Golgi-canalicular reticulum system in ion transporting fibrocytes and outer sulcus epithelium of gerbil cochlea

BACKGROUND

Five types of highly specialized fibrocytes have been identified in the spiral ligament of the gerbil cochlea. Type I, II, and IV fibrocytes function in cycling back to the stria vascularis K+ effluxed from outer hair cells and nerves during auditory transduction. Thus, evidence exists for a transcellular path of K+ movement from outer sulcus cells through fibrocytes to the strial interstitial space, but a mechanism for facilitating such ion flow within the cells has not been elucidated.

METHODS

The spiral ligament of glutaraldehyde-osmium tetroxide-fixed and Epon-embedded gerbil cochlea was examined by transmission electron microscopy.

RESULTS

Ultrastructural examination disclosed an extensive membrane limited reticulum in the cytoplasm of type I, II, IV, and V fibrocytes of the lateral wall and in outer sulcus cells and their root processes. This system resembled the tubulocisternal endoplasmic reticulum present in some ion-transporting epithelia but appeared more to constitute a network of canaliculi and is referred to as the canalicular reticulum (CR). Many typical small Golgi complexes invariably accompanied the CR in the fibrocytes and sulcus cells, as we have found to be true of other epithelia known to contain CR and function in ion transport. Numerous mitochondria populated cytosol-containing CR.

CONCLUSIONS

The data support the concept of transcellular K+ flux in type I, II, IV, and V fibrocytes and outer sulcus cells in the cochlea and lend credence to the view of CR as functioning in the movement of ions through cells. The constant and precise association of Golgi complexes with CR in the different cell types implies a functional relationship possibly concerned with biosynthesis of CR by Golgi elements, and the abundance of mitochondria near CR indicates an energy requirement for function of the reticulum or its biosynthesis.

Scanning transmission electron microscopy mass analysis of fibrillin-containing microfibrils from foetal elastic tissues

We have applied scanning transmission electron microscopy to intact native fibrillin-containing microfibrils isolated from foetal bovine elastic tissues in order to derive new insights into microfibril organisation. This technique provides quantitative data on the mass per unit length and axial mass distribution of unstained, unshadowed macromolecules. Scanning transmission electron microscopy of microfibrils from aorta, skin and nuchal ligament revealed that the beads corresponded to peaks of mass and the interbead regions to troughs of mass. These major features of axial mass distribution were characteristic of all microfibrils examined. Tissue-specific and age-dependent variations in mass were identified in microfibrils that were structurally comparable by rotary shadowing electron microscopy. Increased microfibril mass correlated with increasing gestational age. The additional mass was associated predominantly at, or close to, the bead. Some microfibril populations exhibited pronounced assymetry in their axial mass distribution. These data indicate that intact native microfibrillar assemblies from developing elastic tissues are heterogeneous in composition. Loss of mass following chondroitinase ABC or AC lyase treatment confirmed the presence of chondroitin sulphate in nuchal ligament microfibrillar assemblies.

[Scanning electron microscopic investigations on the anatomy of the fetlock joint in horses]

Striking synovial structures were taken and their surface was investigated by scanning electron microscopy. Depending where the probes were taken from, the stratum synovial was arranged in a different way. The synovial intima seems to miss under the tendon of the long/commune extensor muscle, the collateral ligaments and the sesamoidean collateral ligaments. That is why the subsynovial tissue forms the superficial layer. The surface of the probes taken sidewards to the tendon of the extensor muscle and of the synovial fold, which is situated between the metacarpus/metatarsus and the proximal phalanx as well as from the palmar/plantar recess is dominated by synovial intima. Synovial cells are mainly arranged as monolayer. Synovial cells are variable in their appearance. Some resemble blackberrys, others show a quite undulating surface. The length of processes of synovial cells differs from 2-10 microns, the diameter of the synovial cells from 5-10 microns. The space between two cells amounts to 2-10 microns. The intercellular gap is put in relation to the length of the cells' processes. The synovial intima is supposed to form a barrier between the articular cavity and the surrounding structures.

