bluuebunny/crossref_metadata_2025 huggingface dataset:
Prenatal development of the ductus epididymidis in the rhesus monkey. The effects of fetal castration
Authors: Alexander Nancy J.
Published: February 2005

After formation of the epididymis, the cuboidal epithelial cells of the ductus epididymidis undergo little cytodifferentiation in the fetal rhesus monkey. However, from 130 days of fetal life until birth, the cells undergo a period of differentiation that proceeds in an anterio‐posterior direction along the duct. Concurrently epithelial cells of the ductus efferens and caput epididymidis transform from a cuboidal condition with no surface modifications to cells similar to those of adults. Over 50% of the cells become ciliated and the remainder develop surface modifications resembling those in adult nonciliated cells. The epithelial cells lining the ducts of the corpus epididymidis, and in some cases those of the cauda epididymidis, develop stereocilia.

Castration of the fetus between the 106th and 112th day of gestation prevents differentiation of the epithelium of the epididymis. Administration of medroxy‐progesterone, a drug with androgenic properties, to the mother of a castrated fetus results in normal differentiation of epithelial cells lining the fetal caput epididymidis. These studies indicate that fetal differentiation of the epithelial cells of the epididymis depends on the secretion of androgen by the fetal testes. The androgen level drops at birth, and concomitantly the epithelial cells of the male reproductive tract return to an undifferentiated state until puberty.
Ultrastructural observations on mitosis in myocardial cells of the rat embryo
Authors: Chacko Kurien
Published: February 2005

Cardiac tissue from rat embryos at 10, 11, 12, 13, 14, 15, days of gestation and newborn rats were processed and studied under the electron microscope. A unique observation in the developing myocardium is detection of the simulataneous occurrence of mitosis and synthesis of muscle‐specific contractile proteins (actin and myosin filaments) in the same cells. Mitotic cells containing sites of myofilaments are discernible throughout the gestational period covered in this investigation, including the myocardium of new born. Unlike skeletal muscle, in the myocardium of rat embryos the onset of fibrillogenesis is not correlated with cessation of mitotic activity.
The effect of shedding on skin homografts in the garter snake, thamnophis sirtalis
Authors: Terebey N.
Published: February 2005

All skin homografts shed a layer of keratin or an outer epidermal generation when shedding appeared in the recipient. Skin homografts did not express the timing of the shedding cycle found in the donor animal. It was concluded that the timing of shedding is determined by the recipient but not by the skin. The response of skin homografts was not affected by age, sex or the stage between sheddings when grafts were taken from donors. A review of mammalian work shows that skin homografts in the rat show the timing of the hair growth cycle found in the donor although eventually these homografts also become synchronized with the recipient. Less complex mechanisms seem to be involved in the shedding cycle in garter snakes than in the hair‐growth cycle which evolved in mammals.
Scanning electron microscopy of the lateral ventricles of sheep
Authors: Kozlowski Gerald P. , Scott David E. , Murphy Judith A.
Published: February 2005

The lateral ventricles and choroid plexuses of an adult and near‐term sheep fetus were examined with scanning electron microscopy. The predominant surface structure of the ependymal cells were cilia arranged in clumps with evidence of metachronic activity. Topographical variations of the ependymal surface are described and discussed according to their role in transport of cerebrospinal fluid and their relation to underlying nervous tissue.
Ultrastructure of the interstitium in the rabbit kidney
Authors: Bulger Ruth Ellen , Nagle Ray B.
Published: February 2005

Kidneys from six male New Zealand white rabbits were fixed by perfusion, and the interstitium of all zones was studied by light and electron microscopy. The volume and amount of the basic components varied not only between cortex and medulla, but within each zone itself. Two main cell types were found in the cortical interstitium, the first appeared to be morphologically identical with a fibroblast, although it contained frequent surface depressions. The second cell type was of the mononuclear series, the most frequent of which was characterized by abundant free ribosomes and was frequently wrapped by processes of fibroblasts. Although collagenous fibrils, basement membrane‐like material, and flocculent electron‐dense material have previously been described in the interstitium of other animal species, this paper describes the presence and distribution of microfibrils approximately 150 Å in diameter with electron‐lucent cores throughout the entire kidney interstitium and discusses the distribution of globular deposits which may represent glycosaminoglycans in the various zones of the kidney.
Cytology of eccrine sweat glands in the opossum
Authors: Fortney James A.
Published: February 2005

Eccrine sweat glands occur only within the glabrous foot and toe‐pad skin of the Virginia opossum, Didelphis virginiana, Kerr. Two distinct types of secretory cells are found in the terminal portion of this gland, i.e., dark and clear cells. Thin myoepithelial cells are located between these secretory cells and the outer basal lamina. Histochemical techniques indicate that dark cells contain dense proteinaceous secretory granules. This observation is supported by measuring the refractive index (n) of dark cell granules by interference microscopy. The interferometric properties and certain staining characteristics (acidophilia) displayed by these secretory granules are comparable to those of the stratum corneum layer of opossum glabrous skin. Ultrastructurally, dark cells contain electron‐opaque secretory granules and parallel arrays of granular endoplasmic reticulum, resembling those of other protein‐secreting cells. Subcutaneous injections of pilocarpine nitrate elicit a secretory response from dark cells consisting of granule extrusion, reduction in cell size, and extreme vacuolization of the cell cytoplasm.
Changes in muscle morphology and histochemistry produced by denervation, 3,3′‐iminodipropionitrile and epineurial vinblastine
Authors: Wuerker Raymond B. , Bodley H. Daniel
Published: February 2005

