2 research outputs found
The hindbrain neural crest and the development of the enteric nervous system
The wonder of things is the beginning of knowledge, as was already stated by Aristotle, the
fIrst embryologist known to history. Embryology has remained a source of wonder ever since.
It all starts with the fusion of the female egg and the male sperm. Sperm cells were first
described by Antonie van Leeuwenhoek (1632-1723) in 1678, who believed them to be
parasitic animals present in the male semen, that had nothing to do with reproduction. Nicolas
Hartsoeker (1656-1725), the other discoverer of sperm believed that the entire embryonic
individual lay preformed within the head of the sperm, as depicted in his famous homunculus
(Fig. 1). The fIrst evidence for the existence of the female egg was presented by Reinier de
Graaf (1641-1673), although the egg itself was only described in 1827 by Karl von Raer
(1792-1876). The actual fertilization process was observed only a century ago by Herman Fol,
a Swiss zoologist
Ablation of various regions within the avian vagal neural crest has differential effects on ganglion formation in the foreā, midā and hindgut
The vagal neural crest adjacent to the first seven somites gives rise to both ganglionic and ectomesenchymal derivatives. Ganglionic derivatives are the neurons and supportive cells of the enteric nervous system (ENS), cardiac, and dorsal root ganglia. Ectomesenchymal derivatives are cells in the cardiac outflow tract and the mesenchymal components of thymus and parathyroids. Ectomesenchymal derivatives are formed by a segment of the vagal neural crest, from the level of the otic vesicle down to the caudal boundary of the third somite, called the cardiac neural crest. We performed neural crest ablations to study regional differences within the avian vagal neural crest with regard to the formation of the ENS. Ablation of the entire vagal neural crest from the midāotic vesicle down to the seventh somite plus the nodose placode resulted in the absence of ganglia in the midgut (jejunum and ileum) and hindgut (colon). The foregut (esophagus, proventriculus, gizzard, and duodenum) was normally innervated. After ablation of the vagal neural crest adjacent to somites 3ā5, ganglia were absent in the hindgut. Ablations of vagal neural crest not including this segment had no effect on the formation of the ENS. We surmise that the innervation of the hindgut in vivo depends specifically on the neural crest adjacent to somites 3ā5, whereas innervation of the midgut can be accomplished by all segments within the vagal neural crest. The foregut can also be innervated by a source outside the vagal neural crest. To study intrinsic differences between various vagal neural crest segments regarding ENS formation, we performed chorioallantoic membrane cocultures of segments of quail vagal neural anlage and E4 chicken hindgut. We found that all vagal neural crest segments were able to give rise to enteric ganglia in the hindgut. When the neural crest of somites 6 and 7 was included in the segment, we also found melanocytes in the hindgut, suggesting that this segment is more related to trunk neural crest. Furthermore, we found that the vagal neural anlage from older embryos (>18 somites) showed an increased potential to form enteric ganglia. This suggests that vagal neural crest cells that have been in prolonged contact with the neural tube in vivo, because of either late emigration or delayed migration, have an increased probability to form enteric ganglia