Assessment of anxiolytic potential and acute toxicity study of Combretum micranthum G. Don. leaves (Combretaceae)

Abstract

Background: Combretum micranthum G. Don. (Combretaceae) is an ethnomedicinally valuable, undomesticated and indigenous shrub of West Africa. However, its anxiolytic potential have not been reported despite its ethanolic extract being used ethnomedicinally in the management of anxiety disorders. Aim: To determine the acute toxicity effect and assess the behavioural effects and anxiolytic potential of C. micranthum G. Don. leaves in mice. Settings: This study is an experimental design to evaluate the ethnomedicinal claim of Combretum micranthum G. Don using animal models of anxiety. Methods: Fifty-six male and female mice, ranging in weight between 20 g and 30 g were randomly distributed into three main groups. The first group of mice (n = 6) was assigned for toxicity assessment (LD₅₀) study using the guideline of Organization for Economic Cooperation and Development (OECD). The second group of mice for behavioural study (n = 25) was further divided into five sub-groups. Sub-groups I, II and III were orally administered 500 mg/kg, 1000 mg/kg, 2000 mg/kg of ethanolic extract of C. micranthum (CmEE), respectively, whilst IV and V were intraperitoneally administered 1 mg/kg diazepam and normal saline 0.5 mL, respectively. They were thereafter evaluated for novelty-induced behaviours: locomotion, rearing and grooming using Open Field Test (OFT). The third group of mice (n = 25) was treated similar to the pattern used in behavioural study and evaluated for anxiolytic activity of CmEE using elevated plus maze (EPM) model. Data were expressed as mean ± standard error of mean (S.E.M) and analysed using Student’s-t test, and one-way analysis of variance (ANOVA) followed by Student–Newman– Keuls (SNK) test with values of p < 0.05 considered significant. Results: The percentage yield of ethanolic leaf extract of C. micranthum was 14.28% weight/weight (w/w). Combretum micranthum showed no toxicity when administered orally to mice (LD₅₀ ≥ 2000 mg/kg). Groups administered 500, 1000 and 2000 mg/kg of CmEE exhibited decreased locomotion (p < 0.05) when compared with saline group. There was significant decrease in rearing at 2000 mg/kg but increase in grooming in mice administered 2000 mg/kg of CmEE was recorded. The groups administered 500, 1000 and 2000 mg/kg of CmEE showed increased percentage time spent in the open arm in a dose-dependent pattern (33.3%, 41.6% and 55.4%, respectively) when compared with the saline group. There were significant dose-dependent decreases in the indices of open arm avoidance at 1000 (48.9) and 2000 mg/kg (41.4) of CmEE. Conclusion: Combretum micranthum is non-toxic and preliminary data indicated that it possesses anxiolytic potential. However, it is recommended that further assays using other specific models of anxiety to determine its probable mechanism(s) of action should be explored.