BACKGROUND: Hyperbaric oxygen can reduce brain ischemic-reperfusion injury, and this effect is closely related to the modulation of hyperbaric oxygen on microglias.OBJECTIVE: To explore the influence of hyperbaric oxygen on the activity of in vitro cultured brain microglias and secretion of interleukin-1, tumor necrosis factor α and nitric oxide (NO).DESIGN: Completely randomized grouping design, control experiment.SETTING: Teaching and Research Section of Diving Medicine, Teaching and Research Section of Immunity, Teaching and Research Section of Pathology, and the Experimental Animal Center, the Second Military Medical University of Chinese PLA.MATERIALS: This experiment was carried out at the laboratory of Diving Medicine as well as Teaching and Research Section of Immunity, the Second Military Medical University of Chinese PLA, between May 1999 and January 2000. Thirty neonatal SD rats of 1-day birth age were selected for the experiment.METHODS: [1] Brain microglias from newborn SD rats were cultured with digestion method, and microglias were identified with non-specific phosphodiesterase staining and cellular immunochemical staining. [2] Primary microglias were inoculated on 48-well culture board by 2×105/well and randomized into 5 groups: control group without hyperbaric oxygen pretreatment, and hyperbaric oxygen (0.2 MPa 1 hour) pretreatment 3, 7, 10,14 days groups. Cells in groups with hyperbaric oxygen pretreatment at the above various time points were then further divided into 2 subgroups, with one added with culture medium containing bacterium lipopolysaccharide of 1 mg/L (for microglia activation), but not in the other group. [3] Interleukin-1 activity was determined using thymocyte proliferation method. The activity of tumor necrosis factor-α was assessed with L929 cell toxicity test.Nitrous acid content detected by Griess method represented NO content.[4] t-test was used to compare the differences in non-paired quantitative data between the two groups.MAIN OUTCOME MEASURES: The activity of interleukin-1 and tumor necrosis factor a and NO content in resting and evoked brain microglias in rats at various time points of hyperbaric oxygen pretreatment.RESULTS: Thirty SD rats entered the result analysis. [1] The activity of interleukin-1 and tumor necrosis factor α and NO content in resting brain microglias: The two groups did not differ obviously. [2] Interleukin-1activity and NO content in lipopolysaccharide-evoked brain microglias: They were significantly lower in 10-day and 14-day hyperbaric oxygen pretreatment groups than those in control group [10-day group: 0.409±0.014,(5.21±0.77) μnol/L; 14day group: 0.381±0.004, (4.93±1.02) μmol/L, P ＜ 0.05].[3] The activity of tumor necrosis factor α in evoked brain microglias: It was obviously lower in 14day hyperbaric oxygen pretreatment group than in control group [(51.20±1.13) %, (70.10±2.26) %, P ＜ 0.05].CONCLUSION: Pretreatment with 0.2 MPa hyperbaric oxygen can suppress the secretion of interleukin-1, tumor necrosis factor α and NO by evoked microglias, but has not obvious effects on resting microglias.