- Open Access
Expression changes of microRNA-1 and its targets Connexin 43 and brain-derived neurotrophic factor in the peripheral nervous system of chronic neuropathic rats
- Elena Neumann†1,
- Henning Hermanns†2,
- Franziska Barthel1,
- Robert Werdehausen1 and
- Timo Brandenburger1Email author
© Neumann et al. 2015
- Received: 11 May 2015
- Accepted: 18 June 2015
- Published: 26 June 2015
MicroRNAs (miRNAs) are involved in the neuroplastic changes which induce and maintain neuropathic pain. However, it is unknown whether nerve injury leads to altered miRNA expression and modulation of pain relevant target gene expression within peripheral nerves. In the present study, expression profiles of miR-1 and the pain-relevant targets, brain derived neurotrophic factor (BDNF) and Connexin 43 (Cx43), were studied in peripheral neuropathic pain, which was induced by chronic constriction injury (CCI) of the sciatic nerve in rats. The expression of miR-1 was investigated in the sciatic nerve, dorsal root ganglion (DRG) and the ipsilateral spinal cord by qPCR. Changes of BDNF and Cx43 expression patterns were studied using qPCR, Western blot analysis, ELISA and immunohistochemistry.
In sciatic nerves of naïve rats, expression levels of miR-1 were more than twice as high as in DRG and spinal cord. In neuropathic rats, CCI lead to a time-dependent downregulation of miR-1 in the sciatic nerve but not in DRG and spinal cord. Likewise, protein expression of the miR-1 targets BDNF and Cx43 was upregulated in the sciatic nerve and DRG after CCI. Immunohistochemical staining revealed an endoneural abundancy of Cx43 in injured sciatic nerves which was absent after Sham operation.
This study demonstrates that CCI leads to a regulation of miRNAs (miR-1) in the peripheral nervous system. This regulation is associated with alterations in the expression and localization of the miR-1 dependent pain-relevant proteins BDNF and Cx43. Further studies will have to explore the function of miRNAs in the context of neuropathic pain in the peripheral nervous system.
- Connexin 43 (Cx43)
- Neuropathic pain
- Chronic constriction injury (CCI)
Neuropathic pain is caused by a lesion or disease of the somatosensory system involving alterations in the peripheral and the central nervous system . The exact molecular mechanisms of neuropathic pain are incompletely understood and elucidation of these mechanisms is crucial for the development of new mechanism-oriented treatment strategies . Neuroplastic changes in the peripheral and central nervous system, particularly alterations in protein expression in the pain processing neuronal network play a key role in the development of pathological pain .
MicroRNAs (miRNAs) are small non-coding RNAs which negatively regulate gene expression at the post-transcriptional level and have significant impact on numerous physiological and pathophysiological cellular processes . MiRNA-targeting molecules are considered as possible future therapeutics for a variety of human diseases . The fact that more than 60% of all human protein-coding genes are putative targets of miRNAs  suggests that miRNAs are correspondingly involved in the expression changes in chronic pain states. Increasing evidence suggests a significant role of non-coding RNAs, especially miRNAs, in the pathophysiology and potential treatment options of chronic pain . A possible role of miRNAs in the development of chronic pain has to date been investigated in dorsal root ganglia, the spinal cord or in supraspinal organs . One of the miRNAs being involved in neuropathic pain is miR-1. This miRNA has been shown to be involved in the induction of neuropathic pain . Additionally, miR-1 interacts with the two highly pain-relevant proteins Cx43 and BDNF [10, 11]. It is well known that a multitude of neuroplastic alterations also occur in the peripheral nerve . Furthermore, miRNAs are well abundantly expressed in the peripheral nerve, e.g. in Schwann cells but also in dendrites and axons, where they have been shown to be significantly regulated in response to peripheral nerve injury .
However, to date there is not data exploring the expression of miRNAs and pain relevant miRNA-target proteins in the context of neuropathic pain in peripheral nerves.
