Sedative effects of vapor inhalation of the essential oil of Microtoena patchoulii and its related compounds

Microtoena patchoulii (Labiatae) is a perennial herb that grows in southern China. In the present study, the sedative activity of the essential oil of the leaves was evaluated using mice when the volatile oil was administered by inhalation. The inhalation of the oil by mice significantly reduced the spontaneous motor activity. Fractionation of the oil revealed that the main constituents in the oil were 1-octen-3-ol, terpinolene, patchouli alcohol, and methyl salicylate. Each 1-octen-3-ol, terpinolene, or patchouli alcohol significantly reduce the locomotor activity when it was administered singly. However, the essential oil fraction containing both patchouli alcohol and methyl salicylate did not exhibit any effects. It is suggested that methyl salicylate might negate the sedative effect of patchouli alcohol, and that the concentration ratios of the compounds in vapor would play important roles as sedatives. In order to clarify the mechanism of action, the effects of these compounds on caffeine-induced excitation and pentobarbital-induced elongation of sleeping time in mice were tested. Each 1-octen-3-ol or terpinolene reduced the locomotor activity excited by caffeine to those of normal levels. Elongation of sleeping time induced by pentobarbital was further elongated by the inhalation of terpinolene, but not by that of 1-octen-3-ol. It is indicated that terpinolene is a potent suppressor of the central nervous system.