Endoplasmic reticulum stress induced in motor neurons by transient spinal cord ischemia in rabbits

Objective: The mechanism of spinal cord injury has been thought to be related to the vulnerability of spinal motor neuron cells against ischemia. However, the mechanisms of such vulnerability are not fully understood. Because we previously reported that spinal motor neurons were probably lost as the result of programmed cell death, we investigated a possible mechanism of neuronal death by immunohistochemical analysis for Grp78 and caspase12. Methods: We used a rabbit spinal cord ischemia model with a balloon catheter. The spinal cord was removed at 8 hours or 1, 2, or 7 days after 15 minutes of transient ischemia. Histologic changes were studied with hematoxylin-eosin staining. Western blot analysis for Grp78 and caspase12, temporal profiles of Grp78 and caspase12 immunoreactivity, and double-label fluorescence immunocytochemical studies were performed. Results: The majority of motor neurons were preserved for 2 days but were selectively lost at 7 days of reperfusion. Western blot analysis revealed scarce immunoreactivity for Grp78 and caspase12 in the sham-operated spinal cords. However, immunoreactivity for Grp78 and caspase12 became apparent at 8 hours after transient ischemia, which returned to the baseline level at 1 day. Double-label fluorescence immunocytochemical study revealed that both Grp78 and caspase12 were positive at 8 hours of reperfusion in the same motor neurons that eventually die. Conclusion: This study demonstrated that immunoreactivities for both Grp78 and caspase12 were induced in the same motor neuron that eventually dies. These results suggest that endoplasmic reticulum stress was induced in motor neurons by transient spinal cord ischemia in rabbits.