Ultrastructure of the capillaries of nerve tissue transplants growing in the anterior chamber of the eye

Blood capillaries have been studied electron microscopically in the areas of grafts (rat embryonal hippocamp and septal cerebral parts transplanted to mature rats) containing mainly nervous, glial or connective tissue cells. Certain differences in the capillary wall structure have been revealed. In areas with a great concentration of nervous cells, the blood capillaries are characterized by a dense arrangement of cellular elements in their walls, a continuous layer of the glial end-feet, this is specific for the CNS capillaries providing the blood--brain barrier. In peripheral area of the grafts, where glial elements predominate, the capillaries have loose arrangement of the mural cellular elements, great endotheliocyte activity, thick connective tissue tunic, lack of a dense glial surrounding. These characteristics make dubious the statement whether these capillaries possess the blood--brain barrier function. In places where connective tissue cells make aggregates, the capillaries do not possess the barrier properties because of perforations and fenestrae in endothelium and interruptions of the basal membrane, absence of pericapillary glial elements. All types of the capillaries demonstrate certain signs of a high functional activity. Formation of the capillary structure depends on the surrounding tissue.     

Organization of the coelomic lining and a juxtaposed nerve plexus in the suckered tube feet of Parastichopus californicus (Echinodermata: Holothuroida)

The coelomic lining of the water-vascular canal in a suckered tube foot from the sea cucumber, Parastichopus californicus, is a pseudostratified myoepithelium consisting of flagellated adluminal cells and myofilament-bearing retractor cells. The bodies of adluminal cells flank the water-vascular canal and send basal processes between the underlying retractor cells to confront the podial connective tissue. Retractor cells have a contractile apparatus of unregistered thick and thin myofilaments. The contractile apparatus is confined to the medullary sarcoplasm and oriented parallel to the primary axis of a tube foot. The bodies and processes of retractor cells intermingle with the basal processes of adluminal cells at the basal lamina of the coelomic lining. A ganglionated nerve plexus in the podial connective tissue approximates the basal lamina. Neuronal connectives link the ganglia to one another and to the nerve plexus in deep sectors of the podial epidermis. External laminae enveloping the ganglia and connectives in the podial connective tissue are continuous with the basal lamina of the epidermis. The adventitial nerve plexus, since it merges with the epidermal nerve plexus, is a component of the ectoneural division of the echinoderm nervous system.     

Electron microscopy of the mucosal plexus of the rat colon.

The ultrastructure of neurons, glial cells and axons of the mucosal plexus of the rat colon descendens was studied. Serial semithin sections and a re-embedding technique were used in order to localize the ganglia. The ganglia are free of blood vessels and connective tissue. The ratio of neurons to glial cells is approximately 1. Ganglia and nerve strands are enclosed by a basement membrane, without a well-defined perineural connective tissue. The neurons show a structure similar to other enteric plexus. Synaptic contacts were observed frequently in the neuropil, where nerve endings and varicosities show a diverse outfit in vesicles. The glial cells, which contain immunocytochemically detectable glial fibrillary protein, possess the same ultrastructural attributes in the intra- and extraganglionic localizations. In the nerves, axonic profiles and varicosities appear in close relation with glial cells or their processes. The distance between the nerves and their target cells, i.e. the enterocytes, is 0.5 microns or more with interposed basement membranes and fibroblasts.     

Scanning electron microscopy of the muscle coat of the guinea-pig small intestine

Summary We have studied the layers of the muscular coat of the guinea-pig small intestine after enzymatic and chemical removal of extracellular connective tissue. The cells of the longitudinal muscle layer are wider, have rougher surfaces, more finger-like processes and more complex terminations, but fewer intercellular junctions than cells in the circular muscle layer. A special layer of wide, flat cells with a dense innervation exists at the inner margin of the circular muscle layer, facing the submucosa. The ganglia of the myenteric and submucosal plexuses are covered by a smooth basal lamina, a delicate feltwork of collagen fibrils, and innumerable connective tissue cells. The neuronal and glial cell processes at the surface of ganglia form an interlocking mosaic, which is loosely packed in newborn and young animals, but becomes tightly packed in adults. The arrangement of glial cells becomes progressively looser along finer nerve bundles. Single varicose nerve fibres are rarely exposed, but multiaxonal bundles are common. Fibroblast-like cells of characteristic shape and orientation are found in the serosa; around nerve ganglia; in the intermuscular connective tissue layer and in the circular muscle, where they bridge nerve bundles and muscle cells; at the submucosal face of the special, flattened inner circular muscle layer; and in the submucosa. Some of these fibroblast like cells correspond to interstitial cells of Cajal. Other structures readily visualized by scanning electron microscopy are blood and lymphatic vessels and their periendothelial cells. The relationship of cellular elements to connective tissue was studied with three different preparative procedures: (1) freeze-cracked specimens of intact, undigested intestine; (2) stretch preparations of longitudinal muscle with adhering myenteric plexus; (3) sheets of submucosal collagen bundles from which all cellular elements had been removed by prolonged detergent extraction.     

