N-butanol fraction of Olax subscorpioidea Oliv. (Olacaceae) attenuates lipopolysaccharide-induced depressive-like symptoms in mice.

Abstract Background: The leaves of Olax subscorpioidea have become a mainstay in the management of inflammatory diseases and mental illness in folkloric medicine in Nigeria. Previous studies have shown its antidepressant and anti-inflammatory properties in experimental animals. Recently its antidepressant action was linked to the involvement of monoaminergic transmission. However, with accumulating evidences suggesting link between immuno-inflammatory signaling pathways and depression, there is dearth of information about its beneficial effect on inflammation associated depression. We thus evaluated the effect of n-butanol fraction of O. subscorpioidea leaves on lipopolysaccharide (LPS)-induced depressive-like behaviours and investigated its antidepressant effect with respect to its action on inflammatory and oxidative pathways. Methods: Fifty Swiss male mice were randomly assigned into five groups (n= 10): group 1 (vehicle only), group 2 (nBFOS 5mg/kg), group 3 (nBFOS 10 mg/kg), group 4 (imipramine 10 mg/kg), group 5 (vehicle). Mice were treated with vehicle or nBFOS (5 & 10 mg/kg) or imipramine intraperitoneal for seven days. Thirty minutes after treatment on day seven, animals were injected with LPS (0.83 mg/kg, i.p.) except group 1 (vehicle only). Twenty-four hours following LPS injection, animals were assessed for depressive symptoms using sucrose preference test and immobility using tail suspension test (TST). Brain levels of pro-inflammatory mediators interleukin-1β (IL-1β) and tumor necrosis factor (TNF), oxidative stress biomarkers (malondialdehyde and reduced glutathione) and plasma level of corticosterone were measured by Enzyme Linked immunosorbent assay. Results: LPS significantly (p < 0.05) increased immobility of mice in TST and decreased sucrose preference which is indicative of depressive-like behaviours. The depressive behaviours were significantly (p < 0.05) attenuated by nBFOS and imipramine compared to control. Furthermore, LPS-induced increase in malondialdehyde, corticosterone, TNF, IL-1β, and decrease in reduced glutathione, in the brain were significantly reversed by treatment with nBFOS and imipramine. Conclusion: The findings suggest that attenuation of LPS-induced depressive-like behaviours by the fraction of O. subscorpioidea leaves may be related to suppression of oxidative stress and inhibitory effect on inflammatory mediators in the central nervous system.