Repetitive electroacupuncture causes prolonged increased met-enkephalin expression in the rVLM of conscious rats


      Enkephalinergic neurons in the rostral ventrolateral medulla (rVLM), an important presympathetic region in the brainstem, are activated by 30 min of low frequency (2 Hz) electroacupuncture (EA) at acupoints P5–P6, which overlie the median nerves. To more closely model the clinical application of acupuncture, we administered EA for 30 min twice over a 72 h period to unsedated conscious rats to examine its prolonged action. We hypothesized that repetitive EA would increase preproenkephalin mRNA and met-enkephalin in the rVLM of unsedated conscious rats. Rats received either EA (1–4 mA, 0.5 ms, 2 Hz) or sham stimulation (needle placement without electrical stimulation) twice at P5–P6 acupoints bilaterally. Preproenkephalin mRNA and its peptide met-enkephalin in the rVLM were measured 24 or 48 h after the final EA or sham procedure. Relative ratios of preproenkephalin mRNA levels (normalized with the 18S housekeeping gene) were almost doubled at 24 h compared to sham (6.1±0.79 vs. 3.1±0.47). Met-enkephalin measured in rVLM tissue pooled from several rats exposed to the same treatment was increased by repeated EA by 68% after 24 h and 51% after 48 h, relative to sham. These findings suggest that repeated application of EA in the conscious rats enhances transcription and translation of enkephalin in rVLM for days. Since opioids in the rVLM contribute importantly to the action of EA on sympathetic outflow, this mechanism may contribute to the prolonged action of acupuncture on elevated blood pressure in patients.


      EA (electroacupuncture), P5–P6 (Jianshi–Neiguan acupoints), rVLM (rostral ventrolateral medulla), vlPAG (ventrolateral periaqueductal gray)


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        • Almeida O.F.
        • Hassan A.H.
        • Harbuz M.S.
        • Linton E.A.
        • Lightman S.L.
        Hypothalamic corticotropin-releasing hormone and opioid peptide neurons: functional changes after adrenalectomy and/or castration.
        Brain Res. 1992; 571: 189-198
        • Andersson
        The functional background in acupuncture effects.
        Scand J Rehabil Med Suppl. 1993; 29: 31-60
        • Bloom F.
        • Battenberg E.
        • Rossier J.
        • Ling N.
        • Guillemin R.
        Neurons containing beta-endorphin in rat brain exist separately from those containing enkephalin: immunocytochemical studies.
        Proc Natl Acad Sci USA. 1978; 75: 1591-1595
        • Chao D.M.
        • Shen L.L.
        • Tjen-A-Looi S.C.
        • Pitsillides K.F.
        • Li P.
        • Longhurst J.C.
        Naloxone reverses inhibitory effect of electroacupuncture on sympathetic cardiovascular reflex responses.
        Am J Physiol. 1999; 276: H2127-H2134
        • Chiu Y.J.
        • Chi A.
        • Reid I.A.
        Cardiovascular and endocrine effects of acupuncture in hypertensive patients.
        Clin Exp Hyperten. 1997; 19: 1047-1063
        • Crisostomo M.
        • Li P.
        • Tjen-A-Looi S.C.
        • Longhurst J.C.
        Nociceptin in rVLM mediates electroacupuncture inhibition of cardiovascular reflex excitatory response in rats.
        J Appl Physiol. 2005; 98: 2056-2063
        • Eiden L.E.
        • Giraud P.
        • Affolter H.U.
        • Herbert E.
        • Hotchkiss A.J.
        Alternative modes of enkephalin biosynthesis regulation by reserpine and cyclic AMP in cultured chromaffin cells.
        Proc Natl Acad Sci USA. 1984; 81: 3949-3953
        • Flachskampf F.A.
        • Gallasch J.
        • Gefeller O.
        • Gan J.
        • Mao J.
        • Pfahlberg A.B.
        • Wortmann A.
        • Klinghammer L.
        • Pflederer W.
        • Daniel W.G.
        Randomized trial of acupuncture to lower blood pressure.
        Circulation. 2007; 115: 3121-3129
        • Guo Z.-L.
