ABLATION OF VARIOUS REGIONS WITHIN THE AVIAN VAGAL NEURAL CREST HAS DIFFERENTIAL-EFFECTS ON GANGLION FORMATION IN THE FOREGUT, MIDGUT AND HINDGUT

The vagal neural crest adjacent to the first seven somites gives rise to both ganglionic and ectomesenchymal derivatives. Ganglionic derivat ives are the neurons and supportive cells of the enteric nervous syste m (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 vesic le down to the caudal boundary of the third somite, called the cardiac neural crest. We performed neural crest ablations to study regional d ifferences within the avian vagal neural crest with regard to the form ation of the ENS. Ablation of the entire vagal neural crest from the m id-otic vesicle down to the seventh somite plus the nodose placode res ulted 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 3-5, ganglia were absent in the hindgut. Abl ations of vagal neural crest not including this segment had no effect on the formation of the ENS. We surmise that the innervation of the hi ndgut in vivo depends specifically on the neural crest adjacent to som ites 3-5, whereas innervation of the midgut can be accomplished by all segments within the vagal neural crest. The foregut can also be inner vated by a source outside the vagal neural crest. To study intrinsic d ifferences between various vagal neural crest segments regarding ENS f ormation, we performed chorioallantoic membrane cocultures of segments of quail vagal neural anlage and E4 chicken hindgut. We found that al l vagal neural crest segments were able to give rise to enteric gangli a in the hindgut. When the neural crest of somites 6 and 7 was include d 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 wit h the neural tube in vivo, because of either late emigration or delaye d migration, have an increased probability to form enteric ganglia. (C ) 1993 Wiley-Liss, Inc.