Objective:To evaluate the relationship between the mechanism of preoperative sleep deprivation aggravating postoperative cognitive dysfunction and theta oscillations in the hippocampal CA1 region in aged mice.Methods:Twenty-four SPF male C57BL/6J mice, aged 18 months, weighing 20-30 g, were divided into 3 groups ( n=8 each) by a random number table method: normal control group (group C), operation group (group S) and preoperative sleep deprivation + operation group (group SD+ S). The sleep deprivation model was established using the sleep deprivation rod method, and the sleep deprivation time was 24 h before operation. The sleep deprivation rod was set to rotate continuously at 6 rpm/min, and the direction was randomly reversed to force the mice to exercise to achieve the purpose of sleep deprivation. Group C received no treatment. Group S underwent exploratory laparotomy under isoflurane anesthesia. After sleep deprivation for 24 h, SD+ S group underwent exploratory laparotomy under isoflurane anesthesia. Y-maze and Morris water maze tests were used to evaluate postoperative cognitive function. The theta oscillations in the hippocampal CA1 region were observed and recorded by EEG electrodes in vivo. The animals were then sacrificed and brain tissues were obtained for determination of the density of dendritic spines in the hippocampal CA1 region. Results:Compared with group C, the number of crossing the original platform was significantly decreased, and the time of staying at the original platform quadrant and time of exploring the novel arm were shortened, and the number of entries into the novel arm was reduced, the density of dendritic spines in the hippocampal CA1 region was reduced, and the percentage of theta oscillation power was decreased during the Y maze test in group S ( P<0.05). Compared with S group, the number of crossing the original platform was significantly decreased, and the time of staying at the original platform quadrant and time of exploring the novel arm were shortened, and the number of entries into the novel arm was reduced, the density of dendritic spines in the hippocampal CA1 region was reduced, and the percentage of theta oscillation power was decreased during the Y maze test in SD+ S group ( P<0.01). Conclusions:The mechanisms by which preoperative sleep deprivation exacerbates postoperative cognitive dysfunction may be related to reduction in theta oscillations in the hippocampal CA1 region of aged mice.