Effects of Radix Polygalae on Cognitive Decline and Depression in Estradiol Depletion Mouse Model of Menopause

Abstract

Postmenopausal syndrome refers to symptoms caused by the gradual decrease in female hormones after mid-40 years. As a target organ of estrogen, decrease in estrogen causes various changes in brain function such as a decrease in choline acetyltransferase and brain-derived neurotrophic factor; thus, postmenopausal women experience cognitive decline and more depressive symptoms than age-matched men. Radix Polygalae has been used for memory boosting and as a mood stabilizer and its components have shown neuroprotective, antidepressant, and stress relief properties. In a mouse model of estrogen depletion induced by 4-vinylcyclohexene diepoxide, Radix Polygalae was orally administered for 3 weeks. In these animals, cognitive and depression-related behaviors and molecular changes related to these behaviors were measured in the prefrontal cortex and hippocampus. Radix Polygalae improved working memory and contextual memory and despair-related behaviors in 4-vinylcyclohexene diepoxide-treated mice without increasing serum estradiol levels in this model. In relation to these behaviors, choline acetyltransferase and brain-derived neurotrophic factor in the prefrontal cortex and hippocampus and bcl-2-associated athanogene expression increased in the hippocampus. These results implicate the possible benefit of Radix Polygalae in use as a supplement of estrogen to prevent conditions such as postmenopausal depression and cognitive decline.

Keywords: VCD; cognition; depression; estrogen; radix polygalae.

Figure 1

Schedule of VCD, E2, RP treatment, behavior tests, and tissue collection.

Figure 2

Vaginal cytology of normal and VCD-treated mice. Vaginal smear stained with crystal violet. (A) Vehicle-treated mice completed all 4 estrous stages (proestrus: A-1, estrus: A-2, metestrus: A-3, diestrus: A-4). A-1 (arrows): small nucleus epithelial cells, A-2 (arrows): keratinized epithelial cells, A-3 (arrows): surrounded by keratinized epithelial cells. (B) VCD-treated mice showed the characteristics of diestrus and meta-to-diestrus stages by the presence of small nuclear epithelial cells and neutrophils.

Figure 3

Effect of E2 and RP on uterus weight and serum estradiol concentration in VCD-treated mice. (A) Serum concentration of estradiol (pg/mL). Compared with the control group, estradiol concentration decreased in VCD, VCD + RP1, VCD + RP10, and VCD + RP100, but not in VCD + E2. Compared with the VCD group, estradiol concentration increased in VCD + E2 but not in VCD + RP treated three groups. (B) Uterus-to-body weight ratio (%). Compared with the control group, ratio decreased in the VCD group. Compared with the VCD group, the ratio increased in VCD + E2 but not in RP-treated groups. (C) Representative images of the uterus from Control, VCD, and VCD + E2. All data are the mean ± SEM. Control: Vehicle (sesame oil) i.p.; VCD: VCD 160 mg/kg i.p.; VCD + E2: VCD 160 mg/kg i.p + estradiol 100 μg/kg i.p.; VCD + RP1: VCD 160 mg/kg i.p + RP 1 mg/kg p.o.; VCD + RP10: VCD 160 mg/kg i.p + RP 10 mg/kg p.o.; and VCD + RP100: VCD 160 mg/kg i.p + RP 100 mg/kg p.o.; * p < 0.05, ** p < 0.01, *** p < 0.001 vs. Control, ^## p < 0.01, and ^### p < 0.001 vs. VCD. ANOVA, Tukey’s HSD post hoc test.

Figure 4

Effect of E2 and RP on working and spatial memory in VCD-treated mice. (A) Alternation triplet ratio (%) in the Y-maze test. Compared with the control group, the ratio decreased in VCD. Compared with the VCD group, the ratio increased in the VCD + E2, VCD + RP1, and VCD + RP100, and non-significantly in VCD + RP10 (p = 0.064) group. (B) Target quadrant time (%) in the MWM probe test. Compared with the VCD group, the %time increased in the VCD + E2, VCD + RP1, VCD + RP10, and VCD + RP100. Data are the mean ± SEM. Control: Vehicle (sesame oil) i.p.; VCD: VCD 160 mg/kg i.p.; VCD + E2: VCD 160 mg/kg i.p + estradiol 100 μg/kg i.p.; VCD + RP1: VCD 160 mg/kg i.p + RP 1 mg/kg p.o.; VCD + RP10: VCD 160 mg/kg i.p + RP 10 mg/kg p.o.; and VCD + RP100: VCD 160 mg/kg i.p + RP 100 mg/kg p.o; * p < 0.05, ** p < 0.01 vs. Control, ^# p < 0.05, and ^## p < 0.01 vs. VCD. ANOVA, Tukey’s HSD post hoc test.

