Progesterone modulates the expression of spinal ephrin-B2 after peripheral nerve injury: New insights into progesterone mechanisms.

Recent studies have shown that the ephrin/Eph signaling pathway may contribute to the pathology of neuropathic pain. Drugs like progesterone may be used to counteract both thermal hyperalgesia and mechanical allodynia in different models of neuropathic pain. The present study was designed to determine progesterone's modulatory role on neuropathic pain and spinal expression of ephrin-B2 following chronic constriction nerve injury (CCI). Thirty-six adult male Wistar rats were used. The sciatic nerve was chronically constricted. Progesterone (5 mg/kg and 15 mg/kg) was administrated for 10 days (from day 1 up to day10) following sciatic constriction. Behavioral tests were performed before surgery (day 0) and on days 1, 3, 7, and 14 after CCI and before progesterone administration on the same days. Western blotting was performed on days 3, 7, and 14th post-surgery. The findings showed that after CCI, the expression of spinal cord ephrin-B2 increased significantly in parallel with mechanical allodynia and thermal hyperalgesia. Post-injury administration of progesterone (15 mg/kg but not 5) decreased mechanical allodynia, thermal hyperalgesia, and the expression of spinal ephrin-B2. It is concluded that post-injury repeated administration of progesterone could be an effective way of alleviating neuropathic pain by suppressing ephrin-B2 activation and helps to make the better design of steroid-based therapies to inhibit pain after peripheral injury.

Evaluation of the GABAA Receptor Expression and the Effects of Muscimol on the Activity of Wide Dynamic Range Neurons Following Chronic Constriction Injury of Sciatic Nerve in Rats.

INTRODUCTION: The modality of γ-aminobutyric acid type a receptors (GABAA) controls dorsal horn neuronal excitability and inhibits sensory information. This study aimed to investigate the expression of the GABAA receptor and the effects of its agonist muscimol on Wide Dynamic Range (WDR) neuronal activity in the Chronic Constriction Injury (CCI) model of neuropathic pain. METHODS: Adult male Wistar rats weighing 200 to 250 g were used to induce CCI neuropathy. Fourteen days after surgery, muscimol (0.5, 1, and 2 mg/kg IP) was injected. Then, the behavioral tests were performed. After that, the animals were killed, and the lumbar segments of the spinal cords were collected for Western blot analysis of the GABAA receptor α1 subunit expression. The electrophysiological properties of WDR neurons were studied by single-unit recordings in separate groups 14 days after CCI. RESULTS: The outcomes indicated the development of thermal hyperalgesia and mechanical allodynia after neuropathy; nonetheless, the expression of the GABAA receptor α1 subunit did not change significantly. Moreover, the evoked responses of the WDR neurons to electrical, mechanical, and thermal stimuli increased considerably. Fourteen days after CCI, muscimol administration decreased thermal hyperalgesia, mechanical allodynia, and hyper-responsiveness of the WDR neurons in CCI rats. CONCLUSION: The modulation of the spinal GABAA receptors after nerve injury can offer further insights to design new therapeutic agents to reduce neuropathic pain symptoms.

The Potential Role of Glycogen Synthase Kinase-3ß in Neuropathy-Induced Apoptosis in Spinal Cord.

INTRODUCTION: Glycogen Synthase Kinase-3ß (GSK-3ß) participates in several signaling pathways and plays a crucial role in neurodegenerative diseases, inflammation, and neuropathic pain. The ratio of phosphorylated GSK-3ß over total GSK-3ß (p-GSK-3ß/t-GSK-3ß) is reduced following nerve injury. Apoptosis is a hallmark of many neuronal dysfunctions in the context of neuropathic pain. Thus, this study aimed to evaluate the contribution of p-GSK-3ß/t-GSK-3ß ratio in spinal dorsal horn apoptosis following peripheral nerve injury. METHODS: In this study, adult male Wistar rats (220-250 g) underwent Spinal Nerve Ligation (SNL) surgery. Mechanical allodynia and thermal hyperalgesia were assessed before the surgery (day 0); then, every other day up to day 8. GSK-3ß selective inhibitor, AR-014418 [0.3 mg/kg, Intraperitoneal (IP)] was administrated 1 h prior to SNL on day 0, then daily up to the day 8. The GSK-3ß activity and apoptosis in the lumbar section (L4, L5, or L6) of the study rat's spinal cord were assessed by immunohistochemical and Terminal Deoxynucleotidyl Transferase dUTP Nick End Labeling (TUNEL) staining, respectively on day 8 post-SNL. RESULTS: Following the SNL, the mechanical allodynia and thermal hyperalgesia increased on day 2 up to day 8 post-SNL. The ratio of p-GSK-3ß/t-GSK-3ß decreased, and the number of apoptotic cells increased in the spinal dorsal horn on day 8. However, AR-A014418 administration could increase the p-GSK-3ß/t-GSK-3ß ratio and decreased apoptosis in the SNL rats. In addition, AR-A014418 decreased the mechanical allodynia from day 4 up to day 8; however, it did not affect thermal hyperalgesia. CONCLUSION: The study findings suggested that increasing the p-GSK-3ß/t-GSK-3ß ratio might be a helpful strategy for reducing the apoptotic cells and subsequent neuropathic pain during peripheral nerve injury.

