Hyperbaric oxygen therapy improves spatial learning and memory in a rat model of chronic traumatic brain injury

In the present experiment we use a rat model of traumatic brain injury to evaluate the ability of low-pressure hyperbaric oxygen therapy (HBOT) to improve behavioral and neurobiological outcomes. The study employed an adaptation of the focal cortical contusion model. 64 Male Long–Evans rats received unilateral cortical contusion and were tested in the Morris Water Task (MWT) 31–33 days post injury. Rats were divided into three groups: an untreated control group (N = 22), an HBOT treatment group (N = 19) and a sham-treated normobaric air group (N = 23). The HBOT group received 80 bid, 7 days/week 1.5 ATA/90-min HBOTs and the sham-treated normobaric air group the identical schedule of air treatments using a sham hyperbaric pressurization. All rats were subsequently retested in the MWT. After testing all rats were euthanized. Blood vessel density was measured bilaterally in hippocampus using a diaminobenzadine stain and was correlated with MWT performance. HBOT caused an increase in vascular density in the injured hippocampus (p < 0.001) and an associated improvement in spatial learning (p < 0.001) compared to the control groups. The increased vascular density and improved MWT in the HBOT group were highly correlated (p < 0.001). In conclusion, a 40-day series of 80 low-pressure HBOTs caused an increase in contused hippocampus vascular density and an associated improvement in cognitive function. These findings reaffirm the clinical experience of HBOT-treated patients with chronic traumatic brain injury.