Alteration of early vascular development after ablation of cranial neural crest

A previous study has shown that, subsequent to ablation of cranial neural crest, heart morphology and pharyngeal arch vessels (aortic arches) are altered before septation of the outflow tract normally occurs. In the present study, we concentrated on very early development of the aortic arch apparatus in the chick (incubation days 3-5). The three-dimensional organization of the arch vessel apparatus was studied by scanning electron microscopy after intravascular injection of Mercox, and by serial sections of embryos embedded in plastic. Alterations in the arch vessel apparatus were already present by day three in embryos with neural crest ablation at stage 9-10. Bilateral symmetry frequently was lost. Arch vessels sometimes were enlarged and occupied most of the arch, with little surrounding mesenchyme. Some arch vessels were small or occluded. Mesenchyme was significantly reduced in quantity in the arches, and was not condensed and symmetrical as in controls. There was a significant increase in the proportion of direct apposition of vessel endothelium with epithelium, without the intervening mesenchyme typical of controls. The surgical manipulation used in this study leads to distinct alterations in the arches of components and relationships which are important in development. Altered blood flow likely affects the development of the heart.