Three types of muscle fibers are present in the normal triceps surae of the rat; they are designated large, pale; intermediate; and small, dark. Following denervation, these fibers undergo changes which cause the muscles to become less distinctive with respect to fiber types. The fibers atrophy preferentially, round up, lose their angularity, and lose their staining capacity for succinic dehydrogenase, mitochondrial adenosine triphosphatase, and the periodic acid‐Schiff procedure. Intraperitoneally administered 3,3′‐iminodipropionitrile produces no change in muscle histochemical characteristics. Injection of vinblastine into the epineurium of the sciatic nerve results in a histochemical picture similar to that of denervation, while destruction of the nerve occurs distal to the site of injection.
Structure and function of the hamster corpus luteum during the estrous cycle
Authors: Leavitt W. W. , Basom C. R. , Bagwell J. N. , Blaha G. C.
Published: February 2005

Luteal cell structure and function were studied by electron microscopy in conjunction with measurement of progesterone production by corpora lutea which were isolated and incubated in vitro on successive days of the four‐day hamster estrous cycle. Granulosal cells were primarily responsible for the formation of the corpus luteum. Agranular endoplasmic reticulum and lipid droplets developed during luteinization of granulosal cells on the first post‐ovulation day (day 1). Luteal cell hypertrophy on day 2 resulted from dilation of tubular agranular endoplasmic reticulum and swelling of mitochondria with tubular cristae. Plasma progesterone levels on the first two days of the cycle appeared to be correlated with luteal activity as corpora lutea were demonstrated to synthesize progesterone during this interval. Luteolysis occurred on day 3 with a reduction in luteal cell size accompanied by condensation of the agranular endoplasmic reticulum, regressive changes in the mitochondria, and a marked drop in luteal progesterone synthetic activity. On day 4, extensive phagocytic activity and luteal cell autolysis indicated an advanced involutional state. The short but functional luteal phase in the cyclic hamster does not appear to involve the production of 20α‐hydroxy‐pregn‐4‐en‐3‐one as occurs in the rat. This progestin was not detectable in plasma or luteal tissue before or after incubation at any time during the cycle. Possible mechanisms regulating luteal cell development and regression during the estrous cycle are discussed.
The external glial limiting membrane in Macaca: Ultrastructure of a laminated glioepithelium
Authors: Bondareff William , McLone David G.
Published: February 2005

The external glial limiting membrane in Macaca is a multilaminar epithelium‐like mantle formed by the perikarya and interdigitating cell processes of astrocytes. It is separated from the overlying subarachnoid space by a typical basement membrane. Tonofilaments, about 100 Å in diameter, course through the cytoplasm of the processes in sheaths which run in different planes in successive layers of the mantle, forming a course brushwork. Beneath the surface plasma membrane of the superficial astrocytes is a filamentous layer, 500–700 Å thick, which is composed of microfilaments, about 50 Å in diameter. These microfilaments were continuous with the inner aspect of the plasma membrane. The tonofilaments appeared to terminate in the microfilamentous network. The similarity of these microfilaments to the cytocholasin B‐sensitive microfilaments of epithelial cells suggested contractile properties and their participation in the motility of glial cells at the border of the brain and subarachnoid space.
The influence of a prenatal trauma on formation of Purkinje cells
Authors: Andreoli John , Rodier Patricia , Langman Jan
Published: February 2005

The first goal of this investigation was to determine the time of origin of Purkinje cells and their final location in the various lobes of the cerebellum. DUB/ICR mice were therefore injected with several doses of 3H‐thymidine on day 11, 12, 13, 14, or 15 of gestation. Cells formed on days 11 and 12 appeared in all lobes of the postnatal vermis but those formed on day 13 became located mainly in the anterior lobe.

The second goal was to examine the effect of 5‐fluorodeoxyuridine, a DNA synthesis inhibitor, on Purkinje cell formation and on repair of the rhombic lip after a prenatal trauma. Five hours after treatment with fluorodeoxyuridine cells with darkly stained nuclear clumps appeared and mitotic activity ceased. Twelve hours after treatment mitotic activity remained low and more affected cells appeared in the neuroepithelium of the rhombic lip. By 24 hours abnormal cells had disappeared, mitotic activity was almost normal and the neuroepithelium had regained its regular continuity. Treatment on day 12 led to a significant deficit of Purkinje cells in all lobes of the vermis, while treatment on day 13 caused a deficit in the anterior lobe only. Despite the postnatal Purkinje cell deficit, compensatory cell proliferation had occurred in the rhombic lip. The mitotic index in the treated embryos reached the value of the controls after 24 hours and was extremely high after 48 hours. Part of this proliferative activity leads to Purkinje cell production, for it was possible to label substantial numbers of Purkinje cells on day 14 of gestation in animals treated with fluorodeoxyuridine on day 12, while control animals have virtually completed Purkinje cell formation by day 14. Although Purkinje cell deficits were accompanied by a reduction in the size of the cerebellum, the cytoarchitecture of the cerebellum appeared normal.
Role of the adrenal cortex in maturation of the lymphoid system and immunological competence; the effects of aminoglutethimide in suckling mice
Authors: Clark Sam L. , Schneider Gary B.
Published: February 2005