Fine structure of the ependyma and intercellular junctions in the area postrema of the rat

Summary Ependymal cells and their junctional complexes in the area postrema of the rat were studied in detail by tracer experiments using horseradish peroxidase (HRP) and colloidal lanthanum and by freeze-etch techniques, in addition to routine electron microscopy. The ependyma of the area postrema is characterized as flattened cells possessing very few cilia, a moderate amount of microvilli, a well-developed Golgi apparatus and rough endoplasmic reticulum. Numerous vesicles or tubular formations with internal dense content were found to accumulate in the basal processes of ependymal cells; the basal process makes contact with the perivascular basal lamina. It is suggested that the dense material in the tubulovesicular formations is synthesized within the ependymal cell and discharged into the perivascular space. The apical junctions between adjacent ependymal cells display very close apposition, with a gap of 2–3 nm, but no fusion of adjacent plasma membranes; they thus represent a transitional form between the zonulae adhaerentes present in the ordinary mural ependyma and the zonulae occludentes in the choroidal epithelium. A direct intercommunication between the ventricular cerebrospinal fluid (CSF) and the blood vascular system indicates that a region exists lacking a blood-ventricular CSF barrier.     

Connective tissue in the perivascular spaces of subependymal capillaries of the spinal cord in the rabbit]

The normal structure of the subependymal capillaries and venules of the spinal cord was studied in rabbit. The endothelial cells of the capillaries and venules are surrounded by an irregularly formed perivascular space, about 0.5 to 3.3 micrometer wide, which is delimited by an endothelial and glial basal lamina. The space contains a framework of collagen fibers. A period-acid-bisulfit-aldehydthionine-method (Specht) permits to find the perivascular connective tissue lightmicroscopically, while they can be identified by electron microscopy. The significance of the perivascular connective tissue is open to discussion. Structural and functional problems have been reviewed in this context.     

The fine structure of the ganglia of the guinea-pig trachea

Summary The parasympathetic ganglia of the guinea-pig trachea have been investigated by scanning and transmission electron microscopy. They are covered by a continuous perineurium and connective tissue is found between the neural elements. Blood vessels inside the ganglia have continuous endothelia and are sometimes accompanied by pericytes and a sheath of perineurial cells. Individual neuronal cell bodies and large processes are almost completely covered by a thin layer of satellite cells, except for very small areas that directly face the basal lamina and connective tissue space. Nerve fibres are also completely and individually ensheathed by Schwann cell processes; naked fibres are not found. In some regions of the nerve cell body, there are complex interdigitations between short neuronal processes and satellite cells. Large differences in the size of neurons may indicate the presence of different neuronal populations. Nerve endings containing mainly small clear vesicles are the most common type, and these form synapses on dendrites, but some profiles have many large granular vesicles. These ganglia resemble other parasympathetic, sympathetic and sensory ganglia and not the enteric ganglia. However, an unusual feature of the cytoplasm of the satellite and Schwann cells is the abundance of 10 nm intermediate filaments.     

