ELECTRON MICROSCOPY OF THE HUMAN SYNOVIAL MEMBRANE

The structure of the lining cells at the surface of the synovial membrane facing the joint cavity has been studied by electron microscopy. The long cytoplasmic processes of these cells appear to be oriented toward the surface of the membrane, where they overlap and intertwine. The matrix of the lining cells contains dense material but no fibers with the periodicity of collagen. The lining cells are divided into two cell types or states of activity on the basis of their cytoplasmic contents. Type A is more numerous and contains a prominent Golgi apparatus, numerous vacuoles (0.4 to 1.5 microns in diameter) containing varying amounts of a dense granular material, many filopodia, mitochondria, intracellular fibrils, and micropinocytotic-like vesicles. Type B contains large amounts of ergastoplasm with fewer large vacuoles, micropinocytotic-like vesicles, and mitochondria. The probable functions of these cells are discussed in the light of current knowledge of the metabolism and function of the synovial membrane.     

Ultrastructural characteristics of the human synoviocytes

The purpose of this study was to identify, by the scanning electron microscopy, the behaviour of the different cell types in the normal human synovial intima, in order to obtain information useful for interpreting pathological changes in the synovium. Our observations revealed that, in numerous areas of the synovial membrane (adipose or fibrous type), the synoviocytes were dispersed and the intercellular matrix, covered only by the cytoplasmic processes of cells deeply located, was in direct contact with the joint cavity. In the areolar type of the synovium the synoviocytes were more numerous; they tended to concentrate to give the appearance of a continuous tissue; but between the cells very large intercellular spaces were usually present. In this latter membrane type we identified the two main cellular types of the synoviocytes: A and B. B-synoviocytes were the predominant cell type of the synovium. These cells were characterized by long cytoplasmic processes, perpendicularly directed towards the joint cavity. Both the cellular body and the cytoplasmic processes were covered by small blebs and vesicles of various size. The A-synoviocytes were a small minority, rarely dispersed between the B-synoviocytes. They were characterized by numerous membrane infoldings which delimited intracellular canaliculi of various depth. Our ultrastructural observations demonstrated that, in normal conditions, the B-synoviocyte must be considered as a constitutive element which characterized the synovial intima, responsible for the specific structure of the interstitial tissue and for the regulation of the composition of the synovial fluid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Absorption of intraarticularly injected horseradish peroxidase in synoviocytes of rat synovial membrane: an ultrastructural-cytochemical study

The ability of type A and type S synoviocytes to absorb horseradish peroxidase (HRP) and the intracellular fate of this tracer were studied by electron microscopic cytochemistry. Different concentrations of HRP (0.1-5 mg/ml) were injected into the left knee joint of rats and at intervals ranging from 1 min to 24 hr after injection the synovial membrane was fixed and incubated for HRP. Type A synoviocytes showed a striking ability to absorb HRP at low concentrations. At 1 and 5 min after injection reaction product was localized in coated pits and coated vesicles (110 nm) as well as in smooth-walled vesicles, vacuoles, and tubules. At 15 min to 4 hr postinjection the lysosomal system became increasingly loaded with reaction product. At 24 hr after injection reaction product had disappeared. At higher concentrations of HRP similar observations were made in the A cells, but reaction product was still apparent in lysosomes at 24 hr postinjection. With respect to type S synoviocytes no reaction product was detected within these cells at any time interval after injection of low concentrations of HRP. However, at 5 min after injection of higher concentrations of HRP reaction product was localized in smooth vesicles and vacuoles mainly restricted to the large cytoplasmic processes facing the joint cavity. At 30 min to 4 hr postinjection the lysosomal system became progressively more loaded with HRP reaction product. At 24 hr after injection reaction product still remained in the lysosomal system. The present findings that type A and type S synoviocytes showed major differences with respect to endocytic capacity and cellular structures involved in absorption of HRP support the interpretation that the A and S cells represent two distinct types of cells and further suggest that endocytosis in these two types of cells serve different functions.     

