Expression In Dorsal Root Ganglion Neurons Research Articles

Direct Application of the Tumor Necrosis Factor-α Inhibitor, Etanercept, Into a Punctured Intervertebral Disc Decreases Calcitonin Gene-Related Peptide Expression in Rat Dorsal Root Ganglion Neurons

retrograde neurotracing and immunohistochemistry were used to investigate the effect of the tumor necrosis factor (TNF)-α inhibitor, etanercept, on calcitonin gene-related peptide (CGRP) expression in dorsal root ganglion (DRG) neurons innervating intervertebral discs in rats. to clarify the action of a TNF-α inhibitor on a sensory neuropeptide in DRG neurons innervating intervertebral discs. degeneration of lumbar intervertebral discs is a cause of low back pain. TNF-α in the intervertebral disc is a major contributor to discogenie pain. Effects of TNF-α inhibition on CGRP expression in DRG neurons were evaluated. the neurotracer FluoroGold was applied to the surfaces of L4/5 discs to label their innervating DRG neurons (n = 30). Of 30 rats, 10 were in a nonpunctured disc sham surgery control group, whereas the other 20 were in experimental groups in which intervertebral discs were punctured with a 23-gauge needle. Etanercept or saline was applied into the punctured discs (n = 10 each treatment). After 14 days of surgery, DRGs from L1 to L6 were harvested, sectioned, and immunostained for CGRP. The proportion of FluoroGold-labeled CGRP-immunoreactive DRG neurons was evaluated in all groups. FluoroGold-labeled neurons innervating the L4/5 disc were distributed throughout L1-L6 DRGs in all groups. Of the FluoroGold-labeled neurons, the proportion of CGRP-immunoreactive neurons was 21% ± 4% in the sham surgery control group, 32% ± 7% in the puncture + saline group, and 23% ± 4% in the puncture + etanercept group. The proportion of CGRP-immunoreactive neurons was significantly greater in the puncture + saline group compared with the sham control and puncture + etanercept groups (P < 0.01). in this model, CGRP was upregulated in DRG neurons innervating damaged discs. However, direct intradiscal application of etanercept immediately after disc puncture suppressed CGRP expression in DRG neurons innervating injured discs. This finding may further elucidate the mechanism for the effectiveness of etanercept in upregulation of neuropeptide in DRG neurons innervating intervertebral discs.

Noradrenaline enhances ATP P2X3 receptor expression in dorsal root ganglion neurons of rats

Increasing evidence indicates that both the ATP P2X receptors and adrenergic systems play a very important role in the development of nociception. However, there is little information concerning the interactions between these two systems in the dorsal root ganglia (DRG). In the present study, we examined the effects of noradrenaline (NA) on the P2X3 receptor expression in the DRG of Sprague–Dawley rats. The direct effect of NA on the P2X3 mRNA and protein expression was determined in cultured DRG neurons. Treatment of neuronal cultures with NA (50 nM, 5 h) induced a two-fold increase in P2X3 expression, as detected with real-time RT-PCR and Western blots, but had no effect on P2X2 expression. In electrophysiological experiments, perfusion of neuronal cultures with the P2X3 agonist (αβ-methylene ATP) increased neuronal firing rate by 139% and 273% in neurons treated with either PBS (control) or NA, respectively, indicating that chronic NA treatment significantly enhanced the neuronal response to P2X3 activation. In behavior studies, combination of NA (2 or 20 nmol) with αβ-methylene ATP (10 nmol) produced a significant and long lasting augmentation of thermal hyperalgesia. These results indicate that NA stimulates P2X3 expression in DRG neurons, and this could contribute to the development of pain sensitization.

Axonal projections of mechanoreceptive dorsal root ganglion neurons depend on Ret

Establishment of connectivity between peripheral and central organs is essential for sensory processing by dorsal root ganglion (DRG) neurons. Using Ret as a marker for mechanoreceptive DRG neurons, we show that both central and peripheral projections of mechanoreceptive neurons are severely impaired in the absence of Ret. Death of DRG neurons in Ret-deficient mice can be rescued by eliminating Bax, although their projections remain disrupted. Furthermore, ectopic expression of the Ret ligand neurturin, but not Gdnf, in the spinal cord induces aberrant projection of mechanoreceptive afferents. Our results demonstrate that Ret expression in DRG neurons is crucial for the neurturin-mediated formation of precise axonal projections in the central nervous system.

