Anxiogenic effect of Aloysia polystachya – derived essential oil in mouse

ALMEIRA FLORENCIA; ZUNINO MP; BAIARDI G

Otro; RICIFA. 1º Reunión Internacional de Ciencias Farmaceúticas; 2010

ABSTRACT Aloysia polystachya (Griseb.) Mold., is a commonly used plant in the folk medicine to treat gastrointestinal disorders. Since there are not enough studies about the effect of Aloysia polystachya-derived essential oil on the central nervous system, the aim of this work was to evaluate the chemical composition and the effects of Aloysia polystachya essential oil on the anxiety behavior in mice. The essential oil was obtained under hydro-destillation extracted by hexane. The analysis and quantification was done using a gas-liquid cromatography method. It was used male adult albine Swiss mice. The experimental groups were: Group 1: Control: injected with 0.3 ml of 2 % of Tween 80 solution i.p. (vehicle). Group 2: injected with 100, 10 and 5 mg/kg i.p. of essential oil. Group 3: injected with 5 mg/kg of essential oil plus diazepam 1 mg/kg. Group 4: injected with 4,13 mg/kg of á-thujone. Group 5: injected with 4,13 mg/kg of á-thujone plus diazepam 1 mg/kg. The animals were tested on the elevated plus-maze 30 min after injection of drugs. Open/closed arm quotient and time spent in the open arms were determined as indexes of anxiety. Total number of arm entries and closed arm entries were recorded as a locomotor activity index.  The percentage of essential oil obtained was 3% and the principal component was á-thujone 82.6%. The injection of 100 mg/kg i.p of  A. polystachya essential oil induced convulsions and dead in 100 % of the cases but the dose of 10 mg/kg only induced convulsions. 5 mg/kg of essential oil did not induce convulsions but markedly reduced the time spent in the open arms and the open/closed arm quotient without changes in locomotor activity index. The same response was obtained with the administration of á-thujone alone. The anxiety index was fully reversed by diazepam in all cases. Since the decrease on the anxiety index induced by 5 mg/kg of A. polystachya essential oil were similar to that induced by á-thujone administrated in the same concentration found in the essential oil, we conclude that the behavioral effects are due to their principal component á-thujone. A possible explanation for the behavioral effects induced by A. polystachya essential oil involved the inhibition of GABAA receptors because they could be fully reversed by low doses of diazepam administration. Since the decrease on the anxiety index induced by 5 mg/kg of A. polystachya essential oil were similar to that induced by á-thujone administrated in the same concentration found in the essential oil, we conclude that the behavioral effects are due to their principal component á-thujone. A possible explanation for the behavioral effects induced by A. polystachya essential oil involved the inhibition of GABAA receptors because they could be fully reversed by low doses of diazepam administration.