Antinociceptive Effects of Citronellal in Formalin-, Capsaicin-, and Glutamate-Induced Orofacial Nociception in Rodents and Its Action on Nerve Excitability

Aims: To evaluate the antinociceptive effects of citronellal (CTL) on formalin-, capsaicin-, and glutamate-induced orofacial nociception in mice and to investigate whether such effects might involve a change in neural excitability. Methods: Male mice were pretreated with CTL (50, 100, and 200 mg/kg, ip), morphine (5 mg/kg, ip), or vehicle (distilled water + one drop of Tween 80 0.2%) before formalin (20 µL, 2%), capsaicin (20 µL, 2.5 µg) or glutamate (40 µL, 25 µM) injection into the right vibrissa. Sciatic nerve recordings were made using the single sucrose gap technique in rats. The data obtained were analyzed by ANOVA followed by Dunnett's test for the behavioral analyses and by the Student t test for CAP evaluation. Results: Pretreatment with CTL was effective in reducing nociceptive face-rubbing behavior in both phases of the formalin test, which was also naloxone-sensitive. CTL produced significantly antinociceptive effect at all doses in the capsaicin- and glutamate- tests. Rota-rod testing indicated that such results were unlikely to be provoked by motor abnormality. Recordings using the single sucrose gap technique revealed that CTL (10 mM) could reduce the excitability of the isolated sciatic nerve through a diminution of the compound action potential amplitude by about 42.4% from control recordings. Conclusion: These results suggest that CTL might represent an important tool for management and/or treatment of orofacial pain. Keywords: antinociceptive, citronellal, neuronal excitability, orofacial pain, single sucrose gap technique