HNK-1 epitope in the lens-ciliary zonular region in normal and pseudoexfoliative eyes. Immunohistochemistry and ultrastructure

OBJECTIVE

To determine the specific binding sites for the HNK-1 adhesion molecule epitope in the lens-ciliary zonular region in normal and pseudoexfoliative (PSX) eyes.

METHODS

Normal and PSX eyes and adjacent tissues from individuals aged 10 months to 89 years were investigated for the HNK-1 epitope by immunohistochemistry and immunogold electron microscopy.

RESULTS

Concentration of HNK-1 epitope was high in the anterior central lens capsule into old age, but it tapered earlier and progressively in the inner capsule and elsewhere. On zonular fibers, label was strongest at their lens and ciliary attachments and intense on related elastic microfibrils in adjacent ciliary stroma. Label was also strong on PSX fibers and above normal on PSX central capsule. In contrast, HNK-1 was absent on PSX aggregates in conjunctiva and skin and on normal elastic microfibrils in these tissues.

CONCLUSIONS

The prominent HNK-1 epitope in lens capsule and zonule has age- and site-specific variations that favor adhesive roles in each. The high density of epitope on ocular PSX material suggests an aberrant increase in expression that may contribute to adhesiveness of these aggregates, HNK-1 negativity on extraocular elastic microfibrils and PSX aggregates indicates a unique difference in composition of intraocular and extraocular elastic tissue, of potential significance for ocular function in aging and lens-dislocating diseases.

Comparative morphology of the pectinate ligaments of domestic mammals, as observed under the dissecting microscope and the scanning electron microscope

The pectinate ligaments of ten horses, two donkeys, five oxen, five sheep, ten goats, five dogs, five cats, thirty pigs and two rabbits were studied under the stereomicroscope and the scanning electron microscope. In the horse and the donkey, the pectinate ligament was very prominent and was characterized by sturdy interconnected strands and relatively small intertrabecular spaces. The pectinate ligaments of ruminants were composed of shorter strands, separated by relatively larger spaces. Fusion between adjacent strands, resulting in the formation of fenestrated sheets, was regularly observed in these species, in particular in the superior and inferior ocular segments. In the dog and the cat, the pectinate ligament consisted of slender strands that were separated by large intertrabecular spaces. The strands of the pectinate ligaments of the pig and the rabbit were shorter and their diameters were intermediate between those of the herbivores and the carnivores. The clinical relevance of the normal variability in the structure of the pectinate ligament and proposals for a uniform anatomical nomenclature are discussed.

Immunoelectron microscopic study on neuropeptide Y in the periodontal ligament of the incisor following peripheral nerve injury to the inferior alveolar nerve in the rat

Immunoelectron microscopic analysis was carried out to examine whether neuropeptide Y (NPY)-like immunoreactivity (-LI) is localized in mechanoreceptors in the lingual periodontal ligament of the rat incisor following peripheral nerve injury to the inferior alveolar nerve (IAN). In the lingual periodontal ligament of normal animals, no NPY-like immunoreactive (-IR) primary afferents were observed, except for a very few sympathetic perivascular nerve fibers which showed NPY-LI. Fourteen days following chronic constriction injury to the IAN combined with sympathectomy of the superior cervical ganglion, thick NPY-IR nerve fibers showing tree-like raminifications were detected in the shear zone between the tooth-related part and alveolus-related part as well as in the alveolus-related part. Immunoelectron microscopy revealed that expanded NPY-IR nerve terminals were covered with several Schwann sheaths and that a part of the axoplasm expanded to the surrounding tissues. These ultrastructural features of NPY-IR structures were identical to those of periodontal Ruffini endings, categorized as slowly adapting mechanoreceptors. Thick (6-8 microns in diameter) NPY-IR axons were also observed without any apparent myelin sheath. The present results provide further evidence that NPY is closely associated with thick axons, probably myelinated nerves and Ruffini endings, following peripheral nerve injury.

