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Nitric Oxide Inhibits Nociceptive Transmission by Differentially Regulating Glutamate and Glycine Release to Spinal Dorsal Horn Neurons

  • Xiao-Gao Jin
    Affiliations
    Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030
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  • 金小高
  • Shao-Rui Chen
    Affiliations
    Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030
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  • 陈少瑞
  • Xue-Hong Cao
    Affiliations
    Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030
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  • 曹雪红
  • Li Li
    Affiliations
    Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030
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  • 李莉
  • Hui-Lin Pan
    Correspondence
    To whom correspondence should be addressed: Department of Anesthesiology and Perioperative Medicine, Unit 110, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030-4009. Tel.: 713-563-0822; Fax: 713-794-4590;
    Affiliations
    Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030

    Programs in Neuroscience and Experimental Therapeutics, The University of Texas Graduate School of Biomedical Sciences, Houston, Texas 77225
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  • 潘惠麟
Open AccessPublished:August 03, 2011DOI:https://doi.org/10.1074/jbc.M111.270967
      Nitric oxide (NO) is involved in many physiological functions, but its role in pain signaling remains uncertain. Surprisingly, little is known about how endogenous NO affects excitatory and inhibitory synaptic transmission at the spinal level. Here we determined how NO affects excitatory and inhibitory synaptic inputs to dorsal horn neurons using whole-cell recordings in rat spinal cord slices. The NO precursor l-arginine or the NO donor SNAP significantly increased the frequency of glycinergic spontaneous and miniature inhibitory postsynaptic currents (IPSCs) of lamina II neurons. However, neither l-arginine nor SNAP had any effect on GABAergic IPSCs. l-arginine and SNAP significantly reduced the amplitude of monosynaptic excitatory postsynaptic currents (EPSCs) evoked from the dorsal root with an increase in paired-pulse ratio. Inhibition of the soluble guanylyl cyclase abolished the effect of l-arginine on glycinergic IPSCs but not on evoked monosynaptic EPSCs. Also, inhibition of protein kinase G blocked the increase in glycinergic sIPSCs by the cGMP analog 8-bromo-cGMP. The inhibitory effects of l-arginine on evoked EPSCs and high voltage-activated Ca2+ channels expressed in HEK293 cells and dorsal root ganglion neurons were abolished by blocking the S-nitrosylation reaction with N-ethylmaleimide. Intrathecal injection of l-arginine and SNAP significantly increased mechanical nociceptive thresholds. Our findings suggest that spinal endogenous NO enhances inhibitory glycinergic input to dorsal horn neurons through sGC-cGMP-protein kinase G. Furthermore, NO reduces glutamate release from primary afferent terminals through S-nitrosylation of voltage-activated Ca2+ channels. Both of these actions probably contribute to inhibition of nociceptive transmission by NO at the spinal level.

      Introduction

      Nitric oxide (NO) is freely diffusible across the cell membranes and is synthesized by the nitric-oxide synthase (NOS)
      The abbreviations used are: NOS
      nitric-oxide synthase
      sIPSCs
      spontaneous inhibitory postsynaptic currents
      mIPSCs
      miniature inhibitory postsynaptic currents
      EPSCs
      excitatory postsynaptic currents
      mEPSCs
      miniature inhibitory postsynaptic currents
      sEPSCs
      spontaneous excitatory postsynaptic currents
      CNQX
      6-cyano-7-nitroquinoxaline-2,3-dione
      DRG
      dorsal root ganglion
      nNOS
      neuronal nitric-oxide synthase
      HVACCs
      high voltage-activated calcium channels
      ODQ
      1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one
      sGC
      soluble guanylyl cyclase
      SNAP
      S-nitroso-N-acetylpenicillamine
      TRIM
      1,2-trifluoromethylphenyl imidazole
      VACCs
      voltage-activated calcium channels
      TTX
      tetrodotoxin.
      from l-arginine and different cofactors. The three NOS isoforms, including neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), have distinct structures and functions (
      • Stuehr D.J.
      ,
      • Lipton S.A.
      • Singel D.J.
      • Stamler J.S.
      ). The diverse effects of NO is commonly mediated through increased cGMP production upon activation of NO-sensitive soluble guanylyl cyclase (sGC), S-nitrosylation, tyrosine nitration, and the interaction with superoxide to form peroxynitrite (
      • Rudkouskaya A.
