A mouse model of
barbital-induced
narcosis was used to examine the effects of single
intraperitoneal injections of an extract of Ginkgo biloba (
EGb 761), an extract devoid of
terpene trilactones (
CP 205), and three
terpene trilactone constituents of the extract (
ginkgolides A and B,
bilobalide). Administration of
sodium barbital (180 mg/kg, IP) to the mice caused
narcosis, measured as a loss in righting reflex. Single
injections of
EGb 761 (25 and 50 mg/kg), given 60 min prior to
sodium barbital, significantly shortened
barbital-induced sleeping time, whereas these same doses of
CP 205 were ineffective. Single
injections of
ginkgolide B (1 mg/kg) and
bilobalide (2 and 5 mg/kg) significantly shortened sleeping time, whereas
ginkgolide A was ineffective. The effects of
ginkgolide B and
bilobalide were reflected as increases in latency to onset of sleep and those of
EGb 761,
ginkgolide B, and
bilobalide were correlated with decreases in the number of mice that slept. At the behavioral level, these potent in vivo effects of
EGb 761,
ginkgolide B, and
bilobalide resemble those of certain
antidepressants. At the molecular level, it is hypothesized that interactions with the
picrotoxinin/TBPT site of
GABA-regulated Cl- channels of the CNS may be involved. This information appears useful in explaining the clinically observed "vigilance-enhancing" and "
antidepressant-like" actions of
EGb 761.