Selective degradation of accumulated secretory proteins in the endoplasmic reticulum. A possible clearance pathway for abnormal tropoelastin

The specific pathway of tropoelastin secretion was investigated in fetal calf ligamentum nuchae (FCL) cells using brefeldin A (BFA) to disrupt the secretory pathway. Electron microscopic studies of BFA-treated FCL cells showed ultrastructural changes consistent with the reported effects of BFA on intracellular organelles. When FCL cells were labeled with [3H]leucine in the presence of BFA, radiolabeled tropoelastin was not secreted, nor was there an intracellular accumulation of the protein. In contrast, fibronectin accumulated within the cells in the presence of BFA. Northern analysis of mRNA levels in FCL cells showed that the message for tropoelastin was unaffected by BFA treatment. Pulse chase experiments conducted in the presence of BFA demonstrated that the tropoelastin retained within the cells was rapidly degraded. Ammonium chloride, nocodazole, and cycloheximide had no effect on the degradation of tropoelastin, indicating that the degradation did not involve the endosome/lysosome pathway, movement via microtubules, or a short-lived protein, respectively. Incubation of FCL cells with BFA in the presence of N-acetyl-Leu-Leu-norleucinal, however, allowed tropoelastin to steadily accumulate in the cells. Cells pulsed in the presence of BFA alone showed that tropoelastin initially accumulates within the cells for approximately 1 h prior to being degraded, thus indicating that a critical threshold of tropoelastin must be reached before degradation can occur. Results from this study provide evidence for selective degradation of a soluble secreted protein by a cysteine protease following retention of the protein in the endoplasmic reticulum.

Scanning electron microscopy of the human zonule of the lens (Zonula ciliaris)

In the present study eight human eyeballs were specifically prepared for scanning-electron-microscopic observation of the zonule. The zonule consisted of two main layers of radial fibres, an anterior and a posterior one, that inserted on the anterior and the posterior lens capsules, respectively. Some fibres inserted on the equator of the lens. Posterior zonular fibres originated at the pars plana, entered the dorsal part of the ciliary valleys and then changed their direction towards the posterior face of the lens. Posterior fibres inserted on the posterior capsule of the lens by branched endings 1 mm behind the equator of the lens. Anterior zonular fibres originated mainly at the pars plana and occasionally at the ciliary valleys. After running completely through the ciliary valleys in close contact with the lateral walls of the ciliary processes, they changed their direction at the anterior endings of the pars plicata and reached the anterior lens capsule. Anterior zonular insertions were achieved by webbed endings that diffused into the anterior capsule 2 mm in front of the lens equator. The extraordinary distension capacity of the zonular fibres was demonstrated by pulling the anterior lens capsule after hydrodissection. As a consequence, the anterior fibres were stretched up to four times their original length without breaking or disinserting.

Transection of the accessory ligament of the superficial digital flexor tendon for treatment of tendinitis: long term results in 61 standardbred racehorses (1985-1992)

Medical records and lifetime race results were obtained for 61 Standardbred racehorses treated consecutively from 1985 to 1992 with transection of the accessory ligament of the superficial digital flexor tendon (AL-SDF) for tendinitis of one or both forelimbs. A clinical diagnosis of tendinitis was confirmed in all cases by ultrasonographic examination. After surgery, 50 (82%) horses raced and 42 (69%) completed 5 or more starts. Eight horses (13%) failed to start and/or complete 5 or more races due to a recurrence of tendinitis. Six (10%) horses did not start and/or complete 5 or more starts for reasons unrelated to tendinitis and 5 (8%) horses were lost to follow-up. The median time between surgery and the first post operative start was 39 weeks. Fifty-seven per cent of those horses to start after surgery completed 20 or more starts and 40% raced on 40 or more occasions. Of the 42 horses to complete 5 or more races, the median number of post operative starts was 37 at time of follow-up. Thirty-two of 50 (64%) horses to start after surgery established or lowered lifetime racemarks. Thirty-six horses had raced prior to surgery. Thirty-one of 36 (86%) horses returned to racing after treatment of SDF tendinitis with accessory desmotomy (AD) and 27 horses (75%) completed 5 or more starts. Median earnings per start decreased 25% after surgery. Twenty-five horses had not raced prior to surgery. Nineteen (76%) horses in this group were age 2 years at time of injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of pigment dispersion syndrome and pigmentary glaucoma

