NEURAL CREST ABLATION VERSUS SHAM SURGICAL EFFECTS IN A CHICK-EMBRYO MODEL OF DEFECTIVE CARDIOVASCULAR DEVELOPMENT

In chick embryos, ablation of premigratory neural crest destined for t he third, fourth, and sixth pharyngeal arches results in persistent tr uncus arteriosus and interrupted aortic arch. Studies of cardiogenesis in these embryos have shown decreased ejection fraction and ventricul ar dilation with normal cardiac output. The experimental embryos that survive to d 11 of incubation have a higher cardiac output than nonsur vivors at the same earlier stage of development. We hypothesize that t his survival is due to a surgically induced decrease in vascular resis tance of the embryonic and vitelline vessels. Embryos from 15 opened e ggs, eight sham-operated embryos, and 13 neural crest-ablated embryos were examined at stage 18. The sham-operated embryos were treated iden tically with the experimental embryos except that neural crest was not ablated. Ejection fraction and cardiac output were determined by cine photography. Mean dorsal aortic and diastolic ventricular (approximate s mean atrial) pressures were determined by a servo-null pressure tech nique and used to calculate vascular resistance. The experimental embr yos had a significantly decreased ejection fraction in comparison with either sham-operated embryos or embryos from eggs that remained unope ned until just before cinephotography. The experimental and sham-opera ted embryos had a higher cardiac output than embryos from unopened egg s. The calculated vascular resistance was also significantly lower in both the experimental and sham-operated embryos than in the embryos fr om unopened eggs. Neural crest ablation appears to cause a decreased e jection fraction. Sham surgery is associated with a higher cardiac out put and lower vascular resistance. These hemodynamic changes may be re lated to opening and resealing the egg-shell, which would interfere wi th oxygen delivery and water vapor exchange.