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

AIMTo observe the changes of cyclooxygenase-2 (COX-2) expression and especially the time course of the changes in dorsal horn of the spinal cord during formalin-induced inflammatory pain and hyperalgesia in rats.

METHODSCOX-2 immunohistochemistry staining was used in rat formalin pain model.

RESULTSCompared with control group the number and immunostaining density of COX-2 immunoreactive cells in the laminae I-VI of the dorsal horn of the spinal cord increased significantly 4 h, 1 d and 3 d after formalin injection (P < 0.05). The most obvious increase was observed 1 d after the injection.

CONCLUSIONCOX-2 in the dorsal horn of the spinal cord is involved in the formalin-induced inflammatory pain and hyperalgesia.

Animals ; Cyclooxygenase 2 ; metabolism ; Formaldehyde ; adverse effects ; Pain ; chemically induced ; metabolism ; Posterior Horn Cells ; metabolism ; Rats ; Rats, Sprague-Dawley ; Spinal Cord ; 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

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

OBJECTIVETo observe the effect of electroacupuncture at Zusanli (ST 36) on phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2) in the dorsal horn of spinal cord induced by plantar inflammation in the rat.

METHODSAll the rats were randomly divided into 5 groups: normal control group, simple electroacupuncture group, formalin group, formalin plus ipsilateral electroacupuncture group and formalin plus contralateral electroacupuncture group. The acute inflammation animal model was made by injection of 100 microL of 4% formalin into the right posterior foot pad. Electroacupuncture was given at "Zusanli" (ST 36) for 30 min, with sparse-dense waves, frequency 2-15 Hz, and intensity 2-3 mA. One and a half hours latter, the rats were killed under anesthesia, and pERK1/2 expression in the lumbar dorsal horn were investigated with immunohistochemical method.

RESULTSThe positive cells were rarely seen (6.45 +/- 1.05) in the superficial spinal cord in the control group; a few cells (14.07 +/- 3.19) in ipsilateral superficial spinal cord were found in the electroacupuncture group. The number of pERK1/2-positive neurons (26.57 +/- 4.93) in lamina I - II0 of the ipsilateral dorsal horn in the formalin group increased significantly. After electroacupuncture at ipsilateral Zusanli (ST 36), the number of positive cells (20.79 +/- 5.21) had a tendency to decrease, but with no statistically significant difference. However, after electroacupuncture at contralateral Zusanli (ST 36), the number of positive cells (14.75 +/- 3.03) significantly decreased as compared with the non-acupuncture group (P < 0.05).

CONCLUSIONThe inhibition of ERK1/2 phosphorylation in the spinal cord dorsal horn by electroacupuncture is possibly involved in acupuncture analgesic effect.

Acupuncture Analgesia ; Acupuncture Points ; Animals ; Electroacupuncture ; Male ; Mitogen-Activated Protein Kinase 1 ; metabolism ; Mitogen-Activated Protein Kinase 3 ; metabolism ; Phosphorylation ; Posterior Horn Cells ; enzymology ; Rats ; Rats, Sprague-Dawley

OBJECTIVE: To investigate the effects of N-methyl-D-aspartate receptor (NMDAR) in the spinal dorsal horn in visceral hypersensitivity in rats with colonic inflammation. METHODS: Seventy adult male Sprague-Dawley (SD) rats were randomly divided into the experimental group and the control group. Colonic inflammation was induced in the experimental rats by intraluminal administration of trinitrobenzenesulfonic acid (TNBS). Saline was administered intraluminally in the control rats. After 3, 7, 14, and 28 days of administration, abdominal contractions induced by inflation of a balloon colonically inserted were recorded in rats by implanting electrodes in the abdominal striated muscles. Immunohistochemistry method was used to study the expression of NMDAR1 and NMDAR2A/B in lumbarsacral spinal cord after inflammation. RESULTS: Colonic distension evoked a significant increase of abdominal contractions after 3, 7 and 14 days of TNBS administration. After 28 days of TNBS administration, abdominal contractions were still significantly increased in 2 TNBS-treated rats compared with the control rats. After 7 and 14 days of TNBS administration, NMDAR1 and NMDAR2A/B-immunoreactive cells were significantly increased compared with the control group (P <0.05). Twenty-eight days after TNBS administration, the number of NMDAR1-IR and NMDAR2A/B-IR neurons was still significantly increased in 4 TNBS-treated rats compared with the saline-treated rats (P < 0.05). CONCLUSION NMDAR was involved in the transmission of visceral nociceptive stimuli. After the remission of colonic inflammation, increased expression of NMDAR1 and NMDAR2A/B in the spinal dorsal horn may induce persistent neuronal hyperactivity, which results in visceral hypersensitivity.
Animals ; Colitis ; chemically induced ; metabolism ; Male ; Posterior Horn Cells ; metabolism ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Receptors, N-Methyl-D-Aspartate ; biosynthesis ; genetics ; Trinitrobenzenesulfonic Acid

OBJECTIVETo investigate the distribution pattern of the expressions neuronal nitric oxide synthase (nNOS), Pax3 and connexin 43 (Cx43) proteins in the early developing posterior horn of embryonic and fetal human spinal cord.

