THE APPEARANCE OF ACETYLCHOLINESTERASE IN THE DORSAL ROOT NEUROBLAST OF THE RABBIT EMBRYO : A Study by Electron Microscope Cytochemistry and Microgasometric Analysis with the Magnetic Diver

In the nine day old embryo, acetylcholinesterase (AChE) is found in the reticulum, i.e. the nuclear envelope, endoplasmic reticulum, and Golgi complex, of a few cells in the neural crest. When the neurite first enters the neural tube, reticulum-bound enzyme is present also in the varicosity of the growth cone of the bipolar neuroblast. At later stages, AChE in the neuroblast has a dual distribution; in addition to the reticulum, activity also appears at the axolemmal surface. The axolemmal activity is found initially on the distal portions of axons in the posterior fasciculus and then progressively appears along the nerve roots in a distal to proximal direction. Very little reticulum-bound enzyme is present within the axon proper. After the 13th day the levels of AChE activity in the posterior fasciculus greatly exceed those in the dorsal root or in the ganglion. Enzymatic activity in the dorsal root equals or exceeds that in the posterior fasciculus by day 16, and both areas are considerably more active than the ganglion.