bluuebunny/crossref_metadata_2025 huggingface dataset:
A method for sampling the stages of amelogenesis on mandibular rat incisors using the molars as a reference for dissection
Authors: Smith C. E. , Nanci A.
Published: February 2005

A method for locating specific stages of amelogenesis on continuously erupting incisors was devised for rats weighing 101 ± 5 g (n = 32). The technique is based on reflecting reference lines from the mandibular molars as perpendiculars to the labial surface of mandibular incisors. From these reference lines additional measurements are then made along the midline of the labial surface of the incisor in an apical or incisal direction of find the site desired for sampling. Histological studies on 24 decalcified incisors split into segments by using such reference lines and reconstructed by morphometry indicated that a reference line reflected from the contact point between the 2nd and 3rd molars crossed the enamel organ and adjacent enamel at 3,181 ± 329 μm incisal to the start of the secretory zone of amelogenesis. A reference line from the 2nd and 1st molars crossed the enamel organ and enamel at 1,238 ± 424 μm incisal to the start of the maturation zone of amelogenesis, while a reference line from the mesial side of the 1st molar crossed the enamel organ and enamel almost exactly where the enamel becomes completely soluble following prolonged decalcification in EDTA. Although reference lines were reproducible within a group of male rats having similar body weights, the linear distance between the apical end of the incisor and the point at which they crossed the tooth increased at a rate of 1 mm per 159 g for rats between 50 and 300 g body weight. This suggests that molars do not maintain a fixed relationship to incisors over time, and extreme care must be taken to standardize an experiment to a specific body weight when using this method.
Anatomic distribution of autonomic neural tissue in the developing dog heart: I. Sympathetic innervation
Authors: Ursell Philip C. , Ren Chao Ling , Danilo Peter
Published: February 2005

We used immunocytochemical localization of tyrosine hydroxylase to trace the ontogenesis and anatomic distribution of sympathetic innervation in fetal, neonatal, and mature canine hearts. Sparse tyrosine hydroxylase‐positive neural tissue first appeared in the atrium, including sinoatrial and atrioventricular nodes, and the ventricular epicardium at midgestation and progressively increased in extent to reach the adult pattern by 2 months following birth. Sympathetic innervation of the atrioventricular bundle occurred relatively later, with no nerve processes in the neonate but a mature pattern by 2 months. At each developmental stage the atria contained more tyrosine hydroxylase‐positive neural tissue than the ventricles. Thus, sympathetic nerve processes appear in the developing canine heart earlier than was previously recognized. The time course of sympathetic innervation as defined by this anatomic study is in accord with electrophysiologic studies indicating progressive neonatal development of sympathetic effect which achieves maturity by 2 months of age.
Absence of an osseous patella and other observations in Macropodidae stifle
Authors: Holladay Steven D. , Smith Bonnie J. , Smallwood James E. , Hudson Lola C.
Published: February 2005

The patella is a large sesamoid bone that typically develops in the tendon of insertion of the large extensor muscles of the stifle joint. Although present in almost all species of mammals and birds, it has been found to be absent in the red kangaroo and two wallaby species (family Macropodidae). In its place is a fibrocartilage pad, located in the tendon of the quadriceps femoris muscle. This structure is visible grossly, is palpable, and has the form normally expected of a bony patella. In addition, the femoral trochlea is shallow and asymmetric, and the lateral gastrocnemius sesamoid is unusually prominent. These and other related modifications in the area of the Macropodidae stifle are presented.
Visualization of sulfur‐containing components associated with proliferating chondrocytes from rat epiphyseal growth plate cartilage: Possible proteoglycan and collagen co‐migration
Authors: Landis William J. , Hodgens Karen J.
Published: February 2005

Electron microscopy of epiphyseal growth plate cartilage from normal 4‐5‐week‐old rats has revealed extensive fibrillar aggregates and globules in the pericellular spaces of proliferating chondrocytes. These cells contained small globules and diffusely coiled, fine filaments located within large, membrane‐invested vacuoles. All such structures were observed after a variety of different tissue fixation regimes, including glutaraldehyde, osmium tetroxide, and potassium pyroantimonate. The fibrillar aggregates and globules were often overlapping and intermeshed and extended to 0.5 m̈m in length from their point of origin at cell membranes. Vacuoles were usually found at the periphery of cells, and some, by membrane fusion with the cell envelope, appeared contiguous with extracellular spaces wherein their contents could be discharged. Fine filaments and globules were occasionally observed in the Golgi complex and cisternae of endoplasmic reticulum of the chondrocytes. Further characterization of the cellular and pericellular components by electron microscopic radioautography, electron probe microanalysis, and electron spectroscopic imaging indicated the presence of sulfur, a result suggesting these aggregates, filaments, and globules in part represent proteoglycans in various stages of synthesis, secretion, and assembly. Additional radioautography utilizing 3H‐proline implied that filament bundles are also composed of collagen, a result posing the possibility that this protein and the putative proteoglycans may co‐migrate both intracellularly and within pericellular matrices. In extracellular matrices adjacent to cell lacunae, the fibrillar aggregates appeared in close association with typical collagen type II fibrils, an observation providing evidence for proteoglycan‐collagen network formation in this region of the rat epiphysis. These microscopic and analytical data in situ would support certain studies in vitro of proteoglycan‐collagen type II and IX association and are important in describing the interaction of such cartilage components ultimately involved in matrix formation.
Variation in histochemical enzyme profile and diameter along human masseter intrafusal muscle fibers
Authors: Eriksson Per‐Olof , Thornell Lars‐Eric
Published: February 2005

The histochemical enzyme profile of human masseter intrafusal muscle fibers was analyzed in consecutive serial cross sections along the individual fibers. Two hundred intrafusal fibers in 21 muscle spindles were classified.

