THE INFLUENCE OF BUFFER SYSTEMS ON FIXATION WITH OSMIUM TETROXIDE

Impact of Lipid Composition on Vesicle Protein Adsorption: A BSA Case Study

Investigating the interaction between liposomes and proteins is of paramount importance in the development of liposomal formulations with real potential for bench-to-bedside transfer. Upon entering the body, proteins are immediately adsorbed on the liposomal surface, changing the nanovehicles' biological identity, which has a significant impact on their biodistribution and pharmacokinetics and ultimately on their therapeutic effect. Albumin is the most abundant plasma protein and thus usually adsorbs immediately on the liposomal surface. We herein report a comprehensive investigation on the adsorption of model protein bovine serum albumin (BSA) onto liposomal vesicles containing the zwitterionic lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), in combination with either cholesterol (CHOL) or the cationic lipid 1,2-dioleoyl-3-trimethylammoniumpropane (DOTAP). While many studies regarding protein adsorption on the surface of liposomes with different compositions have been performed, to the best of our knowledge, the differential responses of CHOL and DOTAP upon albumin adsorption on vesicles have not yet been investigated. UV-vis spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed a strong influence of the phospholipid membrane composition on protein adsorption. Hence, it was found that DOTAP-containing vesicles adsorb proteins more robustly but also aggregate in the presence of BSA, as confirmed by DLS and TEM. Separation of liposome-protein complexes from unadsorbed proteins performed by means of centrifugation and size exclusion chromatography (SEC) was also investigated. Our results show that neither method can be regarded as a golden experimental setup to study the protein corona of liposomes. Yet, SEC proved to be more successful in the separation of unbound proteins, although the amount of lipid loss upon liposome elution was higher than expected. In addition, coarse-grained molecular dynamics simulations were employed to ascertain key membrane parameters, such as the membrane thickness and area per lipid. Overall, this study highlights the importance of surface charge and membrane fluidity in influencing the extent of protein adsorption. We hope that our investigation will be a valuable contribution to better understanding protein-vesicle interactions for improved nanocarrier design.

Identification of a pharyngeal mucosal lymphoid organ in zebrafish and other teleosts: Tonsils in fish?

The constant exposure of the fish branchial cavity to aquatic pathogens causes local mucosal immune responses to be extremely important for their survival. Here, we used a marker for T lymphocytes/natural killer (NK) cells (ZAP70) and advanced imaging techniques to investigate the lymphoid architecture of the zebrafish branchial cavity. We identified a sub-pharyngeal lymphoid organ, which we tentatively named "Nemausean lymphoid organ" (NELO). NELO is enriched in T/NK cells, plasma/B cells, and antigen-presenting cells embedded in a network of reticulated epithelial cells. The presence of activated T cells and lymphocyte proliferation, but not V(D)J recombination or hematopoiesis, suggests that NELO is a secondary lymphoid organ. In response to infection, NELO displays structural changes including the formation of T/NK cell clusters. NELO and gill lymphoid tissues form a cohesive unit within a large mucosal lymphoid network. Collectively, we reveal an unreported mucosal lymphoid organ reminiscent of mammalian tonsils that evolved in multiple teleost fish families.

Leptin receptor defect with diabetes causes skeletal muscle atrophy in female obese Zucker rats where peculiar depots networked with mitochondrial damages

Tibialis anterior muscles of 45-week-old female obese Zucker rats with defective leptin receptor and non-insulin dependent diabetes mellitus (NIDDM) showed a significative atrophy compared to lean muscles, based on histochemical-stained section's measurements in the sequence: oxidative slow twitch (SO, type I) < oxidative fast twitch (FOG, type IIa) < fast glycolytic (FG, type IIb). Both oxidative fiber's outskirts resembled 'ragged' fibers and, in these zones, ultrastructure revealed small clusters of endoplasm-like reticulum filled with unidentified electron contrasted compounds, contiguous and continuous with adjacent mitochondria envelope. The linings appeared crenated stabbed by circular patterns resembling those found of ceramides. The same fibers contained scattered degraded mitochondria that tethered electron contrasted droplets favoring larger depots while mitoptosis were widespread in FG fibers. Based on other interdisciplinary investigations on the lipid depots of diabetes 2 muscles made us to propose these accumulated contrasted contents to be made of peculiar lipids, including acyl-ceramides, as those were only found while diabetes 2 progresses in aging obese rats. These could interfere in NIDDM with mitochondrial oxidative energetic demands and muscle functions.