Newborn rats and mice have rudimentary peripheral lymphoid tissues and are immunologically incompetent. The lymphoid system matures late in the third week after birth, shortly before weaning. The adrenal cortex also is relatively inactive neonatally and begins to secrete glucocorticoids in a mature fashion two weeks after birth. These experiments were designed to test the hypothesis that adrenal glucocorticoids induce maturation of the lymphoid system and immunological competence during the third postnatal week. Mice 10–12 days old were injected daily for 4–11 days with aminoglutethimide, an inhibitor of steroid biosynthesis. The adrenal glands and lymphoid tissues were prepared for histological examination 24 hours after the last injection and evaluated without knowledge of the treatment received. Aminoglutethimide caused adrenal dysplasia with a frequency proportional to dose. Effective doses also inhibited growth, and slightly larger doses were fatal. Therefore it was concluded that large doses of aminoglutethimide caused adrenal insufficiency, but the completeness of this insufficiency in surviving animals was not ascertained. Three phases in postnatal maturation of the lymphoid system were identified by examination of untreated littermate controls and reference to previous work. During the first week after birth, the thymus‐dependent lymphoid tissues grow by immigration of thymus‐derived cells that soon have the capacity for cell‐mediated immunity. During the second postnatal week, a new population of wandering lymphoid cells, presumptively derived from bone marrow, settles in lymphoid organs in response to antigenic stimulation, to form primary lymphoid nodules and a few plasma cells. Late in the third week after birth the machinery for humoral antibody synthesis matures with the appearance of germinal centers and numerous plasma cells, coincident with a great increase in production of immunoglobulin. This third phase of maturation was retarded in mice injected with near‐fatal doses of aminoglutethimide. Because these mice suffered neither involution of lymphoid tissue nor suppression of proliferation in thymus or thymus‐dependent lymphoid‐tissue, it was concluded that the effects of aminoglutethimide upon the development of germinal centers and plasma cells were selective and specific. Therefore these experiments support the hypothesis that glucocorticoid secretion plays a decisive role in maturation of immunological competence during the third week after birth in mice. This role appears to be the potentiation of cellular proliferation and differentiation of B cells in response to antigens, culminating in antibody synthesis. Maturation of adrenal glucocorticoid synthesis has also been implicated in the initiation of physiological involution of the thymus and cessation of intestinal absorption of antibodies during the third postnatal week in rats and mice.
Retrograde perfusions of the pineal region and the question of pineal vascular routes to brain and choroid plexuses
Authors: Quay W. B.
Published: February 2005

The purpose of this study was to experimentally and critically examine the possibility of vascular routes from the pineal gland to the brain in the laboratory rat. Vascular perfusions in the pineal region with India ink in heparinized saline were performed on animals of diverse ages (1 month to 2 years) during the early and middle parts of the daily period of light and immediately post‐mortem. Cleared specimens were studied both before and after serial sectioning for light microscopy. Pineal microvasculature was relatively resistant to retrograde perfusion from the adjacent venous sinuses. But the choroid plexus of the suprapineal recess commonly contained perfusate from these sinuses and the pineal gland.

The results define the anatomical limits of possible pineal to brain blood flow, but do not of course provide any direct evidence that such flow exists in vivo. Nevertheless, the results from the perfusions lead to the conclusion that if a direct and non‐systemic vascular path carries pineal hormone to brain, the path consists of the vena cerebri magna and the choroid plexus of the suprapineal recess. This concept assumes reversibility of direction of blood flow in these vessels, an observed physiological property of at least some intracranial veins in other species.
Lateral pterygoid: Two muscles?
Authors: Grant Philip G.
Published: February 2005

Reinterpretation of existing data and introduction of new evidence appear to indicate that this controversial muscle might better be treated as two muscles. Anatomically the lateral pterygoid in man and in the rhesus macaque has two distinct heads, superior and inferior. Biomechanically, the two heads posses different properties: the superior head has a closing moment (or perhaps no moment) while the inferior head has an opening moment. The findings are similar in the two species. Electromyographically the two heads show different activity patterns: the superior head is active during various jaw‐closing movements only, while the inferior head is active during jaw‐opening and protrusion only. Functionally, therefore, the lateral pterygoid of man and rhesus macaque appears to be two muscles.
Developmental cytology of chromatophores in the red‐spotted newt
Authors: S. Forbes M. , A. Zaccaria R. , N. Dent J.
Published: February 2005

