Protective effects of melatonin on learning and memory in rats by noise stress

Abstract

Objective To explore the effect of melatonin(MT) on the behavior of rats treated with noise stress and the related bio-mechanism. Methods Fifty rats were randomly divided into a blank group,two experimental groups and two control groups. The blank group was untreated. The experimental and control groups were exposed to 120dB noise stress for 1 day or 3 days, 8 hours per day, and treated with 15 mg/kg melatonin by intraperitoneal injection,or the same volume of physiological saline 30 minutes before noise stress. After noise stress,the rats' behavior was measured by open field test, learning and memory ability of rats was investigated with the method of Morris water maze and then nitric oxide (NO), superoxide dismutase (SOD) and malondialdehyde (MDA) contents in cerebral cortex and hippocampus of the rats were measured by TBA and Griess method respectively. Results No matter noise stress time was 1 day or 3 days, the excitability and explorative behavior of the 2 experimental groups(total movement distance (TMD) (1322.50 ± 504.32) cm, (1819.55 ± 458.37) cm, faster movement time (FMT) (68.49 ± 23.90) s, (87.34 ± 16.01) s, distance to center (DTC) (63.56 ± 2. 75) cm, (60. 13 ±1.87)cm, inner toriod time(ITT) (7.87 ±2.06)s,(9.60 ±2.89)s) in the open field test decreased significantly compared with those of the control group (TMD (2042.03 ± 449. 19) cm, (2325.73 ± 384.90) cm,FMT (109.32 ±21.84)s,(124.65 ± 16.74)s, DTC (58.00± 1.53)cm,(55.05 ±5.13)cm, ITT (12.84 ±3.62) s, (14.92 ± 2.75) s, P ＜ 0. 05, P ＜ 0.01);the escape latency of the experimental groups (( 10. 69 ±3.37) s, (18.87 ± 4.74) s) in Morris water maze was significantly shorter than that of the control group (( 23.86± 7.66)s, (33.55 ± 7.20)s, P＜ 0.05, P＜0.01). The contents of NO or MDA in cerebral cortex and hippocampus of the experimental groups (NO in cerebral cortex (3.35 ± 0.40) μmol/gprot, (4.50 ± 0.41) μmol/gprot, NO in hippocampus (2.24 ±0.18) μmol/gprot,(3.15 ±0.21) μmol/gprot, MDA in cerebral cortex(1.34 ±0.44)nmol/mgprot, (2.39 ± 0. 18) nmol/mgprot, MDA in hippocampus (0. 13 ± 0. 07) nmol/mgprot, (0.53 ± 0. 10)nmol/mgprot) were lower than those of the control group (NO in cerebral cortex (3.35 ± 0. 40) μmol/mgprot,(5.03 ± 0.44)μmol/mgprot, NO in hippocampus (2.93 ± 0. 31) μmol/gprot, (3.38 ± 0.24) μmol/gprot, MDA in cerebral cortex (2.24 ± 0.26) nmol/mgprot, (4.21 ± 0.21) nmol/mgprot, MDA in hippocampus (0.47 ± 0.29)nmol/mgprot, (1.33 ± 0. 187) nmol/mgprot, P ＜ 0.05, P ＜ 0. 01) respectively and the contents of SOD in cerebral cortex and hippocampus of the experimental groups (in cerebral cortex (763.95 ± 214.36) U/mgprot, (491.33 ±35.85) U/mgprot, in hippocampus (817.02 ± 232.39) U/mgprot, (644.85 ± 28.02) U/mgprot) were higher than those of the control group(in cerebral cortex (556.50 ± 101.51) U/mgprot, (327.35 ± 30.54) U/mgprot, in hippocampus (279.74 ± 117.02) U/mgprot, (108.75 ± 15.52) U/mgprot, P ＜ 0.05, P＜ 0.01) respectively. Conclusion Melatonin is effective in improving the ability of learning and memory in the rats of noise stress,possibly by inhibiting the increase of NO and MDA and increasing the SOD activity in cerebral cortex and hippocampus of the rats. Key words: Melatonin; Noise; Learning and memory; Behavior; NO; SOD; MDA