Hyperalgesia and edema responses induced by rat peripheral blood mononuclear cells incubated with carrageenin

5-hydroxyindolacetic acid (5-HIAA), a main metabolite of serotonin, is responsible for complete Freund's adjuvant-induced thermal hyperalgesia in mice

Background

The role of serotonin (5-hydroxytrptamine, 5-HT) in the modulation of pain has been widely studied. Previous work led to the hypothesis that 5-hydroxyindolacetic acid (5-HIAA), a main metabolite of serotonin, might by itself influence pain thresholds.

Results

In the present study, we investigated the role of 5-HIAA in inflammatory pain induced by intraplantar injection of complete Freund's adjuvant (CFA) into the hind paw of mice. Wild-type mice were compared to mice deficient of the 5-HT transporter (5-HTT-/- mice) using behavioral tests for hyperalgesia and high-performance liquid chromatography (HPLC) to determine tissue levels of 5-HIAA. Wild-type mice reproducibly developed thermal hyperalgesia and paw edema for 5 days after CFA injection. 5-HTT-/- mice treated with CFA had reduced thermal hyperalgesia on day 1 after CFA injection and normal responses to heat thereafter. The 5-HIAA levels in spinal cord and sciatic nerve as measured with HPLC were lower in 5-HTT-/- mice than in wild-type mice after CFA injection. Pretreatment of wild-type mice with intraperitoneal injection of para-chlorophenylalanine (p-CPA), a serotonin synthesis inhibitor, resulted in depletion of the 5-HIAA content in spinal cord and sciatic nerve and decrease in thermal hyperalgesia in CFA injected mice. The application of exogenous 5-HIAA resulted in potentiation of thermal hyperalgesia induced by CFA in 5-HTT-/- mice and in wild-type mice pretreated with p-CPA, but not in wild-type mice without p-CPA pretreatment. Further, methysergide, a broad-spectrum serotonin receptor antagonist, had no effect on 5-HIAA-induced potentiation of thermal hyperalgesia in CFA-treated wild-type mice.

Conclusion

Taken together, the present results suggest that 5-HIAA plays an important role in modulating peripheral thermal hyperalgesia in CFA induced inflammation, probably via a non-serotonin receptor mechanism.

Peripheral mu-, kappa- and delta-opioid receptors mediate the hypoalgesic effect of celecoxib in a rat model of thermal hyperalgesia

AIMS

The endogenous opioids mediate the analgesic effects of celecoxib in a model of mechanical hyperalgesia in rats. As responses to thermal stimuli may differ from those to mechanical stimuli, we have here assessed celecoxib in a rat model of thermal hyperalgesia and the possible involvement of endogenous opioids and their corresponding receptors in these effects.

MAIN METHODS

Injection of carrageenan (CG) into one hind paw induced a dose-related hyperalgesia (decreased time for paw withdrawal) to thermal stimuli (infra-red light beam), over 6h.

KEY FINDINGS

Celecoxib (sc) 30 min before CG (250 microg per paw) induced a dose-dependent reversal of hyperalgesia, with withdrawal times well above basal levels, characterizing development of hypoalgesia. Indomethacin (sc) reversed CG-induced hyperalgesia only to basal levels (an anti-hyperalgesic effect). Naltrexone (sc) prevented hypoalgesia after celecoxib but did not change the response to indomethacin. Local (intraplantar) injection of either a selective antagonist of mu-(beta-funaltrexamine), kappa-(nor-binaltorphimine) or of delta-(naltrindole) opioid receptors also reversed the hypoalgesic effects of celecoxib, without modifying the hyperalgesia due to CG or affecting the nociceptive thresholds in the non-injected paw.

SIGNIFICANCE

Our data show that celecoxib, unlike indomethacin, was hypoalgesic in this model of thermal hyperalgesia, and that this effect was mediated by peripheral mu-, kappa- and delta-opioid receptors.

Local transcutaneous electrical stimulation (TENS) effects in experimental inflammatory edema and pain

Few studies in the literature associated transcutaneous electrical stimulation (TENS) use with an antiinflammatory activity. The purpose of this study was to investigate the effects of low (10 Hz)- and high (130 Hz)-frequency TENS on hyperalgesia and edema that occur after injection of carrageenan in rat paw. After induction of inflammation, either low- or high-frequency TENS was applied in the rat paw for 20 min, and the effect of TENS treatment on escape or paw withdrawal and edema was measured. Both low- and high-frequency TENS inhibited by 100% the hyperalgesia but not the edema response. However, low-frequency TENS presented longer lasting effect as compared with high-frequency TENS. Naltrexone-treated animals showed a complete reversion of the analgesic effect induced by low- but not high-frequency TENS. Thus, our data demonstrated absence of an antiinflammatory effect associated to TENS use and confirmed the participation of endogenous opioids on low TENS-induced analgesia.

A new pyrazolo pyrimidine derivative inhibitor of cyclooxygenase-2 with anti-angiogenic activity

In a previous study, we reported a new pyrazolo pyrimidine derivative, N(4)-benzyl-N(6),N(6)-dimethyl-1-1(tert-butyl)-1H-pyrazolo[3,4-d]pyrimidine-6,4-diamine (DPP), which inhibited potently cyclooxygenase-2 activity in intact cell assays with minor activity against cyclooxygenase-1 (IC(50)=0.9 nM for cyclooxygenase-2 versus IC(50)=59.6 nM for cyclooxygenase-1). In the present work, this behaviour was confirmed in vivo by using the 24-h zymosan-injected mouse air pouch model (ID(50)=1.36 nM/pouch for prostaglandin E(2) level). We also studied the possible beneficial effect of DPP in the angiogenesis-dependent murine air pouch granuloma and rat paw carrageenan-induced hyperalgesia models. DPP exerted analgesic and anti-angiogenic (52% reduction in angiogenesis at 10 mg/kg, i.p.) effects that may be associated with inhibition of cyclooxygenase-2 activity.