      • Sim V.
      • Shah A.A.
      • Feustel P.J.
      • Jourd'heuil D.
      • Mongin A.A.
      ,
      • Feil R.
      • Hartmann J.
      • Luo C.
      • Wolfsgruber W.
      • Schilling K.
      • Feil S.
      • Barski J.J.
      • Meyer M.
      • Konnerth A.
      • De Zeeuw C.I.
      • Hofmann F.
      ,
      • Gow A.J.
      • Farkouh C.R.
      • Munson D.A.
      • Posencheg M.A.
      • Ischiropoulos H.
      ). The spinal dorsal horn is a critical site for nociceptive transmission and modulation. Although both nNOS and sGC are present in the superficial dorsal horn (
      • Guan Y.
      • Yaster M.
      • Raja S.N.
      • Tao Y.X.
      ,
      • Ding J.D.
      • Weinberg R.J.
      ,
      • Terenghi G.
      • Riveros-Moreno V.
      • Hudson L.D.
      • Ibrahim N.B.
      • Polak J.M.
      ), their functions in the control of synaptic transmission in the spinal dorsal horn remain unknown.
      The precise role of NO in nociceptive transmission at the spinal level is still controversial. Some studies suggest that spinal NO is involved in the potentiation of nociception. For example, mechanical hypersensitivity induced by nerve injury or tissue inflammation is reduced by intrathecal administration of nNOS inhibitors and in nNOS-knock-out mice (
      • Guan Y.
      • Yaster M.
      • Raja S.N.
      • Tao Y.X.
      ,
      • Tanabe M.
      • Nagatani Y.
      • Saitoh K.
      • Takasu K.
      • Ono H.
      ,
      • Chu Y.C.
      • Guan Y.
      • Skinner J.
      • Raja S.N.
      • Johns R.A.
      • Tao Y.X.
      ). Also, sGC-knock-out mice show reduced nociceptive responses to tissue inflammation or nerve injury, but their responses to acute pain are not affected (
      • Schmidtko A.
      • Gao W.
      • König P.
      • Heine S.
      • Motterlini R.
      • Ruth P.
      • Schlossmann J.
      • Koesling D.
      • Niederberger E.
      • Tegeder I.
      • Friebe A.
      • Geisslinger G.
      ). In contrast, other studies have shown that spinal NO plays a role in the inhibition of nociceptive processing. In this regard, intrathecal administration of l-arginine increases the mechanical nociceptive withdrawal threshold in rats (
      • Zhuo M.
      • Meller S.T.
      • Gebhart G.F.
      ). Furthermore, spinally administered NO donors predominantly reduce the firing activity of spinal dorsal horn neurons and inhibition of spinal NOS or sGC increases the activity of nociceptive dorsal horn neurons (
      • Pehl U.
      • Schmid H.A.
      ,
      • Hoheisel U.
      • Unger T.
      • Mense S.
      ,
      • Hoheisel U.
      • Unger T.
      • Mense S.
      ). The discrepancy regarding the complex function of NO in nociceptive processing may result from the use of different animal models of pain and the levels of NO produced at the spinal level in different studies. For instance, it has been shown that intrathecal injection of low doses of l-arginine or NO donors reduce nociception, but l-arginine or NO donors at the high doses potentiates nociceptive responses to formalin injection or nerve injury (
      • Li K.
      • Qi W.X.
      ,
      • Sousa A.M.
      • Prado W.A.
      ). In addition, it should be noted that in eNOS-, nNOS-, or iNOS-knock-out mice, an increase in the expression of other NOS isoforms in the spinal cord has been reported (
      • Boettger M.K.
      • Uceyler N.
      • Zelenka M.
      • Schmitt A.
      • Reif A.
      • Chen Y.
      • Sommer C.
      ,
      • Tao F.
      • Tao Y.X.
      • Mao P.
      • Zhao C.
      • Li D.
      • Liaw W.J.
      • Raja S.N.
      • Johns R.A.
      ). This compensatory up-regulation of other NOS subtypes in specific NOS isoform-knock-out mice further confounds the interpretation of the results. Strikingly, little is known about how endogenous NO affects excitatory and inhibitory synaptic input to spinal dorsal horn neurons.