Recovery of inferior alveolar nerve by photobiomodulation therapy using two laser wavelengths: A behavioral and immunological study in rat.

Postoperative sensory disturbances of inferior alveolar nerve (IAN) are major challenges in dental procedures. We aimed to investigate the effect of photobiomodulation therapy (PBMT) with 810 nm and 980 nm diode lasers on behavioral and immunological factors in a rat IAN crush model. Seventy-two rats were randomly assigned to the four groups of 810 nm laser (crush injury+810 nm laser; 6 J/cm2, 15 sessions, every 48 h), 980 nm laser (crush injury+980 nm laser; same protocol), control (crush injury without irradiation), and sham surgery (no crush injury and no irradiation). The neurosensory response of IAN was evaluated by Von Frey behavioral test before (baseline) and post-surgery in a period of one month. Changes of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), nuclear factor-kappa B (NF-κB), TNF-α, and IL-1ß, were assessed on days 2 and 30 post injury. Data were analyzed for significant differences by repeated measures and one-way ANOVA (p < .05). One day after surgery, all rats subjected to nerve injury showed significant increase in the withdrawal threshold of von Frey test compared to the baseline (p = .02 for control and p = .03 for laser groups). The threshold gradually returned to the baseline scores in 810 nm, 980 nm, and control groups from days 11, 17, and 29, respectively. There was a significant lower withdrawal threshold in 810 nm and 980 nm laser groups compared to the control group in days 11 to 19 and 9 to 23, respectively. At both time points, the levels of NGF and BDNF were significantly higher in 810 nm laser group compared to the control group. There was a significant difference between laser and control groups regarding NF-κB expression (all p values<.001). TNF-α and IL-1ß were significantly lower in laser groups compared to the control group (all p values < .001). PBMT with 810 and 980 nm diode laser protocol used in this study, promoted the neurosensory recovery of IAN after crush injury in rats. In addition, application of 810 nm diode laser was associated with more improvement in immunological responses compared to that of 980 nm laser.

Chemical stimulation of the lateral hypothalamus induces antiallodynic and anti-thermal hyperalgesic effects in animal model of neuropathic pain: Involvement of orexin receptors in the spinal cord.

To date several circuities in supraspinal site of the central nervous system have been known to engage in pain modulation. Lateral hypothalamus (LH) is known as part of the circuit of pain modulation among supraspinal sites. Its role in several animal pain models has been well defined. In this study, we examined the role of spinal orexin receptors in antinociceptive response elicited by the LH stimulation in an animal model of neuropathic pain. Male Wistar rats were unilaterally implanted with a cannula into the LH and a catheter into the L4-L5 segments of the spinal cord followed by chronic constriction injury (CCI) surgery. Intra-LH microinjection of carbachol (500 nM; 0.5 µL) was done 5 min after intrathecal administration of the orexin receptor antagonists, SB-334867 or TCS OX2 29; control animals received DMSO. Mechanical allodynia and thermal hyperalgesia were evaluated using von Frey filaments and a thermal stimulus. The results showed that carbachol induces antiallodynic and anti-thermal hyperalgesic effects in a dose-dependent manner. The antiallodynic and anti-thermal hyperalgesic effects induced by intra-LH injection of carbachol were reversed by intrathecal administration of 10 µL-100 nM solutions of SB-334867 or TCS OX2 in neuropathic rats. However, solely intrathecal administration of both antagonists had no effect in neuropathic rats. There appears to be a neural pathway from the LH to the spinal cord, which potentially contributes to the modulation of neuropathic pain. The implications are that there may be novel therapeutic approaches for the treatment of people suffered from chronic neuropathic pain in clinic.

