The leaves of Milicia excelsa (Welw.) C. C. Berg (Moraceae) is used in the treatment of inflammatory and painful disorders and as sedative in the treatment of insanity in Nigerian traditional medicine. The antinociceptive activity of the ethanol extract (50, 100 and 200 mg/kg, p.o.) was investigated using acetic acid-induced writhing, hot plate and formalin-induced paw licking tests while the behavioural assessment was evaluated in holeboard, elevated plus maze and phenobarbitone-induced sleeping time tests. Acetylsalicylic acid, morphine or diazepam and 1% Tween 20 (10 mL/kg) were employed as positive and negative control respectively. Acute toxicity of the extract (200-3200 mg/kg, p.o.) was also determined.
The extract inhibited nociceptive response caused by acetic acid injection and increased latency time in the hot-plate test. In formalin test, the extract decreased paw licking time in both phases. The entry and the duration of time spent in the open arms of the elevated plus maze by animals treated with the extract (100 and 200 mg/kg) increased significantly compared to control. The number of head-dips and line crossed were decreased by the extract in hole board test, resembling the response of diazepam. In pentobarbital-induced sleeping time test, the extract reduced sleep latency and increased the duration of sleep compared to the negative control. No mortality was observed up to the dose of 3200 mg/kg. These results showed the antinociceptive, anxiolytic and sedative effects of the leaf extract of M. excelsa and provide evidence for the traditional use of the plant for pain management and insanity.