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Notes: Summary The nonparenchymal portion of the liver of parasitic adult lampreys (Petromyzon marinus L.) consists of endothelial, Kupffer, fibroblast-like, fat-storing, and granulated cells. The fenestrae of endothelial cells are not organized into sieve plates but are of highly variable size and distribution. The dimension of large molccular size. Small numbers of Kupffer cells possess many features of these cells observed in other vertebrates but they do not have worm-like bodies and endogenous peroxidase activity. They are involved in erythrophagocytosis and perhaps the ingestion of other foreign material but they do not store iron. Fat-storing and fibroblast-like cells share many morphological features and may be different expressions of the same cell type. These perisinusoidal cells are rich in organelles suggesting protein synthesis but the fibroblast-like cells lack fat droplets. A cell with a large Golgi apparatus and associated cytoplasmic granules resembles the pit cell described in the liver of a few other vertebrates. The morphology of nonparenchymal cells of the liver in parasitic adult lampreys does not reflect the absence of bile ducts in this organism.

Notes: Summary Thin-section and freeze-fracture observations of the plasma membranes of hepatocytes from parasitic adult lampreys, Petromyzon marinus, reveal large (250 nm–4.5 μm diameter) gap junctions of highly irregular configuration. The multiformity of these junctions is partially due to the fact that they follow the contours of the undulating cell surface of the irregularly shaped hepatocytes. In addition, junctional membrane is characterized by a slight “rippling” which is not seen on adjacent non-junctional membrane. Although some annular-shaped junctions are associated to non-junctional membrane, others seem completely internalized and they surround portions of the cytoplasm. In P-face replicas the gap junctions are seen to be composed of closely packed particles of 6.0–6.5 nm diameter. E-face replicas of junctional membrane are relatively smooth, a fact which may be related to the small size of the intramembranous particles. Differences in size and shape of gap junctions in hepatocytes of larval (Peek et al. 1979) and adult lampreys may reflect the absence of bile canaliculi and bile ducts in the adult liver and an increased role of these junctions in co-ordination of an endocrine secretory mechanism.

Notes: Summary Osmotic opening of the blood-brain barrier had no effect on the structure of the interendothelial tight junctions located within approximately 9 μm2 of brain capillary endothelial plasma membrane (junction-containing) examined in this study. These tight junctions restrict the passive diffusion between the blood and the brain and constitute the anatomic basis of the blood-brain barrier. Increased permeability of the blood-brain barrier in the cerebral cortex of the right hemisphere of rats, induced by an infusion of a hypertonic solution of arabinose and monitored with the protein tracer horseradish peroxidase (HRP), was evidenced by the extravasation of the tracer into the extracellular compartment of the brain. Freeze-fracture analysis of the capillaries from the same tissue revealed no alterations in the intramembrane components of the endothelial tight junctions. The junctions, which consist of 8–12 highly anastomosed parallel ridges situated on the PF fracture face of the endothelial plasmalemma, showed no loss of ridge continuity or intraridge connections, and were identical to zonulae occludentes from control capillaries. Consistent labeling of numerous vesiculo-tubular elements by HRP in the endothelia of experimental tissue and the threedimensional nature of these elements observed in platinum replicas support the interpretation that these structures represent transendothelial conduits which are continuous with the luminal and abluminal surfaces of the endothelial cells. Absence of similar structures in control endothelia is taken as evidence that their presence in experimental tissues is a direct response to the osmotic insult. It was concluded, therefore, that during osmotic opening of the blood-brain barrier passage of HRP across the endothelium of brain capillaries is not by an inter-endothelial route due to disruption of tight junctions but rather by a transendothelial route due to amplified vesicular activity.

Notes: Summary Brain tumors, benign and malignant, are characteristically more permeable to various types of tracer molecules than the neuropil in which they are embedded. Impermeability of brain neuropil capillaries is imparted by the blood-brain barrier, the anatomic basis of which is the network of interendothelial zonulae occludentes that seal capillary endothelial cells. To explore both the vascular elements of brain neoplasms and the route of tracer extravasation from them, as well as the possible effects of brain tumors on the permeability of peritumoral neuropil capillaries, brain tumors were induced in newborn Wistar rats by intracerebral (i.c.) injection of C-6 astrocytoma cells. The protein tracer horseradish peroxidase (HRP) was injected systemically into both normal and tumorbearing rats to mark the pathway along which it flowed into the tumor parenchyma tissue spaces, and to signal any concomitant tracer loss from the tumor extracellular compartment or peritumoral brain capillaries, into the neuropil extracellular milieu. Electron-microscopic examination on thin plastic sections of tumor and peritumoral neuropil revealed massive extravasation of tracer into the tumor tissue spaces, but none was seen outside of the capillaries in the surrounding brain neuropil. Zonulae occludentes of both tumor capillary endothelium and brain capillary endothelium were devoid of tracer and judged tight (sealed). Tracer was seen in pinocytotic vesicles in the highly attenuated endothelium of tumor capillaries and also in cytoplasmic vesicles within the tumor cells. The peritumoral and contralateral neuropil capillary endothelium exhibited reaction product-filled pinocytotic vesicles and vesiculo-tubular conduits. Often, one end of a HRP-filled vesiculo-tubular channel appeared continuous with either the luminal or abluminal plasmalemma. High-voltage electron microscopy of these conduits often showed them to be continuous with both luminal and abluminal surfaces of the endothelium, thus forming a continuum across the capillary wall. In addition, these transendothelial channels, clearly constituted as chains of fused vesicles, were often seen in close proximity to, or fused with, dense bodies in the endothelial cytoplasm. In spite of the presence of HRP-filled structures in the peritumoral neuropil capillary endothelium of tumor-bearing rats, no evidence of tracer extravasation from these vessels was apparent. These results suggest that although peritumoral and contralateral neuropil capillaries possess the machinery for extravasation of tracer, likely as a response to the presence of the neoplasm, tracer is not lost but, instead, is degraded by endothelial enzymes. The extensive flooding of the tumor extracellular compartment with tracer may be achieved by transport of HRP across the very thin walls of tumor capillaries by single cytoplasmic vesicles which structurally and functionally play the role of transendothelial channels. Based on the results of this study, it is unlikely that molecules delivered systemically to treat brain neoplasms, will leak into the peritumor or contralateral neuropil, either from their own capillaries, or from the extracellular compartment of the tumor parenchyma.

