Improvement of cognitive function in mice by Citrus reticulata var. kinnow via modulation of central cholinergic system and oxidative stress

Memory disorders are a result of a number of factors, of which elevated brain oxidative stress and acetylcholinesterase (AChE) activity are significant hallmarks. A number of Citrus species have cognition-enhancing capacity mediated by their antioxidant and anti-cholinesterase activities. This study was designed to assess the cognitive-enhancing, antioxidant and anticholinesterase potentials of Citrus reticulata var. kinnow (CR) leaf extracts. CR extracts were examined by bioactivity guided fractionation using in-vitro DPPH and Ellman assays to determine antioxidant and AChE inhibitory capacity. The most active component was further evaluated for memory improvement effects using mouse model of scopolamine induced amnesia. Passive shock avoidance test and elevated plus maze test were employed to determine cognitive functions while brain biochemical parameters were measured to establish the neuroprotective mechanism. The methanol extract (ME) showed marked AChE inhibitory and antioxidant activities, therefore, it was fractionated. Comparative analysis of all obtained fractions revealed that ethylacetate fraction (EAF) was most active. Both ME and EAF improved cognitive dysfunction caused by scopolamine in mice by reducing TBARS levels and brain AChE activity. TLC densitometric studies showed appreciable levels of naringenin in ME (0.32% w/w) and EAF (1.14% w/w). The observed memory enhancement effects of ME and EAF could be attributed to their ability to inhibit AChE activity and antioxidant effects due to presence of flavonoids.