Gingko biloba and memory.

Walesiuk A, Braszko J. 2009. Preventive action of Ginkgo biloba in stress-and corticosterone-induced impairment of spatial memory in rats. Phytomed 16;1:40-6.

It is widely accepted that stress and HPA-axis activation have effects on the brain. The hippocampus region, responsible for certain types of learning and memory (including spatial memory) is particularly rich in glucocorticoid receptors, and thus is particularly affected by the detrimental effects of stress. Scientists hypothesise that inhibition of the hippocampus may be responsible for the cognitive deficits that occur in individuals under stress. Excess corticosterone also alters various neurotransmitters in regions of the brain, for example, increasing dopamine turnover in prefrontal cortex, accompanied by decreased spatial memory performance.

Gingko biloba has been shown to have many varied activities, including antioxidant and neuroprotective effects. It has been used in the past to treat cognitive deficits and dementia, and has been shown to improve the fluidity, and decrease deformability, of neuronal membranes that may be altered in aging and several pathological situations. A widely used extract of G. biloba is EGB761, a product standardized to 24% ginkgoflavonoglycosides and 6% terpenoid lactones. Chronic administration of EGB761has demonstrated usefulness in inhibiting stress induced hypersecretion of corticosterone.

In the current study, scientists were interested in determining the effects of EGB761 on post-stress cognitive dysfunction, specifically spatial memory dysfunction.

Six groups of rats were involved in the study:

* A control group

* Stress: rats were exposed to restraint stress for 2 hours over 21 days

* Corticosterone: rats were given corticosterone injections (5 mg/kg) once a day for 21 days

* EGB761: rats were given oral EGB761 at 100 mg/kg for 21 days

* EGB 761 + stress

* EGB 761 + corticosterone

In the study chronic restraint stress altered egocentric spatial memory in the eight arm radial maze, but not allocentric spatial memory in the Morris water test. Pre-administration of EGB761 resulted in complete recovery from stress-induced cognitive deficits. It also had positive effects on working memory in unstressed animals, improving both the reference and working aspects of spatial memory. Finally, EGB761 administration normalised cognitive deficits in those rats treated with an equivalent dose of corticosterone.

Thus EGB761 is useful in ameliorating cognitive deficit and spatial memory impairment produced by stress or corticosterone administration, suggesting the potential for the relief of such conditions in humans exposed to psychosocial stresses.

Tessa Finney-Brown MNHAA

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