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.

Comparison of changes in mRNA expression of spinal glutamate transporters following induction of two neuropathic pain models.

OBJECTIVES: It is now suspected that different kinds of neuropathic pain syndromes may have significantly different mechanisms. To date, much effort has been made to investigate the function of glutamate transporters (GTs) after nerve injury. The aim of this study is to compare the changes in GTs' mRNA expression levels between two distinct models of peripheral neuropathic pain: chronic constriction nerve injury (CCI) and spared nerve injury (SNI). METHODS: Experiments were performed on animal models of mononeuropathy. Several groups of rats were subjected to behavioral experiments before and 4, 7, and 14 days after the induction of mononeuropathy following the CCI and SNI. Allodynia was assessed by Von Frey filaments, and thermal hyperalgesia was assessed by the paw withdrawal tests. To study molecular experiments, the mRNA expression of (GTs) in CCI and SNI rats, reverse transcription polymerase chain reaction (RT-PCR) were used on days 4 and 14. RESULTS AND CONCLUSION: The maximum responses of mechanical allodynia and heat hyperalgesia in two distinct neuropathic pain models were detected on day 14. CCI and SNI induced upregulation of three GTs on day 4, which were followed by GTs downregulation in CCI and downregulation of glutamate aspartate transporter (GLAST) and glutamate transporter (GLT)1 in SNI when examined on day 14. These results indicate that there is an inverse correlation between pain responses and expression of GTs, and also changes in expression of spinal GTs may have a critical function in both the induction and maintenance of neuropathic pain in independent peripheral neuropathic pain models.

Influences of dopamine receptors on chewing behaviour in rats.

1. Intraperitoneal (i.p.) injection of different doses of pilocarpine induced purposeless chewing in rats. Physostigmine (i.p.), but not neostigmine (i.p.) also induced chewing behaviour. 2. Subcutaneous (s.c.) pretreatment of animals with the D-1 receptor blocker SCH 23390 decreased the number of chews induced by pilocarpine. 3. The D-2 dopamine antagonist sulpiride (i.p.) and anticholinergic atropine (i.p.) pretreatment also decreased the frequency of chews induced by the drug. 4. The response induced by pilocarpine (1 mg/kg i.p.) also was dose-dependently decreased in animals pretreated with apomorphine (0.25-1 mg/kg s.c.). 5. Administration of low doses of apomorphine (s.c.) also induced chewing, which was decreased with increasing the doses of the drug. 6. Chewing-induced by apomorphine was decreased by sulpiride or atropine and increased by SCH 23390 pretreatment. 7. Single administration of D-2 dopamine agonist bromocriptine also showed a slight but significant purposeless chewing, which was decreased by sulpiride pretreatment. 8. Single administration of D-2 agonist quinpirole, D-1 agonist SKF 38393 or D-1 antagonist SCH 23390, but not sulpiride caused a slight chewing. 9. It may be concluded that D-1 or D-2 activation exert opposite influences on chewing behaviour in rats, although to prove this effect more elucidation is needed.