Real-time imaging of polymersome nanoparticles in zebrafish embryos engrafted with melanoma cancer cells: Localization, toxicity and treatment analysis

BACKGROUND

The developing zebrafish is an emerging tool in nanomedicine, allowing non-invasive live imaging of the whole animal at higher resolution than is possible in the more commonly used mouse models. In addition, several transgenic fish lines are available endowed with selected cell types expressing fluorescent proteins; this allows nanoparticles to be visualized together with host cells.

METHODS

Here, we introduce the zebrafish neural tube as a robust injection site for cancer cells, excellently suited for high resolution imaging. We use light and electron microscopy to evaluate cancer growth and to follow the fate of intravenously injected nanoparticles.

FINDINGS

Fluorescently labelled mouse melanoma B16 cells, when injected into this structure proliferated rapidly and stimulated angiogenesis of new vessels. In addition, macrophages, but not neutrophils, selectively accumulated in the tumour region. When injected intravenously, nanoparticles made of Cy5-labelled poly(ethylene glycol)-block-poly(2-(diisopropyl amino) ethyl methacrylate) (PEG-PDPA) selectively accumulated in the neural tube cancer region and were seen in individual cancer cells and tumour associated macrophages. Moreover, when doxorubicin was released from PEG-PDPA, in a pH dependant manner, these nanoparticles could strongly reduce toxicity and improve the treatment outcome compared to the free drug in zebrafish xenotransplanted with mouse melanoma B16 or human derived melanoma cells.

INTERPRETATION

The zebrafish has the potential of becoming an important intermediate step, before the mouse model, for testing nanomedicines against patient-derived cancer cells.

FUNDING

We received funding from the Norwegian research council and the Norwegian cancer society.

THE FINE STRUCTURE OF TESTICULAR INTERSTITIAL CELLS IN GUINEA PIGS

In guinea pig testes perfused with either glutaraldehyde or osmium tetroxide fixative, the cytoplasm of the interstitial cells contains an exceptionally abundant agranular endoplasmic reticulum. The reticulum in central regions of the cell is a network of interconnected tubules, but in extensive peripheral areas the reticulum is commonly organized into closely packed, flattened cisternae which are fenestrated. Occasional small patches of the granular reticulum occur in the cytoplasm and connect freely with the agranular reticulum. The mitochondria have a dense matrix and contain cristae and some tubules. The Golgi complex is disperse and shows no evidence of secretory material. The cytoplasm also contains lipid droplets. Lipofuscin pigment granules are probably polymorphic residual bodies and contain three components: (1) a dense material which at high magnification shows a 75-A periodicity; (2) a medium-sized lipid droplet; and (3) a cap-like structure. In glutaraldehyde-perfused testis the interstitial cell cytoplasm appears to have the same density from cell to cell, and the agranular reticulum is tubular or cisternal but not in the form of empty vesicles. Thus the "dark" and "light" cells and the vesicular agranular reticulum sometimes encountered in other fixations may be artifacts. Biochemical results from other laboratories, correlated with the present findings, indicate that the membranes of the agranular endoplasmic reticulum in guinea pig interstitial cells are the site of at least two enzymes of androgen biosynthesis, the 17-hydroxylase and the 17-desmolase.

Elasticity, unexpected contractility and the identification of actin and myosin in lobster arteries

Lobster arteries, which exhibit non-uniform elasticity when stretched, have a trilaminar organization. The inner layer is an elastic connective tissue and the outer layer is a collagenous connective tissue; the middle layer of an artery is an aggregation of cells containing microfilaments. Arterial cells possess actin, myosin and tropomyosin. Except for the dorsal abdominal artery,striated muscle cells are not evident in the walls of any of the vessels. The neurotransmitter glutamic acid and the neurohormone proctolin elicit slow circumferential contractions in all of the arteries leaving the lobster heart. Only the dorsal abdominal artery contracts when stimulated electrically. Longitudinal strips of the arteries do not respond to either drugs or electrical stimulation. Arterial contraction will have profound effects on resistance to blood flow and may be an important component of the control mechanisms regulating blood distribution.

