CYP1B1-derived epoxides modulate the TRPA1 channel in chronic pain

Pain is often debilitating, and current treatments are neither universally efficacious nor without risks. Transient receptor potential (TRP) ion channels offer alternative targets for pain relief, but little is known about the regulation or identities of endogenous TRP ligands that affect inflammation and pain. Here, transcriptomic and targeted lipidomic analysis of damaged tissue from the mouse spinal nerve ligation (SNL)-induced chronic pain model revealed a time-dependent increase in Cyp1b1 mRNA and a concurrent accumulation of 8,9-epoxyeicosatrienoic acid (EET) and 19,20-EpDPA post injury. Production of 8,9-EET and 19,20-EpDPA by human/mouse CYP1B1 was confirmed in vitro, and 8,9-EET and 19,20-EpDPA selectively and dose-dependently sensitized and activated TRPA1 in overexpressing HEK-293 cells and Trpa1-expressing/AITC-responsive cultured mouse peptidergic dorsal root ganglia (DRG) neurons. TRPA1 activation by 8,9-EET and 19,20-EpDPA was attenuated by the antagonist A967079, and mouse TRPA1 was more responsive to 8,9-EET and 19,20-EpDPA than human TRPA1. This latter effect mapped to residues Y933, G939, and S921 of TRPA1. Intra-plantar injection of 19,20-EpDPA induced acute mechanical, but not thermal hypersensitivity in mice, which was also blocked by A967079. Similarly, Cyp1b1-knockout mice displayed a reduced chronic pain phenotype following SNL injury. These data suggest that manipulation of the CYP1B1-oxylipin-TRPA1 axis might have therapeutic benefit.

Regulatory Effects of Ionotropic and GroupⅠ Metabotropic Glutamate Receptors on Temperature Hypersensitivity in Rats / 中国医科大学学报

Objective To study the effects of ionic and group Ⅰ metabotropic glutamate receptors on rats' thermal hypersensitivity by intraplantar administration of drugs. Methods After intraplantar administration of glutamate receptor agonists,L-glutamic acid (Glu), N-methyl-D-aspartic-acid (NMDA),and (RS)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hydrobromide (AMPA);a Group Ⅰ mGluR agonist, (S) 3,5-dihydroxyphenylglycine [(S)-DHPG];a noncompetitive NMDA receptor antagonist, (+)-MK801 maleate (MK-801);a competitive AMPA/kainate receptor antagonist,6-cyano-7-nitroquinoxaline-2,3-dione (CNQX);and a selective GroupⅠ mGluR antagonist,7-hydroxyiminocyclo propan[b]chromen-1a- carboxylic acid ethyl ester (cpccoEt) into the left hind paws of rats whose L5-6 nerves were sham-operated or ligated,we examined the response of the rats to thermal stimuli provided by radiant heat. Results In sham-operated rats,glutamate,NMDA,AMPA,and (S)-DHPG reduced paw withdrawal latency (PWL) but did not have any effect on SNL rats. However,in SNL rats,MK-801,CNQX,and cpccoEt increased PWL but exerted no effect on sham-operated rats. Conclusion These results suggest that changes in sensitivity of peripheral ionic and group Ⅰ metabotropic glutamate receptors can lead to changes in peripheral nerve plasticity;the generation and maintenance of neuropathic pain caused by nerve injury is based on this plasticity.

Role of N-methyl-D-aspartic acid receptor 2B in neuropathic pain induced by spinal nerve ligation in rats / 医学研究生学报

Objective Spinal cord injury-induced neuropathic pain(NP)does not respond well to any existing therapies clinically.This study aimed to explore the molecular metabolisms neuropathic pain by observing the expressions of the N -methyl-D-as-partic acid receptor 2B(NR2B),tumor necrosis factor-alpha(TNF-α)and brain-derived neurotrophic factor(BDNF)in different sta-ges of the condition in SD rats. Methods Thirty-six adult SD rats were randomly divided into a control,a sham operation and an NP model group.The NP model was established by spinal nerve ligation. At 5 and 14 days after modeling,the hindlimb motor function and paw withdrawal threshold(PWT)of the rats were evaluated by the open-field test and the expressions of NR 2B,TNF-αand BDNF in the dor-sal root ganglia of the L4-6 spinal cord were determined by Western blot. Results At 5 days after modeling,the open-field test showed a significantly shorter total distance of movement in the sham operation group than in the control([14 927.93 ±560.87]vs [18 225.15±371.76]mm,P<0.05)and even shorter in the NP model group([3 224.92±89.64]vs[18 225.15±371.76]mm, P<0.01).The time of activity was markedly decreased in the NP model group as compared with that in the control([203.48±19.94]vs [745.95±13.48]s,P<0.01),but with no statistically significant difference between the sham operation and control groups([727.93± 16.29]vs[745.95±13.48]s,P>0.05).At 14 days after modeling,both the total distance of movement and time of activity were re-markably shorter in the NP model than in the sham operation and control groups([3 395.53±96.12]vs[17 382.26±482.31]and [17 975.40±416.56]mm,P<0.01;[195.53±96.12]vs[739.31±18.36]and[775.20±16.84]s, P<0.01).The PWT showed no statistically significant difference among the three groups of rats before modeling(P>0.05)but markedly decreased in the NP model as compared with the sham operation and control groups(P<0.01),with no significant difference between the latter two(P>0.05).The expressions of NR2B,TNF-αand BDNF were remarkably up-regulated in the NP model group in comparison with the sham operation and control groups at 5 days after modeling(P>0.05)and even more significantly at 14 days(P<0.01). Conclusion NR2B and BDNF may be involved in the development and progression of neuropathic pain in rats.

