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Biomedical subjects

M Benjamin

Publications and source records attributed to M Benjamin.

At least 19 recordsLinked to original sources
PubMed1996

An immunohistochemical study of enthesis development in the medial collateral ligament of the rat knee joint.

The changing distributions of collagens and glycosaminoglycans have been studied at the attachments of the medial collateral ligament during postnatal development. The ligament is of particular interest because it has a fibrocartilaginous attachment to the femoral epiphysis, but a fibrous one to the tibial metaphysis. Ligaments were examined in rats killed at birth and at 2, 4, 6, 8, 10, 20, 30, 45, 60, 90 and 120 days after birth. Cryosections were immunolabelled with monoclonal and polyclonal antibodies against types I and II collagen, chondroitin 4 and 6 sulfate, dermatan and keratan sulfate. Although the ligament is attached at both ends to bones that develop from cartilage, there was a striking difference in collagen labelling. Type II collagen was only found in spicules of calcified cartilage in bone beneath the tibial enthesis after ossification had commenced, but there was a continuous band of labelling at all stages of development at the femoral enthesis. Initially, the cartilage at the femoral attachment lacked type I collagen, but by 45 days labelling was continuous from ligament to bone. Continuity of labelling was seen much earlier at the tibial enthesis, as soon as bone had formed. There were also marked changes in glycosaminoglycan distribution. Keratan sulfate was present at both entheses up to 45 days, but only at the femoral enthesis thereafter. Both attachments labelled throughout life for dermatan sulfate, but chondroitin 4 and 6 sulfate were only found at the femoral end. The results suggest that enthesial cartilage at the femoral attachment was initially derived from the cartilaginous bone rudiment but was quickly eroded on its deep surface by endochondral ossification as bone formed at the attachment site. It was replaced by fibrocartilage developing in the ligament. This mechanism allows enthesis cartilage/fibrocartilage to contribute to the growth of a bone at a secondary centre of ossification in addition to dissipating stress at the ligament-bone junction.

Age Factors↗
PubMed1996

High resolution magnetic resonance imaging of the proximal interphalangeal joints. Correlation with histology and production of a three-dimensional data set.

The magnetic resonance imaging appearance of the proximal interphalangeal joints of cadavers was correlated with histology of the same specimen allowing many small-scale features to be identified that might otherwise have been misinterpreted. It enabled the magnetic resonance signal to be understood at a tissue and cellular level, allowing identification of synovial folds extending from the extensor tendon and volar plate, the entheses of the proper collateral ligament, the epitenon of the flexor tendons and the presence of osteophytes and sites of cartilage erosion. The main difficulties in matching two-dimensional magnetic resonance images with histology were the differing section thicknesses of the two methods and shrinkage of histological specimens. There are many advantages in producing high resolution three-dimensional datasets-the magnetic resonance section thickness is reduced and the individual components of the joint can be viewed simultaneously in two or more planes. A unique magnetic resonance atlas of three dimensional joint structure is presented.

Aged↗
PubMed1996

Changing expression of intermediate filaments in fibroblasts and cementoblasts of the developing periodontal ligament of the rat molar tooth.

The distributing of vimentin and cytokeratin intermediate filaments within the cells of the dental follicle and developing periodontal ligament is described during eruption of the rat 1st molar tooth. Alcohol-fixed tissues from animals ranging from neonates to 12 wk old were cryosectioned, immunolabelled with monoclonal antibodies against vimentin and a range of cytokeratins and examined by indirect immunofluorescence. Vimentin was observed in follicular and periodontal ligament fibroblasts in all animals and at all stages of eruption. It was also observed in cementoblasts after disruption of the epithelial root sheath (of Hertwig) which is responsible for determining the shape of the developing root. Prior to eruption, cytokeratins were restricted to epithelial components of the developing tooth, including the root sheath. However, they were seen in cementoblasts on disruption of the root sheath at 2 wk and in periodontal ligament fibroblasts at 3 wk after birth, when the tooth was erupting but had not reached occlusion. On occlusion (at 4 wk), fibroblasts no longer labelled for cytokeratins but cementoblasts associated with acellular cementum formation continued to express them. These results demonstrate temporal and spatial changes within the cells of the developing periodontal connective tissues and suggest that the appearance of cytokeratins in periodontal fibroblasts and cementoblasts may be related to mechanical changes during tooth eruption. Further, the results suggest different origins for cementoblasts associated with cellular and acellular cementum formation.

