Functional Activation of Cerebral Blood Flow and Metabolism before and after Global Ischemia of Rat Brain

The effect of somatosensory stimulation on the local CBF (LCBF), CMRglu (LCMRglu), tissue pH, and tissue content of ATP, glucose, and lactate was studied in chloralose-anesthetized rats before and after 30 min of near-complete forebrain ischemia. In nonischemic rats LCBF in primary somatosensory cortex increased by 33%, LCMRglu increased by 55%, tissue glucose content decreased by 21%, and lactate increased by 30%. Local ATP and tissue pH did not change. Functional activation of the intact chloralose-anesthetized rat, in consequence, is associated with the stimulation of "aerobic" glycolysis but does not result in disturbances of energy or acid-base homeostasis. After 30-min ischemia and 3-h recirculation, somatosensory stimulation did not evoke any metabolic or hemodynamic alterations, although EEG and primary somatosensory evoked potentials recovered. The maintenance of normal energy state despite constant metabolic rate suggests that the postischemic generation of evoked potentials does not require measurable amounts of energy. Stimulation of glycolysis in the intact animal, therefore, may serve other purposes than fueling the energy requirements of evoked cortical activity.