bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acetylcholinesterase- and norepinephrine-containing nerves in developing rat lung
Authors: El-Bermani Al-Walid I. , Bloomquist Eunice I. 
Published: April 2021

ABSTRACT
The lungs of rat fetuses at various stages of gestation and lungs of infant rats were examined histochemically for acetylcholinesterase (AChE) and norepinephrine (NE). No AChE is present in the fetal lungs until 15 days of gestation. At this stage a number of large round cells appear which stain heavily for AChE. These cells disappear by the 18th day of development and at 18 days no AChE-positive structures are demonstrable within the lung. The large AChE-positive cells are of similar size and distribution to fluorescent cells which become apparent after treatment of the mothers with L-DOPA. At 20 days, the day before delivery, a diffuse AChE reaction appears in the walls of large branches of intrapulmonary bronchi. At 20 days, also, sparse NE-containing nerves are present near the hilum and extend along bronchial arteries into the lung. Not until birth do AChE-containing nerves appear in intrathoracic structures. These are vagal preganglionic and postganglionic fibers near the trachea, bronchi, and esophagus. AChE-positive ganglion cells are present in the walls of extrapulmonary bronchi at birth, and perimuscular nerve plexuses containing AChE are also present in the bronchial walls. NE-containing nerves are visible in several divisions of the bronchial artery at birth. Three days postnatally, AChE-containing nerves have not yet invaded intrapulmonary structures, but at this stage the adult pattern of adrenergic innervation is present. By the fifth postnatal day, sparse AChE-positive nerves are associated with intrapulmonary bronchi, and rats 9 days old present the adult pattern of cholinesterase-containing nerves.
Scanning electron microscopy of cells isolated from amphibian early embryos
Authors: Stanisstreet Martin , Smith James L. 
Published: April 2021

ABSTRACT
Cells have been dissociated from Xenopus and Ambystoma late blastulae, allowed to adhere to glass coverslips, and studied by scanning electron microscopy. Xenopus ectoderm cells initially show filopodia; later larger single pseudopodia are formed. Ambystoma ectoderm cells show fewer filopodia than Xenopus ectoderm, but later form pseudopodia. Ectoderm cells of both Xenopus and Ambystoma show links between adjacent cells. Xenopus endoderm cells do not show filopodia initially, but later show large pseudopodia.
The effect of retinoic acid on chondrogenesis in the fetal hamster tibia in vivo
Authors: Fraser B. A. , Travill A. A. 
Published: April 2021

ABSTRACT
Chondrogenesis in the fetal hamster tibia was examined 24, 36 and 48 h after maternal administration of retinoic acid at a known teratogenic dose (80 mg/kg) on day 10 of gestation. Twenty-four hours after treatment the tibial chondroblasts were more closely packed with less intervening fibrillar or granular matrix than in the controls. By 36 h post treatment, an intercellular matrix containing wide clumped fibrils unassociated with matrix granules had begun to accumulate, while the chondroblasts had a relatively poorly developed Golgi apparatus and smooth, non-scalloped cell outlines. Cells frequently maintained contact through pseudopodial processes. Forty-eight hours after retinoic acid treatment, the chondroblasts appeared similar to controls of the same age. It is suggested that the paucity and abnormality of the extracellular matrix prevents the chondroblasts from assuming their normal spatial relations with each other, resulting in a small skeletal blastema.
Developmental studies of the lethal geneBldin the mouse
Authors: Vankin G. Lawrence , Caspari Ernst W. 
Published: April 2021