Animals↗
PubMed1996

Ultrastructure of fibrocartilages at the insertion of the rat Achilles tendon.

The ultrastructure of 3 fibrocartilages is described at the insertion of the adult rat Achilles tendon. Enthesial fibrocartilage lies at the tendon-bone junction, sesamoid fibrocartilage in the deep surface of the tendon where it presses on the calcaneus, and periosteal fibrocartilage covers the opposing surface of the bone. All had some features that could be interpreted as typical of fibrous tissues and other features that were more characteristic of cartilage. The general extracellular matrix was largely fibrous and had relatively little visible proteoglycan. In contrast, the cells had features more common in cartilage--dilated rough endoplasmic reticulum, glycogen and lipid, and pericellular matrix rich in proteoglycans and fine collagen fibrils. The periosteal fibrocartilage was the most 'cartilaginous' in character, probably because it develops rapidly after birth as a secondary cartilage from the calcaneal periosteum whereas enthesial and sesamoid fibrocartilages develop by metaplasia of tendon fibroblasts. A major difference between the 3 fibrocartilages was the arrangement of their collagen fibrils. There were parallel bundles in enthesial fibrocartilage but interweaving networks in the sesamoid and periosteal fibrocartilages. This probably reflects different functional demands of the tissues. The sesamoid and periosteal fibrocartilages directly formed the boundaries of the retrocalcaneal bursa and were not covered by synovium. Both were lined by an electron dense, articular surface lamina that prevented cell contact with the bursa. It significance is unclear, but it could protect against wear and tear, represent material being shed into the bursal cavity or control nutrient exchange with the synovial fluid.

Achilles Tendon↗
PubMed1996

Tendon cells in vivo form a three dimensional network of cell processes linked by gap junctions.

Tendons respond to mechanical load by modifying their extracellular matrix. The cells therefore sense mechanical load and coordinate an appropriate response to it. We show that tendon cells have the potential to communicate with one another via cell processes and gap junctions and thus could use direct cell/cell communication to detect and/or coordinate their load responses. Unfixed cryosections of adult rat digital flexor tendons were stained with the fluorescent membrane dye DiI to demonstrate cell shape. Similar sections were immunolabelled with monoclonal antibodies to rat connexin 32 or connexin 43 to demonstrate gap junctions and counterstained with propidium iodide to show nuclei, or the membrane stain DiOC7 to show cell membranes. Sections were examined with a laser scanning confocal microscope and 3-dimensional reconstructions were prepared from optical section series to demonstrate cell shape and the position of connexin immunolabel. Cells had a complex interconnected morphology with gap junctions at points of contact with other cells. Cell bodies contained the nucleus and extended broad flat lateral cell processes that enclosed collagen bundles and interacted with similar processes from adjacent cells. They also had long thin longitudinal processes interacting with the cell process network further along the tendon. Connexin 43 occurred where cell processes met and between cell bodies, whereas connexin 32 was only found between cell bodies. The results indicate the presence of a 3-dimensional communicating network of cell processes within tendons. The intimate relationship between cell processes and collagen fibril bundles suggests that the cell process network could be involved in load sensing and coordination of response to load. The presence of 2 different types of connexins suggests that there could be at least 2 distinct communicating networks.

Animals↗
PubMed1995

Structure and histopathology of the insertional region of the human Achilles tendon.