Figure 5

Effect of E2 and RP on despair behaviors in VCD-treated mice. (A) Immobility(sec) in the FST. Compared with the control group, immobility increased in the VCD group. Compared with the VCD group, the immobility decreased in VCD + E2, VCD + RP10, and VCD + RP100 group. (B) Immobility in the TST. Compared with the control group, immobility increased in the VCD group. Compared with the VCD group, the immobility decreased in VCD + E2, VCD + RP1, VCD + RP10, and VCD + RP100 group. All data are the mean ± SEM. Control: Control: Vehicle (sesame oil) i.p.; VCD: VCD 160 mg/kg i.p.; VCD + E2: VCD 160 mg/kg i.p + estradiol 100 μg/kg i.p.; VCD + RP1: VCD 160 mg/kg i.p + RP 1 mg/kg p.o.; VCD + RP10: VCD 160 mg/kg i.p + RP 10 mg/kg p.o.; and VCD + RP100: VCD 160 mg/kg i.p + RP 100 mg/kg p.o; ** p < 0.01, *** p < 0.001 vs. Control, ^# p < 0.05, ^## p < 0.01, and ^### p < 0.001 vs. VCD. ANOVA, Tukey’s HSD post hoc test.

Figure 6

Effect of E2 and RP on the prefrontal cortex and hippocampal expression of ChAT and BDNF. (A) Representative blotting images of ChAT. (B) The ChAT band intensity ratio of the prefrontal cortex. Compared with the control group, the intensity ratio decreased in VCD. Compared with the VCD group, the intensity ratio increased in VCD + E2, VCD + RP1, VCD + RP10, and VCD + RP100. (C) ChAT band intensity of the hippocampus. Compared with the control group, the intensity ratio decreased in VCD. Compared with the VCD group, the intensity ratio increased in VCD + E2 and VCD + RP1 but not in VCD + RP10 and VCD + RP100. (D) Representative blotting images of BDNF. (E) BDNF band intensity ratio of the prefrontal cortex. Compared with the control group, intensity ratio decreased in VCD. Compared with the control group, intensity ratio decreased in VCD. Compared with the VCD group, the intensity ratio increased in VCD + E2 and VCD + RP1 but not in VCD + RP10 and VCD + RP100. (F) BDNF band intensity ratio of the hippocampus. Compared with the control group, intensity ratio decreased in VCD. Compared with the VCD group, there were no difference in intensity ratio. All data are the mean ± SEM. Control: Vehicle (sesame oil) i.p.; VCD: VCD 160 mg/kg i.p.; VCD + E2: VCD 160 mg/kg i.p + estradiol 100 μg/kg i.p.; VCD + RP1: VCD 160 mg/kg i.p + RP 1 mg/kg p.o.; VCD + RP10: VCD 160 mg/kg i.p + RP 10 mg/kg p.o.; and VCD + RP100: VCD 160 mg/kg i.p + RP 100 mg/kg p.o; * p < 0.05, ** p < 0.01 vs. Control, ^# p < 0.05, and ^## p < 0.01 vs. VCD. ANOVA, Tukey’s HSD post hoc test.

Figure 7

Effect of E2 and RP on hippocampal expression of GR and BAG1 in VCD-treated mice. (A) Representative blotting images (B) Band intensity ratio of GR. There was no significant difference. (C) Band intensity ratio of BAG1. Compared with the control group, the intensity ratio decreased in VCD. Compared with the VCD group, the intensity ratio increased in VCD + E2, VCD + RP1, VCD + RP10, and VCD + RP100. All data are the mean ± SEM. Control: Vehicle (sesame oil) i.p.; VCD: VCD 160 mg/kg i.p.; VCD + E2: VCD 160 mg/kg i.p + estradiol 100 μg/kg i.p.; VCD + RP1: VCD 160 mg/kg i.p + RP 1 mg/kg p.o.; VCD + RP10: VCD 160 mg/kg i.p + RP 10 mg/kg p.o.; and VCD + RP100: VCD 160 mg/kg i.p + RP 100 mg/kg p.o; * p < 0.05 vs. Control, ^# p < 0.05, and ^## p < 0.01 vs. VCD. ANOVA, Tukey’s HSD post hoc test.