Continuous recordings of brain regional circulation during sleep/wake state transitions in rats.

Continuous measurement of regional blood flow (RBF) in the brain of a freely behaving rat was attained by a combination of laser-Doppler (LD) flowmetry and our originally devised apparatus, which had been developed for the automatic releasing of the twisting of lines connected between experimental apparatus and the freely behaving animal. RBF changes were studied in a ventral region of the rostral basal forebrain along with sleep-wake states. When compared with the RBF level during slow-wave sleep (SWS), levels of RBF during paradoxical sleep (PS) and wakefulness were higher by 24 (P = 0.0001) and 9% (P < 0.05), respectively. The LD signals suggested that the RBF elevation during PS was produced by dilation of both the large brain arteries and small vessels, whereas the elevation during wakefulness was caused by dilation of small vessels that was counteracted by contraction of large arteries. It was noticed that the original circulation tended to begin changing before the onset of SWS. A circadian rhythm was also demonstrated for the RBF, which largely decreased around the onset of the light period and returned to the high level before the beginning of the dark period. Thus continuous and real-time recordings of regional circulation were performed with satisfactorily precision in freely behaving rats.