The Achilles tendon inserts onto the calcaneus, and the retrocalcaneal bursa intervenes between it and the bone immediately proximal to the enthesis. The enthesis, the bursa, and the bursal walls form a complex insertional region protecting against wear and tear. We examined the structure and histopathology of the insertional region in 50 tendons from cadavers (age at time of death, 57-96 years). The enthesis contained fibrocartilage typical of attachment sites. In specimens with a prominent superior tuberosity (the majority), the walls of the bursa also were fibrocartilaginous. On the anterior wall, fibrocartilage replaced the calcaneal periosteum; on the posterior wall, there was a sesamoid fibrocartilage in the deep part of the tendon. When the tuberosity was not prominent, the bursal fibrocartilages were absent. Histopathological features were observed in 31 entheses. Bone spurs extended from the calcaneus into the tendon and probably formed by endochondral ossification of enthesial fibrocartilage. Longitudinal fissures were splits in the fibrocartilage along the lines of the endotenon, and small transverse tears occurred at the tendon-bone junction. Longitudinal fissures showed evidence of repair; they were filled with amorphous material and surrounded by clusters of cells. In the bursal walls, calcification or degradation, or both, were observed in 37 specimens and usually involved both sesamoid and periosteal fibrocartilages. These fibrocartilages could therefore be implicated in retrocalcaneal bursitis.

Achilles Tendon↗
PubMed1995

The development of fibrocartilage in the rat intervertebral disc.

The development of fibrocartilage in rat lumbar intervertebral discs has been correlated with an immunohistochemical analysis of the changing distribution of extracellular matrix components. Disc anlagen were first recognised by embryonic day 14 as segmental cell condensations. By E16, the notochord formed a series of bulges, each representing a future nucleus pulposus, and the annulus fibrosus had differentiated in the disc anlagen. The inner part of the annulus was composed of cartilage which linked that of adjacent vertebral bodies. The outer part was fibroblastic, with layers of parallel fibroblasts. The long axes of the cells in successive layers lay at an angle of approximately 90 degrees to each other. This criss-cross orientation of cells preceded the oriented deposition of collagen fibres to form the lamellae. Disc anlagen were immunolabelled weakly for types I and III collagen, chondroitin 6-sulphate and dermatan sulphate. Later tissue differentiation was marked by the appearance of type II collagen, chondroitin 4-sulphate and keratan sulphate in the inner annulus. These components also appeared in the outer annulus, but only in adult animals, and indicated metaplastic change in the lamellar fibroblasts. Fibrocartilage in the nucleus pulposus was only seen in old animals, and the origin of the tissue was less clear. However, the fibrocartilage cells appeared to be derived from the cartilage end plate and/or from the inner annulus. We conclude that fibrocartilage in the intervertebral disc is derived from several sources and that the radial distribution patterns of extracellular matrix components in the adult disc are explained by the embryonic origins of its parts.

Animals↗
PubMed1995

Role of T lymphocytes in secretory response to an enteric nematode parasite. Studies in athymic rats.

Athymic (nude) rats have been used to assess the role of thymus-dependent T cells in the control of the intestinal response following infection with the enteric parasite, Nippostrongylus brasiliensis. Tissues from infected rats were excised on days 4, 7, 10, and 21 postinfection (p-i) for physiological and morphological studies; uninfected (day 0) rats served as controls. In response to the worm burden, jejunal tissues displayed a secretory response, indicated by an elevated baseline short-circuit current (Isc) on days 7 and 10 p-i, and were more responsive to histamine than control tissues. Despite this enhanced secretory response, approximately 35% of the worm burden was still present on day 21 p-i (compared with expulsion of > 95% by day 14 p-i in normal rats). Mast cell activation and hyperplasia, increased goblet cell (implying increased mucus synthesis) and intraepithelial leukocyte numbers, and abnormalities in Isc responses after electrical stimulation of enteric nerves were identified following infection. These events in nude rats were attenuated or delayed in onset as compared with conventional immunocompetent rats. Our results support the postulate that thymus-dependent T cells regulate the timing and/or nature of the mucosal response to enteric parasitic infections. However, ion secretion was not altered in the absence of T cells and, therefore, is more likely to be a consequence of mast cell activation.

Analysis of Variance↗
PubMed1995

Cytoskeleton of the mesenchymal cells of the rat dental papilla and dental pulp.