ABSTRACTIn matings of Bld/ + × Bld/ + mice a characteristic type of abnormal embryo is found on days 6 and 7 after impregnation which dies at 8 days and accounts for about 25 % of all living embryos. These embryos are regarded as the lethal Bld/Bld homozygotes. Before 6 days the embryos appear slightly retarded. Entodermal cells invade the yolk sac and the trophectoderm does not fuse to the uterine decidua. Late on day 6 the yolk sac is filled with a cap of unorganized cells of entodermal origin, surrounded by both a thick membrane of non-living material, corresponding to Reichert’s membrane, and external to this a con-tinuous layer of trophectoderm; there is still almost no contact with uterine tissue. At 7 days 10 h amniotic folds are formed. Mesoderm appears occasionally but is not always present; when it appears it does not grow out from its place of origin. Entodermal cells, particularly in the proximal part of the extra-embryonic region, become polyploid. At the same time, the trophectoderm makes contact with the uterine decidua and gives rise to primary giant cells. Twelve hours later, the embryonic cells begin to degenerate, first in the region of the amniotic fold and the mesoderm. The embryo dies shortly afterwards.It is suggested that the primary target tissues affected by the Bld/Bld constitution are trophectoderm and entoderm. Many but not all of the abnormal features appearing later can be ascribed to insufficient nutrition of the embryo, due to failure of attachment of the trophectoderm and the filling of the yolk sac with entodermal cells.
Acquisition of differentiative capacity in imaginal wing discs of Drosophila melanogaster
Authors: Bownes Mary , Roberts Sarah 
Published: April 2021

ABSTRACT
The wing discs from larvae undergoing the moult from 1st to 2nd instar are able to differentiate some parts of the adult wing when forced to undergo a premature metamorphosis. The first structures which differentiate are parts of the wing hinge and the wing blade. As development proceeds and older discs are forced through metamorphosis, the capacity to differentiate moves out both proximally and distally until gradually all of the derivatives of a mature wing disc are formed. Individual structures often differentiate from young discs in an incomplete form and pattern elements, such as bristles or sensilla, are added as older discs are tested.
Development of the segmental innervation of the chick forelimb
Authors: Pettigrew A. G. , Lindeman R. , Bennett M. R. 
Published: April 2021

ABSTRACT
A number of recent studies have shown that during embryonic development the initial innervation of a target structure may be made up, in part, by axons which do not form part of the mature innervation of that structure. In the present study we have examined the motor innervation of the major muscles of the chick forelimb at different stages of development using HR.P-uptake-labelling of motoneurons, electrophysiological recording and measurement of muscle contraction.
In the mature White Leghorn chick the major contribution to the motor innervation of the forelimb is from spinal segments 14, 15 and 16. Using the HRP-labelling technique we have shown that at stages 26-29 of development motoneurons in segments 12—17 have axon terminals in the presumptive biceps muscle. Between stages 30 and 35, however, the axon terminals arising from segments 12, 13, 16 and 17 are lost, leaving the mature innervation from segments 14 and 15. We have also observed the loss of innervation of the biceps muscle by segment 16 using electrophysiological recording of compound action potentials in the biceps nerve and by measurement of the local contraction of the biceps muscle in response to stimulation of the segmental nerves. Similar changes in the innervation of the triceps, extensor metacarpi radialis, flexor carpi ulnaris and flexor digitorum profundus muscles have also been observed.
These results are discussed in relation to the hypothesis that (i) the motoneuron pools and muscles in the developing spinal cord and forelimb are matched, (ii) that some axons which arrive in a particular muscle during early development are unable to form a stable connexion and (iii) that the inability of an axon terminal to form a stable connexion in a muscle results in the death of the motoneuron.
Intracellular recording from muscle cells at stage 35 shows that the synaptic site on each cell is innervated by about three separate axons. Over the next few stages, however, all but one of the innervating axons is lost. From our contraction studies it is clear that the removal of the excess axon terminals after stage 35 is not associated with the establishment of the mature segmental innervation pattern of the muscle.
Ventral horn cell counts in a Xenopus with naturally occurring supernumerary hind limbs
Authors: Lamb Alan H. 
Published: April 2021

