Increased cerebral activity suppresses baroreflex control of heart rate in freely moving mice

We assessed whether increased cerebral activity suppressed baroreflex control of heart rate (HR) and, if so, whether this occurred prior to the onset of locomotion in daily activity of mice. We measured mean arterial pressure (MAP, arterial catheter), cerebral blood flow in the motor cortex (CBF, laser-Doppler flowmetry), and electroencephalogram in free-moving mice (n = 8) during 12 daytime hours. The contribution of baroreflex control of HR to MAP regulation was determined during a total resting period for similar to 8 h from the cross-correlation function (R(t)) between spontaneous changes in HR (delta HR) and MAP (delta MAP) every 4 s and the sensitivity was determined from delta HR/delta MAP where R(t) was significant (P < 0.05). The power density ratio of theta to delta wave band in electroencephalogram (theta/delta), determined every 4 s as an index of cerebral activity, was positively correlated with CBF during 73 +/- 3% of the total resting period (P < 0.05) and with R(t) during 59 +/- 2% (P < 0.05). When each measurement during the resting period was divided into seven bins according to the level of theta/delta, CBF was 91 +/- 2% in the lowest bin and 118 +/- 3% in the highest bin (P < 0.001), R(t) was -0.69 +/- 0.06 and -0.27 +/- 0.04 (P < 0.001) and delta HR/delta MAP (beats min-1 mmHg-1) was -12.4 +/- 0.9 and -7.5 +/- 0.9 (P < 0.001), respectively, with significant correlations with theta/delta (all P < 0.002). Moreover, mice started to move in similar to 30 sec after the sequential increases of theta/delta and R(t), mice started to move at 5 times higher probability than after a given time, followed by a rapid increase in MAP by similar to 10 mmHg. These results suggest that increased cerebral activity suppresses baroreflex control of HR and this might be related to the start of voluntary locomotion with a rapid increase in MAP.