      Therefore, in the present study, we determined the role of NO in the control of glutamatergic excitatory and GABAergic and glycinergic inhibitory synaptic input to spinal dorsal horn neurons. We also investigated the downstream signaling mechanisms involved in NO actions on spinal synaptic transmission. Our results indicate that NO enhances inhibitory glycinergic input to dorsal horn neurons through sGC-cGMP-protein kinase G signaling. Furthermore, NO attenuates glutamate release from primary afferent terminals through S-nitrosylation of high voltage-activated Ca2+ channels (HVACCs). Our findings provide new insights into the underlying cellular and signaling mechanisms of NO in the inhibition of nociceptive transmission at the spinal level.

      DISCUSSION

      In this study, we determined systemically the role of endogenous NO in the regulation of excitatory and inhibitory synaptic transmission in the spinal dorsal horn. Previous studies using various nociceptive tests in animal models suggest that NO is either pronociceptive or antinociceptive (
      • Tanabe M.
      • Nagatani Y.
      • Saitoh K.
      • Takasu K.
      • Ono H.
      ,
      • Chu Y.C.
      • Guan Y.
      • Skinner J.
      • Raja S.N.
      • Johns R.A.
      • Tao Y.X.
      ,
      • Zhuo M.
      • Meller S.T.
      • Gebhart G.F.
      ,
      • Li K.
      • Qi W.X.
      ,
      • Sousa A.M.
      • Prado W.A.
      ). The discrepancy may result from the use of different pain models, the amount of NO produced locally, and the specific CNS sites involved. For example, NO-cGMP inhibits dorsal horn neuronal activity at the spinal level but excites spinal dorsal horn neurons at the supraspinal level (
      • Hoheisel U.
      • Unger T.
      • Mense S.
      ,
      • Hoheisel U.
      • Sander B.
      • Mense S.
      ). Also, while low concentrations of NO inhibit NMDA receptor activity (
      • Manzoni O.
      • Prezeau L.
      • Marin P.
      • Deshager S.
      • Bockaert J.
      • Fagni L.
      ,
      • Nicholson R.
      • Spanswick D.
      • Lee K.
      ), high concentrations of NO stimulate TRPV1 and TRPA1 receptors (
      • Miyamoto T.
      • Dubin A.E.
      • Petrus M.J.
      • Patapoutian A.
      ). Yet, little is known about how endogenous NO regulates excitatory and inhibitory synaptic transmission at the spinal level. GABA and glycine are the two predominant inhibitory neurotransmitters in the spinal cord. Blocking GABAA or glycine receptors in the spinal cord induces pain hypersensitivity in rats (
      • Yaksh T.L.
      ,
      • Sorkin L.S.
      • Puig S.
      • Jones D.L.
      ). In the present study, we found that both the NO precursor l-arginine and the NO donor SNAP significantly increased the frequency of glycinergic sIPSCs and mIPSCs in the majority of lamina II neurons. The effects of l-arginine and SNAP on glycinergic sIPSCs were blocked by the nNOS inhibitor TRIM and the NO scavenger carboxy-PTIO, respectively. Of note, l-arginine and SNAP had similar effects on glycinergic sIPSCs and mIPSCs, suggesting that NO can potentiate glycine release from presynaptic terminals of interneurons in the spinal dorsal horn. Thus, our findings indicate that NO potentiates glycinergic input to spinal dorsal horn neurons to attenuate nociceptive transmission.
      Immunocytochemical labeling shows that NOS-positive terminals in lamina II are largely GABA immunoreactive in rats (
      • Valtschanoff J.G.
      • Weinberg R.J.
      • Rustioni A.
      • Schmidt H.H.
      ), and nNOS is present in 14% GAD67-positive neurons in the spinal dorsal horn of mice (
      • Heinke B.
      • Ruscheweyh R.
      • Forsthuber L.
      • Wunderbaldinger G.
      • Sandkühler J.
      ,
      • Bernardi P.S.
      • Valtschanoff J.G.
      • Weinberg R.J.
      • Schmidt H.H.
      • Rustioni A.
      ). Although these reports suggest that NO may be produced by some GABAergic interneurons and terminals in the spinal cord, we obtained no evidence showing that NO is involved in the control of synaptic GABA release to dorsal horn neurons. We found that neither l-arginine nor SNAP had any significant effect on GABAergic sIPSCs in all lamina II neurons tested in our study. It has been reported that GABA- and glycine-like immunoreactivities are often colocalized in the spinal dorsal horn (
      • Todd A.J.
