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  • 1
    Electronic Resource
    Electronic Resource
    The growth of the human brain during the embryonic period proper (1981)
    Springer
    Anatomy and embryology 162 (1981), S. 137-151 
    Details
    ISSN: 1432-0568
    Keywords: Human embryo ; Embryonic brain ; Brain growth ; Brain measurements ; Developmental stages
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Linear axes of the brain were measured in 143 human embryos from Carnegie stages 11 to 23 (3 1/2–8 postovulatory weeks). The embryos ranged from 3 to 30 mm in C.-R. length. Both Born reconstructions and serial sections of the central nervous system were used. The brain axes included were the fronto-occipital diameter, bitemporal diameter, and length and width of both the mesencephalon and cerebellum. A least squares line was fitted to the set of data points corresponding to each brain axis measured, and a t test verified that a linear model was an appropriate representation of the data. Based on these linear measurements it can be concluded that the forebrain grows more rapidly than the rest of the brain at the onset of tubular brain enlargement. Furthermore, as seen by comparing growth along two dimensions, the forebrain and midbrain grow at the same rate, whereas the cerebellum grows at different rates along the length and height axes. In addition, the cerebellum begins to grow later than the rostral part of the brain. Covariance analysis of the data points of the embryonic brain axes with data points of identical brain axes of the fetus showed that the measurements from the embryonic and fetal brain axes cannot be represented by a single regression line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00306486
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  • 2
    Electronic Resource
    Electronic Resource
    Descriptive studies of occlusion and reopening of the spinal canal of the early chick embryo (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 209 (1984), S. 251-263 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Occlusion and reopening of the lumen of the spinal cord, two processes believed to be involved in early brain enlargement, were examined in chick embryos to determine what morphological features characterize these events. Occlusion begins at a particular craniocaudal level near the time that the neural folds become apposed in the dorsal midline and blocklike somites form from the segmental plates. During occlusion, the apical sides of the lateral walls of the neural tube are in close apposition. Interdigitating apical surface protrusions, cross-luminal intercellular junctions, and abundant cell-surface materials are lacking. Reopening has occurred by about stage 20 throughout most of the craniocaudal extent of the spinal cord. A lumen suddenly appears during this process, but correlated structural changes that might account for such a dramatic change in morphology were undetectable. Reopening involves the release of the forces that previously maintained occlusion, or the generation of new forces that overcome those causing occlusion, but what these forces are remains to be determined. Observations suggest that forces generated outside of the neural tube might be largely responsible for occlusion, and experiments are in progress to test this possibility.
    Additional Material: 23 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1092090211
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  • 3
    Electronic Resource
    Electronic Resource
    Description of the occlusion of the spinal cord lumen in early human embryos (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 204 (1982), S. 89-93 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Previous studies of both chick and human embryos have shown that the brain enlarges rapidly once the neural tube becomes a closed, fluid-filled system. Prior to such enlargement, the medial walls of the spinal cord appear fused, occluding the lumen. This study describes occlusion of the lumen in terms of its incidence, location along the neuroaxis, time of occurrence, duration of occurrence, and morphology in human embryos. Eighty-two human embryos (stages 9-15) from the Carnegie Collection were analyzed. Occlusion first occurs (and is most prevalent) in stage 11 embryos and is absent in embryos older than stage 13. In all cases examined, the neuroaxis demonstrated uninterrupted occlusion from the level of the third pair of somites to at least the ninth pair (i.e., approximately 60% of the neuroaxis was occluded). The appearance of the occluded neural tube in cross sections is similar to that of a soda straw that has been pinched between one's fingers.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1092040112
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  • 4
    Electronic Resource
    Electronic Resource
    Reduced number of brain cells in so-called neural overgrowth (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 212 (1985), S. 195-198 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Patten described as neural overgrowth a folding of brain tissue into the ventricles in abnormal human embryos. Intubation of chick embryo brains releases cerebrospinal fluid pressure resulting in a similar folding. These folded brains have 2.5 times less tissue volume than control embryos of identical stage. This study shows, with total DNA measurements, that brain cell number is 50% less in folded brains (intubated embryos) as compared to control brain of identical staged embryos.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1092120214
