bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of high fluoride diets on developing enamel and dentin in the incisors of rats
Authors: Yaeger James A.
Published: February 2005

Three groups of ten rats each were placed on diets containing 0.025, 0.05, and 0.1% sodium fluoride, and killed in pairs at intervals of 1, 2, 4, 8 and 16 weeks. Their maxillary incisors were embedded in methacrylate, transverse and longitudinal sections were cut, and microradiographs prepared. A few teeth were demineralized, embedded in paraffin, and sectioned transversely. These demineralized sections were stained with histochemical methods for polysaccharide‐protein complexes.

In the dentin, four abnormalities were commonly seen; striations, hypoplastic defects, hypomineralized interglobular spaces, and gross deformations of the external outline of the dentin. The number and severity of these abnormalities increased with increasing fluoride levels in the diets, and with increasing time on the diets. Both hypo‐ and hypermineralized striations were seen in the microradiographs. The previously hypomineralized layers and interglobular spaces stained weakly for polysaccharide‐protein complexes in the demineralized sections.

In the enamel, a hypermineralized surface layer covered a diffuse zone in which mineralization was inhibited. Hypoplastic defects were also common.

In the description of the effects of fluoride, these abnormalities form part of a continuum of changes from the histologically distinct and well characterized responses to injected fluoride, to the subtle changes seen in human chronic endemic dental fluorosis.
The effect of relaxin on the endometrium of monkeys histological and histochemical studies
Authors: Dallenbach‐Hellweg G. , Dawson A. B. , Hisaw F. L.
Published: February 2005

Castrated or juvenile monkeys were given estrogen, progesterone and relaxin in various doses and combinations. Relaxin induced: (1) a dilatation of the superficial endometrial blood vessels and proliferation of their endothelial cells; this effect may be regarded as due to relaxin alone; (2) an intensified differentiation of the endometrial stroma cells into predecidual cells and granulocytes, dependent on estrogen priming and the simultaneous injection of progesterone; (3) a periarteriolar mantle‐like accumulation of granulocytes in the basal endometrium dependent on the above pretreatment; (4) a degranulation of the granulocytes and hypersegmentation of their nuclei following prolonged administration of relaxin with estrogen and progesterone. Morphologically and histochemically the granulocytes of the monkey are almost identical with those of the human uterus and with the granular cells in the decidua and mesometrial gland of the pregnant rat. Immunohistologically relaxin has been demonstrated in the granulocytes of man and rat. The changes in the arterioles brought about by exogenous relaxin occur under physiological conditions only with the increased formation of endogenous relaxin during early pregnancy. They have been described in the immediate vicinity of ovum implantation in man, monkey, and rat. Their function possibly lies in the preparation of blood spaces for nutrition of the young embryo.
Morphology of the cells of normal, testosterone‐deprived and testosterone‐stimulated levator ani muscles
Authors: Venable John H.
Published: February 2005

The atrophy of the levator ani following castration of an adult mouse or rat results from the dissolution of the myofilaments from myofibrils and eventual loss of two‐thirds of the sarcoplasm. Within 45 days the atrophy ceases. The morphology of the now smaller muscle fibers is indistinguishable from those from intact males. Treatment of the stable neuter with testosterone produces rapid enlargement of the muscle fibers, but neglegible changes in the morphological patterns of the sarcoplasm. Observations indicate that new myofilaments form in register along the myofibrils, the enlarging myofibrils being divided to maintain a diameter between 0.5 and 1.5 μ. The cytology of each of the five cell types common to the primary bundles is described. Satellite cells of the muscle fibers are a consistent component, but do not contribute to the processes of atrophy or hypertrophy.
Properties of body segments based on size and weight
Authors: Dempster Wilfrid Taylor , Gaughran George R. L.
Published: February 2005

Values are presented for body constants based on a study of nine male white cadavers of normal appearance and average build. The limb data are supplemented by a further analysis of 11 upper and 41 lower limbs. Techniques used in the study form standard procedures that can be duplicated by subsequent workers. Each cadaver was measured, weighed, and somatotyped. Joints were placed in the midposition of the movement range and the body was frozen rigid. Joint angles were bisected in a systematic dismemberment procedure to produce unit segments. These segment lengths were weighed, measured for linear link dimensions, and analysed for segment volumes. The segment centers of mass were located relative to link end points as well as in relation to anatomical landmarks. Finally, each segment was dissected into its component parts and these were weighed. The specific gravity of each body part was calculated separately. Data are expressed in mean values together with standard deviations and, where available, are correlated and evaluated with other values in the literature.
Differences and relationships between the physical properties and the microscopic structure of human femoral, tibial and fibular cortical bone
Authors: Evans F. Gaynor , Bang Seong
Published: February 2005

