Vascular pathways in nonsinusal red pulp—an electron microscope study of the cat spleen

The red pulp of the cat spleen, including terminal segments of arterial capillaries, pulp venules, and the reticular meshwork, was studied by transmission electron microscopy. Splenic congestion and contraction were produced by barbiturate anesthetic and norepinephrine. Terminal segments of arterial capillaries were ampullary and flared. Blood escaped into surrounding pulp spaces through interendothelial gaps. Pulp venules originated as open-ended vessels in the reticular meshwork near trabeculae and drained into trabecular veins. Venule walls were thin and composed of squamous endothelial cells, a continuous basement membrane, and reticular cells. Venules in congested spleens had many mural apertures, but venules in contracted spleens had few. The interstices of the reticular meshwork in congested spleens contained large amounts of blood, which often was concentrated, many macrophages, lymphocytes, and plasma cells. Fewer blood cells and scant plasma were present in contracted spleens. The vascular arrangements are anatomically open. Blood takes pathways through the reticular meshwork from arterial terminations to pulp venules. Some pathways through the reticular meshwork probably function as closed vascular channels conveying rapidly flowing blood. Other pathways are functionally open and probably contain slowly moving blood that constitutes a reservoir of red cells. Macrophages formed associations with mature red cells and with reticulocytes. Mature red cells were attached to macrophages in a manner indicating erythrophagocytosis. Reticulocyte attachment had a different appearance and likely resulted in reticulocyte sequestration. Platelets bore pseudopodia which would impede their passage through irregular and cell-filled pulp spaces. The change in platelet shape probably is responsible for the formation of the splenic pool of platelets.     

Periarterial macrophage sheaths (Ellipsoids) in cat spleen—an electron microscope study

Periarterial macrophage sheaths (PAMS), a term we introduce to replace “ellipsoids,” surround arterial capillaries in the red pulp of the spleen and are major sites for clearance of blood-borne particles. PAMS and their arterial capillaries in cat spleens in various states of congestion and contraction were studied by transmission electron microscopy. Thorotrast, a colloidal suspension of thorium dioxide, was injected to label macrophages. A PAMS consisted of a fine meshwork of reticular cells and reticular fibers which held macrophages and formed a cylindrical sheath around an arterial capillary lying in its longitudinal axis. Some PAMS were spongy due to loosening of cell associations by plasma infiltration; others were tightly compressed. Blood cells were both free in the interstices of the PAMS and attached to macrophages. Reticular cells formed a closely applied but incomplete layer adventitial to the arterial capillary and extended branches which contributed to the meshwork. Small villous processes on the major branches of reticular cells approached each other, sometimes forming intercellular junctions, and fit into complementary indentations in the surfaces of macrophages and endothelial cells. Thin filaments within reticular cells filled the villous processes and formed a border beneath the plasmalemma; intermediate filaments ran through the centers of the branches. Reticular fibers lay between reticular cells. Basement membrane fabricated of the same material as reticular fibers lay between the endothelium and reticular cells. Macrophages contained Thorotrast and abundant debris of phagocytized cells and were joined by extensive interdigitation of micropseudopodia. Endothelial cells were long rods which lay parallel and were joined along their bases by interdigitating lateral processes. Intercellular junctions were present at some points, but at others lateral processes were everted to form open interendothelial slits through which blood cells could pass. Endothelial cells possessed great numbers of randomly oriented intermediate filaments and small patches of thin filaments scattered along the basal plasmalemma and in lateral processes. Thin filaments may function to attach cells to one another and to the basement membrane and may assist in closing interendothelial slits. We believe that the endothelium responds to changes in arterial blood pressure and blood flow. It stretches to allow dilatation and recoils, probably due to the intermediate filaments, squeezing blood cells through interendothelial slits.     

The nigrotectal projection in the cat: an electron microscope autoradiographic study

Recent evidence indicates that the nigrotectal tract plays an important role in regulating the premotor responses of cells in the in the intermediate gray layer of the superior colliculus. The purpose of the present study was to characterize the ultrastructure of nigrotectal terminals and of their postsynaptic targets in the intermediate gray layer. Nigrotectal terminals were identified in the electron microscope by labeling them autoradiographically, following injections of tritiated proline into the substantia nigra pars reticulata. The majority of nigrotectal terminals contain a high proportion of pleomorphic vesicles and form symmetrical synaptic contacts. Most of these terminals synapse with small dendritic profiles (2.00 micron +/- 0.83 SD), which may be the distal dendrites of neurons in the intermediate gray layer. Less than 10% of the labeled contacts are made with cell bodies or initial axonal segments.     

