scholarly journals On The Existence of Regionally Specific Evocators

1952 ◽  
Vol 29 (3) ◽  
pp. 490-495
Author(s):  
C. H. WADDINGTON
Keyword(s):  
Cross Section ◽  
Neural Tube ◽  
Direct Action ◽  
Specific Effect ◽  
Neural Tissue ◽  
Neural Plate ◽  
Normal Embryo ◽  
Tail Bud ◽  
The Brain ◽  
Brain Parts

1. Pieces of the embryonic axis, taken from the anterior and posterior regions of embryos from the open neural plate to the late tail-bud stages which had been coagulated by a few seconds' immersion in water at 90°C, were inserted into flaps of gastrula ectoderm which were then cultivated in Holtfreter solution. No induction of mesoderm occurred, but neural tissue was evoked in a high percentage of cases. 2. In early stages the neural tissue usually formed a more or less chaotic tangle of tubes and rods. At later stages it assumed a variety of forms, some of which were similar to parts of the brain, and such brain-parts might be accompanied by secondary structures such as eyes, nasal pits, ears, etc. No elongated tubes resembling the trunk neural tube were seen, although certain neural vesicles may have a cross-section very like that of the neural tube. 3. The induction of recognizable brain or eye was not uncommon when anterior implants were used, but was not seen at all with posterior implants. There was no other difference between the two sets of experiments. 4. It is suggested that the appearance of such organs is not due to the direct action of a regionally specific inducing factor, but rather that all such definite forms arise by a process of self-individuation which occurs within the induced mass of neural tissue. The direction this self-individuation takes, and thus the nature of the organ finally formed, is supposed to depend on chance resemblances between the mass and shape of parts of the original chaotic mass and some part of the normal embryo. It is argued that this could account for the apparently specific effect of the anterior implants. 5. In other experiments in which mesodermal tissues are also induced (e.g. with implants of adult tissues) it is likely that these take part in the self-individuation processes and tend to direct these towards the formation of posterior organs such as trunk and tail.

Neurodevelopment

2020 ◽  
pp. 91-100
Author(s):  
Karl Zilles ◽  
Nicola Palomero-Gallagher
Keyword(s):  
Spinal Cord ◽  
Nervous System ◽  
Neural Tube ◽  
Neural Plate ◽  
Adult Brain ◽  
The Central Nervous System ◽  
Specialized Region ◽  
The Brain ◽  
Rostral Part ◽  
Human Nervous System

The pre- and post-natal development of the human nervous system is briefly described, with special emphasis on the brain, particularly the cerebral and cerebellar cortices. The central nervous system originates from a specialized region of the ectoderm—the neural plate—which develops into the neural tube. The rostral part of the neural tube forms the adult brain, whereas the caudal part (behind the fifth somite) differentiates into the spinal cord. The embryonic brain has three vesicular enlargements: the forebrain, the midbrain, and the hindbrain. The histogenesis of the spinal cord, hindbrain, cerebellum, and cerebral cortex, including myelination, is discussed. The chapter closes with a description of the development of the hemispheric shape and the formation of gyri.

Somitomeres: mesodermal segments of vertebrate embryos

Development ◽  
1988 ◽  
Vol 104 (Supplement) ◽  
pp. 209-220 ◽  
Author(s):  
Antone G. Jacobson
Keyword(s):  
Electron Microscopy ◽  
Chick Embryo ◽  
Cell Types ◽  
Paraxial Mesoderm ◽  
Tail Bud ◽  
Snapping Turtle ◽  
Vertebrate Embryos ◽  
The Brain ◽  
Brain Parts ◽  
Scanning Electron

