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 GABA_A 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 α2β1γ2L and all α1-containing GABA_A receptor subtypes. At α2β2/3γ2L GABA_A 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 β1/2 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 GABA_A Cl^- currents. In the continued presence of 2′MeO6MF the single-channel conductance increased and these high conductance channels were disrupted by the γ2(381–403) MA peptide, indicating that such currents are mediated by α2/γ2-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 GABA_A receptor subtypes.