Role of NDRG2 in the dorsal horn of the spinal cord in rats with spinal nerve ligation of neuropathic pain / 临床麻醉学杂志

Objective To investigate the effect of NDRG2 on neuropathic pain model rats with spinal cord ligation(SNL)in the dorsal horn of the spinal cordby using intrathecal NDRG2 adenovirus (AD-Ndrg2-RNAi).Methods Forty-two male SD rats weighing 180-230 g were randomly divided into sham operation group (n=6)and SNL group (n=3 6).SNL group underwent lumbar spinal dor-sal ligation.The sham operation group only exposed the spinal nerve without ligation.The mechanical withdraw threshold (MWT)and thermal withdrawlantency (TWL)were measured at 1 d before op-eration and at 1,3,7,10,14 and 21 d after operation.After the behavioral testing,the rats in SNL group were sacrificed and the lumber segment of the spinal cord was removed to test theprotein and mRNA level of NDRG2.Another forty-eight male SD rats were randomly divided into 4 groups after intrathecal catheterization (n=12):group sham operation with saline (group CS);group sham oper-ation with adenovirus (group CA);group SNL with saline (group SS);group SNL with adenovirus(group SA).The rats in groups CS and SS were treated with intrathecal injection of normal saline 10 μl on the third day after operation,while groups CA and SA received the single injection titer of 2× 109PFU/ml of AD-Ndrg2-RNAi on the same day.The rat plantar MWT and TWL were measured at 1 d before SNL and at 1,3,7 and 10 d after SNL.The rats were sacrificed after the lastbehavioral test.Lumbar enlargement of the spinal cord was removed to test the level of NDRG2 and GFAP pro-tein.The expression of NDRG2 mRNA was detected by real-time fluorescence quantitative PCR. Results Compared with sham group,the MWT and TWL was significantly decreased and reduced in SNL group 1,3,7,10,14,21 d and 3,7,10,14,21 d after surgery respectively(P<0.01).Com-pared with 1 d before surgery,protein content and mRNA expression of NDRG2 in the spinal dorsal horn of the SNL group were significantly decreased 1 d after surgery,and they were significantly in-creased on the 7,10,14,and 21 d after operation(P<0.01).Compared with group CS,the MWT and TWL were significantly decreased and reduced in group SS and group SA 1,3,7 and 10 d after surgery(P<0.05).MWT and TWL on 7 and 10 d were increased significantly in group SA (P<0.05)compared with group SS.Compared with group CS,protein content and mRNA expression of NDRG2 in the spinal dorsal horn of group CA were significantly decreased,and increased significantly in group SS 10 d after surgery(P<0.05).Compared with group SS,protein content and mRNA ex-pression of NDRG2 in the spinal dorsal horn of group SA were significantly decreased.Compared with group CS,the protein content of GFAP in spinal dorsal horn of group CA,group SS and group SA were increased significantly 10 d after surgery (P<0.05).Conclusion Intrathecal injection of AD-Ndrg2-RNAi significantly inhibits neuropathic pain caused by spinal cord ligation in rats,suggesting that NDRG2 in astrocytes is involved in the development and progression of neuropathic pain.

