EFFECTS OF SUPRACHIASMATIC LESIONS ON CIRCADIAN-RHYTHMS OF BLOOD-PRESSURE, HEART-RATE AND LOCOMOTOR-ACTIVITY IN THE RAT

To determine whether the circadian rhythms in blood pressure (BP), hea rt rate (HR) and locomotor activity are controlled by an internal biol ogical clock located in the suprachiasmatic nucleus (SCN), we continuo usly measured these parameters in SCN-lesioned rats using a newly deve loped implantable radiotelemetry device and a computerized data collec ting system. Although SCN-lesioned rats showed a weak but significant 24-h periodicity in BP and HR under light-dark (LD) cycles, BP, HR and locomotor activity became completely aperiodic under constant dark (D D) conditions. The amount of locomotor activity was significantly redu ced in SCN-lesioned rats compared to that in intact rats. BP tended to be higher in SCN-lesioned rats, but the differences were significant only in the comparison of systolic blood pressure (SEP) under LD and D D (p<0.05) and of mean blood pressure (MBP) under LD (p<0.05). HR in S CN-lesioned rats was significantly lower under LD (p<0.05), but not un der DD. The standard deviation and the variation coefficient of MBP, a s indices of short-term variability of this parameter, were significan tly larger in SCN-lesioned rats than in intact rats, while those of HR and locomotor activity did not differ significantly between SCN-lesio ned and intact rats. These results indicate that the SCN is important not only for generating circadian rhythms of BP, HR and locomotor acti vity, but also for buffering the short-term variability of BP in rats.