Microglial-induced apoptosis is potentially responsible for hyperalgesia variations during CFA-induced inflammation.

AIMS: Activated microglia is known as a main mediator of inflammatory pain, but the possible mechanisms of its operation are poorly understood. Microglial cells have considered as one of the main sources of pro-inflammatory cytokines in the CNS. PTEN is one of the important targets of pro-inflammatory cytokines and the main mediator of apoptotic cell death. In this study, we investigated the possible effect of microglial activation on PTEN/PI3K/Akt signaling pathway and apoptosis in an inflammatory rat model of Complete Freund's adjuvant (CFA). METHODS: Persistent peripheral inflammation was induced by a subcutaneous injection of CFA into the rats' right hind paw on day 0. Minocycline (a potent selective inhibitor of microglial) was administered intraperitoneally during days 1-21 after CFA injection. Hyperalgesia was assessed on days 0, 7, and 21 using plantar test, then lumbar spinal cord segments were isolated, and the amount of spinal Iba1 (microglial marker), PTEN, P.Akt, and cleaved caspase-3 (a marker of apoptosis activation) were analyzed using Western blot. The spinal TNF-α levels were assayed by ELISA and the microglia numbers were determined using immunohistochemical technique. RESULTS: Results revealed that increased hyperalgesia was concurrent with an increment of Iba1 (P < 0.001), TNF-α (P < 0.001), PTEN (P < 0.01), cleaved caspase-3 (P < 0.001), and a decrement of P.Akt (P < 0.01) during the acute phase of CFA-induced inflammation, while, at the same time as decreasing hyperalgesia during the chronic phase of study, Iba1 and TNF-α expression significantly decreased and PTEN, cleaved caspase-3, and P.Akt restored to baseline on day 0. Minocycline administration reduced the elevation of spinal Iba1 (P < 0.001), TNF-α (0.001), PTEN (P < 0.01), and cleaved caspase-3 (P < 0.001) expression induced by CFA injection, and also restored Akt activity to the baseline on day 0 (P < 0.001). CONCLUSIONS: These results suggest that microglial-mediated pain following CFA injection might be related in part to increased spinal cell apoptosis which probably is mediated by PTEN/PI3K/Akt deregulation.

Thymulin treatment attenuates inflammatory pain by modulating spinal cellular and molecular signaling pathways.

Thymulin is a peptide hormone which is mainly produced by thymic epithelial cells and it has immune-modulatory and anti-inflammatory effects. In this study, we investigated the effects of different doses and various timings of thymulin intraperitoneal administration on spinal microglial activity and intracellular pathways in an inflammatory rat model of Complete Freund's adjuvant (CFA). Thymulin treatment was implemented following CFA-induced inflammation for 21 days. After conducting behavioral tests (edema and hyperalgesia), the cellular and molecular aspects were examined to detect the thymulin effect on inflammatory factors and microglial activity. We demonstrated that thymulin treatment notably reduced thermal hyperalgesia and paw edema induced by CFA. Furthermore, molecular investigations showed that thymulin reduced CFA-induced activation of microglia cells, phosphorylation of p38 MAPK and the production of spinal pro-inflammatory cytokines (TNF-α, IL-6) during the study. Our results suggest that thymulin treatment attenuates CFA-induced inflammation. This effect may be mediated by inhibition of spinal microglia and production of central inflammatory mediators which seems to be associated with the ability of thymulin to reduce p38 MAPK phosphorylation. These data provide evidence of the anti-hyperalgesic effect of thymulin on inflammatory pain and characterize some of the underlying spinal mechanisms.

Anti-hyperalgesia effect of nanchelating based nano particle, RAc1, can be mediated via liver hepcidin expression modulation during persistent inflammation.

