bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructure of a model basement membrane lacking type IV collagen
Authors: Brauer Philip R. , Keller John M.
Published: February 2005

Basement membranes (BMs) are specialized extracellular matrices which have important roles in cell attachment, migration, growth, and differentiation. The major components of these matrices include type IV collagen, laminin, entactin, and heparan sulfate proteoglycan. The framework or scaffold of BMs has been proposed to be type IV collagen (Yurchenco et al., 1986, J. Histochem. Cytochem., 34:93–102). However, a murine teratocarcinoma cell‐line, M1536‐B3, has been described which produces an extracellular matrix (ECM) composed of some of the known components of BM, e.g., laminin, entactin, and sulfated proteoglycan, but lacking type IV collagen (Chung et. al., 1979, Cell, 16:277–287). With the use of morphological techniques, we have found that the ECM assembled by these cells is composed of multiple layers of electron‐dense cords arranged in an interweaving meshwork with short 2–4 nm‐diameter cylindrical rods embedded throughout. This organization closely resembles that reported for naturally occurring BMs, e.g., Reichert's membrane (Inoué et al., 1983, J. Cell Biol., 97:1524–1537). The previous identification of known in vivo BM components in M1536‐B3 ECM and the correspondence in morphological appearance of M1536‐B3 ECM with that present in naturally occurring BMs suggests that a BM‐type of ECM can be assembled without a type IV collagen framework, thus indicating that other components of BMs have a critical role in BM organization and assembly.
Membrane relationships in murine meissner corpuscles: Cytology of freeze‐substituted tissue
Authors: Yoshida Yasuo , Ushiki Tatsuo , Takashio Minoru , Munger Bryce L. , Ide Chizuka
Published: February 2005

Mechanoreceptive sensory corpuscles (murine Meissner corpuscles) in the toe pad skin of mice, consisting of axon terminals and lamellar cells, were studied following freeze‐substitution in order to clarify the plasma membrane relationships between axon terminals and lamellar cells. Tissue preservation of corpuscles was excellent when the corpuscle was located within 10 μm from the contact surface with the precooled metal block.

The axolemmata appeared more electron‐opaque than did plasma membranes of lamellar cells. The inner leaflet of the unit membranes was thicker than the outer leaflet in the axolemma, and the contour of cell plasma membranes was relatively smooth and straight. Characteristic focal or regional approximations of plasma membranes were noted between the axon and abutting lamellae. Such membrane appositions resembled gap junctions, although no gap junctions were found between the axon and lamellae in chemically fixed materials. Similar gap junction‐like close appositions of plasma membranes also were found between neighboring lamellae. These approximations occurred more frequently than typical gap junctions seen in chemically fixed materials. These findings indicate that there may be a relationship of the plasma membranes in the axon terminals and in abutting lamellae as well as between neighboring lamellae that have not been identified as yet in conventional chemically fixed material.

Another striking finding was that basal laminae on lamellar cells exhibited the same electron opacity as the surrounding connective tissue matrix and thus the two are indistinguishable from one another. Furthermore, the lamina lucida was not evident, and basal lamina material was directly contiguous with the plasma membrane. These findings suggest that freeze‐substitution can retain materials that are easily extractable by conventional chemical fixation and dehydration.
Transfer of dorsoventral information from mesoderm to ectoderm at the onset of limb development
Authors: Geduspan Jane S. , Maccabe Jeffrey A.
Published: February 2005

Control of dorsoventral patterns in the chick at the prelimb stages resides in the limb mesoderm. Recombination experiments at stage 14, with dorsoventrally reversed ectoderm, result in wings with mesodermal dorsoventral polarity. Similar recombinations at stage 16 show that the ectoderm has acquired dorsoventral information and can impose this polarity on the patterns of mesodermal differentiation in the distal regions of the wing. The dorsoventral information in the ectoderm comes from the mesoderm, which transfers this information to the overlying ectoderm between stages 14 and 16. The initial dorsoventral information in the ectoderm is not stable and can be reprogrammed by stage 14 mesoderm. Subsequently, there is a gradual stabilization of the ectodermal information. At the same time the mesoderm loses its capacity to reprogram dorsoventral information in the ectoderm.
Autonomic innervation of reproductive organs: Analysis of the neurons whose axons project in the main penile nerve in the pelvic plexus of the rat
Authors: Dail William G. , Trujillo Daniel , Rosa Diana De La , Walton Guy
Published: February 2005

An understanding of the composition of the various nerves of the pelvic plexus is essential in the design of studies to explore the autonomic control of pelvic visceral tissues. As a correlate of this interest, the present study was designed to determine the composition of the main penile nerve in the pelvic plexus of the laboratory rat, an animal commonly used for studies of reproductive physiology. Retrograde tracing studies indicate that the main penile nerve contains neurons which project to the penile crura, the corpus spongiosum, and the bulbourethral glands. The main penile nerve is the major source of neurons which innervate the corpus spongiosum and bulbourethral gland and contains about one‐third of all parasympathetic neurons which project to the penile crura. Dye placed on the proximal cut end of the main penile nerve indicates that neurons in the parasympathetic region of the spinal cord (L6‐S1) and to a lesser extent a sympathetic region of the cord, L1‐L2, provide preganglionic innervation to ganglion cells in the main pelvic nerve. Processes of neurons in dorsal root ganglia L6‐S1 and of neurons in the abdominopelvic sympathetic chain course in the main penile nerve to unknown destinations. In many respects this presumed postganglionic fiber tract is essentially a region of the pelvic plexus which subserves extrapelvic visceral tissues.
Rapid neuromuscular remodeling following limb immobilization
Authors: Fahim Mohamed A.
Published: February 2005

