Neural folds

The majority of analyses on neural crest cell migration, proliferation, and differentiation have been carried out in avian and amphibian embryos because of the relative ease of experimental manipulation (see Le Douarin, 1982). These experiments demonstrated that pigment cells arise from the neural crest. When pieces of neural folds were grafted to the... 

A score of 1 is assigned when there are combinations of marked kinks and bends (Fig. 6h, bracket and arrows), or there is either a failure in neural fold closure along the caudal neural tube, and/or when the posterior neural pore is unusually large (Fig. 6i, circle). 

The primitive brain is assessed for integrity of neural fold closure, relative size and demarcation of each of the three brain ventricles. 

A score of 1 is assigned where the neural folds have failed to close in any or all of the brain segments (exencephaly) (Fig. 8e, bracket. Fig. 8f, arrow), or if one or two of the brain ventricles are not apparent. 

Lack of neural fold fusion Large posterior neuropore... 

Anencephalus is one of a constellation of malformations known collectively as neural tube defects (NTDs). Anencephalus is the end result of failure of neural fold elevation and fusion, a deficiency that can occur only in the most anterior region (Figure 1), along the entire axis (craniorachischisis totalis Figure 2), or localized in areas along the spine (spina bifida Figure 3). Spina bifida is a common... 

Just as partial failure of neural fold apposition and fusion can occur along the spine, it can also occur in the skull. Cephalic malformation can be complete in anencephalus (with little or no involvement of the lower spine) or incomplete as in encephalocele and Arnold-Chiari malformation (Figure 5). Encephalocele (Figure 5) is one such condition in which the brain extends through dura and membranous bone and comes into contact with the scalp. 

The order in which various cell fypes arise is defer-mined by fhe order in which franscripfion factors such as Hunchback, Kriippel, and ofhers are expressed. Mulfipofential neural stem cells provide fhe new cells thaf are requiredNeural tissue from a region called fhe neural plate develops info a neural fold. 

Morris-Wiman, J. and Brinkley, L.L. (1990) Changes in mesenchymal cell and hyaluronate distribution correlate with in vivo elevation of the mouse mesencephalic neural folds. Armt. Rec. 226 383-395. 

Fig. 12.3. Stages in the development of the chick embryo, (a) Blastoderm before invagination of the mesoderm, (b) Blastoderm after the formation of the primitive streak and Henson s node, mesoderm cells forming from the epiblast. (c) Neural fold stage, (d) Differentiation of the somites into sderoderm, myotome and dermatome.

Push the pipet gently into the cranial neural fold or further into the aanial mesoderm. Expel the cell clumps or dye by applying a positive pressure to the de Fonbrune syringe. Expulsion of the cell clumps is accompanied by the simultaneous withdrawal of the pipet. 

Fig. 7. Stage 7 (HH) (26-30 h) shows the segmentation of the first pair of somites from the para-notochrodal mesoderm. This is in fact the second pair of somites. The first somite is a phantom somite. It never forms fully and will disperse again in the next few hours of development. It is a slight mesodermal condensation anterior to the cleavage for the first somite proper. Not all embryos have a visible first somite. Subsequent pairs of somites will segment in two hourly intervals from the para-axial mesoderm. Neural folds reach to the mesencephalon. The wall of the foregut emerges close to the lateral head fold.

Fig. 11. Stage 10 (HH), 10 pairs of somites (36-42h) dorsally anterior neuropore closed, prominent optic vesicles, rhombomere boundary 4/5 formed, and neural folds are closed to almost the level of the node. Ventrally, Hensen s node has regressed almost to the end of the primitive streak (the 10th pair of somites has not fully segmented caudally in this illustration), pronephric tubules develop between somites 6 and 10, heart tube turns asymmetrical bulging out to the right and contractions can be seen, and bilateral vitelline veins fan out toward the area opaca, which shows large blood islands to establish circulation.

Excision of precise pieces of the neural fold or neural plate in the chick host Very thin microscalpels (made up from insect pins or steel needles sharpened on an oil stone) are used to excise precise fragments of the folds and neural plate in 0- to 5-somite stage chick embryos in ovo. An ocular micrometer is used to measure the pieces of tissue to be removed. 

Couly, G. F. and Le Douarin, N. M. (1987) Mapping of the early neural primordium in quail-chick chimeras. II. The prosencephalic neural plate and neural folds implications for the genesis of cephalic human congenital abnormalities. Dev. Biol. 120,198-214. 

Couly, G., Grapin-Botton, A Coltey, P and Le Douarin, N. M. (1996) The regeneration of the cephahc neural crest, a problem revisited the regenerating cells originate from the contralateral or from the anterior and posterior neural folds. Development 122,3393-3407. 

Moury, D. and Jacobson, A. (1989) Neural fold formation at newly created boundaries between neural plate and epidermis in the axolotl. Dev. Biol 133,44-57. 

The neural crest is a small group of ectodermal cells organized before the neural folds fuse, and migration of its cells to colonize endodermal structures was neatly... 

Fig. A Cross section of the middle thoracic region of a control embryo showing the closed neural tube (top) with the paired dorsal aortae. The foregut overlies the pericardial coelom and heart. Cross section of the middle thoracic region of a hamster embryo recovered 10 hr after a teratogenic dose of sodium arsenate. The region shows retardation in approximation and fusion of the neural folds and shows flattening and exposure of the neuroectoderm. (x 350).

Figure 8. A. Transverse section of the upper thoracic region of a sodium arsenate-treated hamster embryo. The embryo shows an obvious schisis (dysraphic) defect of the neural walls with apparent overgrowth of the neuroepithelium. (x 350). Transverse section of the upper thoracic region of a sodium arsenate-treated hamster embryo. The section shows a localized schisis of the anterior region with collapse of the neural folds. Mesodermal consolidation has not occurred as evidenced by poorly formed somites, (x 350).

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