Neuropathic Pain Relieving in Rats by the Inhibition of Monomer of Lamiophlomis Rotata on AKT-mTOR Signaling Pathway in Spinal Dorsal Horn / 中国药师

Objective:To observe the effect of intrathecal administration of 8-O-acetyl-SM(8-OaS) on chronic neuropathic pain in rats by inhibiting the expression of protein kinase B(AKT)-mammalian target of rapamycin(mTOR) signaling pathway in spinal dorsal horn after spinal nerve ligation.Methods:The rat model of neuropathic pain was established by lumbar 5 spinal nerve ligation(SNL), and Von Frey filament was used to investigate the mechanical allodynia. Immunofluorescent histochemistry was adopted to investigate the distribution of pAKT and pmTOR in spinal dorsal horn. The protein levels of pAKT and pmTOR in spinal dorsal horn after drug ad-ministration were quantitatively determined by Western blot. Results: Compared with that in the sham group, the paw withdrawal threshold (PWT) significantly decreased(P<0.01),and the intrathecal administration of 8-OaS attenuated mechanical allodynia ob-viously during the first day and the seventh day after the operation(P<0.05). Meanwhile,double immunofluorescent staining showed the co-expression of pAKT and astrocytes marker glial fibrillary acidic protein(GFAP),and positive labeling of pmTOR was expressed in spinal astrocytes and neurons. The results of Western blot revealed that the protein levels of pAKT and pmTOR in spinal dorsal horn were significantly reduced after the treatment of 8-OaS. Conclusion:Intrathecal administration of 8-OaS attenuates the PWT of SNL-in-duced chronic neuropathic pain. The underlying mechanism of the potential anti-allodynia effect of 8-OaS may be related to the suppres-sion of spinal astrocytes via decreasing the phosphorylation of AKT-mTOR signaling pathway resulting in attenuating the development of neuropathic pain.

The Synergistic Effect of Intrathecally Administered Dexmedetomidine and Ketorolac on Mechanical Allodynia in Rats with Spinal Nerve Ligation / 고신대학교의과대학학술지

OBJECTIVES: This research was carried out to identify the synergistic effect of dexmedetomidine and ketorolac on neuropathic pain alleviation. METHODS: The anti-allodynic effect of intrathecal dexmedetomidine and ketorolac was investigated in rats after L5 spinal nerve ligation (SNL). Mechanical allodynia was assessed using Von Frey filaments. Every day for 3 consecutive days, beginning on the 10th day after SNL, behavioral tests were carried out at 1, 2, and 4 hr after drug injection. RESULTS: Significant increases in ipsilateral paw withdrawal thresholds (PWTs) were observed 1, 2, and 4 hr after drug injection in the groups of rats which received intrathecal injection of either dexmedetomidine (group D) or ketorolac (group K), compared to group S (P < 0.05). And group DK, which received simultaneous intrathecal injection of both dexmedetomidine and ketorolac, showed statistically significantly higher ipsilateral PWTs than groups D and K, which received only one of them (P < 0.05). CONCLUSIONS: The results of this research demonstrated the anti-allodynic effect of dexmedetomidine and ketorolac on neuropathic pain induced by SNL in rats. They also suggest that synergistic analgesia can be induced by the simultaneous injection of dexmedetomidine and ketorolac, and that combination therapy is an effective approach to treating chronic neuropathic pain syndrome.

Mechanical Antiallodynic Effect of Intrathecal Nefopam in a Rat Neuropathic Pain Model

Nefopam has a pharmacologic profile distinct from that of opioids or other anti-inflammatory drugs. Several recent studies demonstrate that nefopam has a mechanism of action similar to those of anti-depressants and anticonvulsants for treating neuropathic pain. The present study investigates the mechanical antiallodynic effect of nefopam using immunohistochemical study and western blot analysis in a rat neuropathic pain model. Twenty-eight male Sprague-Dawley rats were subjected to left fifth lumbar (L5) spinal nerve ligation and intrathecal catheter implantation, procedures which were not performed on the 7 male Sprague-Dawley rats in the sham surgery group (group S). Nefopam, either 10 or 100 microg/kg (group N10 or N100, respectively), and normal saline (group C) were intrathecally administered into the catheter every day for 14 days. The mechanical allodynic threshold of intrathecal nefopam was measured using a dynamic plantar aesthesiometer. Immunohistochemistry targeting cluster of differentiation molecule 11b (CD11b) and glial fibrillary acidic protein (GFAP) was performed on the harvested spinal cord at the level of L5. Extracellular signal-regulated kinase 1/2 (ERK 1/2) and cyclic adenosine monophosphate response element binding protein (CREB) were measured using western blot analysis. The N10 and N100 groups showed improved mechanical allodynic threshold, reduced CD11b and GFAP expression, and attenuated ERK 1/2 and CREB in the affected L5 spinal cord. In conclusion, intrathecal nefopam reduced mechanical allodynia in a rat neuropathic pain model. Its mechanical antiallodynic effect is associated with inhibition of glial activation and suppression of the transcription factors' mitogen-activated protein kinases in the spinal cord.