Cytological observations of the ovarian epithelium in mammals during the reproductive cycle

We have studied the ovarian epithelium at various stages of the reproductive cycle in a number of mammalian species utilizing light microscopy, scanning microscopy, the freeze-fracture technique, transmission microscopy and by employing specialized tracers that use lanthanum and horseradish peroxidase. We found that the epithelial cells are joined by incomplete tight junctions, gap junctions, and desmosomes. The cytoplasmic matrix contains a large irregularly shaped nucleus, few microtubules, microfilaments, mitochondria, endoplasmic reticulum and a host of coated and non-coated vesicles of varying diameters. The saccules comprising the large Golgi complex and its companion vesicles are associated with a basal body-centriole complex: some of these saccules and affiliated vesicles are acid phosphatase positive. Surface modifications of ovarian epithelial cells include numerous microvilli, some of which have a bulbous tip, and plications of the lateral plasma membrane which are thought to accommodate volume changes of the ovary during follicular development. Many coated and non-coated endocytotic caveolae were found on these cells, particularly in the basal area. These caveolae internalized exogeneously administered horseradish peroxidase. We view the marked endocytotic activity as an efficient transport mechanism for partially removing substances from the interstitium of the ovary and the peritoneum.     

Morphology of the bovine epididymis

The epididymis of the bull was divided into six regions, and morphological differences between regions were studied. The epithelium of all regions contained four cell types: principal and basal epithelial cells, and intraepithelial lymphocytes and macrophages. The epithelium of regions II-V also contained a few apical cells. Principal cells of all regions possessed an endocytotic apparatus including stereocilia underlain by canaliculi, coated vesicles, and subapical vacuoles (up to 1 micron in diameter); however, large vacuoles with a flocculent content and multivesicular bodies (up to 5 microns in diameter) were most numerous in regions II, III, and IV. The unique features of principal cells of region I were the presence of well-developed Golgi bodies, few lipid droplets, and whorls of smooth endoplasmic reticulum in the supranuclear cytoplasm. Numerous mitochondria, distended cisternae of rough endoplasmic reticulum, and dense granules characterized the infranuclear cytoplasm of the principal cells of regions II-VI; however, these features were more developed in region V. Apical cells were characterized by the apical location of the nucleus, many mitochondria in the apical cytoplasm, and few microvilli at the luminal border. Basal cells with few cytoplasmic lipid droplets were present throughout the length of the epididymis but appeared more numerous in region V. Intraepithelial lymphocytes were present at all levels of the epithelium but were never seen in the lumen. Intraepithelial macrophages containing heterogeneous granules, eccentric nuclei, and pseudopods were invariably seen near the basal area of the epithelium in all regions. These observations are discussed in an effort to define the role of each cell type in the epididymal epithelium.     

Fine structure of the lysosomes in the two types of synoviocytes of normal rat synovial membrane

Summary The lysosomal system of the two types of synoviocytes (A and S) from the knee joint of normal rat synovial membrane was studied by electron-microscopic acid phosphatase cytochemistry. In random sections of the synovial intima lysosomes were more often encountered in the A-cell profiles than in the S-cell profiles. Characteristically, type-A synoviocytes showed many large and medium-sized lysosomes the cytochemical appearance of which varied considerably. No acid phosphatase activity was detectable in the cisternae of the Golgi apparatus or in the Golgi vesicles. In type-S synoviocytes the lysosomes were smaller, and more uniform in cytochemical appearance. Heavy deposits of acid phosphatase reaction product were constantly demonstrated in cisternae of the Golgi apparatus as well as in smooth-walled Golgi vesicles in type-S cells. The findings that type-A and type-S synoviocytes show distinctly different organization of the lysosomal system indicate that the roles of the lysosomes in these two types of cells may be different.     

Ultrastructure of langur monkey epididymidis prior to and following vasectomy and vasovasostomy.

