Effects of hyperbaric oxygen on cognitive function in rats following traumatic brain injury

Objective To investigate the effect of hyperbaric oxygen (HBO) on cognitive function in rats following traumatic brain injury.Methods Thirty-six male Sprague-Dawley rats were randomly divided into the HBO group,normobaric air therapy group and the sham surgical group,each consisting of 12 animals.Traumatic brain injury model was established by using Feeney's free falling in the animals of the HBO group and the normobaric air therapy group.The HBO group received HBO therapy every day and the normobaric air therapy group was left there in normal atmospheric air.The animals in the sham surgical group just exposed dura mater,but without free fall impact.Cognitive function was assessed by using Morris water maze.Dynamic changes in N-acetylaspartate/creatine (NAA/Cr) levels in hippocampus and NAA/choline (NAA/Ch) levels were closely observed with H-MRS following treatment of traumatic brain injury with HBO,and real-time PCR was used to evaluate changes in the levels of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) mRNA in the ipsilateral hippocampus.Results Seven days after HBO therapy,escape latency decreased [(35.1 ± 2.8) s] and number of times crossing the platform increased for the animals in the HBO group.Statistical significance could be noted,when they were compared with those of the normobaric air therapy group[(59.4 ±5.0) s;2.44 ±0.45] (P ＜0.05).NAA/Cr levels in the HBO group were significantly increased (1.18 ± 0.11) 7 days after HBO therapy,and statistical significance could also be seen,as compared with those of the normobaric air therapy group(0.85 ± 0.03) (P ＜ 0.05).Compared with those of the normobaric air therapy group (8 h:0.79 ± 0.07 ; 7 d:0.86 ± 0.08),NAA/Ch levels in the ipsilateral hippocampus of the HBO group (8 h:1.14 ± 0.10; 7 d:1.33 ± 0.17) displayed statistical significance at h 8 and d 7 (P＜0.05).The levels of NGF(3 d:1.27 ±0.03; 7 d:1.31 ±0.08)and BDNF mRNA for the HBO group (3 d:2.82 ±0.20; 7 d:1.07 ±0.08)and BDNF mRNA(3 d:2.82±0.20; 7 d:1.07 ±0.19)were increased at d 3 and d 7,as compared with those of the normobaric air therapy group(NGF 3 d:0.66 ±0.10,7 d:0.73 ±0.07); (BDNF 3 d:1.51 ±0.11; 7 d:0.65±0.09),with statistical significances (P ＜ 0.05).Conclusions HBO therapy could promote cognitive function in rats with traumatic brain injury,the possible mechanism might be associated with the increases in NAA/Cr and NAA/Ch levels and the levels of NGF and BDNF mRNA in hippocampus. Key words: Traumatic brain injury;  Hyperbaric oxygen;  Magnetic resonance spectroscopy; Nerve growth factor;  Brain-derived neurotrophic factor;  Rats