Role of central opioid on the antinociceptive effect of sulfated polysaccharide from the red seaweed Solieria filiformis in induced temporomandibular joint pain

•F II has antinociceptive and anti-inflammatory effect in the TMJ.•F II inhibits the release of inflammatory cytokines IL-1β and TNF-α.•F II increases the β-endorphin release in the subnucleus caudalis.•The antinociceptive effect of F II depends on the opioid receptors mu, delta e kappa.

This study aimed to investigate the effect of sulfated polysaccharide from red seaweed Solieria filiformis (Fraction F II) in the inflammatory hypernociception in the temporomandibular joint (TMJ) of rats. Male Wistar rats were pretreated (30 min) with a subcutaneous injection (s.c.) of vehicle or FII (0.03, 0.3 or 3.0 mg/kg) followed by intra-TMJ injection of 1.5% Formalin or 5-hydroxytryptamine (5-HT, 225 μg/TMJ). In other set of experiments rats were pretreated (15 min) with an intrathecal injection of the non-selective opioid receptors Naloxone, or μ-opioid receptor antagonist CTOP, or δ-opioid receptor Naltridole hydrochloride, or κ-opioid receptor antagonist Nor-Binaltorphimine (Nor-BNI) followed by injection of FII (s.c.). After 30 min, the animals were treated with an intra-TMJ injection of 1.5% formalin. After TMJ treatment, behavioral nociception response was evaluated for a 45-min observation period, animals were terminally anesthetized and periarticular tissue, trigeminal ganglion and subnucleus caudalis (SC) were collected plasma extravasation and ELISA analysis. Pretreatment with F II significantly reduced formalin- and serotonin-induced TMJ nociception, inhibit the plasma extravasation and inflammatory cytokines release induced by 1.5% formalin in the TMJ. Pretreatment with intrathecal injection of Naloxone, CTOP, Naltridole or Nor-BNI blocked the antinociceptive effect of F II in the 1.5% formalin-induced TMJ nociception. In addition, F II was able to significantly increase the β-endorphin release in the subnucleus caudalis. The results suggest that F II has a potential antinociceptive and anti-inflammatory effect in the TMJ mediated by activation of opioid receptors in the subnucleus caudalis and inhibition of the release of inflammatory mediators in the periarticular tissue.