Pain In Chronic Constriction Injury Research Articles

Based on spinal central sensitization creating analgesic screening approach to excavate anti-neuropathic pain ingredients of Corydalis yanhusuo W.T.Wang

Ethnopharmacological relevanceCorydalis Rhizome (RC) as a traditional analgesic Chinese medicine is the dried tuber of Corydalis yanhusuo W.T.Wang. Many efforts have revealed that RC could effectively alleviate neuropathic pain, while its active ingredients in neuropathic pain are still not clear. Aim of the studySpinal central sensitization contributes greatly to neuropathic pain, and neuron, astrocyte and microglia play important roles in spinal central sensitization. The aim of the present study is to excavate active compounds in RC regulating spinal central sensitization to inhibit neuropathic pain. Materials and methodsImmunofluorescence and western blotting were used to determine protein expression levels. Gene expression levels were detected by RT-PCR. PC12 neuronal cells, C6 astrocyte cells, and BV2 microglia cells were cultured for in vitro studies. Targeting multi types of cells extraction combined with HPLC-Q-TOF-MS/MS was established to identify components binding to above cells. Animal studies were used to verify the analgesic activities of components. ResultsTotal alkaloids of RC (RC-TA) significantly relieved neuropathic pain in chronic constriction injury (CCI) rats and repressed spinal central sensitization. Eight components of RC-TA were found to bind to PC12, C6, or BV2 cells. They could respectively suppress the activation of cells in vitro and alleviate CCI-induced neuropathic pain, among which glaucine and dehydrocorydaline induced antinociception was stronger than l-THP. Meanwhile, glaucine had no effect on acute or chronic inflammatory pain, and its antinociception in neuropathic pain could be abolished by dopamine D1 receptor agonist. ConclusionsEmploying multi types of cells based on spinal central sensitization rather than single cell may allow for more thorough excavation of active substances. Glaucine was firstly found could attenuate neuropathic pain but not other types of pain which indicated that different alkaloids in RC exert distinct analgesic effects on different pain models, and gluacine has the potential to be developed as an analgesic drug specifically for neuropathic pain relieving.

Low level TGF-β1-treated Umbilical mesenchymal stem cells attenuates microgliosis and neuropathic pain in chronic constriction injury by exosomes/lncRNA UCA1／miR-96-5p／FOXO3a

Neuropathic pain is a chronic pain state that usually caused by injuries in peripheral or central nerve. Inhibition of spinal microglial response is a promising treatment of neuropathic pain caused by peripheral nerve injury. In recent years, mesenchymal stem cells (MSCs) that characterized with multipotent ability have been widely studied for disease treatment. TGF-β1 is a well-known regulatory cytokine that participate in the response to cell stress and is closely correlated with the function of nerve system as well as MSC differentiation. This work aimed to determine the effects of exosomes that extracted from TGF-β1-induced umbilical mesenchymal stem cells (hUCSMCs) on the neuropathic pain. In this work, we established a rat model of chronic constriction injury (CCI) of the sciatic nerve and LPS-induced microglia cell model. The hUCSMCs cell surface biomarker was identified by flow cytometry. Exosomes that extracted from TGF-β1-treated hUCSMCs were characterized by transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA) and used for treatment. We observed that TGF-β1 upregulates the level of lncRNA UCA1 (UCA1) in hUCMSC-derived exosomes. Treatment with exosomal lncRNA UCA1 (UCA1) alleviated the neuropathic pain, microgliosis, and production of inflammatory mediator both in vivo and in vitro. UCA1 directly interact with the miR-96-5p, and the miR-96-5p acts as sponge of FOXO3a. Knockdown of UCA1 upregulated the level of miR-96-5p and downregulated the FOXO3a expression, which could be recovered by inhibition of miR-96-5p. In summary, the TGF-β1-stimulated exosomal UCA1 from hUCMSCs alleviates the neuropathic pain and microgliosis. These findings may provide novel evidence for treatment of neuropathic pain caused by chronic constriction injury.

Neuronal C-Reactive Protein/FcγRI Positive Feedback Proinflammatory Signaling Contributes to Nerve Injury Induced Neuropathic Pain.