ABSTRACT
In a Xenopus toad, two partially functioning supernumerary hind limbs developed naturally on the right side and were innervated by the ipsilateral side of the spinal cord. The number of ventral horn cells on the right was 18% higher than on the left while the combined mass of limb muscle on the right was estimated to be a 100 % greater. This result corroborates studies with transplanted supernumerary limbs.
A mutant ofTetrahymena thermophilewith a partial mirror-image duplication of cell surface pattern: I. Analysis of the phenotype
Authors: Jerka-Dziadosz Maria , Frankel Joseph 
Published: April 2021

ABSTRACTCells of a mutant clone, CU-127, of Tetrahymena thermophila (formerly T. pyriformis, syngen 1) manifest three anatomical abnormalities. First, the stable number of ciliary meridians is 21-25, above the usual number (17-21) in this species. Second, up to 30 % of the cells have two oral apparatuses (OAs), one normal and the other abnormal. Third, more than one-half of the cells possess two distinct sets of contractile vacuole pores (CVPs). In some living cells two contractile vacuoles are seen. These abnormalities have persisted unchanged during more than 500 generations of vegetative propagation, and are similarly expressed in subclones. The normal and abnormal OAs are topographically segregated, with normal OAs developing along the ‘primary oral axis’ and abnormal OAs developing along a ‘secondary oral axis’ that is situated 170° of the cell circumference to the cell’s right of the primary oral axis. CVPs always appear within this 170° arc and never within the complementary 190° arc to the left of the primary oral axis.A unique feature of the CU-127 clone is the commonly expressed mirror image reversal of the structural pattern of OAs that develop along the secondary oral axis. The primordia of such OAs initially appear (as usual) to the cell’s left of a ciliary meridian, but as membranelies develop they frequently come to be oriented in a mirror image of the normal pattern, and an undulating membrane sometimes develops on the wrong (left) side of the oral primordium. When two sets of CVPs are formed, their average positions are roughly equidistant with respect to the two oral axes, with the two sets located 50-60° to the right and left respectively of the primary and secondary oral axes. Such cells are thus bilaterally symmetrical about a plane defined by the central longitudinal axis and the halfway point between the two CVP sets (see Fig. 25). This plane bisects the cell into a normal and a ‘reversed’ half-cell. However, only oral asymmetry and large-scale CVP positioning are subject to such reversal ; all ciliary meridians remain of normal asymmetry and all CVPs are situated on the left side of CVP meridians. The fact that major aspects of large-scale cellular organization can be reversed while the ‘fine-positioning’ associated with the ciliary meridians remains normal indicates that the two aspects of cell organization are distinct.
Culture of early somite mouse embryos during organogenesis
Authors: Sadler T. W. 
Published: April 2021

ABSTRACT
Early somite (2-4) mouse embryos were explanted and then maintained in culture for 24 or 48 h intervals. Various types of media were tested and it was determined that rat serum supported normal growth over a period of 48 h, based on total protein analysis and histological comparisons with in vivo specimens. Other media including fetal calf serum and fetal calf serum + Waymouth’s (1:1) supported some growth, but did not equal the success of using rat serum alone. During the 48 h culture period in rat serum, embryos developed to stages indistinguishable from embryos maintained for a similar time in vivo.
Long-term Changes in the Size and Collagen Content of Scars in the Skin of Rats
Authors: Abercrombie M. , James D. W. 
Published: April 2021

