The Effect of Psidium Guajava Leaf Extract on Cognitive Function in Scopolamine-Induced Alzheimer's Disease Wistar Rats

This study evaluated the impact of P. guajava leaf extract on cognitive function of scopolamine-induced Alzheimer’s disease model of Wistar rats. The plant leaf was extracted by maceration using methanol as a solvent. Phytochemical screening and quantification of the bioconstituents of the leaf extract were done The study was done in two phases, with phase one lasting for two weeks and phase two lasting for twelve weeks. A total of 80 male Wistar rats weighing 100 – 230 g were divided into 5 groups each for the two phases (phase 1, n = 8; phase 2, n = 8). The rats in groups 2 to 5 were induced with Alzheimer’s disease (AD) using 1 mg/kg of scopolamine (i.p.) for 7 days before commencement of treatment. Group 1 (normal control) received 2 mL/kg of distilled water only, group 2 (AD control rats) also received 2 mL/kg of distilled water while groups 3 – 5 were AD rats treated with 100 mg/kg, 300 mg/kg of P. guajava leaf extract and 5 mg/kg of donepezil respectively. Neurobehavioural tests for cognitive function were done in weeks one and two, then every two weeks using navigational maze test, radial maze test and Barnes maze test. At the end of the14th and 84^th days of the experiment, the animals were euthanised with 100 mg/kg of ketamine then decapitated to remove the brain. The brain tissues for the ELISA were rinsed in normal saline, homogenised in phosphate buffer using a ceramic mortar and pestle placed on ice, transferred into sample bottles then taken to the laboratory in ice pack for the BDNF assay.  The neurobehavioural results for cognitive function indicated that P. guajava leaf extract significantly (p < 0.05) improved learning and memory in a dose and time dependent manner. The extract was able to improve significantly the levels of BDNF in the brain homogenate. It was concluded from the results that P. guajava leaf may be used in the treatment of AD and it is recommended that the treatment should commence with the low dose (100 mg/kg b.wt.) then progress to the medium dose (300 mg/kg b.wt.).