Ambulation-promoting effect of peppermint oil and identification of its active constituents

Various plant-derived essential oils (EOs) have traditionally been used in the treatment of mental disorders, despite a lack of scientific evidence. I n a previous study, we demonstrated that certain EOs possess behavioral eff ects, a finding that supports our original hypotheses that EOs possess psyc hoactive actions. The present study was conducted in order to obtain farthe r evidence to support our hypothesis. Peppermint oil, a type of EO, is beli eved to be effective for treating mental fatigue. When the oil was administ ered intraperitoneally to ICR mice, the ambulatory activity of mice increas ed dramatically. We identified alpha -pinene, beta -pinene, (R)-(+)-limonen e, 1,8-cineol, isomenthone, menthone, menthol, (R)-(+)-pulegone, menthyl ac etate and caryophyllene as constituent elements of peppermint oil by GC-MS analysis. We then examined the effect of each constituent element of pepper mint oil on ambulatory activity in mice. Intraperitoneal administration of 1,8-cineol, menthone, isomenthone, menthol, (R)-(+)-pulegone, menthyl aceta te and caryophyllene significantly increased ambulatory activity in mice, s uggesting that these chemicals are the behaviorally active elements of pepp ermint oil. Intravenous administration of these substances to mice induced a significant increase in ambulatory activity at much lower doses. The pres ent study provides farther evidence demonstrating that EOs possess pharmaco logical actions on behavior. In addition, our finding revealed that the act ion of peppermint oil comes from its constituent elements. (C) 2001 Elsevie r Science Inc. All rights reserved.