From: Doug Skrecky (oberon@vcn.bc.ca)
Date: Fri Jul 31 1998 - 09:38:16 MDT
Authors
Winter JC.
Institution
Department of Pharmacology and Toxicology, School of Medicine and
Biomedical
Sciences, State University of New York at Buffalo, 14214-3000, USA.
JWINTER:UBMEDG.BUFFALO.EDU
Title
The effects of an extract of Ginkgo biloba, EGb 761, on cognitive
behavior and longevity in the rat.
Source
Physiology & Behavior. 63(3):425-33, 1998 Feb 1.
Abstract
Extracts of the leaves of the Ginkgo biloba tree are widely used
throughout the world for their purportedly beneficial effects on brain
function. In the present investigation, a standardized extract, EGb 761,
was self-administered orally by male Fischer 344 rats that were then tested
in an eight-arm radial maze. The tasks employed were a) continuous learning
and b) delayed nonmatching to position. Chronic postsession administration
of EGb 761 at a dose of 50 mg/kg had no effect on continuous learning but
the same dose given presession resulted in a trend toward fewer sessions to
reach criterion performance as well as fewer errors. In addition, it was
observed that rats chronically treated with EGb 761 lived significantly
longer than
vehicle-treated subjects. In a delayed nonmatching to position task using a
30-min delay in 20-month-old rats. EGb 761 administered presession produced
a dose-related decrease in total, retroactive, and proactive errors; a
repeated-measures design was used, with subjects serving as their own
controls. Following the dose-response determination, the group, now 26
months of age, was divided in two with half receiving EGb 761 at a dose of
200 mg/kg presession and the other half vehicle (sweetened condensed milk).
A statistically significant positive effect of treatment with EGb-761 was
observed. The present data are consistent with the beneficial effects on
cognitive performance which have been widely reported in human subjects. In
addition, the data suggest that the methods employed, i.e., continuous
learning and delayed nonmatching to position tasks in aged rats, are
capable of detecting drugs of possible value in the treatment of human
cognitive impairment. Finally, the present results encourage a search for
the pharmacologically active principles of EGb 761 and for their mechanisms
of action.
Additional quote from text:
"An unexpected observation made during the continuous-learning
experiments was that treatment with EGb 761 appeared to extend the life
span (Fig.2). Because an effect on longevity was not an original goal of
the experiments and because several animals had died before the effect
became apparent, formal assessment of the causes of death was not
undertaken. Based on the well-established fact that caloric restriction
extends the life span in rodents, it might be argued that EGb 761 somehow
acted to alter food intake and weight gain. However, retrospective
evaluation revealed no significant difference in weight between the EGb 761
and control groups at the time of death. Although the mechanism by which
energy restriction extends life is unknown, oxidative stress and free
radical production are thought to be important factors both in aging and in
dementia. Thus, the known effects of Ginkgo biloba as an antioxidant and
free radical scavenger provide alternative, though highly speculative
explanations of the data of Fig.2. Because the data shown in Fig.2 reflect
lifetime administration of a relatively low dose of EGb 761, immediate
questions arise as to whether initiation of treatment later in life would
have had a comparible effect and as to whether higher doses would have been
more effective. I am aware of no previous reports regarding possible
effects of EGb 761 on longevity."
Additional note added by poster:
Here's an interesting project in the field of gerontology: Feed various
subfractions of EGb 761 to aged rodents to determine the ingrediant(s)
active in providing the life span prolongation and note the effect on
various causes of mortality to help ascertain the mode(s) of action.
From Fig.2 the average life span was 26.4 months for the control Fisher
344 rats, and 31.0 months (17% increase) for the EGb 761 treated rats.
Maximum life span was 35 months for the control rats, and 38 months (9%
increase) in the EGb 761 treated rats. Dosage of EGB 761 used was 50 mg/kg
5 times per week.
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