METHODSImmunohistochemistry was used to detect the expressions of nNOS, Pax3 and Cx43 proteins in the posterior horn of the spinal cord during the second, third and fourth month of human embryonic and fetal development.

RESULTSIn the second to fourth month of gestation, the expressions of nNOS and Pax3 proteins increased gradually from weak expression to strong expression in the posterior horn of the spinal cord. In the second to third month of development, Cx43 protein expression was negative in the posterior horn of the spinal cord, but positive in the myelin sheath. In the fourth month, positive Cx43 expression was detected in some of the cells in the posterior horn of the spinal cord.

CONCLUSIONnNOS, Pax3 and Cx43 proteins are closely related to the growth and development of the spinal cord in human embryos and fetuses.

Connexin 43 ; metabolism ; Embryo, Mammalian ; cytology ; metabolism ; Female ; Fetus ; cytology ; metabolism ; Gene Expression Regulation, Developmental ; Humans ; Nitric Oxide Synthase Type I ; metabolism ; PAX3 Transcription Factor ; Paired Box Transcription Factors ; metabolism ; Posterior Horn Cells ; metabolism ; Pregnancy

OBJECTIVETo observe the effect and mechanism of Tianyuan Ketong recipe (TKR) on the pain reaction in formalin induced pain model rats.

METHODSThe analgesic effect of TKR was evaluated using pain behavior graded scoring, the c-fos gene expression and P substance contents in superficial lamella of spinal cord dorsal horn in model rats were analyzed by means of immunohistochemical analysis and computer image analysis technique.

RESULTSTKR could markedly inhibit the pain reaction in model rats (P < 0.05), and the pain induced elevation of c-fos expression and P substance contents could also be suppressed (P < 0.05).

CONCLUSIONTKR shows definite analgesic effect on formalin induced pain model rats, the reduction of neuron's reaction in spinal cord dorsal horn to afferent noxious stimulation is possibly one of the pathways for its analgesic effect.

Analgesics, Non-Narcotic ; pharmacology ; Animals ; Drugs, Chinese Herbal ; pharmacology ; Female ; Formaldehyde ; Immunohistochemistry ; Male ; Oncogene Proteins v-fos ; biosynthesis ; genetics ; Pain ; chemically induced ; metabolism ; Posterior Horn Cells ; metabolism ; Rats ; Rats, Sprague-Dawley ; Spinal Cord ; metabolism ; Substance P ; metabolism

OBJECTIVETo investigate the expression of protein kinase C (PKC) in the spinal dorsal horn of rats with formalin-induced pain and the effect of intrathecal ketamine on PKC expression.

METHODSThirty-two SD rats were randomly divided into 4 equal groups, namely the control group, intrathecal saline group (NS), 50 µg ketamine group (K1) and 100 µg ketamine group (K2). The rats were anesthetized with 10% chloral hydrate, and a microspinal catheter was inserted intrathecally into the lumbar region. Five days later, the rats in groups, K1 and K2 were subjected to intrathecal administration of 50 and 100 µg ketamine (10 µl), respectively, followed by 10 µl saline, and those in NS group received 20 µl saline only. Thirty minutes later, 5% formalin (50 µl) was subcutaneously injected into the left hindpaw. The pain intensity score (PIS) was utilized to assess antinociceptive behavior within 1 h after formalin injection. Twenty-four hours later, the left hindpaw thickness was measured and the expression of PKC in the spinal dorsal horn in the L5 segment was assayed using immunohistochemistry.

RESULTSCompared to group NS, groups K1 and K2 showed significantly decreased PIS (P<0.01) in the second phase of formalin-induced pain; 24 h later, the left hindpaw thickness of group NS increased obviously in comparison with that in the control group (P<0.01), whereas the thickness was significantly reduced in group K1 and K2 as compared to that in group NS (P<0.05). The number of immunoreactive cells and the immunohistochemical score of PKC in the spinal dorsal horn were significantly higher in group NS than in group C (P<0.01), but significantly lower in groups K1 and K2 than in group NS (P<0.05).

CONCLUSIONIntrathecal ketamine produces obvious antinociception against formalin-induced pain in rats and inhibits the enhanced PKC expression in the spinal dorsal horn in response to formalin-induced pain, suggesting the important role of PKC in nociceptive signal transmission and modulation in the spinal cord.

Animals ; Formaldehyde ; adverse effects ; Injections, Spinal ; Ketamine ; administration & dosage ; pharmacology ; Male ; Pain ; chemically induced ; metabolism ; Pain Measurement ; Posterior Horn Cells ; metabolism ; Protein Kinase C ; metabolism ; Rats ; Rats, Sprague-Dawley ; Spinal Cord ; drug effects ; metabolism