The effect of immobilization on endplate morphology of the rat soleus muscles was studied qualitatively and quantitatively. The endplate was visualized by light microscopic zinc iodide osmium (ZIO) staining and by electron microscopy. The soleus muscle was immobilized by pinning of ankle and knee joints at right angles for 5 days. Immobilized muscles were then compared to the contralateral side and to normal litter mates. After 5 days of partial disuse, muscle fibers atrophied and nerve terminal area increased in ZIO‐determined measurements. Neuromuscular junctions (NMJs) of disuse muscle fibers visualized by electron microscopy exhibited greater amounts of degeneration than either contralateral or control NMJs. Degeneration consisted of nerve terminal disruption, exposed junctional folds, and postsynaptic areas which contained little or no postjunctional folds. Regeneration also occurred in the same NMJs, consisting of small terminals associated with large expansion of junctional folds, several small terminals occurring within the same primary synaptic cleft, and several axons wrapped by the same Schwann cell. These observations demonstrate, for the first time, that partial disuse for only 5 days produces muscle atrophy as well as denervation‐like changes at the NMJ, which leads to terminal sprouting within the endplate area and remodelling.
Dentin matrix proteins: Composition and possible functions in calcification
Authors: Linde Anders
Published: February 2005

Dentin may be regarded as a mineralized connective tissue. In its composition as well as its mode of formation, dentin exhibits several similarities with bone, but also definite differences. The dentin organic phase, the matrix, determines its morphology and is believed to be instrumental in the formation of the mineral phase. A fibrous web of collagen type I dominates the organic matrix. Also, minor amounts of other collagen types may be present. The noncollagenous proteins (NCPs), which constitute about 10% of the matrix, fall into several categories: phosphoproteins, Gla‐proteins of the osteocalcin type as well as matrix Gla‐protein, proteoglycans, different acidic glycoproteins, and serum proteins. Some of these NCPs have unique chemical compositions that give them specific properties.

Dentinogenesis occurs by two simultaneous processes: the formation of a collagenous web in predentin, which is followed by the formation of the inorganic phase at the mineralization front. The composition of the predentin organic matrix differs from that of dentin, as some NCP components are secreted extracellularly just in advance of the mineralization front. In addition, some constituents of predentin seem to be metabolized.

The NCPs may be important to several processes during dentinogenesis. Much evidence indicates that noncollagenous components in the matrix are instrumental in mineral formation. New data show that polyanionic NCPs, such as phosphoprotein and proteoglycans, when immobilized on a solid support, induce apatite for‐mation under physiological conditions. These data indicate that polyanionic NCPs may function as mineral nucleators in vivo. They may also act as size and rate regulators for crystallization and promote calcium ion diffusion in the tissue. In addition, NCPs may regulate collagen fibrillogenesis.
Cartilage macromolecules and the calcification of cartilage matrix
Authors: Robin Poole A. , Matsui Y. , Hinek A. , Lee E. R.
Published: February 2005

The calcification of cartilage matrix in endochondral bone formation occurs in an extracellular matrix composed of fibrils of type II collagen with which type X collagen is closely associated. Also present within this matrix are the large proteoglycans containing chondroitin sulfate which aggregate with hyaluronic acid. In addition, the matrix contains matrix vesicles containing alkaline phosphatase. There is probably a concentration of calcium as a result of its binding to the many chondroitin sulfate chains. At the time of calcification, these proteoglycans become focally concentrated in sites where mineral is deposited. This would result in an even greater focal concentration of calcium. Release of inorganic phosphate, as a result of the activity of alkaline phosphatase, can lead to the displacement of proteoglycan bound calcium and its precipitation. The C‐propeptide of type II collagen becomes concentrated in the mineralizing sites, prior to which it is mainly associated with type II collagen fibrils and is present in dilated cisternae of the enlarged hypertrophic chondrocytes. The synthesis of type II collagen and the C‐propeptide, together with alkaline phosphatase, are regulated by the vitamin D metabolites 24,25(OH)2 cholecalciferol and 1,25 (OH)2 cholecalciferol. At the time of calcification, type X collagen remains associated with type II collagen fibrils. It may play a role in preventing the initial calcification of these fibrils focusing mineral formation in focal interfibrillar sites. This process of calcification is clearly very complex, and involves different interacting matrix molecules and is carefully regulated at the cellular level.
Biosynthesis and secretion of enamel proteins in the rat incisor
Authors: Nanci Antonio , Ahluwalia Jatinder P. , Pompura Julia R. , Smith Charles E.
Published: February 2005

