The electrocorticograms of the adult and aged mouse X-irradiated during the perinatal period

Abstract

The electrocorticograms (ECoGs) of the first generation (F 1) hybrid mice of C57BL/6 × C3H irradiated at fetal or neonatal period were studied at 6–8 (young) and 24–26 (old) months of age. Two groups of mice were irradiated on the 17th day of gestation (17-DPC), another 2 groups on the day of birth (0-DPP), and third 2 groups on the 7th day after birth (7-DPP). All animals were irradiated with 300 R of X-rays to the whole body. The ECoGs were recorded from freely moving animals with permanently implanted electrodes fixed over the visual cortical surface. Recordings were continuous for 3 h, starting at 10:00 a.m. The ECoGs were divided into 3 patterns: wakefulness (W), slow wave sleep (SWS), and paradoxical sleep (PS). Six parameters of the 3 patterns were compared for the 6 irradiated and 2 non-irradiated groups at the young and old age. Non-X-irradiated. There was no difference in the proportion of the total SWS time to the total recording time (TRT) between the young and old control groups. The mean SWS cycle time and the mean SWS length were significantly longer in the young group than in the old group. The ratio of the total PS time to the total sleep time (TST) for the old group was significantly high as compared with that for the young group. The old group had significantly shorter mean PS cycle time and mean PS length than did the young group. X-irradiated. The proportion of total SWS time to TRT was significantly less in the old 0-DPP group than in the comparably aged control group. Mean SWS cycle time, and mean SWS and PS length for the 17-DPC and 0-DPP groups at young age were intermediate between those of the control group at young age and the control group at old age. The ratio of total PS time to TST for the 17-DPC and 0-DPP groups at both ages was significantly less than that for the control groups at every age level. Mean PS length of the 0-DPP group at old age was significantly short as compared with that of the control group at the same age. The body weight and brain weight of these 4 irradiated groups except body weight of the old 17-DPC group were lower than those of their control groups. There were little or no changes in the sleep-wakefulness cycle of the ECoGs for the 7-DPP group at both ages. These results may suggest that the adult and aged mouse X-irradiated at fetal or neonatal period show the ECoG pattern which occurs at a later age in their control groups, namely, an acceleration in the aging of the ECoG pattern.