The novel anxiolytic U-101017: in vitro and ex vivo binding profile and effect on cerebellar cGMP

The binding affinities (Ki) of U-101017 and diazepam for the GABA(A) receptor in rat cortical membranes were determined using [3H]flunitrazepam ([3H]FNZ) as the ligand. The inhibition constants of U-101017 and diazepam were 3.78 nM and 6.36 nM, respectively. Brain uptake of U-101017 was studied by the ex vivo [3H]FNZ binding assay. A significant ex vivo inhibition of [3H]FNZ binding was observed 10 min after oral administration of U-101017, and the effect lasted for at least 240 min (the last time point of investigation). The potential anxiolytic activity of U-101017 and diazepam was investigated in nonstressed and stressed (electric foot shock) mice by quantitative estimation of cerebellar cyclic 3',5'-guanosine monophosphate (cGMP). Both U-101017 and diazepam dose-dependently decreased cGMP and attenuated stress-induced elevations in cGMP. These effects were antagonized by the GABA(A) receptor antagonist flumazenil. U-101017 was about two orders of magnitude more potent in stressed animals than in controls. The results of our investigation indicate that the anxiolytic-like activity of U-101017 is mediated via GABA(A) receptors.