On the basis of equatorial nucleation, myosin ATPase‐staining reactions after alkaline and acid preincubations and diameter, four different populations or types of intrafusal fiber were identified: large‐diameter alkaline‐stable and acid‐stable fibers, bag2; two types of fiber with intermediate‐diameter, alkaline‐labile and acid‐labile fibers corresponding to bag1 and alkaline‐labile and acid‐stable fibers designated as AS‐bag1; and small‐diameter alkaline‐stable and acid‐stable (pH 4.6)‐acid‐labile (pH 4.3) fibers called chain fibers. Regional variability in staining and diameter along the individual fibers was noted. In general, intrafusal fibers showed stronger oxidative reactions than did extrafusal fibers.

The enzyme profile of the human masseter intrafusal fibers differed from that of extrafusal fibers in jaw, limb, and trunk muscles and also from that reported for spindles in limb and trunk muscles in man. The result suggests unique properties of human jaw muscle spindles and the jaw motor system.
Isomyosin expression pattern during formation of the tubular chicken heart: A three‐dimensional immunohistochemical analysis
Authors: De Jong F. , Geerts W. J. C. , Lamers W. H. , Los J. A. , Moorman A. F. M.
Published: February 2005

Three‐dimensional (3‐D) distribution of atrial and ventricular isomyosins is analysed immunohistochemically during the formation of the tubular chicken heart (stage 7 to 12 [H/H]) using antibodies specific for adult chicken atrial and ventricular myosin heavy chains, respectively. This analysis revealed that both types of isomyosins can be first detected at stage 8 (H/H, possessing four pairs of somites), i.e., when the heart primordium still exists as two separate cardiogenic plates. The ventricular type of isomyosin is initially expressed in those areas of cardiogenic plates in the vicinity of the anterior intestinal portal. The atrial type of isomyosin is initially expressed in zones caudal and lateral to the areas of ventricular isomyosin expression. Medial to the atrial isomyosin‐expressing areas, cardiogenic plate areas exist that initially lack myosin expression. Those parts of the cardiogenic plates that fuse in front of the anterior intestinal portal, thereby forming the heart tube, are characterized by the expression of both isomyosins; however, the caudolateral parts of the heart primordium maintain their single atrial isomyosin expression during further development. Cardiac contractions are therefore first observed at stage 10 (H/H, possessing ten pairs of somites) in myocardium that coexpresses both isomyosins.
Effect of occlusal functional forces on incisor socket morphology and location in the rat mandible
Authors: Brin Ilana , Steigman Shulamit , Michaeli Yael
Published: February 2005

The effect of functional occlusal stress on dimensional alterations of the rat incisor socket and mandible were studied from roentgenograms. In 12 rats, the lower left incisor was shortened twice weekly, whereas the lower right incisor was allowed to remain in contact with both upper incisors. Thus, the right incisors were subjected to hyperfunction, and the left ones, to hypofunction. The lower incisors of 16 rats with normal occlusal contact served as control. Following an experimental period of 3 months, the animals were killed and standardized radiographs were taken of the cleaned mandibles. Socket and mandibular dimensions were measured on magnified tracings of the roentgenograms. Socket area, its posterior length, posterior mandibular length, and gonial angle changed in the same direction under both hyper‐ and hypofunction. The anterior socket was relocated in opposite directions: under hyperfunction, it assumed a more inferior position, whereas in hypofunction, it moved superiorly. The angulation of the socket became significantly more acute under hyperfunction, whereas in hypofunction, this parameter remained unchanged. It is concluded that altered functional demands affect the morphology of the incisor socket and its location within the mandibular borders.
Skeletal structural adaptations to mechanical usage (SATMU): 1. Redefining Wolff's Law: The bone modeling problem
Authors: Frost H. M.
Published: February 2005

From the nature of a bone's endload and its local surface strains, the theory computes a modeling operator, Gamma (Γ), that predicts whether mechanical factors will cause lamellar bone modeling drifts, and where and of what kind. A given mechanical bone strain history then provides a separate modeling rate function, \documentclass{article}\pagestyle{empty}\begin{document}$ \dot M $\end{document}, to specify the rate of such modeling drifts as fractions of the largest possible ones. Multiplying the two functions, e.g., Γ · \documentclass{article}\pagestyle{empty}\begin{document}$ \dot M $\end{document}, then predicts mechanically controlled bone modeling responses for cortical and trabecular bone, both quantitatively and qualitatively. The theory correctly predicts each of the 6 known “principal adaptations” of lamellar bone, which provide a critical test of any such theory for this organ.