The cytology of pigment‐bearing cells is followed in the integument of the red‐spotted newt, Notophthalmus viridescens viridescens Rafinesque, with observations beginning in the late embryo and continuing through to the adult. Dermal melanophores appear in late tailbud stages, and dermal xanthophores differentiate prior to hatching. In young larvae, both become widely and evenly distributed in the dorsal skin, but in older larvae a pattern develops so that melanophores are absent from certain circumscribed lateral regions designated as melanophore voids. Iridophores differentiate and accumulate among the xanthophores which have remained in the voids. Those xanthophores then are transformed into proerythrophores; that is, their form is altered from stellate to punctate, their nuclei change from fusiform to ovoid, and their pterinosomes are largely replaced by lipid droplets. In some of the voids, the proerythrophores migrate into the epidermis to become the erythrophores of the red spots. The remaining voids cease to exist when their proerythrophores disappear and are replaced by dermal melanophores. At the same time, some dermal melanophores accumulate to form dorsal black spots, and a morphologically different type of melanophore differentiates within the epidermis. In the interspot regions of the eft, xanthophores hypertrophy and pack the dermis, giving an orange color to the skin. In the interspot regions of the adult newt, xanthophores with fewer organelles produce a yellow color on the ventral surface, and, in combination with melanophores and iridophores, produce a greenish color in the dorsum.
Ultrastructural morphology of schwann cell—neuronal relationships in the spiral ganglia of cats
Authors: Jean Adamo Norma , A. Daigneault Ernest
Published: February 2005

Electron microscopic study of the cat's spiral ganglia reveals that neuronal cytoplasmic extensions evaginate into the inner Schwann cell lamellae; some may become surrounded by the ensheathing Schwann cell. Inner lamellae of ensheathing Schwann cells penetrate the neuron and invest small portions of neuronal cytoplasm. Membrane‐bound neuronal regions, completely or partially bare of Schwann cell ensheathment, also are observed within neurons or adjacent to the neuronal plasmalemma. Some of these isolated neuronal regions might represent cytoplasmic extensions of the same or another neuron. Speculations are made as to the mechanism by which the observed relationships are formed.
Functional anatomy of the porpoise larynx
Authors: Blevins Charles E. , Parkins Brian J.
Published: February 2005

This paper describes the anatomy of the larynx of an echolocating porpoise and proposes a limited role for that organ in vocalization. Gross dissection of the larynx of the bottle‐nose porpoise Tursiops truncatus reveals the features of component cartilages, muscles and joints. Arytenoid, cuneiform, and corniculate cartilages are present as an incompletely fused cartilaginous unit with each cartilage being identifiable by slight clefts of demarcation. The arytenoid cartilages are freely movable on the cricoid cartilage as a prerequisite for opening and closure of the larynx. Despite the lack of vocal folds to produce a wide range of sounds, it is proposed that the larynx of this species can produce clicks and is partially responsible for whistles.
Pinocytotic activity of the uterus of the rat
Authors: Enders Allen C. , Nelson D. Michael
Published: February 2005

With both scanning and transmission electron microscopy, large ectoplasmic projections are found intruding into the lumen from the epithelial cells of the rat uterus. These projections, which are abundant both prior to implantation and during delayed implantation, communicate with the underlying cytoplasm only by a small pedicel as though in the process of pinching off. However, introduction of tracer material into the uterine lumen demonstrates the pinocytotic nature of these projections. Within three minutes after introduction of tracer the projections, termed pinopods, contain numerous vacuoles filled with tracer. Within ten minutes large vacuoles containing tracer are present in the apical cytoplasm subjacent to the individual pinopods.

The varied images observed in the experimental and control materials suggest that there is a continual turnover of pinopods. Initially a simple ectoplasmic projection, the pinopod apparently develops rapidly into a mass of ectoplasm 2–3 μ in diameter with multiple folds and pockets at its surface and numerous internal vacuoles. Following a period of active endocytosis of fluid, the pinopod becomes more spherical and, together with contained material, is withdrawn into the apical cytoplasm.

It is suggested that pinocytosis might play a role in producing apposition of the blastocyst to the luminal epithelium, in passing information from the blastocyst to the stroma, and in diminishing the molecular contents of the uterine lumen during specific times in the reproductive process.
Electron microscopic studies of human pituitary tumors. II. Acidophilic adenomas
Authors: Schechter Joel
Published: February 2005

Nine cases of acidophilic adenoma associated with acromegaly were studied by electron microscopy. The tumor parenchyma contained numerous cells identifiable as somatotrophs, many of which appeared “normalt” and apparently engaged in protein synthesis.

In about half of the specimens, there were variations in the electron‐opaque characteristics of the parenchymal cells, most frequently affecting somatotrophs. Characteristic of some somatotrophs was a marked electron‐opacity of the cytoplasmic matrix and nuclear materials, irregular cell contours, hypertrophied cytomembrane systems frequently containing proteinaceous material, and considerable amounts of secretory granules.

Disruptions in plasma membranes were apparent throughout the parenchyma, particularly at the parenchymal‐pericapillary interface. This resulted in the release of large numbers of secretory granules and cytoplasmic fragments to pericapillary or extracellular spaces. Small groupings of the disrupted cells often were characterized by scant secretory granules, an electron‐lucent cytoplasmic matrix, and were considered the counterpart of giant multinucleate chromophobes observed with the light microscope.