Well before the somites form, the paraxial mesoderm of vertebrate embryos is segmented into somitomeres. When newly formed, somitomeres are patterned arrays of mesenchymal cells, arranged into squat, bilaminar discs. The dorsal and ventral faces of these discs are composed of concentric rings of cells. Somitomeres are formed along the length of the embryo during gastrulation, and in the segmental plate and tail bud at later stages. They form in strict cranial to caudal order. They appear in bilateral pairs, just lateral to Hensen's node in the chick embryo. When the nervous system begins to form, the brain parts and neuromeres are in a consistent relationship to the somitomeres. Somitomeres first appear in the head, and the cranial somitomeres do not become somites, but disperse to contribute to the head the same cell types contributed by somites in the trunk region. In the trunk and tail, somitomeres gradually condense and epithelialize to become somites. Models of vertebrate segmentation must now take into account the early presence of these new morphological units, the somitomeres. Somitomeres were discovered in the head of the chick embryo (Meier, 1979), with the use of stereo scanning electron microscopy. The old question of whether the heads of the craniates are segmented is now settled, at least for the paraxial mesoderm. Somitomeres have now been identified in the embryos of a chick, quail, mouse, snapping turtle, newt, anuran (Xenopus) and a teleost (the medaka). In all forms studied, the first pair of somitomeres abut the prosencephalon but caudal to that, for each tandem pair of somitomeres in the amniote and teleost, there is but one somitomere in the amphibia. The mesodermal segments of the shark embryo are arranged like those of the amphibia.

The Mode of Growth of the Tail in Urodele Larvae

Development ◽  
1958 ◽  
Vol 6 (3) ◽  
pp. 466-478
Author(s):  
J. Hubertha Bijtel
Keyword(s):  
Spinal Cord ◽  
Neural Tube ◽  
Cell Mass ◽  
Vital Staining ◽  
Neural Plate ◽  
Tail Bud ◽  
Morphogenetic Movements ◽  
Separate Cell ◽  
A Cell ◽  
Axial Organs

The idea that the hinder part of the trunk together with the tail or the tail alone develops by the outgrowth of a cell mass which is in every respect indifferent has been disproved since 1928 for the Amphibia. The results of experiments with vital staining (Bijtel & Woerdeman, 1928; Bijtel, 1929, 1931) and with microsurgical methods (Bijtel, 1936) have shown that the presumptive rudiments of the tail organs (epidermis, spinal cord, muscle segments, tail-gut) are already present in the neural plate stage as more or less separate cell territories. During and immediately after the transformation of the neural plate into the neural tube, these cell territories are brought together into the tail-bud by morphogenetic movements. Holmdahl (1939 a, b, 1947) and Vogt (1939) have criticized this conception. They adhered to the view that the organs of the hinder part of the runk and of the tail (Holmdahl) or only the axial organs of the tail (Vogt, p. 127) originate from an indifferent blastema.

scholarly journals Hallmarks of primary neurulation are conserved in the zebrafish forebrain

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jonathan M. Werner ◽  
Maraki Y. Negesse ◽  
Dominique L. Brooks ◽  
Allyson R. Caldwell ◽  
Jafira M. Johnson ◽  
...  
Keyword(s):  
Neural Tube ◽  
Time Lapse ◽  
Neural Plate ◽  
Neural Tube Closure ◽  
Developmental Studies ◽  
Underlying Causes ◽  
The Central Nervous System ◽  
Resolution Imaging ◽  
Fold Formation ◽  
Anterior Neural Plate

AbstractPrimary neurulation is the process by which the neural tube, the central nervous system precursor, is formed from the neural plate. Incomplete neural tube closure occurs frequently, yet underlying causes remain poorly understood. Developmental studies in amniotes and amphibians have identified hingepoint and neural fold formation as key morphogenetic events and hallmarks of primary neurulation, the disruption of which causes neural tube defects. In contrast, the mode of neurulation in teleosts has remained highly debated. Teleosts are thought to have evolved a unique mode of neurulation, whereby the neural plate infolds in absence of hingepoints and neural folds, at least in the hindbrain/trunk where it has been studied. Using high-resolution imaging and time-lapse microscopy, we show here the presence of these morphological landmarks in the zebrafish anterior neural plate. These results reveal similarities between neurulation in teleosts and other vertebrates and hence the suitability of zebrafish to understand human neurulation.

