Acetylcholinesterase activity in the neural tube of the early chick embryo.

Abstract

Appearance and localization of acetylcholinesterase (AchE) activity in the nervous system of early chick embryos were histochemically studied using the Karnovsky-Roots thiocholine technique. Using light microscopy, AchE activity was first demonstrated in the basal plate of the neural tube of the 2-day chick embryo (developmental stage 13, Hamburger-Hamilton). In the 3-day embryo (stage 17) AchE activity was seen in the basal and alar plates of the neural tube. In the 4-day embryo (stage 23) AchE activity was evident in the mantle layer of the neural tube, and in the spinal nerve roots and spinal ganglia. By EM, AchE activity was first detected in the 10-somite embryo (stage 10), i.e., the reaction products were seen in a few neuroepithelial cells and undifferentiated neural crest cells. The reaction products were first found exclusively in the cisterns of the nuclear envelope and thereafter in those of the rough endoplasmic reticulum (r-ER). In successive stages, as r-ER increased in volume and in number, the reaction products were found in the r-ER more frequently and more numerously. In these stages, no morphological differences were noticeable between the AchE-positive and -negative cells. Enzymatic (AchE) differentiation may begin earlier than the morphological and functional differentiations.