OBJECTIVE: Rheumatoid arthritis (RA) is a chronic systemic inflammatory disorder accompanied with hyperalgesia, edema and pain. At least 30% of the patients failed to respond to the available treatments and medications, which yet have a lot of serious adverse effects on patients. So, using novel technologies to produce more efficient medications is needed. According to the role of iron manipulation in inflammatory process, we have synthetized RAc1 nano particle, which contains zinc and has iron chelating property. In the present study, we evaluated RAc1 nano particle effects on hyperalgesia and liver hepcidin and serum IL-1ß and TNF-α expression levels during acute and chronic phases of adjuvant-induced inflammation in male rats and compared its effects with Deferoxamine. METHODS AND MATERIALS: Complete Freund's adjuvant (CFA)-induced arthritis was caused by single subcutaneous injection of CFA into the rat's hind paw on day zero. RAc1 with 100, 200 and 400 ng/kg doses and deferoxamin with doses of 200 mg/kg after diluting in vehicles were administered daily (i.p.) during the 21 days of the study after CFA injection. Hyperalgesia, Edema, liver hepcidin and serum IL-1ß and TNF-α expression levels were assessed on days 0, 7, 14 and 21 of the study. RESULTS: The results of this study indicated the role of RAc1 nano particle administration in reducing paw edema, thermal hyperalgesia, and liver hepcidin and serum IL-1ß and TNF-α expression even in comparison with Deferoxamine during different phases of inflammation caused by CFA. CONCLUSION: It seems that RAc1 nano particle exerts its immune modulatory effects by decreasing liver hepcidin expression and serum IL-1ß and TNF-α levels.

Long term treatment by mesenchymal stem cells conditioned medium modulates cellular, molecular and behavioral aspects of adjuvant-induced arthritis.

Neuroinflammation plays a crucial role in expression of symptoms of numerous autoimmune and neurodegenerative diseases such as pain during rheumatoid arthritis. Overproduction of pro-inflammatory cytokines and activation of intracellular signaling pathways have been strongly implicated in the generation of pathological pain states, particularly at central nervous system sites and induction of spinal neuroinflammatory symptoms. The wide ranges of research to define new therapeutic approaches, including neuroimmune-modulators like stem cells are in progress. Mesenchymal stem cells conditioned medium (MSC-CM) has anti-inflammatory factors which can regulate the immune responses. The aim of this study was to investigate the effect of administration of MSC-CM on behavioral, cellular and molecular aspects of adjuvant-induced arthritis in male Wistar rats. Complete Freund's adjuvant (CFA)-induced arthritis (AA) was caused by single subcutaneous injection of CFA into the rat's hind paw on day 0. MSC-CM was administered daily (i.p.) and during the 21 days of the study after injection. Hyperalgesia, Edema, Serum TNF-α levels and p38MAPK and NF-κB activities were assessed on days 0,7,14 and 21 of the study. The results of this study indicated the role of MSC-CM in reducing inflammatory symptoms, serum TNF-α levels and activity of intracellular signaling pathway factors during different phases of inflammation caused by CFA. It seems that MSC-CM treatment due to its direct effects on inhibition of intracellular signaling pathways and pro-inflammatory cytokines can alleviate inflammatory symptoms and pain during CFA-induced arthritis.

Human bone marrow-derived and umbilical cord-derived mesenchymal stem cells for alleviating neuropathic pain in a spinal cord injury model.

BACKGROUND: Stem cell therapy can be used for alleviating the neuropathic pain induced by spinal cord injuries (SCIs). However, survival and differentiation of stem cells following their transplantation vary depending on the host and intrinsic factors of the cell. Therefore, the present study aimed to determine the effect of stem cells derived from bone marrow (BM-MSC) and umbilical cord (UC-MSC) on neuropathic pain relief. METHODS: A compression model was used to induce SCI in a rat model. A week after SCI, about 1 million cells were transplanted into the spinal cord. Behavioral tests, including motor function recovery, mechanical allodynia, cold allodynia, mechanical hyperalgesia, and thermal hyperalgesia, were carried out every week for 8 weeks after SCI induction. A single unit recording and histological evaluation were then performed. RESULTS: We show that BM-MSC and UC-MSC transplantations led to improving functional recovery, allodynia, and hyperalgesia. No difference was seen between the two cell groups regarding motor recovery and alleviating the allodynia and hyperalgesia. These cells survived in the tissue at least 8 weeks and prevented cavity formation due to SCI. However, survival rate of UC-MSC was significantly higher than BM-MSC. Electrophysiological evaluations showed that transplantation of UC-MSC brings about better results than BM-MSCs in wind up of wide dynamic range neurons. CONCLUSIONS: The results of the present study show that BM-MSC and UC-MSC transplantations alleviated the symptoms of neuropathic pain and resulted in subsequent motor recovery after SCI. However, survival rate and electrophysiological findings of UC-MSC were significantly better than BM-MSC.