Effect of Subarachnoid Bupivacaine Block on Anesthetic Requirements for Thiopental in Rats 

1998 ◽  
Vol 88 (4) ◽  
pp. 1036-1042 ◽  
Author(s):  
Sunil Eappen ◽  
Igor Kissin
Keyword(s):  
Local Anesthetic ◽  
Direct Action ◽  
Afferent Input ◽  
Crossover Design ◽  
Hemodynamic Parameters ◽  
Motor Responses ◽  
Withdrawal Reflex ◽  
Corneal Reflex ◽  
To Receive ◽  
The Brain

Background Subarachnoid bupivacaine blockade has been reported to reduce thiopental and midazolam hypnotic requirements in patients. The purpose of this study was to examine if local anesthetically induced lumbar intrathecal blockade would reduce thiopental requirements for blockade of motor responses to noxious and nonnoxious stimuli in rats. Methods After intrathecal and external jugular catheter placement, rats were assigned randomly to two groups in a crossover design study, with each rat to receive either 10 microl of 0.75% bupivacaine or 10 microl of normal saline intrathecally. The doses of intravenously administered thiopental required to ablate the eyelid reflex, to block the withdrawal reflex of a front limb digit, and to block the corneal reflex were compared. In two separate groups of animals, hemodynamic parameters and concentrations of thiopental in the brain were compared between intrathecally administered bupivacaine and saline. Results The thiopental dose required to block the described responses was decreased with intrathecally administered bupivacaine versus intrathecally administered saline from (mean +/- SD) 40 +/- 5 to 24 +/- 4 mg/kg (P < 0.001) for the eyelid reflex, from 51 +/- 6 to 29 +/- 6 mg/kg (P < 0.005) for front limb withdrawal, and from 67 +/- 8 to 46 +/- 8 mg/kg (P < 0.01) for the corneal reflex. The concentration of thiopental in the brain at the time of corneal reflex blockade for the group given bupivacaine was significantly lower than in the group given saline (24.1 vs. 35.8 microg/g, P = 0.02). Conclusion This study demonstrates that lumbar intrathecally administered local anesthetic blockade decreases anesthetic requirements for thiopental for a spectrum of end points tested. This effect is due neither to altered pharmacokinetics nor to a direct action of the local anesthetic on the brain; rather, it is most likely due to decreased afferent input.

scholarly journals Enhanced resolution of histochemical distribution of glucose-6-phosphate dehydrogenase activity in rat neural tissue by use of a semipermeable membrane.

1991 ◽  
Vol 39 (7) ◽  
pp. 937-943 ◽  
Author(s):  
M A Philbert ◽  
C M Beiswanger ◽  
T L Roscoe ◽  
D K Waters ◽  
H E Lowndes
Keyword(s):  
Vestibular Nucleus ◽  
Neural Tissue ◽  
Semipermeable Membrane ◽  
G6pd Activity ◽  
Ependymal Cells ◽  
Regional Localization ◽  
Enhanced Resolution ◽  
Membrane Technique ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
The Brain

We examined the histochemical distribution of glucose-6-phosphate dehydrogenase (G6PD) activity in neural tissue using different diffusion barriers. Although polyvinyl alcohol and agar overlays permitted regional localization of G6PD, a semipermeable membrane revealed cellular differences in G6PD activity within populations of neurons. Distribution of G6PD activity in selected regions of the nervous system was examined using the membrane technique. White matter usually exhibited strong G6PD activity. The neuronal somata of the dorsal root ganglia (L4-L6) and anterior horns of the spinal lumbar enlargement demonstrated a variation in activity which was independent of somal size. Satellite cells showed intense activity when the membrane technique was used. Hippocampal pyramidal and granular cells of the dentate gyrus exhibited moderate, uniform G6PD activity, but only weak activity was seen in hippocampal and dentate molecular layers. High levels of activity were observed in the vascular endothelial cells of the brain, spinal cord, and choroid plexus, and in the ependymal cells of the spinal central canal and ventricles of the brain. The superior vestibular nucleus appeared to have little G6PD activity in either the neuron cell bodies or the surrounding parenchyma. The use of a semipermeable membrane for localization of G6PD activity in neural tissues permits enhanced resolution of neuron elements and may provide a more accurate assessment of G6PD activity in histological preparations.