      ,
      • Todd A.J.
      • Sullivan A.C.
      ). However, functional studies have failed to substantiate the hypothesis that GABA and glycine are co-released from the same synaptic terminal in the superficial dorsal horn. This is because direct paired recordings of dorsal horn neurons show that the IPSCs evoked from a single presynaptic terminal are mediated by either GABAA or glycine receptors but not by both (
      • Lu Y.
      • Perl E.R.
      ,
      • Santos S.F.
      • Rebelo S.
      • Derkach V.A.
      • Safronov B.V.
      ). Furthermore, we have shown that muscarinic receptor subtypes and group II and III metabotropic glutamate receptors are involved in the differential control of GABAergic and glycinergic input to dorsal horn neurons (
      • Zhang H.M.
      • Li D.P.
      • Chen S.R.
      • Pan H.L.
      ,
      • Wang X.L.
      • Zhang H.M.
      • Li D.P.
      • Chen S.R.
      • Pan H.L.
      ,
      • Zhou H.Y.
      • Zhang H.M.
      • Chen S.R.
      • Pan H.L.
      ,
      • Zhou H.Y.
      • Chen S.R.
      • Chen H.
      • Pan H.L.
      ,
      • Zhou H.Y.
      • Chen S.R.
      • Chen H.
      • Pan H.L.
      ). Of note, it has been shown that NO regulates synaptic glycine, but not GABA, release to sympathetic preganglionic neurons in the lateral spinal cord (
      • Wu S.Y.
      • Dun N.J.
      ).
      Glutamate is an excitatory neurotransmitter critically involved in nociceptive transmission in the spinal dorsal horn. In this study, we found that l-arginine and SNAP significantly inhibited the frequency of glutamatergic sEPSCs of lamina II neurons. l-Arginine and SNAP also consistently inhibited glutamatergic EPSCs evoked from primary afferents in most lamina II neurons. The inhibitory effects of l-arginine and SNAP on evoked monosynaptic EPSCs were blocked by TRIM and carboxy-PTIO, respectively. Because the inhibitory effect of l-arginine on evoked EPSCs is associated with an increase in the paired-pulse ratio, our data suggest that NO acts on the presynaptic site to inhibit glutamate release from primary afferents. Consistent with this notion, we found that l-arginine and SNAP significantly inhibited HVACC currents in dissociated DRG neurons. HVACCs are inhibited in the presence of TTX, which can explain why NO failed to affect mEPSCs. In addition, we observed that the glycine receptor antagonist strychnine had no effect on inhibition of evoked EPSCs by l-arginine. Thus, it is unlikely that the inhibitory effect of NO on synaptic glutamate release to dorsal horn neurons is secondary to increased glycine release and stimulation of presynaptic glycine receptors (
      • Lee E.A.
      • Cho J.H.
      • Choi I.S.
      • Nakamura M.
      • Park H.M.
      • Lee J.J.
      • Lee M.G.
      • Choi B.J.
      • Jang I.S.
      ). Our findings strongly suggest that NO attenuates synaptic glutamate release by inhibition of HVACCs at primary afferent terminals.
      Another salient finding of our study is that NO potentiates glycinergic input and inhibits glutamatergic synaptic transmission in the spinal dorsal horn through distinct signaling pathways. We found that the specific sGC inhibitor ODQ abolished the potentiating effect of l-arginine on the frequency of glycinergic sIPSCs, and the membrane-permeable cGMP analog 8-bromo-cGMP mimicked the potentiating effect of NO on glycinergic sIPSCs. In addition, we found that inhibition of the protein kinase G activity with Rp-8-Br-PET-cGMPS abolished the increase in the frequency of glycinergic IPSCs by 8-bromo-cGMP, suggesting that protein kinase G is a downstream mechanism involved in the synaptic release of glycine by an increase in NO and sGC activity in the spinal cord. Currently, little is know about the protein kinase G substrates and synaptic vesicle proteins phosphorylated by protein kinase G at the nerve terminals, which needs to be addressed in future studies. Our study provides novel evidence that NO stimulates glycinergic interneurons in the dorsal horn through sGC-cGMP-protein kinase G signaling. sGC is present in some interneurons in the spinal dorsal horn (
      • Ding J.D.