Neuropathic pain is difficult to treat in clinical practice, and the underlying mechanisms are insufficiently elucidated. Previous studies have demonstrated that the neuronal Fc-gamma-receptor type I (FcγRI) of the dorsal root ganglion (DRG) mediates antigen-specific pain. However, the mechanisms of neuronal FcγRI in neuropathic pain remain to be explored. Here, it is found that the activation of FcγRI-related signals in primary neurons induces neuropathic pain in a rat model. This work first reveals that sciatic nerve injury persistently activates neuronal FcγRI-related signaling in the DRG, and conditional knockout (CKO) of the FcγRI-encoding gene Fcgr1 in rat DRG neurons significantly alleviates neuropathic pain after nerve injury. C-reactive protein (CRP) is increased in the DRG after nerve injury, and CRP protein of the DRG evokes pain by activating neuronal FcγRI-related signals. Furthermore, microinjection of naive IgG into the DRG alleviates neuropathic pain by suppressing the activation of neuronal FcγRI. These results indicate that the activation of neuronal CRP/FcγRI-related signaling plays an important role in the development of neuropathic pain in chronic constriction injury (CCI) rats. The findings may provide novel insights into the neuroimmune responses after peripheral nerve injury and suggest potential therapeutic targets for neuropathic pain.

Co-Combination of Pregabalin and Withaniacoagulans-Extract-Loaded Topical Gel Alleviates Allodynia and Hyperalgesia in the Chronic Sciatic Nerve Constriction Injury for Neuropathic Pain in Animal Model.

The current study reports the fabrication of co-combination gel using Pregabalin and Withania coagulans fruit extract to validate its effectiveness for neuropathic pain in chronic constriction injury (CCI) rat models. Three topical gels were prepared using Carbopol 934 through a pseudo-ternary phase diagram incorporating the Pregabalin (2.5%), Withania coagulans extract (2%), and co-combination of both Pregabalin (2.5%) and Withania coagulans extract (2%). Gels were characterized. FTIR showed a successful polymeric network of the gel without any interaction. The drug distribution at the molecular level was confirmed by XRD. The AFM images topographically indicated the rough surface of gels with a size range from 0.25 to 330 nm. DSC showed the disappearance of sharp peaks of the drug and extract, showing successful incorporation into the polymeric network of gels. The in vitro drug release of co-combination gel was 73% over 48 h. The mechanism of drug release by combination gel was Higuchi+ fickian with values of n (0.282) and R2 (0.947). An in vivo study for pain assessment via four methods: (i) heat hyperalgesia, (ii) cold allodynia, (iii) mechano-hyperalgesia, and (iv) dynamic mechano-allodynia, confirmed that topical treatment with co-combination gel reduced the pain significantly as indicated by the p value: R1 (p < 0.001), R2 (p < 0.001), R3 (p < 0.015), and R4 (p < 0.0344). The significance order was R2 (****) > R1 (***) > R3 (**) > R4 (*) > R5 (ns).

Gut microbiota depletion by antibiotics ameliorates somatic neuropathic pain induced by nerve injury, chemotherapy, and diabetes in mice

BackgroundGut microbiota has been found involved in neuronal functions and neurological disorders. Whether and how gut microbiota impacts chronic somatic pain disorders remain elusive.MethodsNeuropathic pain was produced by different forms of injury or diseases, the chronic constriction injury (CCI) of the sciatic nerves, oxaliplatin (OXA) chemotherapy, and streptozocin (STZ)-induced diabetes in mice. Continuous feeding of antibiotics (ABX) cocktail was used to cause major depletion of the gut microbiota. Fecal microbiota, biochemical changes in the spinal cord and dorsal root ganglion (DRG), and the behaviorally expressed painful syndromes were assessed.ResultsUnder condition of gut microbiota depletion, CCI, OXA, or STZ treatment-induced thermal hyperalgesia or mechanical allodynia were prevented or completely suppressed. Gut microbiota depletion also prevented CCI or STZ treatment-induced glial cell activation in the spinal cord and inhibited cytokine production in DRG in OXA model. Interestingly, STZ treatment failed to induce the diabetic high blood glucose and painful hypersensitivity in animals with the gut microbiota depletion. ABX feeding starting simultaneously with CCI, OXA, or STZ treatment resulted in instant analgesia in all the animals. ABX feeding starting after establishment of the neuropathic pain in CCI- and STZ-, but not OXA-treated animals produced significant alleviation of the thermal hyeralgesia or mechanical allodynia. Transplantation of fecal bacteria from SPF mice to ABX-treated mice partially restored the gut microbiota and fully rescued the behaviorally expressed neuropathic pain, of which, Akkermansia, Bacteroides, and Desulfovibrionaceae phylus may play a key role.ConclusionThis study demonstrates distinct roles of gut microbiota in the pathogenesis of chronic painful conditions with nerve injury, chemotherapy and diabetic neuropathy and supports the clinical significance of fecal bacteria transplantation.

