Wu and Zhu (1999) reported that EGb-761, administered
before or after MPTP injections in mice, can protect against
MPTP-induced reduction in striatal dopamine levels. Given
that monoamine oxidase (MAO) inhibitors can prevent the
metabolism of MPTP to its neurotoxic metabolite MPP+,
Wu and Zhu (1999) also investigated the effects of EGb-761
on mouse brain MAO activity. EGb-761 resulted in a
non-selective inhibition of MAO and the authors concluded
that this action may be associated with its neuroprotective
effect in MPTP-induced toxicity. Current evidence regarding
whether EGb-761 is able to inhibit MAO is controversial.
A behavioural investigation in mice (Porsolt et al.,
2000) and a positron emission tomography investigation in
the human brain (Fowler et al., 2000) found no evidence for
EGb-761-mediated MAO inhibition. A recent study in rats,
however, reported that EGb-761 inhibited both MAO-A and
MAO-B activity, an effect likely to be due to the kaempferol
component of the extract (Sloley et al., 2000).