In this study we show that miR-1 is well expressed in sciatic nerves of rats. Furthermore we show that constriction injury of the sciatic nerve leads to a time dependent downregulation of miR-1 in injured nerves. This is accompanied by an upregulated protein expression of Connexin 43 (Cx43) and brain derived neurotrophic factor (BDNF) which are well established miR-1 targets.
Development of neuropathic pain in rats
Expression of miR-1 and Cx43 and BDNF messenger RNA
In DRG, Cx43 mRNA expression remained unchanged 4, 24 h and 12 days post CCI. Six days after nerve ligation, the expression of Cx43 mRNA was reduced to 0.7-fold vs. Sham (p < 0.05). BDNF mRNA was upregulated in CCI DRG after 24 h (1.5-fold vs. Sham, p = 0.002), 6 days (1.84-fold vs. Sham, p = 0.018) and 12 days (1.58-fold vs. Sham, p = 0.007) post surgery.
Protein expression of the miR-1 targets Cx43 and BDNF
Immunofluorescence staining of Cx43
To date, treatment of neuropathic pain remains challenging and often insufficient . Elucidating the exact molecular mechanisms underlying neuropathic pain is an important prerequisite for developing more specific and more efficient treatment strategies . In the last few years, the involvement of miRNAs in neuropathic pain has been investigated. MiRNAs are involved in the development of the nervous system, neural plasticity and the genesis of neuronal diseases . In 2009, Aldrich et al. showed for the first time a downregulation of miR-96, -182 and -183 in DRG of rats in the context of neuropathic pain . Since then, numerous studies concerning the role of miRNAs in experimental neuropathic pain have been published [17–19]. Several studies have furthermore shown that the application of miRNAs or its antagonists has an antinociceptive effect in various animal models. These include miR-103 , miR-124 , miR-23b  and miR-7a . Beyond that, a role of extracellular miRNAs in pain signalling via direct activation and excitation of nociceptor neurons has been proposed recently . Hence, the potential for miRNAs as biomarkers or therapeutics in chronic pain is now being discussed extensively [7, 8, 24–28]. The role of miRNAs in the peripheral nerve in the context of neuropathic pain has however not been explored, although it is well known that massive protein expression changes accompany nerve damage . In general, the contribution of miRNAs to the regulation of gene expression in peripheral nerves is well recognized, especially in the context of regenerative processes . Viader et al.  identified 87 miRNAs in the sciatic nerve of mice, including mir-1, most of which were downregulated upon peripheral nerve injury. Since Schwann cells represent the vast majority of cells in the sciatic nerve, the authors concluded that the detected miRNAs primarily represent the microRNAome of these glia cells. Yet, a few studies also demonstrated the abundance of numerous mature miRNAs in axons , whereby the functional significance in axonal mRNA translation remains to be elucidated.
In the present study we could demonstrate that miR-1 is expressed in the sciatic nerve of rats. Its expression level was found to be higher in sciatic nerve than in DRG or spinal cord. Furthermore, as a consequence of CCI leading to mechanical allodynia, we found miR-1 to be time-dependently downregulated in the sciatic nerve at the site of the constriction, whereas expression in the ipsilateral DRG and spinal cord remained unchanged. BDNF, a previously established target of mir-1  was significantly upregulated in the sciatic nerve and DRG. Similarly, connexin-43, another established miR-1 target  was upregulated in peripheral nerves and DRG.
Kusuda and co-workers  investigated the expression of mir-1 in the DRG and spinal cord in different experimental models of acute and chronic pain. After partial sciatic nerve ligation, a model of neuropathic pain, miR-1 was time-dependently down-regulated in the DRG. Expression of miR-1 in acute, inflammatory pain, as well as axotomy revealed time- and stimulus-dependent changes in expression patterns which underline the complexity of expression changes in different pain states.