Pigmentary glaucoma results from zonular-pigment dispersion, primarily in young, myopic, white individuals. The concavity of the midperipheral iris allows iridozonular contact. Released pigment is carried to the trabecular meshwork where it resides: (1) benignly, not affecting the intraocular pressure, as in pigment dispersion syndrome; or (2) malignantly, elevating the intraocular pressure, as in pigmentary glaucoma. Small amounts of pigment are quickly phagocytized. If the particulate load is heavy, the cells migrate further along the outflow pathway. The flattening of the iris in pigmentary glaucoma patients receiving iridotomies, along with the backward flow of pigment observed during treatment, demonstrates a greater pressure in the anterior than the posterior chamber. This reverse pupillary block may be due to temporary ocular deformations caused by blinking, as small aqueous aliquots are forced into the anterior chamber. Flattening of the concave iris is the key to current and future management of these patients.

Ultrastructural observations on the ossification of the supraspinous ligament

STUDY DESIGN

This study analyzed the process of ossification of spinal ligaments. Supraspinous ligaments excised during surgery were studied by light and scanning electron microscopy.

OBJECTIVES

The results were correlated to determine the mechanism of ossification of spinal ligaments.

SUMMARY OF BACKGROUND DATA

Ossification of the ligamentum flavum has been described in detail by Hiraoka, Yamaguchi, and others. However, the pathogenesis of ossification of the spinal ligaments remains unclear. Some studies have been performed by light and transmission electron microscopy, but no detailed investigation of the ossification of the spinal ligaments by scanning electron microscopy has been performed.

METHODS

Specimens of supraspinous ligament were taken from 41 patients during spinal surgery. Ossification was diagnosed macroscopically and radiologically for 20 patients. The specimens were examined using light and scanning electron microscopy.

RESULTS

Collagen fibrils were 700-2000 A in diameter and were arranged in parallel. The ligament insertion divided into four zones and seemed to fit the description of Enthesis histologically. Close to the ossification region, there were a region in which some fibrils were thinner and branchings became slightly stronger, tending to form bridges of minute fibrils between other fibrils. Closer to the region of actual ossification, there was a region in which extra-fibrillar substances completely deposited. In the region of actual ossification, there were medullary spaces of varying sizes, and the surrounding collagen fibers were dense and arranged in a lamellar fashion. Osteocyte lacunae had formed and the cells regarded to be the osteocytes were present on the inside.

CONCLUSION

Ossification of the supraspinous ligament possibly occurs as follows. Fibroblasts or chondrocyte-like cells respond to some external stimulus, form an irregular network of fine fibrils, and produce acid mucopolysaccharide. These undergo calcification and capillary invasion. Undifferentiated mesenchymal cells invaded and are transformed into osteoblasts. Then osteogenesis ensues with progressive calcification.

Light and electron microscopy of the human hepato-duodenal ligament: a morpho-functional study

The morpho-functional relationships between the hepato-duodenal ligament and the superior part of the duodenum are analysed. Twenty-four specimens were removed during necropsies of adults and prepared according to various mesoscopic, microscopic, and ultramicroscopical methods, i.e., whole-mounts, membrane preparations, thick and thin histological sections, and polarized light, scanning, and transmission electron microscopy were employed. The hepato-duodenal ligament is formed by longitudinally elongated, type I collagen fiber bundles which are interlinked by more delicate bundles of type III collagen fibers. Longitudinally disposed elastic fibers are the principal component of the elastic fiber system of the ligament. These are in continuity with the elaunin and oxytalan fibers which are intermingled with the muscle cells of the vessels and duodenal wall, and fat cells of the ligament. Part of the muscle bundles of the external, longitudinal, muscle layer of the duodenum is anchored in the adventitial and subserosal collagen and elastic fiber framework of the organ while part inserts directly into the fibrous framework of the ligament. The fibrous system of the ligament is continuous with that of the subserosa and adventitia of the duodenum.

