Abstract
Neurological disorders like Alzheimer's disease, dementia and parkinsonism are associated cognitive impairment. This study aims to evaluate the protective effect of aqueous extract of Hibiscus rosasinensis L. (HRWE) leaves against phenytoin induced cognitive impairment in mice. Phenytoin chronic treatment (50 mg/kg) for 10 days successfully induced learning and memory impairment in animals. HRWE showed antioxidant effects in hydroxyl radical scavenging assay and hydrogen peroxide scavenging assay. Ascorbic acid was used as standard for these assays. IC50 values are found to be 470 mu g/ml and 450 mu g/ ml for H2O2 and hydroxyl radical scavenging assay, respectively. Cognition function of animals is assessed by using common behavioural animal models like morris water maze test (MWM), elevated plus maze test (EPM), cooks pole climbing test (CPC), novel object recognition test (NOR), rotarod test (RTR) and rod walking test (RDW). In all these behavioural models, control group animals showed reduced learning and defective memory indicated by, increase in reaction time, escape and transfer latency, and decrease in recognition index, fall off time and inflexion ratio. However, piracetam (standard drug) and HRWE treatment showed significant decrease in reaction time, escape and transfer latency and significant increase in recognition index, fall off time and inflexion ratio; this restoration indicates effective memory and improved learning behavior. At the end of study, brain homogenates are used to conduct biochemical estimations. Increase in levels of acetylcholinesterase (AChE), lipid peroxidase (LPO) and nitric oxide (NO), and decrease in levels of glutathione (GSH) and superoxide dismutase (SOD) in control group animals shows oxidative stress produced on phenytoin challenge. Piracetam is found to be most effective in restoring these enzymes to normal values. However, HRWE 100 mg/kg showed significant effects only in restoration of AChE, LPO and NO levels. In contrast, HRWE 200 mg/kg showed significant restoration of all biochemical enzymes as compared to control group. Important to state that the HRWE effect is less significant than the effect produced by piracetam. Histopathological studies are also conducted to explore morphological changes in brain samples of all the treatments. Apoptosis of neurons in control group animals' correlates to their abnormal behaviour in study. Whereas, normal histoarchitecture of brain examination of piracetam and HRWE treated animals, extrapolates to their cognitive improved behavior in study. All these results justify the protective effect of water extract of HRWE against phenytoin induced cognitive disabilities.