The sensitization of peripheral C-fibers to lysophosphatidic acid in bone cancer pain

Aims Lysophosphatidic acid (LPA) is released from injured tissue and cancer cells and is involved in the induction of neuropathic pain. The present study explores whether LPA plays a role in the development of osteocarcinoma-induced pain. Main methods The bone cancer model was established using the Walker 256 mammary gland carcinoma cell line, and cancer-related behavioral and physiological changes were observed using von Frey, X-ray and immunohistochemical methods. The role of LPA in the bone cancer model and related mechanisms were examined by using in vitro single fiber recording and western blot. Key findings Rats exhibited severe hyperalgesia 2 weeks after the cancer cell implantation. Several changes were observed at this time point including: ipsilateral dorsal root ganglion (DRG) neurons were labeled by injured neurons marker ATF3; LPA 1 receptor expression in DRG neurons was increased; sural C-fibers were more sensitive to LPA stimuli, and this response could be blocked by LPA receptor and substance P receptor antagonists. Significance These data indicate that LPA is involved in the induction of bone cancer pain through mechanisms of peripheral C-fibers sensitization. LPA and its downstream molecules possibly are promising therapeutic targets for treatment of cancer pain.

Effect of applying p75NTR saporin to a punctured intervertebral disc on calcitonin gene-related peptide expression in rat dorsal root ganglion neurons

BackgroundRecent studies have revealed that the low-affinity nerve growth factor receptor, p75 neurotrophin receptor (p75NTR), is important in inflammatory pain. Moreover, p75NTR immunoreactive sensory nerve and dorsal root ganglion (DRG) neurons have been found to innervate lumbar intervertebral discs. The purpose of the current study was to investigate the effect of p75NTR saporin, a toxin used to destroy p75NTR, on calcitonin gene-related peptide (CGRP), an inflammatory neuropeptide associated with pain, in DRG neurons innervating punctured intervertebral discs in rats. MethodsThe neurotracer fluorogold (FG) was applied to the surfaces of L5/6 discs to label their innervating DRG neurons (n = 30). Of 30 rats, 10 were in a nonpunctured disc sham surgery control group (nonpuncture group), and the other 20 were in experimental groups in which intervertebral discs were punctured with a 23-gauge needle. p75NTR saporin was applied to the discs of 10 rats (puncture + p75NTR saporin group) and the other 10 received the same volume of saline (puncture + saline group). At 14 days after surgery, DRGs from L1 to L6 were harvested, sectioned, and immunostained for CGRP, and the proportions of CGRP-immunoreactive DRG neurons was evaluated. ResultsOf the FG-labeled neurons innervating the L5/6 disc, the proportion of CGRP-immunoreactive neurons was 32% ± 6% (mean ± SE) in the nonpuncture group, 47.2% ± 8% in the puncture + saline group, and 34.6% ± 9% in the puncture + p75NTR saporin group. The proportion of CGRP-immunoreactive neurons was significantly greater in the puncture + saline group compared with the nonpuncture and puncture + p75NTR saporin groups (P < 0.01). ConclusionsHalf of the DRG neurons innervating the discs were positive for CGRP in the puncture + saline group. CGRP is important for mediating inflammatory and nerve-injured pain and may be important in discogenic pain. However, p75NTR saporin suppressed CGRP expression in DRG neurons. Therefore, p75NTR may be an important receptor for mediating discogenic pain via CGRP expression.

Nerve growth factor and norepinephrine regulate galanin expression in primary cultures of dorsal root ganglion neurons

Nerve growth factor (NGF) is one of the well characterized regulators of galanin expression. NGF deprivation can induce galanin expression in dorsal root ganglion (DRG) neurons. Galanin is recognized as one of the DRG injury markers. Norepinephrine (NE) activates alpha-adrenoreceptors usually expressed in sympathetic neuronal membrane. It has been shown that functional alpha-adrenoreceptors are also expressed in primary sensory neurons. Whether NGF association with NE influences the galanin expression in DRG neurons remains unknown. In the present study, we have evaluated the possible regulation of galanin mRNA or galanin peptide expression by co-administration of NGF and NE in primary cultures of rat DRG neurons. After four days incubation with NGF and/or NE in primary cultures of rat DRG neurons, NGF inhibited and NE promoted galanin mRNA and galanin peptide expression as compared with that in control DRG neuron cultures at the same time point. NGF also inhibited the elevation of galanin expression induced by NE when the cultures were incubated with NGF and NE together. NGF but not NE stimulated neurite outgrowth. The results indicate that NE may affect galanin expression rather than stimulating neurite regeneration, whereas NGF stimulates neurite outgrowth and inhibits galanin expression in the absence or presence of NE on cultured DRG neurons.