The synthesis and secretion of enamel proteins (EPs) in rat incisors was examined using cytochemical and biochemical methods. Radioautography after injection of 3H‐methionine showed that ameloblasts in the presecretory, secretory, and maturation stages of amelogenesis actively synthesized and secreted proteins. Immunocytochemistry with an antibody to mouse amelogenins revealed the presence of EPs in the protein synthetic and secretory organelles of thesecellsatallthreestages. Labelingwasalsofoundinelementsoftheendosomal/lysosmal compartment. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) and silver staining of proteins extracted from enamel and enamel organ showed several protein bands. However, transfer to nitrocellulose paper and immunoblotting revealed that most of the proteins recognized by the antibody were situated between approximately 14 and 32 kDa. EPs were further characterized by using lectins to examine their carbohydrate content. Lectin‐gold cytochemistry on sections showed the binding of wheat germ agglutinin and Helix pomatia lectin to secretory stage enamel. Lectin blotting indicated that the amelogenins were heterogeneously glycosylated and contained the sugars N‐acetyl‐glucosamine/N‐acetyl‐neuraminic acid and N‐acetyl‐D‐galactosamine. Fluorography at 6 and 10 min and 1 h after injection of 35S‐methionine revealed four labeled bands in the main amelogenin group near 22, 28, 30, and 32 kDa. A short‐lived protein of approximately 58 kDa was also observed primarily in cells. The appearance of labeled proteins in enamel was paralleled by their disappearance from cells and the intensity of the radiolabeled protein bands, both in enamel and in cells, decreased towards the maturation stage. These data are consistent with the concept that ameloblasts produce multiple amelogenins throughout amelogenesis.
Molecular mechanisms of bone resorption by the osteoclast
Authors: Baron Roland
Published: February 2005

The osteoclast is a multinucleated cell that is actively engaged in the synthesis of lysosomal enzymes, their vectorial transport toward the apical membrane, and the secretion of these enzymes at its apical pole. These secreted enzymes are targeted to the apical ruffled‐border membrane by mechanisms that involve cation‐independent mannose‐6‐phosphate receptors. These receptors bind to an enzyme‐linked mannose‐6‐phosphate recognition marker in the Golgi complex, and the enzyme‐ligand‐receptor complex, carried within small coated transport vesicles, dissociates upon reaching the low pH established in the bone‐resorbing compartment by the osteoclast. The apical bone‐resorbing compartment is sealed off by the attachment of the osteoclast to the calcified matrix and is actively acidified by the osteoclast. The plasma membrane of the cell is divided into distinct domains. The apical membrane at the ruffled‐border shares common antigenic determinants with lysosomal and endosomal membranes, including a 100 kD protein and proton pumps that may be involved in the acidification of the extracellular resorbing compartment. The basolateral membrane is highly enriched in sodium pumps. Finally, the cytoplasm of the osteoclast is highly enriched in carbonic anhydrase, and bicarbonate‐chloride exchange appears to regulate the intracellular pH of this cell. These observations are consistent with a scheme in which, in the low pH environment of the bone‐resorbing lacuna produced by the osteoclast, the mineral phase dissolves, exposing the organic matrix to the action of the secreted enzymes. The activity of these enzymes is in turn presumably favored by the acidic milieu. All constituents of the matrix, whether mineral or organic, then would be reduced to their elemental forms (ions and amino acids) extracellularly. No phagocytic events would be required for the complete degradation of the bone matrix. According to these concepts, therefore, membrane iontransport mechanisms become the most important molecular aspect of bone resorption.
Technique for reconstituting fixed cadaveric tissue
Authors: Blaney Sean P. A. , Johnson Barry
Published: February 2005

Dissecting room cadavers used over a prolonged period inevitably become desiccated, especially in well‐ventilated surroundings. It is particularly desirable that dissections used for end‐of‐year examinations be restored to their original condition. We describe here a quich and simple procedure designed to restore neglected specimens to their former condition at dissection. Specimens were either soaked for 24 hr in a standard solution of fabric conditioner or sprayed with the same standard solution. The specimens were then wrapped with muslin soaked in the conditioner and covered with polythene sheeting for 1 week. The results obtained were excellent and much superior to a short soak in water. The results further indicate that this technique may have other applications in the preparation of fixed histological material.
Effects of cholecystokinin and carbamylcholine on paneth cell secretion in mice: A comparison with pancreatic acinar cells
Authors: Satoh Yohichi , Ishikawa Katsushi , Oomori Yukio , Yamano Miki , Ono Kazuyuki
Published: February 2005

To confirm whether the Paneth cells of mice (ICR, male, 10–12 weeks old) have the same secretory response to hormonal and cholinergic stimulation as do pancreatic acinar cells, ultrastructural changes of Paneth cells and pancreatic acinar cells 1 hr after administration of various doses of cholecystokinin (octapeptide, CCK‐8) and carbamylcholine were morphometrically assessed. After maximal (1.5 μg/kg intraperitoneally [i.p.]) and supramaximal (15 μg/kg, i.p.) stimulation by CCK‐8, pancreatic acinar cells showed, respectively, degranulation or disturbance of secretion (e.g., an increase in lysosome‐like bodies, aggregation of zymogen granules). The Paneth cells, however, were almost unchanged in the parameters examined. After carbamylcholine injection (1,000 μg/kg, subcutaneously [s.c.]), both pancreatic acinar cells and Paneth cells showed degranulation. Paneth cells sometimes developed large vacuoles, probably formed after massive exocytosis; such vacuoles were not observed in pancreatic acinar cells. It is suggested that Paneth cells and pancreatic acinar cells have different secretory responses. Paneth cell secretion, which possibly plays a role in controlling the intestinal bacterial mileu, may be stimulated by cholinergic rather than hormonal mechanisms.
Neuroepithelial endocrine cells in the lung of Ambystoma mexicanum
Authors: Scheuermann Dietrich W. , Adriaensen Dirk , Timmermans Jean‐Pierre , De Groodt‐Lasseel Marie H. A.
Published: February 2005