Ultrastructural and cytochemical studies on the connective tissue of chaetognaths

The hydroskeleton plays a central role in the architecture of the trunk of the Chaetognath. Its fibrous part is composed by a ‘basement membrane’ which separates the epithelial and nervous level from the locomotory muscle and other tissues which surround the general cavity. This structure corresponds to a dense connective tissue sheath; together with the aqueous phase of the general cavity it constitutes the main part of the hydroskeleton. The axes of the lateral and caudal fins are extensions of this connective tissue; they are rich in ground substance and contain several kinds of fibrils and granules.The ‘basement membrane’ is made of a network of densely packed parallel layers of collagen fibrils which form helices which wrap around the trunk. The collagen fibrils of this connective stratum are sandwiched between two basal lamina; they are embedded in a reduced extracellular matrix whose components are closely related to the architecture of the collagen fibrils. In the core of the fin, the ground substance is very abundant and classical cross-striated collagen fibrils are not to be found. A compact fibrillar transition zone is to be noted between the dense connective stratum surrounding the body and the hyaline axis of the fins. In this zone, no crossbanded collagen fibrils are to be seen.The hydroskeleton and the fins show variations within the phylum. They could be related to speciation, and the ancestral pathway of the phylum. Furthermore these variations are related to the general problem of the evolution of the extracellular matrices and collagen molecule itself.     

Topography, architecture and structure of the plexus submucosus internus (Meissner) of the porcine small intestine in scanning electron microscopy

Scanning electron microscopy of whole-mount preparations of the tela submucosa in the porcine small intestine, examined after trypsin digestion, fixation and HCl hydrolysis, visualized a clear differentiation of the submucosal plexuses, i.e., the plexus submucosus internus (Meissner) and the plexus submucosus externus (Schabadasch). The distinctive features refer to the topography, number, size and shape of the ganglia and the number and diameter of the nerve strands. The plexus of Meissner is closely apposed to the external surface of the lamina muscularis mucosae by the enveloping connective tissue and by connecting strands penetrating the lamina muscularis mucosae. Three distinctive subdivisions of connecting strands can be identified. Since the glial cells covering the ganglia and connecting strands have been preserved, neither individual neuronal cells nor axons can be observed.     

Fixed phagocytes in the freshwater snail Lymnaea stagnalis

Morphological and histochemical examination of the blood and connective tissue of the freshwater snail Lymnaea stagnalis injected with various types of foreign particulate materials has shown the existence of free as well as fixed phagocytic cells. The morphology of the fixed phagocytes is described, and the phagocytic system of the snail is compared with that of other molluscan species.     

Effect of thyrotropin releasing hormone on the accumulation of cAMP by parietal ganglia of a gastropod

1. We had previously shown that thyrotropin releasing hormone (TRH) can stimulate the in vitro accumulation of cAMP by the parietal ganglia of the pond snail Lymnaea emarginata (Grimm-J?rgensen, 1980). 2. The mechanism by which TRH affects cAMP metabolism in parietal ganglia was further studied. 3. The TRH-induced accumulation of cAMP is preceded by a lag period and is of long duration. 4. TRH does not stimulate basal or guanylylimidodiphosphate-stimulated adenylate cyclase activity and is unable to cause an increase in cAMP accumulation when the incubation is carried out in the presence of a phosphodiesterase inhibitor. 5. This finding is compatible with the hypothesis that TRH may cause an increase in cAMP accumulation by means of decreasing phosphodiesterase activity. 6. When the ganglia were incubated with 3H-TRH and the localization of the labeled TRH examined by autoradiographic techniques, reduced silver grains were present only over glial and connective tissue elements. 7. The observed effect of TRH on the cAMP metabolism in parietal ganglia may be due to its action on non-neuronal cells.     

Schwann cell-derived Desert hedgehog controls the development of peripheral nerve sheaths.

We show that Schwann cell-derived Desert hedgehog (Dhh) signals the formation of the connective tissue sheath around peripheral nerves. mRNAs for dhh and its receptor patched (ptc) are expressed in Schwann cells and perineural mesenchyme, respectively. In dhh-/- mice, epineurial collagen is reduced, while the perineurium is thin and disorganized, has patchy basal lamina, and fails to express connexin 43. Perineurial tight junctions are abnormal and allow the passage of proteins and neutrophils. In nerve fibroblasts, Dhh upregulates ptc and hedgehog-interacting protein (hip). These experiments reveal a novel developmental signaling pathway between glia and mesenchymal connective tissue and demonstrate its molecular identity in peripheral nerve. They also show that Schwann cell-derived signals can act as important regulators of nerve development.     

