The effect of cinnamaldehyde on passive avoidance memory and hippocampal Akt, ERK and GSK-3β in mice.

Cinnamon, a spice widely used in cuisine, has been reported to exert therapeutic effects. Recently, cinnamon was shown to improve memory in some animal models of memory impairment and in poor learning mice. This study aimed to investigate the effect of cinnamaldehyde, the major compound in cinnamon on passive avoidance memory and activation of hippocampal Akt (protein kinase B), ERK (extracellular signal-regulated kinase) and GSK-3β (Glycogen Synthase Kinase-3beta) in mice. In the present study, oral cinnamaldehyde at doses of 12.5, 25, 30, 40, 45, 50 and 100 mg/kg/daily was administered to adult male NMRI mice, initiated 10 days before training and continued during training and retention days. Training of passive avoidance task was performed on day 10 and a retention trial was done 24 h after. Upon completion of the retention test, hippocampi were removed for Western blot analysis to detect the phosphorylated and total levels of Akt, ERK and GSK-3β proteins. Results showed that cinnamaldehyde exerts a biphasic effect on passive avoidance memory by impairing memory at lower doses while improving at higher doses. Moreover, at memory improving doses, cinnamaldehyde increased the phosphorylated forms of hippocampal Akt, ERK and GSK-3β while these proteins did not change at impairing doses of cinnamaldehyde. For the first time, this study revealed a biphasic effect of cinnamaldehyde on memory as well as indicating that the memory improving effect of higher doses of this substance is accompanied with hippocampal Akt, ERK and GSK-3β signaling alterations in adult mice.