Influência da idade, sexo e dos hormônios gonadais na percepção dolorosa em modelo de dor neuropática em ratos / Influence of age, sex and gonadal hormones on pain perception in neuropathic pain model in rats

Os fatores idade e sexo modificam a experiência dolorosa em animais e seres humanos. Os efeitos dos hormônios gonadais têm sido estudados em diversos modelos experimentais de dor, no entanto, o efeito do envelhecimento na percepção à dor carece de mais investigação. O efeito do envelhecimento na dor neuropática ainda não está bem estabelecido. Neste estudo se procurou avaliar possíveis variações na percepção da dor da hiperalgesia mecânica, em função da idade, presença e ausência de hormônios gonadais e sexo em ratos Wistar machos e fêmeas, jovens e idosos no modelo de dor neuropática, ligadura da quinta raiz lombar. Os animais foram divididos nos seguintes grupos: ratos jovens orquiectomizados e não-orquiectomizados, ratos idosos orquiectomizados e não-orquiectomizados, ratas jovens ooforectomizadas com ou sem reposição de 17beta-estradiol e ratas idosas. Foi testado o limiar de retirada da pata após estímulo mecânico antes da ligadura e no 7º, 14º, 21º e 28o dias após a ligadura. Os resultados mostraram que todos os animais apresentaram comportamento hiperalgésico após ligadura da quinta raiz lombar durante os 28 dias de observação. A hiperalgesia ocorreu independentemente do sexo do animal, da presença ou ausência de hormônios gonadais ou idade. Não houve diferença entre ratos jovens e idosos não-orquiectomizados (p = 0,420), entre ratos jovens e idosos orquiectomizados (p = 0,560). Entre os ratos idosos com e sem orquiectomia houve diferença no 14º (p = 0,038) e 28º (p = 0,002) dias. Ratas jovens ooforectomizadas sem reposição de 17beta-estradiol apresentaram menor hiperalgesia que ratas ooforectomizadas com reposição durante todo o período (p = 0,001). Não houve diferença entre ratos idosos orquiectomizados e ratas idosas (p = 0,09). Ratos jovens não-orquiectomizados apresentaram menor hiperalgesia mecânica que ratas jovens ooforectomizadas com reposição de 17beta-estradiol (p = 0,001), o mesmo não ocorreu entre machos e fêmeas jovens gonadectomizados...

Age and sex modify the pain experience in animals and humans. The effects of gonadal hormones have been studied in various experimental pain models, however, the effect of aging on pain perception needs further investigation. The effect of aging on neuropathic pain is not well established. In this study, we sought to determine how aging and gonadal hormones affect mechanical hyperalgesia using spinal nerve ligation as a neuropathic pain model in aged and young male and female Wistar rats. Animals were divided into seven groups: aged female, ovariectomized young females with 17beta-estradiol replacement, ovariectomized young females without 17beta-estradiol replacement, orchiectomized and non-orchiectomized aged and young males. Rats were tested for mechanical hyperalgesia in the plantar surface of the left hindpaw before nerve ligation and on days 7, 14, 21 and 28 after nerve ligation. All animals of all groups showed mechanical hyperalgesic behavior after spinal nerve ligation during entire period of 28 days. Hyperalgesia was independent of the sex of the animal, the presence or absence of gonadal hormones or age. There was no difference between non-orchiectomized aged and young males (p = 0.420), and between orchiectomized aged and young males (p = 0.560). There was difference between aged male rats with and without orchiectomy in days 14 (p = 0.038) and 28 (p = 0.002). Young ovariectomized female rats without 17beta-estradiol replacement had less hyperalgesia than young ovariectomized female rats with replacement (p = 0.001). There was no difference between aged orchiectomized male rats and old female rats (p = 0.09). Young non-orchiectomized male rats showed less mechanical hyperalgesia than young ovariectomized female rats with 17beta-estradiol replacement (p = 0.001), that did not occur between young orchiectomized males rats and young ovariectomized females rats without 17beta-estradiol replacement (p = 0.51). Young ovariectomized...

