bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mesenchyme formation from the trigeminal placodes of the mouse embryo
Authors: Nichols David H. 
Published: February 2005

AbstractThe trigeminal placode is a thickened region of ectodermal epithelium located along the side of the embryonic head. Mesenchyme escapes from the placode to form neurons of the trigeminal (V) ganglion. To further our knowledge of the morphogenesis of this escape, plastic thick sections were cut from mouse embryos and stained for light microscopy by using a technique which revealed escaping mesenchyme. The escape of trigeminal mesenchyme began at approximately 12 somites of age and was substantially complete by 30 somites. These results provided spatial/temporal orientation for a subsequent electron microscopic study. The first ultrastructural manifestation of escape was the penetration of an otherwise continuous basal lamina by small cell processes. The presence of longitudinally oriented microtubules within these processes suggests that mesenchymal cells escape through the basal lamina by using microtubules to direct/move their contents (e.g., the cell nucleus) into an enlarging process. Nuclei were distorted as they passed into these processes. This distortion suggests that basal lamina, together with a possible contribution from basal microfilaments, forms a rigid obstruction which is disrupted in the region from which a process is formed. In some cases a collar of basal lamina was observed around the necks of processes, but their distal membranes were invariably lamina‐free. This lamina‐free membrane is possibly that which is newly formed to accommodate the growing process. In later stages of escape, instances were observed in which the lamina was completely absent beneath an escaping cell and partially degraded beneath adjacent cells as well. These instances suggest that enzymatic digestion may play a role in degrading the lamina during mesenchymal escape. Apical desmosomes were often retained beyond the initial stages of escape. Mechanisms involved in their disruption are thus not among those which initiate escape.
Processing of concanavalin A‐receptor complexes by rat osteoclasts in vitro
Authors: Popoff Steven N. , Schneider Gary B. 
Published: February 2005

AbstractThe osteoclast is a large multinucleate cell that is widely accepted as the primary effector cell responsible for normal bone resorption. In a previous study, we demonstrated that concanavalin A (con A) has a dose‐dependent biphasic effect on the bone‐resorbing capacity of osteoclasts, using a 45Ca bone‐organ culture system; bone resorption was stimulated at low concentrations and inhibited at high concentrations. The mitogenic property of con A in lymphocyte cultures is well documented; therefore con A has been used extensively to study the manner in which lymphocytes and other mononuclear cells process the cell‐bound lectin. In this study, we have investigated the processing of con A‐receptor complexes by osteoclasts in culture, using con A—FITC to evaluate the redistribution of cell‐bound con A via epifluorescence microscopy and using con A—ferritin to determine whether the lectin receptor complexes are internalized. The osteoclasts were obtained from the long bones of newborn rats and allowed to attach to glass coverslips at 37°C. Following attachment, the nonadherent cells were removed by rinsing. The adherent osteoclasts were preincubated in 50 μg/ml con A–FITC or con A–ferritin at 4°C for 10 min, washed to remove unbound con A, and incubated at 37°C for 15 or 30 min in the absence of con A. Positive controls were fixed immediately after preincubation at 4°C; negative controls were preincubated in con A–FITC and α‐methyl mannoside, the haptenic inhibitor of con A binding. The results demonstrate that redistribution and endocytosis of con A–receptor complexes occurs within 30 min. These findings confirm the hypothesis that cell‐bound con A can alter the structure and activity of osteoclast membrane components in a manner similar to that observed in mononuclear cell cultures. The internalization of con A may be important in altering osteoclastic activity by mediating intracellular mechanisms involved in the bone‐resorbing process.
An ultrastructural comparison of neuromuscular junctions in normal and developmentally arrested Rana pipiens larvae: Limited maturation in the absence of metamorphosis
Authors: Lynch Kathryn , Homer Mary J. , Harris C. Darryl , Morrissey James 
Published: February 2005

