www.elsevier.com/locate/brainres Available online at www.sciencedirect.com Research Report The effects of hyperbaric air and hyperbaric oxygen on blood–brain barrier integrity in rats Nihal Gunes Cevik a , Nurcan Orhan b , Canan Ugur Yilmaz c , Nadir Arican d , Bulent Ahishali e , Mutlu Kucuk c , Mehmet Kaya f,n , Akin Savas Toklu a a Department of Underwater and Hyperbaric Medicine, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey b Department of Neuroscience, The Institute of Experimental Medicine, Istanbul University, Istanbul, Turkey c Department of Laboratory Animal Biology and Biomedical Application Techniques, The Institute of Experimental Medicine, Istanbul University, Istanbul, Turkey d Department of Forensic Medicine, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey e Department of Histology and Embryology, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey f Department of Physiology, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey article info Article history: Accepted 29 July 2013 Available online 3 August 2013 Keywords: Hyperbaric air Hyperbaric oxygen Blood–brain barrier Evans blue Horseradish peroxidase Occludin Aquaporin 4 abstract Hyperbaric oxygen (HBO) treatment yields conflicting results on blood–brain barrier (BBB) integrity under various pathological conditions and the effects of HBO on healthy brain is poorly understood. In this experimental study, the effects of HBO on BBB integrity were investigated in comparison with hyperbaric air (HBA) in intact rats. Four sessions of HBA or HBO were applied to intact rats in 24 h. BBB integrity was functionally and structurally evaluated by determining extravasation of Evans blue (EB) dye and horseradish peroxidase (HRP) tracers. In immunohistochemical evaluation, relative staining intensity for occludin, a tight junction (TJ) protein, and aquaporin 4 (AQP4), a water-channel protein, was detected in the barrier type of microvessels of brain by image analysis. BBB permeability to EB dye significantly increased in animals in HBO treatment group compared to those in HBA and control groups (po0.05). The immunoreactivity of occludin, a tight junction protein, remained essentially unaltered in capillaries of hippocampus in all groups. In animals exposed to HBO, AQP4 immunoreactivity significantly increased in parietal cortex com- pared to those in HBA and control groups (po0.01). Ultrastructurally, frequent vesicles containing HRP reaction products were observed in capillary endothelial cells in cerebral cortex and hippocampus of rats subjected to both HBA and HBO. Our results indicate that the HBO administration to intact rats increased BBB permeability to both EB and HRP while HBA increased only HRP extravasation in these animals. The results of this study suggest that HBA also impairs the BBB integrity in intact rats as well as HBO. & 2013 Elsevier B.V. All rights reserved. 0006-8993/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.brainres.2013.07.052 n Corresponding author. Fax:+90 212 532 41 71. E-mail addresses: mehkaya@istanbul.edu.tr, mkaya942@gmail.com (M. Kaya). brainresearch 1531 (2013)113–121