The theory accounts for biologic, biomechanical, and clinical‐pathologic knowledge not available in Wolff's time nor accounted for by most biomechanicians since. Existing proven methods can provide all numerical data needed to satisfy the theory's mathematical equations and already suggest provisional values for most of them. Its originator views the theory as the kernel of more and better theories to come rather than a finished work, a kernel that suggests a new and in some respects novel logical framework for analysing the problems, and a kernel that invites critique, refinement, and/or exploitation by others.
Absence of cartilage canals in the long bone extremities of four species of skeletally immature marsupials
Authors: Thorp B. H.
Published: February 2005

The cartilaginous epiphyses and physes from the bone extremities of four species of skeletally immature marsupials were studied. The microscopic and ultrastructural features of the marsupial tissues were compared with similar samples from a neonatal lamb and a 1‐day‐old chick. Chondrocyte differentiation and endochondral ossification appeared similar in physes from the marsupials, foetal lamb, and 1‐day‐old chick. However, unlike the lamb and chick, which both contained cartilage canals, there were no cartilage canals in the epiphyseal or physeal cartilage from the marsupials. Many of the epiphyseal chondrocytes from the marsupial specimens contained large lipid droplets. It is suggested that the lipids in marsupial chondrocytes may be utilized in metabolic pathways. Despite hypertrophy of chondrocytes, there were no epiphyseal ossification centers in the femoral heads of the marsupial specimens; this was possibly due to the absence of cartilage canals, which are considered a source of osteoproginator cells. This study indicates that physeal and epiphyseal cartilage in marsupials is viable and functions in an avascular environment; this may be due to unique metabolic properties of the chondrocytes.
Ultrastructural localization of acetylcholinesterase in the guinea pig pineal gland
Authors: Luo Zhongrong , Schultz Robert L. , Whitter Ernest F.
Published: February 2005

The ultrastructural localization of acetylcholinesterase (AChE) activity in guinea pig pineal gland was studied using the copper‐glycine procedure. A small number of pinealocytes and bundles of unmyelinated nerve fibers were labeled by the AChE reaction. The AChE‐positive pinealocytes were located near blood vessels and distributed in small groups. The AChE reaction product was localized in the perinuclear cistern, in the cisternae of the endoplasmic reticulum (ER), and in the saccules of the Golgi apparatus. These findings suggest that the AChE‐positive pinealocytes synthesize AChE. The AChE reaction product was also seen in the intercellular space between pinealocyte processes. Besides pinealocytes, AChE activity was localized on the axolemma of myelinated and unmyelinated nerve fibers and in the basement membrane surrounding unmyelinated nerve fibers. Pseudocholinesterase activity was confined to Schwann cells, which showed the reaction product in their perinuclear cistern, in the cisternae of the ER, and on the plasmalemma.
Early testicular changes after vasectomy and vasovasostomy in Lewis rats
Authors: Flickinger Charles J. , Herr John C. , Howards Stuart S. , Sisak John R. , Gleavy Janice M. , Fusia Tod J. , Vailes Lisa D. , Handley Harold H.
Published: February 2005

The testes of Lewis rats were studied at intervals from 2 weeks to 3 months after bilateral vasectomy, vasectomy followed 1 month later by vasovasostomy, or sham operations. Aims were to determine the nature of early alterations after vasectomy, and to determine whether vasovasostomy after 1 month would result in reversal of vasectomy‐induced changes. Approximately one‐fourth of the testes in the vasectomy and vasovasostomy groups displayed histological changes, which consisted mainly of depletion of germ cells. The extent of the depletion varied greatly in different seminiferous tubules. In tests altered in this way, no abnormal infiltrations of lymphocytes, macrophages, or other cells were observed in the seminiferous epithelium or in the interstitium. The rete testis and straight tubules were normal in testes with altered seminiferous epithelium. A few testes in the vasectomy and vasovasostomy groups had necrotic centers. The results suggest that depletion of germ cells occurred as a result of shedding from the seminiferous epithelium into the lumen of the tubules. A cellular immune response, such as occurs in experimental allergic orchitis in other species, did not appear to be responsible for the observed loss of germ cells. This suggests a possible role for humoral antibody in this model, since there is an association between testicular changes and serum antisperm antibodies at longer intervals after vasectomy. Testicular alterations were not reversed by performance of a vasovasostomy 1 month after vasectomy.
Cellular gene expression for calbidin‐D28k in mouse kidney
Authors: Rhoten William B. , Christakos Sylvia
Published: February 2005

Gene expression for calbindin‐D28k, the 28,000 relative molecular mass vitamin D‐dependent calcium‐binding protein, was measured in cells of the murine nephron by in situ hybridization on tissue sections (hybridization cytochemistry). Radiolabeled (35S‐UTP), single‐stranded RNA complementary to calbinding‐D28k‐mRNA (probe RNA) was prepared from linearized cDNA template and used for the hybridizations. Autoradiography was carried out and cellular levels of hybridization signal (silver grains) were quantified. After corretion for background the concentration of silver grains was more than 350% greater in the distal tubule than in either the proximal tubule or the glomerulus. The relative cellular level of mRNA in the cytoplasm, as reflected in silver grains/cell, of the distal tubules with probe RNA was 3.4 times greater than that with control RNA. Cells of the distal tubule were the only apparent sites of specific hybridization with probe RNA. The presence of calbindin‐D28k‐mRNA in the distal tubule corresponded to the localizations of calbindin‐D28k by immunocytochemistry.
Anatomy of the pancreas and langerhans islets in snakes and lizards
Authors: Moscona A. A.
Published: February 2005