Follicular cells were observed rarely, but when present contained an abundance of fine cytoplasmic filaments and closely resembled follicular cells described in ACTH‐secreting tumors.
The adrenergic cardiac nerves of the cat
Authors: Ellison Jeffrey P.
Published: February 2005

A fluorescence method was used for study of the adrenergic cardiac nerves of the cat. Sixteen regions of the heart were examined. The sinoatrial and atrioventricular nodes and the interatrial septum were the most richly innervated regions of the heart. There was little difference between the density of innervation in sections of atrial and ventricular portions of the myocardium. Most of the adrenergic nerves supplying the ventricles were derived from large bundles in the atrioventricular sulcus and were distributed through the subepicardial plexus. Each coronary artery was sparsely innervated in its initial elastic segment, but the vasa vasorum were well innervated. The main trunks of the coronary arteries were surrounded by plexuses composed only of preterminal axons; adrenergic vasomotor terminals were plentiful on the external surface of the muscular media of major and minor myocardial branches. Dense plexuses of adrenergic nerves were seen in both atrioventricular valves. The pulmonary valve was well innervated and contained more adrenergic nerves than the aortic valve. Perivascular plexuses and freely ending adrenergic terminals were observed in the pericardium. Small intensely fluorescent cells were grouped around small blood vessels in the interatrial septum. Most were in the vicinity of the atrioventricular node. It is suggested that these cells, under neural control may secrete catecholamines into the microcirculation of the interatrial septum. They may exert local humoral control over the atrioventricular node or the atrial parasympathetic ganglia.
Prolactin and luteinizing hormone cells of pregnant and lactating rats as studied by immunohistochemistry and radioimmunoassay
Authors: Merchant Frederick W.
Published: February 2005

The objective was to describe the cytological changes that occur in prolactin and luteinizing hormone (LH) cells of the rat hypophysis during pregnancy and lactation and to correlate these changes with secretory activity of the two cell types. The cells were demonstrated with immunohistochemistry and secretory activity was indicated by pituitary and serum hormone concentrations as measured by radioimmunoassay.

During pregnancy, two forms of prolactin cells were observed in the pars distalis. One form (prolactin cell I) was small, polyhedral, and constituted most of the prolactin cell population. A second form (prolactin cell II) was found occasionally in pituitary glands of nonpregnant rats and became prominent during pregnancy. It was polyhedral, many times larger than prolactin cell I, and had a restricted distribution in the pars distalis. During gestation prolactin cells I exhibited little change in size, number and staining capacity. Similarly, pituitary and serum prolactin concentrations indicated that the hypophysis releases little prolactin during pregnancy, except for the first few days after conception and before parturition. During lactation, the staining intensity of prolactin cells I and the pituitary prolactin concentration varied little. Prolactin cells II were lightly stained and rare throughout lactation.

The staining capacity of luteinizing hormone (LH‐) cells increased as pregnancy progressed in parallel with a rising pituitary concentration of LH during the first half of pregnancy. However, the immunohistochemical procedure appeared to be too insensitive to reflect the gradual fall in pituitary LH concentration during late pregnancy. During early lactation, the reduced staining capacity of LH‐cells was correlated with a low pituitary concentration.
Distribution of calcitonin‐containing cells in the human thyroid
Authors: McMillan Paul J. , Hooker William M. , Deftos Leonard J.
Published: February 2005

Human thyroid glands obtained within 2.5 hours of death were examined for the presence and distribution of calcitonin‐containing cells using horseradish peroxidase as an indicator in an indirect immunohistochemical procedure. The glands were cut into 10 to 20 transverse slices per lobe and fixed in glutaraldehyde. A representative section of each paraffin‐embedded slice was processed and systematically scanned for calcitonin‐containing cells. Of 13 glands examined, ten contained calcitonin cells. The cells were found mostly in the follicular epithelium both singly and in groups. They were most numerous in the central region of each lobe of the gland. The isthmus and poles were devoid of calcitonin cells and only occasionally were these cells found at the surface. Parathyroid glands were examined by the same procedure for the presence of calcitonin cells but none were observed. These results demonstrate that calcitonin‐containing cells are found regularly in human thyroid glands and that the distribution of these cells is centered in the central region of each lobe of the gland.
The cycle of the seminiferous epithelium and spermatogenesis in the bovine testis
Authors: Berndston W. E. , Desjardins Claude
Published: February 2005

Morphological changes in the acrosomic system and nuclei of developing spermatids were evaluated as a basis for classifying the stages of the cycle of the seminiferous epithelium in the bovine testis. Light microscopic examination of periodic acid‐Schiff‐stained testicular tissue permitted identification of 14 steps of spermatid development (spermiogenesis). The first 12 steps in this sequence were utilized as the major criterion to divide the cycle of the seminiferous epithelium into 12 distinct stages. Following this, the pattern of germ cell differentiation was investigated by counting the number of germ cells at each stage of the cycle. Based on cell counts, type A spermatogonia divided primarily during stages VII–VIII and IX–X of the cycle. Some type A cells divided again at the end of stage XII to produce intermediate spermatogonia, while others apparently remained “dormant” until the following cycle. At the end of stage IV, intermediate spermatogonia divided to produce type B1 spermatogonia which in turn divided at the end of stage V to produce type B2 spermatogonia. Primary spermatocytes appeared during stage VIII and divided late in stage XI of the following cycle to form secondary spermatocytes. These divided to form young spermatids at the end of stage XII. It was concluded that changes in the acrosomic system and nuclear morphology of developing spermatids provide useful criteria for dividing the cycle of the seminiferous epithelium into stages as well as investigating the pattern of germ cell development during spermatogenesis in the bovine testis.
Formation of central and peripheral myelin sheaths in the rat: An electron microscopic study
Authors: Caley David W. , Butler Albert B.
Published: February 2005

Formation of the myelin sheath in peripheral nerve of the newborn rat is compared with its formation in postnatal cerebral white matter. The unmyelinated central axon is bare and myelination begins by the spiral wrapping of an oligodendrocytic process around the axon. The paired membranes of this process fuse on their inside surfaces, lengthen, and spiral around the axon to make a loose sheath of major dense lines. Compact myelin results after fusion of the outside surfaces to form the intraperiod line. Cytoplasm is sparse in developing central myelin, usually being restricted to inner and outer tongues.

