Antinociception of intrathecal adenosine receptor subtype agonists in rat formalin test

Adenosine has shown antinociceptive action via spinal adenosine receptors. There are four types of adenosine receptors: A1, A2A, A2B, and A3. We characterized the nature of types of adenosine receptors for the control of nociception at the spinal level. For nociception, formalin solution (5%, 50 microL) was injected into the hindpaw of male Sprague-Dawley rats. The effects of intrathecal adenosine A1 (CPA), A2A (DPMA), and A3 (IB-MECA) receptor agonists were examined. CPA and IB-MECA produced limited or no effect on the early phase response of the formalin test, respectively, but the two drugs depressed the late phase response. DPMA suppressed both phase responses. CPA was the most potent drug among the three in the late phase. These results suggest that spinal adenosine A1 and A2A receptors may be involved in the modulation of the early and the late phase responses of the formalin test, whereas adenosine A3 receptor may be involved in the regulation of the late phase response.     

Effects of radolmidine, a novel alpha2 -adrenergic agonist compared with dexmedetomidine in different pain models in the rat

BACKGROUND: Intrathecally administered alpha2-adrenoceptor agonists produce effective antinociception, but sedation is an important adverse effect. Radolmidine is a novel alpha2-adrenoceptor agonist with a different pharmacokinetic profile compared with the well-researched dexmedetomidine. This study determined the antinociceptive and sedative effects of radolmidine in different models of acute and chronic pain. Dexmedetomidine and saline served as controls. METHODS: Male Sprague-Dawley rats were studied in acute pain (tail flick), carrageenan inflammation, and the spinal nerve ligation model of neuropathic pain. Mechanical allodynia was assessed with von Frey filaments, cold allodynia with the acetone test, and thermal hyperalgesia with the paw flick test. Locomotor activity-vigilance was assessed in a dark field. Dexmedetomidine and radolmidine were administered intrathecally in doses of 0.25 microg, 2.5 microg, 5 microg, and 10 microg. RESULTS: In the tail flick test, radolmidine showed a dose-dependent antinociceptive effect, being equipotent compared with dexmedetomidine. In carrageenan inflammation, intrathecal doses of 2.5 microg or 5 microg of dexmedetomidine/radolmidine produced significant antinociception compared with saline (P < 0.01). The two drugs were equianalgesic. In the neuropathic pain model, an intrathecal dose of 5 microg dexmedetomidine-radolmidine had a significant antiallodynic effect compared with saline (P < 0.01). The two drugs were equipotent. Intrathecal administration of both dexmedetomidine and radolmidine dose dependently decreased spontaneous locomotor acitivity-vigilance, but this effect was significantly smaller after intrathecal administration of radolmidine than after intrathecal dexmedetomidine. CONCLUSIONS: Radolmidine and dexmedetomidine had equipotent antinociceptive effects in all tests studied. However, radolmidine caused significantly less sedation than dexmedetomidine, probably because of a different pharmacokinetic profile.     

Antinociceptive effect of intrathecal administration of taurine in rat models of neuropathic pain

Purpose

Taurine is the most abundant amino acid in many tissues. Although taurine has been shown to be antinociceptive, in this report, our focus is to elucidate the mechanism and action site on neuropathic pain. This study used behavioural assessments to determine whether taurine attenuates neuropathic pain in the spinal cord.

Methods

Chronic constriction injury (CCI) to the sciatic nerve and streptozotocin-induced diabetic neuropathy were introduced to male Sprague-Dawley rats. We then assessed the antinociceptive effect of spinal injections of taurine (100, 200, 400, or 800 μg) using electronic von Frey, paw pressure, and plantar tests. To explore the effect of taurine on motor function, a rotarod test was performed, and in order to determine which neurotransmitter pathway is involved in taurine’s action, we examined how several antagonists of spinal pain processing receptors altered the effect of taurine 400 μg in a paw pressure test.

Results

Taurine alleviated mechanical allodynia, mechanical hyperalgesia, and thermal hyperalgesia in CCI rats and suppressed mechanical allodynia and hyperalgesia in diabetic rats. Significant effects were observed at 200 μg in both models. On the other hand, taurine dose-dependently affected motor performance, and a significant effect was seen at 400 μg. The antinociceptive effects were reversed completely by pretreatment with an intrathecal injection of strychnine, a glycine receptor antagonist.