The pancreas of snakes (18 species) was comparatively examined and classified into five major types, based on structure of the lobes and ducts, spatial relationships with the spleen and the gall bladder, and the disposition of islet cells. These types trend toward fusion of the pancreatic lobes and compaction of the pancreas—a progression that coincides with the phylogeny of the snakes. The more primitive pancreas of lizards (17 species) also was surveyed; that of Varanus is of special interest because its structure is intermediate between the extended, tri‐lobate pancreas of lizards and the compact pancreas of snakes and may represent a transitional link in the evolution of this organ. Islet tissue is always confined to the dorsal lobe and is concentrated in its distal region adjacent to the spleen. In primitive snakes and in Varanus, a large islet mass is sequestered within a distinct juxtasplenic “islet body” distanced from the dorsal lobe and connected to it by a slender stalk. In some of the most advanced snake species, numerous islets of endocrine cells are found within the spleen. The occurrence and formation of these intrasplenic islets is described in detail. The anatomic “affinity” between spleen and the islet region of the pancreas is discussed. A hypothesis for the development of the pancreas from embryonal placodes on the mid‐gut is presented; it proposes that the exocrine and the endocrine components derive from different progenitor cells, and that the endocrine progenitors are located in the center of the dorsal placode. The hypothesis combines embryological and evolutionary views about the origin of the pancreas, and offers a rationale for differences in its structure and in the disposition of the islets.
Endothelial cell division in metaphyseal capillaries during endochondral bone formation in rats
Authors: Hunter William L. , Arsenault A. Larry
Published: February 2005

Endothelial cell division in the metaphyseal capillaries of growing rats was studied by serial sectioning and electron microscopic examination. The endothelium of these capillary sprouts forms a continuous attenuated saqmous lining. During endochodral bone formation these growing vessels possess a region of endothelial cell division which is located behind the sprout tip in an area where the microvascular wall consists of an endothelium and a discontinuous layer of perivascular cells. Examination of this region has shown the presence of junctional attachments between daughter cells even before cell separation is complete. Thus, the integrity of the vascular wall is not compromised during cell division. Junctional complexes with adjacent endothelial cells are also formed along the cleavage plane prior to the completion of cytokinesis. Numerous microvilli from both the daughter cells and adjacent endothelial cells often make contact and form junctions with the plasma membrane of the dividing cells. A model for endothelial junction formation between daughter cells during cytokinesis and the role that microvilli play in the process is proposed.
Cortical alveolus breakdown in the eggs of the freshwater teleost Rhodeus ocellatus ocellatus
Authors: Ohta Tadayuki , Iwamatsu Takashi , Tanaka Masako , Yoshimoto Yasuaki
Published: February 2005

Cortical alveoli and their breakdown in the eggs of the rose bitterling were morphologically investigated. Cortical alveoli of various sizes existed in multiple layers within the cortical cytoplasm of each egg. Two types of cortical alveoli were recognized–one possessed homogeneous contents; the other possessed heterogeneous contents with electron‐less dense spots. The eggs were activated by a penetrating spermatozoon or by immersion in fresh water. The immersion of the eggs into fresh water induced a wave of cortical alveolus breakdown (CABD), which was propagated from the vegetal pole to the animal pole. When eggs were inseminated in fresh water, CABD progressed from both the vegetal and the animal poles of the egg, and was complete within about 20 min. The contents of the cortical alveoli were released into the perivitelline space through a large opening formed by the fusion of the plasma and cortical alveolar membranes. For a short time after CABD, the smooth inner surfaces of the cortical alveoli were readily discernible from the rougher original plasma membrane. About 30 min after immersion in fresh water, the inner surfaces of the cortical alveoli were indistinguishable from the original egg surfaces. Aequorin‐injected eggs became luminescent immediately after their immersion in fresh water. The luminescence reached a maximum level about 15 min later and subsided after roughly 30 min. The result shows that increase in intracellular free Ca ions occurs during CABD.
Pericyte of a teleost fish: Ultrastructure, position, and role in neoplasia as revealed by a fish model
Authors: Couch John A.
Published: February 2005

The morphology and position of the pericyte, a periendothelial cell, is described for a teleost fish, Cyprinodon variegatus. This cell was found attached to the abluminal surfaces of capillaries, venules, and arterioles of the submucosa of the midgut of the fish. The cell was encompassed by a thin basal lamina, possessed numerous plasmalemmal vesicles, a “sole region” which contained thinner actin‐like filaments and possibly thicker myosin‐like filaments, and ranged in form from ovoid to stellate, with long cytoplasmic extensions that partially covered the endothelium of the associated microvessel. The pericyte of C. variegatus has been shown to give rise to hemangiopericytomas (experimentally induced with diethylnitrosamine) and possibly to pericytomas. The range of phnotypic expression of these pericyte‐derived neoplasms is broad, and dependent upon the degree of differentiation of their constituent cells which range from clear cell pericytes to myofilamentous laden cells that resemble smooth muscle cells. In this regard and in regard to its normal ultrastructural morphology, and anatomical position, in relationship to microvasculature in this fish, the cell is very similar to other vertebrate pericytes. Limited evidence suggests that small fish species may be excellent study models for further elucidation of pericyte form, function, and role in disease.
Cholinesterase activity in terminal Schwann cells associated with Ruffini endings in the periodontal ligament of rat incisors
Authors: Maeda Takeyasu , Kannari Koichi , Sato Osamu , Kobayashi Shigeo , Iwanaga Toshihiko , Fujita Tsuneo
Published: February 2005

