2'-Methoxy-6-methylflavone: a novel anxiolytic and sedative with subtype selective activating and modulating actions at GABA(A) receptors.

BACKGROUND AND PURPOSE Flavonoids are known to have anxiolytic and sedative effects mediated via actions on ionotropic GABA receptors. We sought to investigate this further. EXPERIMENTAL APPROACH We evaluated the effects of 2'-methoxy-6-methylflavone (2'MeO6MF) on native GABA(A) receptors in new-born rat hippocampal neurons and determined specificity from 18 human recombinant GABAA receptor subtypes expressed in Xenopus oocytes. We used ligand binding, two-electrode voltage clamp and patch clamp studies together with behavioural studies. KEY RESULTS 2'MeO6MF potentiated GABA at alpha 2 beta 1 gamma 2L and all alpha 1-containing GABAA receptor subtypes. At alpha 2 beta 2/3 gamma 2L GABAA receptors, however, 2'MeO6MF directly activated the receptors without potentiating GABA. This activation was attenuated by bicuculline and gabazine but not flumazenil indicating a novel site. Mutation studies showed position 265 in the beta 1/2 subunit was key to whether 2'MeO6MF was an activator or a potentiator. In hippocampal neurons, 2'MeO6MF directly activated single-channel currents that showed the hallmarks of GABAA Cl-currents. In the continued presence of 2'MeO6MF the single-channel conductance increased and these high conductance channels were disrupted by the gamma 2(381-403) MA peptide, indicating that such currents are mediated by alpha 2/gamma 2-containing GABA(A) receptors. In mice, 2'MeO6MF (1-100 mg . kg(-1); i.p.) displayed anxiolytic-like effects in two unconditioned models of anxiety: the elevated plus maze and light/dark tests. 2'MeO6MF induced sedative effects at higher doses in the holeboard, actimeter and barbiturate-induced sleep time tests. No myorelaxant effects were observed in the horizontal wire test. CONCLUSIONS AND IMPLICATIONS 2'MeO6MF will serve as a tool to study the complex nature of the activation and modulation of GABAA receptor subtypes.