Conclusion

The present study demonstrated that intrathecal administration of taurine attenuates different models of neuropathic pain, and these effects seem to be mediated by the activation of glycinergic neurotransmission. These findings suggest that taurine may be a candidate remedy for neuropathic pain.     

The effect of intrathecal magnesium sulphate on nociception in rat acute pain models

We examined the antinociceptive effect of intrathecally administered magnesium sulphate (MgSO4) in rats, using acute pain models including mechanical pressure, heat and subcutaneous formalin injection. According to the locomotion test 10 microliters of 6.2% MgSO4 did not produce motor paralysis. At the same dose, responses to pressure and heat were intact, compared with controls given saline. MgSO4 produced depression of pain responses only after the first 10 min in the formalin test. Our studies indicated that MgSO4 did not show remarkable antinociceptive effects in acute pain models.     

Characterization of intracavernous pressure increase induced by Ym348, a novel 5-HT2C receptor agonist, in anesthetized rats

PURPOSE: We investigated the effects of the novel 5-HT2C receptor agonist YM348 [(S)-2-(7-ethyl-1H-furo[2,3-g]indazol-1-yl)-1-methylethylamine] on ICP in anesthetized rats and clarified whether behavioral changes such as hypolocomotion induced at a high dose are a cause of the inverted U-shaped PE dose-response curves in conscious rats. MATERIALS AND METHODS: Male Wistar rats (Japan SLC, Shizuoka, Japan) weighing 250 to 315 gm were used. The pro-erectile effect of YM348 (2.03 to 67.7 microg/kg subcutaneously) was examined in conscious rats. ICP was also monitored after YM348 treatment (0.677 to 67.7 mug/kg subcutaneously) in anesthetized rats. Response number, latency, duration, peak pressure and area under the curve were measured. The selective 5-HT2C receptor antagonist SB242084 [(6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy) pyridin-3-yl carbamoyl] indoline)] (0.03 to 1 mg/kg intraperitoneally) was administered 30 minutes before YM348 treatment. RESULTS: YM348 induced PE and ICP increases, and was significantly inhibited by SB242084. Dose-response curves for the number of PEs and ICP increases were an inverted U shape. YM348 decreased the latency of but did not affect the quality of ICP (duration, peak pressure and area under the curve) even at the highest dose. CONCLUSIONS: Activation of 5-HT2C receptor increased ICP and, as a result, induced PE. Since the dose-response curve for the number of ICP increases under anesthetized, behavior independent conditions still showed an inverted U shape, behavioral changes were not likely to have contributed to the inverted U-shaped dose-response curves for the number of PEs in conscious rats. Furthermore, the certain magnitude of ICP increases was likely to have occurred despite the stimulus intensity after the level of 5-HT2C receptor activation crossed the threshold.     

A nonneuronal 5-hydroxytryptamine receptor 3 induces chloride secretion in the rat distal colonic mucosa

BACKGROUND: The 5-HT3 receptor is a serotonin receptor believed to reside on enteric neurons. However, several studies belie an exclusive neural localization. Our hypothesis is that the 5-HT3 receptor agonist, 2-methyl-5-HT (2Me5HT), induces chloride secretion despite neural blockade, which can be blocked by a 5-HT3 receptor antagonist. METHODS: Rat distal colon was stripped of its muscularis, mounted as mucosal sheets in Ussing chambers, and short-circuited. Adjacent sheets were pretreated with 1 micromol/L of the neurotoxin, tetrodotoxin, and incubated with 2Me5HT (50 micromol/L) alone or with a 5-HT3 (0.3 micromol/L ondansetron or 0.3 micromol/L tropisetron) or a 5-HT4 (0.3 micromol/L GR11808) receptor antagonist. Short-circuit current (I(sc)) was measured continuously. RESULTS: 2Me5HT caused an increase in I(sc), which was significantly (P <.01, repeated measures analysis of variance) inhibited by ondansetron (n = 8) and tropisetron (n = 5) but not by GR11808. CONCLUSIONS: A 5-HT3 receptor is present at the mucosal level that mediates chloride secretion by a nonneural pathway.     

