CircFhit Modulates GABAergic Synaptic Transmission via Regulating the Parental Gene Fhit Expression in the Spinal Dorsal Horn in a Rat Model of Neuropathic Pain / 神经科学通报·英文版

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.

Pre- and Postsynaptic Actions of Reactive Oxygen Species and Nitrogen Species in Spinal Substantia Gelatinosa Neurons

Reactive oxygen species (ROS) and nitrogen species (RNS) are involved in cellular signaling processes as a cause of oxidative stress. According to recent studies, ROS and RNS are important signaling molecules involved in pain transmission through spinal mechanisms. In this study, a patch clamp recording was used in spinal slices of rats to investigate the action mechanisms of O₂˙⁻ and NO on the excitability of substantia gelatinosa (SG) neuron. The application of xanthine and xanthine oxidase (X/XO) compound, a ROS donor, induced inward currents and increased the frequency of spontaneous excitatory postsynaptic currents (sEPSC) in slice preparation. The application of S-nitroso-N-acetyl-DLpenicillamine (SNAP), a RNS donor, also induced inward currents and increased the frequency of sEPSC. In a single cell preparation, X/XO and SNAP had no effect on the inward currents, revealing the involvement of presynaptic action. X/XO and SNAP induced a membrane depolarization in current clamp conditions which was significantly decreased by the addition of thapsigargin to an external calcium free solution for blocking synaptic transmission. Furthermore, X/XO and SNAP increased the frequency of action potentials evoked by depolarizing current pulses, suggesting the involvement of postsynaptic action. According to these results, it was estblished that elevated ROS and RNS in the spinal cord can sensitize the dorsal horn neurons via pre- and postsynaptic mechanisms. Therefore, ROS and RNS play similar roles in the regulation of the membrane excitability of SG neurons.

Reactive oxygen species increase neuronal excitability via activation of nonspecific cation channel in rat medullary dorsal horn neurons

The caudal subnucleus of the spinal trigeminal nucleus (medullary dorsal horn; MDH) receives direct inputs from small diameter primary afferent fibers that predominantly transmit nociceptive information in the orofacial region. Recent studies indicate that reactive oxygen species (ROS) is involved in persistent pain, primarily through spinal mechanisms. In this study, we aimed to investigate the role of xanthine/xanthine oxidase (X/XO) system, a known generator of superoxide anion (O₂(·−)), on membrane excitability in the rat MDH neurons. For this, we used patch clamp recording and confocal imaging. An application of X/XO (300 µM/30 mU) induced membrane depolarization and inward currents. When slices were pretreated with ROS scavengers, such as phenyl N-tert-butylnitrone (PBN), superoxide dismutase (SOD), and catalase, X/XO-induced responses decreased. Fluorescence intensity in the DCF-DA and DHE-loaded MDH cells increased on the application of X/XO. An anion channel blocker, 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (DIDS), significantly decreased X/XO-induced depolarization. X/XO elicited an inward current associated with a linear current-voltage relationship that reversed near −40 mV. X/XO-induced depolarization reduced in the presence of La³⁺, a nonselective cation channel (NSCC) blocker, and by lowering the external sodium concentration, indicating that membrane depolarization and inward current are induced by influx of Na⁺ ions. In conclusion, X/XO-induced ROS modulate the membrane excitability of MDH neurons, which was related to the activation of NSCC.

Analgesic Effect and Mechanism of Electroacupuncture on Rats with Chronic Inflammatory Pain / 中国中西医结合杂志

<p><b>OBJECTIVE</b>To 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).</p><p><b>METHODS</b>Totally 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.</p><p><b>RESULTS</b>Compared 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).</p><p><b>CONCLUSION</b>EA 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.</p>

Electroacupuncture attenuates spinal nerve ligation-induced microglial activation mediated by p38 mitogen-activated protein kinase / 中国结合医学杂志

<p><b>OBJECTIVE</b>To investigate whether analgesic effect of electroacupuncture (EA) is affected by p38 mitogen-activated protein kinase (p38 MAPK) on microglia.</p><p><b>METHODS</b>There 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.</p><p><b>RESULTS</b>SNL-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).</p><p><b>CONCLUSIONS</b>The 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.</p>

Attenuated Glial K+ Clearance Contributes to Long-Term Synaptic Potentiation Via Depolarizing GABA in Dorsal Horn Neurons of Rat Spinal Cord

