Development of new assessment for exercise intensity from the view point of brain activation; from brain lactate and hormone in rats with treadmill running.

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Exercise enhances neurogenesis, learning and cognitive function, but it is unknown what kind of exercise would be suit for enhancing brain fitness. To address this, we investigated that how the neurons in rat hippocampus/hypothalamus would be activated during exercise in response to its intensity by monitoring the brain lactate and hormones during treadmill running. Brain lactate is released from astrocytes to extracellular compartment when neuronal activation is occurred, and its increase is considered as the indicator of neuronal activation. First, we established the treadmill running model of rats by estimating LT (Lactate Threshold) as a criterion. In our model, LT was about 15 m/min. The change in lactate level in the hippocampus/hypothalamus during treadmill running was measured by on-line microdialysis which had been established by Takita et al. (1992). The lactate level in hippocampus during a graded treadmill running increased with speed-dependent manner. During a fixed low speed running (10 m/min), the lactate level in hippocampus also increased from on set of running, and became plateou. Pretreatment of sodium channel blocker, TTX (tetrodotoxin, 10 μM), or glutamate uptake inhibitor, PDC (pirrolidine-2-4-dicarboxylate, 1mM) completely blocked the change in hippocampal lactate during a fixed speed. running. The changes of lactate level in hypothalamus were similar as these in the hippocampus. These results suggest that hippocampal neurons could activate with running with speed-dependent manner, though low intensity (below the LT) of exercise. This study suggests the possibility that low intensity exercise would enhance brain fitness.