Investigation of the antinociceptive effectiveness of Eucalyptus globulus Labill essential oil and 1,8-cineol

In this thesis study, based on the pharmacological activities of Eucalyptus species related to the central nervous system, the potential antinociceptive activity of the essential oil obtained from the leaves of Eucalyptus globulus Labill. was investigated. The antinociceptive activity of the essential oil (1 and 10 mg/kg) was evaluated by hot plate, tail immersion and tail clip tests. In all three tests, the essential oil showed antinociceptive activity by increasing % MPE values without causing any change in the motor performances of the mice at the applied doses. The phytochemical analysis results performed by gas chromatography/mass spectrometry revealed that the essential oil carried 87.4% 1,8-cineole. The main component, 1,8-cineole, showed antinociceptive activity similar to the essential oil when administered to mice at doses of 0.1, 0.5, 1, 10 and 25 mg/kg. These findings indicated that both the essential oil and 1,8-cineole exert their antinociceptive effects on nociceptive pathways carrying thermal and mechanical painful stimuli via central mechanisms. In order to investigate whether α2-adrenergic, D2/D3-dopaminergic and muscarinic receptors play a role in the antinociceptive effect of 1,8-cineole, mechanistic studies were conducted with yohimbine (α2-adrenergic receptor blocker), sulpiride (D2/D3 dopaminergic receptor blocker) and atropine (non-selective muscarinic receptor blocker), respectively. These agents antagonized the antinociceptive effect induced by 1,8-cineole in all three nociceptive tests. This study is the first to indicate that the central antinociceptive activity of 1,8-cineole is mediated by α2-adrenergic, D2/D3 dopaminergic and muscarinic receptors. Keywords: Analjezi, Eucalyptus globulus Labill, essential oil, 1,8-cineole.