The effect of central administration of alpha‐pinene on capsaicin‐induced dental pulp nociception

Aim To assess the effects of central administration of α‐pinene alone and in combination with either bicuculline or naloxone, as GABA A and μ‐opioid receptor antagonists, respectively, on capsaicin‐induced dental pulp stimulation in rats. Methodology Forty‐eight adult male Wistar rats aged 2 months (230–270 g) were cannulated via their lateral ventricles for the central administration of the drugs. α‐Pinene was injected at 0.1, 0.2 and 0.4 μmol L −1 . Then, dental pulp stimulation was induced by intradental application of capsaicin solution (100 μg), and nociceptive scores were recorded for up to 40 min. For investigation of the anti‐inflammatory effects of α‐pinene, expression of COX ‐2 in the subnucleolus caudalis (Vc) of rats was determined using immunofluorescence staining. Nonparametric repeated measure Friedman and Kruskal–Wallis tests as well as parametric one‐way analysis of variance were used for the statistical analysis. Results α‐Pinene at 0.2 and 0.4 μmol L −1 was able to decrease capsaicin‐induced nociception. Moreover, there was a significant increase in the expression of COX ‐2‐positive cells in the Vc of capsaicin‐treated rats ( P  < 0.01). This effect was prohibited by α‐pinene (0.4 μmol L −1 ). Co‐administration of bicuculline (1 μg per rat) or naloxone (6 μg per rat) with α‐pinene (0.4 μmol L −1 ), however, prevented the inhibitory effects of α‐pinene on both capsaicin‐induced pulp nociception and COX ‐2 over‐expression. Conclusions Pinene exhibited significant curable effects on capsaicin‐induced pulpal nociception and inflammation mainly via pharmacological interfacing with GABA A and μ‐opioid receptors.