Effective treatments for neuropathic pain are lacking due to our limited understanding of the mechanisms. The circRNAs are mainly enriched in the central nervous system. However, their function in various physiological and pathological conditions have yet to be determined. Here, we identified circFhit, an exon-intron circRNA expressed in GABAergic neurons, which reduced the inhibitory synaptic transmission in the spinal dorsal horn to mediate spared nerve injury-induced neuropathic pain. Moreover, we found that circFhit decreased the expression of GAD65 and induced hyperexcitation in NK1R⁺ neurons by promoting the expression of its parental gene Fhit in cis. Mechanistically, circFhit was directly bound to the intronic region of Fhit, and formed a circFhit/HNRNPK complex to promote Pol II phosphorylation and H2B monoubiquitination by recruiting CDK9 and RNF40 to the Fhit intron. In summary, we revealed that the exon-intron circFhit contributes to GABAergic neuron-mediated NK1R⁺ neuronal hyperexcitation and neuropathic pain via regulating Fhit in cis.
Rats ; Animals ; Posterior Horn Cells/pathology* ; Spinal Cord Dorsal Horn/metabolism* ; Neuralgia ; Synaptic Transmission

This study aims to validate our hypothesis that acid-sensing ion channels (ASICs) may contribute to the symptom of pain in patients with chronic prostatitis (CP). We first established a CP rat model, then isolated the L5-S2 spinal dorsal horn neurons for further studies. ASIC1a was knocked down and its effects on the expression of neurogenic inflammation-related factors in the dorsal horn neurons of rat spinal cord were evaluated. The effect of ASIC1a on the Ca²⁺ ion concentration in the dorsal horn neurons of rat spinal cord was measured by the intracellular calcium ([Ca²⁺]i) intensity. The effect of ASIC1a on the p38/mitogen-activated protein kinase (MAPK) signaling pathway was also determined. ASIC1a was significantly upregulated in the CP rat model as compared with control rats. Acid-induced ASIC1a expression increased [Ca²⁺]i intensity in the dorsal horn neurons of rat spinal cord. ASIC1a also increased the levels of neurogenic inflammation-related factors and p-p38 expression in the acid-treated dorsal horn neurons. Notably, ASIC1a knockdown significantly decreased the expression of pro-inflammatory cytokines. Furthermore, the levels of p-p38 and pro-inflammatory cytokines in acid-treated dorsal horn neurons were significantly decreased in the presence of PcTx-1, BAPTA-AM, or SB203580. Our results showed that ASIC1a may contribute to the symptom of pain in patients with CP, at least partially, by regulating the p38/MAPK signaling pathway.
Acid Sensing Ion Channel Blockers/pharmacology* ; Acid Sensing Ion Channels/genetics* ; Animals ; Calcium/metabolism* ; Chelating Agents/pharmacology* ; Chronic Disease ; Cytokines/metabolism* ; Disease Models, Animal ; Egtazic Acid/pharmacology* ; Gene Knockdown Techniques ; Imidazoles/pharmacology* ; Inflammation/metabolism* ; MAP Kinase Signaling System/genetics* ; Male ; Pain/genetics* ; Peptides/pharmacology* ; Phosphorylation/drug effects* ; Posterior Horn Cells/metabolism* ; Prostatitis/complications* ; Protein Kinase Inhibitors/pharmacology* ; Pyridines/pharmacology* ; Rats ; Spider Venoms/pharmacology* ; Up-Regulation ; p38 Mitogen-Activated Protein Kinases/metabolism*

OBJECTIVETo observe analgesic effect of electroacupuncture ( EA) on rats with chronic inflammatory pain and its regulatory mechanism on ispilateral dorsal root ganglion (DRG) and spinal dorsal horn (SDH) Mas-related G protein-coupled C receptor (MrgprC).

METHODSTotally 40 healthy male SD rats were divided into 4 groups according to random number table, i.e., the normal (N) group, the model (M) group, the acupuncture (Acu) group, the EA group, 10 rats in each group. The model of chronic inflammatory pain was established by subcutaneous injecting 0. 1 mL complete Freund's adjuvant (CFA) into right hind paw. Paw withdrawal thresholds (PWTs) were measured before modeling, at day 1, 3, 5, 7, and after CFA injection, respectively. Expression levels of MrgprC in ispilateral DRG and SDH were detected by Western blot. The content of bovine adrenal medulla 22 (BAM22) in SDH was detected by immunohistochemical assay.

