Abstract
Flavonoid-rich ethanol extracts of licorice root have sedative and anxiolytic
effects. Glabridin is a major flavonoid component from licorice which we
evaluated by examining GABA responses in acutely isolated dorsal raphe
neurons of the rat. Neurons were recorded with patch-clamp methods at a
holding potential of − 50 mV. Glabridin potentiated GABA-induced responses
by positively modulating GABAA receptor responses with different
concentration range. GABA (2 × 10−6 M)-evoked currents were
potentiated in a stepwise pattern increasing glabridin concentration.
Between 10−12 and 10−8 M glabridin increased GABA
responses by about 140 % of the control. At concentrations above 10−
7 M, a much larger, dose-dependent potentiation occurred before
reaching a plateau at 3 × 10−6 M glabridin. A hypnotic drug,
zolpidem, also induced biphasic concentration-potentiation relationship. The
glabridin potentiation ratio was 2.2 times larger than the maximum
potentiation to the benzodiazepine receptor full agonist diazepam.
Benzodiazepine receptor antagonist, flumazenil (3 × 10−7 M),
failed to inhibit glabridin (3 × 10−7 M)-induced potentiation.
This result implies that glabridin may exhibit sedative and hypnotic effects
by potentiating GABAergic inhibition in dorsal raphe neurons by
GABAA receptor actions.
Key words
licorice - flavonoid - benzodiazepine receptor - flumazenil - sedative-hypnotic activity - GABA
A receptor -
Glycyrrhiza glabra
- Fabaceae