      • Weinberg R.J.
      ). Whereas nNOS rarely colocalizes with sGC, nNOS-positive structures are often apposed to sGC-positive structures (
      • Ding J.D.
      • Weinberg R.J.
      ), which suggests that endogenous NO that increases sGC activity and glycine release may be produced in adjacent neurons. Our electrophysiological data indicate that sGC is present only in a subpopulation of glycinergic neurons and terminals in the spinal dorsal horn.
      In contrast, we found that sGC-cGMP signaling is not involved in the regulation of glutamate release by NO in the spinal dorsal horn. We observed that ODQ did not alter the inhibitory effect of l-arginine on evoked glutamatergic EPSCs. Also, 8-bromo-cGMP had no effect on monosynaptic EPSCs of dorsal horn neurons evoked by primary afferent stimulation. The lack of a role of sGC-cGMP in the inhibitory effect of NO on glutamate release from primary afferents could be due to the fact that sGC is not expressed in DRG neurons (
      • Schmidtko A.
      • Gao W.
      • König P.
      • Heine S.
      • Motterlini R.
      • Ruth P.
      • Schlossmann J.
      • Koesling D.
      • Niederberger E.
      • Tegeder I.
      • Friebe A.
      • Geisslinger G.
      ) and the primary afferent terminals in the superficial dorsal horn (
      • Ding J.D.
      • Weinberg R.J.
      ). NO can inhibit HVACCs in cardiomyocytes through S-nitrosylation (
      • Sun J.
      • Picht E.
      • Ginsburg K.S.
      • Bers D.M.
      • Steenbergen C.
      • Murphy E.
      ). We observed that NO inhibited evoked EPSCs and sEPSCs but had no effect on mEPSCs, suggesting that HVACCs on the primary afferent terminals may be the target of S-nitrosylation by NO. NEM covalently modifies sulfhydryl groups and prevents S-nitrosylation (
      • Bolotina V.M.
      • Najibi S.
      • Palacino J.J.
      • Pagano P.J.
      • Cohen R.A.
      ,
      • Broillet M.C.
      • Firestein S.
      ). We found that NEM abolished the inhibitory effects of l-arginine on evoked EPSCs of lamina II neurons and HVACC currents in DRG neurons. Additionally, NEM completely blocked the inhibitory effect of SNAP on N-type HVACCs expressed in G1A1 cells, thus providing further direct evidence that NO inhibits HVACCs through S-nitrosylation. NEM has been reported to be capable of inactivating inhibitory G proteins (
      • Ueda H.
      • Misawa H.
      • Katada T.
      • Ui M.
      • Takagi H.
      • Satoh M.
      ,
      • Winslow J.W.
      • Bradley J.D.
      • Smith J.A.
      • Neer E.J.
      ). Removal of tonic G protein inhibition of HVACCs (
      • Jeong S.W.
      • Ikeda S.R.
      ,
      • Ikeda S.R.
      ) could explain why NEM alone increased the amplitude of evoked EPSCs of lamina II neurons and HVACC currents in DRG neurons observed in our study. Because NEM alone had no effect on HVACC currents in G1A1 cells, it suggests that NEM does not affect HVACCs directly. Therefore, our findings suggest that spinal NO primarily inhibits glutamate release through S-nitrosylation of HVACCs at primary afferent terminals.
      In addition to its inhibitory effect on HVACCs shown in our study, NO can inhibit NMDA receptor currents in recombinant systems (
      • Lei S.Z.
      • Pan Z.H.
      • Aggarwal S.K.
      • Chen H.S.
      • Hartman J.
      • Sucher N.J.
      • Lipton S.A.
      ,
      • Aizenman E.
      • Potthoff W.K.
      ) and in spinal lamina II neurons (
      • Nicholson R.
      • Spanswick D.
      • Lee K.
      ). Because both HVACCs and NMDA receptors are critically involved in nociceptive transmission, it seems difficult to explain the proposed pronociceptive role of NO at the spinal level. Of note, systemic use of NO or NO donors has been shown to reduce pain intensity caused by sickle cell crisis or diabetic neuropathy in patients (
      • Head C.A.
      • Swerdlow P.