Selective inhibition of JNK with a peptide inhibitor attenuates pain hypersensitivity and tumor growth in a mouse skin cancer pain model

Cancer pain significantly affects the quality of cancer patients, and current treatments for this pain are limited. C-Jun N-terminal kinase (JNK) has been implicated in tumor growth and neuropathic pain sensitization. We investigated the role of JNK in cancer pain and tumor growth in a skin cancer pain model. Injection of luciferase-transfected B16-Fluc melanoma cells into a hindpaw of mouse induced robust tumor growth, as indicated by increase in paw volume and fluorescence intensity. Pain hypersensitivity in this model developed rapidly (< 5 days) and reached a peak in 2 weeks, and was characterized by mechanical allodynia and heat hyperalgesia. Tumor growth was associated with JNK activation in tumor mass, dorsal root ganglion (DRG), and spinal cord and a peripheral neuropathy, such as loss of nerve fibers in the hindpaw skin and induction of ATF-3 expression in DRG neurons. Repeated systemic injections of D-JNKI-1 (6 mg/kg, i.p.), a selective and cell-permeable peptide inhibitor of JNK, produced an accumulative inhibition of mechanical allodynia and heat hyperalgesia. A bolus spinal injection of D-JNKI-1 also inhibited mechanical allodynia. Further, JNK inhibition suppressed tumor growth in vivo and melanoma cell proliferation in vitro. In contrast, repeated injections of morphine (5 mg/kg), a commonly used analgesic for terminal cancer, produced analgesic tolerance after 1 day and did not inhibit tumor growth. Our data reveal a marked peripheral neuropathy in this skin cancer model and important roles of the JNK pathway in cancer pain development and tumor growth. JNK inhibitors such as D-JNKI-1 may be used to treat cancer pain.

Acid-Sensing Ion Channel 3 Expression in Mouse Knee Joint Afferents and Effects of Carrageenan-Induced Arthritis

Arthritis is associated with decreases in local pH. Of the acid-sensing ion channels (ASIC), ASIC3 is most sensitive to such a pH change, abundantly expressed in dorsal root ganglion (DRG), and critical for the development of secondary hyperalgesia. The purpose of this study was to investigate the upregulation of ASIC3, using an acute arthritic pain model in mice. We examined ASIC3 expression in DRG neurons innervating the knee joint with and without carrageenan-induced arthritis by means of retrograde labeling and immunohistochemistry. We also examined the difference of DRG phenotype between ASIC3+/+ and ASIC3-/- mice. ASIC3 immunoreactivity was present in 31% of knee joint afferents and dominantly in small cells. After joint inflammation, ASIC3-immunoreactive neurons significantly increased in number by 50%. Calcitonin gene-related peptide (CGRP) increased similarly in both ASIC3+/+ and ASIC3-/- mice. Soma size distribution of ASIC3-immunoreactive neurons without CGRP expression was shifted to smaller-diameter neurons. Our results suggest that ASIC3 plays an important role in acute arthritic pain. Specifically, we propose that ASIC3 upregulation along with CGRP and phenotypic change in ASIC3-immunoreactive neurons without CGRP are responsible for the development of secondary hyperalgesia after carrageenan-induced arthritis. This article shows that ASIC3 is upregulated along with CGRP in knee joint afferents and that there is a phenotypic change in ASIC3-immunoreactive nonpeptidergic neurons in an animal model of acute arthritis. Understanding the basic neurobiology after acute arthritis could lead to future new pharmacological management of arthritis.