Coefficients of correlation between certain physical properties and the histological components of the break area were calculated on an IBM 7090 computer for 56 femoral, 79 tibial and 37 fibular specimens of embalmed cortical bone of standardized size and shape. Strong positive correlations (0.01–0.02 significance level) were found between tensile strength and the percentage of interstitial lamellae in the break area; between hardness and the number of osteons/mm2; and between hardness and the percentage of osteons in the break area. Equally high negative correlations were found between tensile strength and percentage of osteons in the break area; between shearing strength and average area/osteon remnant; between elastic modulus and percentage of spaces in the break area; and an even higher correlation (0.001) between hardness and percentage of spaces in the break area. Negative correlations (at slightly more than 0.05 significance level) were found between shearing strength and modulus and average area/osteon. Osteons tend to reduce the tensile strength and elastic modulus of bone while interstitial lamellae tend to increase them. The probable reason is the relatively greater amount of cement lines, which are sites of weakness where failure can occur, in Haversian bone as compared with lamellar bone. The predominant orientation of collagen fibers and the amount and distribution of calcium may also be involved. These factors are now being investigated.
The mechanism of spermiation in the toad
Authors: Burgos M. H. , Vitale‐Calpe R.
Published: February 2005

The present paper is the first demonstration, at the ultrastructural level, of the mechanism of sperm release from the Sertoli cells. The main target of the immediate effect of LH is the cytoplasm of the Sertoli cells.

Three main stages are recognized in the cellular response: (1) swelling of the endoplasmic reticulum, (2) swelling of the apical cytoplasm, (3) the apical detachment.

The preservation of the nucleated basal portion of the Sertoli cells after the stage of apical detachment is assured by a mechanism of protective overlapping of residual membranes.

It has also been shown that LH is able to increase water and sodium content in the toad testis. It is postulated that water enters after the injection of the LH into the channels of the endoplasmic reticulum, then the water moves into the apical cytoplasm attracted by hydrophilic products derived from enzymatic splitting of cytoplasmic mucoproteins. Finally water passes into the lumen of the seminiferous tubules simultaneously with cell debris and the liberated spermatozoa. The lysosomes present in the cytoplasm of the Sertoli cell in this mucolytic action may be involved.
An electron‐ and light‐microscope study of sinus structure in perfused rabbit and dog spleens
Authors: Thomas Carolyn Eyster
Published: February 2005

The removal of blood cells by low‐pressure perfusion produced well‐delineated views of the sinus wall in rabbit and dog spleens. The sinus wall contained three elements: an inner layer of sinus cells, an intermediate layer of basement membrane, and an outer layer of cord‐limiting cells. Sinus and cord‐limiting cells, apparently similar to each other in cytoplasmic detail, appeared to be reticular cells that possessed only a limited capacity for phagocytosis of gold particles. Apertures in the sinus wall enabled blood cells to pass through the wall. Many apertures in perfused spleen contained no cells and yet remained patent. Sinus cells often were contiguous and commonly did not alternate with apertures. However, sinus‐cell interdigitation was slight, and evidence for tight junctions and desmosomes between sinus cells was inconclusive.
The effects of multiple pregnancies and age on the elastic tissue of uterine arteries in the guinea pig
Authors: Albert Ernest N. , Bhussry B. R.
Published: February 2005

Mesometrial arteries and representative areas of the uterus were obtained from young and old postpartum guinea pigs. The tissues were fixed in Bouin's solution and then stained with Taenzer's Orcein and Verhoeff's elastic stains. Picro‐indigo‐carmine and Van Gieson were used as counterstains.

It was found that the distribution of elastic tissue and the number of elastic and muscle layers in the arterial walls in general reflected the number of pregnancies the animal had had. This was found to be reliable only up to three pregnancies, after which the animals could be referred to only as being multiparous. There appeared to be a continuous increase in the amount of elastin in the blood vessels with each successive pregnancy. Further, aged animals showed more elastin in their vessels than younger ones of comparable parity. The formation of the new internal elastic membrane appeared to be delayed in older females.

Our observations suggest that there might be a decrease in the postpartum resorption of elastin as a result of successive pregnancies and aging. They also suggest that the delay in the formation of the new internal elastic membrane in older postpartum females is probably due to aging.
Movement of palatine shelves in untreated and teratogen‐treated mouse embryos
Authors: Ross Lawrence M. , Walker Bruce E.
Published: February 2005

Movement of palatine shelves in living mouse embryos after tongue displacement was evaluated by direct observation and by re‐examination of the shelves after freezing or submersion in fixative. Effect on shelf function of suspending the embryos in saline or plasma was compared with manipulations in air. Measurements were made of head dimensions and residual space between the palatine shelves in embryos fixed in the cornua or after experimental manipulation. All methods of evaluating palatine shelf behavior indicated movement toward the midline by the anterior portions of the shelves after tongue displacement. Experiments with complete detachment of the tongue demonstrated that the tongue contributes to the flattening of the shelves into a horizontal plane by exerting pressure from below.

The same techniques applied to embryos treated with cortisone, vitamin A and x‐ray demonstrated reduced movement of palatine shelves toward the midline when compared with untreated embryos. The reduction was greatest with x‐irradiation and least with hypervitaminosis A.
Notes on the development of the lung in infancy and early childhood
Authors: Boyden Edward A.
Published: February 2005

This account is based upon graphic reconstructions and wax models of the lungs of an infant five and one‐half months of age and of a child 3.7 years old; also upon plastic injections of a 10‐month lung and upon modelled serial sections of the bronchioles in a child six and two‐thirds years of age.

