Effect of the Ginkgo biloba extract, EGb 761, on memory formation in day-old chicks

Previous studies indicate that the Ginkgo biloba extract, EGb 761, has a fa cilitative effect on deficient memory. The temporal parameters of this effe ct, however, have not been clearly defined or distinguished from the effect on normal memory. The aim in the current study was to investigate the effe cts of EGb 761 on memory using a well-controlled animal model. Day-old chic ks were trained on either a weakly or strongly reinforced version of a pass ive avoidance task. Long-term memory formation of the weakly reinforced ver sion of the task was improved significantly by EGb 761 (3 mg/ml) when admin istered between 10 and 30 min after training. However, the same dose of EGb 761 impaired retention when administered prior to strongly reinforced trai ning. These data provide convincing evidence that posttraining administrati on of EGb 761 initiates long-term memory in chicks with only short-term mem ory, but that the same dose-administered pretraining can be deleterious for normal retention. This dual effect has important implications for the clin ical use of Ginkgo biloba extracts. (C) 2001 Elsevier Science Inc. All righ ts reserved.