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Antidepressant effect of Eucalyptus globulus leaf extracts, neurochemical and pharmacological evaluations, identification of the active ingredients
Eucalyptus leaves extracts are traditionally used in oral treatments to cure respiratory affections. In this present study, we have shown an antidepressant action by neurochemical and pharmacological evaluations. When assessed in vitro in rat brain homogenates [1,2] an ethanolic extract of Eucalyptus leaves demonstrated a significant and concentration-dependant effect on the synaptosomal uptake inhibition of the monoamine neurotransmitters serotonin (5-HT), dopamine (DA) and norepinephrine (NA) with IC50 values of 3.4µg/ml, 27µg/ml and 11µg/ml respectively. Purification of the ethanolic extract allows to detect a serie of bioactive compounds namely some macrocarpals, acylphloroglucinols derivates inherent to the genus Eucalyptus . Macrocarpals A,B,C,G, and L are the more active and more selective for the uptake of DA like the native extract. A macrocarpals-rich extract quantified to 25.6% by a H.P.L.C. method was evaluated in vivo in the forced swimming test  and the learned helplessness test , animal models sensitive to antidepressant drugs. In the first, the macrocarpals-rich extract (60mg/kg) has been shown to induce a significant reduction of the immobility higher than a St John's wort extract but smaller than that of imipramine. In the second, the antidepressant effect was elicit with the amount of 200mg/kg but was smaller than that of imipramine. The present results show that Eucalyptus leaf extracts contain pharmacologically actives compounds in depression and may be used if the effectiveness is confirmed by clinical studies as another alternative to St John's extracts in the treatment of the depression.
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