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In mice implanted subcutaneously with osmotic minipumps releasing the neurotoxic agent N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 7 days (105 micrograms h-1/mouse) (approximately 100 mg kg-1 day-1) a significant reduction (approximately 25%) in the striatal dopaminergic nerve endings was observed. This neurotoxic effect was prevented by the semi-chronic ingestion of a Ginkgo biloba extract for 17 days (GBE 761, approximately 100 mg kg-1 day-1). The high concentrations (approximately 1 g L-1) at which GBE 761 in-vitro either prevented the uptake of [3H]dopamine by synaptosomes prepared from striatum, or prevented the specific binding of the pure dopamine uptake inhibitor [3H]GBR 12783 to membranes prepared from striatum suggests that the prevention of the MPTP neurotoxicity does not depend on an inhibition of the MPTP uptake by dopamine neurons. This is also suggested by the lack of prevention of the in-vitro striatal binding of [3H]GBR 12783 administered i.v. at a tracer dose, in mice pretreated for 8 days with GBE 761 (100 mg kg-1 p.o.) and receiving a supplementary gastric administration of GBE 761 (100 mg kg-1) 1 h before testing. Similar treatment with GBE 761 did not modify the toxicity for dopamine neurons of 6-hydroxydopamine (20 micrograms) directly injected into the striatum of rats.

The Ginkgo biloba extract (EGb 761) added to a synaptosomal fraction prepared from mice cerebral cortex modified [3H]5-hydroxytryptamine ([3H]5-HT) uptake in a biphasic manner. Between 4 and 16 micrograms mL-1 EGb 761 increased significantly the [3H]5-HT uptake (maximum + 23%). A similar increase was also obtained when synaptosomes were prepared from the cortex of mice treated orally with EGb 761, either acutely (100 mg kg-1, 14 h and 2 h before death) or semi-chronically (2 x 100 mg-1 kg daily for 4 consecutive days). The in-vitro increase in [3H]5-HT uptake induced by EGb 761 was not observed in the presence of 10(-6) M clomipramine, a 5-HT-uptake inhibitor. EGb 761 did not increase [3H]dopamine uptake by synaptosomes prepared from striatum of mice. We investigated different fractions of EGb 761 in order to determine the compounds inducing the increase in [3H]5-HT uptake. The BN 52063 extract (corresponding to the EGb 761 devoid of flavonoid substances) did not increase [3H]5-HT uptake. The Cp 202 extract (corresponding to the EGb 761 devoid of terpenic substances and containing mostly flavonoid substances) increased [3H]5-HT uptake. Among the flavonoids, quercetin has been tested and had no effect on the [3H]5-HT uptake. Since at the usual therapeutic doses of EGb 761, the effective concentrations of the components responsible for this increase are likely to be reached in the brain, one may suggest that this effect could contribute to the therapeutic effect of EGb 761.

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