Honokiol, a putative anxiolytic agent extracted from magnolia bark, has no diazepam-like side-effects in mice.

Use of the elevated plus-maze experiment and activity and traction tests in mice have revealed that seven daily treatments with 0.2 mg kg(-1) and higher doses of honokiol, a neolignane derivative extracted from Magnolia bark, had an anxiolytic effect without change in motor activity or muscle tone. Diazepam, 1 mg kg(-1), had the same anxiolytic potential as 0.2 mg kg(-1) honokiol but induced muscle relaxation. The aim of this study was to determine whether honokiol had diazepam-like side-effects. Mice treated with 1-10 mg kg(-1) diazepam, but not those treated with 0.1-2 mg kg(-1) honokiol, for 12 days showed withdrawal symptoms characterized by hyperactivity and running-fit when they were challenge-administered intraperitoneal flumazenil (10 mg kg(-1)) 24 h after the last treatment with diazepam. Oral diazepam (0.5-2 mg kg(-1), 10 min before) dose-dependently prolonged hexobarbital (100 mg kg(-1), i.p.)-induced sleeping, disrupted learning and memory, and inhibited (+)-bicuculline (40 mg kg(-1), i.p.)-induced death. Honokiol (0.2-20 mg kg(-1), p.o., 3 h before) had no such effects. The prolongation by diazepam (1 mg kg(-1)) of hexobarbital-induced sleeping was not modified by honokiol (0.2-20 mg kg(-1)). These results suggest that honokiol is less likely than diazepam to induce physical dependence, central depression and amnesia at doses eliciting the anxiolytic effect. It is also considered that honokiol might have no therapeutic effect in the treatment of convulsion.