Ginkgo biloba extract improves cognitive function and increases neurogenesis by reducing Aβ pathology in 5×FAD mice

Abstract

Previous studies have indicated that the generation of newborn hippocampal neurons is impaired in the early phase of Alzheimer's disease (AD). A potential therapeutic strategy being pursued for the treatment of AD is increasing the number of newborn neurons in the adult hippocampus. Recent studies have demonstrated that ginkgo biloba extract (EGb 761) plays a neuroprotective role by preventing memory loss in many neurodegenerative diseases. However, the extent of EGb 761's protective role in the AD process is unclear. In this study, different doses of EGb 761 (0, 10, 20, and 30 mg/kg; intraperitoneal injections once every day for four months) were tested on 5×FAD mice. After consecutive 4-month injections, mice were tested in learning memory tasks, Aβ, and neurogenesis in the dentate gyrus (DG) of hippocampus and morphological characteristics of neurons in DG of hippocampus. Results indicated that EGb 761 (20 and 30 mg/kg) ameliorated memory deficits. Further analysis indicated that EGb 761 can reduce the number of Aβ positive signals in 5×FAD mice, increase the number of newborn neurons, and increase dendritic branching and density of dendritic spines in 5×FAD mice compared to nontreated 5×FAD mice. It was concluded that EGb 761 plays a protective role in the memory deficit of 5×FAD mice.

Keywords: Alzheimer’s disease; Aβ; ginkgo biloba exact; memory; neurogenesis.

Figure 1

Effect of EGb 761 on nonspatial learning memory in NOR and spatial memory in MWM. A. Effect of EGb 761 improved the memory of NOR in Tg mice. B. Escape latencies. C. The number of platform crossings. D. The percentage of time spent searching in the target quadrant where the platform had been located by individual mice in the treatment groups. Data are represented as mean ± SD. * indicates P < 0.05; # indicates P < 0.05.

Figure 2

Effects of EGb 761 on neurogenesis in hippocampus of 5×FAD mice. A. Representative images of BrdU⁺ cells in the DG (20×). B. Density of BrdU⁺ cells in the DG. C. Representative images of DCX⁺ cells in the CA1 (20×). D. Density of DCX⁺ cells in the DG. The number of DCX⁺ cells in the CA1 of 5×FAD mice were decreased in contrast with control mice (P < 0.05). Chronic 30 mg/kg EGb 761 treatment could increase the number of DCX⁺ cells in the 5×FAD mice. * indicates P < 0.05 vs. control. # indicates P < 0.05 vs. 5×FAD group. Data are presented as mean ± SD.

Figure 3

Effect of EGb 761 on Aβ expression in hippocampus of 5×FAD mice. A. Soluble Aβ1-40 and Aβ1-42 from brains of 8-month-old mice were measured using ELISA. B, C. Representative immunofluorescence images of Aβ deposits (6E10) and number (g) of Aβ deposits. Data shown are the means ± SEM, with 4 mice in each group. * indicates P < 0.05 vs. control. # indicates P < 0.05 vs. 5×FAD group. Data are presented as mean ± SD.

Figure 4

Effect of EGb 761 on the ThS positive signals in the hippocampal DG region of 5×FAD mice. A. Representative immunofluorescence images of ThS-positive signal. B. EGb 761 inhibits the ThS positive signals in the hippocampal DG region of 5×FAD mice. Data shown are the means ± SD, with 4 mice in each group. * indicates P < 0.05 vs. control. # indicates P < 0.05 vs. 5×FAD group.

Figure 5

The effect of EGb 761 on the dendritic morphology of hippocampal CA1 neurons. A. Representative images of spine density in hippocampus. Scale bar = 100 μm. B. Representative images of dendritic branches in hippocampus. C. Analysis of branch number in hippocampus. D. Dendritic spine types found in the CA1 field. Spine maturity progresses (from left to right) from long, thin spine structures (yellow) to wide-headed mushroom spines (blue). Geometric characteristics of spines are listed below for each type. E. Golgi-stained secondary dendritic branch of a CA1 field neuron in mouse. Different spine types are indicated by arrowheads, which are color-coded to match. Scale bar, 5 um. F. The percentages of different types of spines treated by 30 EGb 761. Number of mature spines in 5×FAD mice were significantly decreased in contrast with those of control mice (P < 0.05). This can be reversed by 30 mg/kg EGb 761 choronic treatment. Data are expressed as mean ± SD. * indicates a significant difference between groups (P < 0.05).