Control of brain temperature during experimental global ischemia in rats

Temperature control during experimental ischemia continues to be of major i nterest. However, if exposure of brain tissue is necessary during the exper iment, regional heat loss may occur even when the core temperature is maint ained. Furthermore, valid non-invasive brain temperature monitoring is diff icult in small rodents. This paper describes a method for both monitoring a nd maintenance of brain temperature during small animal preparations in a s tereotaxic frame. The device used includes an ear-bar thermocouple probe an d a small near-infrared radiator. The new equipment permitted to maintain p eri-ischemic brain temperature at a desired level while carrying out non-in vasive continuous recordings of cerebral blood flow (laser Doppler-flowmetr y) and of electrical brain function (EEG). In contrast, without extracrania l heat application, superficial and basal brain temperatures decreased duri ng global cerebral ischemia by 4.1 +/- 0.1 and 4.6 +/- 0.4 degrees C (mean +/- SEM), respectively, returning to baseline values at 15-30 min of reperf usion while rectal (core) temperature remained stable at baseline values. T he ear-bar thermocouple probe (tympanic membrane) reliably reflected basal brain temperature, and temperature in superficial brain areas correlated we ll with that in the temporal muscle. Our data show that the new system allo ws to exclude unwanted hypothermic neuroprotection, and does not interfere with optical and electrical measurement techniques. (C) 1999 Elsevier Scien ce B.V. All rights reserved.