[Histochemical demonstration of cholinesterase during the folding off of the chick embryo].

The localization of cholinesterase activity in chick embryo of stage 5 up to stage 21 has been studied in cell layers that are involved in the formation of the primitive body tube.During the formation of the neural tube, cholinesterase activity can be demonstrated in cells of the neural plate. This pattern of enzyme activity disappears after formation of the neural tube. Thereafter, the enzyme is localized in neuroblasts.In the ectodermal layer, cholinesterase activity is found during the formation of the head fold and the lateral body folds. Again, the enzyme disappears after the development of the cephalic outgrowth.Formation of the entodermal folds and their fusion in the midline - thus establishing the gut tube - is associated with cholinesterase activity in palisade cell layers. There is no enzyme activity in the completed gut.During the formation of the gut tube, the mediad invading entodermal folds are covered by mesodermal cell palisades, which are positive for cholinesterase. After the formation of the gut tube, the palisades disappear as does the enzyme activity.