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Relationship between hippocampal neuron activity and regional cerebral blood flow during sleep‐wake cycle in rats

The present study was designed to study neurovascular coupling in the hippocampus during sleep‐wake cycle. Wistar male rats were instrumented chronically with multiple electrodes (100 micro‐meter stainless steal wire) for the measurement of the hippocampal CA1 neuron activity and bipolar electrodes for measurement of electroencephalogram (EEG) and electromyogram (EMG). In a separate group, rats were instrumented chronically with a laser‐Doppler flow probe made with a pair of glass fiber (0.25mm outer diameter) in the CA1 region of the hippocampus, and EEG and EMG electrodes. The mean value of the CA1 neuron activity was lowest during REM sleep compared with the other behavioral states including non‐REM sleep, quiet awake, moving, grooming states while the CA1 neuron activity was highest during moving states. However, the mean value of the local cerebral blood flow in the CA1 region of the hippocampus was the highest during REM sleep compared with other behavioral states. These data suggest that neurovascular coupling was modified in behavioral state‐dependent manner. Thus, regional cerebral blood flow in the hippocampus does not always represent changes in neuron activity during sleep‐wake cycle in rats.