Monoamine oxidase (MAO) inhibition In vitro tests in rat brains suggest that EGb 761 may exert MAO-A and MAO-B inhibitor activity (Wu & Zhu 1999). Tests with isolated constituents kaempferol, apigenin and chrysin have demonstrated these to be potent MAO inhibitors, with greater effect on MAO-A than MAO-B (Sloley et al 2000). It is unclear whether MAO inhibition occurs in vivo. Serotonin Another in vitro study found that oral EGb 761 significantly increases the uptake of serotonin, but not dopamine, in cerebral cortex samples from mice (Ramassamy et al 1992) and another in vivo study identified an anti-aggressive effect mediated by 5-HT2A receptors (Shih et al 2000).
Cholinergic effects Considering that G. biloba appears to be as effective as anticholinesterase drugs, several researchers have investigated whether it exerts cholinergic effects. Evidence from behavioural, in vitro and ex vivo tests with G. biloba has shown both direct and indirect cholinergic activity (Das et al 2002, Nathan 2000). The extract appears to increase the rate of acetylcholine turnover and stimulate the binding activity of ligands to muscarinic receptors in the hippocampus (Muller 1989). GABA receptors Bilobalide in G. biloba is a competitive antagonist for GABA-A receptors according to in vitro tests (Huang et al 2003). The effect is almost as potent as bicuculline and pictrotoxinin.
Corticosterone In vivo tests have found EGb 761 has stress-alleviating properties mediated through its moderation of corticosterone levels (Puebla-Perez et al 2003).
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