Na+-dependent inactivation of vascular Na+/Ca2+ exchanger responsible for reduced peripheral blood flow in neuropathic pain model

Reduced skin blood flow has been reported in neuropathic pain patients as well as various peripheral neuropathic pain model animals. We have previously shown that vasodilators, which improves reduced skin blood flow, correlatively alleviate neuropathic pain in chronic constriction injury (CCI) mice, a model of neuropathic pain from peripheral nerve injury. Here, we sought to elucidate the mechanism underlying the reduced skin blood flow in CCI rats. The skin blood flow of the ipsilateral plantar arteries was significantly reduced compared to that of the contralateral ones 4 weeks after loose ligation of the sciatic nerve. The contraction induced by noradrenaline, serotonin, and U46619, a thromboxane receptor agonist, in the isolated ipsilateral plantar arteries was significantly enhanced compared to that in the contralateral ones. KB-R7943, a Na+/Ca2+ exchanger (NCX) inhibitor, shifted the concentration-response curves of noradrenaline to the left in the contralateral arteries but had no effect on the ipsilateral side. There was no significant difference in concentration-response curves of noradrenaline between the ipsilateral and contralateral arteries in the presence of KB-R7943. Amiloride, a non-specific inhibitor of Na+ channels and transporters, comparably shifted concentration-response curves of noradrenaline to the left in both the contralateral and ipsilateral arteries. One hundred nM of noradrenaline induced intracellular Ca2+ elevation in the ipsilateral arteries, which was significantly larger than that induced by 300-nM noradrenaline in the contralateral arteries. These results suggest that reduced peripheral blood flow after nerve injury is due to Na+-dependent inactivation of NCX in the ipsilateral plantar arteries.

Effect of Yokukansan on sleep disturbance and neuropathic pain in chronic constriction injury using a rat model

Patients with chronic pain develop peripheral neuropathy and experience sleep disturbance. Yokukansan is used to treat insomnia and control neuropathic pain. We studied if Yokukansan affects neuropathic pain and sleep disturbance using a rat model of chronic constriction injury (CCI). Male Wistar rats (4-week age) were divided into the following groups (n = 7, per group): CCI rats fed normal chow (CCI-0); CCI rats fed powdered chow mixed with 1% Yokukansan (CCI-1); CCI rats fed powdered chow mixed with 3% Yokukansan (CCI-3); and sham-operated control rats fed normal chow (SHAM). We examined sleep duration and quality using electroencephalograms and assessed pain using the von Frey and Hargreaves tests. Results were analyzed by one-way analysis of variance and Bonferroni post hoc tests. The CCI-0 group exhibited an increased wake period, decreased non-rapid eye movement (REM) sleep time, and no change in REM sleep time in comparison to the SHAM group. The CCI-1 group exhibited a decreased wake period, increased non-REM sleep time, and no change in REM sleep time compared to the CCI-0 group. The CCI-3 group exhibited increased non-REM sleep time but no changes in wake and REM sleep times compared to the CCI-1 group. The von Frey and Hargreaves test findings revealed an increase in the pain threshold in the CCI-1 group compared to the CCI-0 group. There was no difference in pain threshold between the CCI-1 and CCI-3 groups. In our rat model of CCI, sleep disturbance was reflected. Yokukansan inhibited CCI-induced sleep disturbance.

Antinociceptive effects of oleuropein in experimental models of neuropathic pain in male rats.

