Hyperbaric oxygenation (HBO) is an attractive procedure that has been used in treatment of hypoxic-ischemic encephalopathy (HIE). However, depending on the HBO protocol, especially the time point of starting treatment of HBO, different and conflicting results were obtained. This study was undertaken to search for the optimal therapeutic window of ABO in neonatal rat with hypoxic-ischemic brain damage (HIBD).Eighty-four healthy seven-day-old SD rats were used as research subjects and were randomly divided into seven groups with 12 in each: sham group, HI group, HI (1 h) + HBO group (HBO starting 1 h after HI), HI (3 h) + HBO group (HBO starting 3 h after HI), HI (6 h) + HBO group (HBO starting 6 h after HI), HI (12 h) + HBO group (HBO starting 12 h after HI), HI (24 h) + HBO group (HBO starting 24 h after HI). Single HBO treatment (2.5 atmospheres absolute, ATA for 1.5 h) was used in this study. Two indexes were used to assess the effect of HBO that included short-term (48 h after HI) histology change (the cell density in CA1 of hippocampus and cortex) and long-term (5 w and 6 w after HI) neurobehavioral testing (grip test and treadmill test for evaluating the deficits of sensor motor; step-down avoidance test for assessing the deficits of memory).In HI (1 h) + HBO, HI (3 h) + HBO and HI (6 h) + HBO groups, neuron density of cortex and CA1 of hippocampus were 1981.76 +/- 299.55, 1841.53 +/- 241.21, 1525.78 +/- 189.00 and 4430.56 +/- 1180.31, 4507.54 +/- 1374.32, 3883.48 +/- 821.87, respectively, which were significantly higher than HIBD group (987.86 +/- 285.39 and 1813.59 +/- 295.33, P < 0.05, ANOVA). But in HI (12 h) + HBO and HI (24 h) + HBO, the neuron density of cortex and CA1 of hippocampus compared with those in HIBD group had no statistical significance (P > 0.05, ANOVA). In the sensor motor testing performed at 5 w after HI of rat, the grip time in grip test and the stay time in treadmill test of HI (1 h) + HBO, HI (3 h) + HBO and HI (6 h) + HBO groups were 193.39 +/- 51.19, 168.39 +/- 34.02, 168.95 +/- 34.93 and 130.34 +/- 42.56, 128.20 +/- 27.69, 125.74 +/- 36.99, respectively, which, compared with HIBD group, were significantly prolonged (P < 0.05, ANOVA). But in HI (12 h) + HBO and HI (24 h) + HBO groups, the time was not significantly longer compared with HI (P > 0.05, ANOVA). In the step-down avoidance test which was performed at 6 w after HI, the step-down latencies of HI (1 h) + HBO, HI (3 h) + HBO and HI (6 h) + HBO were 96.91 +/- 29.91, 90.35 +/- 28.44 and 76.46 +/- 38.70, respectively, which were significantly prolonged (P < 0.05, ANOVA), but in HI (12 h) + HBO and HI (24 h) + HBO, the latencies did not significantly increase compared with HIBD, P > 0.05, ANOVA.The optimal therapeutic window of HBO in neonatal rat with HIBD was within the first 6 hours after HI. In this therapeutic window, HBO was highly effective in reducing the cell loss in CA1 of hippocampus and cortex.
To investigate the effect of hyperbaric oxygen (HBO) on long-term learning-memory disabilities and brain injury induced by hypoxia-ischemia in neonatal rat.In the study, eighteen rats aged seven days were divid into three groups: (1) sham-operated group (SHAM), (2) hypoxia-ischemia group (HIBD), (3) HBO-treated hypoxia-ischemia group (HIBD + HBO). In hypoxia-ischemia groups, left common carotid artery was ligated permanently on the seventh postnatal day, two hours after the procedure; hypoxia (92% nitrogen and 8% oxygen) was induced for 2 h. In HBO-treated hypoxia-ischemia group, single HBO (2. 5 ATA, 1.5 h) was administered at one hour after the hypoxia period. At the six weeks old, step-down inhibitory avoidance test was used to evaluate the short-term memory of rats. Learning and long-term spatial memory deficits were tested using Morris water maze at eight weeks old of rats. Rats were then perfused and brains removed for macroscopic and microscopic evaluation. The cell density of hippocampus were used to evaluate the degree of brain injure.In HIBD+HBO group, the latency to step down the platform was significantly longer than that of HIBD group (P<0.05); in HIBD+HBO group, the mean latencies to reach the platform was significantly shorter than that of HIBD group (P < 0.05); in HIBD + HBO group, the time spent in the target quadrant was significantly lower than that in HIBD group (P<0.05). Histopathological evaluation demonstrated that HBO also significantly diminished brain injury and decreased the cell loss of hippocampal CA1 region.Single HBO (2.5 ATA, 1.5 h) can significantly improve long-term learning-memory deficits and attenuate brain injury in rats with hypoxia-ischemia brain damage.
Neuroinflammation mediated by activated microglia plays a pivotal role in the pathogenesis of neurological disorders, including hypoxic injury of the developing brain. Thymosin β4 (Tβ4), the major G-actin-sequestering molecule, has an anti-inflammatory effect and has been used to treat various neurological diseases. However, the effect of Tβ4 on hypoxia-induced microglia activation in the developing brain remains unclear. We investigate here the effect of Tβ4 on microglia activation of neonatal rats after hypoxia exposure. Tβ4 treatment was carried out on 1-day-old rats and BV-2 cells. Tβ4 expression in microglia was determined by quantitative real time-PCR, western blotting, and immunofluorescence staining. Secretion of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and nitric oxide (NO) was assessed by enzyme-linked immunosorbent assay and colorimetric assay. mRNA expression of TNF-α and IL-1β, and microRNA 146a expression was determined by quantitative real time-PCR. We showed that Tβ4 treatment significantly inhibited secretion of inflammatory mediators in the cerebellum of neonatal rats following hypoxia injury. Increased expression of endogenous Tβ4 in microglia was observed both in hypoxic rats and in BV-2 cells. Tβ4 treatment significantly inhibited the expression and secretion of hypoxia-induced TNF-α, IL-1β, and NO. Remarkably, microRNA 146a expression was found to have increased in Tβ4-treated BV-2 cells. We demonstrated the anti-inflammatory effect of Tβ4 in neonatal rats following hypoxic brain injury. More importantly, our data reveal, for the first time, that Tβ4 inhibits microglia activation in vitro. Therefore, this study contributes to understanding the role and mechanism of Tβ4 function in central nervous system diseases.
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