In passing from the second postnatal month to the sixth month the general pattern of a terminal bronchiole and its branches seems not to have changed. However, angulation of the crowded alveolar ducts becomes visible in the tenth month and may have produced small accessory saccules at such angles.

Sometime before the fourth year numerous alveoli of a new type have appeared, designated here as ductular alveoli, since they arise as invaginations of bronchiolar diverticula lined originally by columnar epithelium. These become the “spherical alveoli” of the adult and transform terminal bronchioles at this late stage into respiratory bronchioles. By the seventh year narrow ductular processes, radiating from preterminal or terminal bronchioles, are beginning to penetrate adjacent alveoli, initiating the Lambert type of collateral ventilation. Thus, the centripetal advance of differentiation continues.
An electron microscopic study of ciliogenesis in developing epidermis and trachea in the embryo of Xenopus laevis
Authors: Steinman Ralph M.
Published: February 2005

This paper describes the ultrastructural phenomena occurring during the differentiation of cilia in the epidermis and trachea of Xenopus laevis. The sequence of developmental events seems to begin with the de novo formation of clusters of small, dense “procentriole precursor bodies” which are apparently transformed into procentrioles under the influence of dense amorphous masses here termed “procentriole organizers.” The procentriole so formed is a cylinder 150 mm̈ in diameter with nine single microtubules in its wall which probably give rise to the nine “triplet” microtubles in the wall of the definite centrioles (200 mm̈ in diameter). The appearance of multiple centrioles in the apical cytoplasm is correlated with disappearance of procentriole precursor bodies and procentrioles. Smooth‐surfaced vesicles seemingly produced in the well developed Golgi zones may contribute to the development of the ciliary membrane. Following their formation in the supranuclear cytoplasm, the centrioles or presumptive basal bodies align with their longitudinal axes perpendicular to the apical plasmalemma. A ciliary shaft then appears distal to each basal body and simultaneously small, dense bodies like those termed “procentriole precursor bodies” reappear. At this time we call the dense bodies, “axonemal precursor bodies,” because they probably provide material for the synthesis of new axial microtubules at the tip end of the growing cilium. Centriolar rootlets develop during centriolar alignment and ciliary shaft formation from a distinct, low electron‐opaque, precursor substance.
The pattern of glycogen distribution in the liver
Authors: Corrin Brian , Aterman Kurt
Published: February 2005

The behaviour of glycogen in the rat liver under conditions of fasting, refeeding, and cortisone administration has been investigated in a combined chemical and histochemical study. In contrast to the observations of others the distribution of glycogen in the liver was found to be reasonably uniform. Histochemically, the periodic acid‐Schiff reaction was considered to be the method of choice for the assessment of glycogen, particularly at low levels. In sections from frozen dried liver, however, reasonably good results could also be obtained with Best's carmine stain, although this stain was not very sensitive at the lower, and was thought to be too dense for accurate visual assessment at the higher levels of glycogen. As far as the intralobular distribution of glycogen was concerned, no fixed zones of “glycogen deposition” and “glycogen withdrawal” were found, since the intralobular gradient could be altered by varying the experimental conditions. This observation led to the postulate of a “glycogenic wave,” which not only helps to explain some of the contradictory findings in the literature on the localization of glycogen in the liver, but which can also be reconciled with the traditional concept of the liver lobule. The “heterogeneity of the cell population” in the liver lobule was considered to be a function of time rather than of fixed anatomical features.
The primary human oocyte: Some observations on the fine structure of Balbiani's vitelline body and the origin of the annulate lamellae
Authors: Hertig Arthur T.
Published: February 2005

The ultrastructural details of human oocytes from four primordial follicles and one early primary follicle are presented. A fifth primordial follicle is represented by a paraffin section stained by hematoxylin and eosin. The paranuclear Balbiani vitelline body, contsisting of a centrosome surrounded by endoplasmic reticulum, Golgi complexes, compound aggregates, annulate lamellae, and mitochondria is described. The annulate lamellae arise as an evagination from the outer leaflet of the nuclear envelope and interdigitate with folds of the endoplasmic reticulum which also is continuous with the outer leaflet of the nuclear envelope. Structural aspects of annulate lamellae are discussed in relationship to current ideas of nuclear membrane ultrastructure and to their possible role in nucleo‐cytoplasmic transfer. A biographical note on the life of Edouard Gérard Balbiani is presented.
Re‐examination of spermatogonial renewal in the rat by means of seminiferous tubules mounted “in toto”
Authors: Clermont Y. , Bustos‐Obregon E.
Published: February 2005

Observations on dissected tubules, fixed in Carnoy, stained with hematoxylin and mounted “in toto” revealed that there were five distinct classes of type A spermatogonia. The type A1 found in stages II–VIII of the cycle of the seminiferous epithelium had round, pale‐stained nuclei, typically arranged in linear clusters of four or eight along the tubular wall. They all divided at stage IX to produce type A2 cells. These in turn divided at stage XII to produce type A3 spermatogonia. The type A2 and A3 cells had large ovoid nuclei containing globular masses of deeply stained chromatin and were randomly distributed in the space between Sertoli nuclei. The type A3 spermatogonia divided at stage XIV to produce type A4 cells. These had smaller nuclei, sometimes lobulated, containing more deeply stained chromatin granulation, free in the nucleus or adhering to the nuclear membrane. They divided in stage I of the cycle to yield two classes of spermatogonia: intermediate type and new type A1. Hence, type A1–type A4 spermatogonia were considered as “renewing stem cells.” The fifth class of type A spermatogonia (A0) was found at all stages of the cycle. Rare, isolated or in pairs, they had oval nuclei with deeply stained chromatin granulations. Seldom seen to divide, they did not appear to be actively involved in cell renewal and were tentatively considered as “reserve stem cells”.
On movement of muscles by galen of pergamon
Authors: Goss Charles Mayo
Published: February 2005