A nonspecific cholinesterase activity was demonstrated in terminal Schwann cells associated with Ruffini endings in the periodontal ligament of rat incisors at the light and electron microscopic levels. The terminal Schwann cells are ultrastructurally characterized by a well‐developed Golgi apparatus and rough endoplasmic reticulum. The cells in this study were positive for nonspecific cholinesterase, whereas ordinary Schwann cells associated with more proximal nerve fibers reacted negatively. The reaction products were densely deposited in the cisternae of the rough endoplasmic reticulum and along the nuclear envelop. A moderately intense labeling was found in the cytoplasmic extensions, in which the reaction products gathered in caveolae and vesicles. These findings indicate that nonspecific cholinesterase is a useful marker to distinguish terminal Schwann cells from ordinary Schwann cells and that the enzyme may be synthesized in the rough endoplasmic reticulum and conveyed toward the axon terminals. Since this enzyme has been known to be shared by the inner bulb of Pacinian corpuscles and the lamellar cells of Meissner's corpuscles, its possible involvement in mechanore‐ceptive functions in these specialized Schwann cells deserves further investigation.
High‐resolution localization of hyaluronic acid in the golden hamster oocyte‐cumulus complex by use of a hyaluronidase‐gold complex
Authors: Kan Frederick W. K.
Published: February 2005

The distribution of hyaluronic acid in the oocyte‐cumulus complexes collected from the oviduct ampulla of superovulated hamsters was revealed by use of hyaluronidase coupled to colloidal gold. On thin sections of Lowicryl‐embedded oocyte‐cumulus complexes, gold particles were associated specifically with interconnecting fibrillar materials that make up the cumulus matrix. Inside the cumulus cells, gold particles were found over the cisternal membrane of the rough endoplasmic reticulum, in the contents of lysosomes and multivesicular bodies, and over Golgi vesicles of some cumulus cells. A high concentration of gold labeling was observed over the peripheral condensed chromatin and perinucleolar components in the nucleus. The cell surface of the cumulus cells also appeared to be labeled. Gold particles, however, were absent over the mitochondria and lipid vacuoles. In the oocytes, labeling was found to be associated mainly with rough endoplasmic reticulum and arrays of lamellar structures; cortical granules, mitochondria, and coated vesicles were essentially devoid of gold particles. Gold particles were also seen along the plasma membrane of the oocytes and within the perivitelline space. The zona pellucida was not labeled by hyaluronidase‐gold. Different control experiments confirmed the specificity of the labeling. Digestion of thin sections with hyaluronidase prior to incubation with hyaluronidase‐gold abolished the initial reaction, whereas treatment of thin sections with chondroitinase did not prevent labeling of oocyte‐cumulus complexes by hyaluronidase‐gold. Although the function of hyaluronic acid in the oocyte‐cumulus complex at the time of ovulation and fertilization is not known, the high concentration of this particular compound in the cumulus matrix and the cumulus cells and its specific locations in the perivitelline space and in the superovulated oocytes implicate the significance of its presence and warrant future investigations.
Calcium in the developing Ambystoma neural axis shown by 3H and fluorescent chlortetracycline and atomic absorption spectrometry
Authors: Moran Denis J.
Published: February 2005

The calcium ion has been implicated in the mediation of the morphogenetic movements that occur during neural tube formation. The present study identifies high levels of calcium in the neuroepithelium of the neural plate, folds, and tube. These levels are substantially higher than those discerned elsewhere in the embryo. The calcium is localized in morphogenetically active regions by using the antibiotic chlortetracycline (CTC) which chelates calcium and is demonstrated in this investigation by both autoradiography and calcium‐linked fluorescence. The specificity of CTC reaction for calcium in the developing neural axis is confirmed by EGTA competition.

A comparison of the actual calcium levels in the developing neural axis (dorsal) with equivalently weighted ventral tissues was obtained by atomic absorption spectrometry (AAS). This method provides a total count of the calcium without any loss during tissue processing. For AAS, living tissues were precisely excised and immediately dessicated. Each tissue sample (dry weight 1.5 mg) was then solubilized for analysis. The spectrometric data reveal that the embryonic dorsal aspect forming the neural tube contains 57% more calcium than an equivalent weight of the ventral aspect.
Ectopic colonization of primordial germ cells in the chick embryo lacking the gonads
Authors: Nakamura Masao , Kuwana Takashi , Miyayama Yukihiko , Yoshinaga Kazuya , Fujimoto Toyoaki
Published: February 2005

