Journal of Neuroscience, Vol 1, 478-492, Copyright © 1981 by Society for Neuroscience
Differentiation of autonomic neuron precursors in vitro: cholinergic and adrenergic traits in cultured neural crest cells
M Fauquet, J Smith, C Ziller and NM Le Douarin
The development of autonomic neuronal precursors was studied in cultures of
microsurgically excised quail neural crest grown alone and associated with
other young embryonic tissues. Biochemical differentiation in the cultures
was followed by measuring their ability to synthesize acetylcholine (ACh)
and catecholamines (CA) from radioactive precursors; cytochemical aspects
of their differentiation were examined by techniques including electron
microscopy, cholinesterase histochemistry, and CA cytofluorescence.
Mesencephalic crest, which can make ACh before explantation, always
synthesized ACh after 7 d in culture and often, but not invariably,
elaborated small quantities of CA as well. Association with 2-d somite and
notochord, 2- d heart, or 4-d hindgut, in medium supplemented with horse
serum, resulted in the synthesis of increased amounts of both transmitters.
ACh-synthesizing activity was lower and the cholinergic-stimulating effects
of somite and heart were abolished in the presence of fetal calf serum.
Cervicothoracic (trunk) crest, taken from the level where the dorsal
mesoderm is still unsegmented, always produced ACh after culture, but CA
was detectable only when the cultures were obtained by initially explanting
the entire neural primordium. Co-culture of trunk crest with young
embryonic tissue increased ACh-synthesizing ability and initiated CA
production. Despite their capacity to elaborate neurotransmitter, cultures
of either type of neural crest, alone or in association with the
above-mentioned tissues, contained very few cells resembling neurons in
their phase contrast appearance and none that reacted positively to any of
the cytological tests applied. On the other hand, when the sclerotomic
moiety of 3-d somite was cultured, trunk neural crest cells that had
already migrated into the rudiment in vivo but which had not yet begun to
produce detectable amounts of CA underwent rapid differentiation into
neurons that synthesized and accumulated large quantities of CA. Stores of
CA were detectable cytochemically as early as 24 hr after explantation and
the presence of many small, dense core vesicles in neurons and processes
was revealed by electron microscopy. ACh-synthesizing activity,
demonstrable in freshly dissected sclerotomes, was also present in all of
the cultures examined. These results show that (1) during ontogeny,
cholinergic traits appear earlier than adrenergic ones in the neuronal
precursors contained in the neural crest; (2) some decisive step in the
differentiation of the precursor cells of the sympathetic ganglia takes
place in vivo within a few hours of the onset of trunk neural crest
migration. This coincides with a maturation of the somitic mesenchyme. A
similar developmental process does not occur in vitro when 2-d somites and
neural crest are associated in histiotypic cultures.