Carrageenan induces anomalies in the chick embryo. A light microscopic study.

Chick embryos injected with lambda-carrageenan prior to incubation and studied with light microscopy at 48 hours of development presented various anomalies. Lack of closure at different levels of the neural tube was one of the lesions most frequently seen. Rachischisis and craniorachischisis were commonly associated with various degrees of hyperplasia of the neural tube wall. Diverse patterns of neural hyperplasia ranged from total occlusion of the neural tube to localized thickening of lateral walls leading to a typical "hourglass" appearance of the ependymal lumen. Multiple septa and cavitations of the neural tube lumen were also recorded. Cephalic and/or trunk duplication of the body as well as disorganization of notochord and somites were frequently associated with rachischisis and areas of necrosis or pyknosis of neural tissue. Neural crest cells, which are normally present in paraneural areas at the stages studied, were not encountered in the carrageenan-injected embryos. These areas were frequently occupied by hyperplastic ectodermic folds. Similarity of present findings on carrageenan-treated embryos with the anomalies induced by selective destruction or impairment of migration of neural crest cells suggests that involvement of this cell population may have a role in the causation of the anomalies observed.