Nucleus raphe pallidus participates in midbrain-medullary cardiovascular sympathoinhibition during electroacupuncture.
We have shown that electroacupuncture (EA) inhibits sympathoexcitatory rostral ventrolateral medulla (rVLM) neurons and reflex responses following activation of a long-loop pathway in the arcuate nucleus and ventrolateral periaqueductal gray (vlPAG). Additionally, EA at P 5-6 acupoints (overlying the median nerve) activates serotonin-containing neurons in the nucleus raphé pallidus (NRP), which, in turn, inhibit rVLM neurons. Although direct projections from the vlPAG to the rVLM exist, it is uncertain whether an indirect pathway through the NRP serves an important role in vlPAG-rVLM cardiovascular modulation. Therefore, the splanchnic nerve (SN) was stimulated to induce cardiovascular sympathoexcitatory reflexes, and EA was applied at P 5-6 acupoints in α-chloralose-anesthetized cats. A single-barreled recording electrode was inserted into the NRP or rVLM. Microinjection of DL-homocysteic acid (DLH) into the vlPAG increased the NRP neuronal response to SN stimulation (5 ± 1 to 12 ± 2 spikes/30 stim). Likewise, EA at P 5-6 for 30 min increased the NRP response to SN stimulation (3 ± 1 to 10 ± 2 spikes/30 stim), an effect that could be blocked by microinjection of kynurenic acid (KYN) into the caudal vlPAG. Furthermore, the reflex increase in blood pressure induced by application of bradykinin to the gallbladder and the rVLM cardiovascular presympathetic neuronal response to SN stimulation was inhibited by injection of DLH into the vlPAG, a response that was reversed by injection of KYN into the NRP. These results indicate that EA activates the vlPAG, which excites the NRP to, in turn, inhibit rVLM presympathetic neurons and reflex cardiovascular sympathoexcitatory responses.
Li
Peng
P
Susan Samueli Center for Integrative Medicine, Department of Medicine, School of Medicine, University of California, Irvine, Irvine, California 92697-4075, USA. pengli@uci.edu
Tjen-A-Looi
Stephanie C
SC
Longhurst
John C
JC
D000200:Action Potentials; D000818:Animals; D001794:Blood Pressure; D001920:Bradykinin / Q000008:administration & dosage; D002319:Cardiovascular System / Q000187:drug effects / Q000294:innervation*; D002415:Cats; D015671:Electroacupuncture; D018691:Excitatory Amino Acid Antagonists / Q000008:administration & dosage; D005260:Female; D006710:Homocysteine / Q000008:administration & dosage / Q000031:analogs & derivatives; D007736:Kynurenic Acid / Q000008:administration & dosage; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D008636:Mesencephalon / Q000187:drug effects / Q000502:physiology*; D008845:Microinjections; D009433:Neural Inhibition / Q000187:drug effects; D009434:Neural Pathways / Q000502:physiology; D011903:Raphe Nuclei / Q000187:drug effects / Q000502:physiology*; D012018:Reflex; D013153:Splanchnic Nerves / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
D018691:Excitatory Amino Acid Antagonists; D006710:Homocysteine; C007956:homocysteic acid; D007736:Kynurenic Acid; D001920:Bradykinin