Fibrillin-1 and fibrillin-2 show temporal and tissue-specific regulation of expression in developing elastic tissues

The recent characterization of multiple fibrillin genes raises the question of whether each of the fibrillin proteins is a component of elastic fiber microfibrils and whether their expression during development of elastic tissues is consistent with a function associated with elastogenesis. To address these possibilities, the expression of fibrillin-1 and fibrillin-2 was compared with expression of MAGP and tropoelastin in two elastogenic tissues that undergo different developmental programs. For both fibrillins, the greatest increase in expression occurred during the last half of fetal development when elastin production is highest. In fetal bovine nuchal ligament, mRNA levels for fibrillin-1 and fibrillin-2 increased approximately threefold during this period, whereas tropoelastin increased 20-fold. Although the relative increase in expression of both fibrillins was equivalent, the basal level of fibrillin-1 expression was greater than fibrillin-2. In developing bovine aorta, fibrillin mRNA levels again paralleled tropoelastin expression although, compared to ligament, elastin synthesis began at an earlier fetal age in this tissue. Furthermore, the relative increase in aortic fibrillin-2 expression was greater than that for fibrillin-1 and the ratio of fibrillin-2 to fibrillin-1 was higher than in the ligament. In contrast to the fibrillins, MAGP expression in nuchal ligament and aorta remained at a constant high level throughout the fetal period. Indirect immunofluorescent staining and immunoelectron microscopy localized both fibrillins as well as MAGP to elastic fiber microfibrils in these developing tissues. The coordinate upregulation of fibrillin-1 and fibrillin-2 expression with the onset of tropoelastin production is consistent with a role in elastic fiber assembly. Our findings also suggest temporal and tissue-specific regulation for the fibrillins during development.

Mechanical connections between elastin and collagen

The ligament supporting the leading edge of birds' wings is a connective tissue structure with unusual morphologic and elastic features. Its center section is made of a highly extensible composite of elastin and collagen fibers and its two end sections of nearly inextensible pure collagen; these are joined end-to-end in short interdigitating junctions. Substantial forces are transmitted through the junctions showing that collagen and elastin are mechanically connected. The junctions and elastic segment are sufficiently strong that when the intact ligament is maximally strained, the point of failure is commonly in the collagenous segments or their attachments to the tissues of origin or insertion. Here we outline the morphology and describe static force-length properties of this ligament.

A scanning electron microscopic and immunohistochemical study of spinal ligaments innervation

Neural elements in the interspinous and longitudinal ligaments of the human lumbar spine were investigated by means of scanning electron microscopy (SEM) and immunohistochemistry for neurofilament protein (NFP). The SEM results agree with our previous findings of nerve fibers and localized them in the superficial layers of the ligaments as well as in the deeper ligamentous substance. The immunohistochemical staining for NFP has clearly confirmed the presence of sensory nerve endings. Most of the nerve fibers terminated as simple free endings which are thought to be nociceptors.

Immunohistochemical localization of beta 1-integrins in anterior cruciate and medial collateral ligaments of human and rabbit

The integrins are a family of adhesion-mediating cell surface receptors that play critical roles in cell-extracellular matrix interactions and have been shown to be important in the healing response in several tissues. We have studied integrin expression in normal human and rabbit anterior cruciate (ACL) and medial collateral (MCL) ligaments of the knee as a preamble to studies of beta 1-integrin expression in healing ligaments. Histologic sections of human and rabbit ACL and MCL were probed for integrin expression utilizing integrin-specific monoclonal antibodies (mAbs) followed by immunoperoxidase detection. Staining of human specimens with mAbs revealed the presence of beta 1-, alpha 1-, and alpha 5-integrin chains on the tissue fibroblasts of both ACL and MCL, while staining of rabbit specimens with rabbit integrin-reactive monoclonals revealed the presence of beta 1- and alpha 5-integrin on these ligaments. Equivalent amounts of the integrins studied were present on normal ACL and MCL. We conclude that the rabbit is an appropriate model for analyzing the expression and functional role of integrins in ligament wound healing.

