Anti-Stress Effects of Ethanol Extract and Fractions of the Stem-Back of Milicia Excelsa (Moraceae) in Mice

Aiyelero, Oyeronke Medinat (2020)

xxviii,180 Pages

Thesis

Thesis

The study determined the oral acute toxicity (LD50) and evaluated the anti-stress effects of the ethanol stem bark of Milicia excelsa (ESB) and its fractions in mice. The study also determined the most effective fraction of ESB in addition to determination of its mechanism of action. This was with a view to providing the scientific basis for its folkloric use in the management of anxiety and stress-related disorders. The lethal median dose (LD50) of the extract and its n-hexane (HF), ethyl acetate (EAF), n-butanol (BF) and aqueous (AF) fractions via oral route were estimated using OECD protocol of 425. The central nervous system (CNS) depressant effect of ESB and fractions was assessed using novelty-induced behavioural test (rearing, grooming and locomotion). The anxiolytic effect was also evaluated using hole board test and elevated plus maze (EPM).The anti-stress potential of extract and fractions was studied using acute restraint (ARM) and sub-chronic restraint stress models (SRM) in mice. Further, anxiolytic effects of the extract and its various fractions using the elevated plus maze and antidepression-like effect on tail suspension test (TST) were carried out following exposure of the mice to ARM and SRM. The effect of the most active fraction on serum corticosterone was also assayed in mice. The statistical tool used was one way analysis of variance (ANOVA), followed by post hoc analysis using GraphPad InStat® The LD50 of all the fractions was > 5000 mg/kg. The extract significantly reduced novelty-induced rearing (vehicle control (vc):104.17±7.22, 39.50±3.66, p < 0.05), grooming (vc:36.17±1.64, 18.50±1.18, p < 0.05) and locomotion (vc:191.67±15.1,87.00±8.52, p < 0.05) and increased open arm entries (54.55±3.72) and duration (56.30±6.16) on EPM suggesting CNS depressant and anti-anxiety effect respectively. Acute restraint in stressed control mice significantly reduced locomotion (175±4.42) and grooming (16.67±1.15), but increased rearing (121±5.57) significantly when compared with control (212±6.63,34.50±1.46 and 87.00±3.57 respectively) . Acute restraint changes were significantly reversed by ESB and its fractions; suggestive of antistress effects. ESB and its fractions demonstrated anxiolytic indices of open arm avoidance index (OAAI) consistent with anti-anxiety effects on elevated plus maze, in stressed control mice compared to unstressed animals following both ARM and SRM. Furthermore, there was significant (p < 0.05) increase in immobility time of the stressed mice (ARM,157.17±8.25; SRM,147.83±8.89) compared to the unstressed mice (ARM,112±4.61; SRM,113.67±5.87) following ARM and SRM in the TST, which was significantly (p < 0.05) attenuated by ESB and its fractions suggesting anti-depressant effect. However, BF at all the tested doses significantly (p < 0.05) decreased the corticosterone level compared to the treated mice indicating that BF acted to counter the stress-induced increase in blood corticosterone levels. The study concluded that ESB and its fraction(s) exhibited antistress, anxiolytic- and antidepressant like-actions, in the models used in this study.