The Electrocorticograms of the Aged Mouse X-Irradiated at Juvenile or Young Adult

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The electrocorticograms (ECoGs) of the (C57BL/6 x C3H)F_1 mice irradiated at juvenile or young adult were studied when they attained the age of 24-26 months. One group of mice was irradiated 35 days post partum (35-DPP) and another 105 days (105-DPP). All the animals were irradiated with 300 R of X-rays to whole body. The ECoGs were recorded from the freely moving animals with the permanently implanted electrodes fixed over the visual cortical surface. The resulted ECoGs were divided into 3 patterns: wakefulness (W), slow wave sleep (SWS), and paradoxical sleep (PS). Six parameters of the 3 patterns were compared among the 2 irradiated groups and the non-irradiated control group. The mean SWS- and PS-cycle times, and mean SWS length were significantly longer in the 35-DPP group than in the control group. Changes in the ECoGs were less profound in the 105-DPP group than those in the 35-DPP group: only a significant change due to irradiation at 105-DPP was a decrease in the ratio of the total PS time to the total sleep time (TST = total SWS time + total PS time).