An improved experimental model for peripheral neuropathy in rats

A modification of the Bennett and Xie chronic constriction injury model of peripheral painful neuropathy was developed in rats. Under tribromoethanol anesthesia, a single ligature with 100% cotton glace thread was placed around the right sciatic nerve proximal to its trifurcation. The change in the hind paw reflex threshold after mechanical stimulation observed with this modified model was compared to the change in threshold observed in rats subjected to the Bennett and Xie or the Kim and Chung spinal ligation models. The mechanical threshold was measured with an automated electronic von Frey apparatus 0, 2, 7, and 14 days after surgery, and this threshold was compared to that measured in sham rats. All injury models produced significant hyperalgesia in the operated hind limb. The modified model produced mean ± SD thresholds in g (19.98 ± 3.08, 14.98 ± 1.86, and 13.80 ± 1.00 at 2, 7, and 14 days after surgery, respectively) similar to those obtained with the spinal ligation model (20.03 ± 1.99, 13.46 ± 2.55, and 12.46 ± 2.38 at 2, 7, and 14 days after surgery, respectively), but less variable when compared to the Bennett and Xie model (21.20 ± 8.06, 18.61 ± 7.69, and 18.76 ± 6.46 at 2, 7, and 14 days after surgery, respectively). The modified method required less surgical skill than the spinal nerve ligation model.

Identification of Differentially Expressed Genes by Gabapentin in Cultured Dorsal Root Ganglion in a Rat Neuropathic Pain Model

Neuropathic pain is a chronic pain disorder caused by nervous system lesions as a direct consequence of a lesion or by disease of the portions of the nervous system that normally signal pain. The spinal nerve ligation (SNL) model in rats that reflect some components of clinical pain have played a crucial role in the understanding of neuropathic pain. To investigate the direct effects of gabapentin on differential gene expression in cultured dorsal root ganglion (DRG) cells of SNL model rats, we performed a differential display reverse transcription-polymerase chain reaction analysis with random priming approach using annealing control primer. Genes encoding metallothionein 1a, transforming growth factor-beta1 and palmitoyl-protein thioesterase-2 were up-regulated in gabapentin-treated DRG cells of SNL model rats. The functional roles of these differentially expressed genes were previously suggested as neuroprotective genes. Further study of these genes is expected to reveal potential targets of gabapentin.

Antinociceptive Effects of Amiloride and Benzamil in Neuropathic Pain Model Rats

Amiloride and benzamil showed antinocicepitve effects in several pain models through the inhibition of acid sensing ion channels (ASICs). However, their role in neuropathic pain has not been investigated. In this study, we investigated the effect of the intrathecal amiloride and benzamil in neuropathic pain model, and also examined the role of ASICs on modulation of neuropathic pain. Neuropathic pain was induced by L4-5 spinal nerve ligation in male Sprague-Dawley rats weighing 100-120 g, and intrathecal catheterization was performed for drug administration. The effects of amiloride and benzamil were measured by the paw-withdrawal threshold to a mechanical stimulus using the up and down method. The expression of ASICs in the spinal cord dorsal horn was also analyzed by RT-PCR. Intrathecal amiloride and benzamil significantly increased the paw withdrawal threshold in spinal nerve-ligated rats (87%+/-12% and 76%+/-14%, P=0.007 and 0.012 vs vehicle, respectively). Spinal nerve ligation increased the expression of ASIC3 in the spinal cord dorsal horn (P=0.01), and this increase was inhibited by both amiloride and benzamil (P<0.001 in both). In conclusion, intrathecal amiloride and benzamil display antinociceptive effects in the rat spinal nerve ligation model suggesting they may present an alternative pharmacological tool in the management of neuropathic pain at the spinal level.

The Antiallodynic Effect and the Change of the alpha2 Adrenergic Receptor Subtype mRNA Expression by Morphine Administration in a Spinal Nerve Ligation Rat Model

BACKGROUND: The neuropathic pain arising from nerve injury is difficult to treat and the therapeutic effects of opioid drugs remain debatable. Agonists acting at the alpha2 adrenergic and opioid receptors have analgesic properties and they act synergistically when co-administered in the spinal cord. The lack of subtype-selective pharmacological agents has previously impeded the synergistic effects that are mediated by the adrenergic receptor subtypes. METHODS: We created neuropathic pain model by ligating the L5 spinal nerve in Sprague-Dawley rats (n = 18). We divided the rats into three groups (n = 6 for each group), and we administered intraperitoneal morphine (1 mg/kg, 3 mg/kg, 5 mg/kg) and then we measured the mechanical allodynia with using von-Frey filaments for 8 hours. We then injected morphine (5 mg/kg) intraperitoneally, twice a day for 2 weeks. We measured the tactile and cold allodynia in the morphine group (n = 9) and the saline group (n = 9). After 2 weeks, we decapitated the rats and harvested the spinal cords at the level of lumbar enlargement. We compared the alpha2 subtype mRNA expression with that of control group (n = 6) by performing real time polymerase chain reaction (RTPCR). RESULTS: Intraperitoneal morphine reduced the neuropathic pain behavior in the dose-dependent manner. Chronic morphine administration showed an antiallodynic effect on the neuropathic pain rat model. The rats did not display tolerance or hyperalgesia. The expression of the mRNAs of the alpha2A, alpha2B, alpha2C subtypes decreased, and morphine attenuated this effect. But we could not get statistically proven results. CONCLUSIONS: Systemic administration of morphine can attenuate allodynia during both the short-term and long-term time course. Morphine has an influence on the expression of alpha2 receptor subtype mRNA. Yet we need more research to determine the precise effect of morphine on the alpha2 subtype gene expression.