It has been reported that long-term enhancement of superficial dorsal horn (DHs) excitatory synaptic transmission underlies central sensitization, secondary hyperalgesia, and persistent pain. We tested whether impaired clearance of K+ and glutamate by glia in DHs may contribute to initiation and maintenance of the CNS pain circuit and sensorimotor abnormalities. Transient exposure of the spinal cord slice to fluorocitrate (FC) is shown to be accompanied by a protracted decrease of the DHs optical response to repetitive electrical stimulation of the ipsilateral dorsal root, and by a similarly protracted increase in the postsynaptic response of the DHs like LTP. It also is shown that LTP(FC) does not occur in the presence of APV, and becomes progressively smaller as [K+]o in the perfusion solution decreased from 3.0 mM to 0.0 mM. Interestingly LTP(FC) is reduced by bath application of Bic. Whole-cell patch recordings were carried out to evaluate the effects of FC on the response of DHs neurons to puffer-applied GABA. The observations reveal that transient exposure to FC is reliably accompanied by a prolonged (>1 hr) depolarizing shift of the equilibrium potential for the DHs neuron transmembrane ionic currents evoked by GABA. Considered collectively, the findings demonstrate that LTP(FC) involves (1) elevation of [K+]o in the DHs, (2) NMDAR activation, and (3) conversion of the effect of GABA on DHs neurons from inhibition to excitation. It is proposed that a transient impairment of astrocyte energy production can trigger the cascade of dorsal horn mechanisms that underlies hyperalgesia and persistent pain.

Role of muscarinic cholinergic receptor subtypes in regulating glutamatergic synaptic transmission in rat spinal dorsal horn / 南方医科大学学报

<p><b>OBJECTIVE</b>To 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.</p><p><b>METHODS</b>Whole-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.</p><p><b>RESULTS</b>The 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.</p><p><b>CONCLUSIONS</b>Activation 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.</p>

Effect of electroacupuncture on phosphorylation of NR2B at Tyr 1742 site in the spinal dorsal horn of CFA rats / 中国中西医结合杂志

<p><b>OBJECTIVE</b>To 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.</p><p><b>RESULTS</b>PWTs 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.</p><p><b>CONCLUSION</b>EA 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.</p>

Reasearch on mechanism of neurotrophins in discogenic low back pain / 中国骨伤

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.

Nonlinear dynamic analysis of electrical signals of wide dynamic range neurons in the spinal dorsal horn evoked by acupuncture manipulation at different frequencies / 中国中西医结合杂志

<p><b>OBJECTIVE</b>To study the encoding information of electrical signals of wide dynamic range (WDR) neurons in the spinal dorsal horn evoked by acupuncture manipulation at different frequencies using nonlinear dynamics analysis.</p><p><b>METHODS</b>Microelectrode extracellular recordings were used to observe the WDR neuron discharge evoked by acupuncture manipulation at Zusanli point (ST36) with different frequencies (0.5, 1, 2, and 3 Hz) in SD rats. The nonlinear dynamics analysis method was used to extract the nonlinear characteristic parameters, such as interspike interval, the Lyapunov exponent, Lempel-Ziv complexity, and the neural coding of the electrical signal evoked by acupuncture manipulations at different frequencies.</p><p><b>RESULTS</b>Different characteristics were manifested with acupuncture manipulations at 4 different frequencies. More than a simple linear correlation was shown between the firing rate of the WDR neurons and the frequency of the acupuncture manipulation. The electrical signals evoked by acupuncture manipulation at Zusanli point (ST36) showed distinguished chaotic features.</p><p><b>CONCLUSIONS</b>It is applicable and feasible to describe and summarize the rhythm of the acupuncture electrical signal using the concepts and terminology of the nonlinear dynamics. Different acupuncture manipulation methods could interfere the transmission, coding, and processing of electrical signals in the spinal dorsal horn.</p>

Analgesic effect of calpain inhibitor ALLN on the zymosan-induced paw inflammatory pain and its effect on the expression of cyclooxygenase-2 in the spinal dorsal horn / 中国医学科学院学报

<p><b>OBJECTIVE</b>To 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.</p><p><b>METHODS</b>Forty-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.</p><p><b>RESULTS</b>MWT 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).</p><p><b>CONCLUSION</b>Administration 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.</p>

Effect of intrathecal sufentanil and protein kinase C inhibitor on pain threshold and the expression of NMDA receptor/ CGRP in spinal dorsal horn in rats with neuropathic pain / 中南大学学报(医学版)

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.