Neuroepithelial endocrine (NEE) cells were for the first time identified in the lung of the entirely aquatic urodele, Ambystoma mexicanum, by using light and electron microscopy, histochemistry, and immunocytochemistry. In the basal part of the ciliated epithelium and, less often, in the respiratory portion of the lung, NEE cells were found to occur both solitarily and in small clusters. No typical neuroepithelial bodies could be found. Using the method of Fernandez Pascual, some NEE cells were found to be argyrophilic. Microspectrofluorimetric analysis of formaldehyde‐induced fluorescence and immunocytochemistry revealed the presence of 5‐hydroxytryptamine. With antibodies to neuron‐specific enolase only a few NEE cells exhibited a faint immunostaining. Electron‐microscopically, the NEE cells are provided with distinctive cytoplasmic membranebound dense granules of variable size, which gave a positive argentaffin reaction. The images of emiocytotic granule release are indicative of a secretory function. In the tracheal epithelium, NEE cells seem to occur only solitarily. They bear the same ultrastructural characteristics as the intrapulmonary NEE cells but here, the dense granules are larger and associated with numerous bundles of microfilaments. Intraepithelial nerve endings were observed near the airway lumen. Between nerve terminals and NEE cells, synaptic complexes with aggregations of clear‐centered vesicles close to the presynaptic membrane thickenings were observed. In addition, some nerve endings from “reciprocal synapses” with NEE cells. A receptosecretory function for NEE cells in the lung of A. mexicanum is supposed.
Differentiation of trophoblast of the baboon blastocyst
Authors: Enders Allen C. , Lantz Katherine C. , Schlafke Sandra
Published: February 2005

The structure of trophoblast of the baboon blastocyst undergoes a number of maturational changes from the early blastocyst to the late blastocyst stage. The striking expansion of the blastocyst that occurs during the preimplan tation period is accompanied by the development of an extensive endocytic apparatus. Cationized ferritin labels coated depressions and vesicles near the apical cell surface, numerous uncoated tubules and larger apical vesicles, and multivesicular bodies within trophoblast cells. Basally and laterally the labeled components are primarily small uncoated vesicles and tubules. Small, discrete clusters of ferritin particles were seen within the basolateral compartment between trophoblast and its basal lamina and beneath trophoblast cells that do not have a basal lamina. The results indicate that ingested materials may be directed in two pathways, one involving breakdown within the lysosomal system and one involving transcytosis. The zona pellucida is a trilaminar structure consisting of a fibrillar outer layer that often contains spermatozoa, an intermediate zone, and an inner layer containing columns of dense zonal material. Loss of the zona occurs after expansion of the blastocyst and development of the endocytic organelles. During the late blastocyst stage, syncytial trophoblast differentiates at the margin of the polar trophoblast. Because blastocysts were flushed from the uterus, it could not be determined whether azonal blastocysts had been adherent to the uterine surface prior to collection.
Formation of multinucleated cells with osteoclast precursor features in human cord monocytes cultures
Authors: Orcel Philippe , Bielakoff Josette , De Vernejoul Marie Christine
Published: February 2005

A common lineage between monocytes and osteoclasts has been suggested but not yet proved, and an osteoclast precursor might be an immature cell of the monocyte‐macrophage family. We therefore compared the ability of cord blood and adult monocytes in long‐term culture to differentiate toward osteoclasts. Both adult and cord monocytes were cultured for 3 weeks in the presence of 20% horse serum. The proportion of multinucleated cells formed was influenced by 1,25(OH)2D3 in cord, but not in adult monocyte cultures: 10−9M 1,25(OH)2D3 increased multinucleated cells from 13 ± 2 to 26 ± 1% of total cells in cord monocyte cultures. The formation of multinucleated cells in cord monocyte cultures, in the presence of 10−9 M 1,25(OH)2D, was decreased by salmon calcitonin (dose dependently from 10−8 to 10−6 M) and increased by 1—34 parathormone (100 ng/ml). None of these hormones induced any modification of the proportion of multinucleated cells formed in adult monocytes culture. Specific antigens on the membrane of the cells obtained after 3 weeks culture in the presence of 10−9 M 1,25(OH)2D3 were assessed by immunocytochemistry. The respective proportion of adult and cord labeled cells was 64 ± 11 vs. 63 ± 6% with Leu M5 (specific for monocyte) and 68 ± 7 vs. 30 ± 10% (P<0.05) with the anti‐HLA DR antibody. The monoclonal antibody 23C6 is specific to the vitronectin receptor, which is highly expressed by osteoclasts–41 ± 2% of the cells in cord monocyte cultures–but none in the adult monocytes culture were labeled with 23C6 at the end of the culture period. The ability of cells formed in cord monocyte culture to resorb devitalized bone on which they were cultured was investigated after 3 weeks culture. These cells did not release 45Ca from devitalized 45Ca‐prelabeled rat calvaria; they did not form an acidic extracellular compartment, as assessed by acridine orange fluorescence, and there was no ultrastructural evidence of a brush border at the interface with bone. In conclusion, cord blood monocytes in long‐term culture do not form mature osteoclasts. However, in contrast to adult monocytes, some acquire, in culture, characteristics of osteoclast precursors: sensitivity to osteotropic hormones and expression of an osteoclast membrane‐specific antigen.
Characterization of the synthetic capacities of isolated placental binucleate cells from sheep and goats
Authors: Morgan G. , Whyte A. , Wooding F. B. P.
Published: February 2005