        • Longhurst J.
        Expression of c-Fos in arcuate nucleus induced by electroacupuncture: relations to neurons containing opioids and glutamate.
        Brain Res. 2007; 1166: 65-76
        • Guo Z.-L.
        • Moazzami A.R.
        • Longhurst J.C.
        Electroacupuncture induces c-Fos expression in the rostral ventrolateral medulla and periaqueductal gray in cats: relation to opioid containing neurons.
        Brain Res. 2004; 1030: 103-115
        • Guyenet P.G.
        Role of ventral medulla oblongata in blood pressure regulation.
        in: Loewy A.D. Spyer K.M. Central Regulation of Autonomic Functions. Oxford University Press, New York1990: 145-167
        • Ho F.-M.
        • Huang P.-J.
        • Lo H.-M.
        • Lee F.-K.
        • Chern T.-H.
        • Chiu T.-W.
        • Liau C.-S.
        Effect of acupuncture at Nei-Kuan on left ventricular function in patients with coronary artery disease.
        Am J Chin Med. 1999; 27: 149-156
        • Hua X.B.
        Acupuncture Manual for Small Animals. Experimental Acupuncture.
        Shanghai Science and Technology Publisher, Shanghai1994 (pp. 269–290)
        • Lantos T.A.
        • Gorcs T.J.
        • Palkovits M.
        Immunohistochemical mapping of neuropeptides in the premamillary region of the hypothalamus in rats.
        Brain Res Brain Res Rev. 1995; 20: 209-249
      1. Li, P. and Longhurst, J. C., 2007. Long-lasting inhibitory effect of EA on blood pressure in patients with mild to moderate hypertension. Soc Neurosci 37.

        • Li P.
        • Pitsillides K.F.
        • Rendig S.V.
        • Pan H.-L.
        • Longhurst J.C.
        Reversal of reflex-induced myocardial ischemia by median nerve stimulation: a feline model of electroacupuncture.
        Circulation. 1998; 97: 1186-1194
        • Li P.
        • Tjen-A-Looi S.C.
        • Longhurst J.C.
        Rostral ventrolateral medullary opioid receptor subtypes in the inhibitory effect of electroacupuncture on reflex autonomic response in cats.
        Auton Neurosci. 2001; 89: 38-47
        • Li P.
        • Ayannusi O.
        • Reed C.
        • Longhurst J.C.
        Inhibitory effect of electroacupuncture (EA) on the pressor response induced by exercise stress.
        Clin Auton Res. 2004; 14: 182-188
        • Li P.
        • Tjen-A-Looi S.C.
        • Longhurst J.C.
        Excitatory projections from arcuate nucleus to ventrolateral periaqueductal gray in electroacupuncture inhibition of cardiovascular reflexes.
        Am J Physiol. 2006; 209: H2535-H2542
        • Li P.
        • Tjen-A-Looi S.C.
        • Guo Z.L.
        • Fu L.-W.
        • Longhurst J.C.
        Long-loop pathways in cardiovascular electroacupuncture responses.
        J Appl Physiol. 2009; 106: 620-630
        • Li M.
        • Tjen A.L.S.
        • Longhurst J.C.
        Electroacupuncture enhances preproenkephalin mRNA expression in rostral ventrolateral medulla of rats.
        Neurosci Lett. 2010; 477: 61-65
        • Li M.
        • Tjen-A-Looi S.C.
        • Longhurst J.C.
        Repetitive electroacupuncture causes prolonged enhancement of preproenkephalin mRNA expression in rostral ventrolateral medulla of unanesthetized rats.
        FASEB J. 2010; 24: 809.5
        • Li P.
        • Tjen-A-Looi S.C.
        • Guo Z.L.
        • Longhurst J.C.
        An arcuate-ventrolateral periaqueductal gray reciprocal circuit participates in electroacupuncture cardiovascular inhibition.
        Auton Neurosci Basic Clin. 2010; 158: 13-23
        • Li P.
        • Tjen-A-Looi S.C.
        • Longhurst J.C.
        Nucleus raphé pallidus participates in midbrain–medullary cardiovascular sympathoinhibition during electroacupuncture.
