bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth pressure can drive early chick lens geometries
Authors: Hendrix Richard , Madras Neal , Johnson Robert
Published: February 2005

Over a number of morphological stages during chick lens morphogenesis, a flat plate of cuboidal ectodermal cells infolds to form a deep cup of tall, pyramidal lenticular cells. This invagination process is accompanied by asynchronous cellular multiplication over a basal region constrained by an adhesive extracellular matrix. A lens placode is formed as the cells crowd into columnar ‘palisades.’ A lens cup forms as the cells pyramidalize owing to basal nuclear movements. Invagination ends when the opening into the lens cup is closed to form a lens vesicle. In this paper, equations are developed that provide a quantitative, mathematical formulation of an earlier theory that explains this invagination as a growth driven process. The equations take into account the lens cell cycle, the extracellular matrix, and nuclear migratory behaviors. Based on the equations, geometries simulating the morphological stages and the cell cycle phases are generated for the 1st day of lens development. The mathematical formulation of lens invagination helps demonstrate how growth pressure alone can be the primary driving force for tissue folding. In this view, recruitment occurs before the shape changes; and cell‐autonomous mechanisms of invagination, involving the cytoskeleton or differential adhesion alone, offer inadequate explanations of these changes. © 1993 wiley‐Liss, Inc.
Ectopic expression of MyoD1 in mice causes prenatal lethalities
Authors: Faerman Alexander , Pearson‐White Sonia , Emerson Charles , Shani Moshe
Published: February 2005

A variety of differentiated cell types can be converted to skeletal muscle following transfection with the myogenic regulatory gene MyoD1. To determine whether MyoD1 is a dominant muscle regulator in vivo, mouse fertilized eggs were microinjected with a β‐actin/MyoD1 gene. Ectopic expression of MyoD1 during mouse embryogenesis led to embryonic lethalities, the cause of which is not known. Transgenic embryos died before midgestation. The majority of tested embryos between 7.5 and 9.5 days, although retarded compared to control littermates, differentiated normally into tissues representative of all three germ layers. In most transgenic embryos there was no indication of myogenic conversion. The expression of the introduced gene was detected in all ectodermal and mesodermal tissues but was absent in all endodermal cells. Forced expression of MyoD1 was associated with the activation of myogenin and MLC2 (but not myf5 or MRF4) genes in non‐muscle cell types, demonstrating the dominant regulatory function of MyoD1 during development. These results demonstrate that ectopic MyoD1 expression and activation of myogenin and MLC2 have no significant effects in the determination of cell lineages or the developmental fate of differentiated mesodermal and ectodermal cell lineages. © 1993 wiley‐Liss, Inc.
Expression of N‐cadherin mRNA during development of the mouse brain
Authors: Redies C. , Takeichi M.
Published: February 2005

The expression of N‐cadherin mRNA was mapped in the brain of mice between embryonic day 12 (E12) and the adult stage by in situ hybridization of digoxigenin‐labeled riboprobe. Two phases of N‐cadherin expression can be distinguished. During the first phase (about E12 to E16), expression is ubiquitous throughout the brain and most prominent in the proliferative neuroepithelium. During the second phase (about E16 to postnatal day 6), N‐cadherin expression is restricted to particular nuclei or laminae that share common functional features and neuroanatomical connections. Several of the N cadherin‐positive structures receive direct afferents from retinal ganglion cells or from the superior colliculus. Others belong to the reticular system and to the limbic system of the brain. In neocortex, N‐cadherin is expressed by deeper layer cells. In the adult brain, only low levels of N‐cadherin expression remain in very few types of cells, for example in the Purkinje cells of the cerebellum.

These results are similar to data from chicken brain and suggest that the generalized expression of N‐cadherin during the early phase and the restriction expression of this molecule in particular functional systems during the later phase is, at least in part, phylogenetically conserved between chicken and mouse. Moreover, the results show that N‐cadherin expression extends to phylogenetically newer structures, e.g., the mammalian neocortex. © 1993 Wiley‐Liss, Inc.
Regulative ability of the prospective cardiogenic and vasculogenic areas of the primitive streak during avian gastrulation
Authors: Inagaki Takayuki , Garcia‐Martinez Virginio , Schoenwolf Gary C.
Published: February 2005

Four types of microsurgical experiments were conducted to analyze heart and blood vessel development during gastrula stages of avian embryos, stages during which prospective cardiogenic and vasculogenic cells reside within the primitive streak. Experiments addressed whether cells not normally destined to form heart could form heart when given the opportunity to do so and vice versa; cells destined to form rostral levels of the heart (or, alternatively, head blood vessels) could form caudal levels of the heart (or, alternatively, trunk blood vessels) and vice versa; the early endoderm imparts rostrocaudal organization to the heart and associated blood vessels; and ingression of cells from the primitive streak and their subsequent migration into the mesodermal mantle is a cell‐autonomous event for migrating cells. Our results demonstrate the lability of prospective cardiogenic and vasculogenic cells of the primitive streak, both in terms of the type of mesodermal structures they are capable of forming (or of being formed from) and in terms of the rostrocaudal patterning of the cardiovascular system. In addition, our results show that cell ingression and migration is directed by environmental cues and is not a cell‐autonomous process for migrating cells. Finally, our results suggest that patterning of the cardiovascular system occurs after cells enter the mesodermal mantle, presumably through cell‐cell inductive interactions. However, the early endoderm is not the primary source of the patterning influence. What is the source remains to be established. © 1993 Wiley‐Liss, Inc.
Evidence of early topographic organization in the embryonic olivocerebellar projection: A model system for the study of pattern formation processes in the central nervous system
Authors: Paradies Michele A. , Eisenman Leonard M.
Published: February 2005

