Increased serum IL-6 level time-dependently regulates hyperalgesia and spinal mu opioid receptor expression during CFA-induced arthritis

Interleukin (IL)-6 is known to cause pro- and anti-inflammatory effects during different stages of inflammation. Recent therapeutic investigations have focused on treatment of various inflammatory disorders with anti-cytokine substances. As a result, the aim of this study was to further elucidate the influence of IL-6 in hyperalgesia and edema during different stages of Complete Freund’s Adjuvant (CFA)-induced arthritis (AA) in male Wistar rats. AA was induced by a single subcutaneous injection of CFA into the rats’ hindpaw. Anti-IL-6 was administered either daily or weekly during the 21 days of study. Spinal mu opioid receptor (mOR) expression was detected by Western blotting. Daily and weekly treatment with an anti-IL-6 antibody significantly decreased paw edema in the AA group compared to the AA control group. Additionally, daily and weekly anti-IL-6 administration significantly reduced hyperalgesia on day 7 in the AA group compared to the AA control group; however, there were significant increases in hyperalgesia in the antibody-treated group on days 14 and 21 compared to the AA control group. IL-6 antibody-induced increases in hyperalgesia on the 14th and 21st days after CFA injection correlated with a time-dependent, significant reduction in spinal mOR expression during anti-IL-6 treatment. Our study confirmed the important time-dependent relationship between serum IL-6 levels and hyperalgesia during AA. These results suggest that the stages of inflammation in AA must be considered for anti-hyperalgesic and anti-inflammatory interventions via anti-IL-6 antibody treatment

Effect of intrathecal transplantation of adrenal medullary tissue on the sciatic nerve regeneration following chronic constriction injury in the rat

Introduction: It has been demonstrated that the adrenal medullary transplants into the spinal subarachnoid space can alleviate neuropathic pain behaviors. The aim of the present study was to test the possibility that histological changes of the sciatic nerve in a neuropathic model as well as sensory dysfunction are repaired by adrenal medullary transplantation. Material and Methods: Left sciatic nerve was ligated in three groups of rats by 4 loose ligatures (CCI). After one week of nerve constriction, rats of first group were implanted with adrenal medullary tissue (CCI + adrenal medulla) and rats of the second group with striated muscle at the level of L1-L2 (CCI + muscle). The third group received only left ligature (CCI) and in the fourth group the sciatic nerve was exposed and then muscle and skin sutured (sham). Behavioral assessment was evaluated before surgery and 2, 4, 7, 10, 14, 21, 28, 42, and 56 days after the onset of experiment. According to behavioral results, 4 rats in each group were anesthetized and then the distal part of sciatic nerve were isolated and prepared for histological quantitative investigation of nerve regeneration. Results: The results showed that CCI was accompanied with hyperalgesia and morphological changes in the distal part of sciatic nerve. In animals with adrenal medullary transplantation, not only hyperalgesia was markedly reduced or even eliminated, but also the number of myelinated fibers in the distal segment of nerve increased to nearly normal. Conclusions: Our findings showed that the implantation of adrenal medullary tissue might have caused regeneration of ligated nerves as well as alleviation of pain behavior

Time Profile of nNOS Expression in the Spinal Dorsal Horn After L₅ Spinal Root Transection in Rats

Using immunohistochemical analysis, we investigated the time profile of neuronal nitric oxide synthase (nNOS) expression in the lumbar spinal cord up to day 28 after transection of the L₅ spinal root. On day 14 after injury, we also evaluated the effect of intrathecal application of 7-nitroindazole (7-NI), a selective nNOS inhibitor (8.15 µg in 5 µl), on thermal hyperalgesia. Our results indicated that nerve transection increased the intensity of nNOSimmunoreactivity in superficial and deep laminae of the dorsal horn within a late stage (days 7 to 28) of the neuropathy model used. Furthermore, 7-NI attenuated nerve injury-evoked thermal hypersensitivity on day 14 but did not reduce it between days 2 and 5 after transection. These data suggest that nNOS overexpression is more involved in the development than in the initiation of thermal hyperalgesia in L₅ -transected rats.Ми досліджували часовий профіль експресії нейронної NOсинтази (nNOS) у люмбальному відділі спинного мозку щурів протягом 28 діб після перерізання спінального корінця L₅ , використовуючи імуногістохімічну методику. Ми також оцінювали впливи інтратекальних аплікацій 7-нітроіндазолу (7-NI) – селективного інгібітора nNOS (8.15 мкг у 5 мкл) на термічну гіпералгезію через 14 діб після ушкодження. В результаті секції корінця кількість nNOS-імунореактивних клітин у поверхневих та глибоких пластинах дорсального рога зростала на відносно пізніх етапах (із сьомої по 28-му добу) використаної моделі нейропатії. Аплікації 7-NI зменшували термічну гіперсенситивність, викликану пошкодженням нервових волокон, на 14-ту добу, але не впливали на цей феномен протягом другої–п’ятої діб після індукції нейропатії. Подібні дані вказують на те, що після перетину корінця L₅ у щурів підвищена експресія nNOS більшою мірою залучена в процес розвитку, ніж в ініціацію термічної гіпералгезії

