Alzheimer’s disease is first characterised by memory loss related to the central cholinergic system alteration. Available drugs provide symptomatic treatment with known side effects. The present study is aimed to evaluate the properties of Carissa edulis aqueous extract on a Scopolamine mouse model as an attempt to search for new compounds against Alzheimer’s disease-related memory impairment. Memory impairment was induced by administration of 1 mg/kg (i.p.) of Scopolamine for 7 days, and mice were treated with Carissa edulis aqueous extract. Behavioural studies were performed using T-maze and novel object recognition task for assessing learning and memory and open field test for locomotion. Brain acetylcholinesterase enzyme (AChE) activity was measured to evaluate the central cholinergic system. The level of MDA, glutathione, and catalase activity were measured to evaluate the oxidative stress level. Administration of Scopolamine shows a decrease in learning and memory enhancement during behavioural studies. A significant decrease in the time spent in the preferred arm of T-maze, in the time spent in the exploration of the novel object, and in the discrimination index of the familiar object was also observed. The significant impairment of the central cholinergic system was characterised in mice by an increase of AChE activity to 2.55±0.10 mol/min/g with an increase in oxidative stress. Treatment with the different doses of Carissa edulis (62.8, 157, 314, and 628 mg/kg orally administrated) significantly increased the memory of mice in T-maze and novel object recognition tests and also ameliorated locomotion of mice in the open field. Carissa edulis aqueous extract treatment also decreases the AChE activity and brain oxidative stress. It is concluded that administration of Carissa edulis aqueous extract enhances memory of mice by reducing AChE activity and demonstrating antioxidant properties. This could be developed into a novel therapy against memory impairment related to Alzheimer’s disease.

Ethnopharmacological relevance: Dysphania ambrosioides (L.) Mosyakin & Clemants (Chenopodiaceae) is a medicinal plant known for its anxiolytic, antidepressant and anticonvulsant activities in Cameroonian folk medicine. Aim of the study: The aim of this work is to evaluate the anxiolytic effects of Dysphania ambrosioides aqueous extracts and investigate its mechanism of action. Materials and methods: Elevated plus maze test and open field test were used for detecting it anxiolytic properties. The possible mechanism of action of the aqueous extracts were investigated after pretreatment of animals with different antagonists of GABAA complex receptors (5 mg/kg N-methyl-β-carboline-3-carboxamide, 4 mg/kg flumazenil or 2 mg/kg bicuculline) 30 minutes prior to the oral administration of 370 mg/kg Dysphania ambrosioides aqueous extract. Results: Dysphania ambrosioides increased the percentage of entries into and percentage of time in open arms, and reduced rearing, head dipping, and percentage of time in closed arms, in the elevated plus maze. It reduced rearing and defecation, and increased crossing, in the open field. In addition, anxiolytic-like properties of Dysphania ambrosioides were blocked by different antagonists of GABAA complex receptors (N-methyl-β-carboline-3-carboxamide, flumazenil or bicuculline) as examined in elevated plus maze test. Finally, the activity of GABA-T activity was inhibited and the brain GABA concentration was increased by the extracts, respectively. Conclusion: These results suggest that Dysphania ambrosioides possess anxiolytic-like properties in mice that might involve an action on benzodiazepine and/or GABA sites in the GABAA receptor complex or by modulating brain GABA concentration in the central nervous system.

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