Adrenergic influence on bile secretion—an experimental study in the cat

The influence on bile secretion of electrical stimulation of the splanchnic nerves and arterial infusion of adrenergic agonists was studied in anaesthetized cats. The bile salt secretion was supported by a continuous intravenous infusion of sodium glycocholate. Electrical stimulation of the splanchnic nerves reduced the volume outflow of bile from 0.71 to 0.44 ml h^-1 kg^-1 body wt and raised the bile acid concentration in bile, while the bile salt secretion rate was not affected. This response was reduced but not blocked by pretreatment with phentolamine, an α-adrenergic blocker, at a dose that prevented the blood pressure response. Infusion of noradrenaline, a mainly α-adrenergic agonist, into the hepatic artery mimicked the response. Infusion of isoprenaline, a β-adrenergic agonist, also reduced the volume outflow of bile from the liver. The biliary clearances of mannitol and polyethylene glycol 900, both of which are suggested to reflect canalicular events, were reduced by stimulation of the splanchnic nerves and infusion of noradrenaline. It is concluded that stimulation of the α-adrenergic receptors reduces the bile acid-independent bile secretion. This reduction in bile flow induced by stimulation of the splanchnic nerves and infusion of noradrenaline is elicited mainly at the canalicular level.     

Specialized intercellular junctions in tumor cells—An electron microscope study of mouse sarcoma cells

Specialized intercellular junctions have been observed in 3-methylcholanthrene-induced mouse sarcomas. These junctions are of two morphologic types and appear to be focal in nature. The first type consists of an approximation of the plasma membranes of adjacent cells to within 200 Å of one another. In the junctional region the intercellular space and the adjacent cytoplasm are of increased density. The second type of junction is more complex, the intercellular space being of greater width and containing a dense central plaque. The intercellular space and the adjacent cytoplasm are of increased density. Such junctions may serve a role in structural support of the tumor mass.     

A study of the dipeptidylpeptidase IV activity in cat fungiform papillae: light and electron microscope histochemistry

The present paper describes histochemical study of the dipeptidylpeptidase IV activity in the nerve structures of cat fungiform papillae at the light and electron microscope levels. The dipeptidylpeptidase IV activity was found in blood vessels and nerve bundles entering the connective tissue stroma of fungiform papillae. The taste buds exhibited a moderate staining for the dipeptidylpeptidase IV activity. Ultracytochemical findings revealed this enzyme as membrane-bound in the endothelium of blood vessels, in plasma membrane of the Schwann cells at the axon-Schwann cell interface as well as in the taste bud cells. A possible function of the dipeptidylpeptidase IV activity in the peripheral nerve structures is discussed in view of the ability of this enzyme to cleave the substance P to the minor fragments with inherent physiological roles.     

Identification of axon terminals of the cerebello-olivary fibers in the cat: an electron microscope study using the anterograde horseradish peroxidase method

After injection of horseradish peroxidase (HRP) into the lateral cerebellar nucleus of the cat, axon terminals containing electron-dense HRP-granules were identified contralaterally within the principal olive. These terminals contained spherical synaptic vesicles, and made asymmetrical synaptic contacts with dendritic profiles of small or medium size.     

Atypical fibroxanthoma of skin: an electron microscope study.

The ultrastructure of two atypical fibroxanthomas of skin is described. Most of the tumour cells were elongate, and contained abundant rough endoplasmic reticulum, well developed Golgi zones, and numerous small vesicles and filaments, the latter sometimes being related to masses of electron-dense material near the plasma-lemma. Their nuclei often showed deep surface indentations. The appearances were similar to those found in the socalled myfibroblasts that occur in granulation tissue. Multinucleated giant cells and lipid-laden cells in the tumours appeared to be merely modified forms of the basic cells type.     

Morphology of human intracardiac nerves: an electron microscope study

Since many human heart diseases involve both the intrinsic cardiac neurons and nerves, their detailed normal ultrastructure was examined in material from autopsy cases without cardiac complications obtained no more than 8 h after death. Many intracardiac nerves were covered by epineurium, the thickness of which was related to nerve diameter. The perineurial sheath varied from nerve to nerve and, depending on nerve diameter, contained up to 12 layers of perineurial cells. The sheaths of the intracardiac nerves therefore become progressively attenuated during their course in the heart. The intraneural capillaries of the human heart differ from those in animals in possessing an increased number of endothelial cells. A proportion of the intraneural capillaries were fenestrated. The number of unmyelinated axons within unmyelinated nerve fibres was related to nerve diameter, thin cardiac nerves possessing fewer axons. The most distinctive feature was the presence of stacks of laminated Schwann cell processes unassociated with axons that were more frequent in older subjects. Most unmyelinated and myelinated nerve fibres showed normal ultrastructure, although a number of profiles displayed a variety of different axoplasmic contents. Collectively, the data provide baseline information on the normal structure of intracardiac nerves in healthy humans which may be useful for assessing the degree of nerve damage both in autonomic and sensory neuropathies in the human heart.     

Antigens in immunity: XVI. A light and electron microscope study of antigen localization in the rat spleen*

This paper describes the ultrastructural location of labelled antigens and carbon in the spleens of rats from 4 minutes to 5 days after injection. Particular attention was focused on the sites of deposition 4 minutes after intra-arterial injection of microgram quantities of ¹²⁵I-labelled Salmonella flagellar antigens, crayfish haemocyanin and BSA, using colloidal carbon for comparison. The combination of radioautography with both light and electron microscopy showed the importance of antigen binding by lymphocytes in the marginal zone of the spleen. Macrophage sequestration of antigens was not prominent in the spleen, although it occurred in the liver with the flagellar antigens and haemocyanin.