      • McDade W.A.
      • Joshi R.M.
      • Ikuta T.
      • Cooper M.L.
      • Eckman J.R.
      ,
      • Yuen K.C.
      • Baker N.R.
      • Rayman G.
      ). We found in the present study that intrathecal administration of l-arginine or SNAP in rats significantly increased the nociceptive mechanical thresholds. Pretreatment with intrathecal TRIM and carboxy-PTIO blocked the antinociceptive effect of l-arginine and SNAP, respectively. In the central nervous system, nNOS is located at the postsynaptic density and is closely linked to NMDA receptors (
      • Christopherson K.S.
      • Hillier B.J.
      • Lim W.A.
      • Bredt D.S.
      ,
      • Valtschanoff J.G.
      • Weinberg R.J.
      ). Hence, NMDA receptor activation could lead to increased NO production and release, and NO can diffuse to the presynaptic site to reduce glutamate release from primary afferent terminals. By reducing glutamatergic transmission, NO could serve as a feedback regulator to attenuate nociceptive transmission at the spinal level during painful conditions. We found that SNAP consistently increased the frequency of glycinergic sIPSCs and reduced the amplitude of evoked EPSCs of dorsal horn neurons in a concentration-dependent manner. These data suggest that the pro- and antinociceptive effects of NO are less likely dependent on different NO concentrations at the spinal level.
      In summary, our study provides important new evidence that spinal NO potentiates inhibitory glycinergic input but reduces glutamatergic synaptic transmission between primary afferents and dorsal horn neurons through distinct signaling mechanisms. The opposing effects of NO on glutamatergic and glycinergic synaptic transmission could contribute to the antinociceptive effect of NO at the spinal level. This new information is important for our understanding of the synaptic actions underlying the antinociceptive effect of NO at the spinal level.

      Acknowledgments

      We thank Dr. Heidi Hamm (Vanderbilt University) for providing G1A1 cells used for this study.

      REFERENCES

        • Stuehr D.J.
        Annu. Rev. Pharmacol. Toxicol. 1997; 37: 339-359
        • Lipton S.A.
        • Singel D.J.
        • Stamler J.S.
        Prog. Brain Res. 1994; 103: 359-364
        • Rudkouskaya A.
        • Sim V.
        • Shah A.A.
        • Feustel P.J.
        • Jourd'heuil D.
        • Mongin A.A.
        Free Radic. Biol. Med. 2010; 49: 757-769
        • Feil R.
        • Hartmann J.
        • Luo C.
        • Wolfsgruber W.
        • Schilling K.
        • Feil S.
        • Barski J.J.
        • Meyer M.
        • Konnerth A.
        • De Zeeuw C.I.
        • Hofmann F.
        J. Cell Biol. 2003; 163: 295-302
        • Gow A.J.
        • Farkouh C.R.
        • Munson D.A.
        • Posencheg M.A.
        • Ischiropoulos H.
        Am. J. Physiol. Lung Cell Mol. Physiol. 2004; 287: L262-268
        • Guan Y.
        • Yaster M.
        • Raja S.N.
        • Tao Y.X.
        Mol. Pain. 2007; 3: 29
        • Ding J.D.
        • Weinberg R.J.
        J. Comp. Neurol. 2006; 495: 668-678
        • Terenghi G.
        • Riveros-Moreno V.
        • Hudson L.D.
        • Ibrahim N.B.
        • Polak J.M.
        J. Neurolog Sci. 1993; 118: 34-37
        • Tanabe M.
        • Nagatani Y.
        • Saitoh K.
        • Takasu K.
        • Ono H.
        Neuropharmacology. 2009; 56: 702-708
        • Chu Y.C.
        • Guan Y.
        • Skinner J.
        • Raja S.N.
        • Johns R.A.
        • Tao Y.X.
        Pain. 2005; 119: 113-123
        • Schmidtko A.
        • Gao W.
        • König P.
        • Heine S.
        • Motterlini R.
        • Ruth P.
        • Schlossmann J.
        • Koesling D.
        • Niederberger E.
        • Tegeder I.
        • Friebe A.
        • Geisslinger G.
        J. Neurosci. 2008; 28: 8568-8576
        • Zhuo M.
        • Meller S.T.
        • Gebhart G.F.