Many projection systems within the peripheral and central nervous system are topographically organized, and it has become increasinging clear that interactions which occur during development determine the projection patterns these systems exhibit in the adult. The olivocerebellar system was chosen as a model system for this study of afferent pattern formation because it has several characteristics which lend themselves to a study of this type. Applications of horseradish peroxidase were made to both the cerebellar primordium and to the inferior olive of embryonic and neonatal mice using an in vitro perfusion system to support the tissue during the transport period. Fibers labeled after restricted olivary applications are limited to particular mediolateral regions of the cerebellum. Similarly, olivary cells retrogradely labeled after discrete cerebellar applications are restricted to particular olivary subdivisions. The results indicate that the olivocerebellar projection displays elements of topographic organization as early as E15 and that the pattern displayed is roughly comparable to that of the adult mammal. The observed trajectories of olivocerebellar fibers and their concomitant association with both Purkinje and cerebellar nuclear cells during embryonic development suggests a role for either or both cell types in the pattern formation process. © 1993 Wiley‐Liss, Inc.
Cell‐cell communication correlates with pattern formation in molting Manduca midgut epithelium
Authors: Baldwin Kate M. , Hakim Raziel S. , Stanton Gregory B.
Published: February 2005

The midgut epithelium of larval Manduca sexta is constructed of single goblet cells surrounded by a one‐cell‐thick reticulum of columnar cells. This pattern is expanded at each molt by the addition of new cells. Between molts, these epithelial cells are not dye coupled, even though gap junctions are present. Proliferating stem cells are dye coupled in small groups early in the molt. Then, at mid‐molt, the whole epithelium temporarily becomes dye coupled. This is when the new (expanded) pattern is being established. Later, at the end of the molt, the epithelium returns to the non‐coupled state. These results suggest that cell communication via gap junctions may play a role in cell patterning. © 1993 Wiley‐Liss, Inc.
Role of the brachial somites in the development of the appendicular musculature in rat embryos
Authors: Lee Kenneth K. H. , Sze Lung‐Yam
Published: February 2005

DiI, a fluorescent lipophilic dye, was micro‐injected into the brachial somites of 10.5 day rat embryos to determine whether these somites can contribute cells to the development of the fore‐limb bud. The injected embryos were cultured and harvested at the 20–25‐somite stage. The dye did not interfere with somitogenesis because, at the injection site, the DiI‐labelled somites were able to differentiate into dermomyotome and sclerotome. We have analyzed cryo‐sections of 20–21‐somite stage embryos and were unable detect the presence of DiI‐labelled cells in the fore‐limb buds. However, at the 22‐somite stage, a few DiI‐positive cells were found in the proximal region of the limb bud. These labelled cells had migrated into the limb from the lateral border of the dermomyotome. From the 23‐somite stage onwards, there were even more DiI‐positive cells inside the limb. We have performed an additional set of experiments to confirm that the somitic cells do have the ability to invade and colonize the limb bud. This was achieved by first labelling newly formed somites isolated from the caudal region of 10.5 day embryos with DiI and then grafting them into corresponding regions in 8–11‐somite stage hosts. The donor somites were not orientated when they were implanted into the host. However, this did not disrupt their ability to undergo normal somitogenesis. We have detected the presence of DiI‐positive cells in the limb buds of approximately 71% of the 19–30‐somite stage embryos that have been examined. This is similar to what we obtained for the injected embryos. Nevertheless, there is one slight difference and that is the stage the somitic cells begin their invasion of the limb. For the injected embryos, migration began at the 22‐somite stage but in the transplanted embryos, it commenced as early as the 18‐somite stage. We have also investigated the myogenic potential of the fore‐limb bud at various stages of development to ascertain whether there is a correlation between the stage the somitic cells first appear in the limb bud and the stage the bud acquires the capacity to form skeletal muscles. This was realized by culturing fore‐limb buds excised from 18–30‐somite stage embryos conventionally and in the kidney capsules of adult rats. In both methods, bone and cartilage were present in all of the cultures whereas skeletal muscles were only present in cultured explants older than the 21–22‐somite stage. The appearances of skeletal muscles in the cultures correlated exactly with the stage somitic cells began their invasion of limb (as seen in the DiI injected embryos). Based upon the indirect evidence that has been obtained, we tentatively propose that the brachial musculature of the rat embryo is derived from the somites while bone and cartilage are formed by the somatopleure of the limb. © 1993 Wiley‐Liss, Inc.
Backtransplantation of chick cardiac neural crest cells cultured in LIF rescues heart development
Authors: Kirby Margaret L. , Kumiski Donna H. , Myers Tammy , Cerjan Chris , Mishima Noboru
Published: February 2005