Differential contribution of the Na + ‐K + ‐2Cl − cotransporter NKCC1 to chloride handling in rat embryonic dorsal root ganglion neurons and motor neurons

Plasma membrane chloride (Cl(-)) pathways play an important role in neuronal physiology. Here, we investigated the role of NKCC1 cotransporters (a secondary active Cl(-) uptake mechanism) in Cl(-) handling in cultured rat dorsal root ganglion neurons (DRGNs) and motor neurons (MNs) derived from fetal stage embryonic day 14. Gramicidin-perforated patch-clamp recordings revealed that DRGNs accumulate intracellular Cl(-) through a bumetanide- and Na(+)-sensitive mechanism, indicative of the functional expression of NKCC1. Western blotting confirmed the expression of NKCC1 in both DRGNs and MNs, but immunocytochemistry experiments showed a restricted expression in dendrites of MNs, which contrasts with a homogeneous expression in DRGNs. Both MNs and DRGNs could be readily loaded with or depleted of Cl(-) during GABA(A) receptor activation at depolarizing or hyperpolarizing membrane potentials. After loading, the rate of recovery to the resting Cl(-) concentration (i.e., [Cl(-)](i) decrease) was similar in both cell types and was unaffected by lowering the extracellular Na(+) concentration. In contrast, the recovery on depletion (i.e., [Cl(-)](i) increase) was significantly faster in DRGNs in control conditions but not in low extracellular Na(+). The experimental observations could be reproduced by a mathematical model for intracellular Cl(-) kinetics, in which DRGNs show higher NKCC1 activity and smaller Cl(-)-handling volume than MNs. On the basis of these results, we conclude that embryonic DRGNs show a higher somatic functional expression of NKCC1 than embryonic MNs. The high NKCC1 activity in DRGNs is important for maintaining high [Cl(-)](i), whereas lower NKCC1 activity in MNs allows large [Cl(-)](i) variations during neuronal activity.

Upregulation of Ryk expression in rat dorsal root ganglia after peripheral nerve injury

To study changes of Ryk expression in dorsal root ganglia (DRG) after peripheral nerve injury, we set up an animal model of unilateral sciatic nerve lesioned rats. Changes of Ryk protein expression in DRG neurons after unilateral sciatic nerve injury were investigated by immunostaining. Changes of Ryk mRNA were also tested by semi-quantitative PCR concurrently. We found, both at the level of protein and mRNA, that Ryk could be induced in cells of ipsilateral DRG after unilateral sciatic nerve lesion. Further investigation by co-immunostaining confirmed that the Ryk-immunoreactive (Ryk-IR) cells were NeuN-immunoreactive (NeuN-IR) neurons of DRG. We also showed the pattern of Ryk induction in DRG neurons after sciatic nerve injury: the number of Ryk IR neurons peaked at 2 weeks post-lesion and decreased gradually by 3 weeks post-lesion. The proportions of different sized Ryk IR neurons were also observed and counted at various stages after nerve lesion. Analysis of Ryk mRNA by RT-PCR showed the same induction pattern as by immunostaining. Ryk mRNA was not expressed in normal or contralateral DRG, but was expressed 1, 2 and 3 weeks post-lesion in the ipsilateral DRG. Ryk mRNA levels increased slightly from 1 to 2 weeks, decreased then by 3 weeks post-lesion. These results indicate that Ryk might be involved in peripheral nerve plasticity after injury. This is a novel function apart from its well-known fundamental activity as a receptor mediating axon guidance and outgrowth.

Role of sodium ferulate in the nociceptive sensory facilitation of neuropathic pain injury mediated by P2X 3 receptor

Neuropathic pain usually is persistent and no effective treatment. ATP plays an important role in the initiation of pain. P2X 3 receptors are localized in the dorsal root ganglion (DRG) neurons and activated by extracellular ATP. Sodium ferulate (SF) is an active principle from Chinese herbal medicine and has anti-inflammatory activities. This study observed the effects of SF on the nociceptive facilitation of the primary sensory afferent after chronic constriction injury (CCI) mediated by P2X 3 receptor. In this study, the content of ATP in DRG neurons was measured by high-performance liquid chromatography (HPLC). P2X 3 agonist-activated currents in DRG neurons was recorded by the whole-cell patch-clamp skill. The expression of P2X 3 mRNA in DRG neurons was analyzed by in situ hybridization. The ATP content of DRG was increased after CCI. In CCI rats treated with SF, the content of ATP in DRG neurons was reduced. SF decreased the increment of P2X 3 agonist-activated currents and P2X 3 mRNA expression in DRG neurons during CCI. SF may inhibit the initiation of pain and primary afferent sensitization mediated by P2X 3 receptor during CCI.