The ultrastructural changes in langur monkey epididymis prior to and following vasectomy or vasovasostomy were studied. The epididymal epithelium of the intact langur monkey was found to consist mainly of principal cells and basal cells and frequently apical or mitochondria rich cells were found. Besides these cells intraepithelial lymphocytes were also a consistent feature of the epididymal epithelium. Principal cells identified by means of the tuft of the stereocilia on their apical surface, bear well developed Golgi bodies, endoplasmic reticulum, vesicles, vacuoles and multivesicular bodies. This suggests their active involvement in absorption and secretion. Basal cells present at the base of the lamina bear a few cellular organelles and strong interdigitations with the adjacent cells. Apical or mitochondria rich cells were characterized by clusters of mitochondria in the apical region of the cell and few microvilli on their apical surface. Lymphocytes with a large nucleus and a pale rim of cytoplasm were also found at the base of the epithelium. Secretory and absorptive functions of principal cells of the epididymal epithelium were found to be increased after vasectomy, as indicated by bulging of the apical portion of the principal cells and membrane bound structure in the lumen. An extensive increase in the number of lysosomes, vesicles and vacuoles was also observed. An increase in the number of macrophages with spermatozoa remnants in the lumen of epididymis suggests that the principal mechanism for spermatozoa disposal following vasectomy is intraluminal endocytosis by macrophages. Changes following vasectomy persisted in vasovasostomized animals even after 12 months of recanalization, which may contribute to the failure of functional reanastomosis.     

FINE STRUCTURE OF NERVE FIBERS AND GROWTH CONES OF ISOLATED SYMPATHETIC NEURONS IN CULTURE

The leading tips of elongating nerve fibers are enlarged into "growth cones" which are seen in tissue culture to continually undergo changes in conformation and to foster numerous transitory slender extensions (filopodia) and/or a veillike ruffling sheet. After explantation of 1-day-old rat superior cervical ganglia (as pieces or as individual neurons), nerve fibers and tips were photographed during growth and through the initial stages of aldehyde fixation and then relocated after embedding in plastic. Electron microscopy of serially sectioned tips revealed the following. The moving parts of the cone, the peripheral flange and filopodia, contained a distinctive apparently filamentous feltwork from which all organelles except membranous structures were excluded; microtubules were notably absent from these areas. The cone interior contained varied forms of agranular endoplasmic reticulum, vacuoles, vesicles, coated vesicles, mitochondria, microtubules, and occasional neurofilaments and polysomes. Dense-cored vesicles and lysosomal structures were also present and appeared to be formed locally, at least in part from reticulum. The possible roles of the various forms of agranular membranous components are discussed and it is suggested that structures involved in both the assembly and degradation of membrane are present in the cone. The content of these growing tips resembles that in sensory neuron growth cones studied by others.     

The fine structure of the nephronic tubule of the mudskipper Periophthalmus koelreuteri (Pallas)

Ultrastructural examination of the head kidney of Periophthalmus koelreuteri (Pallas) (Teleostei, Gobiidae) revealed that the nephronic tubule cells are bound by tight junctions and desmosomes with little intercellular space. The first proximal segment (PI) consists of low columnar cells with well developed brush borders, indented nuclei, and numerous apical endocytic vesicles and lysosomes. A second cell type possessing clusters of apical cilia and lacking brush border and lysosomes is occasionally found between PI cells. The second proximal segment (PII) is formed of high columnar cells with brush border, regular spherical nuclei and numerous mitochondria located between well developed infoldings of the basal membrane. Single ciliary structures protrude into the lumen from PI and PII cells. The distal segment is lined by low columnar epithelium with few microvilli, regular spherical nuclei, numerous scattered mitochondria, and microbodies. The collecting tubule cells are cuboidal with few euchromatic nuclei, some mitochondria, and secondary lysosomes.     

Study on the origin of apical tubules in ileal absorptive cells of suckling rats using concanavalin-A as a membrane-bound tracer

Summary The ileal absorptive cells of suckling rats exhibit high levels of endocytic activity being engaged in nonselective uptake of macromolecules from the intestinal lumen. The apical cytoplasm usually contains an extensive network of small, membrane-limited tubules (apical tubules: AT), in addition to newly formed endocytic vesicles and large endocytic vacuoles. To determine whether the AT are directly involved in the endocytic process by carrying the tracer into the cell, we have analysed movements of the apical cell membrane of the ileal absorptive cells by using a membrane-bound tracer (horseradish peroxidase-labelled cancanavalin-A: Con-A HRP). The ileal absorptive cells were exposed in vitro to Con-A HRP for 10 min at 4° C, incubated for different times in Con-A free medium at 37° C, and prepared for electron microscopy. After 1 min incubation at 37° C, invaginations of the apical cell membrane, including coated pits, and endocytic vesicles were labelled with HRP-reaction product, whereas the AT and large endocytic vacuoles were negative. After 2.5 min, almost all the large endocytic vacuoles were labelled with reaction product, which was seen in their vacuolar lumen and along the luminal surface of their limiting membrane. A few AT with reaction product were seen in the apical cytoplasm; they were in frequent connection with the reaction-positive large endocytic vacuoles. With increasing incubation time, the number of the labelled AT increased. Thus, after 15 min at 37° C, the apical cytoplasm was fully occupied by the reaction-positive AT. The ends of these AT were often continuous with small spherical coated vesicles. No reaction product was detected in the Golgi complex at any time after incubation. These observations indicate that the AT located in the apical cytoplasm probably originate by budding off from the large endocytic vacuoles, rather than being involved in the process of endocytosis.     