Comparison of antiallodynic effect of intrathecal morphine, brimonidine and rilmenidine between neuritis and ligation injury induced neuropathic pain / 대한마취과학회지

BACKGROUND: Mechanical allodynia is generally resulted from nerve damage by direct injury or inflammation. Thus, this study was designed to compare the antiallodynic effect of morphine, brimonidine and rilmenidine in two models of neuropathic pain, that is, induced by nerve ligation and neuritis. METHODS: Rats were prepared with tight ligation of the L5/L6 spinal nerves (SNL group) or with Freund's complete adjuvant (FCA) administration evoked sciatic inflammatory neuritis (SIN group). Antiallodynic effects by intrathecal morphine, brimonidine and rilmenidine were measured by applying von Frey filaments to the lesioned hind paw. Thresholds for withdrawal response were assessed and converted to % MPE to obtain an effective dose 50% (ED 50) and a dose response curve. RESULTS: Either SNL group or SIN group showed marked mechanical allodynia in the lesioned hind paw. Antiallodynic effects of morphine were different between two groups. That is ED 50 was 0.16 microgram (SIN) and 8.12 microgram (SNL), and dose response curve of the SIN group shifted left from that of the SNL group. The difference between SIN and SNL groups was statistically significant (P < 0.05). With the brimonidine or rilmenidine administration, ED 50 s were 0.12 microgram (SNL) and 0.37 microgram (SIN) and 2.16 microgram (SIN) and 11.46 microgram (SNL), respectively. And the shift to left of dose response curve from the SNL group is more prominent with rilmenidine administration. CONCLUSIONS: These results suggest morphine and rilmenidine showed a better effect on reducing the mechanical allodynia induced by FCA administration.

Spinal alpha2 Adrenoceptor and Antiallodynic Effect by Clonidine after Chronic Administration of 4-Methylcatechol in Neuropathic Rat Pain Model / 대한통증학회지

BACKGROUND: The adrenergic nervous system in the spinal cord contributes to the development of neuropathic pain after nerve injury. Brain derived neurotrophic factor may facilitate the sympathetic change in the spinal cord and influence the state of neuropathic pain. We probed the effect of chronic repetitive administration of systemic 4-methylcatechol, which is known to be a neurotrophic factor inducer, in a spinal nerve ligation model. METHODS: We made the rat neuropathic pain model by the ligation of the L5 spinal nerve. Intraperitoneal 4-methylcatechol (10microgram/kg) or the same volume of saline wasadministrated twice daily just after the operation for 7 days. The tactile allodynia was measured by using von Frey filaments and its change was followed up from 3 days after SNL. The lumbosacral enlargement of the spinal cord was taken out and the mRNA contents of the alpha(2)-adrenoceptor subtypes were measured by real time polymerase chain reaction and this was then compared with the control groups. The antiallodynic effect of intrathecal clonidine (3, 10, 30 microgram) was evaluated and compared in the 4-methylcatechol treated rats and the control rats. RESULTS: The expression of the alpha(2A) and alpha(2C) adrenoceptor subtypes did not change after 4-methylcatechol treatment. Intrathecal clonidine showed an earlier and better effect at the highest dose (30 microgram intrathecal), but not with any other doses. CONCLUSIONS: Chronic intraperitoneal administration of 4-methylcatechol may improve the effect of intrathecal clonidine, but we could not prove the increase of alpha(2A) and alpha(2C) adrenoceptors in the spinal cord of 4-methylcatechol treated rats.

Comparison of the Antiallodynic Effects of Intrathecal Lidocaine and MK-801 on Mechanical Allodynia in Two Neuropathic Pain Rat Models / 대한마취과학회지