Association of substance-P-immunoreactive nerves with the murine olfactory mucosa

Location and distribution of nerve fibers immunoreactive to substance P were studied in the mouse olfactory mucosa. A moderately dense plexus of fibers is present at the interface of the olfactory epithelium and the connective tissue of the lamina propria. In addition, many immunoreactive nerve fibers are noted in close association with Bowman's glands and blood vessels in the lamina propria. However, such fibers were not observed in olfactory epithelium proper nor in the fila olfactoria. Substance-P-immunoreactivity is almost totally abolished by treatment of animals with capsaicin, an agent known to deplete substance P from primary sensory neurons. It is suggested that the substance-P-immunoreactive fibers are of sensory origin, with their perikarya most likely located in the trigeminal ganglia. Functionally, they might influence local blood flow and/or the secretion of Bowman's glands.     

Studies on the innervation of the endometrium

Summary The innervation of the endometrium of rabbit, rat, mink, mongoose and pig has been investigated electron microscopically. Large bundles of nerve fibers can be observed in the connective tissue spaces within the basal layer of the endometrium. Unmyelinated nerve fibers enter the lamina functionalis, terminal nerve fibers penetrate the basal lamina and make contact with the glandular and the cavum epithelial cells. The terminal axons contain abundant synaptic vesicles, dense core vesicles and mitochondria. To date, no specialized presynaptic or postsynaptic membranes have been found.Supported by the Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg (Grants Ku 210/5 and Be 524/4).Dedicated to Prof. Dr. Drs. h.c. Wolfgang Bargmann on his 70th birthday in friendship and admiration.     

Fine Structure of Subepithelial “Free” and Corpuscular Trigeminal Nerve Endings in Anterior Hard Palate of the Rat

Axonally transported protein labeled many trigeminal nerve endings in subepithelial regions of the anterior hard palate of the rat. Sensory endings were most numerous in the lamina propria near the tips of the palatal rugae where large connective tissue and epithelial papillae interdigitated. Two kinds of sensory ending were found there: “free” endings, and a variety of corpuscular endings. The “free” sensory endings consisted of bundles of unmyelinated axons separated from the connective tissue by relatively unspecialized Schwann cells covering part or all of their surface and a completely continuous basal lamina; they were commonly found running parallel to the epithelium or near corpuscular endings. The corpuscular sensory endings all had a specialized nerve form, specialized Schwann cells, and axonal fingers projecting into the corpuscular basal lamina or connective tissue. There were at least four distinct types of corpuscular ending: Ruffini-like endings were found among dense collagen bundles, and they had a flattened nerve ending with a flattened Schwann lamella on either side. Meissner endings had an ordered stack of flattened nerve terminals with flattened Schwann cells and much basal lamina within and around the corpuscle. Simple corpuscles were single nerve endings surrounded by several layers of concentric lamellar Schwann processes. Glomerular endings were found in lamina propria papillae or encircling epithelial papillae; they were a tangle of varied neural forms each of which had apposed flattened Schwann cells, and a layer of basal lamina of varied thickness. Fibroblasts often formed incomplete partitions around Meissner and simple corpuscles.

The axoplasm of all kinds of subepithelial sensory endings contained numerous mitochondria and vesicles, as well as occasional multivesicular bodies and lysosomes; the axoplasm of all endings was pale with few microtubules and neurofilaments. The specialized lamellar Schwann cells had much pinocytotic activity. Four kinds of junctions were found between the corpuscular sensory endings and the lamellar Schwann cells: (1) symmetric densities that resemble desmosomes; (2) asymmetric densities with either the neuronal or glial membrane more dense; (3) neural membrane densities adjacent to Schwann parallel inner and outer membrane densities; and (4) sites of apparent Schwann endocytosis associated with neural blebs. The “free” sensory endings only made occasional desmosome-like junctions with their Schwann cells.

These observations are discussed in relation to possible mechanosensory transduction mechanisms, with particular attention to axoplasmic structure, axonal fingers, and neural and nonneural cell associations.     

