Aqueous extracts of two tropical ethnobotanicals (Tetrapleura tetraptera and Quassia undulata) improved spatial and non-spatial working memories in scopolamine-induced amnesic rats: Influence of neuronal cholinergic and antioxidant systems.

BACKGROUND

Tetrapleura tetraptera (TT) and Quassia undulata (QU) are two predominant tropical ethnobotanicals with various medicinal values but are commonly used in folklore for the treatment of mental illness without justifiable mechanisms of action.

OBJECTIVE

To investigate the effects of aqueous extracts from TT fruits and QU leaves on the spatial and non-spatial working memory, antioxidant status and activities of neuronal marker enzymes of scopolamine-induced amnesic rats and thus, understand the possible mechanism of action of these plants.

METHODS

Fifty-five albino rats were divided into eleven groups. Group I (normal rats) received normal saline (p.o), Group II-V (normal rats) administered with 50 and 300 mg/kg of each extract group VI (induced rats) received 2 mg/kg of scopolamine (i.p.), groups VII-X (induced rats) pretreated with 50 and 300 mg/kg of TT and QU extracts (p.o) before scopolamine administration, group XI (induced rats) treated with 2.5 mg/kg of donepezil. The treatment lasted for 14 days and amnesia was induced by a single dose of 2 mg/kg of scopolamine on the last day. Spatial (Y-maze) and non-spatial (novel objectect recoginiton test) working memories of the rats were tested. Thereafter, the animals were sacrificed and homogenates of isolated brain samples were assayed for cholinesterase activity and malondialdehyde (MDA) content. The phenolic characterisation of the samples was also carried out using HPLC-DAD chromatography.

RESULTS

Administration of 2 mg/kg of scopolamine brought about a decrease in spatial and non-spatial memory indeces, increase in acetylcholinesterase and butyrylcholinesterase activities, as well as increased MDA content compared to the control. However, pretreatment with both extracts improved both spatial and non-spatial working memories and ameliorated the increased enzyme activities and MDA contents. Furthermore, the HPLC-DAD characterization of the extracts revealed the presence of p-coumaric acid, rutin, catechin, ellagic acid, quercetin, caffeic acid, chlorogenic acid and galic acid.

CONCLUSIONS

The ability of the extracts to improved cognitive function and ameliorate impairment in cholinergic enzyme activities and antioxidant status in scopolamine-induced amnesic rats could help justify the possible neuroprotective properties of TT and QU and also explain possible mechanism of action of these ethnobotanicals as obtained in folklore medical practices.