Influence of graded postischemic reoxygenation on reperfusion alterations in rabbit dorsal root ganglion neurons

Ultrastructural postischemic changes in the rabbit dorsal root ganglion (DRG) neurons were studied after 20 min infrarenal aortic occlusion followed by normoxic or graded postischemic reoxygenation (GPIR) with survival times ranging from 1 to 4 days. After normoxic reoxygenation with 1 day survival, in A-type neurons a dispersal of Nissl bodies and nuclear changes characterized by crenated nuclear membrane, chromatin condensation and increased density of karyoplasm were observed. After 2 days of reperfusion, alterations of B-type neurons became more pronounced. Their nuclei contained numerous myelinoid bodies and the nucleoli showed an apparent sequestration of the nucleolonema. At 4 days postischemia, degenerating extensively vacuolated B-cells were frequently seen. Graded reoxygenation achieved by the blood pO2 hypotension and its gradual increase during early reperfusion phase (30 min) had a significant neuroprotective effect, as indicated by morphological and quantitative analysis showing a good preservation of cytoplasmic and nuclear structures in both types of neurons which were evident even 4 days postischemia. The changes are discussed in relation with the effect of tissue hyperoxia during early reperfusion and its involvement in the development of ischemic neuronal injury.