Electronmicroscopy of the buccal proper lamina in leukoplakia

The observations included the connective tissue laminae originating from samples of the buccal mucous membrane in leukoplakia. Following fixation and dehydration the materials were embedded in Epon 812, and the electronograms for the evaluation were obtained with the use of a Tesla BS 500 electron microscope. The macrophages were encountered close to the basal membrane in the proper lamina. The space between the basal cells and the macrophages was filled with the connective tissue matrix and numerous collagen fibres, as well as the fibroblast cells. Numerous mast cells, characterized by a specific activity, were noted. Additionally, the proper lamina contained few nerve fibres, usually nonmyelinated. The vascular bed was normal. The electronograms in leukoplakia revealed an active synthesis of the connective tissue matrix and collagen fibres. The marked activity of the mast cells was manifested by a high number of cells containing a relatively differentiated amount of granulation. This might be related to the chronic character of the disease. A significant activity of particular elements of the proper lamina, i.e. the cellular elements, collagen fibres and the connective tissue matrix appears to be characteristic of leukoplakia.     

Structure of the perineurium of the peripheral nervous system]

The structure of the perineurium in different parts of the peripheral nervous system of rats, rabbits and cats was studied by light-optical and electron microscopic methods. The structure of the perineurium in all the animals studied is sim8lar and consists of different number of the epithelial type layers of the perineural cells, with bundles of cooagnous fibres between them. The greatest anount of layers is found in the perineurium of the sensory and vegetative ganglia, their amount being less between the nerve trunks and bundles. Solitary sensory mielinated nerve fibres are surrounded with a perineural etui consisting of one or two cellular layers. The thickness of the perineural cells varies from 300 to 1500 A and only in the nucleus field it is equal to 1-2 mu. Every layer of the perineural cells is surrounded by a basal membrane. In their cytoplasm there are many pinocytic vesicles in addition to main organells. Between the perineural cells there exist close contacts. The internal layer of the perineurium is the place of origin of intraganglionic septa and in certain distance surrounds the vessels entering the ganglion. Ultrastructurally the perineural cells are similar to the endothelium of the vessels.     

Network organization of interstitial connective tissue cells in the human endolymphatic duct.

The human endolymphatic duct (ED) and sac of the inner ear have been suggested to control endolymph volume and pressure. However, the physiological mechanisms for these processes remain obscure. We investigated the organization of the periductal interstitial connective tissue cells and extracellular matrix (ECM) in four freshly fixed human EDs by transmission electron microscopy and by immunohistochemistry. The unique surgical material allowed a greatly improved structural and epitopic preservation of tissue. Periductal connective tissue cells formed frequent intercellular contacts and focally occurring electron-dense contacts to ECM structures, creating a complex tissue network. The connective tissue cells also formed contacts with the basal lamina of the ED epithelium and the bone matrix, connecting the ED with the surrounding bone of the vestibular aqueduct. The interstitial connective tissue cells were non-endothelial and non-smooth muscle fibroblastoid cells. We suggest that the ED tissue network forms a functional mechanical entity that takes part in the control of inner ear fluid pressure and endolymph resorption.     

Contamination Expérimentale In Vivo et In Vitro par Aggregata eberthi: Etude Ultrastructurale1

The mechanism of host invasion by Aggregata has been experimentally investigated both in vivo (in the crab), and in vitro (in mollusc cell cultures) and followed by electron microscopy. A few hours after the infesting meal, sporozoites escaped from sporocysts in the crab stomach: then they reached the small intestine. There, they pussed through the epithelium, making their way between the cells. Perforation of the thick basal lamina was induced by means of the elaboration of a dense product, probably an enzyme. Sporozoites stretched themselves passing through the basal lamina and entered the connective tissue surrounding the digestive tract. Damages inflicted on the host were minimal. In vitro, merozoites were able to enter cells from several molluscs by penetrating the cell's plasmalemma. A nucleolus appeared in the nuclei of intracellular merozoites.     

Melanogenesis in cultures of peripheral nervous tissue: I. The origin and prospective fate of cells giving rise to melanocytes

Chick embryo spinal ganglia, peripheral nerves, and connective tissue usually associated with ganglia were cultured separately using several combinations of media and substrata. Melanocytes appear in cultures of both ganglia and peripheral nerves. The only cell type common to both the ganglion and peripheral nerve that could account for the observed pigment cells was the population of small cells with intensely staining nuclei that normally associates closely with nerve cell bodies and fibers. These cells could be distinguished morphologically from fibroblastic cells, which originated in the connective tissue capsule and did not undergo melanogenesis. We conclude that these small cells are supportive (Schwann, satellite, and perineurial) cell precursors and are one source of melanocytes in cultured peripheral nervous tissue.