Anxiolytic Activity of Apocynum venetum L. and its Proposed Mechanism of Action

Apocynum venetum (AV, Apocynaceae) is a wild shrub native to parts of northern Asia and the Mediterranean region. A leaf extract from AV has been shown to possess various beneficial effects including antidepressant and anxiolytic activities [1]. This study evaluated further the anxiolytic-like activity of five fractions (A, B, C, D, and E) prepared from an ethanolic AV leaf extract using the elevated plus-maze (EPM) test in mice. Male C57BL/6 mice were either treated orally with AV extract and fractions or diazepam and buspirone as positive control 1 hour before behavioral evaluation in the EPM. A single treatment of AV extract markedly increased the percentage time spent on the open arms of the EPM in doses of 30 mg/kg p.o. and 125 mg/kg p.o., indicating an anxiolytic-like activity. These anxiolytic-like effects were partially antagonized by the benzodiazepine antagonist flumazenil (3 mg/kg i.p.) and the 5-HT_1A receptor antagonist WAY-100635 (0.5 mg/kg i.p.). Active fractions of AV according to 30 (fractions C, D, and E) and 125 (fractions A, C, and E) mg/kg of whole extract were also antagonized using flumazenil and WAY-100635. While flumazenil blocked the anxiolytic action of the fractions in a dose equivalent to 125 mg/kg whole extract, WAY-100635 antangonized the fractions according to 30 mg/kg of AV extract. In conclusion, these results indicate that the anxiolytic activity of an AV extract acts via both the GABA (in 125 mg/kg) and serotonin (in 30 mg/kg) receptor systems in a dose dependent manner. References: [1] Grundmann O, et al. (2007)J Ethnopharmacol. 110(3): 406–11.