蒙古黄鼠（Citellus dauricus）松果腺的超微结构观察

The distal part of pineal gland of the Mongolian ground squirrel was ultrastructurally studied. The gland was composed of low electron-dense parenchymal cells, among which glial cells, pigment cells, blood vessels and neural elements were occasionally interspersed. The pinealocytes contained numerous mitochondria, lysosomes, microtubules, microfilaments, Golgi apparatus and free ribosomes, as well as less prominent profiles of rough- and smooth-surfaced endoplasmic reticula and some cilia, centrioles, synaptic ribbons and few subsurface cisterns. Some pinealocytes were vacuolated. The content of the vacuoles released into the extracellular space by exocytosis could be observed. The gap junctions between pinealocytes were also observed. Of particular interest was that many mitochondria "fused together" and formed gap junction-like structure in about five percent pinealocytes. The pigment cell has a amorphous nucleus which contains many aggregated chromatin, its cell membrane has a few microvilli projecting into a central lumen, these features may indicated that this kind of cell differs either from the pinealocyte or astrocyte. There are axo-axonic synapses or axo-dendritic synapses between neuron processes or between neuron processes and pinealocytes.     

The vas deferens of the spider crab,Libinia emarginata

Sperm enter the anterior vas deferens individually in the spider crab male. There they become surrounded by secretion products from the cells of the vas deferens, and are compartmentalized into spermatophores of varying size. The anterior vas deferens can be divided into three regions. The epithelium of the anterior vas deferens varies regionally from low to high columnar. The cytoplasm contains vast arrays of rough endoplasmic reticulum and Golgi complexes but few mitochondria. Intercellular spaces contain septate junctions, gap junctions and vesicles. Once the spermatophores have been formed in the anterior vas deferens, they are moved posteriorly to the middle vas deferens where they are stored and surrounded by seminal fluids. The epithelial cells of the middle vas deferens contain large amounts of rough endoplasmic reticulum and Golgi complexes. Numerous micropinocytotic vesicles appear, forming at the cell surface and within the apical cytoplasm. Their suggested function is the resorption of secretion products of the anterior vas deferens which initiated compartmentalization of the spermatozoa into spermatophores. The posterior vas deferens functions primarily as a storage center for spermatophores until they are released at the time of copulation. Seminal fluid surrounding the spermatophores is produced in this region as well as in the middle vas deferens. The cells of this region contain vast arrays of vesicular rough endoplasmic reticulum and Golgi complexes. The cells are multinucleate. Microtubules are numerous throughout the length of the cells and appear to insert on the plasma membrane.     

Unique localization of protein gene product 9.5 in type B synoviocytes in the joints of the horse.

Fibroblast-like (Type B) synoviocytes are cells in the synovial membrane that are responsible for production of both synovial fluid and the extracellular matrix in the synovial intima. Immunostaining of the horse synovial membrane for protein gene product (PGP) 9.5, which is a neuron-specific ubiquitin C-terminal hydrolase, demonstrated selective localization of the immunoreactivity in a synoviocyte population different from acid phosphatase-positive Type A synoviocytes. The immunoreactive cells were lined up in the synovial intima and extended dendritic processes towards the joint cavity to form a dense plexus on the surface. Electron microscopic examination clearly identified the PGP 9.5-immunoreactive cells as Type B synoviocytes characterized by developed rough endoplasmic reticulum and free ribosomes. Immunoreactivity for PGP 9.5 was diffusely distributed throughout the cytoplasm, including the tips of fine processes. Western and Northern blot analyses could not distinguish the corresponding protein and mRNA obtained from the brain and synovial membrane. The existence of the neuron-specific PGP 9.5 in Type B synoviocytes suggests a common mechanism regulating the protein metabolism between neurons and synoviocytes, and also provides a new cytochemical marker for identification of the cells.     