Unmyelinated peripheral axons are enclosed within a mesaxon formed by the invagination and fusion of the outside surfaces of the Schwann cell plasma membranes. Loose myelin is produced by lengthening and spiralling of the mesaxon (intraperiod line) around the axon. As Schwann cell cytoplasm is extruded from between the spirals, the major dense line forms and compact myelin results. Trapped cytoplasm, a characteristic of developing peripheral myelin, is found in the internodal compact myelin sheath as the inner and outer collars and the Schmidt‐Lanterman clefts.
A fine structural study of human oral epithelium separated from the lamina propria by enzymatic action
Authors: Scaletta Lawrence J. , MacCallum Donald K.
Published: February 2005

Incubation of human oral mucosa in physiological solutions containing proteolytic enzymes permits separation of the preparation into its epithelial and connective tissue components. Trypsin, collagenase and elastase were utilized to effect epithelium‐connective tissue separation. Elastase was the most suitable in that a reliable separation of the epithelium from the connective tissue occurred at the lamina lucida (the electron‐lucent zone between the basal cell and basal lamina) with only minimal alteration of the epithelium. The most common change observed in separated epithelium was the formation of cytoplasmic protrusions or blebs on the inferior surface of the epithelial basal cell. Bleb formation was quite extensive when preparations were incubated one to two hours beyond the point where the epithelium could be separated from the connective tissue. With prolonged incubations inferior aspects of epithelial basal cells demonstrated the formation of an entirely new cytoplasmic front apparently resulting from fusion of membranes and subsequent confluence of the cytoplasm contained within the blebs. Individual hemidesmosomes or small lengths of the original inferior epithelial basal cell membrane became enclosed in membrane‐bound vacuoles within the cytoplasm of the epithelial basal cell. These vacuoles were shown to have been interiorized by the absence of a ruthenium red reaction product within the vacuolar spaces. Bleb formation was shown to be strictly enzyme‐induced since intact specimens demonstrated extensive basal cell blebbing following prolonged incubation. Occasional desmosomes were broken and the component halves interiorized in membrane‐bound vacuoles within the cell cytoplasm. Alterations observed in epithelial basal cells as a consequence of exposure to exogenous proteolytic enzymes mimic alterations observed in many disease processes and during certain stages of development.
A study of fine structural changes in the cartilage‐to‐bone transition within the developing chick vertebra
Authors: Crissman Robert S. , Low Frank N.
Published: February 2005

Forty‐eight chick embryos were killed at 9–16 days of incubation age. Tissue was obtained from the fourth or fifth cervical vertebra, immersed in Karnovsky's fluid, post‐fixed in osmium tetroxide, dehydrated in ethanol, stained “en bloc” with uranyl acetate in ethanol, and embedded in Epon 812. Vertebrae were oriented for cross‐sectional microtomy in cephalic to caudal sequence. Thin sections were stained with uranyl and lead salt solutions saturated with tribasic calcium triphosphate to prevent decalcification.

Chondrocytes within the cartilaginous vertebral body occur in various stages of degeneration without orderly arrangement. Both reversible and irreversible stages are found at the cartilaginous resorption front. Electron‐lucent osteoid and mineralization appear in the intercellular matrix at about 12.5 days. Rapidly invading blood vessels form a highly variable resorption front and irregular marrow cavity. Capillaries with accompanying cells border on the front, but else‐where open capillaries allow blood elements to be in direct contact with cartilage. Chondroclasts are associated with small areas of calcified cartilage. At about 14 days trabeculae are formed at the resorption front by osteoblasts which deposit bone osteoid on uncalcified cartilaginous matrix. The matrix is eroded away. A free trabecula of bone without a core of calcified cartilaginous matrix remains.

Basic differences between developmental growth processes in the epiphyseal plate and vertebral body may stem from the large amount of uncalcified cartilaginous matrix at the latter's resorption front.
Electron microscope immunohistochemical localization of vasopressin in the hypothalamus and neurohypophysis of the normal and brattleboro rat
Authors: Leclerc Rachel , Pelletier Georges
Published: February 2005

Using an immunoperoxidase technique at the ultrastructural level, vasopressin was localized in the axons of both the supraoptic and paraventricular nuclei, in the internal zone of the median eminence and the posterior pituitary but not in the perikarya of the neurosecretory neurons. A complete absence of histochemical reaction was found in the hypothalamo‐neurohypophyseal tract of the rat with hereditary hypothalamic diabetes insipidus (Brattleboro strain).
Molar development in the Mongolian gerbil (Meriones unguiculatus)
Authors: Hiatt James L. , Gartner L. P. , Provenza D. V.
Published: February 2005