The cardiac neural crest is essential for normal development of the cardiovascular system. Cardiac neural crest cells are derived from the neural folds located between the mid‐otic placodes and the caudal limit of somite 3. These crest cells can differentiate into a variety of mesenchymal cell types that support cardiovascular development, in addition to neurogenic cells. When cultured, many expressα‐smooth muscle actin or neurofilaments and lose their undifferentiated neural crest phonotype as shown by a decrease in HNK‐1 reactivity. We wanted to determine whether cultured cardiac neural crest cells maintained the potency to support normal heart development when backtransplanted into embryos lacking their native cardiac neural crest. Under usual circumstances removal of the cardiac neural crest results in 80–100% incidence of persistent truncus arteriosus. The present study report a system in which cardiac neural folds are cultured for 3 days and the cells backtransplanted into chick embryos after laser‐induced ablation of the intrinsic cardiac neural folds. Rescue of heart development was improved 50% when cultured cells were backtransplanted and almost 200% when the backtransplanted cells had been cultured in leukemia inhibitory factor (LIF). To determine whether the cultured cells are capable of following normal migratory routes, cultured homospecific cardiac neural crest cells were tagged with DiI. Initially, fluorescent cells were found concentrated around the neural tube. By the second day following backtransplantation, the cells had migrated to the circumpharyngeal crest, populated the pharyngeal arches and aortic arch arteries, and were in the region of the cardiac outflow tract. By the third day, the labeled cells had dispersed, but could be found around the neural tube, esophagus, cardiac outflow tract, and within the dorsal root ganglia. Interestingly, a cranial migration to the periphery of the eyes was also noted. With the exception of the cranial migration to the eyes, cultured and backtransplanted cardiac neural crest cells followed normal migratory pathways to the cardiac outflow tract. LIF is used for the in vitro maintenance of the pluripotential phenotype of embryonic stem cells. In an effort to understand why LIF improves the ability of cultured neural crest cells to support normal heart development, we have examined the relationship of neural crest expression of HNK‐1 antigen,α‐smooth muscle actin, and neurofilament protein in neural crest cells cultured in LIF. LIF treatment resulted in an expanded period of expression of HNK‐1 antigen, associated with a decrease in expression ofα‐smooth muscle actin. The expanded period of HNK‐1 expression is associated with proliferation of the HNK‐1 positive cell population. Expression of the neurofilament was the same in cells cultured with or without LIF. © 1993 Wiley‐Liss, Inc.
Embryonic expression patterns of the drosophila decapentaplegic gene: Separate regulatory elements control blastoderm expression and lateral ectodermal expression
Authors: Jackson P. David , Hoffmann F. Michael
Published: February 2005

Patterns of decapentaplegic (dpp) transcripts derived from the intact gene were compared to the patterns of transcripts generated by partial dpp transgenes in Drosophila embryos. Sequences closest to the dpp coding regions, the dpp hin region, were sufficient to express lacZ‐tagged mRNA in patterns indistinguishable from the patterns of endogenous dpp expression in the dorsal and terminal cells at the blastoderm stage, in the dorsal ectoderm during germ band elongation, and in narrow stripes of ectodermal cells along the dorsal edge of the ectoderm and at the boundary between the lateral and ventral neurogenic regions during germ band shortening. The latter pattern of expression responded to the segment polarity genes naked and wingless. However, these dpp sequences were not sufficient to drive lacZ‐tagged mRNA expression in other cells normally expressing dpp, including cells in the gnathal segments, the clypeolabrum, the foregut, the midgut visceral mesoderm, and the hindgut. Two separate regulatory regions were found in the dpp hin region. A 479 bp region upstream of the promoter was necessary for the segmented pattern of expression in the lateral ectoderm and for expression in the midgut endoderm. Cis‐acting elements in the 2 kbp second intron directed expression in the dorsal and terminal regions of the blastoderm, acted on a heterologous promoter, the P‐element promoter, and responded to pattern information derived from the maternal effect dorsal/ventral patterning genes. © 1994 Wiley‐Liss, Inc.
Apoptosis in human skin development: Morphogenesis, periderm, and stem cells
Authors: Polakowska Renata R. , Piacentini Mauro , Bartlett Russell , Goldsmith Lowell A. , Haake Anne R.
Published: February 2005

During human skin development, embryonic‐ and fetal‐specific periderm cells and incompletely keratinized cells are replaced by keratinocytes that differentiate while stratifying to form the fully functional epidermis. Proliferating basal cells of fetal skin also develop into epidermal appendages such as hair follicles and glands. We demonstrate that programmed cell death, not emphasized in conventional epidermal biology, has an important function in establishing the final architecture of the human epidermis and its appendages. Immunohistochemical localization of transglutaminases in fetal periderm, intermediate epidermal cells, and within appendages coincides with DNA fragmentation indicating that apoptosis is involved in deletion of these stage‐specific cells and remodeling of appendages. The data also suggest that terminal differentiation of epidermal cells might be a specialized form of apoptosis. The pattern of expression of bcl‐2, a gene associated with survival of some cells, is exclusive of the distribution patterns of markers of the cell death pathway. Bcl‐2 protein is correlated with specific morphogenetic events in hair follicles and eccrine sweat glands, and its presence in single cells of the hair follicle bulge suggests that Bcl‐2 may be a stem cell marker. © 1994 Wiley‐Liss, Inc.
Computations of post‐inductive dynamics in axolotl heart formation
Authors: Holloway David M. , Harrison Lionel G. , Armstrong John B.
Published: February 2005

