Memory-Enhancing Effects of the Crude Extract of Polygala tenuifolia on Aged Mice

Abstract

Learning and memory disorders arise from distinct age-associated processes, and aging animals are often used as a model of memory impairment. The root of Polygala tenuifolia has been commonly used in some Asian countries as memory enhancer and its memory improvement has been reported in various animal models. However, there is less research to verify its effect on memory functions in aged animals. Herein, the memory-enhancing effects of the crude extract of Polygala tenuifolia (EPT) on normal aged mice were assessed by Morris water maze (MWM) and step-down passive avoidance tests. In MWM tests, the impaired spatial memory of the aged mice was partly reversed by EPT (100 and 200 mg/kg; P < 0.05) as compared with the aged control mice. In step-down tests, the nonspatial memory of the aged mice was improved by EPT (100 and 200 mg/kg; P < 0.05). Additionally, EPT could increase superoxide dismutase (SOD) and catalase (CAT) activities, inhibit monoamine oxidase (MAO) and acetyl cholinesterase (AChE) activities, and decrease the levels of malondialdehyde (MDA) in the brain tissue of the aged mice. The results showed that EPT improved memory functions of the aged mice probably via its antioxidant properties and via decreasing the activities of MAO and AChE.

Figure 1

Experimental procedure.

Figure 2

Effect of EPT on locomotive activities of mice. Data represent the mean ± S.E.M, n = 8–10 in each group. Gal represents galantamine 3 mg/kg group. The total distance traveled by mice was measured after repeated administrations of EPT (50, 100, and 200 mg/kg) for 4 weeks. *P < 0.05 compared with the aged control group.

Figure 3

Effect of EPT on the acquisition phase in MWM tests of the aged mice. Training trials were carried out on day 2 to day 7 of behavioral tests, (a) escape latency, (b) escape rate, and (c) swimming speed. Gal 3 mg/kg represents galantamine 3 mg/kg group. Values represent mean ± S.E.M (n = 8–10 in each group). ^# P < 0.05 compared with the normal group; *P < 0.05 and **P < 0.01 compared with the aged control group.

Figure 4

Effect of EPT on the probe and memory retention in MWM tests of the aged mice. The probe trial was performed 24 h after the acquisition test, (a) swimming time in target quadrant, (b) crossing numbers, (c) swimming distance in target quadrant, (d) swimming speed, and (e) escape latency on memory retention test. Gal 3 mg/kg represents galantamine 3 mg/kg group. Values represent mean ± S.E.M (n = 8–10 in each group). ^# P < 0.05 and ^## P < 0.01 compared with the normal control group; *P < 0.05 and **P < 0.01 compared with the aged control group.

Figure 5

Effect of EPT on memory deficits of the aged mice in the step-down passive avoidance test. Figures 5(a)–5(c), 5(d) and 5(e), and 5(f)–5(h) represent the tests of acquisition, consolidation, and retrial, respectively. Figures 5(a), 5(e), and 5(f) show the time spent on electric grid; Figures 5(c) and 5(h) show latency; and Figures 5(b), 5(d), and 5(g) show the time spent in safety zone. Values represent mean ± S.E.M (n = 8–10 in each group). Gal 3 mg/kg represents galantamine 3 mg/kg group. ^# P < 0.05 and ^## P < 0.01, versus the normal control group; *P < 0.05 and **P < 0.01, versus the aged control group.

Figure 6

Effect of EPT on the changes of MDA levels and CAT and SOD activities in mice brain tissue. (a) MDA levels, (b) CAT activity, and (c) SOD activity. Values represent the mean ± S.E.M (n = 8–10 in each group). Gal represents galantamine 3 mg/kg group. ^# P < 0.05 and ^## P < 0.01, versus the normal control group; *P < 0.05 and **P < 0.01, versus the aged control group.

Figure 7

Effect of EPT on the changes of MAO (a) and AChE (b) activities in mice. Each value represents the mean ± S.E.M (n = 8–10 in each group). Gal represents galantamine 3 mg/kg group. ^# P < 0.05, versus the normal control group; *P < 0.05 and **P < 0.01, versus the aged control group.