Sheep and goat binucleate cells (BNC) play a central role in placental growth and development. This study reports a simple method for isolating 60‐70% pure populations of BNC of high viability. After incubation of the isolated BNC with a brief pulse of 14C‐leucine or 3H‐fucose or 3H‐galactose, electron microscope autoradiography showed that label was eventually incorporated into the characteristic BNC granules via the Golgi body. Fucose and galactose initially showed a much higher Golgi body label than leucine, which was at first predominantly localised in the endoplasmic reticulum. 35S‐methionine incorporation by BNC suspensions was extensive enough to allow an immunoprecipitation investigation which demonstrated that the protein hormone ovine placental lactogen and the SBU‐3 antigen were synthesised de novo. Previous studies with isolated BNC have shown a remarkable range of substances to be released into the incubation medium but not necessarily synthesised during the incubation. The results demonstrate unequivocally that isolated BNC's are capable of total synthesis in vitro of two of the proteins that these same cells are known to secrete in vivo.
Developmental morphology of vascular and lymphatic capillaries in the working myocardium and purkinje bundle of the sheep septomarginal band
Authors: Smolich Joseph J. , Shimada Tatsuo , Canale Enrico , Campbell Gordon R.
Published: February 2005

The normal development of vascular and lymphatic capillaries in the right ventricular septomarginal band of the sheep heart was studied in 9 fetuses aged 60—143 days (term = 147 days), 14 lambs aged 1 day to 16 weeks, and 3 adults. Tissue was fixed by perfusion and examined with light and transmission electron microscopy.

The septomarginal band is composed of working myocardium and a well‐defined peripheral bundle of Purkinje cells. Vascular capillaries of the working myocardium were closely apposed to myocardial cells. By contrast, vascular capillaries of the Purkinje bundle were situated within the connective tissue sheath and septa, at variable distances from the Purkinje cells. After birth, the capillaries of the Purkinje bundle were also found in grooves and tunnels within the Purkinje strands. The ultrastructure of fetal vascular capillaries associated with myocardial and Purkinje cells was initially similar, and characterized by an abundance of synthetic organelles in endothelial cells and pericytes. However, after 115 days in utero, capillary endothelium with diaphragmed fenestrae, 40—60 nm in width, were observed within the Purkinje bundle. The fenestrae attained an average frequency of 1 per 11 capillary cross sections just before term, and this was maintained in lambs and adults. The ultrastructure of lymphatic capillaries, which were not observed in the septomarginal band until just before term, changed little during development.
Androgen‐induced changes in nuclear pore number and in tight junctions in rat seminal vesicle epithelium
Authors: Ortiz Hector E. , Cavicchia Juan Carlos
Published: February 2005

The numbers of nuclear pore complexes and tight junctions were quantified in the seminal vesicle epithelial cells of castrated and castrated‐plus‐androgen‐treated male rats, which received subcutaneous pellets of testosterone propionate (1 mg/kg body weight) for 1 week. Seminal vesicle weights were 0.284 ± 0.02 g for castrated, 1.006 ± 0.006 g for androgen‐treated, and 0.918 ± 0.04 g for untreated groups. Tissue samples were processed for light or electron microscopy and for freeze‐fracture techniques. Nuclear areas were measured: controls were 279.34 ± 8 m̈m2; these increased significantly (P < .001) in castrated‐plus‐androgen‐treated rats (324.66 ± 11 m̈m2) and decreased (P < .001) in castrated animals (173.14 ± 6.3 m̈m2). Nuclear pore density increased (P < .001) in castrated‐plus‐androgen‐stimulated rats (5.38 ± 0.24 pores/ m̈m2) (control: 4.78 ± 0.14 pores/m̈m2), and decreased (P < .001) in castrated rats (3.16 ± 0.14 pores/m̈m2). A significant (P < .001) increase in numbers of tight junction strands that extended in the lateral cell membranes was detected in castrated‐plus‐androgen‐treated rats vs. controls or castrated‐only animals.
Microanatomy of the lung of the bowhead whale balaena mysticetus
Authors: Henk William G. , Haldiman Jerrold T.
Published: February 2005

The lungs from six bowhead whales harvested by Alaskan Eskimos have been examined with light and electron microscopes. Airways ranging from 1 to 40 mm in luminal diameter are lined by a pseudostratified ciliated epithelium containing numerous mucus‐secreting cells. The underlying lamina propria‐tela submucosa of these airways contains tubuloalveolar glands, plasma cells, and lymphatic accumulations in addition to both elastic and collagenous fibrillar elements. Cartilage extends to the level of the respiratory airways, but smooth muscle is absent from airways larger than 3 mm, and tubuloalveolar glands are absent from airways smaller than 3 mm. Respiratory airways are lined by pseudostratified, simple cuboidal, and simple squamous epithelia. Alveolar ducts are lined by simple squamous epithelium exclusively. A connective tissue core composed mostly of elastic fibers supports the walls of the alveolar ducts. Neither smooth muscle nor cartilage has been observed in these structures. Alveoli contain the typical cetacean double capillary bed separated by a thick septum composed mainly of collagenous connective tissue. Alveoli are lined by a simple squamous epithelium similar to that encountered in alveolar ducts and respiratory airways. This epithelium is composed of type I and II pneumocytes closely appressed to an underlying capillary network. The type II pneumocytes contain typical lamellar bodies and tubular myelin can be seen in the air spaces. The lung is surrounded by a thick (X = 2.5 mm) visceral pleura rich in blood vessels and elastic fibers.
Influence of age, growth, and sex on cardiac myocyte size and number in rats
Authors: Bai Shuling , Campbell Scott E. , Moore Jo Ann , Morales Martha C. , Martin Gerdes A.
Published: February 2005