Chick primordial germ cells (PGCs) first appear in the extraembryonic region in the early embryo, then temporarily circulate via the blood vascular system and finally migrate into the gonadal anlagen. In the present study, we examined the trend of ectopic distribution of PGCs in the chick embryo when its future gonadal region had been removed a t an early stage. Embryos at stage 10, from which the caudal third region was excised, were incubated until they reached stages 14 to 20. In embryos at stage 14, about 80% of the total PGCs were found in the capillaries of the yolk sac, whereas others were observed in the head, mainly in the mesenchyme and small vessels close to the neural tube. From stage 18 onward, many PGCs accumulated in the embryo proper; about 90% of them colonized in the head region around the neural tube. These ectopic PGCs in the head were found in the capillaries, sometimes as thrombi or emerging from them into the adjacent mesenchyme. These results show that, when the chick embryo lacked gonads, the PGCs could be concentrated in the head region and migrated from the capillaries into the mesenchyme.
Spatial disorder of collagens in the great vessels, associated with congenital heart defects
Authors: Rosenquist Thomas H. , Módis László
Published: February 2005

Surgical ablation of the cardiac neural crest from the chicken embryo results in persistent truncus arteriosus (PTA) and a change in the elastic laminae of the great vessels, wherein elastin and the elastin microfibril show significant spatial disorder. The purpose of this study was to test the hypothesis that the interstitial collagens would also be disordered in the elastic laminae of chicken embryos with PTA. The birefringence characteristics of interstitial collagen were examined to evaluate spatial ordering. The results showed that collagen in the elastic laminae assumed an orderly configuration of well‐defined fiber bundles in the great vessel walls of control embryos, whereas vessels from embryos with PTA lacked any distinct spatial order. Collagens type I and III were localized in the vessel walls. Type III collagen was the principal collagen of the elastic laminae, but was absent from the intima of all vessels. In the elastic laminae of vessels from control embryos, collagen type III showed well‐defined fiber bundles whereas embryos with PTA had diffuse collagen type III in poorly defined laminae that were not separated by discrete layers of smooth muscle cells. Collagen type I was a minor component of the elastic laminae but formed robust pericellular fiber bundles throughout the media and intima. Collagen type I fibers appeared to be coarsened and less uniform in the vessels from embryos with PTA.
Heterogeneity in granulosa cells of developing rat follicles
Authors: Rao I. M. , Mills T. M. , Anderson E. , Mahesh V. B.
Published: February 2005

The present study was designed to characterize the granulosa cell subpopulations derived from rats in which ovarian growth was induced by diethylstilbestrol (DES) or in which growth and differentiation was induced by pregnant mare's serum gonadotropin (PMSG). In the DES model, immature rats were given two separate injections of 2 mg DES/rat s.c. on 25 and 26 days of age and were killed 24 hr after the second injection. In the PMSG model, rats on day 28 were given 8 IU of PMSG s.c. and were killed 54 hr later. Granulosa cells were isolated from the ovaries, separated on a continuous Percoll density gradient, and divided into 12 fractions. The cells in each fraction were cultured in the presence of androstenedione with or without 20 ng/ml of follicle‐stimulating hormone (FSH) and estradiol and progesterone in the incubation medium were measured. In DES‐treated rats, granulosa cells in fractions 4 and 5 and fractions 9 and 10 contained about 30–40% of total cell yield and showed high steroidogenic potential. Granulosa cells from fractions 6, 7, and 8, which represent 55–60% of total cell yield, produced relatively low amounts of steroids on a per‐million‐cell basis. FSH was required for the stimulation of steroidogenesis. In granulosa cells from the PMSG treated rats, aromatase activity appeared maximally induced and incubation with FSH in vitro did not bring about any further increase. However, in vitro incubation with FSH was required for progesterone production. Furthermore, the granulosa cells from the PMSG treated rats also showed much more active estradiol and progesterone synthesis in fractions 9–12 as compared with lower density fractions. These studies suggest functional heterogeneity of granulosa cell populations in their response to FSH‐induced steroidogenesis. In addition, it was observed that in both models, there are two major populations of granulosa cells as evidenced by light and electron microscopy. The functional role of small and large granulosa cells in steroidogenesis is unclear; further studies are in progress.
Bone‐cell changes in estrogen‐induced bone‐mass increase in mice: Dissociation of osteoclasts from bone surfaces
Authors: Liu Chung‐Ching , Howard Guy A.
Published: February 2005

Early studies in certain avian and mammalian species have described estrogen‐associated bone‐cell changes, which were based on bone cells that were neither quantified nor identified histochemically (osteoclasts). In the experiments described here, weanling female mice were given a pharmacological dose of 17β‐estradiol benzoate (1 mg/week) for 1 and 4 weeks, and changes in osteoclasts and osteoblasts were assessed in tibial metaphyses and diaphyses. In the proximal metaphysis, the number of osteoclasts/mm surface length was significantly reduced by estrogen at 1 week (43%) and 4 weeks (64%), which was accompanied by significant increases in the number of osteoclasts in the marrow space not in contact with bone surfaces (no./mm2: 382% and 999%, respectively). These increases, along with observations of decreased osteoclast size (19%), of changes in osteoclast morphology, and of numerous acid‐phosphatase‐positive fragments in the marrow space, suggest that estrogen treatment causes the dissociation and disintegration, and thus decreased activity, of osteoclasts. The above changes were accompanied by more than 48% increases in the number of trabecular osteoblasts. In the diaphysis, the number of endosteal osteoclasts was significantly decreased by estrogen at 1 week (32%), but was not significantly changed at 4 weeks. These changes were attended by significant increases in the number of osteoclasts in the marrow space not in contact with bone surfaces (no./mm2: 393% at 1 week and 342% at 4 weeks). The number of endosteal osteoblasts was also increased by estrogen at 1 week (132%), and so was the size of endosteal osteoblasts (39% at 1 week and 81% at 4 weeks). Comparable results were obtained when a lower dose of 17β‐estradiol benzoate (20 μg/week) was given to ovariectomized mice. The increase in bone mass and its associated cell changes following estrogen treatment were also found in athymic nude mice, suggesting that these bone/bone cell changes are independent of the thymus.
Immunoelectron microscopic study of tyrosine hydroxylase immunoreactive nerve fibers and ganglion cells in the rat adrenal gland
Authors: Oomori Yukio , Okuno Sachiko , Fujisawa Hitoshi , Ono Kazuyuki
Published: February 2005

