The present study investigated the role of peripheral group I
metabotropic glutamate receptors (mGluRs) in MO-induced nociceptive behaviour and
inflammation in the masseter muscles of lightly anesthetized rats. Experiments were carried out on male Sprague-Dawley rats weighing 300-400 g. After initial
anesthesia with
sodium pentobarbital (40 mg/kg, i.p.), one femoral vein was cannulated and connected to an
infusion pump for
intravenous infusion of
sodium pentobarbital. The rate of infusion was adjusted to provide a constant level of
anesthesia. Mustard oil (MO, 30 microl) was injected into the mid-region of the left masseter muscle via a 30-gauge needle over 10s. After 30 microl injection of 5, 10, 15, or 20% MO into the masseter muscle, the total number of hindpaw shaking behaviour and extravasated
Evans' blue dye concentration in the masseter muscle were significantly higher in the MO-treated group in a dose-dependent manner compared with the vehicle (
mineral oil)-treated group. Intramuscular pretreatment with 3 or 5%
lidocaine reduced MO-induced hindpaw shaking behaviour and increases in extravasated
Evans' blue dye concentration. Intramuscular pretreatment with 5mM MCPG, non-selective group I/II mGluR antagonist, or MPEP, a selective group I mGluR5 antagonist, produced a significant attenuation of MO-induced hindpaw shaking behaviour and increases in extravasated
Evans' blue dye concentration in the masseter muscle while
LY367385, a selective group I
mGluR1 antagonist, did not affect MO-induced nociceptive behaviour and
inflammation in the masseter muscle. These results indicate that peripheral mGluR5 plays important role in mediating MO-induced nociceptive behaviour and
inflammation in the craniofacial muscle.