Neuropharmacological effects of the essential oil and aqueous extract of cymbopogon citratus (Poaceae) in mice
This study determined the effects of the oil and aqueous extract of Cymbopogon citratus (Poaceae) Stapf on learning and memory, it further evaluated the anti-depressant and analgesic properties of the oil and aqueous extract in mice. This was with a view to providing information on the neuropharmacological effects of the oil and aqueous extract. The essential oil of the plant was obtained by hydrodistillation using Clavenger apparatus while the aqueous extract was obtained using a reflux apparatus. Acute toxicity (LD50) of both oil and extract were determined by Lorke’s method for oral route only. The oil (50, 100, 150 and 200 mg/kg) and the extract (250, 500, 1000 and 2000 mg/kg) were individually evaluated for novelty-induced behaviours (locomotion, rearing and grooming) in open field, anxiolytic (hole board and elevated plus-maze), analgesic (hot plate model), anti-depressant (forced swimming test) and learning and memory (Y-maze) effects in mice. The data were analyzed using the GraphPad® primism 4.0 statistical software. The test doses were compared with control by one way analysis of variance (ANOVA) followed by post hoc analysis using Student Newman-Kuels multiple comparison tests. The results obtained for acute toxicity studies indicate that the LD50 of the essential oil (EO) and aqueous extract (AQ) of C. citratus were 948.68 and 5000 mg/kg, by the oral route respectively. The oil induced no significant (p>0.05) effect on novelty induced rearing (NIR) but the extract (1000-2000 mg/kg) caused significant (F (5, 30)= 7.95; p<0.05) increase in locomotor activity when compared to control. The EO and AQ at all the doses caused significant increase in the number of head dips (F (5, 30)=12.63; p<0.05), (F (5, 30)=15.88; p<0.05) and increase in the time spent in the open arms of the elevated plus-maze (F (5, 30)=4.66; p<0.05), (F (5, 30)= 9.96; p<0.05) respectively, indicating anxiolytic effects. The EO and the AQ at all the dose levels caused a significant ( F (5, 30)= 23.25; p<0.05), ( F (5, 30)= 76.82; p<0.05) reduction in the immobility time in the FST respectively, indicating anti-depressant effect. Finally at these dose levels, the EO and AQ significantly (F (5, 30)= 14.55; p<0.05), (F (5, 30)= 19.68; p<0.05) caused increase in the reaction time on the hot plate model respectively, indicating analgesic effects. The study concluded that the essential oil and aqueous extract of C. citratus possessed significant anxiolytic, analgesic and anti-depressant properties.