The present immunocytochemical study used an antiserum to tyrosine hydroxylase (TH), the first enzyme in the biosynthetic pathway of catecholamines, and revealed TH immunoreactivity in the ganglion cells and in the varicose nerve fibers of the cortex and medulla in the rat adrenal gland. TH immunoreactive nerve fibers in the cortex and medulla contained large and small granular vesicles, and also small clear vesicles. The immunoreactive nerve fibers were in close apposition to cortical cells in the cortex and in apposition to smooth muscle cells of blood vessels in both the cortex and medulla. Furthermore, TH immunoreactive nerve fibers were sometimes in close apposition to pericytes of blood vessels in the cortex and chromaffin cells in the medulla. The present results suggest that the catecholaminergic nerve fibers in the rat adrenal gland may be both intrinsic and extrinsic in origin.
Pathways of lymph flow from the intestine of the horse
Authors: Nikles Stephen A. , Heath Trevor J.
Published: February 2005

The intestine of horses differs from that of most other domestic animals in having a huge ascending colon and cecum, which together act as a large fermentation vat. The lymph drainage from this intestine occurs through a complex network of lymph vessels and lymph nodes, of which there are several thousand.

The pathways taken by lymph through these vessels and nodes were studied by tracing injections of dye, by examining Microfil casts, and with light and transmission electron microscopy.

Lymph vessels transporting lymph from the intestinal wall generally terminate on a single node within a group of primary nodes. Efferent lymphatics form networks in the immediate vicinity of groups of nodes. In these networks, the vessels branch, anastomose, entwine amongst one another, and sometimes form recircu‐lating loops. Usually 2–9 lymphatic vessels course away from these networks to secondary or higher‐order nodes in both local and more central locations. Vessels reaching these nodes generally terminate on more than one node within each group. This pattern of lymph distribution is repeated as lymph passes through a succession of five or more nodes before flowing into the cisterna chyli. The complexity of the lymph pathways, it is suggested, would promote the mixing of lymph from different parts of the intestine and from different nodes, thus collating, integrating, and potentiating the immunological responses of these nodes.

The walls of lymphatic vessels are well endowed with smooth muscle cells and elastic fibres, suggesting that intrinsic contractility of these vessels is a major mechanism in the propulsion of lymph from the intestine of the horse.
The architecture of adventitial elastin in the canine infrarenal aorta
Authors: Haas Kent S. , Phillips Steven J. , Comerota Anthony J. , White John V.
Published: February 2005

Although the artery wall consists of three distinct layers, only the structures of the intima and media have been well characterized. The adventitia has generally been overlooked. Our examination focused on the organization of elastin and collagen which are the major components of this tunic. Canine infrarenal aortas were excised, stretched to their in vivo length, then pressure fixed in formalin. Transverse, longitudinal, and frontal sections were prepared with specific elastin and collagen stains. Areas of adventitia in these sections were examined with LM, and interconnections between collagen and elastin were photographed at various magnifications. Subsequently, the slides were fractured for attachment to SEM stubs, and the coverslips were demounted. The identical areas were then examined with SEM using the LM micrographs as a guide to identify elastin and collagen. Whole mount aortic ring preparations were digested in formic acid for 72 and 96 h at 45°C to confirm adventitial elastin architecture. The adventitia was organized in alternating lamellae of collagen and elastin. The elastin lamellae consisted of continuous sheets of elastin with a longitudinal fibrillar substructure. Finer circumferential elastin fibers were also identified. These attached to both longitudinal elastin and adjacent collagen lamellae. Collagen lamellae were arranged in broad corrugated bands of fibrils. The unique architecture of the adventitia may explain some of the visco‐elastic properties of the aorta in both normal and pathologic states.
Morphology of the enamel organ in the miniature swine
Authors: McKee M. D. , Aoba T. , Moreno E. C.
Published: February 2005