The effects of altered neonatal nutrition on cardiac myocyte size and number was examined in 21‐day‐old and 3‐month‐old rats. Nutritional differences in growth rate were produced in newborns by adjusting litter size to four (fast‐growing), eight (normally growing), or 16 (slow‐growing) pups per litter. Isolated myocytes were prepared from animals in each group to evaluate changes in cell size and number. Heart weight (mg ± S.D.), at 21 days of age, was 398 ± 51 for “fast‐growing” rats, 329 ± 43 for “normally growing” rats, and 228 ± 24 for “slow‐growing” rats. Body weights showed a comparable decline with reduced nutrition. In adults, treatment‐related differences in body and heart weight were present in males but not females.

“Slow‐growing” rats had 21% fewer myocytes than “fast‐growing” rats at 21 days of age, a change that persisted in adults. Values for myocyte number from “normally growing” rats were intermediate between those of “fast and slow‐growing” rats at both 21 days and 3 months of age. In each heart region of weanling rats, myocyte length and volume were smallest in 16 per litter rats. Cellular dimensions increased progressively with better nutrition. In adults, differences in myocyte size as a function of altered neonatal nutrition were not statistically significant.

Sex‐related differences in myocyte size or number were not found in males and females from any group at the time of weaning. In adults, it was also noted that males and females have a similar number of cardiac myocytes, but the larger heart weight found in males was primarily due to increased myocyte size. Myocyte size and number were also examined in 2‐year‐old female rats. There were no differences in cardiac myocyte size or number between 2‐year‐old females and 8‐month‐old weight‐matched females.
Differentiation of the inner cell mass of the baboon blastocyst
Authors: Enders Allen C. , Lantz Katherine C. , Schlafke Sandra
Published: February 2005

During the blastocyst stage of development in the baboon, the inner cell mass changes from an irregular accumulation of cells within the cavity of the blastocyst to a disk at one side of the blastocyst and finally to a spherial mass of epiblast cells exhibiting a distinct polarity. The cells that will become the primitive endoderm are first seen as flattened but undifferentiated cells on the cavity side of the disk‐shaped inner cell mass. After endoderm cells develop their typical cytological characteristics, they extend well beyond the inner cell mass to form parietal endoderm. A basal lamina develops associated with the epiblast cells and mural trophoblast, but not with either parietal or visceral endoderm. Cytological differentiation of inner cell mass cells includes increased numbers of polyribosomes and a change in mitochondria from long, convoluted structures to short, more typical shapes. Evidence that epiblast is polarized is seen by the late zonal blastocyst stage. Apical junctional complexes develop within the center of the epiblast. These junctions presage the development of the potential amniotic cavity. Large vacuoles containing cell debris, some of which contain nuclear fragments, are present at all stages. Extensive cell death occurs during growth of the blastocyst, but the pattern appears to be random and products of cell death are readily phagocytized by adjacent cells.
Smooth muscle cells of neural crest origin form the aorticopulmonary septum in the avian embryo
Authors: Beall Arthur C. , Rosenquist Thomas H.
Published: February 2005

Previous studies have shown that the cells of the aorticopulmonary (AP) septum are similar to the smooth muscle cells of the mediae of the great vessels in their common origin from the cardiac neural crest and in their common expression of an elastic extracellular matrix. The purpose of this study was to test the cells of the AP septum for the presence of certain cytoplasmic proteins, especially smooth muscle alpha‐actin (SMAA) whose presence is definitive of smooth muscle.

A monoclonal antibody against SMAA was applied to normal chicken embryos at 3.5–8 days of incubation and to age‐matched embryos from which the cardiac neural crest had been ablated surgically. Antibodies against the intermediate filaments desmin, cytokeratin, and vimentin also were applied.

The results showed that the AP septal cells expressed SMAA during the process of septation, days 5–8; but when the cardiac neural crest was ablated and septation was defective, no cells in the conotruncal connective tissue expressed SMAA. None of the intermediate filament proteins were detected in the septum.