ABSTRACT
A description is provided of the changes in area, wet weight, and collagen content of the scar left by a small skin wound in young adult rats during the period between 15 days and 300 days after wounding. The corresponding changes in normal skin were also followed. A standard square area of skin of about 20 mm.2 was marked by tattooing on the back of each of a number of rats, averaging about 250 g. in body-weight. The area was then excised and its collagen content estimated by the hydroxyproline technique of Neuman & Logan (1950). The wound was allowed to heal without dressing. At 15, 50, 100, 200, and 300 days after wounding groups of the animals were killed, the scars measured, and their hydroxyproline content estimated. Control areas of normal skin, similarly tattooed at the same time as the wounded area, were measured in the 100-, 200-, and 300-day groups, and excised for collagen estimation at the same time as the scars. After the period of contraction and the following phase of stationary area, which according to previous work lasts until about 25 days after wounding, the scar starts to expand, and probably continues to do so throughout the period of observation. The expansion is rapid at first, but diminishes in rate. An initially comparable area of normal skin also grows throughout at a diminishing rate per day, but, at least up to about 50 days after wounding, at a lower rate per unit of area already present than the scar. The wet weight of the scar increases proportionately to its increase in area. The wet weight of normal skin probably increases a little faster than its area, and the wet weight per unit of area of normal skin eventually surpasses that of the scar. Collagen formation in the scar probably occurs throughout the period of scar expansion, at such a rate as to increase the content per unit of area and of wet weight. Normal skin is at the same time also increasing its collagen content per unit of area and of wet weight, but not so fast as the scar. Consequently by about 50 days the scar concentration per unit of wet weight or of area has caught up with that of control skin; by 100 days the scar clearly surpasses the normal skin in collagen per unit of wet weight, and by 200 days in collagen per unit of area. The growth of the scar is interpreted according to the hypothesis of Billingham & Medawar (1955), as a response to tension.
The relationship between retinal and tectal growth in larvalXenopus:implications for the development of the retino-tectal projection
Authors: Gaze R. M. , Keating M. J. , Ostberg A. , Chung S-H. 
Published: April 2021

ABSTRACTThe modes of retinal and tectal histogenesis, as well as the patterns of terminal distribution of optic axons in larval Xenopus were studied, using anatomical techniques. We show that the retina grows by adding strips of cells at its ciliary margin. The pattern of retinal growth is asymmetrical along the dorso-ventral axis of the retina. On the other hand, the tectum grows by adding newly formed cells caudo-medially. The most rapid tectal growth takes place between stages 50 and 53, and thereafter only a small proportion of cells are added near the midline of the caudal tectum. Despite such incongruent modes of retinal and tectal growth, retinotopic order is maintained throughout larval life.We present here further evidence supporting the idea that connexions between the arrays of retinal and tectal cells shift progressively caudo-medially on the tectum during the period of growth. When the temporal pole of the retina is destroyed at various developmental stages, the density of degenerating synapses is always highest in the rostral pole of the tectum. Moreover, optic terminals stemming from the central retina spread caudally, invading newly maturing regions of the tectum. Quantitative analysis of the terminal distributions of optic axons suggest that orderly shifts in synaptic contacts between optic axons and tectal dendrites take place in the course of development. Ultrastructural observations on the maturing tectal neuropil are consistent with this view.
Surface potentials and the control of amphibian limb regeneration
Authors: Lassalle B. 
Published: April 2021

ABSTRACT
The relationship between surface potentials and amphibian limb regeneration is examined. The wound surface becomes increasingly positive for several days after amputation but then decreases again, often becoming negative for a variable period during blastemal growth. The same changes of surface potentials are observed during wound healing alone, in the absence of amputation and following amputation of irradiated or denervated limbs. Similar changes occur in non-regenerating frog arms. These observations and other cited reasons lead to the conclusion that surface potentials do not control regeneration.
The use of avian double monsters in studies on induction of the nervous system
Authors: Ulshafer R. J. , Clavert A. 
Published: April 2021

ABSTRACT
Ninety-eight duck double monsters (siamese twins) were studied between 48 and 72 h of incubation in whole-mount or serial-sectioned preparations. Each case was classified into one of four categories depending on the orientations of the two embryonic axes. In all classes, defects in primary neural induction of various parts of the embryonic nervous system were observed which depended to a large extent on the distance separating the anterior tips of the two notochords or on the relative positions of the notochords. Our observations suggest that: when the same inducing field of one embryo overlaps to a critical extent with that of the twin, the two inducers act as one; induction of forebrain and optic vesicles is purely prechordal; the notochord exerts an inhibition on induction of forebrain by prechordal mesoderm; and the presence of rhombencephalic structures depends on both prechordal and chordamesodermal interactions.
Somitogenesis in amphibia: II. Origins in early embryogenesis of two factors involved in somite specification
Authors: Elsdale Tom , Pearson Murray 
Published: April 2021