Our results obtained in the spinal cord are in line with those described by Kusuda et al. In contrast, we found no changes of miR-1 expression in the DRG, which might result from the differences in species or surrogate model of neuropathic pain.
The fact that BDNF is upregulated in Schwann cells of peripheral nerves as response to neuronal damage is long known , as is the contribution of Schwann cell-mediated responses to nerve injury in neuropathic pain . Also the effect of BDNF as an ubiquitous pain mediator in the nervous system is sufficiently documented, although its action in the peripheral system is less extensively investigated . These results are in line with our observation that mRNA of BDNF is absent in Sham sciatic nerves, while it is detectable in injured nerves, most likely as a consequence of expression by Schwann cells.
The expression of BDNF in our study could at least in part be explained by an upregulation in DRG neurons independently of miRNAs. However, the dysregulation of miR-1 expression in injured nerves could at least in part be involved in the expression of Cx43 in nerves. Interestingly, Cx43 is highly upregulated in the endoneural region of nerves where it might contribute to an increased electrochemical coupling of cells contributing to the induction and/or maintenance of pain. Cx43 is the major connexin of astrocytes . A recent study by Chen et al. showed that the upregulation of spinal Cx43 contributes to the maintenance of neuropathic pain by chemokine release. Moreover, inhibition of Cx43 by intrathecal injection of GAP27, a selective Cx43-blocker, effectively reduced mechanical allodynia in CCI mice . To the best of our knowledge, the present study is the first to show a marked upregulation of Cx43 within the endoneurium of injured nerves which might—besides a transcriptional activation of Cx43 expression—in part be explained by a downregulation of miR-1. This differential regulation of miR-1 in the peripheral nerve, most likely in Schwann cells, might contribute to hypersensitivity following nerve damage. However, also the transcriptional activation of Cx43 mRNA might contribute to the protein changes observed in nerves after CCI and further studies are needed to clarify the impact of the miR-1 dysregulation in nerves.
In summary, our findings suggest an involvement of regulated miR-1 in the peripheral nerve in neuropathic pain. If these findings are confirmed in future studies, a local therapy with compounds regulating miR-1 or other relevant miRNAs could be a theoretical approach for the treatment of neuropathic pain. Ultimately, future research on the involvement of miRNAs in the development of neuropathic pain should also consider the contribution of miRNAs in the peripheral nervous system.
The study was conducted with male Wistar rats (weight 300–350 g, 10–12 weeks old) after approval of the local animal care and use committee (LANUV). Neuropathic pain was induced by the chronic constriction injury (CCI) model  as described previously . Sham-operated animals served as controls. The development of mechanical allodynia was assessed with modified von Frey hairs (Plantar Aesthesiometer, Ugo Basile Inc., Comerio, Italy) before initial surgery and at every time point before tissue extraction. The withdrawal threshold as response to mechanical stimulation was registered. At the end of the experiment, the left sciatic nerve (1 cm including the site of the ligations), lumbar DRG (L4–L6) and the ipsilateral spinal cord (L4–L6) were extracted 4, 24 h, 6 and 12 days after CCI or Sham operation and immediately frozen in liquid nitrogen (n = 6 each).
Total RNA of sciatic nerve, DRG and spinal cord tissue was isolated using Trizol reagent (Invitrogen, Carlsbad, USA) according to the manufacturer’s protocol. RNA quantity was determined by UV spectrophotometry (Nanodrop 1000, Thermo Scientific, Waltham, MA, USA) and RNA integrity was verified by Agilent microfluid chips using an Agilent 2100 Bioanalyzer (Agilent, Santa Clara, CA, USA). Only RNA with a RNA integrity number (RIN) higher than 8 was included in the study.