BACKGROUND: Neuropathic pain can be induced by nerve injury or inflammation. An N-methyl-D-Aspartate (NMDA) antagonist (MK-801), and a sodium channel blocker (lidocaine) have been found to reduce mechanical allodynia. This study was conducted to determine whether intrathecal lidocaine or MK-801 had an antiallodynic effect on established mechanical allodynia in two well-characterized neuropathic pain rat models. METHODS: Male Sprague Dawley rats (n = 107) were anesthetized, and the left L5 and L6 spinal nerves were ligated (SNL group) or Freund complete adjuvant (FCA) was administrated to the same spinal nerves (FCA group) in order to cause neuropathic pain. A catheter was then implanted into the lumbar intrathecal space. After obtaining the baseline scores, time-effect curves of each drug were established for the antiallodynic effects of lidocaine (30g, 100g and 300g) and MK-801 (1g, 3g, 10g and 30g). The allodynic thresholds for the left hind paw withdrawal to von Frey hairs were assessed and converted to %MPE, and the ED50 value was then calculated using the %MPE. The antiallodynic effects of the two groups were then compared by analyzing the dose-response curves and the ED50 values. RESULTS: Both intrathecal lidocaine and MK-801 resulted in a dose dependent antiallodynic effect. ED50 values and the analysis of dose response curves showed that intrathecal lidocaine provided more effective antiallodynia in the SNL group, whereas intrathecal MK-801 resulted in a greater antiallodynic effect in the FCA group. CONCLUSIONS: In the SNL group, lidocaine had a better effect in reducing allodynic pain, whereas in the FCA group, MK-801 showed a greater antiallodynic effect.

Tramadol, Alpha-2 Adrenalin Receptor Subtype and Neuropathic Rat Model / 대한마취과학회지

BACKGROUND: Spinally administered alpha(2)-adrenergic agonists show analgesic effects in normal and neuropathic states. Their effects are mediated via alpha(2)-adrenoceptors. Plasticity of nervous system after nerve injury can change the expressions of the related receptors in spinal cord. The expression of alpha(2)-adrenoceptor subtypes in spinal cord and the effect of chronic systemic administration of tramadol was probed in neuropathic rat pain model. METHODS: Sprague-Dawley rats were prepared to make neuropathic pain model by L5 and L6 spinal nerve ligation. Withdrawal threshold for tactile allodynia was evaluated with von Frey hair throughout experiment. Tramadol (15 mg/kg) or equivalent volume of saline was injected intraperitoneally twice a day for 21 days. In the 14th day and 21st day, allodynia and the systemic effect of tramadol was measured and compared with control group. At the 21st day, rat spinal cords were harvested and the expression of alpha(2)-adrenoceptor subtypes were measured and compared with real time PCR. RESULTS: Chronic administration of tramadol did not improve the allodynia nor the effect of tramadol in spinal nerve ligation model. The mRNA of alpha(2A)-adrenoceptor in nerve injury site decreased compared to controlateral site. The mRNA of alpha(2C)-adrenoceptor subtype in nerve injury rat decreased compared with normal animal, and chronic administration of tramadol increased it compared to saline group. CONCLUSIONS: Rats with neuropathic pain by spinal nerve ligation showed the expression of alpha(2)-adrenoceptors subtypes in spinal cord, and chronic systemic administration of tramadol may influence the expression of alpha(2)-adrenoceptors subtypes.

Comparison of Antiallodynic Effects between Intrathecal Cholinesterase Inhibitors and NMDA Antagonists on Two Neuropathic Pain Rat Models / 대한마취과학회지

BACKGOUND: Cholinesterase inhibitors and N-methyl-D-aspartate (NMDA) antagonists reduce the mechanical allodynia in neuropathic pain models. In this study our aim was to compare the antiallodynic effects between intrathecal cholinesterase inhibitors and NMDA antagonists on two well-characterized neuropathic pain rat models. METHODS: Male Sprague Dawley rats were anesthetized and either had the left L5 and L6 spinal nerves ligated (SNL group) or Freund complete adjuvant (FCA) administrated to the sciatic nerve (FCA group) in order to cause neuropathic pain. A catheter was implanted into the intrathecal space for drug administration. After obtaining baseline values, edrophonium (3-100microgram), neostigmine (0.3-10microgram), AP-5 (0.3-3microgram) and MK-801 (1-30microgram) were administered intrathecally to each group. The allodynic left hind paw withdrawal thresholds to von Frey hairs were assessed and converted to % MPE. Antiallodynic effects on the two groups were compared by analyzing dose-response curves and ED 50 values. Motor weakness was also checked. RESULTS: Intrathecal edrophonium, neostigmine, AP-5 and MK-801 had a dose-dependent antiallodynic effect on the two neuropathic pain models. Comparing the antiallodynic effect dose response curves, intrathecal cholinesterase inhibitors had lower ED 50 with steep slopes in the SNL model, whereas intrathecal NMDA antagonists had lower ED 50 in the FCA model, but there were no statistically significant differences between the two models. CONCLUSIONS: Intrathecal cholinesterase inhibitors and NMDA antagonists have relatively better antiallodynic effects on the SNL and FCA neuropathic pain rat models, respectively.