ABSTRACT
A somite pre-pattern is established shortly before visible segmentation. The pre-pattern results from the interaction of two components: a wave of cell behavioural change that passes along the axis, and, an underlying co-ordination of the cells that is the basis for their association into large somite-sized groupings. The evidence is derived from studies of the zones of abnormal segmentation that follow temperature shocks delivered between the neurula and tail-bud stages (Pearson & Elsdale, 1979).
Temperature shock given earlier at the mid-gastrula stage is however ineffective in inducing abnormalities in somitogenesis. Shocks given before the mid-gastrula stage reveal a prior period of sensitivity stretching back into the blastula. Thus early and late sensitive periods can be defined separated by a short refactory period. Quite different patterns in the distribution of somite abnormalities characterize the results of shock during the two sensitive periods, suggesting different aetiologies.
It is concluded that the wave of rapid cell change is set up early in embryogenesis during the blastula stage, and each cell of the prospective paraxial mesoderm carries a determination to change after a specific length of time, i.e. a countdown is set in each cell. As a result of the movements of gastrulation, the prospective paraxial mesoderm cells become laid out along the axis of the neurula in the order (antero-posterior sequence) in which they will change. The achievement of the correct redistribution of the cells depends crucially on the conservation of the sequence in the blastula by the maintenance of topological integrity throughout gastrulation. It is suggested that early shock disturbs gastrulation movements, causing some mixing up of the cells resulting in incoherence of the wavefront.
Whereas early shocks are thus assumed to affect the wave, the evidence suggests that late shock undoes co-ordination. It is concluded therefore that co-ordination is established later, after the refractory period, around the late gastrula stage.
Cell number in relation to primary pattern formation in the embryo of Xenopus laevis: II. Sequential cell recruitment, and control of the cell cycle, during mesoderm formation
Authors: Cooke Jonathan 
Published: April 2021

ABSTRACT
Morphological evidence is presented that definitive mesoderm formation in Xenopus is best understood as extending to the end of the neurula phase of development. A process of recruitment of cells from the deep neurectoderm layers into mesodermal position and behaviour, strictly comparable with that already agreed to occur around the internal blastoporal ‘lip’ during gastrula stages, can be shown to continue at the posterior end of the presumptive body pattern up to stage 20 (earliest tail bud).
Spatial patterns of incidence of mitosis are described for the fifteen hours of development between the late gastrula and stage 20–22. These are related to the onset of new cell behaviours and overt cyto-differentiations characterizing the dorsal axial pattern, which occur in cranio-caudal and then medio-lateral spatial sequence as development proceeds. A relatively abrupt cessation of mitosis, among hitherto asynchronously cycling cells, precedes the other changes at each level in the presumptive axial pattern. The widespread incidence of cells still in DNA synthesis, anterior to the last mitoses in the posterior-to-anterior developmental sequence of axial tissue, strongly suggests that cells of notochord and somites in their prolonged, non-cycling phase are G2-arrested, and thus tetraploid. This is discussed in relation to what is known of cell-cycle control in other situations.
Best estimates for cell-cycle time in the still-dividing, posterior mesoderm of the neurula lie between 10 and 15 h. The supposition of continuing recruitment from neurectoderm can resolve an apparent discrepancy whereby total mesodermal cell number nevertheless contrives to double over a period of approximately 12 h during neurulation when most of the cells are leaving the cycle.
Because of pre-existing evidence that cells maintain their relative positions (despite distortion) during the movements that form the mesodermal mantle, the patterns presented in this paper can be understood in two ways: as a temporal sequence of developmental events undergone by individual, posteriorly recruited cells as they achieve their final positions in the body pattern, or alternatively as a succession of wavefronts with respect to changes of cell state, passing obliquely across the presumptive body pattern in antero-posterior direction. These concepts are discussed briefly in relation to recent ideas about pattern formation in growing systems.