Effect of selective brain hypothermia on regional cerebral blood flow and tissue metabolism using brain thermo-regulator in spontaneously hypertensive rats

To investigate the effect of selective hypothermia of the brain (brain cool ing) on regional cerebral blood flow and tissue metabolism, we have develop ed a brain thermo-regulator. Brain temperature was modulated by a water-coo led metallic plate placed on the surface of the rats' scalp to get the appr opriate brain temperature precisely with ease. Regional cerebral blood flow and brain temperature were measured simultaneously using a Teflon-coated p latinum electrode and thermocouple probe inserted stereotaxically into the parietal cortex and thalamus in spontaneously hypertensive rats. Experiment al forebrain ischemia was induced by the occlusion of bilateral common caro tid artery under normo- and hypothermic brain condition, and the supratento rial brain tissue metabolites were measured enzymatically after 60 min of f orebrain ischemia. When cortical temperature was set to hypothermia, cortic al blood flow was significantly lowered by 40% at 30 degrees C and 20% at 3 3 degrees C as compared with that at 36 degrees C (p < 0.0001 and p < 0,05, respectively), Thalamic blood flow was also significantly reduced by 20% w hen cortical temperature was set to 30 degrees C as compared with 36 degree s C (p < 0.05). There were no significant differences in arterial blood pre ssure and gas parameters throughout these experiments. In the rats with sel ective brain hypothermia (30 degrees C) immediately after the induction of cerebral ischemia, the level of brain ATP concentration after 60 min of isc hemia was significantly higher than that in normothermia rats (36 degrees C ) (p < 0.05). Our findings indicate that: 1) the metallic plate brain therm o-regulator is useful in small animal experiments; 2) regional brain temper ature regulates regional cerebral blood flow; and 3) selective brain hypoth ermia, even started after the forebrain ischemia, ameliorates the derangeme nt of brain metabolism, suggesting its effectiveness as a cytoprotective st rategy.