Galen begins with definitions, giving the special differentiating characteristics of nerves, muscles, tendons, aponeuroses, fascia, and other connective tissue elements. He demonstrates that contraction is the specific activity of muscles. It occurs voluntarily through impulses from the brain carried by the nerves. Protagonists and antagonists are described and demonstrated by experiments with severing individuals and groups as well as with a model made of articulated bones and thongs attached in proper places to represent muscles. Attention is called to passive motion of muscles. The action of gravity is related to muscular action. Sustained contraction of muscles is called tonic activity. The effect of habit on muscles and the subconscious control of voluntary muscles are explained. Visceral organs and blood vessels are under the control of nature rather than the brain, and are thus contrasted with the muscles.
Development of the gonads in the female japanese quail
Authors: Kannankeril J. V. , Domm L. V.
Published: February 2005

The germ cells in the Japanese quail, appear in the gonadal area between two to two and one half days incubation with a preferential distribution favoring the left gonad. Proliferation of the primary or medullary cords from the germinal epithelium was observed between four and five and one half days. The secondary or cortical cords were found to proliferate in the left gonad on the sixth day. The right gonad revealed neither cortical cords nor cortex in any of the cases studied. It began to involute around eighth day and reached its minimum size by seven to ten days after hatching. In the adult it was composed of loose, or occasionally cord‐like, epithelial cells, sparsely scattered “fat laden” cells, masses of lymphocytes and fibrous connective tissue, the latter predominating in older stages. Germ cells either disappeared or could no longer be recognized in the right gonad by four days after hatching. In the left ovary oogonia began to show meiotic changes by the eleventh day and primary follicles were present on the day of hatching. Ovulation was observed as early as 45 days after hatching. In female embryos the right Mullerian duct underwent atrophy and became a rudimentary cloacal remnant between eight and 14 days. In males complete atrophy of both left and right Mullerian ducts occurred between seven and 13 days. The mesonephric ducts persisted in females and were demonstrable throughout post‐hatch period as thread‐like structures.
Observations on epidermal differentiation in the fetal rat
Authors: Bonneville Mary A.
Published: February 2005

Study of fetal rat epidermis has revealed the presence of a single layer of nonkeratinizing cells, the periderm, that covers the free surface of the skin during embryonic life. The periderm resembles structurally the epithelium lining the amniotic cavity, and the two are believed to be similar in function and embryonic origin.

Observations of keratinization have shown that keratohyalin granules formed initially during fetal life may differ in structure from those formed during later fetal life and in the adult. Those formed first contain lipidlike globules embedded in a dense granular matrix. Those formed next contain dense patches of finely granular material embedded in a less dense matrix. Granules formed late in fetal life have a homogeneous structure and resemble those of adult skin.

As in adult epidermis, tonofibrils, abundant in epidermal cells prior to cornification, probably contribute to formation of the keratohyalin granules. Also, as in adult tissue, ribosomes lie close to the surfaces of developing keratohyalin granules and seem to be involved in their formation.
An ultrastructural and histochemical study of rat atrial myocardium
Authors: Hibbs Richard G. , Ferrans Victor J.
Published: February 2005

A study was made of the ultrastructural and histochemical characteristics of atrial muscle cells. The myofibrils of these cells do not converge at the nuclear poles as in the ventricular cells, but leave large sarcoplasmic spaces in the central cores, which contain mitochondria, small amounts of rough‐surfaced sarcoplasmic reticulum, free ribosomes and one or more well developed Golgi complexes. Numerous cytoplasmic granules, many of which are closely associated with the Golgi material, are present in these cells. These granules can be demonstrated in paraffin sections by the Bowie stain. The smooth‐surfaced sarcoplasmic reticulum of atrial fibers consists of a meshwork of interconnected tubules which pass uninterruptedly from one sarcomere to another. No transverse dilatations or T tubules are present as in ventricular cells; however, there are numerous subsarcolemmal cisterns consisting of flattened dilatations of sarcoplasmic reticulum which lie in close proximity to the internal surface of the sarcolemma. There is considerable variation from one cell to another in the number and compactness of arrangement of the myofibrils, and in the abundance of other cellular components.

