The effects of two routes of melatonin administration on the behavior and histopathology in focal cerebral ischemic rats

Objective\r\nTo explore the effects of two routes of melatonin (MT) administration including intraperitoneal and caudal vein injection on the behavior, histopathology and the expression of myelin basic protein (MBP) and active caspase-3 protein in focal cerebral ischemic rats.\r\n\r\n\r\nMethods\r\n84 male Sprangue-Dawley rats were randomly divided into normal control group(CON, n=12), middle cerebral artery occlusion group(MCAO, n=24), MT-intraperitoneal group (n=24) and MT-intravenous injection group (n=24) by random number table. Twenty-four hours after ischemia reperfusion (IR), Morris water maze was used to observe the effects of two routes of MT administration on behavior in focal cerebral ischemic rats. 7 d after IR, MBP immunohistochemical and hematoxylin eosin (HE) staining were used to examine the expression of MBP in striatum and histopathological changes in hippocampal CA1 region. 24 h, 72 h and 7 d after IR, the expression of active caspase-3 in hippocampal CA1 region was observed by immunohistochemical staining.\r\n\r\n\r\nResults\r\nThe average escape latencies in Morris water maze in MT-intravenous injection group at different time points were all lower than those of the MT-intraperitoneal, and they were all lower than those of the MCAO group. Swimming time percentage of target quadrant in MT-intravenous injection group were higher than those of the MT-intraperitoneal, and they were all higher than those of the MCAO group (all P\u003c0.01); 7 d after IR, the results of HE staining showed that the hippocampus cells in MCAO group were disarranged with hyperchromatic nucleus and cytoplasm. More hippocampal cells were observed in MT-intraperitoneal and MT-intravenous injection groups, and they were relatively well arranged. The optical density (OD) of MBP in MT-intravenous injection group (105.60±4.04) was significantly higher than those in MCAO group (95.60±2.07) and MT-intraperitoneal injection group (98.00±4.18) (both P\u003c0.01). Immunohistochemical results showed that the number of active caspase-3 positive cells in MT-intravenous injection group ((116.93±12.58)/mm2, (130.16±21.22)/mm2, (88.25±7.80)/mm2) at each time point were significantly lower than those in MT-intraperitoneal injection group ((156.64±32.54)/mm2, (176.49±17.44)/mm2, (127.96±16.73)/mm2)(all P\u003c0.05). At the time points of 24 h and 72 h after IR, there were less active caspase-3 positive cells in MT-intraperitoneal and MT-intravenous injection group compared with those in MCAO group((273.56±32.54)/mm2, (288.63±35.17)/mm2)(all P\u003c0.01).\r\n\r\n\r\nConclusion\r\nMT administration by both intraperitoneal and intravenous injection can significantly improve the behavior and attenuate the histopathology and white matter damage, and reduce the cell apoptosis in hippocampal CA1 region in focal cerebral ischemic rats, and the therapeutic effects of MT-intravenous injection are better than MT-intraperitoneal injection.\r\n\r\n\r\nKey words: \r\nMorris water maze; Brain ischemia; Melatonin; Active caspase-3; Myelin basic protein(MBP); Rat