Realtime quantitative PCR
1 µg of total RNA was reverse transcribed using the High Capacity RNA-to-cDNA Master Mix (Applied Biosystems, Life Technologies, Carlsbad, CA, USA). qPCR assays for rno-miR-1 (Assay ID: 002064, Applied Biosystems), U6 (for normalization, Assay ID: 001973, Applied Biosystems), BDNF (Assay ID: Rn02531967_s1) and actin beta (Rn00667869_m1) were applied according to the manufacturer’s instructions. The qPCR assay for Cx43 was designed by and purchased from TIB Molbiol (Berlin, Germany) and has the following sequences: Primer_for: AGGAGTTCCACCAACTTTGGC, Primer_rev: TGGAGTAGGCTTGGACCTTGTC and Taqman probe: FAM-AGCTTCCCCAAGGCACTCCAGTC-BBQ. qPCR conditions: 50°C for 2 min, 95°C for 10 min, 40 cycles of 95°C for 15 s, 60°C for 60 s on an Applied Biosystems 7300HT thermocycler (Applied Biosystems). All samples were run in duplicates. Relative expression was estimated using the ΔΔCq-method  and the relative expression software tool .
Protein isolation and Western Blot experiments
To analyze Cx43 protein expression in the sciatic nerve and DRG, samples were pulverized in liquid nitrogen, homogenized in a buffer of pH 8.0 (50 mM Tris, 150 mM NaCl, 1% NP40, 0.5% Na-Deoxycholate, 0.1% SDS, 40 μl/ml Complete) and centrifuged at 4°C, 8,000g for 10 min. The supernatant was harvested and the protein content was measured according to Lowry et al. Sodium dodecyl sulfate polyacrylamide gel electrophoresis separated equal amounts of protein (40 μg per lane). The gel was run for 85 min at 100 V and the proteins were transferred to a polyvinylidene difluoride membrane at 220 mA for 1 h. The membrane was blocked with 5% dried skimmed milk in Tris-buffered saline with 0.1% Tween for 2 h at room temperature and incubated with the primary antibody (Cx43, ab11370, abcam, Cambridge, UK, 1:1,000) overnight at 4°C. After washing with cold TBS-T three times for 10 min the secondary antibody was applied for 2 h. The membrane was washed again in TBS-T and bound antibodies were visualized using the enhanced chemoluminescent detection method by a digital camera (cool snap HQ2; Photometrics®, Tuscon, AZ). Signals were quantified and standardized against GAPDH (Abcam ab8245, Cambridge, UK) by densitometry (GelScan; BioSciTec GmbH, Frankfurt/Main, Germany).
BDNF protein levels of sciatic nerve and DRG were analysed using the BDNF Emax® ImmunoAssay System (Promega, Madison, WI, USA) according to the manufacturer’s protocol as described previously . Briefly, 96-well plates were coated with anti-BDNF monoclonal antibody and incubated at 4°C overnight. The plates were washed with TBS-T and incubated with 200 μl of Block and Sample buffer (BDNF Emax™ ImmunoAssay System, Promega, Madison, WI, USA) for 1 h at room temperature. 100 μl of each sample prepared as described above was transferred to the anti-BDNF-coated ELISA plate. BDNF levels were determined from the standard curve prepared for each plate. The standard curves were linear within the range used (0–500 pg/ml).
Immunohistochemical staining and confocal microscopy
DRG and nerve tissue was removed and embedded in Tissue -Tek® O.C.T. (Sakura Finetek Europe, Alphan aan den Rijin, The Netherlands) in cryomolds at −40°C without prior treatment and stored at −20°C. Cryosections of rat DRG and nerve tissue (8 µm) were fixed in 4% PFA containing 0.1 M phosphate buffer for 10 min and washed in 3× PBS for 10 min. Slices were blocked with 10% goat serum in PBS containing 0.2% saponin. Cross sections of sciatic nerves were incubated with Cx43 (Cx43, ab11370, abcam, Cambridge, UK, 1:1,000), DRG sections were incubated with Cx43 and NeuN antibodies (Anti-NeuN, clone A60, Cat. # MAB377, Millipore, Temecula, USA) at 4°C overnight. After washing with PBS/saponin, slices were incubated with Cy3-labeled anti-rabbit IgG (Lot number 81,350, Dianova, Hamburg, Germany, 1:500) and Alexa Fluor 488 conjugated goat anti-mouse IgG (A-11029, Life Technologies Carlsbad, USA, 1:500) containing Hoechst 34580 (1:10,000) as nuclear counterstain for 1 h at room temperature. After washing with PBS/saponin, slices were mounted with FuoroMount G medium. Immunostained samples were analysed using a Zeiss LSM510META confocal microscope (Jena, Germany).
