CELL-DEATH SUGGESTIVE OF APOPTOSIS AFTER SPINAL-CORD ISCHEMIA IN RABBITS

Background and Purpose After spinal cord ischemia, some neurons remain viable after an ischemic insult but may be at risk of dying during re perfusion. We searched for morphological and biochemical features of a poptosis, which is a mechanism of delayed neuronal death, in a rabbit model of spinal cord ischemia. Methods The infrarenal aorta of White N ew Zealand rabbits (n=24) was occluded for 40 minutes using a loop tou rniquet. Rabbits were killed after 12, 24, or 48 hours (n=8 per group) . The loop was placed but never tightened in sham-operated rabbits (n= 6). The lumbar segment of the spinal cord (L5 to L7) was used for morp hological studies, including hematoxylin and eosin staining and a modi fied terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick en d-labeling (TUNEL) staining method. Electron microscopy was used to ex amine ultrastructural morphology. In addition, lumbar tissue was used for biochemical investigation of DNA laddering by agarose gel electrop horesis. Results After ischemia, the affected areas contained neurons with positive TUNEL staining. Positive neurons were located in laminae III to IX, although most were concentrated in the intermediate and ve ntral areas. Adjacent sections stained with hematoxylin and eosin exhi bited ischemic cell changes (red and ghost neurons), while apoptotic b odies were also apparent. In addition, electron microscopy of ischemic tissue samples exhibited ultrastructural characteristics of apoptosis , including nuclear condensation and relatively normal organelle morph ology. Finally, isolated DNA revealed a ladder on agarose gel electrop horesis, indicating DNA fragmentation into approximate to 180 multiple s of base pairs. Conclusions Spinal cord ischemia in rabbits induces m orphological and biochemical changes suggestive of apoptosis. These da ta raise the possibility that apoptosis contributes to neuronal cell d eath after spinal cord ischemia.