Background
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It was proved that higher haematocrit (Hct) might improve the function of brain after hypothermia circulation arrest (HCA). In the present study we develop a new rat HCA model and investigate whether retrograde cerebral perfusion of oxygenated compacted red blood cells (RBC) could attenuate the brain injury after HCA.

Methods
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A new rat HCA model was developed. Forty-eight rats were randomly distributed into three groups: HCA alone group, HCA combined with retrograde perfusion oxygenated compacted red blood cell group (HCArcp group), and sham operation group (sham op group); 16 rats in each group. All experimental group animals underwent HCA for 90 min at 18°C. We evaluated the brain injury after HCA with the light microscopy and electron microscopy. By the immunohistochemistry and RT-PCR techniques we measured the different expression of the C-Fos, Bcl-2, Bax mRNA and protein between groups. Additionally we measured the wet/dry ratio of the brain in order to evaluate the edema degree after HCA.

Results
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The new HCA model of the rat we developed was comparable with the clinical setting not only in terms of the intubation and anesthesia method and materials employed, but also in terms of the priming capacity in relation to body weight. The numbers of degeneration and necrosis neurons in the hippocampus CA1 and parietal cortex but not in the thalamus of the HCA alone group were significantly greater than those of the HCArcp group (*P*\< 0.05). The mean score of mitochondrion of the hippocampus CA1 in the HCA alone group was significantly higher than that of the HCArcp group (*P*\< 0.05). The expression of C-Fos, Bax mRNA and protein in hippocampus CA1 and/or parietal cortex area was higher in the HCA alone group than that of the HCArcp group (*P*\< 0.05). Expression of the mRNA and protein of Bcl-2 was higher in the HCArcp group than that of the HCA alone group (*P*\< 0.05). The degree of edema after HCA between the two experiment groups had no significant difference (*P*\> 0.05).

Conclusion
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We made a new rat model of HCA comparable with the clinical setting. Retrograde cerebral perfusion of oxygenated compacted RBC is a safe and effective method to protect the brain during HCA. Adjusting the gene expression related with apoptosis might contribute to the neuroprotective effects of retrograde oxygenated compacted RBC.