On the basis of the above findings, we suggest that atrial muscle cells may have a secretory as well as a contractile function.
Cytological aspects of trophoblast‐uterine interaction in early implantation
Authors: Enders Allen C. , Schlafke Sandra
Published: February 2005

Trophoblast‐uterine epithelial cell interrelationships were studied using implantation sites from the rat, rabbit, guinea pig, armadillo, bat and ferret. It was found that in all species trophoblast cells extend over several epithelial cells at the apposition stage of implantation. Trophoblast can adhere to the apical ends of uterine epithelial cells by primitive junctional complexes. More surprisingly, in most species desmosomal junctions are formed between trophoblast and the lateral aspects of uterine epithelial cells by primitive junctional complexes. More surprisingly, in most species desmosomal junctions are formed between trophoblast and the lateral aspects of uterine epithelial cells by primitive junctional complexes. More surprisingly, in most species forms the complementary protion of the apical junctional complexes with the adjacent luminal epithelial cells. Certain basement membranes appear to be barriers to trophoblast invastion in some species but not in others. There is little evidence that trophoblast is cytolytic, whereas all of the trophoblast examined gave some evidence of phagocytic activity, and the trophoblast of some of the more invasive forms showed evidence of being histolytic.

It is suggested that the capacity of trophoblast to form junctions with epithelial cells is an important part of the implantation process, facilitating penetration of the endometrium without dislodgment of the blastocyst.
Nucleoside phosphatase activity in atrial and ventricular myocardium of the rat: A light and electron microscopic study
Authors: Ferrans Victor J. , Hibbs Richard G. , Buja Louis M.
Published: February 2005

Nucleoside phosphatase activity was studied in glutaraldehyde‐fixed rat myocardium. At pH 7.2, ATPase, nucleoside diphosphatase and thiamine pyrophosphatase activity were demonstrated in the transverse elements of the sarcoplasmic reticulum of ventricular fibers and in the subsarcolemmal cisterns of atrial and ventricular muscle cells. The remainder of the sarcoplasmic reticulum of atrial and ventricular fibers showed reactions only with nucleoside diphosphates. The T tubules and intercalated discs of ventricular muscle reacted strongly with nucleoside monophosphates at pH 7.2; atrial myocardium showed this reaction only in the intercalated discs and in the spaces between closely apposed muscle cells.

Thiamine pyrophosphatase and nucleoside diphosphatase were demonstrated in the Golgi apparatus of both atrial and ventricular muscle cells; however, reactive cisterns were more numerous in atrial than in ventricular myocardium. These enzymes were also demonstrated in some of the membranes surrounding the specific cytoplasmic granules of atrial muscle cells. Acid phosphatase activity was also detected in some of these membranes when cytidine monophosphate was used as substrate.
Ultrastructure of human yolk sac: Endoderm, mesenchyme, tubules and mesothelium
Authors: Hesseldahl H. , Larsen J. Falck
Published: February 2005

The ultrastructure of human yolk sacs obtained by hysterotomy or hysterectomy from the third to the eleventh week of pregnancy is described with reference to the endoderm, mesenchyme, endodermal tubules and mesothelium. During the fourth to the sixth week of pregnancy the endoderm proliferates to form cords of cells projecting into the mesenchyme. The endodermal cells contain abundant endoplasmic reticulum, glycogen and iron‐containing material. Various types of tubules in the endoderm are described. The mesenchymal cells vary in appearance; some are stellate with slender cytoplasmic processes, while others are round. A few show signs of phagocytic capacity. Both the endodermal and the coelomic epithelia possess microvilli and pinocytotic vesicles. A hypothesis relating to the function of the human vitelline endoderm is proposed.
Reactive dyes as vital indicators of bone growth
Authors: Seiton Elsa C. , Engel Milton B.
Published: February 2005

Certain reactive dyes of the procion M and remazol group were effective for vital staining of growing bones. These compounds appear to form covalent bonds with the protein matrices and are preservedin situafter decalcification. Dye concentrations in sera of animals receiving one injection were followed. There was a precipitous drop in optical density in the first 24 hours; the remainder of the dye was largely cleared from the serum in 11–21 days. Dye concentrations and staining of bone were correlated. The width of the stained bone appeared to be related to rate of growth and disappearance of dye from the blood. On electrophoresis, the dyes moved with the albumin fraction. Dialysis and electrophoresis experiments favored the conclusion that they form covalent bonds with the protein. Growth of the rabbit mandible at 5–13 weeks, was studied by microscopy in decalcified sections. Using multicolored dyes, the sites of growth were marked in known sequence and sites of resorption were identified by interruption of stained zones. Principles of growth and remodelling advanced by Enlow were confirmed and the growth pattern of the rabbit mandible was elucidated.
Microscopy of the living pancreas in situ
Authors: McCuskey Robert S. , Chapman Thomas M.
Published: February 2005

The purpose of this investigation was to study the microscopic anatomy of the living pancreas in situ. The results indicate that: (1) it is possible to study cellular detail in the living pancreas with resolution closely approaching the limit of resolution of the light microscope; (2) blood flow through indivdual capillaries in both acinar and islet tissue is intermittent; (3) local blood flow through acinar capillaries is regulated by smooth muscle precapillary sphincters and by endothelial sphincters, while flow through capillaries in islets is regulated locally by endothelial sphincters only: (4) insular‐acinar capillary anastomoses exist but are not frequent; (5) secretory canaliculi between adjacent acinar cells exist in life and pass between centro‐acinar cells to reach the lumen of the ducts; (6) processes of beta cells may pass between two adjacent cells to provide additional surface area for transcapillary exchange; (7) the formation and release of zymogen granules occurs within 45‐90 minutes in acinar cells stimulated with pancreozymin and the formation and release of beta granules occurs within 20‐60 minutes in beta cells stimulated with tolbutamide; and (8) cytological changes during the secretory cycle in acinar and beta cells are consistent with the current ultrastructural theory of secretion.
Fine structure of the human menstrual corpus luteum at its stage of maximum secretory activity,
Authors: Gillim Stuart W. , Christensen A. Kent , McLennan Charles E.
Published: February 2005