This paper reports modelling of heart localization in the axolotl (Ambystoma mexicanum). The region of heart specification in the mesoderm defined by classical induction from the endoderm is larger than the area of final myocardial differentiation. For localizing the area of differentiation within the area of specification, we postulate a mesoderm in response to induction from the endoderm. This mechanism generates a spatial pattern for two chemicals, an activator and an inhibitor, corresponding to the area of myocardial differentiation. We postulate a diffusible chemical rescuer, which is absent in the cardiac lethal mutant, and which is a precursor to the reaction‐diffusion mechanism. The activator, inhibitor, rescuer, and product of endodermal induction are presented in an enzyme mechanism with rate equations similar to the Gierer‐Meinhardt equations. These equations were solved numerically in both one and two spatial dimensions. We have attained quantitative agreement with the experimental data for sizes of tissue regions and for times to heartbeat. Experiments modelled include wild‐type heart localization as well as both in vitro and in vivo rescue of cardiac lethal mesoderm with wild‐type mesoderm. Based upon the parameters necessary to model heart localization, we make a series of predictions. We predict: a specific profile for the endodermal inducer gradient; the possibility of producing multiple hearts in vivo; and a greater contribution to the heart from the wild‐type mesoderm for in vivo transplants with cardiac lethal mesoderm. We make some suggestions as to the possible chemical nature of the substances in the model. We indicate that the inhibitory field and mechanochemical theories are probably not as promising as reaction‐diffusion for the mechanism of heart localization. © 1994 Wiley‐Liss, Inc.
Amyl acetate: A useful solvent for embedding masses
Authors: Barron Donald H.
Published: February 2005

Pages missing at the time of shipment.
Histochemical observations on the oxidative enzyme activity and hemoglobin synthesis in the developing erythrocytic cells of the embryonic liver,
Authors: Ackerman G. Adolph
Published: February 2005

A histochemical study of the variations in oxidative enzymes, protein‐bound amino acids (histidine, tyrosine, tryptophane, cysteine and cystine), ribonucleo‐protein and hemoglobin was made on the erythrocytic cells during the process of erythropoiesis in the embryonic liver of the rabbit.

Increases in the cytoplasmic content of protein‐bound sulfhydryls and histidine were noted prior to the appearance of histochemically detectable hemoglobin and were nearly inversely related to the staining reaction for ribonucleoprotein. Changes in the oxidative enzyme activity of the developing erythrocytic elements appeared to reflect changes in the number of mitochondria present within these cells at various stages in the process of maturation. No visible changes were observed in the intensity or localization of the histochemical reactions for oxidative enzymes in the mitochondria of the erythrocytic elements except for an apparent slight increase in activity during mitosis. Two forms of hemoglobin were identified, one acid‐soluble localized to the orthochromatic normoblasts and erythrocytes of the primary erythrocytic linage and the other acid‐resistant present in the erythrocytes and late stages of the developing erythrocytic cells of the secondary erythroid series. Histochemical variations occurring during erythpoiesis were discussed in relation to biochemical data concerning hemoglobin synthesis.
A new system of melanocytes in the skin of the potto (Perodicticus potto)
Authors: Quevedo Walter C. , Montagna William
Published: February 2005

Dendritic cells which contain alkaline phosphatase and which are darkened by osmium iodide are found both in the nonpigmented and in the pigmented epidermis of the potto (Perodicticus potto). Similar cells are numerous in the pilary canals of the hair follicles. These cells, which are DOPA‐negative, are found throughout the epidermis, from the dermoepidermal junction to the stratum granulosum. In distribution and in appearance, these dendritic cells are identical to the “Langerhans” cells or to “high‐level” branched cells. Even though we have not been able to ascertain whether or not the melanotic melanocytes contain demonstrable alkaline phosphatase, we conclude, tentatively, that in the potto the dendritic cells in the basal layer, whether melanotic or amelanotic, and “high‐level” branched cells belong to the same cell line.
Arterial supply of the suprarenal gland
Authors: Merklin Robert J.
Published: February 2005

The arterial supply of the suprarenal gland was studied in 25 fetal or neonatal specimens consisting of both suprarenal glands, kidneys, diaphragm and associated vessels and 50 selected, adult postmortem specimens. The suprarenal arteries are derived from the aorta but the superior and inferior artery invariably become the chief supply of the diaphragm and kidney, respectively.

The arteries supplying the gland are end arteries which branch profusely on the surface of the suprarenal capsule. These in turn give rise to smaller vessels in and under the capsule. At this level a unique capillary system forms vascular caps on glomerular clusters of cells. The vascular channels through the cortex are either cleft‐like sinusoids passing through or between glomerular cell groups or arteriae medullae. The former supply the cortical cells and the latter supply the medulla. The sinusoids of the inner cortex are wide, filled with red blood cells and constitute the first order of venous drainage.