        Am J Physiol Regul Integr Comp Physiol. 2010; 299: R1369-R1376
        • Lin M.C.
        • Nahin R.
        • Gershwin M.E.
        • Longhurst J.C.
        • Wu K.K.
        State of complementary & alternative medicine in cardiovascular, lung and blood research: executive summary of a workshop.
        Circulation. 2001; 103: 2038-2041
        • Lovick T.
        • Li P.
        Integrated function of neurones in the rostral ventrolateral medulla.
        Prog Brain Res. 1989; 81: 223-231
        • Macklin E.A.
        • Wayne P.M.
        • Kalish L.A.
        • Valaskatgis P.
        • Thompson J.
        • Pian-Smith M.C.
        • Zhang Q.
        • Stevens S.
        • Goertz C.
        • Prineas R.J.
        • Buczynski B.
        • Zusman R.M.
        Stop Hypertension with the Acupuncture Research Program (SHARP): results of a randomized, controlled clinical trial.
        Hypertension. 2006; 48: 838-845
        • Mansi J.A.
        • Laforest S.
        • Drolet G.
        Effect of stress exposure on the activation pattern of enkephalin-containing perikarya in the rat ventral medulla.
        J Neurochem. 2000; 74: 2568-2575
        • Moazzami A.
        • Tjen-A-Looi S.C.
        • Guo Z.-L.
        • Longhurst J.C.
        Serotonergic projection from nucleus raphe pallidus to rostral ventrolateral medulla modulates cardiovascular reflex responses during acupuncture.
        J Appl Physiol. 2010; 108: 1336-1346
        • Obici S.
        • Feng Z.
        • Karkanias G.
        • Baskin D.G.
        • Rossetti L.
        Decreasing hypothalamic insulin receptors causes hyperphagia and insulin resistance in rats.
        Nat Neurosci. 2002; 5: 566-572
        • Paxinos G.
        • Watson C.
        The Rat Brain in Stereotaxic Coordinates. Academic Press, 2009
        • Tjen-A-Looi S.C.
        • Li P.
        • Longhurst J.C.
        Prolonged inhibition of rostral ventral lateral medullary premotor sympathetic neuron by electroacupuncture in cats.
        Auton Neurosci. 2003; 106: 119-131
        • Tjen-A-Looi S.C.
        • Li P.
        • Longhurst J.C.
        Medullary substrate and differential cardiovascular response during stimulation of specific acupoints.
        Am J Physiol. 2004; 287: R852-R862
        • Tjen-A-Looi S.C.
        • Li P.
        • Longhurst J.C.
        Midbrain vlPAG inhibits rVLM cardiovascular sympathoexcitatory responses during acupuncture.
        Am J Physiol. 2006; 290: H2543-H2553
        • Tjen-A-Looi S.C.
        • Li P.
        • Longhurst J.C.
        Role of medullary GABA, opioids, and nociceptin in prolonged inhibition of cardiovascular sympathoexcitatory reflexes during electroacupuncture in cats.
        Am J Physiol. 2007; 293: H3627-H3635
        • Tjen-A-Looi S.C.
        • Li P.
        • Longhurst J.C.
        Processing cardiovascular information in the vlPAG during electroacupuncture in rats: roles of endocannabinoids and GABA.
        J Appl Physiol. 2009; 106: 1793-1799
        • Yao T.
        • Andersson S.
        • Thoren P.
        Long-lasting cardiovascular depression induced by acupuncture-like stimulation of the sciatic nerve in unanaesthetized spontaneously hypertensive rats.
        Brain Res. 1982; 240: 77-85
        • Yao T.
        • Andersson S.
        • Thoren P.
        Long-lasting cardiovascular depressor response following sciatic stimulation in spontaneously hypertensive rats. Evidence for the involvement of central endorphin and serotonin systems.
        Brain Res. 1982; 244: 295-303
        • Zhou W.
        • Fu L.-W.
        • Guo Z.L.
        • Longhurst J.C.
        Role of glutamate in rostral ventrolateral medulla in acupuncture-related modulation of visceral reflex sympathoexcitation.
        Am J Physiol. 2007; 292: H1868-H1875