Targeting adenoviral transgene expression to neurons

Adenovirus (Ad) is an efficient and safe vector for CNS gene delivery since it infects non-replicating neurons and does not cause insertional mutagenesis of host cell genomes. However, the promiscuous Ad CAR receptor targets cells non-specifically and activates a host immune response. Using Ad5 containing an expression cassette encoding the gene for green fluorescent protein, gfp, regulated by the neuron specific promoter synapsin-1 and the woodchuck post-transcriptional regulatory element (WPRE), we demonstrate efficient, prolonged and promoter-restricted gfp expression in neurons of mixed primary adult rat dorsal root ganglion (DRG) and retinal cell cultures. We also demonstrate restricted gfp expression in DRG neurons after direct injections of Ad5 containing the synapsin-1 gfp /WPRE construct into L4 DRG in vivo, while Ad5 CMV gfp transfected both DRG glia and neurons. Moreover, since the effective titres of delivered Ad5 are reduced with this neuron specific promoter/WPRE expression cassette, the viral immune challenge should be attenuated when used in vivo.

Transient Receptor Potential Vanilloid-4 Has a Major Role in Visceral Hypersensitivity Symptoms

The transient receptor potential vanilloid-4 (TRPV4) is an osmosensitive channel that responds to mechanical stimulation. We hypothesized that TRPV4 could be important in visceral nociception and in the development of hypersensitivity. TRPV4 expression was investigated by immunohistochemistry and reverse transcription-polymerase chain reaction. Calcium signaling and patch-clamp studies were performed in dorsal root ganglia (DRG) neurons validating the use of 4alphaPDD as a selective TRPV4 agonist. The effects of TRPV4 activation on visceral nociception were evaluated in mice that received intracolonically TRPV4 agonist (4 alpha-phorbol 12,13-didecanoate [4alphaPDD]) and in TRPV4-deficient mice in which abdominal muscle contractions in response to colorectal distention (CRD) were recorded. Intervertebral injections of TRPV4 or mismatch small interfering RNA (siRNA) were used to specifically down-regulate TRPV4 expression in sensory neurons and to investigate the role of TRPV4 in basal visceral nociception or in protease-activated receptor 2 (PAR(2)) activation-induced visceral hypersensitivity. TRPV4 agonist 4alphaPDD specifically activated a cationic current and calcium influx in colonic projections of DRG neurons and caused dose-dependent visceral hypersensitivity. TRPV4-targeted but not mismatched siRNA intervertebral treatments were effective at reducing basal visceral nociception, as well as 4alphaPDD or PAR(2) agonist-induced hypersensitivity. Effects of the TRPV4 ligand were lost in TRPV4-deficient mice. 4alphaPDD selectively activates TRPV4 in sensory neurons projecting from the colon, and TRPV4 activation causes visceral hypersensitivity. TRPV4 activation is implicated in the nociceptive response to CRD in basal conditions and in PAR(2) agonist-induced hypersensitivity. These results suggest a pivotal role for TRPV4 in visceral nociception and hypersensitivity.

Monocyte chemoattractant protein-1 immunoreactivity in sensory ganglia and hindpaw after adjuvant injection

Monocyte chemoattractant protein-1 (MCP-1)/CCL2 is a member of the CC chemokine family that exhibits potent chemotactic activity for monocytes/macrophages. In the current study, the proportion of monocyte chemoattractant protein-1-immunoreactive (IR) neurons in the dorsal root ganglion (DRG) of rats was shown to increase markedly following adjuvant injection into the hindpaw. MCP-1-IR axon terminals were not found in the spinal cord or hindpaw of control or adjuvant-treated rats. Instead, the inflamed hindpaw dermis was infiltrated by numerous MCP-1-IR inflammatory cells. Following adjuvant injection, the majority of MCP-1-IR neurons in the DRG colocalized with IB4 binding. Our findings suggest that peripheral tissue inflammation induces increased MCP-1 expression in DRG neurons and this may be dependent upon glial cell line-derived neurotrophic factor.