Human corpora lutea from the period of maximum progesterone secretion during the menstrual cycle were examined with the electron microscope. Both the granulosa lutein and theca lutein cells contain abundant tubular smooth endoplasmic reticulum, mitochondria with tubular cristae, lipid droplets and numerous free ribosomes. Cisternae of rough endoplasmic reticulum occur in stacks and as scattered profiles in the lutein cells. Golgi elements are seen throughout the granulosa lutein cell cyoplasm and are associated with multivesicular bodies, lysosome‐like granules, coated vesicles and microtubules. The coated vesicles apparently arise from the Golgi cisternae. Unlike the granulosa lutein cells, theca lutein cells are generally smaller and darker, exhibit a wider range of cell densities, have a Golgi complex clustered at one nuclear pole, and their lipid droplets are extracted by tissue preparation. Patches of microvilli that protrude into the perivascular spaces and a peripheral, fibrillar terminal web are unique to the granulosa lutein cells. The perivascular macrophages correspond to the “K” cells of light microscopy. No cells in the theca externa or the central coagulum exhibit the fine structure of steroid‐secreting cells.

The correlation of fine structure with function in human lutein cells is probably similar to that established for other steroid‐secreting cells. The role of the theca lutein cells in steroidogenesis by the human corpus luteum remains unresolved.
Atrioventricular node innervation in ultrastructural three dimensions
Authors: Thaemert J. C.
Published: February 2005

Atrioventricular nodal tissue was obtained from a two‐week‐old mouse heart which was fixed with phosphate‐buffered osmium tetroxide, embedded in Epon 812, serially sectioned for both light and electron microscopy and stained with uranyl acetate. From study of electron micrographic montages of the first 115 serial sections of the most inferior portion of the atrioventricular node it was determined that the intercellular spaces of this portion of the node contain fibrocytes, bundles of collagen fibrils, capillaries and a plexus of unmyelinated nerve bundles which are insheathed by Schwann cells. Relatively large nerve bundles divide to form smaller ones, the vesiculated nerve processes of which make intimate contact with the sarcolemmae of nodal cells. These neuromuscular contiguities, on the basis of the physical interrelationships of their respective vesiculated nerve processes and nodal cells, exist in various forms. They may be categorized as follows: (1) individual vesiculated nerve processes which dwell in sarcolemma‐lined tunnels or in culs‐de‐sac inside the nodal cells; (2) individual vesiculated nerve processes which lie within shallow or deep grooves on the surfaces of nodal cells; (3) vesiculated nerve processes which remain part of a small bundle while dwelling in a groove on the surface of an individual nodal cell or in grooves on the surfaces of two or more nodal cells; and (4) small individual bundles of vesiculated nerve processes and their Schwann cell investments which reside within sarcolemma‐lined tunnels inside nodal cells. These neuromuscular contiguities are fully described and their significance is discussed in relation to the present status of the nature and organization of the postganglionic ramifications of the autonomic nervous system within the conduction system of the heart.
A quantitative description of the intestinal epithelium of the mouse
Authors: Hagemann Ronald F. , Sigdestad Curtis P. , Lesher S.
Published: February 2005

The use of combined cell kinetic, tritiated thymidine labeling and liquid scintillation counting techniques has permitted quantification of several intestinal epithelial cell parameters. Wet weight and/or whole intestinal values for the following were obtained in C57B1/6 mice. Crypts/mg wet weight of intestine numbered 855 in the duodenum (D), 892 in the jejunum (J) and 1164 in the ileum (I). Crypts were subdivided into proliferative cells with the following values being obtained: 1.6 × 105/mg (D), 1.6 × 105 (J) and 1.7 × 105 (I), and for nonproliferative cells, 1.1 × 105/mg (D), 1.1 × 105 (J) and 1.2 × 105 (I). A cell cycle analysis permitted the proliferative cells to be further subdivided, and the numbers of cells in G1, S, and G2 + M were determined.

Division of the total number of proliferative cells by the mean cell generation time provided a value of 1.4 × 107 cells/hour for the cell production rate in the entire intestine. Division of cell production rate/mg by crypts/mg gave values for cell production rate/crypt of 15.2 cells/crypt/hour (D), 14.6 (J) and 11.2 (I).

Epithelial cells per villus (J) numbered 3025, and there were 3.1 × 105 villous epithelial cell per milligram of jejunum. Division gave a value of 102 villi/mg (J). Dividing crypts/mg by villi/mg gave a value of 8.7 crypts/villus (J).

