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Electrocardiograms in Neonate Mice
Victor Chu, Ajit Kale*, Jose M. Otero, Ivo Amende, and Thomas G. Hampton;
Mouse Specifics, Inc. and *The CuraVita Corporation, Boston, MA. USA.
Web published: January 1, 2002
Abstract
The electrocardiogram is becoming an increasingly important tool for phenotyping mice, not only for evaluating cardiovascular health, but also for neurological assessment. Especially as many neurogenetic mutations in mouse models result in death at young ages, evaluation of physiology in neonates can help establish the genotype/phenotype link. In conscious mice, however, physiology is usually limited to qualitative description of motor function. Accordingly, here we apply our non-invasive conscious mouse ECG screening system to neonate mice. We demonstrate important phenotypic characteristics indicative of age-dependent modulation of autonomic nervous control of heart rate.
Methods
Figure 1.
FVB mice and C57BL/6 mice were obtained from The Jackson Laboratory. The AnonyMOUSETM ECG screening system was used to record ECGs.1 Neither anesthetic nor surgery was required. Data were acquired at 2kHz for at least 2 seconds to provide equivalent continuous recordings of 20 to 30 beats. e-MOUSETM was used to interpret the signals. Time domain indices of heart rate (HR) variability (var) were calculated as described previously.2
Results
Developmental ECG changes.
FVB mice
6-days (n=5)
3-4 weeks (n=5)
HR (bpm)
338 ± 26
755 ± 16*
HR var (bpm)
0.9 ± 0.1
7.0 ± 1.6*
PR (ms)
45.5 ± 3.2
25.2 ± 0.5*
C57BL/6 mice
6-days (n=8)
3-4 weeks (n=8)
HR (bpm)
679 ± 21
717 ± 13
HR var (bpm)
2.5 ± 0.4
21 ± 2*
PR (ms)
24.2 ± 0.6
23.0 ± 0.5
Discussion
The ECG from a 6-day old C57BL/6 neonate female mouse is shown in Figure 1. Heart rate in neonates was found to be remarkably steady and HR var was significantly less than in adults. Gender differences in heart rate we reported in adult mice1 were absent in 6-day old and 12-day old neonates. Upon weaning (21 days old), however, gender differences in heart rate became apparent [697 ± 14 bpm vs. 750 ± 8 bpm (n=3), P<0.05.] The disparity in heart rate between neonates and young adults was much more pronounced in FVB mice than in C57BL/6 mice. Despite strain-dependent differences in basal heart rate3, HR var was nearly 10-fold lower in neonates compared to adults in the two strains examined here. The observations in neonates may be attributable to reduced sympathetic and parasympathetic signaling.4 The developmental changes we observed in mice parallel those in human neonates5,6, lambs7, and newborn rats8. Our approach, adaptable to the study of neonatal mice with limited lifespan, might be valuable in examining developmental changes and abnormalities in mouse models for neurological disorders.9
References
Chu, V. et al. 2001. BMC Physiology 1:6.
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Desai, K.H. et al. 1997. Am. J. Physiol. Heart Circ. Physiol. 272:H1052-H1061.
Sugihara, G. et al. 1996. Proc. Natl. Acad. Sci. 93:2608-2613.
Harper, R.M. et al. 1982. Sleep 5:28-38.
Schechtman, V.L. et al. 1988. Sleep 11:413-426.
Siimes, A.S.I et al. 1984. Acta. Physiol. Scand. 537:7-15.
Hofer, M.A. and M.F. Reiser. 1969. Psychosom. Med. 31:372-388.
Sprunger, L.K. et al. 1999. Hum. Mol. Gen. 8:471-479.