RESULTSCompared with N group at each time point, PWTs significantly decreased in M group (P <0. 01). Compared with M group, PWTs significantly increased at day 5 of EA and after EA in EA group (P < 0.05, P < 0.01). Compared with Acu group at each time point, post-EA PWTs significantly increased in the EA group (P < 0.05). Compared with N group, expression of MrgprC in ispilateral DRG and ratio of BAM22 positive cells in ispilateral SDH increased in M group (P < 0.01). Compared with M group, expression of MrgprC in ispilateral DRG and ratio of BAM22 positive cells in ispilateral SDH increased in the EA group (P < 0.05).

CONCLUSIONEA had favorable analgesic effect on chronic inflammatory pain induced by CFA, and its mechanism might be possibly associated with up-regulating MrgprC expression in ispilateral DRG and BAM22 content in ispilateral SDH.

Analgesia ; Animals ; Electroacupuncture ; Enkephalins ; metabolism ; Freund's Adjuvant ; Ganglia, Spinal ; drug effects ; Inflammation ; chemically induced ; drug therapy ; Male ; Pain Management ; methods ; Peptide Fragments ; metabolism ; Posterior Horn Cells ; drug effects ; Random Allocation ; Rats ; Rats, Sprague-Dawley

OBJECTIVETo investigate whether analgesic effect of electroacupuncture (EA) is affected by p38 mitogen-activated protein kinase (p38 MAPK) on microglia.

METHODSThere were two experiments. The experiment 1: 40 male Sprague-Dawley (SD) rats were randomly divided into the normal, surgery, EA and sham EA groups, and the L5 spinal nerve ligation (SNL) on the right side was used to establish neuropathic pain model. EA was applied to bilateral Zusanli (ST36) and Kunlun (BL60) at 24, 48 and 72 h after SNL for 30 min, once per day. The paw withdrawal thresholds (PWTs) were measured before surgery (as base) and at 24, 25, 49 and 73 h after surgery. Phospho-p38 MAPK (p-p38 MAPK), oxycocin-42 (OX-42, marker of microglia), and glial fibrillary acidic protein (GFAP, marker of astrocyte) in bilateral spinal cord dorsal horn (SCDH) were detected by immunofluorescence, respectively. The experiment 2: 40 male SD rats were cannulated for SNL-induced neuropathic pain, and then were randomly divided into the dimethyl sulfoxide (DMSO), EA plus DMSO, 4-(4-fluorophenyl)-2-(4-methylsulfonylpheny)-5-(4-pyridyl)-1H-imidazole (SB203580) and EA plus SB203580 groups. SB203580 (30 nmol/L) was administered 5 min prior to EA treatment. The PWTs and OX-42 in bilateral SCDH were measured as mentioned above.

RESULTSSNL-induced neuropathic pain reduced PWTs and increased the expression of p-p38 MAPK and OX-42 in bilateral lumbar SCDH of rats (P<0.01). Spinal p-p38 MAPK was only co-localized with OX-42 in our study. EA treatment significantly alleviated SNL-mediated mechanical hyperalgesia, and suppressed the expression of p-p38 MAPK and OX-42 in lumbar SCDH (P<0.05 or P<0.01). Intrathecal injection of low dose SB203580 had no influence on PWTs (P>0.05), but significantly inhibited the expression of OX-42 positive cells in bilateral SCDH (P<0.01 or P<0.05). EA plus SB203580 synergistically increased PWTs, and reduced the expression of bilateral spinal OX-42 (P<0.01 or P<0.05).

CONCLUSIONSThe central mechanism of EA-induced anti-hyperalgesia may be partially associated with the reduced expression of p-p38 MAPK, and subsequently reducing the activation of OX-42 in neuropathic pain. Therefore, EA may be a new complementary and alternative therapy for neuropathic pain.

