The neuroprotective effect of hyperbaric oxygen therapy at different times after spinal cord injury

Objective To investigate the neuroprotective effect of hyperbaric oxygen therapy at different times after spinal cord injury. Methods A total of 60 Sprague-Dawley rats were randomly divided into a normal group (n=12), a spinal cord injured (SCI) group (n=12) and a hyperbaric oxygen (HBO) group (n=36). The HBO group was further subdivided into an HBO-8 h group, an HBO-48 h group and an HBO-1 w group with 12 rats in each. Spinal cord injury was modelled in the SCI and HBO groups. Hyperbaric oxygen therapy was administered once daily for 12 days to the 3 HBO subgroups, beginning 8 h, 48 h and one week after establishment of the SCI. At the end of the HBO therapy the rats were assessed in terms of Basso-Beattie-Bresnahan (BBB) movement function score and motor evoked potentials (MEP) before being sacrificed for sampling of spine and serum to detect iNOS mRNA and NO expression. The expression of iNOS mRNA was measured using a reverse transcriptase polymerase chain reaction, the synthesis of iNOS in the injured spinal cord tissue was detected by immunohistochemical methods and the content of NO was measured by colorimetry. Results Compared with the other subgroups and with the SCI group, the HBO-48 h group had significantly decreased expression of iNOS mRNA, iNOS and NO. The standard BBB score in the HBO-48 h group was significantly higher than in the other groups, on average. Moreover, in the HBO-48 h group MEP latency was shorter, while the average MEP amplitude was significantly higher than in the SCI group or the other HBO subgroups. Conclusion HBO therapy beginning 48 h after SCI has the best neuroprotective effects, at least in rats. The mechanism may be related to decreased expression of iNOS in the mRNA-iNOS-NO signal pathway. Key words: Hyperbaric oxygenation; Spinal cord injury; Neuroprotection