Inhibition of microglial activity alters spinal wide dynamic range neuron discharge and reduces microglial Toll-like receptor 4 expression in neuropathic rats.

It is believed that neuropathic pain results from aberrant neuronal discharges although some evidence suggests that the activation of glia cells contributes to pain after an injury to the nervous system. This study aimed to evaluate the role of microglial activation on the hyper-responsiveness of wide dynamic range neurons (WDR) and Toll-like receptor 4 (TLR4) expressions in a chronic constriction injury (CCI) model of neuropathic pain in rats. Adult male Wistar rats (230 ± 30 g) underwent surgery for induction of CCI neuropathy. Six days after surgery, administration of minocycline (10, 20, and 40 mg/kg, i.p.) was initiated and continued until day 14. After administration of the last dose of minocycline or saline, a behavioral test was conducted, then animals were sacrificed and lumbar segments of the spinal cord were collected for Western blot analysis of TLR4 expression. The electrophysiological properties of WDR neurons were investigated by single unit recordings in separate groups. The findings showed that after CCI, in parallel with thermal hyperalgesia, the expression of TLR4 in the spinal cord and the evoked response of the WDR neurons to electrical, mechanical, and thermal stimulation significantly increased. Post-injury administration of minocycline effectively decreased thermal hyperalgesia, TLR4 expression, and hyper-responsiveness of WDR neurons in CCI rats. The results of this study indicate that post-injury, repeated administration of minocycline attenuated neuropathic pain by suppressing microglia activation and reducing WDR neuron hyper-responsiveness. This study confirms that post-injury modulation of microglial activity is a new strategy for treating neuropathic pain.

Cellular events during arthritis-induced hyperalgesia are mediated by interleukin-6 and p38 MAPK and their effects on the expression of spinal mu-opioid receptors.

Activation of mitogen-activated protein kinase (MAPK) enzymes in nociceptive plasticity has been extensively studied. P38 MAPK enzyme, which can be activated by cytokines, acts as a crucial intracellular regulator of environmental changes. The aim of this study was to elucidate the cellular events during arthritis-induced hyperalgesia that are mediated by interleukin-6 and p38 MAPK, and their effects on the expression of spinal mu-opioid receptors (MORs), in different stages of arthritis in male Wistar rats. Complete Freund's adjuvant (CFA)-induced arthritis (AA) was caused by subcutaneous injection of CFA into the rats' hindpaw. Anti-IL-6 antibody and p38 MAPK phosphorylation inhibitor were administered during 21 days of study. Spinal MOR, p38, and phosphorylated-p38 (pp38) proteins expressions were detected by Western blotting. Daily treatment with anti-IL-6 antibody and p38 MAPK phosphorylation inhibitor, SB203580, significantly decreased paw edema in AA group. Daily anti-IL-6 and SB203580 administration caused a significant reduction in hyperalgesia in the first week of the study, but increased hyperalgesia in the next 2 weeks in experimental groups compared to the AA control group. Expression of pp38 MAPK protein significantly decreased on the 3, 7, 14, and 21 days in AA+SB203580 and AA+anti-IL6 groups compared to AA group. Additionally, daily treatment with anti-IL6 antibody and SB203580 in AA group caused significantly decrease in spinal MOR expression compared to AA control group. The results of our study can confirm that activated spinal p38 MAPK enzyme may play an important role in cellular IL-6 signaling pathways in hyperalgesia variation during different stages of AA inflammation. Also, it can be suggested that at least a part of p38 MAPK effects on hyperalgesia is mediated by spinal MOR expression variation.

Post-injury repeated administrations of minocycline improve the antinociceptive effect of morphine in chronic constriction injury model of neuropathic pain in rat.