AbstractNeuromuscular junctions in the rectus abdominis muscles of normal and developmentally arrested Rana pipiens larvae were studied with freeze fracture and conventional electron microscopy to determine whether structural aspects of junctional maturation depend on metamorphosis. Comparison was made between junctions in premetamorphic larvae 1–3 months old and junctions in larvae that had remained in premetamorphosis for more than a year (more than four times as long as normal). In most respects, junctions from the two groups of larvae were similar. Unlike adult junctions, nerve‐muscle contacts in both larval groups were pleomorphic and often involved more than one neuronal process; Schwann cell processes very rarely extended between nerve and muscle. Active zone structure ranged from total disorganization to an adult pattern of highly ordered double rows of particles aligned over junctional folds. Only quantitative analysis revealed differences between junctions in old and young larvae. The older larvae had fewer nerve‐muscle contact sites involving multiple neuronal elements and a higher ratio of active zone length to presynaptic membrane area, although the mean active zone length was the same in the two groups. The results indicate that the maturation of junctional shape, the branching pattern of the axons, and the relationship of presynaptic axons to Schwann cells must be directly or indirectly dependent on the hormonal or behavioral changes associated with metamorphosis.
The microfibrils of connective tissue: I. Ultrastructure
Authors: Inoué S. , Leblond C. P. 
Published: February 2005

AbstractThe ultrastructure of connective tissue microfibrils was examined in two sites: the ciliary zonule of the eye and the foot pad, in 20‐day‐old mice perfused with glutaraldehyde. The microfibrils were classified into two categories, referred to as typical and atypical.Typical microfibrils predominate in both sites; they are unbranched, straight or gently curving, tubular structures of indefinite length with an overall diameter of 12.8 ± 1.7 nm in the zonule and 13.8 ± 2.8 nm in the foot pad. They are composed of two parts: tubule proper and surface band. The tubule is 7‐ to 10‐nm wide and characterized in cross section by an approximately pentagonal wall and an electron‐lucent lumen containing a 1‐ to 2‐nm bead referred to as a spherule. When longitudinal sections of microfibrils are examined at high magnification, the wall of the tubule does not appear as a continuous line but as a series of successive dots. The interpretation of these findings is that the tubule is composed of successive annular segments with an approximately pentagonal outline. The surface band is a 3‐nm‐wide, ribbon‐like structure wrapped around the tubule. The band has dense borders called tracks. Along the tracks, densely stained, 4.6‐nm‐long “spikes” are attached at 4.0‐nm intervals. The wrapping of the bands is somewhat irregular. They may be in a transverse position across single or several microfibrils, in which case each band might constitute a distinct belt; more frequently, the bands are oblique and appear to form a continuous helix. It is proposed that surface bands play a role in holding together the juxtaposed segments making up a tubule. A model has been constructed to represent the association of tubule and band into a typical microfibril.Atypical microfibrils, which are more common in foot pad than in ciliary zonule, appear wavy, lack a definite tubule, and are characterized by distorted, irregular surface bands. They are attributed to proteolysis of typical microfibrils.
Cell surface of mouse blastocysts at the trophectoderm‐uterine interface during the adhesive stage of implantation
Authors: Chávez Daniel J. 
Published: February 2005

AbstractThe molecular basis for the acquisition of adhesiveness between blastocysts and uterine luminal epithelium is an interesting problem in reproductive biology. It is rather difficult to study implantation‐stage blastocysts of mice because during the implantation period each blastocyst becomes lodged within a crypt formed by decidualizing stroma. After trophectoderm adheres to uterine luminal epithelium, it is not possible to flush intact blastocysts from the uterus by standard recovery procedures. By identifying implantation sites with the Evans blue technique and splitting or gently separating the apposed epithelium of finely trimmed sites, it was possible to expose nonadhesive and adhesive trophectoderm to polycationized ferritin (PCF) and a series of ferritin‐conjugated lectins. Examination by transmission electron microscopy revealed that both adhesive and nonadhesive trophectoderm bound PCF, concanavalin A, wheat‐germ agglutinin, Ricinus communis agglutinin I, and Limulus polyhemus agglutinin, but not Dolicos biflorus agglutinin or peanut agglutinin. Nonadhesive trophectoderm bound succinylated wheat germ agglutinin but adhesive trophectoderm did not. There was no apparent difference in the relative amounts of each lectin bound to adhering and nonadhering cells.
The clustering of acetylcholine receptors and formation of neuromuscular junctions in regenerating mammalian muscle grafts
Authors: Womble Mark D. , Carlson B. M. 
Published: February 2005