Effect of intrathecal ketamine injection on protein kinase C expression in the spinal dorsal horn of rats with formalin-induced pain / 南方医科大学学报

<p><b>OBJECTIVE</b>To 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.</p><p><b>METHODS</b>Thirty-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.</p><p><b>RESULTS</b>Compared 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).</p><p><b>CONCLUSION</b>Intrathecal 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.</p>

Curcumin down-regulates CX3CR1 expression in spinal cord dorsal horn and DRG in neuropathic pain rats / 中国中药杂志

<p><b>OBJECTIVE</b>To 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).</p><p><b>METHOD</b>Seventy-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.</p><p><b>RESULT</b>Compared 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.</p><p><b>CONCLUSION</b>The 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.</p>

Neuronal Hyperexcitability Mediates Below-Level Central Neuropathic Pain after Spinal Cord Injury in Rats / 한국실험동물학회지

Spinal cord injury often leads to central neuropathic pain syndromes, such as allodynic and hyperalgesic behaviors. Electrophysiologically, spinal dorsal horn neurons show enhanced activity to non-noxious and noxious stimuli as well as increased spontaneous activity following spinal cord injury, which often called hyperexcitability or central sensitization. Under hyperexcitable states, spinal neurons lose their ability of discrimination and encoding somatosensory information followed by abnormal somatosensory recognition to non-noxious and noxious stimuli. In the present review, we summarize a variety of pathophysiological mechanisms of neuronal hyperexcitability for treating or preventing central neuropathic pain syndrome following spinal cord injury.

Effect of pre-electroacupuncture on p38 and c-Fos expression in the spinal dorsal horn of rats suffering from visceral pain / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Acupuncture is an effective way to relieve pain, but the mechanism by which electroacupuncture (EA) decreases the visceral pain state still remains unclear. This study aimed to evaluate the effects of pre-electroacupuncture on pain behaviors, p38 phosphorylation, and c-Fos protein and mRNA expression in both the colonic wall and spinal dorsal horn of rats suffering from visceral pain. This study also investigated the probable signaling regulatory mechanism of the analgesic effect induced by electroacupuncture.</p><p><b>METHODS</b>All rats were randomized into the control (Con) group, the Con + EA group, the visceral pain (VP) group, and VP + EA group (n = 8 for all groups). The visceral pain model was established using 40 microl of 5% formalin solution injected into the colon of rats. EA was applied to the bilateral Jiaji acupoints for 20 minutes before application of visceral pain. Parameters for EA were set at a continuous wave (20 Hz) and intensity where the rats shook their whiskers but did not scrabble (< or = 1 mA). The visceral pain score was recorded and the expressions of p38 and c-Fos protein were detected using Western blotting. Real-time quantitative PCR was also used to determine the expression of c-Fos mRNA.</p><p><b>RESULTS</b>Rats in the VP group immediately presented with obvious visceral pain behaviors after being injected with formalin. p38 activity and c-Fos protein and mRNA expression in both the colonic wall and spinal dorsal horn were higher in the VP group than in the Con group (P < 0.05). By contrast, visceral pain behaviors were delayed in rats from the VP + EA group. p38 activity and c-Fos protein and mRNA expression were lower in the VP + EA group than that in the VP group (P < 0.01).</p><p><b>CONCLUSIONS</b>Pre-electroacupuncture of the Jiaji acupoint has prophylactic analgesic effects on rats suffering from visceral pain. The p38 signal transduction pathway may be partly involved in the regulatory mechanism of this analgesic effect.</p>

Expression of nNOS, Pax3 and Cx43 proteins in early developing posterior horn of embryonic and fetal human spinal cord / 南方医科大学学报

<p><b>OBJECTIVE</b>To 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.</p><p><b>METHODS</b>Immunohistochemistry 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.</p><p><b>RESULTS</b>In 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.</p><p><b>CONCLUSION</b>nNOS, Pax3 and Cx43 proteins are closely related to the growth and development of the spinal cord in human embryos and fetuses.</p>

Tramadol inhibits c-fos expression in spinal cord dorsal horn and serum IL-6 levels induced by plantar incision in rats / 浙江大学学报·医学版

