Effect of different programs of hyperbaric oxygen preconditioning on spinal cord ischemia- reperfusion injury in rabbits

Objective To investigate the effect of different programs of preconditioning with hyperbaric oxygen (HBO) on spinal cord ischemia-reperfusion injury (I/R) in rabbits. Methods Forty-five New Zealand rabbits aged 4-5 months weighing 2.0-2.5 kg were randomly divided into 5 groups: group S, sham operation ( n = 5);group IR, spinal cord I/R injury (n = 10);group H_(1～3) , the animals were pretreated with 100% O_2 at 2.5 ATA 1 h/d for 5 (group H_1 ), 10 (group H_2 ) , or 20 (group H_3 ) consecutive days respectively 24 h before spinal cord I/R. The animals were anesthetized with iv pentobarbital sodium 30 mg/kg. The artery in the ear and left femoral artery were cannulated for proximal and distal mean blood pressure monitoring. Spinal cord ischemia was produced by cross-clamping of abdominal aorta distal to renal artery for 20 min. Hind-limb motor function was assessed at 48 h after reperfusion according to the modified criteria established by Tarlov (0 = no spontaneous movement, 4= normal motor function) . The animals were then killed and the L_5 segment of the spinal cord was removed for detection of neuronal survival (by HE staining), apoptosis (by TUNEL) and degeneration (by Fluoro-Jade B staining). Results Preconditioning with 5 or 10 d of HBO improved the hind-limb motor function and preserved more normal neurons in the spinal cord after I/R injury. Both apoptotic and degenerative cell death were attenuated in H_1 and H_2 groups. There was no significant difference in hind-limb motor dysfunction and the number of normal neurons in the lumbar spinal cord between H_3 group and I/R group. Conclusion Preconditioning with 5 d or 10 d HBO induces tolerance against spinal cord I/R injury, whereas preconditioning with 20 d of HBO fails to protect the spinal cord from I/R injury. Key words: Hyperbaric oxygenation; Ischemic preconditioning; Reperfusion injury; Spinal cord