Sedative, hypothermic and muscle relaxant effects of the essential oils of Dennettia tripetala G. baker (Annonaceae) and its mechanisms in mice

Abstract

The essential oil of the fruits of Dennettia tripetala G. Baker (Annonaceae) has been reported to have depressant effects on the central nervous system in mice. This study was carried out to evaluate sedative, hypothermic and muscle relaxant effects of the oil and its mechanism(s) in mice. Different groups of mice were administered varying doses (12.5-50.0 mg/kg) of the essential oils following intraperitoneal (i.p.) routes. The sedative effect was assessed by sodium pentobarbitone (50 mg/kg, i.p.) - induced sleeping time, while hypothermic effect was evaluated by estimating rectal temperature variation after administration of various doses of the oil using digital thermometer. The muscle relaxant effect was determined using the hind limb-grip test. In order to determine the mechanism(s) involved in the sedative effect of the oil, mice were pretreated with flumazenil (2 mg/kg), a specific GABA-benzodiazepine antagonist 30 minutes prior to administration of25 mg/kg of the essential oils and its effect on sleep latency and total sleeping time recorded. The mechanism(s) of hypothermic effects of the oil was determined in another set of experiments. The results obtained showed that the essential oils of D.tripetala significantly (p<0.05) showed sedative, hypothermic and muscle relaxant effects. Pretreatment with flumazenil prior to the administration of essential oils (25 mg/kg, i.p.) showed that the prolongation of the total sleeping time effects of the oil was completely blocked while the reduction in rectal temperature induced by the oil in mice was blocked by both flumazenil and atropine. It is concluded that the sedative effect of the essential oils of D.tripetala may be mediated through GABA-benzodiazepine receptors and its hypothermic effects may be mediated through both GABA-benzodiazepine and cholinergic muscarinic pathways.

Key words: Dennettia tripetala, sedation, hypothermia, cholinergic, GABA pathways.