The development of acetylcholinesterase activity in the embryonic nervous system of the frog, Xenopus laevis

Abstract

Histochemical detection of acetylcholinesterase (AChE) activity in Xenopus embryos was found first in primary motoneurons, Rohon-Beard neurons and somitic myotubes at early tail bud stages. At late tail bud stages all primary neurons, including primary interneurons, cranial ganglion cells and ventral brainstem cells expressed this enzyme. The onset of detectable AChE activity in some primary neurons occurred near the time of initial axon outgrowth, whereas in others it occurred at much later stages. At early independent-feeding and continuous-swimming stages nearly all seemingly postmitotic neurons began to express AChE activity, and by the beginning of limb bud stages, when many secondary neuronal populations were going through their final rounds of mitosis, nearly all CNS cells outside the ventricular zone were intensely stained. Thus, the onset of detectable AChE activity in secondary neurons occurred near the time of their final mitoses. In trunk somites the enzyme activity initially was located diffusely throughout the myotube, and with progressing development it became localized to the myocommata. From the onset of AChE activity both head somites and head muscles had discrete patches of reaction product all over their surfaces. The onset of detectable AChE activity occurred in muscles near the time that they were contacted by motor axons. These data demonstrate that the primary neurons are the first to express AChE activity, and that as the secondary neurons begin to proliferate, AChE is expressed by nearly all embryonic neuronal populations.