胫骨癌痛大鼠脊髓背角5-羟色胺水平的变化

目的 评价胫骨癌痛大鼠脊髓背角5-羟色胺(5-HT)水平的变化.方法 雌性SD大鼠60只,体重160～180 g,采用随机数字表法,将其随机分为3组(n=20):对照组(C组)、假手术组(S组)和胫骨癌痛组(P组).C组不做任何处理;S组于右侧胫骨上段骨髓腔注射D-hank液10 μl;P组于右侧胫骨上段骨髓腔接种Walker 256大鼠乳腺癌细胞悬液10μl制备胫骨癌痛模型.于接种前1d、接种后3、5、7、9、11、14、16、18和21 d时测定机械痛阈.于接种前1 d、接种后7、14和21 d时,每组痛阈测定结束后随机处死大鼠4只,取脊髓组织,采用高效液相色谱法测定脊髓背角5-HT含量;接种后14 d取接种侧胫骨组织,光镜下观察胫骨破坏情况.脊髓背角5-HT含量与机械痛阈进行直线相关分析.结果 与C组和S组比较,P组接种后7～21 d时机械痛阈降低,接种后7、14和21 d时脊髓背角5-HT含量升高(P＜0.05),且5-HT含量与机械痛阈呈负相关(r=-0.973,P＜0.05).C组和S组各时点机械痛阈和脊髓背角5-HT含量比较差异无统计学意义(P＞0.05).光镜下P组大鼠术侧胫骨骨质严重破坏.结论 大鼠胫骨癌痛的形成与维持可能与脊髓背角5-HT水平升高有关.

Abstract：

Objective To investigate the change in 5-hydroxytryptomine (5-HT) content in spinal dorsal horn in a rat model of tibial bone cancer pain (BCP). Methods Sixty female SD rats weighing 160-180 g were randomly divided into 3 groups ( n = 20 each): control group (group C), sham operation group (group S) and BCP group. BCP was induced by intra-tibial inoculation of 10 μl Walker 256 breast cancer cell suspension in group BCP, while group S received intra-tibial inoculation of 10 μl D-hank solution. Paw withdrawal threshold to mechanical stimulation with yon Frey filaments (MWT) was measured 1 d before (baseline) and at 3, 5, 7, 9, 11,14, 16, 18 and 21 d after breast cancer cell inoculation. At 1 d before and 7, 14 and 21 d after breast cancer cell inoculation, four animals in each group were sacrificed after measurement of MWT. Their lumber segments of the spinal cord were removed for assay of 5-HT content in spinal dorsal horn using HPLC with fluorescence detector.HE staining was used to detect the damage to the tibia. Correlation between the 5-HT content and MWT was analyzed. Results MWT was significantly decreased after breast cancer cell inoculation in group BCP ( P ＜ 0.05).Microscopic examination showed serious bone destruction of tibia at the injection site in group BCP, while no bone destruction was found in groups C and S. 5-HT content in spinal dorsal horn was significantly higher in group BCP than in groups C and S (P ＜ 0.05). There was strong negative linear correlation between 5-HT content in spinal dorsal horn and MWT ( r = - 0.973, P ＜ 0.05 ). Conclusion The 5- HT content in spinal dorsal horn is significantly increased in rats with tibial BCP and is involved in the development of BCP.     

鞘内注射加巴喷丁和/或吗啡对切口痛大鼠脊髓氨基酸含量的影响

Objective To study the effects of intrathecally administering gabapentin and/or morphine on the amino acid neurotransmitters in spinal cord of rat incision pain models.Methods Forty male SD rats were randomly divided into five groups (n=8) and were intrathecally inserted catheter.Paw incision models were made 5d later.Gabapentin (50 μg,group Ⅲ) or morphine(2.5 μg,group Ⅳ) or both (group Ⅴ) were intrathecally injected 30 min before incision.Another two groups were regarded as shame (group Ⅰ) or control (group Ⅱ).Pain behavior was determined 2 h later using mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL).The content of four amino acids including glutamate,aspartate,glycine and γ-aminobutyric acid in rat spinal cord were detected.Results MWT and TWL decreased and the content of glutamate and aspartate in spinal cord increased significantly 2 h after incision(P＜0.05)in groups Ⅱ,Ⅲ and Ⅳ (without statistically differences among three groups),but not in group Ⅴ,compared to them in group Ⅰ.There were no differences in the content of glycine and γ-aminobutyric acid in rat spinal cord 2 h after incision among four groups.Conclusion Intrathecal gabapentin significantly enhances the antinociceptive effect of intrathecal morphine in rat incision pain model,which may owe to the decreased level of excitatory amino acids in spinal cord.     

