Comparative assessment of the anxiolytic-like activities of honokiol and derivatives

Honokiol has previously been shown to be an effective anxiolytic-like agent in mice when administered for 7 days at 0.2 mg/kg/day prior to evaluation in an elevated plus-maze, while 20 mg/kg is required for efficacy as a single oral dose. The aim of this study was to find analogs of honokiol that are more effective for acute administration. Among the eight analogs evaluated, one partially reduced derivative of honokiol [3′-(2-propenyl)-5-propyl-(1,1′-biphenyl)-2,4′-diol] exhibited significant anxiolytic-like activity at 0.04 mg/kg. Following oral administration of 1 mg/kg of this analog, anxiolytic-like activity was clearly evident at 1 h, peaked at 3 h, and remained significant for longer than 4 h after treatment. Combined administration of the derivative with diazepam led to enhanced anxiolytic-like efficacy. Moreover, as with diazepam, the anxiolytic-like effect of the analog was reduced by flumazenil. In contrast, bicuculline, a GABA_A antagonist, had no effect on the activity of the derivative. Taken together, these results suggest that this analog of honokiol acts at the benzodiazepine recognition site of the GABA_A-benzodiazepine receptor complex.