BackgroundThe present investigation explored the therapeutic actions of oleuropein along with the possible signaling pathway involved in attenuating neuropathic pain in chronic constriction injury (CCI) and vincristine-induced neuropathic pain in male rats.MethodsFour loose ligatures were placed around the sciatic nerve to induce CCI, and vincristine (50 μg/kg) was injected for 10 days to develop neuropathic pain. The development of cold allodynia, mechanical allodynia, and mechanical hyperalgesia was assessed using different pain-related behavioral tests. The levels of H2S, cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), orexin, and nuclear factor erythroid-2-related factor 2 (Nrf2) were measured in the sciatic nerve.ResultsTreatment with oleuropein for 14 days led to significant amelioration of behavioral manifestations of neuropathic pain in two pain models. Moreover, oleuropein restored both CCI and vincristine-induced decreases in H2S, CSE, CBS, orexin, and Nrf2 levels. Co-administration of suvorexant, an orexin receptor antagonist, significantly counteracted the pain-attenuating actions of oleuropein and Nrf2 levels without modulating H2S, CSE and CBS.ConclusionsOleuropein has therapeutic potential to attenuate the pain manifestations in CCI and vincristine-induced neuropathic pain, possibly by restoring the CSE, CBS, and H2S, which may subsequently increase the expression of orexin and Nrf2 to ameliorate behavioral manifestations of pain.

17beta estradiol ameliorates neuroinflammation driven neuropathic pain in chronic constriction injury – induced peripheral neuropathy in rats

17beta estradiol ameliorates neuroinflammation driven neuropathic pain in chronic constriction injury – induced peripheral neuropathy in rats

Investigating the possible pain attenuating mechanisms of pregabalin in chronic constriction injury-induced neuropathic pain in rats

Aim of the study: The current study was aimed to investigate the neuropathic pain attenuating mechanism of pregabalin using chronic constriction injury (CCI) model in rats.Material and Methods: The sciatic nerve was ligated by placing four loose ligatures around it to induce neuropathic pain. The pain development in terms of cold allodynia, mechanical hyperalgesia, and heat hyperalgesia was assessed on the 7th and 14th day after surgery, using acetone drop, pinprick, and hot plate tests. On the 14th day after the injury, pain parameters were assessed 30 minutes after administration of pregabalin (30 mg/kg) and sodium nitroprusside (5 mg/kg) in CCI-subjected rats.Results: CCI led to induction of neuropathic pain, which was more prominent on 14th day in comparison to 7th day. A single administration of pregabalin and sodium nitroprusside on 14th day, markedly reduced pain parameters and increased serum nitrite levels. Pretreatment with L-NAME abolished neuropathic pain attenuating effects of pregabalin suggesting that pregabalin may increase the levels of nitric oxide to mitigate neuropathic pain. Pretreatment with naloxone significantly abrogated pain attenuating effects of pregabalin and sodium nitroprusside in CCI-subjected rats suggesting that pregabalin and nitric oxide-mediated analgesic action are mediated through release of endogenous opioids. Moreover, naloxone failed to modulate pregabalin-induced increase in nitric oxide levels suggesting that the opioid system does not control the nitric oxide levels, and opioids may be downstream modulators of nitric oxide.Conclusion: Pregabalin may increase the release of nitric oxide, which may increase the release of endogenous opioids to attenuate neuropathic pain in CCI subjected rats.

Pregabalin on Hdac2 and Inpp5f levels in rats with CCI-induced neuropathic pain.

Hdac2/Inpp5f on the therapeutic effect of pregabalin on neuropathic pain in chronic constriction injury (CCI) rats was investigated. A total of 90 healthy SD rats were selected and divided into the treatment group, the model control group and the normal control group with 30 rats in each group. Rats in the treatment and model control groups were used to construct CCI model. The control group was treated with sham surgery. The model control group was not treated after surgery. The treatment group was treated with pregabalin on the 8th day after operation. Behavioral experiments were performed to measure mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL). The expression of inflammatory cytokines TNFα and IL-1β was detected by ELISA kit and expression of Hdac2 and Inpp5f mRNA was detected by RT-qPCR. Before treatment, compared with the normal control group, MWT and TWL values of the treatment and model control groups were significantly decreased (P<0.05). At different time-points after treatment, MWT and TWL were higher in the treatment group than in the model control group and were lower than in the normal control group. At 21 days after operation, the levels of TNFα and IL-1β in the model control and treatment groups were higher than those in the normal control group (P<0.05). The expression level of Hdac2 was higher in the treatment group than in the normal control group (P<0.05). The expression level of Inpp5f mRNA in the treatment and normal control groups was significantly higher than that in the model control group (P<0.05), but the expression level of Inpp5f mRNA in the treatment group was lower than that in the normal control group (P<0.05). Therefore, pregabalin can effectively relieve neuropathic pain in CCI rats, and its efficacy is related to Hdac2 and Inpp5f. Our study provides reference for clinical treatment of neuropathic pain induced by CCI.