Characterization of the intrinsic properties of the anterior cruciate and medial collateral ligament cells: an in vitro cell culture study

The poor healing abilities of the anterior cruciate ligament (ACL) in contrast to those of the medial collateral ligament (MCL) are well known. Different intrinsic properties of the constituent cells of these ligaments have been proposed to be one of the factors in the differential repair mechanisms. To examine this hypothesis, we have established primary cell lines of ACL and MCL from the tissue explants of approximately similar dimensions and have studied their behavior in vitro. The outgrowth of cells from ACL explants was slower than from MCL explants, as shown by the size of the surrounding clusters of cells. Both ACL and MCL cultures exhibited typical fibroblastic morphology. No significant differences were observed in either attachment or growth of cells from the attached explants derived from various segments of ACL and MCL. Growth curves of ACL and MCL cultures at both passage numbers 2 and 6 showed a slower rate of proliferation of ACL cells than MCL cells (p less than 0.005). DNA synthesis measured in terms of [3H]thymidine incorporation (CPM/10(3) cells) of both log phase (ACL = 607.5 +/- 5.4 vs. MCL = 1356.4 +/- 11.3) and confluent (ACL = 83.0 +/- 3.6 vs. MCL = 189.8 +/- 5.4) cultures, supports the conclusion that differential proliferation rates of these cells exist in culture. FITC-phalloidin staining (for actin) of later passage cultures (P3-P5) showed a spread-out appearance of ACL cells and an elongated appearance of MCL cells. Relatively more stress fibers were seen within ACL cells. SDS-PAGE and Western blot analysis of cellular proteins revealed higher actin (43 kDa) content in ACL cells than in MCL cells. In vitro wound closure assay was performed by creating a uniform wound of 0.6 mm width in the confluent layer of ACL and MCL cultures. By 48 h postwounding, cell-free zones created in ACL cultures were occupied partially by single cells in a nonconfluent fashion. In contrast, the wounded zone in the MCL cultures was almost completely covered by the cells. Results presented in this report demonstrate a lower proliferation and migration potential of ACL cells in comparison with MCL cells. These differences in intrinsic properties of ACL and MCL cells that were observed in vitro might contribute to the differential healing potentials of these ligaments in vivo.

An immunoelectron microscope study of the aged human lens capsule

The distribution of types I-IV collagen and laminin was studied in seven aged human lens capsules using the immunogold EM technique on LR White embedded tissue. Samples were taken from the anterior, equatorial and posterior regions. Labelling for type II collagen was not observed. Type IV collagen was evenly distributed throughout the thickness of the capsule but was absent from the zonules. However, an unexpected finding was strong labelling for types I and III collagen, again evenly distributed throughout the capsule. The presence of type III collagen makes the lens capsule unique among ocular basement membranes. Laminin was present in linear densities, zonular lamellae and zonular fibres, suggesting that linear densities are an integral part of the zonular apparatus.

Coffin-Lowry syndrome associated with calcium pyrophosphate crystal deposition in the ligamenta flava

Clinical and ultrastructural study of four cases of Coffin-Lowry syndrome (CLS), a heritable disorder with peculiar facies, stooped posture, vertebral changes, and mental retardation, is reported. Three of the four cases had myelopathy caused by calcification of the ligamenta flava in early adulthood. These patients demonstrated that CLS is a calcium pyrophosphate dihydrate crystal deposition disease, and it is postulated that a metabolic abnormality in collagen and in proteoglycans are responsible for some aspects of CLS.