<p><b>OBJECTIVE</b>To investigate effect of tramadol on c-fos expression in spinal cord dorsal horn and serum IL-6 levels induced by plantar incision in rats.</p><p><b>METHODS</b>The Brennan pain model was induced by incision on the planter surface of left hind paw in rats. Forty-eight rats were randomly divided into six groups: Sham group (Group C), control group (Group I,pretreatment with saline 5 ml), three tramadol pretreatment groups (Group T1, T10 and T20,pretreated with 1 mg/kg, 10 mg/kg and 20 mg/kg tramadol, respectively) and one tramadol treatment group (Group PT10, treated with tramadol 10 mg/kg immediately after operation). Pain behavior was assessed by withdrawal threshold to von Frey filament stimulation intensity, response latency of the hind paw to radiant thermal and a cumulative pain score 2 h after incision. Fos-positive neurons in spinal cord were identified by the immunohistochemical technique. Serum IL-6 levels were measured by enzyme-linked immunosorbent assay (ELISA).</p><p><b>RESULTS</b>WithdrawIal threshold to von Frey filament stimulation intensity and response latency of the hind paw to radiant thermal in Group I were significantly lower than those in Group C (P<0.01). Cumulative pain score in Group I was significantly higher than that in Group C (P<0.01). In Groups of T10 and T20, withdrawal threshold to von Frey filament stimulation intensity and response latency of the hind paw to radiant thermal were significantly higher than those in Group I (P<0.01), cumulative pain score was significantly lower than that in Group I in a dose-dependent manner (P<0.01), and were also those in Group PT10. The greatest density of Fos-positive neurons was located in lamine I-II in Group I. Serum IL-6 levels were significantly elevated in Group I. Pretreatment with tramadol showed a dose-depended inhibitory effect on c-fos expression and serum IL-6 production,but not in Group T1. Administration of tramadol postoperatively also suppressed the c-fos expression and serum IL-6 production as showed in PT10 but were weaker than those in Group T10.</p><p><b>CONCLUSION</b>Pretreatment with tramadol can produce dose-dependent inhibitory effect on c-fos expression in spinal cord dorsal horn and then suppress the inflammatory response to the trauma.</p>

Effects of Somatostatin on the Responses of Rostrally Projecting Spinal Dorsal Horn Neurons to Noxious Stimuli in Cats

Somatostatin (SOM) is a widely distributed peptide in the central nervous system and exerts a variety of hormonal and neural actions. Although SOM is assumed to play an important role in spinal nociceptive processing, its exact function remains unclear. In fact, earlier pharmacological studies have provided results that support either a facilitatory or inhibitory role for SOM in nociception. In the current study, the effects of SOM were investigated using anesthetized cats. Specifically, the responses of rostrally projecting spinal dorsal horn neurons (RPSDH neurons) to different kinds of noxious stimuli (i.e., heat, mechanical and cold stimuli) and to the A delta-and C-fiber activation of the sciatic nerve were studied. Iontophoretically applied SOM suppressed the responses of RPSDH neurons to noxious heat and mechanical stimuli as well as to C-fiber activation. Conversely, it enhanced these responses to noxious cold stimulus and A delta-fiber activation. In addition, SOM suppressed glutamate-evoked activities of RPSDH neurons. The effects of SOM were blocked by the SOM receptor antagonist cyclo-SOM. These findings suggest that SOM has a dual effect on the activities of RPSDH neurons; that is, facilitation and inhibition, depending on the modality of pain signaled through them and its action site.

Changes in response properties of nociceptive dorsal horn neurons in a murine model of cancer pain / 生理学报

Pain associated with cancer that metastasizes to bone is often severe and debilitating. A better understanding of the neural mechanisms that mediate cancer pain is needed for the development of more effective treatments. In this study, we used an established model of cancer pain to characterize changes in response properties of dorsal horn neurons. Fibrosarcoma cells were implanted into and around the calcaneus bone in mice and extracellular electrophysiological recordings were made from wide dynamic range (WDR) and high threshold (HT) dorsal horn neurons. Responses of WDR and HT neurons evoked by mechanical, heat, and cold stimuli applied to the plantar surface of the hind paw were compared between tumor bearing mice and control mice. Mice exhibited hyperalgesia to mechanical and heat stimuli applied to their tumor-bearing hind paw. WDR neurons in tumor-bearing mice exhibited an increase in spontaneous activity, and enhanced responses to mechanical, heat, and cold stimuli as compared to controls. Our findings show that sensitization of WDR neurons, but not HT neurons, contributes to tumor-evoked hyperalgesia.