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BACKGROUND: As an important part of systemalimbica, hippocampus involves in emotion, perceiving and learning memory and can be affected by anesthesia.OBJECTIVE: With target controlled infusion of propofol, the depth of anesthesia was well controlled. And under anesthesia in various depths, cfos gene expressions in different regions of hippocampus in rabbits were detected to find the target site for central nervous inhibition by propofol.DESIGN :It was a randomized controlled study.SETTING:Department of Anesthesiology ,Shenzhen Second People's Hospital; Department of Anesthesiology, Union Hospital of Tongji Medical College, Huazhong University of Science and Technology.MATERIALS: The experiment was conducted in the Neurobiological Laboratory of Tongji Medical College, Huazhong University of Science and Technology from May 2000 to June 2001. Thirty Japanese white rabbits were selected and randomly divided into control group, light anesthesia group and deep anesthesia group, with 10 rabbits in each group.METHODS:Intravenous cannulas were placed in external jugular vein (EJV) and femoral artery in all animals. According to the propofol plasma concentration, the infusion of propofol and the depths of anesthesia were well controlled. In light anesthesia group, the plasma concentration of propofol was (9.28±0.12)mg/L. In deep anesthesia group, the plasma concentration of propofol was (11.63±0.29)mg/L. Thirty minutes after being anesthetized, the animals in the two experimental groups were decapitated and the animals in control group were killed by air embolism through ear vein. Coronal sections were sliced continuously, in thickness of 7μm and 1 slice in 100 μm tissue was selected. In situ hybridization was performed to detect the c-f os mRNA in Area CA1, CA3 and dentate gyrus of the hippocampus. In each rabbit, 5 sections were selected randomly.Under a light microscope, photos were taken in 15-20 fields. And then average absorbency and average grayscale were calculated. The grayscale scores were classified as 256 scales. A lower grayscale score indicated a higher positive rate.MAIN OUTCOME MEASURES: ①Under various depths of anesthesia,in situ hybridization results of Area CA1, CA2 and dentate gyrus of the anesthesia, average grayscale scores of Area CA1, CA2 and dentate gyrus of the hippocampus in rabbits were assessed.② Under various depths of anesthesia, average grayscale scores of Area CA1, CA2 and dentate gyrus of the hippocampus in rabbits were calculated.RESULTS:Thirty rabbits entered the statistical analysis procedure.①Under various depths of anesthesia, in situ hybridization results of Area CA1 of the hippocampus in rabbits: In control group, brown, sparse or dense, light-stained or deep-stained c-fos positive cells could be observed. In light anesthesia group, dense, moderately stained c-fospositive neurons could be observed. In deep anesthesia group, cells were denser with deeper stained cytoplasma. ② Under various depths of anesthesia, in situ hybridization results of dentate gyrus of the hippocampus in rabbits: In light anesthesia group, positive cells were strongly stained in deep brown with transparent and vacuolar nuclei. In deep anesthesia group, a large number of c-fos positive cells in great dense could be observed. ③Under various depths of anesthesia, grayscale scores of different regions of the hippocampus in rabbits: Compared with control group, grayscale scores of Area CA1 and dentate gyrus of the hippocampus were significantly decreased in both light and deep anesthesia groups [(168±5), (80±7), (59±5)% ,P ＜ 0.05; (163±8),(103±15), (67±6)%,P ＜ 0.05,P ＜ 0.01]. This was more significant in deep anesthesia group than in light anesthesia group (P ＜ 0.01 ). For Area CA3, the grayscale scores in each group were similar.CONCLUSION: ①With the increasing depth of propofol anesthesia, c-fos gene expression is increased in hippocampus in rabbits. ② After anesthesia, the average grayscale score of Area CA1 and dentate gyrus of the hippocampus are significantly decreased, and this is more significant after deep anesthesia. However, there is no significant change in Area CA3. This indicates that the central inhibitory receptor sites of propofol are various in different brain regions, which supposes that the Area CA3 is not the central receptor sites of propofol.