Mean cell transit time from crypt to villus apex was 43.1 hours (D), 41.8 hours (J) and 42.6 hours (I).
Cytoarchitecture of the substantia nigra in the rat
Authors: Hanaway Joseph , McConnell Jo Ann , Netsky Martin G.
Published: February 2005

Midbrains of ten young adult rats were sectioned serially in three planes to study the detailed cytoarchitecture of the substantia nigra. These neurons measure 8 to 17 μ in diameter. In comparison, the largest neurons in the midbrain measure 20 to 40 μ; hence, neurons are designated according to size as follows: those measuring 18 to 40 μ, large; 12 to 17 μ, medium; and 8 to 11 μ, small. The substantia nigra of the rat contains non‐pigmented neurons in three divisions: pars reticulata, pars compacta, and pars lateralis. The pars reticulata is the largest division and has the longest rostrocaudal extent. It contains neurons of small size medially and of medium size laterally. This finding correlates with described differences in connections. Three‐dimensionally, the pars reticulata is an oblate spheroid with the long axis in the rostrocaudal plane. The pars compacta is a triangular layer dorsal to reticulata. It is subdivided into rostral and caudal portions at the level of the fibers of the basal optic root. Neurons in both subdivisions are medium in size, but cells rostrally are darker than those caudally. The pars lateralis is a column of neurons with its long axis located in the rostrocaudal plane. It lies dorsolateral to the pars reticulata and the pars compacta, with occasional connections to both by cellular strands. The pars lateralis has rostral and caudal portions; neurons rostrally are medium in size and round; caudally, however, neurons are variable in size, dark, stellate or fusiform, and have long processes.
Electron microscope studies of frozen‐substituted marine eggs. I. Conditions for avoidance of intracellular ice crystallization
Authors: Rebhun L. I. , Sander G.
Published: February 2005

Eggs of the marine clam Spisula solidissima were examined by the technique of freeze‐substitution. Morphology of the cytoplasm was investigated as a function of cellular water content using osmotic means to control water concentration. In eggs frozen in less than double strength sea water, ice crystallization usually occurred throughout the cell. In eggs frozen in double to triple strength sea water, 10–75% of the eggs were devoid of ice crystals in the cytoplasm and in triple strength sea water, also in the nucleus. From these results and from a detailed analysis of cells in which both ice crystals and ice crystal‐free regions occurred it is concluded that cells or parts of cells may be frozen free of ice crystals if their free water content is reduced. Reduction in free water content may occur in several ways: deliberate dehydration by osmotic means; accidental dehydration by evaporation of water from cells prior to freezing; osmotic dehydration of one region by an adjacent one in which ice crystallization is in progress. In ice crystal‐free cells, all common cell inclusions could be recognized.
Electron microscope studies of frozen‐substituted marine eggs. II. Morphology of ice crystal‐free unfertilized eggs
Authors: Rebhun L. I. , Sander G.
Published: February 2005

Studies of ice crystal‐free eggs of the clam Spisula solidissima using freeze‐substitution techniques are described. Formation of ice in cells may be avoided by removing sufficient intracellular water prior to freezing. After such treatment, most subcellular inclusions can be recognized and have dimensions similar to those seen after chemical fixation. Golgi regions, ribosomes, endoplasmic reticulum, nuclear envelope, annulate lamellae, yolk and the vitelline membrane resemble their counterparts in chemically fixed eggs. Mitochondria, however, lack the space normally found between cristae walls, and the resulting structure resembles two unit membranes “back to back.” Several inclusions and structures not seen in chemically fixed eggs are described: light bodies are found in groups of two to eight near the Golgi regions; cores occur in the microvilli of the vitelline membrane, microtubules are found in the cytoplasm of the unfertilized egg and 220 to 250 Å particles, which are not ribosomes, occur regularly arranged along microtubules.
Argentaffin and other “endocrine” cells of the small intestine in the adult mouse. II. Renewal
Authors: Ferreira M. N. , Leblond C. P.
Published: February 2005

Argentaffin and other “endocrine” cells of the gastrointestinal tract were investigated in the mouse jejunum by electron microscopic radio‐autography after administration of 3H‐thymidine either in a single injection or by continuous infusion.

One hour after a single injection or after a 24‐hour infusion of 3H‐thymidine, no labeling is seen in the three main types of “endocrine” cells: Type EC (true argentaffin) or biconcave granule cells, Type L or large spherical granule cells, and Type S or small spherical granule cells. Furthermore, no mitosis of these cells may be observed. Hence, they are not capable of division.

However, when continuous infusion is prolonged for one and one‐half days, examination of the lower half of the crypts shows labeling in some cells of the three types. The number of granules in these cells is small.

By three days, labeled cells of the three types appear in villi, while the number of their granules increases. With time, the percentage of labeled cells rises gradually to reach over 60% after four days and over 80% after six to eight days of continuous infusion.

After the infusion is stopped, the number of labeled cells decreases. Thus, eight days after the end of a four‐day infusion less than 10% cells are labeled.