AbstractThe present investigation was undertaken to study the relationship between acetylcholine receptor (AchR) clustering and endplate formation within regenerating skeletal muscle grafts. Silver staining of nerves was combined with rhodamine‐alpha‐bungarotoxin labeling of AchR clusters in heterotopic grafts of the rat soleus muscle. Two major graft procedures were used: whole muscle grafts and grafts which lacked the zone of original motor endplates (MEP‐less grafts). These categories were subdivided into standard grafts, where subsequent innervation was allowed, and noninnervated grafts, which were experimentally deprived of innervation. Grafting brought about the death and removal of muscle fibers, followed by regeneration of myotubes within surviving basal lamina sheaths. A transient population of small extra‐junctinal AchR clusters spontaneously appears shortly after myotube formation in all four muscle graft types. Early myotubes of whole muscle grafts (both innervated and standard grafts, prior to the time of innervation) also develop presumptive secondary synaptic clefts and large, organized aggregations of AchRs at original synaptic sites. At later times, nerves regenerating into standard whole muscle and MEP‐less grafts lead to the formation of numerous ectopic endplates. In whole muscle grafts, endplates may also form at original synaptic sites. Functional graft innervation is achieved in whole muscle and MEP‐less grafts as early as 20 days postgrafting. The results of this study support the existence of still‐unknown factors associated with the original synaptic site which can direct postsynaptic differentiation independent of innervation. They also demonstrate that functional endplates may form in mammalian muscle grafts at both original synaptic sites and ectopic locations, thus indicating that the zone of original synaptic sites is not necessary for the establishment of numerous functional and morphologically well‐differentiated endplates.
Formation and distribution of neural crest mesenchyme to the first pharyngeal arch region of the mouse embryo
Authors: Nichols David H. 
Published: February 2005

AbstractMurine neural crest mesenchyme begins its escape from columnar epithelium near the tips of the midbrain‐rostral hindbrain neural folds at 4+ to 5 somites of age. At that time the tip of each fold is located dorsolateral to the pharynx. Once crest formation is complete at this earliest site, it leaves behind both crest mesenchyme and overlying squamous epithelium. Crest formation then progresses medially, into the lateral margin of the neural plate. At the same time, this lateral margin elevates as the tip of the neural fold. By the time crest formation ceases at approximately 10 somites, the result of these simultaneous activities is to passively distribute the earliest mesenchyme, formed from the lateralmost epithelium, dorsolateral to the pharynx and the later, more medially derived mesenchyme lateral to the neural tube. Once formed, the crest mesenchyme dorsolateral to the pharynx is displaced ventromedially in a narrow, transient subectodermal space functionally similar to that observed in the chick embryo. Displacement might result from cell motility or the formation of matrix‐filled spaces between cells of the mesenchyme. Displaced cells are closely associated with the overlying columnar epithelium. This association precedes their subsequent induction and may reflect preliminary patterning. The crest mesenchyme passively distributed lateral to the neural tube is subsequently displaced medially. Here the formation of enlarged (matrix‐filled?) spaces is clearly involved in the initial displacement. Displaced cells proliferate to form the anlage of the trigeminal ganglion. The other major contributor to this ganglion is the trigeminal placode. The placodal epithelium is located dorsolateral to the pharynx of the 12‐somite embryo. If the epithelia of the head maintain their relative positions, this placode is derived from the squamous epithelium formed together with the earliest crest mesenchyme. If not, an alternative source is the columnar epithelium located ventromedial to the tip of the 4 + ‐ to 5‐ somite neural fold.
Different pharmacological anatomy in the paraventricular hypothalamic nucleus, supraoptic nucleus, and suprachiasmatic nucleus of rats: Quantitative autoradiography on angiotensin II receptor binding sites
Authors: Hwang Bang H. , Wu Jang‐Yen , Wieczorek Caroline M. , Harding Joseph W. , Erickson Joel B. , Wamsley James K. 
Published: February 2005

