Methodological Requirements for Accurate Measurements of Brain and Body Temperature during Global Forebrain Ischemia of Rat

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Abstract
The methodological requirements for accurate measurements of brain and body temperature during brain ischemia have been validated in Wistar rats submitted to 30 min of four-vessel occlusion. During ischemia, brains were exposed to three different temperature profiles: Spontaneous cooling from 36 to 31°C ( n = 10), constant hypothermia at 30°C ( n = 19), and constant normothermia at 36°C ( n = 21). Direct and indirect brain temperature recordings were carried out by placing fine thermocouples (200 μm diameter) into the striate nucleus, the temporal muscle, and the epidural space. Body temperature was measured with a flexible thermocouple inserted at various depths into the rectum. Accurate measurements of body temperature required insertion of the rectal probe to a depth of at least 6 cm; lesser insertion resulted in an underestimation of up to 6°C. Accurate estimates of brain temperature were obtained in all three experimental conditions by recording of the epidural temperature. The temperature in the temporal muscle, by contrast, differed from the brain temperature by up to 2°C, depending upon the experimental condition and the duration of ischemia. We therefore suggest that indirect measurements of brain temperature during ischemia are carried out in the epidural space in order to avoid misinterpretations of temperature-sensitive pathological changes.