Anterior mesendoderm induces mouse Engrailed genes in explant cultures

Development ◽  
1993 ◽  
Vol 118 (1) ◽  
pp. 139-149 ◽  
Author(s):  
S.L. Ang ◽  
J. Rossant
Keyword(s):  
Direct Evidence ◽  
Neural Tissue ◽  
Explant Culture ◽  
Neural Plate ◽  
Explant Cultures ◽  
Neural Marker ◽  
Engrailed Genes ◽  
Anterior Posterior

We have developed germ layer explant culture assays to study the role of mesoderm in anterior-posterior (A-P) patterning of the mouse neural plate. Using isolated explants of ectodermal tissue alone, we have demonstrated that the expression of Engrailed-1 (En-1) and En-2 genes in ectoderm is independent of mesoderm by the mid- to late streak stage, at least 12 hours before their onset of expression in the neural tube in vivo at the early somite stage. In recombination explants, anterior mesendoderm from headfold stage embryos induces the expression of En-1 and En-2 in pre- to early streak ectoderm and in posterior ectoderm from headfold stage embryos. In contrast, posterior mesendoderm from embryos of the same stage does not induce En genes in pre- to early streak ectoderm but is able to induce expression of a general neural marker, neurofilament 160 × 10(3) M(r). These results provide the first direct evidence for a role of mesendoderm in induction and regionalization of neural tissue in mouse.

A developmental pathway controlling outgrowth of the Xenopus tail bud

Development ◽  
1999 ◽  
Vol 126 (8) ◽  
pp. 1611-1620 ◽  
Author(s):  
C.W. Beck ◽  
J.M. Slack
Keyword(s):  
Normal Development ◽  
Posterior Part ◽  
Neural Plate ◽  
General Mechanism ◽  
Developmental Pathway ◽  
Tail Bud ◽  
Neural Tubes ◽  
Tailbud Stage ◽  
Tail Tip ◽  
Host Embryo

We have developed a new assay to identify factors promoting formation and outgrowth of the tail bud. A piece of animal cap filled with the test mRNAs is grafted into the posterior region of the neural plate of a host embryo. With this assay we show that expression of a constitutively active Notch (Notch ICD) in the posterior neural plate is sufficient to produce an ectopic tail consisting of neural tube and fin. The ectopic tails express the evenskipped homologue Xhox3, a marker for the distal tail tip. Xhox3 will also induce formation of an ectopic tail in our assay. We show that an antimorphic version of Xhox3, Xhox3VP16, will prevent tail formation by Notch ICD, showing that Xhox3 is downstream of Notch signalling. An inducible version of this reagent, Xhox3VP16GR, specifically blocks tail formation when induced in tailbud stage embryos, comfirming the importance of Xhox3 for tail bud outgrowth in normal development. Grafts containing Notch ICD will only form tails if placed in the posterior part of the neural plate. However, if Xwnt3a is also present in the grafts they can form tails at any anteroposterior level. Since Xwnt3a expression is localised appropriately in the posterior at the time of tail bud formation it is likely to be responsible for restricting tail forming competence to the posterior neural plate in our assay. Combined expression of Xwnt3a and active Notch in animal cap explants is sufficient to induce Xhox3, provoke elongation and form neural tubes. Conservation of gene expression in the tail bud of other vertebrates suggests that this pathway may describe a general mechanism controlling tail outgrowth and secondary neurulation.