It is confirmed that pharmacological attenuation of glial cells can alleviate neuropathic pain by lowering proinflammatory cytokine expression. The present study tries to confirm that post-injury administration of glia inhibitor, minocycline, can attenuate the neuropathic pain symptoms and improves the efficacy of morphine anti-nociception in chronic constriction injury (CCI). Male Wistar rats (230-270 g) underwent surgery for induction CCI model of neuropathy. For assessment of the thermal hyperalgesia and mechanical allodynia after CCI induction, morphine (2.5, 5, 7.5, 10 and 15 mg/kg; s.c.) and saline were administered on post-operative days (PODs) 0, 6 and 14. Hargreaves and Von-Frey tests were performed before and 30 min after morphine administration, respectively. The results showed significant decrease in antinociceptive effect of morphine on POD 6 compared to POD 0 only at the dose of 5 mg/kg. On the other hand, on POD 14 the antinociceptive effect of morphine (5, 7.5, 10 and 15 mg/kg) significantly decreased in comparison with POD 0. In another set of experiments, animals received minocycline (10, 20 and 40 mg/kg; i.p.) for eight days from POD 6 to 13 and then the antinociceptive effect of single dose of morphine 5 mg/kg was tested on POD 14. Behavioral tests showed that minocycline (40 mg/kg) could effectively attenuate the thermal hyperalgesia and mechanical allodynia on POD 13. Moreover, minocycline (40, 20 mg/kg) improved the anti-hyperalgesic, and minocycline (40 mg/kg) improved the anti-allodynic effects of morphine 5 mg/kg on POD 14. It seems that the reduction of antinociceptive effect of morphine after CCI may be mediated through glia activation. Modulation of glial activity by minocycline can attenuate CCI-induced neuropathic pain. It is also shown that repeated post-injury administration of minocycline improves the antinociceptive effect of morphine in neuropathic pain.

Achillea santolina reduces serum interleukin-6 level and hyperalgesia during complete Freund's adjuvant-induced inflammation in male Wistar rats.

OBJECTIVE: Immune system is involved in the etiology and pathophysiologic mechanisms of inflammation. Medicinal plants are an important source of substances which are claimed to induce non-specific immunomodulatory effects. In view of this and on account of the interleukin (IL)-6's role in inflammation and pain induction, this study investigated the effects of Achillea santolina extracts on inflammation which was induced by complete Freund's adjuvant (CFA) in male Wistar rats. METHODS: Both methanolic and defatted extracts prepared from aerial parts of the plant were examined. Inflammatory symptoms such as hyperalgesia and paw edema in CFA-injected rats' paw were measured by radiant heat and plethysmometer during different stages of study respectively. Serum IL-6 level was checked by rat standard enzyme-linked immunosorbent assay specific kit. RESULTS: The results indicated dose-related effects of methanolic extract on paw edema, hyperalgesia and serum IL-6 level reduction in rats. Methanolic extract of A. santolina exhibited significant antihyperalgesic and anti-inflammatory effects during pretreatment and short-term treatment at dose of 200 mg/kg and there was no significant difference between 200 and 400 mg/kg doses of this extract. Defatted extract did not show significant effect on CFA-induced inflammation during different stages of treatment (P>0.05). Short-term treatment with methanolic extract at dose of 200 mg/kg was more effective than indomethacin in edema, hyperalgesia and serum IL-6 level reduction (P<0.01, P<0.01 and P<0.05 respectively). CONCLUSION: These results suggest that methanolic extract of A. santolina possesses potent anti-inflammatory and immunomodulatory activities during pretreatment and short-term administration.

Suppression of interleukin-6 by minocycline in a rat model of neuropathic pain.

Inflammatory mediators produced in the injured nerve have been proposed as contributing factors in the development of neuropathic pain. In this regard an important role is assigned to interleukin-6. The present study, evaluated the effect of pretreatment with minocycline, on pain behavior (hyperalgesia and allodynia) and serum level of interleukin-6 in chronic constriction injury (CCI) model of neuropathic pain in rat. Minocycline (5, 10, 20 and 40 mg/kg, i.p.) was injected 1 h before surgery and continued daily to day 14 post-ligation. Behavioral tests were recorded before surgery and on postoperative days 1, 3, 5, 7, 9, 10, 14, and the serum concentration of interleukin-6 was determined at day 14. We observed that minocycline which was reported to have a neuroprotective effect in some neurodegenerative diseases, reversed hyperalgesia and allodynia due to sciatic nerve ligation and inhibited the interleukin-6 production. It seems that minocycline could have an anti-inflammatory and analgesic effect in some chronic pain states.