Effects of chronic administration of Ginkgo biloba extract (EGb 761®) on levels of dopamine, noradrenaline and serotonin in the prefrontal cortex of the awake rat

Abstract

The special Ginkgo biloba extract (EGb 761®) has been shown to exert beneficial effects in the therapy of age-related neurological disorders such as Parkinson's and Alzheimer's disease [1]. Besides neuroprotective effects, EGb 761® has been demonstrated to improve cognitive functions in animal models [2] and in clinical studies [3]. Thus, it was the aim of the present study to investigate whether EGb 761® influences monoamine levels in brain areas implicated in cognitive function, motivation and mood behaviour. For this purpose, the effect of sub-chronic (14 days) daily administration of EGb 761® on basal extracellular levels of dopamine (DA), noradrenaline (NA) and serotonin (5-HT) were monitored by microdialysis in the prefrontal cortex of awake rats. Administration of EGb 761® at a dose of 100mg/kg p.o., caused a significant increase in DA levels during 40–180min, reaching a maximum level of 163% of the control group. The extracellular levels of NA increased only by about 120% and the concentrations of 5-HT were not changed from the pre-drug levels. These findings supports previous observations suggesting that Ginkgo biloba extracts could increase monoaminergic function via inhibition of MAO activity. However, the minimal effects on NA and 5-HT concentrations indicate that EGb 761® may affect brain monoaminergic system also through other mechanisms than direct inhibition of MAO activity. These results suggest that treatment with EGb 761® can lead to increased dopaminergic function in the prefrontal cortex which may be an underlying factor to clinically observed effects on improved cognitive function.