Fine structure of spermatogonia and primary spermatocytes in rabbits

Summary The fine structure of rabbit Spermatogonia and primary spermatocytes in meiotic prophase has been studied with different methods of preparation, including a technique for acid phosphatase activity. The spermatogonial cytoplasm is rich in free ribosomes and containes moderate amounts of vesicular, smooth-surfaced endoplasmic reticulum and mitochondria, a simple Golgi-apparatus, some micropinocytotic vesicles, and occasional multivesicular bodies, vacuoles and dense bodies with acid phosphatase activity. The large type A Spermatogonia have a prominent nucleolus and their mitochondria sometimes form clusters with a dense intermitochondrial substance, similar to that in spermatocytes.The nucleus and cytoplasm of primary spermatocytes increase markedly in volume and density during meiotic prophase. The Golgi apparatus enlarges and becomes more differentiated and finally forms small proacrosome granules. The endoplasmic reticulum produces numerous small, mainly smooth vesicles and might also be the source of a new organelle: numerous piles of narrow cisternae with opaque contents. These piles disintegrate late in prophase. The mitochondria become aggregated in clusters with dense intermitochondrial substance and their internal structure is characterized by highly dilated cristae and small particles, interpreted as mitochondrial ribosomes, in the matrix. The role of these structures in the formation of new mitochondria is discussed. The clusters of mitochondria finally disperse and their cores of dense intermitochondrial substance, possibly containing ribonucleoprotein, coalesce into a large chromatoid body similar to that in spermatids. Micropinocytosis and a few lysosomes occur in most spermatocytes. The pachytene nuclei show prominent nucleoli and a distinct sex vesicle without any synaptinemal complex.The importance for spermatid differentiation of some events taking place in the cytoplasm of primary spermatocytes is emphasized.Financial support for this study was received from the Swedish Medical Research Council.     

A freeze-fracture study of the papillary layer of the rat incisor enamel organ

After tooth enamel has been secreted it undergoes maturation or hardening. This process is mediated by ruffled and smooth-ended ameloblasts and associated papillary layer cells. The cells of the papillary layer are characterized by large numbers of mitochondria, coated vesicles, microvilli, and gap junctions. These features have led numerous investigators to speculate that the papillary layer is an ion-transporting epithelium. We have conducted freeze-fracture studies of the rat papillary layer in order to better characterize the surface features of these cells. The cell membranes of the papillary cells contained large numbers of intramembrane particles of various sizes ranging from 4 to 9 nm in diameter. Gap junctions were present at the cell surface and in the cytoplasm in the form of annular gap junctions. The intramembrane particles or connexons of both types of gap junctions were about 8-9 nm wide and were either packed randomly or present in the so-called 'crystallized' state. At the interface between smooth-ended ameloblasts and papillary layer cells, a well-developed zonula occludens was present along the basal surfaces of the ameloblasts and several large gap junctions were formed between the two cell types. The capillary network associated with the papillary layer was characterized by a thin endothelium containing large numbers of fenestrations.     

Fine structure of the parotid gland in the crest-tailed marsupial-rat (Dasyuroides byrnei).

The parotid gland of Dasyuroides byrnei was examined by light microscopy, and transmission and scanning electron microscopy. The acini were composed predominantly of seromucous cells with a few mucous cells. The seromucous cells were light or dark cells containing acidophilic spherical granules of moderate to high electron density and had well-developed cytoplasmic organelles-ordinary mitochondria and large mitochondria with tubular cristae, RER with vesicular or tubular elements, and Golgi apparatus with lamellae, vesicles and vacuoles. The mucous cells had basophilic amorphous granules of low electron density, like those of ordinary mucous cells. The intercalated ducts were composed of simple cuboidal light cells having a few electron-dense granules. The striated ducts consisted of tall columnar light cells containing numerous vesicles and mitochondria with tubular cristae, the same as found in acinar seromucous cells.     