These results indicate that the AP septal cells are smooth muscle and therefore may be hypothesized to have an active role in septation.
Skeletal structural adaptations to mechanical usage (SATMU): 4. Mechanical influences on intact fibrous tissues
Authors: Frost H. M.
Published: February 2005

This paper proposes that the growth in length of living fibrous tissue structures (tendon, ligament, fascia) responds primarily to circulating systemic rather than mechanical factors. However, growth of the thickness of those structures responds primarily to their mechanical tension loads in the special sense that, when the tissue's typical peak mechanical strains exceed a threshold value, its cells begin to add new collagen to increase its thickness, strength, and tension stiffness. When subsequent peak strains reduce to the threshold value, then further additions of collagen stop. That process defines mechanically controlled modeling of fibrous tissues. The collagen in these tissues can also develop mechanical microdamage (MDx) under repeated tension load‐deload cycles. Special maintenance mechanisms normally repair that MDx to prevent accumulations that would threaten structural integrity. As a result, spontaneous complete ruptures of these structures can happen when MDx production exceeds its repair. These maintenance mechanisms also prevent gradual stretching under continuous tension loads, a process the author suggests calling creep compensation. When the creep compensation mechanism becomes incompetent, structures can stretch under continuous loads; when it becomes overactive, contractures can occur. The above meld of fact and inference provides the kernel of a general theory for the responses of the architecture and mechanical competence of intact fibrous tissues to mechanical usage.
Three‐dimensional reconstruction of adult female mouse submandibular gland secretory structures
Authors: Denny Paul C. , Chai Yang , Pimprapaiporn Watchara , Denny Patricia A.
Published: February 2005

Computer‐assisted reconstructions of adult female mouse submandibular gland have been used to positionally characterize within the three‐dimensional structure likely intermediates in secretory cell replacement. The locations of striated granular duct cells and granular intercalated duct cells are consistent with a role as intermediates between intercalated duct cells and granular duct cells or acinar cells, respectively. Average volumes of the two putative intermediate cell types are also consistent with this role. The reconstructions suggest that, in addition to a “streaming” mechanism for secretory cell replacement, formation of new secretory structures composed of multiple acini and second‐order intercalated ducts may also contribute to the cell replacement process.
Peripubertal human breast development
Authors: Monaghan Paul , Perusinghe Nina P. , Cowen Philip , Gusterson Barry A.
Published: February 2005

The microanatomical and histological appearance of the human breast has been studied during puberty. The macroscopic architecture of the mammary epithelial tree was identified and correlated with the histological appearance of material excised from defined regions of the breast preparations. Between ages 13 yrs and 15 yrs the human breast shows evidence of ductal elongation and branching, with lobules formed by lateral and dichotomous branching. The majority of ducts are lined by a two‐layered epithelium consisting of recognisable myoepithelial and luminal cells. Less‐well‐defined multilayered regions were also observed in some areas, apparently at the site of lateral branching or early lobular development.
Adaptation of cancellous bone to aging and immobilization in the rat: A single photon absorptiometry and histomorphometry study
Authors: Li Xiao Jian , Jee Webster S. S. , Chow Sien‐Yao , Woodbury Dixon M.
Published: February 2005

Nine‐month‐old female rats were double‐labled with bone markers and subjected to right hindlimb immobilization or served as control for 0, 2, 10, 18, or 26 weeks. The right limb was immobilized against the abdomen, thus unloading it, while the left limb was overloaded during ambulation. Single photon absorptiometry and cancellous bone histomorphometry were performed on dissected intact femur and 20‐m̈m‐thick undecalcified specimens of the proximal tibial metaphysis. In the unloaded limb, immobilization‐induced muscle and cancellous bone loss occurred rapidly before 10 weeks and stabilized at 50% less bone mass after 18 weeks. Unloading caused a negative bone balance from a combination of elevated bone resorption and depressed bone formation. At 2, 10, and 18 weeks of immobilization, the ratios of bone resorption to bone formation surfaces were 1.6, 1.5, and 1.3, respectively; at 26 weeks, the ratio was 1. The bone loss was accompanied by poorer trabecular architecture (trabecular number decreased and trabecular separation increased), reaching the maximum at 18 weeks and stabilizing thereafter. These observations are in general agreement with Frost's postulate for mechanical effects on lamellar bone remodeling, and the findings on disuse osteoporosis in man. Therefore, the one‐legged immobilization model can be useful in studies of the mechanisms of structural adaptation to mechanical usage.
Elastic and collagenous fibers in the temporomandibular joint capsule of the rabbit and their functional relevance
Authors: Savalle Willem P. M. , Weijs Wim A. , James Jan , Everts Vincent
Published: February 2005

This study deals with the form and function of the temporomandibular joint capsule and compares the histogical structure of the capsule and kinetics of condylar and disc movement in rabbit and man.

The morphology of the capsule of the jaw joint of the rabbit was studied by means of histological sections of isolated capsules, cellodin sections of decalcified heads, and cryostat sections containing the joint, fixed in jaw open and closed positions. General staining methods and selective methods for elastin and collagen were used. The volume density of the elastic fibers was determined morphometrically. The capsule consists of a portion connecting disc and skull and a portion connecting disc and mandible. The former portion has a fibrous outer layer of dense connective tissue. It contains numerous bundles of specifically oriented collagen but hardly any elastic fibers. Few irregularly arranged elastic fibers are present in the lateral and medial areas of the capsule. In contrast, the portion connecting disc and condylar process contains not only oriented collagen but also large amounts of elastic fibers. Anteriorly, there is a thin elastic band that is streched greatly at jaw opening. Posteriorly, the capsule takes the appearance of a large fibro‐elastic pad that covers the posterior extension of the condyle. This part is somewhat stretched when the jaw is closed. The findings correlate well with the results of jaw movement studies, showing a remarkable capability for condylar protrusion and retrusion. In contrast to the situation in humans, this movement occurs mainly between condyle and disc. It is made possible by the rather tight connections between skull and disc and flexible ones between disc and condyle.
Development of the rat meninx: Exerimental study using bromodeoxyuridine
Authors: Kamiryo Toshifumi , Orita Tetsuji , Nishizaki Takafumi , Aoki Hideo
Published: February 2005

