Non-invasive ultrasonographic characterization of phenotypic changes during embryo development in non-anesthetized mice of different genotypes.
This study aimed to determine phenotypic changes during embryo development in the mouse, and the influence of genetic background, by non-invasive real-time ultrasonography. Serial scannings were performed from Day 4.5 after the appearance of the vaginal plug in a total of 34 adult mice of different strains (9BALB/c, 10C57BL/6 and 15 CD1). Embryonic vesicle diameter was measurable from Day 4.5 of pregnancy. Images of embryos were obtainable from Day 5.5 of gestation onwards, and crown-rump length and trunk parameters (diameter and area) were measured. At more advanced stages, the positions of fetuses prevented accurate measurement of crown-rump length; therefore, head diameters (occipito-snout length and biparietal diameter) were used as an alternative index of fetal size. All measurements correlated highly with gestational age (P<0.0005). No significant differences were observed between genotypes in early pregnancy, but during the last week of gestation trunk measurements were larger in CD1 embryos (P<0.05) while head diameters were larger in C57BL/6 conceptuses (P<0.05). There was a significant effect of genetic background on heart rate throughout pregnancy; although heart rate was similar in CD1 and C57BL/6 embryos (154.5+/-2.8 and 147.8+/-4.5 beats/min, respectively), it was significantly lower in BALB/c mice (127.0+/-2.1; P<0.005 vs. CD1 and C57BL/6).
Pallares
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Unidad de Animalario, Fundación Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Melchor Fernandez Almagro 3, 28029 Madrid, Spain. ppallares@cnic.es
Gonzalez-Bulnes
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D000818:Animals; D004622:Embryo, Mammalian / Q000000981:diagnostic imaging*; D047108:Embryonic Development / Q000502:physiology*; D005260:Female; D005838:Genotype; D006339:Heart Rate / Q000502:physiology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D010641:Phenotype; D011247:Pregnancy; D012044:Regression Analysis; D013045:Species Specificity; D018608:Ultrasonography, Doppler; D016216:Ultrasonography, Prenatal