TIME OF ORIGIN OF THE NEUROBLASTS IN THE NEURAL TUBE OF THE CHICK EMBRYO DETERMINED BY HISTOCHEMICAL OBSERVATION OF ACETYLCHOLINESTERASE ACTIVITY

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The time of origin of the neuroblasts in the neural tube of the chick embryo was determined by histochemical observation of acetylcholinesterase (AChE) activity.
In the central nervous system, the neuroblasts appeared first in the caudal half of the rhombencephalon of the 1.5-day chick embryo (13-somite, stage 11). They were round medium-sized cells and located in both the ventral and the dorsal halves of the wall of the neural tube. In the cervical, thoracic and lumbosacral neural tubes, the neuroblasts first appeared at stage 12, 14 and 17 respectively. At these levels, they were large and located in the ventral half of the wall of the neural tube. Occasionally they provided an axon which extended to the ventrolateral edge of the neural tube.
The time of origin of the neuroblasts in the neural tube of the chick embryo is more accurately determined by histochemical observation of AChE activity than by ³H-thymidine autoradiography. The time difference between the actual neuroblastic differentiation and the appearance of AChE moderately positive cells is much smaller than that between the actual neuroblastic differentiation and the differentiation determined by ³H-thymidine autoradiography.