抄録
To study cardiac function of newborn small animals, it should be considered that they show freezing response and HR drop when they are held by our hands (Hofer & Reiser, 1969). In this respect, no basal HR of them has been obtained hitherto. A noninvasive measurement by using piezoelectric sensor without inducing the freezing response revealed for the first time the basal HR of freely-moving newborn mice (Sato, 2007). The HR increased in exponential-like curve from 320 to 670 (b/m) during the first two postnatal weeks and it was considerably higher than that reported previously by Cedrini and Rostagno (1985), in which mice might had been decreased their HR due to the freezing response induced by handling procedure. On the other hand, attaching ECG electrodes to the same mice induced freezing response and marked HR drop. Patterns of the HR drop during 5 min of recording shifted from constant decrease in HR (slow cardiodeceleration) at P0-3 to rappid HR drop followed by its recovery (transient bradycardia) at P9-14. Both patterns were observed at P4-8. Analysis of the patterns in HR drop by autonomic blockade suggests that the slow cardiodeceleration and the transient bradycardia is likely mediated by tonic sympathetic withdrawal and phasic parasympathetic activation, respectively, and that vagal control on HR matures in P4-9. Comparing HR responses to attaching ECG electrodes with noninvasive PZT readings may provide us a novel tool for investigating the development in autonomic control on HR of newborn small animals including baroreflex. [J Physiol Sci. 2008;58 Suppl:S48]