        Pain. 1993; 54: 71-78
        • Pehl U.
        • Schmid H.A.
        Neuroscience. 1997; 77: 563-573
        • Hoheisel U.
        • Unger T.
        • Mense S.
        Pain. 2005; 117: 358-367
        • Hoheisel U.
        • Unger T.
        • Mense S.
        Pain. 2000; 88: 249-257
        • Li K.
        • Qi W.X.
        Neurosci. Bull. 2010; 26: 211-218
        • Sousa A.M.
        • Prado W.A.
        Brain Res. 2001; 897: 9-19
        • Boettger M.K.
        • Uceyler N.
        • Zelenka M.
        • Schmitt A.
        • Reif A.
        • Chen Y.
        • Sommer C.
        Eur. J. Pain. 2007; 11: 810-818
        • Tao F.
        • Tao Y.X.
        • Mao P.
        • Zhao C.
        • Li D.
        • Liaw W.J.
        • Raja S.N.
        • Johns R.A.
        Neuroscience. 2003; 120: 847-854
        • Pan Y.Z.
        • Pan H.L.
        J. Neurophysiol. 2004; 91: 2413-2421
        • Zhou H.Y.
        • Chen S.R.
        • Chen H.
        • Pan H.L.
        J. Neurosci. 2010; 30: 4460-4466
        • Li D.P.
        • Chen S.R.
        • Pan Y.Z.
        • Levey A.I.
        • Pan H.L.
        J. Physiol. 2002; 543: 807-818
        • Wu Z.Z.
        • Pan H.L.
        Neurosci. Lett. 2004; 368: 96-101
        • Wu Z.Z.
        • Chen S.R.
        • Pan H.L.
        J. Biol. Chem. 2005; 280: 18142-18151
        • Chen S.R.
        • Pan H.L.
        Anesthesiology. 2003; 98: 217-222
        • Handy R.L.
        • Harb H.L.
        • Wallace P.
        • Gaffen Z.
        • Whitehead K.J.
        • Moore P.K.
        Br J. Pharmacol. 1996; 119: 423-431
        • Akaike T.
        • Yoshida M.
        • Miyamoto Y.
        • Sato K.
        • Kohno M.
        • Sasamoto K.
        • Miyazaki K.
        • Ueda S.
        • Maeda H.
        Biochemistry. 1993; 32: 827-832
        • Heinke B.
        • Ruscheweyh R.
        • Forsthuber L.
        • Wunderbaldinger G.
        • Sandkühler J.
        J. Physiol. 2004; 560: 249-266
        • Valtschanoff J.G.
        • Weinberg R.J.
        • Rustioni A.
        • Schmidt H.H.
        Neurosci. Lett. 1992; 148: 6-10
        • Zhao Y.
        • Brandish P.E.
        • DiValentin M.
        • Schelvis J.P.
        • Babcock G.T.
        • Marletta M.A.
        Biochemistry. 2000; 39: 10848-10854
        • Li D.P.
        • Chen S.R.
        • Pan H.L.
        J. Neurophysiol. 2002; 88: 2664-2674
        • Sekhar K.R.
        • Hatchett R.J.
        • Shabb J.B.
        • Wolfe L.
        • Francis S.H.
        • Wells J.N.
        • Jastorff B.
        • Butt E.
        • Chakinala M.M.
        • Corbin J.D.
        Mol. Pharmacol. 1992; 42: 103-108
        • Butt E.
        • Pöhler D.
        • Genieser H.G.
        • Huggins J.P.
        • Bucher B.
        Br J. Pharmacol. 1995; 116: 3110-3116
        • Jeong H.J.
        • Jang I.S.
        • Moorhouse A.J.
        • Akaike N.
        J. Physiol. 2003; 550: 373-383
        • Lee E.A.
        • Cho J.H.
        • Choi I.S.
        • Nakamura M.
        • Park H.M.
        • Lee J.J.
        • Lee M.G.
        • Choi B.J.
        • Jang I.S.
        J. Neurochem. 2009; 109: 275-286
        • Bolotina V.M.
        • Najibi S.
        • Palacino J.J.
        • Pagano P.J.
        • Cohen R.A.
        Nature. 1994; 368: 850-853
        • Broillet M.C.
        • Firestein S.
        Neuron. 1996; 16: 377-385
        • McDavid S.