AbstractAngiotensin II (AII) and vasopressin (VP) play important roles in cardiovascular function. Using 125I‐[Sar1, Ile8]‐angiotensin II (125I‐SI‐AII), a potent AII antagonist, AII receptor binding sites were autoradiographically localized in three VP‐producing areas of the hypothalamus and compared in hypertensive and normotensive rats. Within three major VP‐producing areas, AII receptor binding was highest in the paraventricular hypothalamic nucleus and lowest in the supraoptic nucleus, suggesting that a differential AII regulation of separate VP systems exists in the brainstem. No statistical difference in 125I‐SI‐AII receptor binding was found between WKY and SHR rats in each of the three major VP‐producing nuclei studied. These results are consistent with a role of AII receptors in a subtle and complicated regulation of VP in cardiovascular function.
Demonstration of differential immunohistochemical localization of the neuron‐specific enolase antigen in rat pinealocytes
Authors: McClure Chalmer D. , McMillan Paul J. , Miranda C. Alfonso 
Published: February 2005

AbstractA refined method for the immunohistological demonstration of neuron‐specific enolase (NSE) on 1‐ to 2‐μm Epon‐812 section gave characteristic staining of cerebral and cerebellar neurons. This method has made it possible to obtain a more detailed characterization of the heterogeneity of rat pinealocytes in the superficial portion of the rat pineal complex. Thirty adult male rats have been studied, five of which were used in a photometric analysis of the distribution of NSE. Pinealocytes stained either intensely or weakly for the NSE antigen and exhibited an uneven distribution within a given region. Further analysis of the gland revealed a distal to proximal decrease in stain intensity. It is suggested that the more strongly stained cells, being concentrated distally, are under sympathetic control.
Ultrastructure of the submandibular gland in the rabbit
Authors: Toyoshima Kuniaki , Tandler Bernard 
Published: February 2005

AbstractThe secretory endpieces of the rabbit submandibular gland are unusual in that they consist of seromucous acini (not demilunes) that empty into serous tubules that in turn drain into intercalated ducts. Seromucous granules consist of a moderately dense spherule in a fibrillogranular matrix. Serous granules contain a feltwork of filaments, which are liberated as a tangled skein during exocytosis. Peculiar granulated cells that have secretory granules of complex morphology are present at each end of the serous tubules. Intercalated ducts are, cytologically speaking, relatively simple, but the duct cells may contain a few oblong secretory granules. Striated ducts are typical in structure, although postfixation with ferrocyanide‐reduced osmium reveals significant amounts of glycogen in the basal processes. Modified mitochondria are present in striated duct cells, but their frequency varies from rabbit to rabbit. Such mitochondria contain either an array of parallel, rigid cristae linked by intermembranous bridges, or a bundle of helical filaments within an expanded crista. Interspersed with the striated duct cells, especially near the duct origin, are some highly vacuolated cells with sparse mitochondria. Excretory ducts consisting of stratified columnar (sometimes pseudostratified) epithelium often show bleb formation of the luminal surface of the tall cells.
The renal cortical lymphatic system in the rat, hamster, and rabbit
Authors: Niiro George K. , Jarosz Harriet M. , O'Morchoe Patricia J. , O'Morchoe Charles C. C. 
Published: February 2005

