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Long-loop pathways in cardiovascular electroacupuncture responses

Department of Medicine and Susan-Samueli Center for Integrative Medicine, School of Medicine, University of California, Irvine, California

Submitted 23 September 2008 ; accepted in final form 9 December 2008

We have shown that electroacupuncture (EA) at P 5–6 (overlying median nerves) activates arcuate (ARC) neurons, which excite the ventrolateral periaqueductal gray (vlPAG) and inhibit cardiovascular sympathoexcitatory neurons in the rostral ventrolateral medulla (rVLM). To investigate whether the ARC inhibits rVLM activity directly or indirectly, we stimulated the splanchnic nerve to activate rVLM neurons. Micropipettes were inserted in the rVLM, vlPAG, and ARC for neural recording or injection. Microinjection of kainic acid (KA; 1 mM, 50 nl) in the ARC blocked EA inhibition of the splanchnic nerve stimulation-induced reflex increases in rVLM neuronal activity. Microinjection of D,L-homocysteic acid (4 nM, 50 nl) in the ARC, like EA, inhibited reflex increases in the rVLM neuronal discharge. The vlPAG neurons receive convergent input from the ARC, splanchnic nerve, P 5–6, and other acupoints. Microinjection of KA bilaterally into the rostral vlPAG partially reversed rVLM neuronal responses and cardiovascular inhibition during D,L-homocysteic acid stimulation of the ARC. On the other hand, injection of KA into the caudal vlPAG completely reversed these responses. We also observed that ARC neurons could be antidromically activated by stimulating the rVLM, and that ARC perikarya was labeled with retrograde tracer that had been microinjected into the rVLM. These neurons frequently contained β-endorphin and c-Fos, activated by EA stimulation. Therefore, the vlPAG, particularly, the caudal vlPAG, is required for ARC inhibition of rVLM neuronal activation and subsequent EA-related cardiovascular activation. Direct projections from the ARC to the rVLM, which serve as an important source of β-endorphin, appear also to exist.

arcuate nucleus; ventrolateral periaqueductal gray; rostral ventrolateral medulla; D,L-homocysteic acid; kainic acid

This article has been cited by other articles:

				S. C. Tjen-A-Looi, P. Li, and J. C. Longhurst Processing cardiovascular information in the vlPAG during electroacupuncture in rats: roles of endocannabinoids and GABA J Appl Physiol, June 1, 2009; 106(6): 1793 - 1799. [Abstract] [Full Text] [PDF]

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