Behavioral data, Western Blot data and BDNF ELISA results were analyzed by student’s t test (GraphPad Prism version 6, GraphPad Software, San Diego, CA USA). qPCR data was analyzed using the relative expression software tool . Data are presented as mean ± SD. p < 0.05 was considered statistically significant.
EN and FB conducted animal experiments. EN and TB have conducted and performed qPCR and WB experiments. TB conducted and interpreted immunohistochemical experiments. TB, RW and HH conducted the study and wrote the manuscript. All authors read and approved the final manuscript.
The excellent technical assistance of Nadine Lottmann and Claudia Dohle is gratefully acknowledged. The authors are grateful for the support of Dr. Boris Görg (Department Gastroenterology, Hepatology and Infectiology, University Hospital Düsseldorf, 40225 Düsseldorf, Germany) with confocal laser scanning microscopy.
Compliance with ethical guidelines
Competing interests The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- von Hehn CA, Baron R, Woolf CJ. Deconstructing the neuropathic pain phenotype to reveal neural mechanisms. Neuron. 2012;73(4):638–52.View ArticleGoogle Scholar
- Baron R, Binder A, Wasner G. Neuropathic pain: diagnosis, pathophysiological mechanisms, and treatment. Lancet Neurol. 2010;9(8):807–19.PubMedView ArticleGoogle Scholar
- Gangadharan V, Kuner R. Pain hypersensitivity mechanisms at a glance. Dis Model Mech. 2013;6(4):889–95.PubMed CentralPubMedView ArticleGoogle Scholar
- Bartel DP. MicroRNAs: target recognition and regulatory functions. Cell. 2009;136(2):215–33.PubMed CentralPubMedView ArticleGoogle Scholar
- Li Z, Rana TM. Therapeutic targeting of microRNAs: current status and future challenges. Nat Rev Drug Discov. 2014;13(8):622–38.PubMedView ArticleGoogle Scholar
- Friedman RC, Farh KK, Burge CB, Bartel DP. Most mammalian mRNAs are conserved targets of microRNAs. Genome Res. 2009;19(1):92–105.PubMed CentralPubMedView ArticleGoogle Scholar
- Bali KK, Kuner R. Noncoding RNAs: key molecules in understanding and treating pain. Trends Mol Med. 2014;20(8):437–48.PubMed CentralPubMedView ArticleGoogle Scholar
- Andersen HH, Duroux M, Gazerani P. MicroRNAs as modulators and biomarkers of inflammatory and neuropathic pain conditions. Neurobiol Dis. 2014;71C:159–68.View ArticleGoogle Scholar
- Kusuda R, Cadetti F, Ravanelli MI, Sousa TA, Zanon S, De Lucca FL, et al. Differential expression of microRNAs in mouse pain models. Mol Pain. 2011;7:17.PubMed CentralPubMedView ArticleGoogle Scholar
- Yang B, Lin H, Xiao J, Lu Y, Luo X, Li B, et al. The muscle-specific microRNA miR-1 regulates cardiac arrhythmogenic potential by targeting GJA1 and KCNJ2. Nat Med. 2007;13(4):486–91.PubMedView ArticleGoogle Scholar
- Brandenburger T, Grievink H, Heinen N, Barthel F, Huhn R, Stachuletz F, et al. Effects of remote ischemic preconditioning and myocardial ischemia on microRNA-1 expression in the rat heart in vivo. Shock. 2014;42(3):234–8.PubMedView ArticleGoogle Scholar
