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Abstract
One of the most important issues nowadays is memory disorders. The exact circadian modulation of learning and memory is still under investigation. The present study was carried out to evaluate the probable enhancing and neuroprotective effects of the Egyptian Moringa peregrina; administered at two different Zeitgeber times (ZT), on learning and memory in mice. M. peregrina dried leaves were aqueously extracted and intranasally (IN) administered at four doses (viz. 12.5, 25, 50, and 100 mg/kg). Twenty animal groups (n = 8/group) were treated with M. peregrina at ZT 3:00 vs. 15:00 representing the rest (day) vs. active (night) phases, respectively. Additionally, sub-chronic effect of daily IN administration of the 25 mg/kg dose for two weeks was examined at ZT 3:00 vs. 15:00. Memory performance was assessed after 1, 2 weeks of treatment and a 3rd recovery week. Memory test was performed at ZT 17:00 by measuring the percentage of time spent in novel arm of Y-maze. Dose-response curve revealed that both 25 and 50 mg/kg doses administered at ZT 3:00 significantly improved memory efficiency. Rest phase administration significantly enhanced memory functions after 1, 2 weeks as well as after the recovery week. Moreover, IN pretreatment with M. peregrina (25 mg/kg) revealed a protective effect against scopolamine-induced amnesia. In conclusion, these findings clearly indicated that M. peregrina possesses valuable enhancing and protective effects on learning and memory processes in mice which is circadian-phase dependent.