鞘内注射曲古菌素A对树胶脂毒素诱导的大鼠神经痛的影响

目的评价曲古菌素A(trichostatin A,TSA)在树胶脂毒素(resiniferatoxin,RTX)诱导的神经病理性疼痛模型(模拟PHN)中的作用。方法雄性健康SD大鼠32只,体重250~280g,采用随机数字表法分成四组:溶媒对照组(C组)、神经痛模型组(RTX组)、二甲基亚砜(Dimethyl sulfoxide)治疗组(DMSO组)和TSA治疗组(TSA组)。C组单次腹腔注射RTX溶剂1ml,RTX组建立病理性神经痛模型,建模方式为每只大鼠在异氟醚(2%O_2)麻醉下接受单次腹腔注射RTX 210μg/kg;DMSO组建立病理性神经痛模型,在建模前60 min和建模后每天鞘内注射TSA溶媒5%DMSO 10μl,持续至建模后7天;TSA组建立病理性神经痛模型,在建模前60min和建模后每天鞘内注射等容量溶于DMSO的TSA 0.5μg/kg,持续到建模后7天。于建模前60min和建模后第1、3、5和7天采用一系列校准的von Frey毛针测定四组大鼠机械痛阈值(MWT),于第7天行为学测定结束后检测脊髓IL-1β、TNF-α和胶质纤维酸性蛋白(GFAP)等分子mRNA表达量。结果与C组比较,建模后第3、5和7天RTX、DMSO和TSA组MWT明显降低(P0.05)。与RTX和DMSO组比较,建模后第3、5和7天TSA组MWT明显升高(P0.05)。RTX和DMSO组不同时点MWT差异无统计学意义。与C组比较,RTX、DMSO和TSA组IL1-βmRNA,TNF-αmRNA和GFAP mRNA表达量明显增多(P0.05)。与RTX和DMSO组比较,TSA组IL-1βmRNA、TNF-αmRNA表达量明显减少(P0.05)。RTX和DMSO组各指标差异无统计学意义。结论鞘内注射TSA通过减缓脊髓炎性反应缓解RTX诱导的神经病理性痛。     

Marked enhancement of anti-allodynic effect by combined intrathecal administration of the adenosine A1-receptor agonist R-phenylisopropyladenosine and morphine in a rat model of central pain

BACKGROUND: There is often no satisfactory treatment for chronic pain after spinal cord injury. We have previously reported that intrathecal (i.t.) administration of the adenosine A1-receptor agonist R-phenylisopropyl-adenosine (R-PIA) or the opioid morphine has anti-allodynic effects in a model of presumed chronic central pain after photochemically induced spinal cord injury in rats. In the present study, we set out to investigate the possible interaction between i.t. R-PIA and morphine in spinally injured rats. METHODS: Sprague-Dawley rats displaying allodynia-like behaviors to mechanical and cold stimuli after photochemically induced spinal cord injury with minor motor deficits were used. R-PIA and morphine, either alone or in combination, were administered i.t. through an implanted catheter to lumbar spinal cord. RESULTS: Cumulative doses of R-PIA or morphine dose-dependently reduced the mechanical allodynia-like behavior, with a threshold of 1 nmol and 1.5 nmol, respectively. When co-administrated, R-PIA and morphine produced marked suppression of mechanical allodynia at doses of 5 pmol and 7.5 pmol, respectively. The effect of i.t. co-administration of R-PIA and morphine on cold allodynia was comparable to i.t. R-PIA alone. The combination of R-PIA and morphine did not increase adverse effects such as motor deficits in comparison to either drug alone. CONCLUSION: These results demonstrate a supra-additive interaction between the adenosine A1-receptor agonist R-PIA and morphine to reduce mechanical allodynia-like behavior in rats with chronic spinal cord injury. The combination of R-PIA and morphine administered spinally may be superior to R-PIA or morphine alone for treating such pain.     