The inner, provisional cortex of the fetal suprarenal gland is described and contrasted with the X zone of the mouse which is completely different in histological structure and manner of appearance and disappearance.
The development and hormonal response of the autotransplanted interpubic joint in mice
Authors: Crelin E. S.
Published: February 2005

The ventral portion of the immature pelvis of 12‐day‐old female mice, consisting of the interpubic cartilage and the angles of the pubic bones, was excised and either autoimplanted into its original pelvic site or autotransplanted to the thoracic region. Half the number of mice with pelvic implants and half with thoracic transplants received subcutaneous injections of estrogen and relaxin prior to necropsy. All were sacrificed at 63 days of age.

All the pelvic implants and the majority of thoracic transplants were present at necropsy. The grafts from the untreated mice were similar to the intact pubic symphysis ofa 63‐day‐old mature mouse both in size and morphology. The grafts from the hormone‐treated mice had undergone a pregnancy‐type response of cartilage transformation to ligamentous tissue and resorption of the medial ends of the pubic bones. The possible significance of the cells of the interpubic joint in its response to hormones is discussed.
Effects of transitory pteroylglutamic acid (PGA) deficiency on embryonic and placental development in the rat
Authors: Johnson E. Marshall , Nelson M. M. , Monie I. W.
Published: February 2005

Female Long‐Evans rats, were given a purified PGA‐deficient diet containing 10 mg% of the antimetabolite, 9‐methyl‐PGA, from days 8 to 10 of gestation, followed by a PGA‐supplemented diet from day 10 to autopsy. Thisregimen resulted in 18% embryonic death by day 11, 65% by day 12, and 100% by day 13 of pregnancy.

No morphological differences between PGA‐deficient and control embryos were observed at nine or nine and one‐half days but ten‐day embryos showed retardation of growth and development and decreased mitosis, especially in the neural epithelium. In 11‐day PGA‐deficient embryos the cranial portion of the neural tube was markedly retarded or anomalous. PGA‐deficient embryos still living on day 12 exhibited severely retarded or abnormal development of the cranial region with moderate retardation in other areas. The placentas of PGA‐deficient embryos were normal until the twelfth or thirteenth day when vacuolization and pyknosis of giant cells in the junctional zone occurred. These changes as well as placental involution through day 16 appeared morphologically identical with those observed in placentas of embryosdestroyed surgically on day 12. PGA‐deficiency appeared primarily to affect embryonic rather than placental tissues.
Retardation of the newt limb regeneration with semicarbazide, an inhibitor of histamine formation
Authors: Deck J. David , Shapiro Samuel L.
Published: February 2005

It is widely known that the substance histamine is a noxious agent released from cells when they are injured. At the outset these experiments were intended to show whetherhistamine, persumably released by newt limb amputation, might also promote beginning steps in regeneration. In addition, according to a new view of the physiology of histamine, its formation metabolically by the decarboxylation of histidine is an attribute of the rapid growth of many tissues. These experiments were mainly designed to interfere with histamine production and thereby disrupt the rapid growth of the limb regenerate.

Semicarbazide has been used successfully in mammals to inhibit histidine decarboxylase and decrease the rate of histamine formation. In these experiments, semicarbazide was administered to stumps of amputated newt limbs by microinfusion for many hours at a time in efforts to decrease histamine formation and retard growth.

When semicarbazide was infused into the limb only in preblastemal stages of regeneration, it seemed to have no effect on the course of regeneration. When it was infused directly into the early mesenchymatous blastema, however, it retarded the expansion and differentiation of the blastema. From present evidence, it appears that histamine production may not be concerned in the initiation of limb regeneration but is probably concerned in the phase of rapid blastemal enlargement, whose primary histological attribute is cellular mitosis.
Observations on the sequence of blastemal condensations in the limbs of the mouse embryo
Authors: Forsthoefel Paulinus F.
Published: February 2005

In the forelimbs, the sequence of blastemal condensation is: scapula and humerus, ulna, digit IV, digit V, radius, digit III, digit II, digit I. In the hind limb, the sequence is: innominate bone and femur, fibula, digit IV, digit V, tibia, digit III, digit II, digit I. The sequence described may lead to loss of preaxial parts of the limb in cases of severe over‐all reduction of limb bud material due to genetic or teratogenic agents. The main reason why ectrodactyly and polydactyly in the mouse are usually preaxial is the localization for some unknown reason of alterations in growth rate in the preaxial margin of the footplate. However, the fact that blastemal condensations begin postaxially will tend to confine these and similar skeletal anomalies of the limb to the preaxial part.
Differentiation of vaginal epithelium in mice given estrogen and thymidine‐H3
Authors: Husbands Milton E. , Walker Bruce E.
Published: February 2005

Adult mice of the A/Jax strain were given injections of thymidine‐H3 at proestrus and injections of estrogen at one day intervals thereafter, up to eight days. Mice were killed at daily intervals and longitudinal sections of vagina were radioautographed. Cells which were immediately above the basal layer at proestrus, and which would have given rise to the mucous, nucleated cell layer, eventually produced an interruption in the otherwise continuous cornification of the surface layers. A similar experiment, begun at late metestrus, produced comparable results, except that the interruption of cornification was more pronounced.