In the spleen marginal zone, avid antigen-binding cells were found in situ 4 minutes after the injection of labelled haemocyanin. These appear to be the counterpart in vivo of antigen-binding lymphocytes prepared in vitro. Such cells also occurred infrequently after the injection of labelled polymerized flagellin, but were not found with either BSA or carbon.

The apparent movement of flagellar antigen from the marginal zone to the white pulp between 1 and 2 hours after injection was seen to involve lymphocyte-associated antigen. The follicular antigen localization occurring from 1 day onwards after injection was on the dendritic reticular cells of germinal centres, as has been described in lymph nodes after subcutaneous injection.

Carbon particles were rapidly sequestered in macrophages of the spleen and liver, although some particles were found between cells in the marginal zone for as long as 2 hours after injection. By 2 and 5 days, however, all the carbon was in phagocytes, even in the white pulp. Differences between the localization of antigens and carbon were clear, even in the ultrastructural sites of their location in tingible body macrophages of germinal centres.

The unexpected emphasis of lymphocyte association with labelled antigens in the spleen marginal zone has allowed a revison of the mechanism previously proposed for the movement of antigens within the microenvironments of the spleen.

     

An electron microscope study of the perfusion-fixed spleen. II. Fine structure of the sinus lining cells with respect to filamentous structures in monkey spleens.

In the perfusion-fixed spleen of monkey (Macaca mulatta) were studied with the electron microscope the cytoplasmatic structures of the sinus lining cells. The particular interest find the contractile filaments in this cells, which are important for the cell contraction. The connections to the smooth endoplasmatic reticulum are very strong as in the muscle fiber or muscle cell.     

The retinotectal projections in the pigeon. an experimental optical and electron microscope study.

Optical and electron microscope studies have been made of the termination pattern of the retinotectal projection in the pigeon. The use of Golgi impregnation and orthograde transport of peroxidase concurred to show that: (i) the majority of retinotectal preterminal segments descend obliquely rather than radially through the superficial layers of the tectum opticum; (ii) terminals in Cajal's layers 2–3 and 7 arborize tangentially, terminals in layer 4 arborize diffusely in a loose way, and, in layer 5, terminal arborizations are arranged in radial columns in which terminal ramifications are tightly packed. Radioautographic labeling of the retinotectal terminals confirmed that they do not extend beyond layer 7. It demonstrated that the total thickness of the superficial tectum opticum tends to decrease from rostral to caudal, and that the density of retinotectal terminals is higher in the plexiform 3rd and 5th layers than in the 4th and 7th layers. Fink-Heimer staining of the terminal degeneration consecutive to an enucleation confirmed the results of radioautographic studies. It showed that the evolution of the silver impregnation differs from one layer to the next. This evolution is roughly parallel in the 3rd and 5th layers on the one hand, in the 4th and 7th layers on the other hand.The electron microscope study disclosed three successive stages of terminal degeneration over the whole projection area. They respectively present a dilatation of synaptic vesicles, a hyperplasia of the neurofibrillar system, and a darkening of the axoplasm. The three stages do not appear simultaneously in the 3rd and 5th layers and in the 4th and 7th layers. Comparison between the evolution of the terminal degeneration at the electron microscopic level and that of Fink-Heimer staining at the optical microscope level shows that the Fink-Heimer technique impregnates the earliest stage of degeneration (with vesicle dilatation), but not that with neurofibrillar hyperplasia.Following the resorption of retinotectal boutons, most of the postsynaptic differentiations disappear. However, some persist and become partially reoccupied by small terminals. The possible origin of these new synaptic relations is discussed.     

An electron microscopic study of the spleen of the rat in an acute myelogenous leukemia

The spleens of rats were studied by light and electron microscopy during the course of an acute myelogenous leukemia, with special reference to infiltration of leukemic myeloblasts in the spleens and to the correlation of leukemic cell infiltration with splenic hematopoiesis and splenomegaly. Leukemic myelo-blasts infiltrated the cordal space of the red pulp. Many of them appeared in groups. Even in spleens which were heavily infiltrated, leukemic myeloblasts did not penetrate the white pulp. Massive infiltration and proliferation of the leukemic myeloblasts in the red pulp resulted in splenomegaly. The spleen increased its he-matopoietic activity, while the medullary hematopoiesis diminished due to the invasion of leukemic myeloblasts in the bone marrow. Compensatory splenic hemato-poiesis occurred in most of the leukemic spleens, but diminished in spleens which were very heavily infiltrated with leukemic myeloblasts. Thus, the degree of splenomegaly and splenic hematopoiesis did not necessarily correspond to the percentage of leukemic myeloblasts in the bone marrow, but rather related to the number of leukemic myeloblasts present in the spleen. A possible role for the splenic sinus walls in promoting compensatory hematopoiesis in the spleen is discussed. A consistent association of type “C” virus particles with leukemic myeloblasts was observed.