Protection of mitochondrial function and improvement in cognitive recovery in rats treated with hyperbaric oxygen following lateral fluid-percussion injury

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Hyperbaric oxygen (HBO2) has been shown to improve outcome after severe traumatic brain injury, but its underlying mechanisms are unknown. Following lateral fluid-percussion injury (FPI), the authors tested the effects of HBO2 treatment as well as enhanced normobaric oxygenation on mitochondrial function, as measured by both cognitive recovery and cellular adenosine triphosphate (ATP) levels.


Adult male Sprague–Dawley rats were subjected to moderate lateral FPI or sham injury and were allocated to one of four treatment groups: 1) FPI treated with 4 hours of normobaric 30% O2; 2) FPI treated with 4 hours of normobaric 100% O2; 3) FPI treated with 1 hour of HBO2 plus 3 hours of normobaric 100% O2; and 4) sham-injured treated with normobaric 30% O2. Cognitive outcome was assessed using the Morris water maze (MWM) on Days 11 to 15 after injury. Animals were then killed 21 days postinjury to assess hippocampal neuronal loss. Adenosine triphosphate was extracted from the neocortex and measured using high-performance liquid chromatography. The results showed that injured animals treated with HBO2 or normobaric 100% O2 alone had significantly higher levels of cerebral ATP as compared with animals treated using normobaric 30% O2 (p ≤ 0.05). The injured animals treated with HBO2 had significant improvements in cognitive recovery, as characterized by a shorter latency in MWM performance (p ≤ 0.05), and decreased neuronal loss in the CA2/3 and hilar regions as compared with those treated with 30% or 100% O2 (p ≤ 0.05).


Both hyperbaric and normobaric hyperoxia increased cerebral ATP levels after lateral FPI. In addition, HBO2 treatment improved cognitive recovery and reduced hippocampal neuronal cell loss after brain injury in the rat.

Abbreviations used in this paper:ADP = adenosine diphosphate; AMP = adenosine monophosphate; ANOVA = analysis of variance; ata = atm absolute; ATP = adenosine triphosphate; DHR = dihydrorhodamine 123; FPI = fluid-percussion injury; HBO2 = hyperbaric oxygen; HPLC = high-performance liquid chromatography; ICP = intracranial pressure; MWM = Morris water maze; NAD = nicotinamide adenine dinucleotide; NADH = reduced form of nicotinamide adenine dinucleotide; ROS = reactive oxygen species; SEM = standard error of the mean; TBI = traumatic brain injury.

Article Information

Address reprint requests to: M. Ross Bullock, M.D., Ph.D., Department of Neurosurgery, Medical College of Virginia, Virginia Commonwealth University, 1200 East Broad Street, West Hospital 8 South, Richmond, Virginia 23298-0631. email: address for Dr. Daugherty: Department of Neurosurgery, Mayo Clinic, Rochester, Minnesota.

© AANS, except where prohibited by US copyright law.



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    Bar graph demonstrating cerebral ATP, ADP, AMP, and NAD+ levels 1 hour after FPI and hyperoxia treatment. The ATP level in injured animals breathing 30% O2 is significantly reduced compared with levels in sham-injured animals (*p ≤ 0.05, four rats from each treatment group). The ATP level is significantly increased in injured animals treated with hyperoxia compared with the level in animals breathing 30% O2 (#p ≤ 0.05, four rats from each treatment group). The ADP level is significantly reduced in injured animals breathing 30% O2 compared with the level in sham-injured animals (*p ≤ 0.05). The AMP level is also significantly reduced in the 100% O2–treated group compared with that in sham-injured animals (*p ≤ 0.05) and is significantly reduced in both the HBO2- and the 100% O2–treated groups compared with that in the animals breathing 30% O2 (#p ≤ 0.05). The NAD+ level is significantly reduced in the injured animals breathing 30% O2 compared with that in the sham-injured animals (*p ≤ 0.05).

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    Line graph depicting the effect of O2 treatment on MWM performance following TBI. The MWM test was performed on Days 11 to 15 post-FPI. All three injured animal groups had a significantly longer latency period compared with the sham-injured animals (*p ≤ 0.05, 10 rats for each group). The HBO2-treated group took a significantly shorter time to find and mount the hidden platform than the 100% O2– and 30% O2–treated groups of injured animals on all days tested (#p ≤ 0.05). The 100% O2–treated group had a significantly shorter latency compared with the 30% O2–treated group of injured animals (+p ≤ 0.05). Data are expressed as the means ± SEMs.

  • View in gallery

    Bar graph demonstrating neuronal cell counts in the CA2/3 region of the ipsilateral hippocampus. Both 100% O2– and 30% O2–treated groups of injured animals had significant neuronal cell loss compared with the sham-injured group (*p ≤ 0.05). The HBO2-treated group had significantly less neuronal cell loss compared with both the 100% O2– and 30% O2–treated groups of animals (#p ≤ 0.05). Data are expressed as the means ± SEMs.

  • View in gallery

    Bar graph showing neuronal cell counts in the hilar region of the ipsilateral hippocampus. All three injured animal groups had significant neuronal cell loss compared with the sham-injured group (*p ≤ 0.05). The HBO2-treated group had significantly less neuronal cell loss than the 30% O2–treated injured animals (#p ≤ 0.05). Data are expressed as the means ± SEMs.


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