Animals ; Biomarkers ; metabolism ; CD11b Antigen ; metabolism ; Electroacupuncture ; Fluorescent Antibody Technique ; Hyperalgesia ; pathology ; therapy ; Imidazoles ; pharmacology ; Ligation ; Male ; Microglia ; drug effects ; enzymology ; pathology ; Neuroglia ; drug effects ; metabolism ; Phosphorylation ; drug effects ; Posterior Horn Cells ; drug effects ; enzymology ; pathology ; Pyridines ; pharmacology ; Rats, Sprague-Dawley ; Spinal Nerves ; drug effects ; pathology ; p38 Mitogen-Activated Protein Kinases ; metabolism

OBJECTIVETo observe the effect of electroacupuncture (EA) on phosphorylation of spinal NR2B at Tyr 1742 site in complete Freund's adjuvant (CFA) induced inflammatory pain rats. METHods Forty male Sprague Dawley rats were randomly divided into normal group (N group, n = 10), the model group (CFA group, n = 15), and the EA group (n = 15). The inflammatory pain model was established by subcutaneous injecting CFA (0.1 mL per rat) into the right hind paw. Paw withdrawal thresholds (PWTs) were measured before CFA injection (as the base), as well as at 24 h, 25 h, 3rd day, and 7th day after CFA injection. Phosphorylation of NR2B at Tyr 1742 site in the ispilateral spinal dorsal horn at the 3rd day post-injection were detected using immunohistochemical assay.

RESULTSPWTs in the CFA group were significantly lower than those of the N group at every detective time point post-injection (P < 0.01). PWTs were obviously lower in the EA group than in the N group at 24 h post-injection (P < 0.01). It showed increasing tendency, markedly higher than those of the CFA group at 25 h and 3rd day post-injection (P < 0.01). Compared with the N group, the ratio of p-NR2B positive cells in the ispilateral spinal dorsal horn of rats in the CFA group was up-regulated. Compared with the CFA group, the ratio of p-NR2B positive cells in the ispilateral spinal dorsal horn of rats showed a decreasing tendency in the EA group.

CONCLUSIONEA might effectively inhibit CFA-induced inflammatory pain possibly associated with down-regulating phosphorylation of NR2B at Tyr 1742 site in the ispilateral spinal dorsal horn.

Adjuvants, Pharmaceutic ; pharmacology ; Animals ; Electroacupuncture ; methods ; Male ; Pain ; chemically induced ; metabolism ; Phosphorylation ; Posterior Horn Cells ; metabolism ; Rats ; Rats, Sprague-Dawley ; Receptors, N-Methyl-D-Aspartate ; metabolism

OBJECTIVETo investigate the role of muscarinic cholinergic receptor (mAChR) subtypes in the regulation of glutamatergic input to the spinal dorsal horn neurons and the possible mechanism.

METHODSWhole-cell voltage-clamp recordings on acute spinal slice was utilized to investigate the effect of activation of mAChRs and blockade of M2/M4 subtypes on glutamatergic synaptic transmission in rat spinal dorsal horn neurons.

RESULTSThe nonselective mAChRs agonist oxotremorine-M concentration-dependently decreased the amplitude of monosynaptic and polysynaptic evoked glutamate-mediated excitatory postsynaptic currents (eEPSCs) in most of the neurons. The M2/M4 antagonist himbacine completely blocked the inhibitory effect of oxotremorine-M in 92.3% of monosynaptic and 75% of polysynaptic neurons in the spinal cord slices. In the remaining 16% neurons, himbacine partially blocked the inhibitory effect of oxotremorine-M.

CONCLUSIONSActivation of mAChRs in the spinal cord attenuates synaptic glutamate release to the dorsal horn neurons mainly through M2 and M4 receptor subtypes, indicating that a presynaptic inhibition in the spinal cord may be involved in the regulation of nociception by the cholinergic system and mAChRs.