Long noncoding RNA MRAK009713 is a novel regulator of neuropathic pain in rats.

Long noncoding RNAs have been implicated in neuropathy. Here, we identify and validate a long noncoding RNA, MRAK009713, as the primary regulator of neuropathic pain in chronic constriction injury (CCI) rats. MRAK009713 expression was markedly increased in CCI rats associated with enhanced pain behaviors, and small interfering RNA against MRAK009713 significantly reduced both mechanical and thermal hyperalgesia in the CCI rats. MRAK009713 is predicted to interact with the nociceptive P2X3 receptor by CatRAPID, a bioinformatics technology. Overexpression of MRAK009713 markedly increased expression of P2X3 in the dorsal root ganglia of the control rats, and MRAK009713 small interfering RNA significantly inhibited the P2X3 expression in the dorsal root ganglia of the CCI rats. MRAK009713 directly interacted with the P2X3 protein heterologously expressed in the human embryonic kidney (HEK) 293 cells and potentiated P2X3 receptor function. Thus, MRAK009713 is a novel positive regulator of neuropathic pain in rats through regulating the expression and function of the P2X3 receptor.

Forced exercise attenuates neuropathic pain in chronic constriction injury of male rat: an investigation of oxidative stress and inflammation.

Background and objectiveInitial peripheral/central nerve injuries, such as chronic constriction injury (CCI)/spinal cord injury, are often compounded by secondary mechanisms, including inflammation and oxidative stress, which may lead to chronic neuropathic pain characterized by hyperalgesia or allodynia. On the other hand, exercise as a behavioral and non-pharmacological treatment has been shown to alleviate chronic neuropathic pain. Therefore, this study was conducted to examine whether or not exercise reduces neuropathic pain through modifying oxidative stress and inflammation in chronic constriction injury of the sciatic nerve.Materials and methodsWistar male rats weighing 200±20 g were randomly divided into five groups (normal, sham, CCI, pre-CCI exercise, and post-CCI exercise group). Sciatic nerve of anesthetized rats was loosely ligated to induce CCI, and they were then housed in separate cages. The rats ran on treadmill at a moderate speed for 3 weeks. Mechanical allodynia and thermal hyperalgesia were determined using von Frey filament and plantar test, respectively. Tumor necrosis factor-alpha (TNF-α) assayed in the cerebrospinal fluid, malondialdehyde, and total antioxidant capacity were measured in the serum using Western blot test, thiobarbituric acid, and ferric reducing ability of plasma (FRAP), respectively.ResultsThe mechanical allodynia (P=0.024) and thermal hyperalgesia (P=0.002) in the CCI group were higher than those in the sham group. Exercise after CCI reduced (P=0.004) mechanical allodynia and thermal hyperalgesia (P=0.025) compared with the CCI group. Moreover, the level of FRAP in the CCI group was (P=0.001) lower than that in the sham group, and post-CCI exercise reversed FRAP amount toward the control level (P=0.019). The amount of malondialdehyde did not differ between groups. Level of TNF-α increased in the CCI group (P=0.0002) compared with sham group and post-CCI exercise could reverse it toward the level of control (P=0.005).ConclusionPost CCI-exercise but not pre CCI-exercise reduces CCI-induced neuropathic pain. One of the possible involved mechanisms is increasing the total antioxidant capacity and reducing the amount of TNF-α.