Innervation of spinal ligaments of patients with disc herniation. An immunohistochemical study

The purpose of this work was to demonstrate whether neural elements are present in the spinal ligaments removed from patients with disc herniation. The tissue samples were stained by an immunohistochemical technique using antibodies to neurofilament protein (NFP) subunits as specific markers. Numerous NFP-immunoreactive nerve fibers and free nerve endings were demonstrated within the ligamentous structures. These findings were discussed relative to the low-back pain of disc herniated patients.

Ultrastructural differences between the cells of the medical collateral and the anterior cruciate ligaments

The anterior cruciate ligament (ACL) does not heal after an interstitial tear, in contrast to the medial collateral ligament (MCL), whose interstitial tears heal readily. The light microscopic and ultrastructural differences between the cells of the two ligaments were studied in rabbit knees to observe the healing characteristics of the two ligaments. A rabbit knee was chosen because the rabbit ACL, like that of humans, does not heal following interstitial injury. The cells populating the MCL have the characteristics of fibroblasts. The cells of the ACL resemble fibrocartilage cells. The phenotypic differences in the cells of the two ligaments may be important determinants of the differences in healing.

Congenital ectopia lentis and secondary buphthalmos likely occurring as an autosomal recessive trait

A family from Turkey with congenital ectopia lentis, likely occurring as an autosomal recessive trait, is presented. No systemic disorders such as homocysteinuria, Marfan's or Weill-Marchesani's syndromes were found in any of the patients. However, all patients except one were less than 2 years old when first examined so that lens luxation must have happened very early in life. Besides almost total lack of zonular threads the patients presented anomalies of ocular dimensions with increased corneal diameters and axial lengths, and in several cases glaucomatous distension of the optic discs could also be found. A possible explanation for these buphthalmic changes and their relation to lens luxation taking place very early in life is proposed. The importance of early diagnosis and treatment is discussed.

Ultrastructure of the bovine nuchal ligament

Nuchal ligament is composed almost exclusively of elastic fibres and collagen fibrils, interwoven very closely and lying parallel to the main ligament axis. Elastic fibres are very large, straight and roughly cylindrical; the collagenous matrix consists of septa of diminishing size forming a 3-dimensional matrix that envelops fibre bundles as well as individual elastic fibres. In all areas examined, collagen fibrils are of very uniform size and, on replicas, they reveal a spiral subfibrillar arrangement with an inclination angle of 17 degrees. Collagen fibrils appear to adhere to the elastic fibres very closely, conforming to their irregular shape. Sometimes they impinge directly upon the elastic fibres, while in other cases a space is visible between collagen fibrils and elastic fibres that contains a rich fabric of intermediate filaments. The collagen-elastin complex of the ligamentum nuchae may be considered a fibre-reinforced composite material comprising tough fibres immersed in an amorphous elastic matrix. Its mechanical behaviour is the result of the combined properties of its components and their interactions.

Development of actin polygonal arrays in rabbit lens epithelial cells

In searching for a clue to the role of actin filament bundles organized into polygonal arrays, or geodomes, in lens epithelial cells, we examined several physical events occurring in the young rabbit lens which may initiate their formation. We used NZW rabbits between the ages of 24 days gestation and 50 days postnatal. Data were obtained from TEM, SEM and fluorescence microscopy. Parameters measured were lens weights, apical surface areas of cells in epithelial whole mounts, epithelial cell thickness, and timing of eyelid opening, breakdown of the tunica vasculosa lentis (TVL) and formation of the ciliary zonules; these findings were correlated with the first signs of development of the arrays. Polygonal arrays formed slowly beginning at one to two days after birth, and with advancing time these thickened and made more numerous connections with the lateral plasma membranes. Development of the arrays was not correlated with onset of vision or disappearance of the TVL or a sudden increase in cell area, since these events occur postnatally at about 9-10 days, nor with the development of zonular fibers since these are already in place at 24 days of gestation. Only lens weights showed a dramatic increase between 24 days gestation and birth. It is surmised that the expanding lens mass may be involved in some way in signaling the organization of actin filaments into geodomes.