DIURNAL-VARIATION OF CEREBRAL BLOOD-FLOW IN RAT HIPPOCAMPUS

We measured local cerebral blood flow over 24 hours in 10 unanesthetized, freely moving rats to determine whether blood flow in the hippocampus fluctuated as a function of time of day. We measured hydrogen clearance at 1-hour intervals using a polyurethane-coated platinum electrode with a 1-mm bare tip implanted in the dorsal hippocampus. Individual rats displayed a wide range of local cerebral blood flow values (from 30 to 100 ml/min/100 g tissue) in a day. In seven of the 10 rats, the overall mean hippocampal blood flow for the dark cycle (7PM-5 AM) was significantly (p<0.001, 0.01, or 0.05) greater than that for the light cycle (6 AM-6 PM), showing an average increase of 20%. Further, the maximum mean hippocampal blood flow at 11 PM in all 10 rats was 42% greater than the minimum at noon. Our study demonstrates for the first time that local cerebral blood flow in the hippocampus shows diurnal variation. © 1990 American Heart Association, Inc.