A study of the properties, morphogenetic potencies and prospective fate of outer and inner layers of ectodermal and chordamesodermal regions during gastrulation, in various Anuran amphibians

Development ◽  
1983 ◽  
Vol 75 (1) ◽  
pp. 67-86
Author(s):  
T. A. Dettlaff
Keyword(s):  
Outer Layer ◽  
Normal Development ◽  
Neural Plate ◽  
Ependymal Cells ◽  
Epithelial Layer ◽  
Bombina Bombina ◽  
Cell Layers ◽  
The Brain ◽  
Early Gastrula

In both the ectodermal and the chordamesodermal regions of Anuran embryos, the outer layer of cells possesses epithelial properties and has the same restricted morphogenetic potencies. It is thus interchangeable between the regions, capable of epiboly and, when underlain by notochord material, of the formation of bottle-shaped cells as at the blastoporal groove, and invagination. When taken from the chordamesoderm region, this outer layer has no inducing effect on the ectoderm of the early gastrula. In normal development the outer layer of the neural plate takes an active part in forming the neural tube cavity. It gives rise to the neuroepithelial roof of the diencephalon and medulla oblongata and, when underlain by neuroblasts that develop from the inner cell layers, to ependymal cells of the brain wall. The outer layer of the notochord material is included in the epithelial layer underlying the roof of the gastrocoel - the hypochordal plate. The inner layers of these regions consist of loosely arranged cells and normally have no epithelial properties although, when taken from the ectoderm region, they may acquire such properties upon long-term contact with the environment. However they have wide morphogenetic potencies; the differences in these potencies between cells taken from the various presumptive regions being less than the differences between outer and inner cell layers in each region. Maps are provided which show the arrangement of presumptive rudiments in the ectoderm and chordamesoderm on sagittal sections through Bombina bombina embryos in early and late gastrulation.

scholarly journals Neural Progenitor Cells Undergoing Yap/Tead-Mediated Enhanced Self-Renewal Form Heterotopias More Easily in the Diencephalon than in the Telencephalon

2018 ◽  
Vol 43 (1) ◽  
pp. 180-189 ◽  
Author(s):  
Kanako Saito ◽  
Ryotaro Kawasoe ◽  
Hiroshi Sasaki ◽  
Ayano Kawaguchi ◽  
Takaki Miyata
Keyword(s):  
Progenitor Cells ◽  
Neural Tube ◽  
Neural Progenitor Cells ◽  
Three Dimensional ◽  
Neural Progenitor ◽  
Hippo Signaling ◽  
Apical Surface ◽  
Elevated Expression ◽  
Underlying Mechanisms ◽  
The Brain

Abstract Spatiotemporally ordered production of cells is essential for brain development. Normally, most undifferentiated neural progenitor cells (NPCs) face the apical (ventricular) surface of embryonic brain walls. Pathological detachment of NPCs from the apical surface and their invasion of outer neuronal territories, i.e., formation of NPC heterotopias, can disrupt the overall structure of the brain. Although NPC heterotopias have previously been observed in a variety of experimental contexts, the underlying mechanisms remain largely unknown. Yes-associated protein 1 (Yap1) and the TEA domain (Tead) proteins, which act downstream of Hippo signaling, enhance the stem-like characteristics of NPCs. Elevated expression of Yap1 or Tead in the neural tube (future spinal cord) induces massive NPC heterotopias, but Yap/Tead-induced expansion of NPCs in the developing brain has not been previously reported to produce NPC heterotopias. To determine whether NPC heterotopias occur in a regionally characteristic manner, we introduced the Yap1-S112A or Tead-VP16 into NPCs of the telencephalon and diencephalon, two neighboring but distinct forebrain regions, of embryonic day 10 mice by in utero electroporation, and compared NPC heterotopia formation. Although NPCs in both regions exhibited enhanced stem-like behaviors, heterotopias were larger and more frequent in the diencephalon than in the telencephalon. This result, the first example of Yap/Tead-induced NPC heterotopia in the forebrain, reveals that Yap/Tead-induced NPC heterotopia is not specific to the neural tube, and also suggests that this phenomenon depends on regional factors such as the three-dimensional geometry and assembly of these cells.

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