It is concluded that the three main types of “endocrine” cells observed in the mouse jejunum arise from unidentified precursors in the lower half of the crypts. They migrate from crypts to villi and are probably extruded from villus tips. Even though the three cell types seem to evolve independently, their turnover time is the same, that is, about four days.
Organ cultures of fetal mouse ovaries. I. Light microscopic structure
Authors: Odor D. Louise , Blandau Richard J.
Published: February 2005

Ovaries from 16‐day mouse fetuses were cultured as whole organs in a modified Eagle's medium for two through 45 days. In the course of the experiment a single layer of follicular cells resting on a basement membrane surrounded the majority of the surviving oocytes, resulting in unilaminar follicles. A small number lay in multilaminar follicles having two to three layers of follicular cells. No follicles with antra were seen regardless of the length of time in culture. Initiation of zona pellucida formation occurred after three days in culture. In general, the thickness of the zona pellucida was not as great as that around an oocyte of similar size in vivo. Some of the large oocytes attained diameters of 68–73 μ, which is within the normal range for fully grown mouse oocytes in vivo. Only one oocyte in all the cultures examined had a first meiotic metaphase spindle. In many follicles the initial step in degeneration was the migration of macrophages into the follicular epithelium and their attachment to the zona pellucida. The follicular epithelium often was completely replaced by an enclosing layer of macrophages; the oocyte in some such instances still appeared normal. Subsequently, the germinal vesicle became pycnotic and the ooplasm, PAS‐positive. At the end of the degenerative process the zona pellucida appeared as an empty shell with macrophages attached to both its external and internal surfaces.
Gonocytes in fetal guinea pig testes: Phagocytosis of degenerating gonocytes by Sertoli cells
Authors: Black Virginia H.
Published: February 2005

In fetal testes of non‐inbred guinea pigs, virus‐like particles were seen in the primordial germ cells, but not in the somatic cells. Using the particles as a marker for the gonocytes it was possible to trace the phagocytosis of degenerating gonocytes by the Sertoli cells in the fetal testis.
Biochemical, histochemical and ultrastructural studies of thyroid serotonin, parafollicular and follicular cells during development in the dog
Authors: Gershon Michael D. , Belshaw Bruce E. , Nunez Eladio A.
Published: February 2005

A study was made of the concentration and cellular localization of serotonin in the thyroid gland of the dog. This species is characterized by a low level of serotonin in the adult thyroid gland. Endogenous serotonin consequently cannot be demonstrated by fluorescence microscopy following treatment of frozen‐dried adult thyroid tissue with formaldehyde vapor. In contrast, the thyroid concentration of serotonin was found to be high, in both beagle and basenji (purebred dogs of European or African origin respectively), around the time of birth. The serotonin concentration then fell rapidly as development of the animals proceeded. This pattern also seemed true of the rabbit. When the concentration of serotonin was high, just prior to birth, a yellow fluorophore, probably the condensation product formed between serotonin and formaldehyde could, as in other species, be demonstrated in parafollicular cells after exposure of tissue to formaldehyde gas. Thyroid follicular cells never showed serotonin but instead, a striking accumulation of autofluorescent apical dense bodies (0.3–1.0 μ in diameter), probably lysosomes, occurred during the first year of life.
The anterior abdominal fat body
Authors: Merklin Robert J.
Published: February 2005

The anterior abdominal fat body is a mixture of multilocular and unilocular fat cells. It is found deep to the rectus sheath and immediately beneath the peritoneum of the anterior abdominal wall. It is first seen in the sixth month fetus as thin lobules of tissue arranged on either side of the umbilical vein but receiving blood supply from specific ensiform branches of the superior epigastric or internal thoracic artery and vein. Continued growth results in a coalescence of the bilateral lobules into a single fat body that completely overgrows the supportive blood vessels. In its cytology this body is comparable to the interscapular fat pad. It is unique in that vascular connections develop between it and the liver and in the fact that in a significant number of specimens it attains proportions that appear to represent pathological hypertrophy.
Brunner's glands of the duckbilled platypus (Ornithorhynchus anatinus)
Authors: Krause William J.
Published: February 2005

Brunner's glands in the platypus form a lobulated, glandular collar confined to the submucosa of the most distal portion of the stomach. The glands end immediately proximal to the gastrointestinal junction and excretory ducts empty in the region where the stratified squamous epithelium lining the stomach changes abruptly to the intestinal lining epithelium of the duodenum. An individual gland of Brunner is composed of several elongate lobules drained by intralobular ducts which often join to form a single excretory duct.

Light and electron microscopic studies have shown the secretory tubules to be comprised of large, pyramidal cells limited basally by a delicate basal lamina. The ergastoplasm, cisternae of which are dilated and contain amorphous material, is associated with numerous ribosomes. In basal and perinuclear regions intercisternal granules and smooth surfaced vesicles are found. Numerous small vesicles found in supranuclear areas apparently form from the smooth membrane portions of ergastoplasm located adjacent to Golgi complexes. Membrane‐bound amorphous granules of varying electron density occupy the apical cytoplasm and show a tendency to coalesce before emptying their contents into the adjacent lumen.

The intralobular duct system is lined initially by a columnar epithelium which changes to a simple squamous form before the ducts combine to form a short excretory duct lined by stratified squamous epithelium. The epithelium lining the duct system contains relatively few organelles but appears to be engaged in a limited amount of synthesis and release of secretory material.

Histochemical studies indicate that both the secretory tubules and the duct system elaborate a neutral mucopolysaccharide.