Ischemia and reperfusion-induced nuclear and nucleolar changes of the lumbosacral dorsal root ganglia neurons were studied in a spinal cord ischemic model of a rabbit. Twenty and forty min abdominal aorta ligation followed immediately by perfusion fixation, 20 min abdominal aorta ligation followed by 1 h of normoxic reoxygenation and 20 min abdominal aorta ligation followed by 1 h of graded postischemic reoxygenation were tested. In animals subjected only to a 20 and 40 min aorta ligation irregularly undulated nuclear membrane and occurrence of dark osmiophilic dense clumps often located close to interchromatin granules were found. The segregation of the nucleolar granular and fibrillar components became apparent but fibrillar centers were almost completely absent. In animals subjected to 20 min ligation followed by 1 h of normoxic reoxygenation a high number of dense clumps, loosely disseminated throughout the nucleoplasm was detected along with almost complete fragmentation and segregation of the nucleolus. The application of the graded postischemic reoxygenation has proven effective as a neuroprotective and antisegregatory adjunct whereby the nucleolar fibrillar and granular components regained almost normal appearance, and the occurrence of dense intranuclear clumps was greatly reduced.