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  • 5
    Electronic Resource
    Electronic Resource
    Second messenger regulation of occlusion of the spinal neurocoel in the chick embryo (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Developmental Dynamics 197 (1993), S. 291-306 
    Details
    ISSN: 1058-8388
    Keywords: cAMP ; Adenyl cyclase ; Protein kinase C ; Phosphodiesterase ; Ca2+ ; Verapamil ; Ionophore ; Calmodulin ; Brain ; CNS morphogenesis ; Ionophore A23187 ; Methylisobutylxanthine ; Forskolin ; Dibutyl cyclic adenosine ; Chlorpromazine ; Trifluperazine ; W-7 ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We know that, once rostral neurulation is completed in the neuroaxis of the chick embryo, the caudal neurocoel becomes occluded and the brain rapidly expands. However, very little is known about the mechanisms maintaining occlusion. Studies had shown that occluded neurocoels reopened in embryos treated with chelators of cations, but the reasons remained unclear and the cations unidentified. To begin defining the role of cations, this study explored the effect of Ca2+, calmodulin, and cAMP on maintaining the occluded neurocoel. Chick embryos during the natural phase of neurocoel occlusion (stage 12) were cultured in vitro with drugs known to modulate Ca2+ transport, to inhibit calmodulin activity, or to elevate cAMP levels. To test if occlusion is a Ca2+ -dependent process, embryos were treated with verapamil and ionophore A23187. To test if occlusion requires calmodulin, embryos were treated with antipsychotic agents. To test if occlusion is cAMP dependent, embryos were treated with methylisobutylxanthine (MIX), forskolin (FOR), or dibutyl cyclic adenosine (DbC). Following each treatment, occlusion of the neurocoel was tested by injecting dye into the midbrain. All treatments resulted in a predominant number of precocious reopenings of the occluded neurocoels. MIX-treated, naked neural tubes had a fourfold increase in cAMP, whereas FOR- and DbC-treated neural tubes showed ten- and 14-fold increases, respectively. The presence of calmodulin in the cells of the neural tube was confirmed by fluorescent tagging and 3H-chlorpromazine labelling. The combined results of this study show that occlusion of the spinal neurocoel depends on exogenous Ca2+, requires calmodulin, and is cAMP sensitive. © 1993 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001970407
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  • 6
    Electronic Resource
    Electronic Resource
    Quantification of the initial phases of rapid brain enlargement in the chick embryo (1986)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 175 (1986), S. 403-411 
    Details
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Rapid brain enlargement requires a hydraulic mechanism in the chick embryo. Such a mechanism involves a closed, fluid-filled system that generates positive pressure. For the chick embryo this study (1) determined when rapid brain enlargement begins, (2) assessed the relative contributions of cavity expansion and tissue growth to overall brain enlargement, and (3) evaluated mathematical models of overall brain enlargement and expansion and growth of the component parts. Three to five embryos were collected at each Hamburger and Hamilton stage (11, 12, 14, 16, and 18) and processed for paraffin serial sectioning. Brain growth was determined over a 24-hr period (stages 11-18) by calculating volumes from area measurements of sections of brains from individual embryos by using a computerized image-analysis system. Statistical analysis indicated that a linear model adequately described cavity expansion, and a linear model was rejected for the description of tissue growth and total brain enlargement. At the onset of brain enlargement, the cavity expands faster than the tissue grows; but after 12 hr the reverse is true. Initially (i.e., at stage 11), the cavity accounts for 60% of the total brain volume and tissue for 40%. At stages 12-16, cavity and tissue contribute 50% each. Finally at stage 18, cavity accounts for 55% and tissue for 45%. In order to better distinguish changes in cavity expansion and tissue growth over the 24-hr period studied, this period was divided into four intervals (I-IV). The rates of both cavity expansion and tissue growth increase between intervals I and II, decrease between intervals II and III, and increase between intervals III and IV. Overall, the brain enlarges 8.5 times, the cavity expands 9.8 times, and the tissue grows 7.6 times. Change in cavity expansion for fixed time intervals is constant; for tissue growth it increases continually. Our results describe the cavity and tissue kinetics that occur during rapid brain enlargement. Such information is important for understanding normal development of the brain and may provide insight into the mechanisms of genesis of certain congenital malformations such as microcephaly and hydrocephaly.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001750402
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