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

Abstract

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 ∼8 h from the cross-correlation function (R(t)) between spontaneous changes in HR ( HR) and MAP ( MAP) every 4 s and the sensitivity was determined from HR/ MAP where R(t) was significant (P < 0.05). The power density ratio of θ to δ wave band in electroencephalogram (θ/δ), 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 θ/δ, 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 HR/ MAP (beats min −1 mmHg −1 ) was −12.4 ± 0.9 and −7.5 ± 0.9 (P < 0.001), respectively, with significant correlations with θ/δ (all P < 0.002). Moreover, mice started to move in ∼30 sec after the sequential increases of θ/δ 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 ∼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. Abbreviations CBF, cerebral blood flow; EEG, electroencephalogram; HR, heart rate; MAP, mean arterial pressure; R(t), cross-correlation function between spontaneous changes in HR and MAP; Z R (t) , transformed R(t); HR/ MAP, HR response to the spontaneous change in MAP; θ/δ, the power density ratio of θ to δ wave band in EEG.

Hippocampal functional hyperemia mediated by NMDA receptor/NO signaling in rats during mild exercise

“…Furthermore, LDF enables continuous and realtime monitoring of rCBF, even in moving rodents (18,30,32,35). By using LDF, Nakajima et al (32) reported that treadmill walking (2.4 m/min) increased Hip-CBF in rats, and the in- crease was partially suppressed by an intravenous injection of mecamylamine, a nicotinic acetylcholine receptor antagonist.…”

Voluntary locomotion linked with cerebral activation is mediated by vasopressin V1a receptors in free‐moving mice

“…2006), it is plausible that V1a receptors in the medulla might act as a mediator that receives signals from the higher brain regions and modulates baroreflex control of HR. If so, via this pathway, V1a receptors might significantly contribute to the start of voluntary locomotion, which we have reported to occur at high probability after voluntary cerebral activation (Masuki & Nose, 2009).…”

“…After anaesthesia with pentobarbital sodium (50 mg kg −1 body weight, i.p. ), three stainless‐steel screws (OD 1 mm) of electroencephalogram (EEG) electrodes were placed on the skull surface according to stereotaxic coordinates (Franklin & Paxinos, 2008); AP −1.0 and L +1.0, AP −3.0 and L −1.0 mm from bregma, and AP +1.0 and L +1.0 mm from lambda in mice for both experiments (Masuki & Nose, 2009). In addition, for the 1st experiment, a stainless‐steel guide cannula (OD 0.80, ID 0.57, length 8.0 mm) was inserted through the skull so that the tip was positioned on the cortex surface (AP +1.5, L −1.0 and V +1.0 mm from bregma), which was used to hold a laser‐Doppler flow probe for cerebral blood flow (CBF) measurement (Masuki & Nose, 2009).…”

“…Moreover, we found that after the suppression reached its peak, there was a 5‐fold higher probability that the mice started to move in comparison to other time periods. These results suggest a tight link between cerebral activity, baroreflex control of HR and voluntary locomotion (Masuki & Nose, 2009); however, there have been no studies to assess possible mediators of these sequential and dynamic responses.…”

“…If locomotion, with more than zero counts for 30 s, occurred within 40 s after that time, we judged that it was associated with the increase in θ/δ. We used this time frame based on the results of Masuki & Nose (2009) and the delay time between an increase in θ/δ, a subsequent increase in Z R ( t ) and locomotion (Fig. 1).…”