An improved elevated plus-maze test in mice revealed that seven daily treatments with two different traditional Chinese medicines, known as Kampo medicines in Japan, Hange-koboku-to (composed of extracts of 5 plants) and Saiboku-to (composed of extracts of 10 plants), produced an anxiolytic effect, and the effect was mainly due to the presence of honokiol derived from magnolia. This study was carried out to evaluate the anxiolytic potential of honokiol, Hange-koboku-to and Saiboku-to, which were prescribed with two different magnolia samples: Kara-koboku (Magnoliae officinalis) (KA) or Wa-koboku (Magnoliae obovata) (WA). The doses of test samples were adjusted to ensure a constant dose of honokiol at 0.2 mg kg(-1). Although the doses of magnolol (an isomer of honokiol), as well as those of undetermined chemicals, varied among samples, the seven daily treatments with 9 out of 10 test samples produced an anxiolytic effect almost equivalent to that produced by 0.2 mg kg(-1) honokiol. The only exception was the sample containing the lowest amount of honokiol. Magnolia-free preparations of Hange-koboku-to or Saiboku-to did not have any anxiolytic effect. These results confirm that honokiol derived from magnolia is the causal chemical of the anxiolytic effect of Hange-koboku-to and Saiboku-to.
Previous studies in this laboratory revealed that dihydrohonokiol-B (DHH-B; 3'-(2 propenyl)-5-propyl-(1,1'-biphenyl)-2,4'-diol), a partially reduced derivative of honokiol, was an effective anxiolytic-like agent in mice at an oral dose of 0.04 mg kg(-1), and at higher doses, when evaluated by the elevated plus-maze test. The aim of this study was to further confirm the anxiolytic-like effect of DHH-B using an additional behavioural procedure (Vogel's conflict test in mice) and a biochemical assessment (in-vitro determination of muscimol-stimulated 36Cl- uptake into mouse cortical synaptoneurosomes). As in earlier experiments, DHH-B (0.04-1 mg kg(-1), p.o.) was shown to prolong the time spent in the open-sided arms of the elevated plus-maze in a dose-dependent manner. Moreover, in the Vogel's conflict test, DHH-B (5 mg kg(-1), p.o.) significantly increased punished water intake. In tests with mouse cerebral cortical synaptoneurosomes, 10 and 30 microM of DHH-B significantly increased 36Cl- influx in the absence of muscimol. In the presence of 25 microM muscimol, the addition of 1 microM DHH-B led to significant enhancement of 36Cl- uptake, while 30 microM DHH-B was required to further stimulate the 36Cl- uptake induced by 250 microM muscimol. The results of these studies confirm that DHH-B is a potent anxiolytic-like agent and that GABA(A) receptor-gated Cl(-)-channel complex is involved in the anxiolytic-like efficacy of DHH-B.
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