The fine structure and histochemistry of the caecal epithelium of Calicotyle kröyeri (Monogenea: Monopisthocotylea)

The caecal epithelium of Calicotyle kröyeri consists of a single cell type which functions in the uptake and intracellular digestion of host epidermis and associated mucus. Each cell is columnar with a small basal nucleus and prominent nucleolus. Perinuclear cytoplasm contains narrow profiles of GER and mitochondria with numerous cristae. Golgi complexes are small and indistinct. Most of the cell is filled with vacuoles of heterogeneous content, the largest occupying the cell apex. There is in each cell an apical endocytotic complex comprising cell surface lamellae, apical vesicles and numerous tubular invaginations of the plasmalemma. The limiting membrane of all these components is structurally modified and bears a highly organized array of peg-like structures on its luminal surface. The complex is capable of ingesting particulate food material from the gut lumen for transfer, via vesicles, to the vacuoles for digestion. Most of the vacuoles represent the digestive elements of the cell and, histochemically, are reactive for protein, mucus and carboxylic esterases. Indigestible residues and lipid droplets accumulate in the large apical vacuole and are periodically released to the lumen by exocytosis. Small, undifferentiated caecal cells were occasionally observed in the epithelium, but their development has not been recorded.     

蒙古黄鼠(Citellus dauricus)松果腺的超微结构观察

蒙古黄鼠松果腺主要由低电子密度的松果腺细胞和少量的胶质细胞、含色素细胞、神经突起及血管等组成。松果腺细胞内含有大量的线粒体、溶酶体、微丝、高尔基器、游离核糖体及中等量的光面和粗面内质网。纤毛、中心粒、突触带和致密芯小泡很少。松果腺细胞之间及胶质细胞之间存在电突触。最新被观察到的是大约有5%松果腺细胞内的线粒体产生“融合”现象,形成类似电突触的结构。神经突起可形成轴—轴突触,轴—树突触,并与松果腺细胞形成突触。     

The blood-brain barrier in a reptile, Anolis carolinensis

An electron microscopic study was made of the ultrastructure and permeability of the capillaries in the cerebral hemispheres of the lizard, Anolis carolinensis. The brain of Anolis is vascularized by a loop-type pattern consisting exclusively of arteriovenous capillary loops. The ultrastructure of the endothelium and the arrangement of the various layers from the capillary lumen to the central nervous tissue is similar to that of mammals. The endothelial cells form a continuous layer around the lumen and are joined by tight interendothelial junctions. The basal lamina of the endothelium is also continuous and encloses pericyte processes. The cells of the nervous tissue rest directly on the basal lamina of the capillary and are separated from each other by a 200 Å space. Intravenously injected horseradish peroxidase (MW 40,000) and ferritin (MW 500,000) were used to study the permeability of the capillaries. The entry of horseradish peroxidase and ferritin into the intercellular spaces of the brain is restricted by the tightness of the interendothelial junctions. No vesicular transport of either tracer occurs; however, ferritin does enter the endothelial cells in vacuoles. No tracer molecules are present in the basal lamina, pericytes, or nervous tissue. The different responses of the endothelial cell to the tracers used in this study suggest that endocytotic activities of endothelial cells involve different processes. Vacuoles formed by marginal folds, vacuoles formed by endothelial surface projections or deep invaginations of the plasma membrane, 600–800 Å vesicles, and coated vesicles all seem to differ in the nature of the substances which they endocytose.     

Functional ultrastructure of the midgut of the fire ant Solenopsis saevissima Forel 1904 (Formicidae: Myrmicinae)

Solenopsis saevissima has a midgut composed of columnar, regenerative, and goblet cells. The midgut epithelium was covered by a basal lamina. Outside the basal lamina, layers of inner oblique, circular, and outer longitudinal muscles were present. Columnar cells showed a basal plasma membrane containing numerous folds, mitochondria, and the nucleus. Rough endoplasmic reticulum, Golgi bodies, membrane bounded vacuoles, and spherocrystals were found in this region. The apical plasma membrane was constituted by microvilli, which were above a region rich in mitochondria. Regenerative cells were found in groups lying by the basal lamina. Goblet cells were associated with an ion-transporting mechanism between the haemolymph and the midgut epithelium. These cells were lying by the midgut lumen and large microvilli were evident, but the cytoplasmic features were similar to the columnar cells.