- Gold MS, Gebhart GF. Nociceptor sensitization in pain pathogenesis. Nat Med. 2010;16(11):1248–57.PubMedView ArticleGoogle Scholar
- Wu D, Murashov AK. Molecular mechanisms of peripheral nerve regeneration: emerging roles of microRNAs. Front Physiol. 2013;4:55.PubMed CentralPubMedView ArticleGoogle Scholar
- Dworkin RH, O’Connor AB, Backonja M, Farrar JT, Finnerup NB, Jensen TS, et al. Pharmacologic management of neuropathic pain: evidence-based recommendations. Pain. 2007;132(3):237–51.PubMedView ArticleGoogle Scholar
- Sun E, Shi Y. MicroRNAs: small molecules with big roles in neurodevelopment and diseases. Exp Neurol. 2015;268:46–53.PubMedView ArticleGoogle Scholar
- Aldrich BT, Frakes EP, Kasuya J, Hammond DL, Kitamoto T. Changes in expression of sensory organ-specific microRNAs in rat dorsal root ganglia in association with mechanical hypersensitivity induced by spinal nerve ligation. Neuroscience. 2009;164(2):711–23.PubMed CentralPubMedView ArticleGoogle Scholar
- Brandenburger T, Strehler EE, Filoteo AG, Caride AJ, Aumuller G, Post H, et al. Switch of PMCA4 splice variants in bovine epididymis results in altered isoform expression during functional sperm maturation. J Biol Chem. 2011;286(10):7938–46.PubMed CentralPubMedView ArticleGoogle Scholar
- Favereaux A, Thoumine O, Bouali-Benazzouz R, Roques V, Papon MA, Salam SA, et al. Bidirectional integrative regulation of Cav1.2 calcium channel by microRNA miR-103: role in pain. EMBO J. 2011;30(18):3830–41.PubMed CentralPubMedView ArticleGoogle Scholar
- Sakai A, Suzuki H. Nerve injury-induced upregulation of miR-21 in the primary sensory neurons contributes to neuropathic pain in rats. Biochem Biophys Res Commun. 2013;435(2):176–81.PubMedView ArticleGoogle Scholar
- Willemen HL, Huo XJ, Mao-Ying QL, Zijlstra J, Heijnen CJ, Kavelaars A. MicroRNA-124 as a novel treatment for persistent hyperalgesia. J Neuroinflammation. 2012;9:143.PubMed CentralPubMedView ArticleGoogle Scholar
- Im YB, Jee MK, Jung JS, Choi JI, Jang JH, Kang SK. miR23b ameliorates neuropathic pain in spinal cord by silencing NADPH oxidase 4. Antioxid Redox Signal. 2012;16(10):1046–60.PubMedView ArticleGoogle Scholar
- Sakai A, Saitow F, Miyake N, Miyake K, Shimada T, Suzuki H. miR-7a alleviates the maintenance of neuropathic pain through regulation of neuronal excitability. Brain. 2013;136(Pt 9):2738–50.PubMedView ArticleGoogle Scholar
- Park CK, Xu ZZ, Berta T, Han Q, Chen G, Liu XJ, et al. Extracellular microRNAs activate nociceptor neurons to elicit pain via TLR7 and TRPA1. Neuron. 2014;82(1):47–54.PubMed CentralPubMedView ArticleGoogle Scholar
- Kynast KL, Russe OQ, Geisslinger G, Niederberger E. Novel findings in pain processing pathways: implications for miRNAs as future therapeutic targets. Expert Rev Neurother. 2013;13(5):515–25.PubMedView ArticleGoogle Scholar
- Kress M, Huttenhofer A, Landry M, Kuner R, Favereaux A, Greenberg D, et al. microRNAs in nociceptive circuits as predictors of future clinical applications. Front Mol Neurosci. 2013;6:33.PubMed CentralPubMedView ArticleGoogle Scholar
