Effect of graded hypothermia (27 degrees to 34 degrees C) on behavioral function, histopathology, and spinal blood flow after spinal ischemia in rat.

Abstract

We used a rat model of reversible spinal ischemia to assess the effect of spinal cord temperature on the development of neurological and histopathologic changes after 20 minutes of reversible aortic occlusion. Spinal cord blood flow and CO2 reactivity was tested by using laser Doppler before and 60 minutes after ischemia. In halothane (1%)-anesthetized rats, the spinal cord temperature as assessed by using thermocouple in the paraspinal muscles was lowered to 34 degrees, 31 degrees, or 27 degrees C. After ischemia, spinal cord temperature was raised to 37 degrees C for the next 30 minutes. Animals were maintained in this normothermic condition for 8 hours, after which motor and sensory function were assessed. All animals were then anesthetized and perfused with 10% formalin for light microscopic analysis of spinal cords. In normothermic animals, 20 minutes of ischemia resulted in a loss of CO2 reactivity and hind limb paraplegia with an attendant allodynia that persisted for the 8 hours of reperfusion. Even mild (34 degrees C) hypothermia resulted in significant improvement of neurological function compared with the normothermic group. In paraplegic animals, lumbosacral interneuronal pools localized primarily in laminae III through VII displayed heavy argyrophilic neurons and areas of localized necrosis. In moderate and deep hypothermic animals preservation of CO2 responsivity and complete recovery of neurological function were seen with no detectable histopathologic changes. These results show that a slight decrease in spinal cord temperature in the peri-ischemic period provides significant protection as measured by histopathology and neurological function.