The development of the rat meninx from the viewpoint of cell proliferation was studied microscopically and immunohistochemically using bromodeoxyuridine (BUdR). A compact cell layer around the neural tube, the meninx primitiva, was observed in 12‐ and 13‐day fetuses. A reticular structure resembling the subarachnoid space appeared in the 14‐day fetus. The ectomeninx, consisting of a collagen fiber layer, part of which became the dura mater, appeared in 15‐day fetuses, allowing discrimination of the endomeninx, the arachnoid cell layer. The primordium of the choroid plexus also appeared in the lateral ventricle on the same day. Bone appeared in the primitive dura mater, and stratification of the meninx was almost complete in 21‐day fetuses. BudR‐positive cells were confirmed in the meninx from day 12 of gestation to day 15 postpartum. The number of BudR‐positive cells was greatest in fetuses aged about 12 or 13 days, reaching nearly 50%, but decreased gradually toward the neonatal period. The findings of this study suggest that, after the migration of neural crest cells, marked cell proliferation in the meninx begins. Differentiation into various layers then follows and is almost complete before birth, whereas the proliferation of arachnoid cells continues even in the early neonatal period.
Vascular invasion of the epithyseal growth plate: Analysis of metaphyseal capillary ultrastructure and growth dynamics
Authors: Hunter William L. , Arsenault A. Larry
Published: February 2005

Metaphyseal blood vessels which invade the calcifying epiphyseal growth plate were examined by a variety of techniques to determine their morphology, cell division, and growth patterns as they relate to endochondral ossification. Four regions of these vessels were characterized: 1) sprout tips—the terminal ends of the capillary sprouts which impinge upon the hypertrophic chondrocytes of the growth plate; 2) region of extended calcified cartilage—those deeper vessels within the metaphysis which are surrounded by an extracellular matrix predominantly composed of extended septa of calcified cartilage; 3) region of bone deposition—further still from the epiphysis these microvessels are contained within a network of active bone deposition laid upon a scaffold of calcified cartilage; 4) region of primary vessels—at a distance of 350–500 μm from the epiphysis are dilated vessels with one or two layers of smooth muscle in their walls, which supply and drain the metaphyseal capillary plexus. The sprout tips are continuous blind‐ended vessels lined with an attenuated endothelium with no underlying basement membrane. Dividing endothelial cells are most frequently found in the region of bone deposition 175–200 μm behind the apices of the growing sprout tips. A time‐coursed, autoradiographic examination of cytokinesis revealed radio‐labelled endothelial cells to appear at the epiphysis after a 24 hr period. The metaphyseal capillary sprouts represent a continuous, unidirectional angiogenic vascular network which grows by elongation from the region of bone deposition; this region remians a fixed distance behind the sprout tips. These findings are discussed in light of the growth dynamics between this vascular plexus and the epiphyseal growth plate.
Dynamics of neuroepithelial body (NEB) formation in developing hamster lung: Light microscopic autoradiography after 3H‐thymidine labeling in vivo
Authors: Hoyt Richard F. , McNelly Nancy A. , Sorokin Sergei P.
Published: February 2005

Autoradiographs were prepared from lungs of a newborn Syrian golden hamster exposed continuously to 3H‐thymidine for the final 4.5 days of a normal 16 day gestation. Silver grain were counted over nuclei of 1,298 smallgranule endocrine cells in 165 neuroepithelial bodies (NEBs) in the right upper lobe and along the left axial bronchus, where nodal NEBs occured at branch points and internodal NEBs in the airway between them. Nuclei of 1,005 nonendocrine airway epithelial cells were counted next to the NEBs. Label was distributed differently in the two populations: All nonendocrine cells were labeled, whereas many endocrine cells were not. In NEBs of the right upper lobe, total label (net grains/nuclear profile) averaged only 23% of that in nonendocrine cells. Along the left axial bronchus, mean label in nonendocrine cells and internodal NEBs rose 10‐fold between the hilum and the periphery. Increase for both populations were linear and parallel, but total label in the NEBs was consistently lower than that in the surrounding epithelium by 15 grains/nuclear profile. Nodal NEBs were more lightly labeled than those of the internodes, consistent with their earlier formation. A few very heavily labeled small‐granule cells (0.9%) occurred singly in the periphery of large, otherwise lightly labled NEBs. Statistically these belonged to the labeling distribution of nearby nonendocrine cells. In contrast to NEBs, neurons in 10 bronchial ganglia of the right lung were virtually unlabeled. These aris from vagal neural crest and seem to comprise an entirely distinct population. We conclude that NEBs belong intrinsically to pulmonary endoderm, not neural crest. During fetal life each develops from a cell or cells programmed to stop dividing well ahead of other elements in the epithelium. Their formation is linked closely to early proliferation of the bronchial tree and is an integral part of growth and differentiation of the airway lining. After a wave of initial formation has passed down the airway, small‐granule cells are added slowly to mature NEBs, probably through diffierentiation from adjoining airway epithelial cells—a potential mechanism for cell replacement in adult life.