This study describes the immunolocalization of actin, cytokeratins and vimentin during differentiation of the dental papilla in the rat. Incisors and first molars were sectioned from mandibles of Wistar rats from embryonic day (E)-14 to (E)-21 and weeks 1, 2, 3, 12 and 104 after birth, fixed in 90% alcohol, decalcified in EDTA, infiltrated with 5% sucrose, frozen in dry ice, and cryosectioned at 10 microns. The sections were immunolabelled using indirect immunofluorescence with a panel of monoclonal antibodies and FITC-phalloidin for F-actin localization. F-actin was present in follicular mesenchyme and odontoblast processes. Vimentin labelled dental papilla fibroblasts, differentiating, functional (secretory) and aged odontoblasts. Vimentin was uniformly localized in the cytoplasm of pre-odontoblasts but was redistributed to the apical pole of these cells during polarization. Of the cytokeratins, only cytokeratin 19 was found in differentiating odontoblasts. It was not present in dental papilla fibroblasts, functional or aged odontoblasts. These results suggest that actin and the redistribution of vimentin may be involved in odontoblast differentiation and odontoblast process formation/support and that these events may be preceded by the expression of cytokeratin 19.

Actins↗
PubMed1995

Variations in the quality of uncalcified fibrocartilage at the insertions of the extrinsic calf muscles in the foot.

It has been suggested that fibrocartilage at entheses (tendon-bone junctions) prevents collagen fibres bending at the hard tissue interface. We have investigated this function by exploring the relationship between the presence or amount of fibrocartilage at the attachments of the major extrinsic muscles in the foot, and the extent to which these tendons bend near their entheses during movement. The tendons were taken from each of 5 formalin-fixed dissecting room cadavers and prepared for routine histology, and sections were collected systematically throughout the blocks. Tendons that attached to the tarsus and metatarsus had fibrocartilaginous entheses, but those attached to the phalanges had fibrous entheses. In all tarsal and metatarsal tendons, the fibrocartilage was significantly thicker (P < 0.05) in the deepest part of the enthesis. Here the greatest amount of fibrocartilage was in the Achilles tendon (mean thickness +/- S.E.M.: 1560 +/- 161 microns). There were moderate amounts at the medial cuneiform attachment of tibialis anterior (533 +/- 82 microns), peroneus brevis (472 +/- 64 microns) and tibialis posterior (454 +/- 26 microns), small quantities at the first metatarsal attachment of tibialis anterior (104 +/- 14 microns) and peroneus longus (21 +/- 8 microns), but only traces at the attachments of the flexor and extensor tendons of the phalanges. The differences can be related to variations in the freedom of movement of the tendons near their attachments. This depends on the extent to which the tendons are bound by retinacula and the range of movement of the joint nearest the enthesis. The results suggest that more 'mobile' tendons have more fibrocartilage.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Fibrocartilage associated with human tendons and their pulleys.

The presence of fibrocartilage in tendons that wrap around bony or fibrous pulleys is well known. It is an adaptation to resisting compression or shear, but the extent to which the structure of most human tendons is modified where they contact pulleys is less clear, for there has been no single comprehensive survey of a large number of sites. Less is known of the structure of the corresponding pulleys. In the present study, 38 regions of tendons that wrap around bony pulleys or pass beneath fibrous retinacula have been studied in routine histology sections taken from each of 2 or 3 elderly dissecting room cadavers. Most of the corresponding pulleys have also been examined. Fibrocartilage was present in 22 of the 38 tendon sites and it was most conspicuous where the tendons pressed predominantly against bone rather than retinacula and where they showed a large change in direction. Fibrocartilage was more characteristic of tendons at the ankle than the wrist, probably because the long axis of the foot is at right angles to that of the leg. There was considerable variation in the structure of tendon fibrocartilage. The most fibrocartilaginous tendons had oval or round cells embedded in a highly metachromatic matrix with interwoven or spiralling collagen fibres. At other sites, fibrocartilage cells were arranged in rows between parallel collagen fibres. The differences probably relate to differences in development. A single tendon could be modified at successive points along its length and fibrocartilage could be present in the endotenon and epitenon as well as in the tendon itself. Pathological changes seen in 'wrap around' tendons were fragmentation and partial delamination of the compressed surface, chondrocyte clustering, fatty infiltration and bone formation. Three types of pulleys were described for tendons--bony prominences and grooves, fibrous retinacula and synovial joints. The extent of cartilaginous differentiation on the periosteum of bony pulleys frequently mirrored that in the corresponding tendon. The cartilage or fibrocartilage prevents the tendon from 'sawing' through the bone. Some of the best known retinacula were largely fibrous, though the inferior peroneal retinaculum and the trochlea for the superior oblique were cartilaginous. The results underline the considerable regional heterogeneity in different tendons and their pulleys. They show that one tendon is not like another and that tendons may need to be carefully selected for particular surgical transfers or joint reconstructions.

