Transient receptor potential channel involvement in antinociceptive effect of citral in orofacial acute and chronic pain models.

This study aimed to test for the possible antinociceptive effect of the naturally occurring terpene citral in rodent models of acute and chronic orofacial pain and to test for the possible involvement of transient receptor potential (TRP) channels in this effect. Acute nociceptive behavior was induced in one series of experiments by administering formalin, cinnamaldehyde, menthol or capsaicin to the upper lip. Nociceptive behavior was assessed by orofacial rubbing, and the effects of pre-treatment with citral (0.1, 0.3 or 1.0 mg/Kg) or vehicle (control) were tested on the behavior. Nociceptive behavior was also induced by formalin injected into the temporomandibular joint or mustard oil injected into the masseter muscle, preceded by citral or vehicle (control) treatment. The chronic pain model involved infraorbital nerve transection (IONX) that induced mechanical hypersensitivity which was assessed by von Frey hair stimulation of the upper lip. Motor activity was also evaluated. Docking experiments were performed using TRPV1 and TRPM8 channels. Citral but not vehicle produced significant (p<0.01, ANOVA) antinociception on all the acute nociceptive behaviors, and these effects were attenuated by TRPV1 antagonist capsazepine, TRPM3 antagonist mefenamic acid and by TRPM8 desensitization, but not by ruthenium red and TRPA1 antagonist HC-030031. The IONX animals developed facial mechanical hypersensitivity that was significantly reduced by citral but not by vehicle. The docking experiments revealed that citral may interact with TRPV1 and TRPM8 channels. These results indicate the potential use of citral as an inhibitor of orofacial nociception in both acute and chronic pain states through TRPV1, TRPM3 and TRPM8 channels. See also Figure 1(Fig. 1).

Anxiolytic-like effect of chalcone N-{4'[(2E)-3-(3-nitrophenyl)-1-(phenyl)prop-2-en-1-one]} acetamide on adult zebrafish (Danio rerio): Involvement of the 5-HT system.

The action of anxiolytic compounds that act on selective serotonin receptors (SSRIs) have been scarcely evaluated. Serotonergic drugs have been shown to be effective in treating anxiety without presenting adverse effects as benzodiazepines. However, the anxiolytic effects take days to occur. This study aimed to evaluate the anxiolytic effect of the synthetic chalcone, 4'-[(2E) -3- (3-nitrophenyl) -1- (phenyl) prop-2-en-1-one] acetamide (PAAMNBA), and its possible mechanism of action in adult zebrafish (Danio rerio). PAAMNBA was synthesized with a yield of 51.3% and its chemical structure was determined by 1H and 13C NMR. Initially, PAAPMNBA was intraperitoneally administered to zebrafish (n = 6/group) at doses of 4, 12, or 40 mg/kg, and the animals were subsequently subjected to acute and open field toxicity tests. PAAMNBA was administered to the other groups (n = 6/group) for analyzing its effect in the light and dark test. The involvement of the serotonergic (5HT) system was also evaluated using 5-HTR 1, 5-HTR 2A/2C, and 5-HTR 3A/3B receptor antagonists, namely, pizotifeo, granizetron, and ciproeptadina, respectively. Molecular coupling was performed using the 5-HT1 receptor. PAAMNBA was found to be non-toxic, reduced the locomotor activity, and had an anxiolytic effect in adult zebrafish. The effect was reduced by pretreatment with pizotifene and was not reversed by treatment with granizetron and cyproeptadine. A previous in vivo molecular coupling study indicated that chalcones interact with the 5-HT1 receptor. The results suggested that the chalcone, PAAPMNBA, has anxiolytic activity, that is mediated by the serotonergic system via the 5-HT1 receptor. The interaction of PAAPMNBA with the 5-HT1 receptor was confirmed by molecular docking studies.

Orofacial Antinociceptive Effect of Nifedipine in Rodents Is Mediated by TRPM3, TRPA1, and NMDA Processes.

AIMS: To test for the possible antinociceptive effect of nifedipine in rodent models of acute and chronic neuropathic orofacial pain and the possible involvement of TRP- and NMDA-related processes in this effect. METHODS: Acute nociceptive behavior was induced by administering formalin, cinnamaldehyde, glutamate, capsaicin, or acidified saline to the upper lip or hypertonic saline to the cornea of Swiss mice. Acute nociceptive behavior was also induced by formalin injected into the TMJ or mustard oil injected into the masseter muscle of Wistar rats. The chronic pain model involved infraorbital nerve transection (IONX) in Wistar rats to induce mechanical hypersensitivity, which was assessed with von Frey hair stimulation of the upper lip. The effects of pretreatment with nifedipine or vehicle (control) were tested on the nociceptive behaviors. Docking experiments were also performed. Statistical analysis included one-way ANOVA followed by Tukey post hoc test and two-way ANOVA followed by Bonferroni post hoc test (statistical significance P < .05). RESULTS: Nifedipine produced significant antinociceptive effects in all of the acute nociceptive behaviors except that induced by capsaicin. The antinociceptive effects were attenuated by NMDA, TRPA1, or TRPM3 receptor antagonists. The IONX animals developed facial mechanical hypersensitivity, which was significantly reduced by nifedipine. The docking experiments suggested that nifedipine may interact with TRPM3 and NMDA receptors. CONCLUSION: The present study has provided novel findings in a variety of acute and chronic orofacial pain models showing that nifedipine, a selective inhibitor of L-type Ca2+ channels, can suppress orofacial nociceptive behavior through NMDA, TRPA1, and TRPM3 receptor systems.