- Elramah S, Landry M, Favereaux A. MicroRNAs regulate neuronal plasticity and are involved in pain mechanisms. Front Cell Neurosci. 2014;8:31.PubMed CentralPubMedView ArticleGoogle Scholar
- Lutz BM, Bekker A, Tao YX. Noncoding RNAs: new players in chronic pain. Anesthesiology. 2014;121(2):409–17.PubMedView ArticleGoogle Scholar
- Sakai A, Suzuki H. Emerging roles of microRNAs in chronic pain. Neurochem Int. 2014;77:58–67.PubMedView ArticleGoogle Scholar
- Viader A, Chang LW, Fahrner T, Nagarajan R, Milbrandt J. MicroRNAs modulate Schwann cell response to nerve injury by reinforcing transcriptional silencing of dedifferentiation-related genes. J Neurosci. 2011;31(48):17358–69.PubMed CentralPubMedView ArticleGoogle Scholar
- Natera-Naranjo O, Aschrafi A, Gioio AE, Kaplan BB. Identification and quantitative analyses of microRNAs located in the distal axons of sympathetic neurons. RNA. 2010;16(8):1516–29.PubMed CentralPubMedView ArticleGoogle Scholar
- Meyer M, Matsuoka I, Wetmore C, Olson L, Thoenen H. Enhanced synthesis of brain-derived neurotrophic factor in the lesioned peripheral nerve: different mechanisms are responsible for the regulation of BDNF and NGF mRNA. J Cell Biol. 1992;119(1):45–54.PubMedView ArticleGoogle Scholar
- Campana WM. Schwann cells: activated peripheral glia and their role in neuropathic pain. Brain Behav Immun. 2007;21(5):522–7.PubMed CentralPubMedView ArticleGoogle Scholar
- Smith PA. BDNF: no gain without pain? Neuroscience. 2014;26(283):107–23.View ArticleGoogle Scholar
- Bennett MV, Garre JM, Orellana JA, Bukauskas FF, Nedergaard M, Saez JC. Connexin and pannexin hemichannels in inflammatory responses of glia and neurons. Brain Res. 2012;1487:3–15.PubMed CentralPubMedView ArticleGoogle Scholar
- Chen G, Park CK, Xie RG, Berta T, Nedergaard M, Ji RR. Connexin-43 induces chemokine release from spinal cord astrocytes to maintain late-phase neuropathic pain in mice. Brain. 2014;137(Pt 8):2193–209.PubMedView ArticleGoogle Scholar
- Bennett G, Xie Y. A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man. Pain. 1988;33(1):87–107.PubMedView ArticleGoogle Scholar
- Brandenburger T, Castoldi M, Brendel M, Grievink H, Schlosser L, Werdehausen R, et al. Expression of spinal cord microRNAs in a rat model of chronic neuropathic pain. Neurosci Lett. 2012;506(2):281–6.PubMedView ArticleGoogle Scholar
- Pfaffl MW. A new mathematical model for relative quantification in real-time RT-PCR. Nucleic Acids Res. 2001;29(9):e45.PubMed CentralPubMedView ArticleGoogle Scholar
- Pfaffl MW, Horgan GW, Dempfle L. Relative expression software tool (REST) for group-wise comparison and statistical analysis of relative expression results in real-time PCR. Nucleic Acids Res. 2002;30(9):e36.PubMed CentralPubMedView ArticleGoogle Scholar
- Brandenburger T, Huhn R, Galas A, Pannen BH, Keitel V, Barthel F, et al. Remote ischemic preconditioning preserves Connexin 43 phosphorylation in the rat heart in vivo. J Transl Med. 2014;12:228.PubMed CentralPubMedView ArticleGoogle Scholar