Mice which had been ovariectomized two weeks previously were given injections of estradiol and thymidine‐H3. Cells at the surface continued to show a low frequency of mitotic activity and retained their nuclei after estradiol treatment. They were finally sloughed by the squamous transformation of underlying cells. The latter were derived originally from the basal layer under the influence of estradiol, which led to greatly accelerated mitotic activity in that layer. It is concluded that the course of cellular differentiation in these migrating cells is fixed when they are produced by mitosis of basal cells. This differentiation can only be modified, not reversed, by subsequent estradiol treatment even when the cells involved are still capable of undergoing mitosis.
The site of action of trypan blue in cardiac teratogenesis
Authors: Smith W. N. Adams
Published: February 2005

Pregnant Wistar rats were injected subcutaneously with trypan blue and the heart was studied in 206 embryos removed at daily intervals from ten and one‐half to fourteen and one‐half days of gestation.

Cardiac anomalies appeared to be largely due either to malpositioning of the atria consequent upon an abnormal looping of the bulbo‐ventricular loop, or to a decreased formation of cardiac jelly.

The hearts of a further 46 embryos at ten and one‐half days were studied histochemically and 40 of these (24 experimental and 16 control) were stained with Best's carmine. Glycogen granules were found in the hearts of experimental embryos but not in the hearts of control embryos.

It is suggested that trypan blue may act directly on the cells of the myoepicardium of the developing rat heart, causing a precocious transition to the biochemical characteristics of the adult tissue with a consequent decrease in the amount of cardiac jelly formed. The abnormal looping of the bulbo‐ventricular part of the cardiac tube might also be consequent upon such a biochemical change.
An electron microscopic study of thymic corpuscles in the guinea pig and the mouse
Authors: Kohnen Paul , Weiss Leon
Published: February 2005

Thymus of guinea pigs and C3H mice was fixed in 1% osmium tetroxide, embedded in Araldite or Maraglas, and studied under the electron microscope.

Hassall's corpuscles showing the typical concentric, lamellated pattern are observed. Reticular cells form layers around central elements of variable appearance. One or more reticular cells or cystic structures often constitute the centers of corpuscles. Nuclear degeneration, swollen cytoplasm, and intracellular fibrils are characteristic findings. Desmosomes may be quite numerous and may cover a large portion of a cell's surface. Intracellular fibrils are particularly dense at membranous sites and often are apparently unrelated to desmosomes. Reticular cells at the periphery of thymic corpuscles may be contiguous with cells of the cytoreticulum. Many reticular cells contain organelles generally associated with protein synthesis or active transport.

Intercellular and intracellular cysts are regularly seen and are frequently related to thymic corpuscles. Some cysts may be manifestations of cell synthesis and storage.

The epithelial nature of thymic corpuscles and cysts is evident. Thymic corpuscles may arise by localized collapse of the cytoreticulum.
A possible mechanism responsible for the melanocyte distribution of the perineal pigment spot of the mouse
Authors: Schultz John H. , Chase Herman B.
Published: February 2005

The perineal pigment spot of the C57 Black mouse was examined macro‐ and microscopically in animals ranging in age from 14 days post‐fertilization to 28 days post‐parturition. Dendritic pigment‐containing cells first become evident in the dermis of the area on the sixteenth day post‐fertilization. Throughout later stages of development, these pigmented cells continue to be restricted to the dermis of this area. Since the dopa treatment reveals the presence of a melanin synthesizing system within these cells, they are true melanocytes which have become restricted to this layer of the integument.

Histological examination reveals a population of melanocytes in the epidermis and/or hair follicles also. These are rarely found over the center of the area but are seen in increasing numbers laterally from the ventral midline. In contrast, dermal melanocytes are heavily concentrated near the ventral midline but decrease in numbers laterally. There are, therefore, two opposing but complementary gradients of melanocytes in the integument of the pigment spot. This suggests the possibility that a precocious differentiation of the basement membrane in this area during embryonic development inhibits the passage of melanoblasts into the epidermis thereby causing them to be restricted to the dermis.
The primary ossification of the human ilium
Authors: Laurenson R. D.
Published: February 2005

In seven human fetuses of C.R. lengths ranging from 38 mm to 100 mm primary ossification of the ilium has been described.

In the 38 mm fetus the perichondrium at the caudal border of the ilium in the vicinity of the greater sciatic notch is intensely basophilic and contains osteoblasts. In another 38 mm fetus in the same area new bone is present.

In the 50 mm fetus bone has spread cephalad over the internal and external surfaces of the ala of the ilium without invading the underlying cartilage.

In the 58 mm fetus pores are present in the bone and through them osteoblasts and vascular elements are invading the disintegrated cartilage to form the primary marrow cavity.

In the 66 mm fetus the primary marrow cavity has spread into the ala of the ilium.

