Methanol leaf extract of Leptadenia hastata ameliorates chronic, unpredictable, mild stress-induced depression

Leptadenia hastata (Pers) Decne is a tropical herb widely used in the phytotherapy of neuropsychiatric disorders, including depression. Despite the availability of synthetic antidepressant drugs, depression remains a major medical problem. The study aimed to evaluate the effect of methanol leaf extract of Leptadenia hastata (LHME) on chronic unpredictable mild stress-induced depression. Acute toxicity of Leptadenia hastata was determined using Organization for Economic Co-operation and Development (OECD) guidelines. The chronic unpredictable mild stress (CUMS) model-induced depression involves the evaluation of baseline behavioural changes in the sucrose preference test, open field test, and tail suspension test. The brain-derived neurotrophic factor (BDNF) concentrations and serum cortisol were assessed using an enzyme-linked immunosorbent assay (ELISA). The levels of superoxide dismutase (SOD) and malondialdehyde (MDA) were also assessed using standard procedure. The median lethal dose (LD50) value was > 5000 mg/kg. LHME at doses of 250 – 1000 mg significantly (p<0.01) decreased CUMS-induced depression in a dose-dependent manner.  LHME significantly (p<0.01) reversed depression associated weight loss from 14.00±0.62 g in week two to 22.57±1.13 g in week five of the experiment. It also increased sucrose consumption in the sucrose preference test (SPT) from 4.29±0.52 ml in week two to 9.71±0.68 ml in week five. The LHME also significantly (p<0.01) decreased the duration of immobility from 190.00±4.55 sec in week two to 158.00±3.83 sec in week five in the tail suspension test (TST). Furthermore, LHME at the tested dose significantly (p<0.01) increased the locomotor activity from 36.29±1.25 sec in week two to 62.43±1.73 sec in week five in the open field test (OFT). LHME significantly (p<0.01) and dose-dependently increased the levels of BDNF (204.74±22.97 pg/ml) and decreased the levels of plasma cortisol (0.98±0.06 ng/ml). However, treatment with LHME and the standard drug imipramine did not significantly change SOD activity and the MDA level in CUMS-induced mice.  The findings demonstrated that LHME ameliorates CUMS-induced depressive-like behaviours, and its effect is possibly mediated via the neuroendocrine (cortisol) and neurotrophic (BDNF).