Activation of Extracellular Signal-Regulated Protein Kinase in Sensory Neurons After Noxious Gastric Distention and Its Involvement in Acute Visceral Pain in Rats

Changes in the properties of visceral sensory neurons contribute to the development of gastrointestinal pain. However, little is known about the molecules involved in mechanosensation from the gastrointestinal tract. We investigated the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), a member of the mitogen-activated protein kinase cascade, in dorsal root ganglion (DRG) and nodose ganglion (NG) neurons by noxious gastric distention (GD) and its involvement in acute visceral pain in rats. Electromyographic responses to gastric balloon distention through gastrostomy were recorded from the acromiotrapezius muscle in rats after splanchnic nerve resection or vagotomy and in control rats. We then examined the phosphorylated-ERK1/2 (p-ERK1/2) labeling in the DRG and NG after GD using immunohistochemistry. Gastric distention induced p-ERK1/2 in DRG and NG neurons with a peak at 2 minutes after stimulation. We found a stimulus intensity-dependent increase in the number of activated neurons, and this activation corresponded well with the incidence of the visceromotor response. Most of these p-ERK1/2-labeled neurons were small- and medium-sized neurons that coexpressed transient receptor potential vanilloid 1 ion channel and acid-sensing ion channel 3. Splanchnic nerve resection, but not vagotomy, affected the visceromotor response, and attenuated the ERK1/2 activation in DRG neurons produced by GD. Furthermore, intrathecal administration of the mitogen-activated protein kinase kinase 1/2 inhibitor, U0126, altered the response to noxious GD. The activation of ERK1/2 pathways in DRG neurons by noxious GD may be correlated with functional activity, and may be involved in acute visceral pain.

Didanosine causes sensory neuropathy in an HIV/AIDS animal model: impaired mitochondrial and neurotrophic factor gene expression

Antiretroviral toxic neuropathy (ATN) has become a common peripheral neuropathy among HIV/AIDS patients, for which the underlying pathogenesis is uncertain. Indeed, no models exist for ATN that assess the interaction between retroviral infection and antiretroviral therapy. Herein, we developed ex vivo and in vivo models of ATN induced by didanosine (ddI) following infection by the lentivirus, feline immunodeficiency virus (FIV), permitting us to address the working hypothesis that ddI mediates ATN through mitochondrial injury in neurons. We investigated neuronal morphology, neurobehavioural testing, viral load, mitochondrial and neurotrophic factor gene expression after ddI treatment of FIV-infected and uninfected animals or dorsal root ganglia (DRG) cultures. ddI caused concentration-dependent neuronal injury in cultured feline DRGs (P < 0.05), together with reduced viral replication and diminished expression of mitochondrial cytochrome C oxidase subunit I gene (mtCOX I) and the neurotrophin, brain-derived neurotrophic factor (BDNF). Indeed, BDNF treatment reversed neuronal injury caused by FIV infection in the presence or absence of ddI exposure (P < 0.05). In vivo FIV infection revealed delays in withdrawal latency to a noxious stimulus, which were exacerbated by ddI treatment. Epidermal density of nerve endings was reduced after FIV infection (P < 0.05), especially with ddI treatment. Although viral replication in blood was suppressed in ddI-treated animals (P < 0.05), ddI had a limited effect on viral abundance in DRGs of the same animals. ddI decreased mtCOX I expression in DRG neurons of FIV-infected animals (P < 0.05). BDNF expression was downregulated by ddI in DRG Schwann cells following FIV infection. Thus, ddI treatment during FIV infection resulted in additive pathogenic effects contributing to the development of ATN, which was associated with mitochondrial injury on neurons and reduced BDNF production by Schwann cells in DRGs, highlighting the convergent pathogenic effects that antiretroviral drugs might have in patients with HIV infection.

Activation of extracellular signal‐regulated protein kinases 5 in primary afferent neurons contributes to heat and cold hyperalgesia after inflammation

Heat and cold hyperalgesia is a common feature of inflammatory pain. To investigate whether activation of extracellular signal-regulated protein kinase 5 (ERK5), also known as big mitogen-activated protein kinase 1, in primary sensory neurons participates in inflammatory pain, we examined the phosphorylation of ERK5 in the dorsal root ganglion (DRG) after peripheral inflammation. Inflammation induced by complete Freund's adjuvant produced heat and cold hyperalgesia on the ipsilateral hind paw and induced an increase in the phosphorylation of ERK5, mainly in tyrosine kinase A-expressing small- and medium-size neurons. In contrast, there was no change in ERK5 phosphorylation in the spinal dorsal horn. ERK5 antisense, but not mismatch, oligodeoxynucleotide decreased the activation of ERK5 and suppressed inflammation-induced heat and cold hyperalgesia. Furthermore, the inhibition of ERK5 blocked the induction of transient receptor potential channel TRPV1 and TRPA1 expression in DRG neurons after peripheral inflammation. Our results show that ERK5 activated in DRG neurons contribute to the development of inflammatory pain. Thus, blocking ERK5 signaling in sensory neurons that has the potential for preventing pain after inflammation.

