Effects Of Intrauterine Hypoxia On Rat Brain Functional Outcome And The Efficacy Of Hyperbaric Oxygen On Brain Rehabilitation

【Objective】To explore the effects of intrauterine hypoxia on brain functional outcome and the mechanism of hyperbaric oxygen (HBO) in the brain rehabilitation of infant rats with hypoxic-ischemic brain damage (HIBD).【Methods】A rat model with HIBD in uterus was set up by a delayed cesarean section, which either of the SD pregnant rats'uterine vessels was ligated for 15 min to produce asphyxia. The adjacent horn was not ligated and the fetuses in it served as the controls.Animals were divided into six groups --- HIBD group,normobaric oxygen (NBO)-treated HIBD group,HBO-treated HIBD group,the control group,NBO- treated the control group and HBO- treated the control group at random. Each group included 10 rats for statistics analysis. After 24h of the operation, the rats of the HBO-treated groups received HBO (2ATA, 1h/d) for 14 days, and the rats of the NBO-treated groups received NBO (5L/min, 1h/d) for 14 days. The rats of the HIBD groups and the control groups were kept in a standard condition without any intervention. The rats'brain functional outcome was evaluated by suspension test,the balancing test and brainstem auditory evoked potential (BAEP). The histopathology in brain tissues was observed under the microscope and the electron microscope. The p38 expression in the brain was detected immunohistochemically.SPSS13.0 statistical software package proceeds were used for statistics analysis.【Results】1. Behavior tests The time of suspension and the score of the balancing test in the HIBD group were (14.50±2.22)s and (10.20±1.03)points respectively, which were much less than those in the control group [(20.60±3.34)s and (13.20±0.92) points, P<0.05] . Compared with those in the control group, both the time of suspension and the score of the balancing test were improved in the HIBD group (P<0.05) after receiving HBO therapy. They were (17.90±2.02)s and (12.10±1.20) points after receiving HBO therapy. There were no significant difference in the suspension test and the balancing test between the HIBD group and NBO-treated HIBD group (P>0.05). The time of suspension and the score of the balancing test in the HBO- treated control group were also no significant changes compared with those for the control group and the NBO- treated control group (P>0.05).2. Brainstem auditory evoked potential (BAEP) In the HIBD group, the peak latency (PL) of waves I,II,Ⅳwere (1.13±0.06),(2.15±0.22),(4.51±0.70)ms respectively and the interpeak latency (IPL) of wave II～Ⅳ,I～Ⅳwere (2.36±0.57),(3.38±0.67) ms separately, which were prolonged than those of the control group [(1.04±0.02),(1.91±0.06),(3.70±0.09)ms and (1.79±0.07),(2.65±0.08)ms] (P<0.05). After receiving HBO therapy, the PLs and IPLs above in the HIBD group were no significant changes compared with those in the control group (P>0.05). The PLs and the IPLs of all waves in the NBO-treated HIBD group were also no significant changes compared with those for the HIBD group (P>0.05). In the HBO-treated control group, the PL of waveⅣwas (3.04±0.38)ms and the IPL of waves II～Ⅳ,I～Ⅳwere (1.24±0.20),(2.04±0.29)ms,which were much shorter than those of the control group and the NBO- treated control group(P<0.05).3. The histopathology in brain tissues①Under the microscope,the neurological manifestations of the HIBD+HBO group was minimal,while the changes were obvious in both HIBD group and HIBD+NBO group by HE staining. In the frontal cortex,brain stem,basal ganglia and hippocampus CA1 in HIBD group and the HIBD+NBO group, the number of surviving neurons were (75.00±15.90,77.40±14.36,75.10±12.04,73.40±9.72) cells/0.2mm2 and (77.40±21.28,81.50±18.41,78.70±18.68,75.80±16.40) cells /0.2mm2 respectively, which were less than those in the HIBD+HBO group [(105.50±26.83,119.40±23.34,110.40±24.05,100.00±24.19) cells/0.2mm2] by Nissl's staining (P<0.05).②Under the electron microscopy, the ultrastructure of pyramidal neuron of hippocampal CA1 was distorted in HIBD group, compared with that in HBO-treated HIBD group and the control group.4. The p38 expression by immunohistochemistry staining The corrected optical densities (COD) of p38 immunoreactive products in frontal cortex,brain stem,basal ganglia and hippocampus CA1 were 0.07±0.03,0.36±0.14,0.38±0.20,0.18±0.09 in the HIBD group and 0.08±0.03,0.38±0.16,0.41±0.19,0.21±0.11 in the HIBD+NBO group separately, which were less than those in the HIBD+HBO group (0.26±0.10,0.63±0.16,0.58±0.19,0.46±0.17)(P<0.05). The COD of p38 immuno -reactive products in the HBO- treated control group were (0.74±0.15,1.11±0.17,1.01±0.14,0.87±0.17), which were higher than those in the control group(0.46±0.13,0.86±0.14,0.77±0.17,0.67±0.16) and the NBO- treated control group(0.53±0.15,0.91±0.17,0.82±0.16,0.70±0.16)(P<0.05).【Conclusions】Early HBO therapy might effectively moderate the brain injury and dysfunction by hypoxia-ischemia in the immature rat. Underlying the induction of synaptic plasti -city and reducing the ultrastructural damage may be involved in the mechanism of HBO in the brain rehabilitation in perinatal brain damage with hypoxic-ischemia.