AbstractRat, hamster, and rabbit renal cortical lymphatics were examined by light and electron microscopy. Rat and hamster kidneys possessed both intra‐ and interlobular lymphatics that were structurally similar at the light microscopic level. Ultrastructural examination of the hamster lymphatic endothelium, however, revealed an unusual arrangement of cytoplasmic extensions not seen in the other two species. The intralobular lymphatics were related primarily to tubules, afferent arterioles, and renal corpuscles and were consistent with lymph formation from both plasma filtrate and tubular reabsorbate. Interlobular lymphatics were seen in connective tissue associated with the interlobular blood vessels. Rabbit cortex contained only interlobular lymphatics. Cross‐sectional area, maximum diameter, volume density, and profile density were determined by stereological measurements using a computer‐based image analyzer. The morphological data from the rat were used, in combination with published values for lymph flow, to calculate the rate of lymph formation per unit area of endothelium in lymphatics of the renal cortex. Among kidneys fixed by retrograde perfusion, the cortical lymphatic system was most extensive in maximum diameter, volume density, and profile density. It was smallest in the rabbit and intermediate in the rat. Lower volume and profile density were found for rat kidneys fixed by the dripping technique. It was concluded that: (1) tubular reabsorbate probably contributes to renal lymph in the rat and hamster, but not in the rabbit; (2) significant differences exist in the extent of the renal lymphatic systems among the three species, with the hamster kidney having the richest network and the rabbit the poorest; (3) the method of fixation influences the measured size and density of renal cortical lymphatics; and (4) the estimated rate of lymph formation in the kidney of the rat is roughly comparable to that in the dog.
In vivo exocytosis of lysosomes by the endothelium of the venous sinuses of bone marrow and liver: Visualization at normal and low body temperature
Authors: De Bruyn Peter P. H. , Cho Yongock 
Published: February 2005

AbstractWe have visualized the exocytosis of lysosomes into the peripheral circulation by the phagocytic endothelia of the venous sinuses of liver and bone marrow of rats. Perfusion fixation at normal body temperature produced images of the earliest stages of lysosomal exocytosis. After fixation at low body temperatures (7–12°C), advanced stages of this process became evident, showing extrusion of lysosomes and their contents into the circulation. It is postulated that this form of exocytosis has escaped structural detection because of its rapidity and relative infrequency as compared to merocrine secretory exocytosis, and that fixation at low body temperatures arrests or slows down these exocytic events in sufficient measure for ultrastructural visualization. The possibility that this lysosomal exocytosis contributes to the presence of lysosomal enzymes detected in the peripheral blood should be considered. In addition, it is likely that lysosomal degradation products may be discharged by exocytosis into the circulation.
Scanning electron microscopy of isolated epithelium of the murine gastrointestinal tract: Morphology of the basal surface and evidence for paracrinelike cells
Authors: Magney J. E. , Erlandsen S. L. , Bjerknes Matthew L. , Cheng Hazel 
Published: February 2005

AbstractBy using the method of Bjerknes and Cheng, isolated murine gastrointestinal epithelial sheets were prepared for scanning electron microscopy. Examination of isolated epithelium from fundic stomach revealed numerous branched gastric glands. Parietal cells were easily detected bulging from the basal surface of the glandular epithelium. The basal surface membrane of parietal cells appeared smooth, with only sparse microvilluslike projections, whereas adjacent glandular cells had numerous 1‐ to 2‐μm fingerlike projections which interdigitated laterally with similar processes from adjacent cells. Occasionally, paracrinelike cells having long cytoplasmic processes ranging from 10 to 20 μm in length were observed on the basal epithelial surface of the stomach and the colon, but not the small intestine. In isolated intestinal epithelia, the basal surface of crypt epithelial cells showed extensive cytoplasmic interdigitations, but no distinct morphology permitting recognition of individual cell types. Various stages of intestinal crypt bifurcation were seen. Craterlike spaces in the basal surface of crypt epithelium, presumably due to migrating leukocytes, were also numerous. Examination of the luminal surface of the isolated intestinal epithelium revealed that intimate associations between epithelium and mucosal‐associated microorganisms were maintained, thus suggesting that minimal alterations in surface morphology were incurred by epithelial isolation. These observations on epithelial structure suggest that isolated gastrointestinal epithelia may be well suited for physiological studies of epithelial function and interactions with the microbial flora.