Notes: Abstract Since the extracellular matrix (ECM) has a role in regulating cell proliferation it has been hypothesized that unregulated growth of transformed cells results from an inability of cells to interpret the constraints on growth as dictated by the ECM. The most likely candidate to communicate the restraint on growth to the nucleus is the cytoskeleton because it is the only cytoplasmic structure to physically connect the nucleus and plasma membrane. The purpose of this study was to determine whether the cytoskeleton, specifically the microfilaments (MF), of the C6-glioma cell line prossesses the ability to respond to changes in the ECM. The C6-glioma cell line was chosen as a model because it exhibits the characteristics of a tumor cell, both in vivo and in vitro. In this study cells were grown on bare glass, Matrigel, laminin and type IV collagen prior to staining with phalloidin tetramethylrhodamine B isothiocyanate or antibodies specific to vinculin to visualize MF and adhesion plaques, respectively. On the basis of MF orientation, network complexity and location of adhesion plaques, this study reports that the cytoskeletal arrangements of C6 cells grown on various substrates are distinctly different. Each distinct organization pattern may reflect a change of cell behavior promoted by the different culture conditions. The significance of this study is that it demonstrates that the process of transformation in C6-glioma cells has not interfered with the cells ability to recognize, interpret and adapt to changes in the ECM.

Notes: Summary The fine structure of identified neuromuscular synapses of the single excitatory axon to the distal accessory flexor muscle in lobster limbs was examined with freeze-fracture and serial thin-section electron microscopy. The latter technique reveals presynaptic dense bars with synaptic vesicles aligned on either side of these bars and often fused to the membrane, suggesting exocytosis and confirming our previous contention that these bars are active zones of transmitter release. The intramembranous organization of these active zones, as revealed in freeze-etched tissue, is a ridge-like elevation of the P-face of the axolemma with a matching trough on the complementary E-face. The ridge on the P-face has rows of large scattered intramembranous particles along the apex and is often bordered by a series of small, circular depressions which are presumed to represent exocytotic vesicles attached to the presynaptic membrane. Complementing these depressions are a few volcano-like protuberances seen occasionally on the E-face membrane. Because such evidence for transmitter release occurred in both stimulated and non-stimulated preparations, it demonstrates that chemical fixatives employing aldehydes induce transmitter release. The postsynaptic receptor sites of these excitatory synapses are characterized by oval-shaped patches of densely packed particles on the E-face, arranged in a random pattern on the sarcolemma. The complementary P-face view exhibits a regular square array of particle imprints or pits.

Notes: Summary The lobster mandibular organ is well vascularized and its polygonal cells are arranged loosely around blood vessels and blood sinuses. Numerous mitochondria and microbodies (peroxisomes) give the acidophilic cytoplasm a finely granular appearance, but there is no evidence of secretory granules. The abundant endoplasmic reticulum is almost entirely agranular and occurs in two morphologically distinct forms: tubular and cisternal. The tubular reticulum is randomly distributed and may represent the site of synthesis and transport of the mandibular organ product. The cisternal reticulum is frequently associated with microbodies. Both forms of endoplasmic reticulum proliferate during mid to late premolt. Mandibular organ ultrastructure closely resembles that of cells known to synthesize steroids or lipids, which suggests that this organ may have a similar function. There is no functional evidence of involvement in molt control in Homarus, but ultrastructural and other evidence suggests an analogy with the insect corpus allatum.

Notes: A morphological comparison was made of the green livers of male and female lampreys (Petromyzon marinus L.) collected during the upstream (prespawning) migration. Light and electron microscope histochemistry for iron, and both thin sections and freeze-fracture replicas in the electron microscope, revealed some sexual dimorphism in these livers. Ferric iron is much more abundant in the liver of females and is present in the cytoplasmic matrix, in dense bodies, and in vacuoles of hepatocytes. The numerous vacuoles of females may be the deposition site of biliverdin and other bile components that would account for the darker green coloration of the liver compared to males. Hepatocytes in females are also characterized by prominent rough endoplasmic reticulum and Golgi apparatus that reflect the involvement of the cells in vitellogenesis. The presence of numerous lipid droplets in the hepatocytes of males indicates that the liver is an important storage site for fat. The lipid droplets are associated with electron-dense deposits of unknown nature. Large gap junctions typify the parenchymal cells of both male and female livers. Perisinusoidal and sinusoidal cells are similar to those in the nonparenchymal region in other vertebrate livers, namely, endothelial and Kupffer cells, lipocytes (Ito), and some granulated cells. The relationship of lipocytes to fibrous tissue and fibrogenesis is discussed.