In recent years, the dentition of the pig has been increasingly used as a model for the study of amelogenesis. Indeed, much of our current knowledge on enamel formation derives from biochemical and physicochemical analyses of the organic and inorganic components, respectively, of porcine enamel. As an extension of this previous work, and as the first step in our attempt to correlate known enamel matrix and mineral changes with adjacent enamel organ morphology, the present study was undertaken to provide a description of the morphological events occurring in the enamel organ during porcine amelogenesis. Two‐week‐old miniature swine (minipigs) were fixed by vascular perfusion with glutaraldehyde, the deciduous teeth present at this age were embedded in Epon resin and sectioned, and the cells of the enamel organ at each of the various developmental stages of amelogenesis were examined by light and transmission electron microscopy. In many respects, the morphology of the porcine enamel organ was similar to that previously described in other mammalian species. On the other hand, several particularities were noted and these are discussed in the context of available data correlating cell ultrastructure with putative function during enamel formation.
Immunohistochemical comparison of T‐cell and macrophage populations in mammary tissue of control and Trichinella spirails‐infected rats
Authors: Kumar Shantha N. , Steven William M. , Stewart George L. , Seelig Leonard L.
Published: February 2005

We have shown that antigen‐specific T lymphocytes can mediate maternal‐to‐neonatal immunity during lactation. Present studies address the dynamics of lymphocyte accumulation in the mammary gland during normal and disease stimulated conditions. Monoclonal antibodies specific for total T cells, suppressor/cytotoxic and helper subsets, and macrophages were used in conjunction with immunohistochemistry to identify and count the individual cell types. In unstimulated mammary tissue, following a rise in T cells to maximal numbers in late pregnancy, the total number of T cells/high power field (HPF) was significantly diminished in early lactation and continued to decline to the late lactation period. Both the numbers of T cells/HPF located in the mammary alveolar epithelium and surrounding connective tissue were significantly reduced in early lactation as compared to late pregnancy. This indicates the possible passage of cells into the milk during lactation. Prior infection of the mother with Trichinella spiralis and a secondary challenge 48 h. before sacrifice caused a significant reduction in the number of T cells in the mammary tissue in early lactation as compared with unstimulated controls, indicating the possibility of an even greater outflow of T cells into milk. In controls, the T‐suppressor/cytotoxic subtype showed a reduction in early lactation versus late pregnancy but showed no shifts in total cells/HPF during infection. The T‐helper subtype in controls remained unchanged from late pregnancy to early lactation with a considerable decline in late lactation. However, the T‐helper cells were significantly decreased in T. spiralis‐treated animals as compared with noninfected controls in early lactation. The population of macrophages declined from late pregnancy to early lactation but remained unchanged between normal and T. spiralis‐infected animals.
Differential distribution of salivary agglutinin and amylase in the Golgi apparatus and secretory granules of human salivary gland acinar cells
Authors: Takano Kunio , Bogert Meredith , Malamud Daniel , Lally Edward , Hand Arthur R.
Published: February 2005

The secretory granules of salivary glands often display complex internal substructures, yet little is known of the molecular organization of their contents or the mechanisms involved in packaging of the secretory proteins. We used post‐embedding immunogold labeling with antibodies to two secretory proteins, agglutinin and α‐amylase, to determine their distribution in the Golgi apparatus and secretory granules of the human submandibular gland acinar cells. With monoclonal antibodies specific for carbohydrate epitopes of the agglutinin, reactivity was found in the trans Golgi saccules, trans Golgi network, and immature and mature secretory granules. In the granules, labeling was seen in regions of low and medium electron density, but not in the dense cores. Reactivity seen on the apical and basolateral membranes of acinar and duct cells was attributed to a shared epitope on a membrane glycoprotein. Labeling with a polyclonal antibody to amylase was found in the Golgi saccules, immature and mature secretory granules, but not in the trans Golgi network. In the granules, amylase was present in the dense cores and in areas of medium density, but not in the regions of low density. These results indicate that these two proteins are distributed differently within the secretory granules, and suggest that they follow separate pathways between the Golgi apparatus and forming secretory granules. Small vesicles and tubular structures that labeled only with the antibodies to the agglutinin were observed on both faces of the Golgi apparatus and in the vicinity of the cell membrane. These structures may represent constitutive secretion vesicles involved in transport of the putative membrane glycoprotein to the cell membrane.
A fine morphological study of germ cells in asymmetrically developing right and left ovaries of the chick
Authors: Ukeshima Atsumi , Fujimoto Toyoaki
Published: February 2005

Germ cells of the chick ovary which develop asymmetrically on the right and left sides of the embryo were observed by electron microscopy from 7 to 17 days of incubation. Germ cells showed different patterns in the right and left‐ovaries, and also differences in the cortex and in the medulla. At 7 to 9 days, germ cells were individually present in both the right and left ovaries. They proliferated from 10 days onward and formed many cell aggregates. In each aggregate, germ cells were joined by intercellular bridges, and their cell cycles were synchronized. Although meiotic features of the germ cells were frequently found in the cortex of the left ovaries at 16 days, some germ cells exhibited these features at earlier days. In the meiotic germ cells, the “Balbiani body,” which was composed of a concentration of cell organelles shifted to one pole of the cell, was always seen. The apperance of a meiotic nucleus and Balbiani body was characteristic of germ cells located in the left ovarian cortex, whereas those were never seen in the left medulla and in the right ovary. At 16 and 17 days, some germ cells were released into the lacunae of the medulla of both the right and left ovaries. The meaning of this phenomenon is discussed. Degenerating germ cells were frequently observed in the right ovary, but rarely in the left.