Odontogenesis was studied in the Mongolian gerbil (Meriones unguiculatus) molar from the dental lamina stage of development to the appositional stage. Fertilization, determined by vaginal lavage technique, was counted as day 0. Prior to the eighteenth post‐coital day no dental primordia could be detected. Beginning on day 18, pregnant females were sacrificed and the fetuses were decapitated. The heads were frozen and sectioned in a cryostat. The tissue was stained, dehydrated, cleared, and covered. Light microscopy was utilized in evaluating molar odontogenesis. Odontogenesis of the molar began at the dental lamina stage on day 18 followed by the bud stage on day 19 prenatal. The cap stage of development was observed on day 19 or 20. Development of the bell stage was noted on day 22. By the fourth postnatal day, the first molar had reached the appositional stage of development. Development of molars in the gerbil resembles that in other rodents.
Ultrastructural observations of anterior pituitary somatotrophs following pituitary portal vessel infusion of dibutyryl cAMP
Authors: Wilbur Donald L. , Worthington W. Curtis , Markwald Roger R.
Published: February 2005

Dibutyryl cyclic adenosine monophosphate (4.6 x 10−7M) was infused with a microcannula into hypothalamo‐hypophysial stalk portal vessels of adult male rats. Anterior pituitary glands were prepared for electron microscopic examination at 1, 5, 15, 30 and 60 min after microinfusion. Ultrastructural observations give evidence of stimulated protein synthesis, and emiocytosis. Emiocytosis occurs at 1, 5 and 15 min only. Evidence of protein synthesis does not develop until 15 min. It persists through the 30 min time period. These observations suggest that dbcAMP may be a potent stimulus to protein synthesis, and may be a sufficient stimulus for emiocytosis.
The growth of infant hearts grafted to young and adult rats
Authors: Dittmer J. E. , Goss R. J. , Dinsmore C. E.
Published: February 2005

Hearts from infant rats were grafted to the abdominal cavities of infant or adult hosts by end‐to‐side anastomosis of the graft's aorta to the host dorsal aorta, and of the donor's pulmonary artery to the inferior vena cava of the host. In such transplants, circulation through the heart bypassed the left atrium and ventricle. Four months after operation, the grafts had grown to normal adult sizes and their right ventricles had hypertrophied commensurate with the left side.
Ultrastructure of the placenta of antarctic seals during the first third of pregnancy
Authors: Sinha Akhouri A. , Erickson Albert W.
Published: February 2005

The chorioallantoic placenta from six crabeater seals (Lobodon carcinophagus) with fetuses from 15–180 mm crown rump length (CRL), and two leopard seals (Hydrurga leptonyx) with fetuses 76 and 86 mm CRL was lobulated, zonary, labyrinthine and endotheliochorial. The fine structure of the placenta was essentially similar in both species. Maternal capillaries of the labyrinth had attenuated endothelial cells unlike the fissiped carnivores. They were surrounded by an outer syncytiotrophoblast, incomplete inner cytotrophoblast, and a core of mesenchymal tissue containing fetal vessels. In general, the cytotrophoblastic cells were less electron‐opaque than the syncytium; the former possessed abundant free ribosomes, while the latter had many nuclei, mitochondria, and numerous strands of rough endoplasmic reticulum. Mitotic figures were observed only in the cytotrophoblast. Plasma membranes between the trophoblastic layers had interdigitating processes which showed many desmosomes along the intercellular spaces, whereas membranes surrounding the maternal capillaries were usually smooth. In the limb‐bud stage embryo, the syncytiotrophoblast had thick and thin areas which became progressively attenuated in older fetuses. Instances of intratrophoblastic fetal capillaries were observed in seals with fetuses of 40 mm CRL and older, with consequent greatly thinned placental barriers. By Perl's reactions, Turnbull's method, and electron microscopy, rows of granular bodies positive for iron were demonstrated along the basement membrane of the trophoblastic cells and in the mesenchymal cells of the crabeater seals, but not the leopard seals. Furthermore, it is suggested that the deposits of granular bodies show the sites of iron storage in the placentas. In the limb‐bud stage embryo the hematome borders and isolated pouches of the central hematome were observed. The central hematome was antimesometrial. The hematomes were lined by columnar cytotrophoblastic cells which phagocytized extravasated maternal blood and absorbed histiotrophic material.
Effects of Cytochalasin‐B and colcimide on cells in muscle cultures
Authors: Holtzer H. , Croop J. , Gershon M. , Somlyo A.
Published: February 2005

Cytochalasin‐B (CB) induces cells to contract. This contraction is biphasic. The rapid response peaks in 30 minutes and is followed by a slower contraction that leads to the “arborized” configuration. If fully arborized cells are removed from CB and exposed to colcimide they are induced to form twisting, birefringent bands. These bands consist of massive numbers of 100 Å filaments.
A discrepancy between measurements of bone resorption in vivo and in vitro in newborn osteopetrotic rats
Authors: Marks Sandy C.
Published: February 2005

Bone resorption in newborn osteopetrotic rats and their normal littermates was measured in vivo and in vitro with different results. The resorption measured in vivo was that induced by injection of parathyroid extract after labeling bone matrix with 3H. Resorption was measured in vitro, by a commonly used method, as the release into the culture medium of 45Ca and 3H previously incorporated in vivo into bone mineral and matrix respectively. In osteopetrotic rats resorption induced by parathyroid extract in vivo was 34 percent less than in littermate controls, whereas the resorption measured in vitro was 26 percent greater in bone from osteopetrotic rats. In addition, the hypercalcemia induced by injections of parathyroid extract was only half as great in osteopetrotic rats as in normal littermates.

