the reflex increase in BP induced by application of bradykinin on gallbladder and the rVLM neuronal response to SN stimulation was inhibited (~58%) by injection of DLH into the vlPAG, a response that could be blocked by injection of KYN into the NRP. Thus, EA activates the arcuate and vlPAG, which excites the NRP and, in turn, inhibits the rVLM activity and sympathoexcitatory cardiovascular reflex responses. (HL‐63313)