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

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.

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.

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.

Pinene exhibited significant curable effects on capsaicin-induced pulpal nociception and inflammation mainly via pharmacological interfacing with GABA_A and μ-opioid receptors.