Selective and segmentally restricted antinociception induced by MPV-2426, a novel alpha-2-adrenoceptor agonist, following intrathecal administration in the rat

BACKGROUND: MPV-2426 (radolmidine) is a novel alpha-2-adrenoceptor agonist developed for spinal pain therapy. In the present study we determined the segmental distribution and selectivity of the antinociceptive effect induced by MPV-2426 following i.t. administration in rats. METHODS: The experiments were performed in lightly anesthetized rats with an i.t. catheter for administration of drugs into the lumbar spinal cord level. To determine segmental distribution of antinociception, the withdrawal latency of the tail and forepaw from a hot water bath was measured. To determine selectivity of reflex modulation, the effect of i.t. MPV-2426 on the innocuous H-reflex was determined. RESULTS: In the hot water immersion test MPV-2426 produced a dose-dependent (0.3-3.0 microg) prolongation of tail withdrawal latency whereas the effect on forepaw withdrawal latency was short of significance. Dexmedetomidine, the reference alpha-2-adrenoceptor agonist, produced a significant dose-related prolongation of both the tail and the forepaw withdrawal (0.3 and 1.0 microg). MPV-2426 (1.0 and 3.0 microg) produced no significant change in the amplitude of the H-reflex or M-response induced by electrical stimulation of the tibial nerve, nor any change in the modulation of the H-reflex amplitude induced by conditioning sural nerve stimulation. The antinociception induced by MPV-2426 was completely reversed by atipamezole (1 mg/kg s.c.), an alpha-2-adrenoceptor antagonist. CONCLUSION: MPV-2426 produces a selective and segmentally more restricted antinociceptive effect than dexmedetomidine following i.t. administration. The antinoception induced by MPV-2426 is due to action on spinal alpha-2-adrenoceptors.     

Effect of sarpogrelate hydrochloride,a 5-hydroxytryptamine2 receptor antagonist,on allograft arteriosclerosis after aortic transplantation in rats

BackgroundSarpogrelate hydrochloride, a 5-hydroxytryptamine₂ receptor antagonist, is known to prevent serotonin-induced neointimal hyperplasia. We examined the effect of this agent on allograft arteriosclerosis in a rat model of aortic transplantation.MethodsRats were given an aortic isograft or allograft and oral administration of either saline vehicle alone or 20 mg/kg daily of sarpogrelate for 8 weeks. The grafts were then harvested, and the lumen diameter and the thickness of the intima and media were measured. Comparisons were made between measurement results in isografts and allografts from rats treated and not treated with sarpogrelate. Immunohistochemistry assessments were used to detect expression of serotonin in graft specimens.ResultsFor both allografts and isografts, significantly less intimal thickening was observed in specimens from rats given sarpogrelate compared with rats given saline. Sarpogrelate had no effect on medial thickening in either graft type. Serotonin was detected in allografts from rats given saline alone but not in allografts from rats given sarpogrelate or in isografts.ConclusionsSarpogrelate hydrochloride may mitigate arteriosclerosis in allografts. Platelet aggregation and serotonin may be correlated with intimal thickening associated with chronic rejection.     

神经病理性疼痛大鼠鞘内注射SB203580的镇痛作用

目的 观察神经病理性疼痛大鼠鞘内注射p38丝裂原活化蛋白激酶（p38MAPK）抑制剂SB203580的镇痛作用,探讨p38MAPK信号转导通路在慢性神经病理性疼痛中的作用。方法雄性SD大鼠,体重220～250g,建立坐骨神经结扎性损伤（CCI）疼痛模型,第一部分40只CCI大鼠,随机分为5组,对照组、SB0．1μg组、SB0．5μg组、SB2．5μg组和SB5μg组,（n=8）,CCI后7d,鞘内注射2％二甲基亚砜或不同剂量的SB203580（0．1、0．5、2．5、5μg）10μl,在给药前和给药后0．5、3、6、12、24h用von Frey丝测定大鼠术侧后爪机械缩足反射阈值（MWT）;另外36只大鼠,随机分为6组（n=6）：Sham组、CCI组、DMSO组、SB0．1、0．5、5μg组,CCI后7d鞘内注射相应剂量SB203580 10μl,给药后6h取L4.5脊髓,用免疫组织化学方法检测脊髓背角磷酸化环磷酸腺苷反应元件结合蛋白（pCREB）的表达。结果CCI后大鼠产生了机械痛敏。鞘内注射SB203580剂量依赖性地提高了MWT。CCI后脊髓背角pCREB阳性神经元增加,鞘内注射SB0．5、5μg抑制了CCI引起的脊髓背角pCREB表达增加（P〈0．01）。结论鞘内注射SB203580能减轻CCI引起的痛敏,抑制脊髓背角CREB的磷酸化,p38MAPK信号通路参与慢性神经病理性疼痛。