Effect of Administering Freund's Complete Adjuvant to Spinal Nerves on the Development of Allodynia in the Rat / 대한마취과학회지

BACKGROUND: Spinal nerve ligation injury causes a neuropathic pain syndrome that includes allodynia. Neuropathic pain is also induced by Freund's complete adjuvant (FCA)-induced inflammation. This study was designed to examine the development of mechanical and cold allodynia after FCA administration at the L4/L5 spinal nerves and to compare it with the effects of spinal nerve ligation at the same site. METHODS: Rats were randomly allocated into three groups: (i) treatment with tight ligation of the left L5/L6 spinal nerves, (ii) wrapping of the L5/L6 spinal nerves with Spongostan(R) soaked in FCA, or (iii) wrapping of the L5/L6 spinal nerves with Spongostan(R) soaked in saline. Mechanical and cold allodynia were measured by applying von Frey filaments or acetone in both hind paws. To examine the development of allodynia, the frequencies of hind paw withdrawal to each type of stimulus were measured. RESULTS: Both FCA administration and nerve ligation injury caused a marked mechanical and cold allodynia in the lesioned hind paw compared to saline treatment (P < 0.05). Furthermore, the frequencies of response of the lesioned hind paw to both types of stimulus were significantly greater than those on the contralateral side. CONCLUSIONS: These results suggest that administration of FCA to the spinal nerves can produce a mechanical and cold allodynia with a similar profile of pain facilitation as nerve ligation.

Effects of Cyclooxygenase Inhibitors on Neuropathic Pain following Spinal Nerve Ligation in Rats / 대한마취과학회지

BACKGROUND: The facilitatory effect of spinal prostaglandins (PGs) on nociceptive transmission suggests that early PG synthesis after nerve injury could be important in the development of allodynia. METHODS: The aim of this study is to examine the effects of diclofenac (nonselective COX inhibitor), SC-560 (selective COX-1 inhibitor), and NS-398 (selective COX-2 inhibitor) on mechanical allodynia and thermal hyperalgesia in the neuropathic pain model. The rats underwent right L5 spinal nerve ligation (SNL) and were assigned to three COX inhibitor groups to be injected intraperitoneally with different administration dosages (0.2 mg, 1 mg, 5 mg) 30 minutes before, and at 1, 2, and 3 days after SNL. The withdrawal threshold of both hindpaws in response to mechanical stimulation was measured by dynamic plantar anesthesiometer and the withdrawal ratio of right to left hindpaw was calculated. The thermal stimulation applied to both hindpaws by the plantar test was calculated different administration dosages were compared with the vehicle group. RESULTS: There were no differences in mechanical allodynia among the lower dosage groups (0.2 mg) until 14 days after SNL. However, 1 mg of NS-398 decreased mechanical allodynia compared with the vehicle group at 14 days after SNL, and 5 mg of NS-398 decreased mechanical allodynia at 3 days after SNL. However, there was no difference in thermal hyperalgesia between the groups. CONCLUSIONS: These results suggest that intraperitoneal administration of COX inhibitor (especially selective COX-2 inhibitor) after nerve ligation injury can attenuate the development of mechanical allodynia.

Decrease in Zinc Concentration in the Rat Spinal Gray Matter Induced by Peripheral Nerve Ligation, and its Relations with Increased Pain Threshold / 대한해부학회지

This study was designed to investigate any correlation between the mechanism of pain development and changes of histochemically-reactive zinc contents in the rat spinal cords following peripheal nerve ligation. Male Sprague-Dawley rats (270 ~290 g) were used for this study. We ligated a left-sided lumbar spinal nerve with silk under anesthesia using pentobarbital (50 mg/kg). Semmes-Weinstein monofilaments (Stoelting Company, Wood Dale, IL) was used to test for mechanical hyperalgesia. 30 micrometer-thick spinal cord cryosections were stained by automet-allography (Danscher, 1981). The density of zinc was significantly decreased in zinc concentration in the dorsal horn of 4th, 5th and 6th lumbar segments at 5 and 10 days after the spinal nerve ligation. Here, zinc depletion was apparent in superficial gray matter, especially layer III-IV. In addition the nerve ligated rats showed lower pain threshold. This increased pain sensation might be related with lowered vesicular zinc level in the superficial gray matter in the spinal cord. The present findings offer a proposed link between zinc and pain. Our interpretation is that there may be an extension of fine primary afferent fibers into lamina III and possibly lamina IV following peripheral nerve ligation. If further work bears out this conclusion, this would provide a possible explanation for the chronic pain states that sometimes follow peripheral nerve damage.