Analgesic Effect of Methanol Leaf Extract of Alstonia Boonei De Wild (Apocynaceae)

Purpose: To evaluate the possible analgesic properties of the methanol leaf extract of Alstonia boonei (De Wild, Apocynaceae) a locally available plant used in traditional medicine for the management of pain and other conditions. Methods: Alstonia boonei leaves were extracted with methanol. Rodent models were employed in screening the analgesic effect of the extract. Pain indices evaluated in hot plate and tail flick tests, formalin pain test and mouse writhing assay were mean reaction time to latent heat, time spent in licking of injected paw and abdominal writhes, respectively. Results: Oral administration of the extract caused a significant (p < 0.05) dose-dependent reduction in the number of abdominal writhes (control, 84.67 ± 9.58; 100 mg/kg, 57.86 ± 3.07; 200 mg/kg, 24.40 ± 3.92; and 400 mg/kg, 22.50 ± 2.53). The extract also produced significant (p < 0.05) but non-dose dependent increase in elevation of pain threshold in the hot plate (ranging from 27.99 to 42.26 % inhibition) and tail flick tests (ranging from 34.73 to 81.42 % inhibition) in mice and rats, respectively. All doses of the extract used produced significant (p < 0.05) inhibition of both phases of the formalininduced pain in mice, with a more pronounced anti-inflammatory effect on the late (ranging from 46.96 to 74.12 %) phase than the early anti-neurogenic (ranging from 49.52 to 51.47 %) phase. Conclusion: The results obtained suggest that the analgesic effect of Alstonia boonei may be mediated via both central and peripheral mechanisms.