Effects of Sun ginseng on memory enhancement and hippocampal neurogenesis

Panax ginseng C.A. Meyer has been used in traditional herb prescriptions for thousands of years. A heat-processing method has been used to increase the efficacy of ginseng, yielding what is known as red ginseng. In addition, recently, a slightly modified heat-processing method was applied to ginseng, to obtain a new type of processed ginseng with increased biological activity; this new form of ginseng is referred to as Sun ginseng (SG). The aim of this study was to investigate the effect of SG on memory enhancement and neurogenesis in the hippocampal dentate gyrus (DG) region. The subchronic administration of SG (for 14 days) significantly increased the latency time in the passive avoidance task relative to the administration of the vehicle control (P < 0.05). Western blotting revealed that the levels of phosphorylated extracellular signal-regulated kinase (pERK) and phosphorylated protein kinase B (pAkt) were significantly increased in hippocampal tissue after 14 days of SG administration (P < 0.05). Doublecortin and 5-bromo-2-deoxyuridine immunostaining revealed that SG significantly enhanced the neuronal cell proliferation and the survival of immature neurons in the subgranular zone of the hippocampal DG region. These results suggest that SG has memory-enhancing activities and that these effects are mediated, in part, by the increase in the levels of pERK and pAkt and by the increases in cell proliferation and cell survival.