A histopathologic study of spinal cord ischemia using an isohistogenic rat upper-half-body transplantation model. To study the histopathologic changes of spinal cords exposed to long-duration complete ischemia, the authors developed an upper-half-body transplantation model of inbred rat. In this model, an infant Lewis rat is transplanted to the inguinal region of another adult Lewis rat using microsurgical vascular anastomosis. Even when 2-week-old donor rats were exposed to complete ischemia for 90 minutes, functions of the spinal cord were comparatively preserved. In histopathologic observations, degeneration proportional to complete ischemia duration was noted. In the 60-minute ischemia group of 2-week-old donor rats, however, no substantial differences from normal spinal cord were observed. Under conditions of equal ischemia duration, it appeared the younger animal had the greater ischemic tolerance. 