Roles of extracellular signal‐regulated protein kinases 5 in spinal microglia and primary sensory neurons for neuropathic pain

Neuropathic pain that occurs after peripheral nerve injury is poorly controlled by current therapies. Increasing evidence shows that mitogen-activated protein kinase (MAPK) play an important role in the induction and maintenance of neuropathic pain. Here we show that activation of extracellular signal-regulated protein kinases 5 (ERK5), also known as big MAPK1, participates in pain hypersensitivity caused by nerve injury. Nerve injury increased ERK5 phosphorylation in spinal microglia and in both damaged and undamaged dorsal root ganglion (DRG) neurons. Antisense knockdown of ERK5 suppressed nerve injury-induced neuropathic pain and decreased microglial activation. Furthermore, inhibition of ERK5 blocked the induction of transient receptor potential channels and brain-derived neurotrophic factor expression in DRG neurons. Our results show that ERK5 activated in spinal microglia and DRG neurons contributes to the development of neuropathic pain. Thus, blocking ERK5 signaling in the spinal cord and primary afferents has potential for preventing pain after nerve damage.

Up-regulation of p55 TNF alpha-receptor in dorsal root ganglia neurons following lumbar facet joint injury in rats

The rat L5/6 facet joint is multisegmentally innervated from the L1 to L6 dorsal root ganglia (DRG). Tumor necrosis factor (TNF) is a known mediator of inflammation. It has been reported that satellite cells are activated, produce TNF and surround DRG neurons innervating L5/6 facet joints after facet injury. In the current study, changes in TNF receptor (p55) expression in DRG neurons innervating the L5/6 facet joint following facet joint injury were investigated in rats using a retrograde neurotransport method followed by immunohistochemistry. Twenty rats were used for this study. Two crystals of Fluorogold (FG; neurotracer) were applied into the L5/6 facet joint. Seven days after surgery, the dorsal portion of the capsule was cut in the injured group (injured group n = 10). No injury was performed in the non-injured group (n = 10). Fourteen days after the first application of FG, bilateral DRGs from T13 to L6 levels were resected and sectioned. They were subsequently processed for p55 immunohistochemistry. The number of FG labeled neurons and number of FG labeled p55-immunoreactive (IR) neurons were counted. FG labeled DRG neurons innervating the L5/6 facet joint were distributed from ipsilateral L1 to L6 levels. Of FG labeled neurons, the ratio of DRG neurons immunoreactive for p55 in the injured group (50%) was significantly higher than that in the non-injured group (13%). The ratio of p55-IR neurons of FG labeled DRG neurons was significantly higher in total L1 and L2 DRGs than that in total L3, 4, 5 and 6 DRGs in the injured group (L1 and 2 DRG, 67%; L3, 4, 5 and 6 DRG, 37%, percentages of the total number of p55-IR neurons at L1 and L2 level or L3-6 level/the total number of FG-labeled neurons at L1 and L2 level or L3-6 level). These data suggest that up-regulation of p55 in DRG neurons may be involved in the sensory transmission from facet joint injury. Regulation of p55 in DRG neurons innervating the facet joint was different between upper DRG innervated via the paravertebral sympathetic trunks and lower DRG innervated via other direct routes.

Roles of extracellular signal-regulated protein kinases (ERK) 5 in spinal microglia and primary sensory neurons for neuropathic pain

Neuropathic pain that occurs after peripheral nerve injury is poorly controlled by current therapies. Increasing evidence shows that mitogen-activated protein kinase (MAPK) play an important role in the induction and maintenance of neuropathic pain. Here we show that activation of extracellular signal-regulated protein kinases 5 (ERK5), also known as big MAPK1, participates in pain hypersensitivity caused by nerve injury. Nerve injury increased ERK5 phosphorylation in spinal microglia and in both damaged and undamaged dorsal root ganglion (DRG) neurons. Antisense knockdown of ERK5 suppressed nerve injury-induced neuropathic pain and decreased microglial activation. Furthermore, inhibition of ERK5 blocked the induction of transient receptor potential channels and brain-derived neurotrophic factor expression in DRG neurons. Our results show that ERK5 activated in spinal microglia and DRG neurons contributes to the development of neuropathic pain. Thus, blocking ERK5 signaling in the spinal cord and primary afferents has potential for preventing pain after nerve damage.