Animals ; Excitatory Postsynaptic Potentials ; Female ; Neurotransmitter Agents ; metabolism ; Posterior Horn Cells ; metabolism ; Rats ; Rats, Sprague-Dawley ; Receptors, Muscarinic ; metabolism ; Synaptic Transmission

OBJECTIVETo examine the analgesic effect of calpain inhibitor ALLN on the zymosan-induced paw inflammatory pain and its effect on the expression of cyclooxygenase-2 (COX-2) in the spinal dorsal horn.

METHODSForty-eight Sprague-Dawley rats were equally divided into three groups: control group, sham-operated group, and zymosan group. According to Meller's method, zymosan (1.25 mg) was injected intraplantarly to induce paw inflammation in zymosan group; an equal volume of PBS was administered in the sham-operated group. Mechanical withdrawal threshold (MWT) and maximum thickness of paw were tested or measured before and 0.5, 1, 2, 4, 8, and 24 hours after injection. All rats were killed at different occasions following surgery to examine calpain activity in the spinal dorsal horn with Western blot analysis. Another sixty-four Sprague-Dawley rats were divided into three groups: sham-operated group, zymosan-induced paw inflammation with intraperitoneal dimethyl sulphoxide (DMSO) treatment group, and zymosan-induced paw inflammation with intraperitoneal calpain inhibitor ALLN treatment group. MWT and maximum thickness of paw were tested or measured before and 0.5, 1, 2, 4, 8, and 24 hours after injection. All rats were killed at different occasions following surgery to examine the COX-2 expression in the spinal dorsal horn with Western blot analysis.

RESULTSMWT significantly decreased in the rats with zymosan-induced paw inflammation, while the maximum thickness of paw significantly increased, compared with control and sham-operated rats (P < 0.05). Calpain in the ipsilateral spinal dorsal horn was dramatically activated after zymosan injection (P < 0.01). Intraperitoneal ALLN injection significantly increased zymosan-induced MWT and decreased paw edema at the same time points after zymosan injection compared with DMSO treatment group (P < 0.05). Meanwhile, calpain inhibitor ALLN treatment significantly decreased the COX-2 expression in the spinal dorsal horn compared with DMSO treatment (P < 0.01).

CONCLUSIONAdministration of calpain inhibitor ALLN is effective to attenuate zymosan-induced paw inflammatory pain. Calpain activation may be one aspect of the signaling cascade that increases the COX-2 expression in the spinal cord and contributes to mechanical hyperalgesia after peripheral inflammatory injury.

Analgesics ; pharmacology ; Animals ; Cyclooxygenase 2 ; metabolism ; Disease Models, Animal ; Glycoproteins ; pharmacology ; Male ; Pain ; chemically induced ; drug therapy ; enzymology ; Posterior Horn Cells ; drug effects ; enzymology ; Rats ; Rats, Sprague-Dawley ; Spinal Cord ; drug effects ; enzymology ; Zymosan ; adverse effects

Discogenic low back pain is the common type of chronic low back pain. However,its mechanism has not been completely clarified. Considerable evidence shows that neurotrophins play an important role in discogenic low back pain. The paper summarizes the mechanism of neurotrophins on discogenic low back pain according to the pain transfer pathway of neurotrophins in intervertebral disc, dorsal horn ganglia and spinal trigeminal nucleus. Changing the pain transmission by regulating neurotrophins and its receptor will provide a new way for the treatment of discogenic low back pain.
Humans ; Intervertebral Disc ; metabolism ; pathology ; Low Back Pain ; metabolism ; pathology ; Nerve Growth Factors ; metabolism ; Posterior Horn Cells ; pathology ; Trigeminal Nucleus, Spinal ; pathology