The whole process is similar to that seen in the primary ossification of the shaft of a typical long bone and follows the sequence described by Streeter ('49).
Histochemical distribution of cholinesterases in the testis, epididymis and vas deferens of the rat
Authors: Risley Paul L. , Skrepetos Chris N.
Published: February 2005

Testes, epididymides, and vasa deferentia of rats were examined for the distribution of cholinesterases using the Koelle thiocholine method. Activity of these enzymes was studied from birth to maturity. Acetylcholinesterase appeared first in Schwann cells of the nerve plexus of the vas deferens and auda epididymidis at birth. Epithelial cell pseudo‐cholinesterase appears in the vas deferens at four days, and an adult distribution is attained at thirty days. Testis, rete testis, ductuli efferentes, and upper caput epididymidis are mainly negative for cholinesterases. In the remainder of the epididymis, three zones of intense epithelial cell reactivity are preceded by regions of lesser intensity. Smooth muscles of the epididymis are negative, but the vas deferens musculature reacts for pseudo‐cholinesterase. The nerve plexus is positive for both acetyl‐ and pseudo‐cholinesterase, and is confined to the corpus and cauda epididymidis and vas deferens. The increasing density of the enzyme‐positive nerves, and the cholinesterase reaction of the musculature distally suggests a probable inhibitory role in the regulation of smooth muscle function in these regions under normal conditions. The absence of an enzyme‐positive innervation and the presence of an enzyme‐negative musculature of the caput is correlated with an active rhythmic contractility in this region, which gradually disappears distally.
Renewal of intestinal epithelium in the freshwater turtle, Chrysemys picta
Authors: Wurth Sister Mary Alan , Musacchia X. J.
Published: February 2005

The area of new cell formation, the rate of proliferation, and the manner in which cells are lost from the intestinal epithelium in the turtle, Chrysemys picta, were studied using a cell labeling technique with tritiated thymidine and mitotic inhibiting technique with colchicine.

In the intestinal epithelium of Chrysemys picta, cellular proliferation was observed to occur in the layer of cells adjacent to the basement membrane. Mitosis occurred throughout the epithelium at a fairly low rate (mitotic index 0.0016). In the upper intestine fewer labeled cells were found in the apical one‐third of a villusfold than in either the mid or basal one‐third. The time required to renew the intestinal epithelium, was estimated to be about eight weeks in winter turtles maintained at 20° to 24°C.

Cell loss from the system appeared to be due to a randomly located movement of cells lumenward from the basement membrane.

Mitotic activity in cold torpid turtles (11°C ambient temperature) appeared to be completely suppressed as shown by a lack of incorporation of tritiated thymidine and an absence of mitotic figures in the intestinal epithelium.

The term villi‐folds was proposed to provide a category for those animals possessing structures having characteristics both of villi and of folds as found in C. picta.
Correlation between morphometric measurements of the aorta and visual scoring of avian atherosclerosis
Authors: Weiss Harold S. , Griminger Paul , Fisher Hans
Published: February 2005

An analysis was made on 140 adult chickens of the relationship between visual estimation of the degree of encroachment of the lumen of the vessel by plaques and such morphometric variables as weight, length, circumference, thickness, density, and combinations thereof of the thoracic and abdominal segments of the aorta. Aortic weight and thickness functions were found to be significantly correlated to scores, accounting in the two highest cases (thickness and weight/area of the abdominal segment, body weight held constant) for 46% (r = 0.68) and 42% (r = 0.65) respectively, of the variability in score. Correlations were considerably lower in the thoracic segment, the highest being r = 0.36 for weight/circumference. The scoring thoracic segment, the highest being r = 0.36 for weight/circumference. The scoring system thus has a basis in measurable physical changes in the wall of the blood vessel, but scoring apparently evaluates considerably more than was measured by the morphometric variables. The morphometric variables would probably serve best as means of comparing different scoring systems and as objective supplements to scoring. The procedure of choice would appear to be weight/area with body weight held constant (i.e. — partial correlation and/or covariance analysis).
Etiology of trypan blue induced antenatal hydrocephalus in the albino rat
Authors: Stempak Jerome G.
Published: February 2005

Wistar strain albino rats were injected with 1 cm3 of a 1% solution of trypan blue. Three types of dye were used: Matheson, Coleman and Bell, Chroma‐Gesellschaft and a highly purified sample. The dyes were injected on days 6, 7, and 8 of gestation. Fetuses were excised from days 16 through 20, fixed, decalcified where necessary, embedded in paraffin, serially sectioned and stained. Newborn young were treated similarly. Chroma‐Gesellaschaft trypan blue was without reproductive or teratogenic effect at the above doses. Increasing the dose did not increase the teratogenicity but did yield a decrease in litter size. Both Matheson, Coleman and Bell trypan blue and the purified sample were teratogenic. The most frequent neural defect observed was hydrocephalus. Serial sections of the newborn hydrocephalics showed an occluded or extremely tenotic aqueduct of Sylvius in 31 of 33 sectioned animals. The fetuses collected from days 18 through 20 also had occluded or stenotic aqueducts if hydrocephalic. Aqueductal stenosis or occlusion was present in 17‐day‐old fetuses, but hydrocephalic was not conclusively demonstrated at this age. Sixteen‐day‐old fetuses did not have aqueductal occlusion in any of those examined, but stenosis was evident. It is concluded that the defect predisposing to hydrocephalus in the young of trypan blue treated rats of this strain is aqueductal stenosis or occlusion.
An experimental study of cerebral lesions produced by the balloon cannula method of stereoencephalotmy
Authors: Epstein Joseph A. , Epstein Bernard S. , Smulewicz Jacob , Jacobs George
Published: February 2005