Role of serum interleukin-6 level on hyperalgesia and spinal mu-opioid receptor expression during the complete Freund's adjuvant-induced chronic inflammation

Background: Interleukin (IL-6) is known to cause pro- and anti-inflammatory effects during different stages of inflammation. The purpose of this study was to elucidate the effects of IL-6 on hyperalgesia, edema and the changes in the spinal mu opioid receptor expression during different stages of complete Freund’s adjuvant (CFA)-induced arthritis (AA) in rats. Materials and Methods: In this study, AA was induced by a single subcutaneous injection of CFA into rats’ hindpaw. The rats with arthritis were divided into four groups, each consisted of three subgroups (n= 6). Anti-IL-6 was administered either daily or weekly during the 21-day study period. Spinal mu-opioid receptor (mOR) expression was detected by Western blotting. Results: Daily treatment with an anti-IL-6 antibody significantly decreased the paw edema in the AA group compared to the control one (P=0.001), but daily and weekly anti-IL-6 administrations significantly increased the hyperalgesia in the antibody-treated group on the 14th and 21st days post-treatment (P=0.001, P=0.01, respectively). The administration of IL-6 antibody not only increased hyperalgesia in a time-dependent manner, but also caused a significant reduction in the spinal mOR expression on the 14th and 21st days post-CFA injection (P=0.01, P=0.001, respectively). Conclusion: Results can indicate the importance of a time-dependent relationship between the serum IL-6 level and hyperalgesia during the AA. Moreover, the results suggest that the stages of inflammation in AA must be considered for anti-hyperalgesic and anti-inflammatory interventions via anti-IL-6 antibody treatment

Comparison of behavioural responses of two neuropathic pain models in male rats

Background: Neuropathic pain syndromes are changes resulted from damage to neuronal pathways which is characterized by spontaneous burning pain with accompanying allodynia and hyperalgesia. The mechanisms underlying neuropathic pain are poorly understood. The present study explores behavioral characteristics of the neuropathic pain models chronic constriction injury (CCI) and spared nerve injury (SNI). Materials and Methods: Experiments were performed on four groups (n= 8) of male Sprague-Dawley rats (230-280 g). Anesthesia was initially induced with sodium pentobarbital (i.p.) at a dose of 50 mg/kg. The CCI model was made by loose ligation of the sciatic nerve. Also a lesion of two of three terminal branches of the sciatic nerve leads to a SNI model. The animals were tested for behavioral responses cold-and mechano-allodynia and heat-and mechano-hyperalgesia. The cold and mechanical stimulations in the cold- and mechano-allodynia phenomena were applied through acetone and von Frey filament respectively. Pin-prick and radiant heat were applied as thermal and mechanical stimulations in the heat- and mechano-hyperalgesia respectively. Behavioral tests were conducted on the animals prior to surgery (the day 0), and 3, 7, 14, 21 and 28 days post-operation. Results: Our results indicate that, in comparison to the controlled group, the rats in both SNI and CCI groups reveal an obvious difference in behavioral responses. Although the SNI, compared to the CCI group were more sensitive to mechano-allodynia shortly after surgery (p<0.5) however, both groups share a similar pattern of behavior. In the heat-hyperalgesia testing, again, the animals in the CCI and SNI groups behaved differently than those in the controlled group, but no variation was evident among the test groups, themselves. Conclusion : These findings clearly show that the two neuropathic models produce abnormal pain-related disorders in the rats. A major feature of the SNI model was the very marked hypersensitivity to normally innocuous mechanical stimuli

Evaluation of the L5 spinal nerve ligation on Aδ- and C-fibers activation threshold and also LTP-induced by electrical high frequency stimulation of sciatic nerve in spinal dorsal horn of rats

Background: The underlying central mechanisms for the development and maintenance of neuropathic pain are unknown. The current study aimed to evaluate the long-term potentiation (LTP) changes in spinal dorsal horn wide dynamic range (WDR) neurons following a peripheral neuropathy model. Materials and Methods: This study was conducted on 26 male Wistar rats. The spinal nerve ligation (SNL) model was performed to induce neuropathy. After surgery, thermal hyperalgesia and mechanical allodynia were evaluated one day before neuropathy, and then on days 2, 5, 7, 14, 21 and 28 after neuropathy. Single-unit recording was used to study the changes of LTP. The changes of LTP and Aδ- and C-fiber evoked responses by high-frequency stimulation (100 Hz and current intensity six times that of the threshold for activation of C- fibers) of sciatic nerve in spinal WDR synapses were studied on day 14 after surgery up to 2 hours. Results: Neuropathy was induced thermal hyperalgesia and mechanical allodynia on day 2 and persisted for 28 days after neuropathy. Electrophysiological recording revealed that HFS induced LTP either in the Aδ- or in the C-fibers in both sham and neuropathy groups up to 2 hr on day 14 after neuropathy. Neuropathy also significantly decreased the threshold of these fibers.Conclusion: LTP-induced HFS in spinal WDR neurons can be one of the underlying central mechanisms in the maintenance of neuropathic pain