Acid phosphatase appears to be important in bone resorption; osteoclasts are rich in the enzyme and it is released from them during bone resorption. Newborn osteopetrotic rats have more osteoclasts which are richer in acid phosphatase than normal littermates. Therefore, it is proposed that the enhanced resorption found in bone from osteopetrotic rats in vitro is the result of release of this excessive acid phosphatase from osteoclasts under the conditions of culture and does not truly reflect resorption in vivo.
The effect of supernumerary cartilaginous implants upon rabbit ear regeneration
Authors: Grimes L. Nichols
Published: February 2005

Full thickness holes through rabbit ears are filled from their margins by the regeneration of missing tissue, including the ear's cartilaginous sheet. However, no regeneration of ear tissue occurs if the cartilaginous sheet is removed. If a second sheet of cartilage is implanted into the ear, only one layer of cartilage differentiates in the regenerate. Therefore, although the original cartilaginous sheet is necessary for chondrogenesis in the regenerate, it does not dictate morphogenetic information to the blastema.
Origin, differentiation and renewal of the four main epithelial cell types in the mouse small intestine II. Mucous cells
Authors: Cheng Hazel
Published: February 2005

The mucous cell population of duodenum, jejunum and ileum was investigated in the light and electron microscopes with the help of radioautography in mice sacrificed at various times after single injection or continuous infusion of 3H‐thymidine.

Mucous cells are characterized by globules of mucus and by dilated cisternae of rough endoplasmic reticulum. Two subgroups of mucous cells, one called common and the other granular, may be identified. The granular mucous cells differ from the common ones by the presence of small dense granules embedded within the mucous globules. Each subgroup is further divided into immature oligomucous cells containing few mucous globules, and mature goblet cells with a large accumulation of mucous globules.

Common and granular oligomucous cells are found exclusively in the crypt, mainly within the lower mid‐crypt, whereas the corresponding two types of goblet cells are present in the upper part of the crypts and in the lower part of the villi. Only common mucous cells are observed in the upper part of the villi.

The two types of oligomucous cells, but not goblet cells, have the ability to take up 3H‐thymidine and divide. Electron microscopic radioautography demonstrates that, as oligomucous cells migrate upwards, they transform into goblet cells. The latter then migrate to the villus epithelium.

In the case of granular mucous cells, this migration is associated with a gradual loss of the characteristic dense granules, so that the granular goblet cells reaching the upper part of the villi become common goblet cells. The goblet cells in the villus epithelium, regardless of their origin, ascend towards the villus tips where they are lost through the extrusion zones.

The turnover time of common mucous cells is about three days, as for columnar cells; and that of granular mucous cells, somewhat shorter. In both cases, the divisions of oligomucous cells account only for the production of about half the mucous cells present. Hence, the other half must be derived from precursors other than oligomucous cells. Since a few crypt‐base columnar cells contain the odd mucous globule, they are suspected of being the precursors of the two types of oligomucous cells and, through them, of the entire mucous cell population.
Origin, differentiation and renewal of the four main epithelial cell types in the mouse small intestine V. Unitarian theory of the origin of the four epithelial cell types
Authors: Cheng Hazel , Leblond C. P.
Published: February 2005

The previous articles of this series provided presumptive evidence that the four main differentiated cell types in the epithelium of the mouse small intestine: villus columnar, mucous, entero‐endocrine, and Paneth cells, originate from the same precursor, the crypt‐base columnar cell. In the present work, direct evidence was obtained in support of this view. It was first found that crypt‐base columnar cells phagocytose non‐viable cells in their vicinity, with the result that a large phagosome appears in the cytoplasm. Such phagosomes were then used as markers to follow the evolution of crypt‐base columnar cells.

In normal control animals, a rare crypt‐base columnar cell includes a large phagosome containing Paneth cell remnants. By six hours after injection of two μCi 3H‐thymidine per g body weight, a fair number of crypt‐base columnar cells include a different type of phagosome containing labeled nucleus and granulefree cytoplasm, which is attributed to phagocytosis of a labeled crypt‐base columnar cell killed by beta‐radiation from the incorporated 3H‐thymidine.

By 12 hours after 3H‐thymidine injection, phagosomes have appeared in partly differentiated mid‐crypt columnar cells and oligomucous cells; by 18–24 hours, in fully differentiated columnar cells and in Paneth cells; and by 30 hours, in an entero‐endocrine cell. Since phagosomes are first found in crypt‐base columnar cells and only later in the four differentiated cell types, it is concluded that crypt‐base columnar cells transform into cells of these four types and, therefore, behave as the stem cells of the epithelium.

The finding of rare epithelial cells containing two different types of secretory material (either mucous globules and entero‐endocrine granules, or mucous globules and Paneth cell granules) confirms that the stem cells are multipotential. These findings support the Unitarian Theory of epithelial cell formation in the small intestine.