Dexmedetomidine attenuates neuropathic pain in chronic constriction injury by suppressing NR2B, NF-κB, and iNOS activation

The effective treatment of patients suffering from neuropathic pain remains challenging. Dexmedetomidine (DEX) possesses anti-inflammatory activity. However, the role of DEX in neuropathic pain is still unclear. The aim of the present study was to examine DEX an α2-adrenoceptor agonist could improve pain hypersensitivity and reduce inflammatory in a chronic constriction injury (CCI) model of the sciatic nerve in Sprague-Dawley rats. Dex was intrathecally administrated 1-h after operation. The paw mechanical withdrawal threshold (MWT) and paw withdrawal thermal latency (PWTL) were measured on day 1 before operation and on days 1, 7, 14 and 21 after operation, respectively. On day 21, all the rats were decapitated to collect the L4-6 segments of the spinal cord to examine IL-1, TNF-α, IL-6, NR2B, NF-κB, and iNOS mRNA levels using RT-PCR. The postoperative MWT and PWTL were significantly decreased in CCI, and DEX groups as compared to those before surgery and Sham group (P<0.05). And DEX reversed this trend (P<0.05). Interleukin 1 (IL-1), tumor necrosis factor α (TNF-α), IL-6 mRNA expression significantly increased postsurgery in CCI group as compared to that of Sham group (P<0.05); DEX blocked increased IL-1, TNF-α, IL-6, N-methyl-D-aspartate (NMDA) receptor 2B (NR2B), nuclear factor κB (NF-κB), and inducible isoform of nitric oxide synthase (iNOS) mRNA levels (P<0.05). DEX may alleviate neuropathic hypersensitivity and inflammation partially by inhibiting NR2B, NF-κB, and iNOS expression in the spinal cord of rats with neuropathic pain resulting from CCI of the sciatic nerve.

Redistribution of voltage-gated sodium channels after nerve decompression contributes to relieve neuropathic pain in chronic constriction injury

Nerve decompression is an important therapeutic strategy to relieve neuropathic pain and promote the peripheral nerve regeneration. To address these issues, we investigated the effects of nerve decompression on relief of neuropathic pain behaviors, redistribution of voltage-gated sodium channels (VGSCs), and skin reinnervation with chronic constriction injury (CCI). At post-operative week (POW) 4, animals were divided into a decompression group, in which the ligatures were removed, and a CCI group, in which the ligatures remained. Thermal hyperalgesia and mechanical allodynia at POW 8 had distinct reductions in decompression group compared to CCI group. At that time in CCI group, morphological evidence of pan VGSCs (Pan Nav) and isoforms of VGSCs (Nav1.6, Nav1.9, except for Nav1.8) were shown the widely distribution along the injured sciatic nerve. All of the VGSCs in decompression group became clustering around the node of Ranvier, similar to the pattern of control sciatic nerve at POW 8. Skin reinnervation was demonstrated by epidermal nerve density (END) for protein gene product 9.5 (PGP 9.5)-immunoreactive (IR) nerve fibers and a significant difference between groups only at POW 24 (p=0.01). Growth-associated protein 43 (GAP-43) is participated in the nerve fiber growth and sprouting, a difference in END for GAP-43-IR nerve fibers at POW 24 between groups were also significant (p=0.02). These observations demonstrated that nerve decompression was accompanied with the disappearance of neuropathic pain behaviors after CCI. Morphological studies provided the evidence that redistribution of VGSCs along the injured sciatic nerve but still with an incomplete skin reinnervation. These significant findings demonstrated a role of VGSCs in the pathogenesis of neuropathic pain, and gave an approaching in pharmacological basis of therapeutics.

Delayed Granulocyte Colony-Stimulating Factor Treatment in Rats Attenuates Mechanical Allodynia Induced by Chronic Constriction Injury of the Sciatic Nerve

