Demonstration of the "anti-stress" activity of an extract of Ginkgo biloba (EGb 761) using a discrimination learning task.

1. Young (4-month-old) and old (20-month-old) rats, maintained under water restriction, were trained to discriminate to obtain a small amount of drinking water as a reward. Each animal had to learn to press a lever corresponding to a light that was randomly distributed on the left or right. 2. Introduction of an auditory perturbation ("stress") during the discriminative phase of learning modified the capacity and rate of acquisition in both young and old animals, changes that were correlated with increases in plasma concentrations of epinephrine, norepinephrine and corticosterone. 3. Stress-induced detrimental changes in both discrimination learning and plasma hormones were suppressed by 20 days of oral treatment with an extract of Ginkgo biloba leaves (EGb 761; 50 or 100 mg/kg/day) in both young and old rats, effects that became statistically significant by the third day of learning (time of maximal acquisition rate). 4. EGb 761 treatment was less effective in increasing the percentage of efficient lever presses in old than in young rats, but more effective in decreasing the number of inefficient lever presses and reaction time in the older animals. 5. These results indicate that EGb 761 can facilitate behavioral adaptation despite adverse environmental influences, a property that supports its clinical use in treating cognitive impairment, especially in elderly patients.