Effect of Viola tricolor on pentobarbital-induced sleep in mice

Traditionally, Viola tricolor has been recommended for its sedative property. However, no pharmacological studies have yet evaluated the effect of this plant on sleep. The hydro-alcoholic extract (HAE) was prepared by the extraction of the aerial parts of V. tricolor in 70% ethanol using a Soxhalet apparatus. Also, with solvent-solvent extraction, the HAE was further fractionated to water fraction (WF), ethyl acetate fraction (EAF) and N-butanol fraction (NBF). The extract (50, 75, 100, 150, 200, 300 mg/kg, ip) and its fractions (200 mg/kg, ip) were administrated to mice, 30 min before pentobarbital (30 mg/kg, ip) injection. Furthermore, the possible neurotoxicity of the plant was assessed using PC12 neuron cell line. The HAE, at 300 mg/kg, significantly prolonged (34%) duration of pentobarbital-induced sleep. Similarly, the EAF significantly increased (51%) the sleep duration. None of the HAE doses or the fractions could significantly change the sleep latency time. The sedative effect of V. tricolor accompanied with no neuron toxicity, except for very high concentrations of EAF. The results suggest that V. tricolor potentiates pentobarbital hypnosis and the main component(s) responsible for this effect is most likely found in EAF. Isolation and purification of the active compound(s) may yield novel sleep-prolonging agents.