Animal experimental study with intervention. The aim of this study was to elucidate therapeutic effects of delayed granulocyte colony-stimulating factor treatment for mechanical allodynia induced by chronic constriction injury (CCI) of the sciatic nerve in rats. Granulocyte colony-stimulating factor (G-CSF) is used clinically for patients with hematological disorders. Previous reports showed that immediate G-CSF attenuates neuropathic pain in CCI of the sciatic nerve. However, the acute treatment for neuropathic pain prior to accurate diagnosis is not realistic in clinical settings. Adult, female Sprague-Dawley rats were subjected to the CCI model. This model induces mechanical allodynia on the ipsilateral hind paw within the first week after the injury. One week after CCI, rats received intraperitoneal G-CSF (15.0 μg/kg) for 5 consecutive days. Mechanical allodynia was assessed using the von Frey hair test. Immunohistochemistry for phosphorylated p38 mitogen-activated kinase (p-p38MAPK) and OX-42 (a marker for activated microglia) on tissue slides from a subset of rats 2 weeks after surgery. Western blot analyses were carried out to determine protein expression level of p-p38MAPK and interleukin-1 β on spinal cord homogenates 2 weeks after CCI. Results of the von Frey filament test showed that G-CSF significantly attenuates mechanical allodynia induced by the CCI model. Immunohistochemistry revealed that G-CSF reduced the number of p-p38MAPK-positive cells in the ipsilateral dorsal horn compared with that in the vehicle group rats. Immunofluorescent double staining revealed that p-p38MAPK-expressing cells in the spinal cord dorsal horn are mainly microglia. Western blot analysis indicated that G-CSF decreased the expression levels of both p-p38MAPK and interleukin-1 β in the ipsilateral dorsal horn compared with that in the vehicle group rats. The present results indicate a beneficial effect of delayed G-CSF treatment in an animal model of peripheral nerve injury-induced neuropathic pain. N/A.

Antiallodynic Effect of Herbal Medicine Yokukansan on Peripheral Neuropathy in Rats with Chronic Constriction Injury

Yokukansan, one of the traditional Japanese herbal medicines, ameliorated neuropathic pain symptoms in patients. In this study, we investigated the effects of yokukansan on neuropathic pain in chronic constriction injury (CCI) model. Oral administration of yokukansan significantly inhibited mechanical and cold allodynia in the von Frey hair or acetone test, respectively. In comparison, amitriptyline, a tricyclic antidepressant, demonstrated moderate, but not significant, antiallodynic effects in the mechanical and cold tests. Yokukansan significantly inhibited the cerebrospinal fluid dialysate level of glutamate that had increased by the stimulation of brush or acetone. Glutamate transporter inhibitors, DL-threo-beta-hydroxy aspartate and dihydrokainate, decreased the yokukansan-induced antiallodynic actions in CCI rats. Our results suggest that yokukansan was confirmed to have antiallodynic effects in CCI rats, which are related to a blockade of glutamatergic neurotransmission via activation of glutamate transporters in the spinal cord.

Antinociceptive effect of linear polarized 0.6 to 1.6 um irradiation of lumbar sympathetic ganglia in chronic constriction injury rats

Linear polarized near-infrared light created with linear polarized near-infrared light therapy equipment (Super Lizer HA-550, Tokyo Iken Co, Ltd, Tokyo, Japan) has been used for the treatment of various painful disorders in Japan. Irradiation near the stellate ganglion with a Super Lizer (ISGL) is an especially notable therapeutic method used with stellate ganglion block (SGB) or substitutes for SGB. ISGL is a safe, simple, well-tolerated, and effective treatment. We examined the effects of irradiation with a Super Lizer applied to an area near the lumbar sympathetic ganglia on the ligated side in a chronic constriction injury (CCI) model, which is believed to be an animal model of complex regional pain syndrome (CRPS). Rats showing thermal hyperalgesia in a radiant heat test 1 wk postoperatively were used in Experiments 1 and 2: (1) Thermal hyperalgesia of irradiation group (n = 11) was less than that of the control or nonirradiation (n = 11) group at 1, 3, and 8 h after irradiation; however, the effect disappeared 12 h after irradiation. (2) Daily irradiation (n = 16) and 1 wk (n = 14) from 7 days after nerve ligation significantly shortened the interval from thermal hyperalgesia until recovery. Rats showing mechanical hyperalgesia in the von Frey hair test 1 wk postoperatively were used in Experiment 3: 1 wk irradiation beginning 7 days after nerve ligation (n = 9) did not promote the recovery from mechanical hyperalgesia. We speculate that repeated ISGL may be more effective than a single ISGL in alleviating pain in CRPS patients. We cannot explain the discrepancy between the results obtained in Experiments 2 and 3. We believe the results of this study are relevant to the effect of ISGL for patients with upper-limb CRPS: irradiation near the lumbar sympathetic ganglia of the rat is effective for thermal but not mechanical pain in CCI.