A method is described for making simple balloon cannulas. These may be inserted into the depths of the brain of the experimental animal and inflated, resulting in the production of a permanent destructive lesion characterized by hemorrhagic necrosis of the parenchyma, elements of the stroma being preserved peripherally. In time, a smooth, well‐defined membrane delineates the oval shaped cavity resulting in a sharply punched‐out lesion. A reversible lesion cannot be produced by this technique. Such lesions may have further clinical or experimental value. The local application of radioactive isotopes to specific areas of the brain under controlled situations permitting withdrawal of solutions may be possible by this method.
Effects of maternal folic acid deficiency on cytologic phenomena in the rat embryo
Authors: Johnson E. Marshall
Published: February 2005

A purified diet lacking folic acid and containing 20 mg% of the antimetabolite, 9‐methyl pteroylglutamic (folic) acid was fed to female Long‐Evans rats during days eight and nine of pregnancy. Embryos were removed at autopsy on the tenth day of gestation for study and comparison with embryos from normal control pregnancies.

Analysis of mitotic counts revealed that 18.6% of the cells in control embryos were in mitosis in contrast to only 5.7% in PGA‐deficient embryos. A disproportionate reduction in anaphase and telophase stages was observed in conjunction with an increased percentage of cell at metaphase. Concomitantly with these mitotic changes a marked reduction in histochemically demonstrable RNA and in numbers of ribosomes as revealed by electron microscopy was observed.
An experimental and descriptive analysis of the melanocyte population in the venter of the PET mouse
Authors: Rovee David T. , Reams Willie M.
Published: February 2005

Although melanoctyes appear to be limited to the hair folicles of adult belly skin of the PET mouse, they are found throughout the integument of the newborn. Trauma applied to the ventral belly skin of newborn PET mice results in the maintenance and augmentation of the melanocytes within the skin, even after the formation and growth of hair. The area immediately surrounding the site of trauma shows an increase in the number of melanocytes, apparently due in part to the disruption of the developing follicles and the consequent release of their pigment cells to the skin. UV irradiation also maintains a system of melanocytes within the ventral belly skin of PET mice.

The significance of the maintenance and augmentation of melanocytes from the newborn into the adult by surgical trauma or UV radiation is discussed.
Lymphocyte formation in the thymus of the embryonic chick
Authors: Ackerman G. Adolph , Knouff Ralph A.
Published: February 2005

Embryonic thymus provides a distinct advantage over the definitive thymus because the earliest formation of lymphocyte and lymphocytic precursors can be observed in a relatively simple and uncomplicated situation. Special cytological techniques combined with light, phase, and electron microscopy have been performed in this investigation involving over 150 chick embryos between 5 and 18 days of embryonic development.

Sequential cytological changes in the development of the thymus into an active lymphocytopoietic organ indicate that lymphoblasts develop by the gradual proliferation and transformation of “undifferentiated” epithelial cells comprising the primordial thymus. Lymphoblastic transformation begins on the seventh day of embryonic development in the chick and is characterized by increased cytoplasmic and nucleolar basophilia and chromatin condensation. “Undifferentiated” epithelial cells undergo two distinct lines of differentiation between the seventh and tenth days: into lymphoblasts and into stellate reticular‐epithelial cells which constitute the organ parenchyma. All stages of lymphocytic maturation may be observed by 10–11 days as the thymus assumes a predominately lymphocytic character. Absence of lymphocytes or lymphocytic precursors in the connective tissue surrounding the embryonic thymus before and during the period of initial lymphoblastic transformation; presence of a continuous basement membrane surrounding the developing thymus; and absence of cells passing through this membrane during this phase of development indicate that the lymphocytic elements appearing in the embryonic thymus parenchyma are of epithelial rather than mesenchymal derivation. Although a contribution of mesenchymal elements to the lymphocytic population via vascular invasion and lobular formation in later stages of thymic development is unlikely, this question cannot be answered at this time. In spite of functional immunological distinctions between the lymphocytes of the chick thymus and bursa of Fabricius, the similarity of origin of the lymphocytic elements of these lympho‐epithelial organs is apparent.
The ultrastructure of megakaryocytes and blood platelets in the rat spleen
Authors: Han Seong S. , Baker Burton L.
Published: February 2005

The cytoplasm of the megakaryocyte in the rat spleen possesses three zones, the perinuclear, intermediate and marginal. The perinuclear zone is characterized by the presence of Golgi apparatus, ribosomes, endoplasmic reticulum, and mitochondria. These organelles are found also in the more voluminous intermediate zone which in addition exhibits platelet granules and an extensive development of vesicles from smooth‐surfaced endoplasmic reticulum to form demarcation membranes by coalescence. The marginal zone is almost devoid of the organelles and inclusions present elsewhere. Shedding of platelets appears to occur by extension of a paired demarcation membrane from the intermediate zone to the cell membrane and subsequent separation of its lamellae so that all of the essential organelles and inclusions of the intermediate zone may be included within the platelet. In addition, platelets contain vesicles which are probably pinocytotic in nature. Platelets are sometimes engulfed by the cytoplasm of phagocytic cells.