Aged↗
PubMed1994

Cytoskeleton of cartilage cells.

The cytoskeleton of chondrocytes consists of microfilaments made of actin, microtubules made of tubulin, and intermediate filaments made of a variety of subunits. Actin filaments are not prominent in vivo but may form in vitro. In culture, changes in filament polymerisation are important in determining cell shape, initiating chondrogenesis, and maintaining the chondrogenic phenotype. Microtubules, besides their role in cell division, organise the distribution of organelles and are involved in secretory transport mechanisms in collagen and proteoglycan synthesis. A variety of intermediate filaments may be present, frequently forming large whorled aggregates. The filaments include vimentin, cytokeratins, and glial fibrillary acidic protein. These may occur at different depths in articular cartilage. Vimentin accumulates during development of some fibrocartilages with increased mechanical loading. Together with other elements of the cytoskeleton, intermediate filaments could form part of a mechanotransduction system by which cells respond to external forces and sense changes in their external environment.

Actin Cytoskeleton↗
PubMed1994

A comparative study of the fetal electrocardiogram recorded by the STAN an Nottingham systems.

OBJECTIVE: To compare the T:QRS ratio recorded by the STAN and Nottingham fetal electrocardiogram (FECG) monitors. DESIGN: Prospective observational study. SETTING: London teaching hospital delivery suite and research unit. METHODS AND SUBJECTS: The T:QRS ratios generated by the STAN and Nottingham FECG monitors were simultaneously recorded and compared using signals generated from a computer-produced ECG signal and signals from 11 term fetuses recorded during labour. RESULTS: There was an acceptable level of agreement between the two systems with the computer-generated signals, but it was not clinically acceptable with the signals from the fetuses recorded during labour. Disagreements in the T:QRS values were probably due to differences in the reference points for the measurement of the S-T segment and T-wave height. CONCLUSION: The different points of reference for measurement of S-T segment and T-wave height can explain poor agreement between the two methods of FECG waveform analysis. The suggested adopted points of reference are those corresponding to adult electrocardiographic methodology.

Delivery, Obstetric↗
PubMed1994

The joint capsule: structure, composition, ageing and disease.

The joint capsule is vital to the function of synovial joints. It seals the joint space, provides passive stability by limiting movements, provides active stability via its proprioceptive nerve endings and may form articular surfaces for the joint. It is a dense fibrous connective tissue that is attached to the bones via specialised attachment zones and forms a sleeve around the joint. It varies in thickness according to the stresses to which it is subject, is locally thickened to form capsular ligaments, and may also incorporate tendons. The capsule is often injured, leading to laxity, constriction and/or adhesion to surrounding structures. It is also important in rheumatic disease, including rheumatoid arthritis and osteoarthritis, crystal deposition disorders, bony spur formation and ankylosing spondylitis. This article concentrates on the specialised structures of the capsule--where capsular tissues attach to bone or form part of the articulation of the joint. It focuses on 2 joints: the rat knee and the proximal interphalangeal (PIP) joint of the human finger. The attachments to bone contain fibrocartilage, derived from the cartilage of the embryonic bone rudiment and rich in type II collagen and glycosaminoglycans. The attachment changes with age, when type II collagen spreads into the capsular ligament or tendon, or pathology--type II collagen is lost from PIP capsular attachments in rheumatoid arthritis. Parts of the capsule that are compressed during movement adapt by becoming fibrocartilaginous. Such regions accumulate cartilage-like glycosaminoglycans and may contain type II collagen, especially in aged material.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