        • Currie K.P.
        J. Neurosci. 2006; 26: 13373-13383
        • Hoheisel U.
        • Sander B.
        • Mense S.
        Neurosci. Lett. 1995; 188: 143-146
        • Manzoni O.
        • Prezeau L.
        • Marin P.
        • Deshager S.
        • Bockaert J.
        • Fagni L.
        Neuron. 1992; 8: 653-662
        • Nicholson R.
        • Spanswick D.
        • Lee K.
        Neurosci. Lett. 2004; 359: 180-184
        • Miyamoto T.
        • Dubin A.E.
        • Petrus M.J.
        • Patapoutian A.
        PLoS One. 2009; 4: e7596
        • Yaksh T.L.
        Pain. 1989; 37: 111-123
        • Sorkin L.S.
        • Puig S.
        • Jones D.L.
        Pain. 1998; 77: 181-190
        • Bernardi P.S.
        • Valtschanoff J.G.
        • Weinberg R.J.
        • Schmidt H.H.
        • Rustioni A.
        J. Neurosci. 1995; 15: 1363-1371
        • Todd A.J.
        Eur. J. Neurosci. 1996; 8: 2492-2498
        • Todd A.J.
        • Sullivan A.C.
        J. Comp. Neurol. 1990; 296: 496-505
        • Lu Y.
        • Perl E.R.
        J. Neurosci. 2003; 23: 8752-8758
        • Santos S.F.
        • Rebelo S.
        • Derkach V.A.
        • Safronov B.V.
        J. Physiol. 2007; 581: 241-254
        • Zhang H.M.
        • Li D.P.
        • Chen S.R.
        • Pan H.L.
        J. Pharmacol Exp. Ther. 2005; 313: 697-704
        • Wang X.L.
        • Zhang H.M.
        • Li D.P.
        • Chen S.R.
        • Pan H.L.
        J. Physiol. 2006; 571: 403-413
        • Zhou H.Y.
        • Zhang H.M.
        • Chen S.R.
        • Pan H.L.
        J. Neurophysiol. 2007; 97: 871-882
        • Zhou H.Y.
        • Chen S.R.
        • Chen H.
        • Pan H.L.
        J. Pharmacol Exp. Ther. 2008; 327: 375-382
        • Zhou H.Y.
        • Chen S.R.
        • Chen H.
        • Pan H.L.
        J. Pharmacol Exp. Ther. 2011; 336: 254-264
        • Wu S.Y.
        • Dun N.J.
        J. Physiol. 1996; 495: 479-490
        • Ueda H.
        • Misawa H.
        • Katada T.
        • Ui M.
        • Takagi H.
        • Satoh M.
        J. Neurochem. 1990; 54: 841-848
        • Winslow J.W.
        • Bradley J.D.
        • Smith J.A.
        • Neer E.J.
        J. Biol. Chem. 1987; 262: 4501-4507
        • Jeong S.W.
        • Ikeda S.R.
        Neuron. 1998; 21: 1201-1212
        • Ikeda S.R.
        Nature. 1996; 380: 255-258
        • Lei S.Z.
        • Pan Z.H.
        • Aggarwal S.K.
        • Chen H.S.
        • Hartman J.
        • Sucher N.J.
        • Lipton S.A.
        Neuron. 1992; 8: 1087-1099
        • Aizenman E.
        • Potthoff W.K.
        Br. J. Pharmacol. 1999; 126: 296-300
        • Head C.A.
        • Swerdlow P.
        • McDade W.A.
        • Joshi R.M.
        • Ikuta T.
        • Cooper M.L.
        • Eckman J.R.
        Am. J. Hematol. 2010; 85: 800-802
        • Yuen K.C.
        • Baker N.R.
        • Rayman G.
        Diabetes Care. 2002; 25: 1699-1703
        • Christopherson K.S.
        • Hillier B.J.
        • Lim W.A.
        • Bredt D.S.
        J. Biol. Chem. 1999; 274: 27467-27473
        • Valtschanoff J.G.
        • Weinberg R.J.
        J. Neurosci. 2001; 21: 1211-1217
        • Sun J.
        • Picht E.
        • Ginsburg K.S.
        • Bers D.M.
        • Steenbergen C.
        • Murphy E.
        Circ. Res. 2006; 98: 403-411