Rosmarinic acid from Perillae Herba produces an antidepressant-like effect in mice through cell proliferation in the hippocampus

Rosmarinic acid (RA) is one of major polyphenolic ingredients of Perillae Herba (a leaf of Perilla frutescens), and has an antidepressant-like property in animal models of depression. However, the mechanism(s) underlying this activity are unknown. Recent studies have reported that regulation of hippocampal neurogenesis is associated with the pathogenesis of depression. To elucidate the mode of action of RA-induced antidepressant like activity, proliferative effect of RA on newborn cells in the dentate gyrus of mouse hippocampus was investigated using immunohistochemical analysis with bromodeoxyuridine (BrdU), a marker of proliferating cells. RA treatment for 7 or 14d significantly increased in the number of BrdU-positive cells in inverse correlation with significant reductions in immobility in a forced swimming test, an animal model of depression, in a dose-dependent manner. However, locomotor activities were not affected. These results suggest that RA produces an antidepressant-like effect at least in part via the proliferation of newborn cells in the dentate gyrus of the hippocampus.