OBJECTIVE: To investigate the effect of intrathecal sufentanil and protein kinase C inhibitor on pain threshold and the expression of N-methyl-D-aspartate receaptors (NMDAR)/calcitonin generelated peptide (CGRP) in spinal dorsal horn in rats with neuropathic pain. METHODS: Fifty-four healthy male Sprague-Dawley rats were randomly divided into 6 groups (9 in each group). The rats in the sham group(Group S) + spared nerve injury (SNI), SP+SNI, and P+SNI were intrathecally injected sufentanil (1 μg), sufentanil (1 μg) and chelerythrine chloride (11 μg), chelerythrine chloride (11 μg) followed by 10 μL normal saline once every day for 14 days postoperatively, respectively. Similarly, rats in the control group (Group C), the sham group (Group S), and SNI model group (Group SNI) were intrathecally injected 20 μL normal saline in the uniform interval. Pain behaviours were measured on Day 1 pre-surgery and on Day 1, 2, 7, and 14 after the intrathecal injection. The expressions of NMDAR and CGRP in the spinal dorsal horn of L5 segment were determined by immunohistochemistry on Day 2, 7, and 14 after the intrathecal injection. RESULTS: Compared with Group C and Group S, mechanical allodynia threshold in group SNI was decreased after the surgery (P<0.01), and expressions of NMDAR and CGRP immunoreactive soma in the spinal dorsal horn was significantly increased (P<0.01). Mechanical stimulation pain threshold was elevated in Group S+SNI, Group P+SNI, and Group SP+SNI compared with Group SNI (P<0.01), while expressions of NMDAR and CGRP immunoreactive soma in Group S+SNI, Group P +SNI, and Group SP+SNI were significantly decreased (P<0.05 or 0.01). CONCLUSION Intrathecal administration of sulfentanil and protein kinase C inhibitor can provide significant antinociception in rats with neuropathic pain and obviously inhibit the upregulation of NMDAR and CGRP expressions in the spinal dorsal horn of SNI rat models.
Animals ; Benzophenanthridines ; administration & dosage ; Calcitonin Gene-Related Peptide ; metabolism ; Injections, Spinal ; Male ; Neuralgia ; drug therapy ; metabolism ; physiopathology ; Pain Measurement ; Posterior Horn Cells ; metabolism ; Protein Kinase C ; antagonists & inhibitors ; Rats ; Rats, Sprague-Dawley ; Receptors, N-Methyl-D-Aspartate ; metabolism ; Sufentanil ; administration & dosage

OBJECTIVETo investigate the effects of curcumin on the behavior of chronic constrictive injury (CCI) rats and the CX3CR1 expression in spinal cord dorsal horn and dorsal root ganglia (DRG).

METHODSeventy-two male SD rats were randomly divided into 4 groups: 1) Sham operation group (Sham); 2) Chronic constrictive injury group (CCI); 3) Curcumin treated group (Cur), administrated with curcumin 100 mg x kg(-1) x d(-1) ip for 14 days after CCI; 4) Solvent contrast group (SC), administrated with an equal volume of solvent for 14 days after CCI. Paw thermal withdrawal (PTWL) and paw mechanical withdrawal threshold (PMWT) were measured on 2 pre-operative and 1, 3, 5, 7, 10, 14 post-operative days respectively. The lumbar segments L4-5 of the spinal cord and the L4, L5 DRG were removed at 3, 7, 14 days after surgery. The expression of CX3CR1 was determined by immunohistochemical staining.

RESULTCompared with Sham group, PTWL and PMWT in CCI group were significantly lower on each post-operative day (P<0.01), which reached a nadir on the 3rd day after CCI (PTWL was 6.5 +/- 1.1, PMWT was 22.6 +/- 5.1), and the expression of CX3CR1 were markedly increased in spinal cord dorsal horn and DRG. In Cur group, PTWL were higher than in CCI group on 7, 10, 14 post-operative day (P<0.05), and PMWT were higher than those in CCI group on 10 and 14 post-operative day (P<0.05). The administration of curcumin could significantly attenuate the activation of CX3CR1 induced by CCI.

CONCLUSIONThe study suggests that curcumin ameliorates the CCI-induced neuropathic pain, probably by attenuating the expression of CX3CR1 in spinal cord dorsal horn and dorsal root ganglia.

Analgesics ; administration & dosage ; Animals ; CX3C Chemokine Receptor 1 ; Curcumin ; administration & dosage ; Disease Models, Animal ; Down-Regulation ; drug effects ; Ganglia, Spinal ; drug effects ; metabolism ; Injections, Intraperitoneal ; Male ; Neuralgia ; drug therapy ; metabolism ; Posterior Horn Cells ; drug effects ; metabolism ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Receptors, Chemokine ; drug effects ; metabolism