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This Article Full Text Full Text (PDF) All Versions of this Article: 294/4/H1708    most recent 01122.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Sato, S. PubMed PubMed Citation Articles by Sato, S.

Quantitative evaluation of ontogenetic change in heart rate and its autonomic regulation in newborn mice with the use of a noninvasive piezoelectric sensor

Department of Physiology, Akita University School of Medicine, Akita, Japan

Submitted 28 September 2007 ; accepted in final form 6 February 2008

A reliable basal heart rate (HR) measurement in freely moving newborn mice was accomplished for the first time by using a novel noninvasive piezoelectric transducer (PZT) sensor. The basal HR was 320 beats/min at postnatal day (P)0 and increased with age to 690 beats/min at P14. Contribution of autonomic control to HR was then assessed. Sympathetic blockade with metoprolol significantly reduced basal HR at both P6 (–236 ± 23 beats/min; mean ± SE) and P12 (–105 ± 8 beats/min), but atropine was without effect, indicating the predominant tonic adrenergic stimulation and absence of vagal control for basal HR in newborn mice. In contrast to stable basal HR during 5-min recording, HR measured by ECG (ECG-HR) was markedly decreased because of the restraint stress of attaching ECG electrodes, with accompanying freezing behavior. ECG-HR lowered and further decreased gradually during 5 min (slow cardiodeceleration) at P0–P3 and rapidly decreased and gradually recovered within 5 min (transient bradycardia) at P9–P14. The response was not uniform in P4–P8 mice: they showed either of these two patterns or sustained bradycardia (9–29%), and the number of mice that showed transient bradycardia increased with age (30–100%) during the period. Studies with autonomic blockade suggest that the slow cardiodeceleration and transient bradycardia are mediated mainly by withdrawal of adrenergic stimulation and phasic vagal activation, respectively, and the autonomic control of HR response to restraint stress is likely to change from the withdrawal of adrenergic stimulation to the phasic vagal activation at different stages during P4–P8 in individual mice. The PZT sensor may offer excellent opportunities to monitor basal HR of small animals noninvasively.

slow cardiodeceleration; circulating catecholamine; phasic vagal activation; transient bradycardia; baroreflex