Establishment of a local cooling model against spinal cord ischemia representing prolonged induction of heat shock protein

Objectives: Paraplegia is one of the serious complications of thoracoabdominal aortic operations. Regional hypothermia protects against spinal cord ischemia although the protective mechanism remains unknown. We attempted to create a simple model of local cooling under transient spinal cord ischemia and evaluated the effect using functional and histologic findings. Methods: Male domesticated rabbits were divided into 3 groups: control, normothermic group (group N), and local hypothermic group (group H). A balloon catheter was used for spinal cord ischemia by abdominal aortic clamping. A cold pack attached to the lumbar region could lower the regional cord temperature initially. Neurologic function was evaluated by the Johnson score. Cell damage was analyzed by observing motor neurons with the use of hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated deoxy-uracil triphosphate biotin in situ nick end labeling (TUNEL), and immunoreactivity of heat shock protein. Results: Physiologic estimation showed that local hypothermia improved the functional deficits (group N, 1.3 ± 0.9; group H, 4.9 ± 0.3; P = .0020). Seven days after reperfusion, there was a significant difference in the motor neuron numbers between groups N and H (group N, 7.2 ± 1.9; group H, 20.4 ± 3.2; P = .0090). The number of TUNEL-positive motor neurons was reduced significantly (group N, 7.2 ± 2.4; group H, 1.0 ± 0.7; P = .0082). Heat shock protein immunoreactivity was prolonged up to 2 days after reperfusion in the hypothermic group. Conclusions: These results suggest that local hypothermia extended the production of heat shock protein in spinal cord motor neurons after reperfusion and inhibited their apoptotic change.