Processing biological tissues for ultrastructural study

Biological tissues are passed through numerous procedures before they can be studied at the ultrastructural level with the electron microscope. Chemical fixation is widely used as a method for preserving structural detail and can be performed by simple immersion or total body vascular perfusion. A 2 to 4% solution of glutaraldehyde buffered with 0.1 M sodium phosphate, or a combination of similarly buffered glutaraldehyde and paraformaldehyde, can be used successfully to preserve the fine structure of biological tissues. The material next is washed briefly in the buffer vehicle and then secondarily fixed in 1% osmium tetroxide (osmic acid), which also is buffered with sodium phosphate. The tissue then is thoroughly dehydrated in solutions of ethanol at increasing concentrations of 50%, 70%, 95%, and 100%. After dehydration, tissues are infiltrated for a prescribed time interval with an epoxy embedding medium. After infiltration, specimens are transferred into fresh epoxy resin and polymerized at 60 to 70 degrees C for several hours. This orderly process ultimately yields fixed tissues that are encased in hardened blocks that can be thin-sectioned with an ultramicrotome. The thin sections are counterstained with solutions of heavy metals to add contrast. The material then can be subjected to the electron beam in an electron microscope to produce useful images for ultrastructural study. This overall procedure has been used successfully since the advent of biological electron microscopy to define the minute details of cells and tissues.

Organization of the coelomic lining and a juxtaposed nerve plexus in the suckered tube feet ofParastichopus 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.

Effect of serotonin on ciliary beating and intracellular calcium concentration in identified populations of embryonic ciliary cells

Embryos of the pond snail Helisoma trivolvis express three known subtypes of ciliary cells on the surface of the embryo early in development:pedal, dorsolateral and scattered single ciliary cells (SSCCs). The pedal and dorsolateral ciliary cells are innervated by a pair of serotonergic sensory-motor neurons and are responsible for generating the earliest whole-animal behavior, rotation within the egg capsule. Previous cell culture studies on unidentified ciliary cells revealed that serotonin(5-hydroxytryptamine; 5-HT) produces a significant increase in the ciliary beat frequency (CBF) in a large proportion of ciliary cells. Both Ca2+ influx and a unique isoform of protein kinase C (PKC) were implicated in the signal transduction pathway underlying the cilio-excitatory response to 5-HT. The goal of the present study was to characterize the anatomical and physiological differences between the three known populations of superficial ciliary cells. The pedal and dorsolateral ciliary cells shared common structural characteristics, including flat morphology, dense cilia and lateral accessory ciliary rootlets. By contrast, the SSCCs had a cuboidal morphology, reduced number of cilia, increased ciliary length and absence of lateral accessory rootlets. In cultures containing unidentified ciliary cells,the calcium/calmodulin-dependent enzyme inhibitor calmidazolium (2 μmol l–1) blocked the stimulatory effect of 5-HT (100 μmol l–1) on CBF. In addition, 50% of unidentified cultured cells responded to 5-HT (100 μmol l–1) with an increase in[Ca2+]i. To facilitate the functional analyses of the individual populations, we developed a method to culture identified ciliary subtypes and characterized their ciliary and calcium responses to 5-HT. In cultures containing either pedal or dorsolateral ciliary cells, 5-HT (100μmol l–1) produced a rapid increase in CBF and a slower increase in [Ca2+]i in all cells examined. By contrast,the CBF and [Ca2+]i of SSCCs were not affected by 100μmol l–1 5-HT. Immunohistochemistry for two putative 5-HT receptors recently cloned from Helisoma revealed that pedal and dorsolateral ciliary cells consistently express the 5-HT1Helprotein. Intense 5-HT7Hel immunoreactivity was observed in only a subset of pedal and dorsolateral ciliary cells. Cells neighboring the SSCCs,but not the ciliary cells themselves, expressed 5-HT1Hel and 5-HT7Hel immunoreactivity. These data suggest that the pedal and dorsolateral ciliary cells, but not the SSCCs are a homogeneous physiological subtype that will be useful for elucidating the signal transduction mechanisms underlying 5-HT induced cilio-excitation.

Coordinated development of identified serotonergic neurons and their target ciliary cells in Helisoma trivolvis embryos

Embryonic neuron C1s (ENC1s) are bilateral serotonergic neurons that function as cilioexcitatory motor neurons in embryonic development of the pond snail, Helisoma trivolvis. Recent experiments demonstrated that these neurons stimulate cilia-driven embryo rotation in response to hypoxia. In the present study, a comprehensive anatomic analysis of these cells and their target ciliary structures was done to address the following questions: (1) Does ENC1 have a morphology consistent with an oxygen-sensitive sensory cell; (2) Is the development of ENC1's neurite outgrowth pathway coordinated with the development of its target effectors, the pedal and dorsolateral ciliary bands; and (3) What is the anatomic basis of ENC1-ciliary communication? By using an array of microscopic techniques on live and serotonin-immunostained embryos, we found that each ENC1 possessed an apical dendrite that was capped with an integral dendritic knob penetrating the embryo surface. The dendritic knobs contained both microvilli and nonmotile cilia that suggested a sensory transduction role. Each ENC1 also possessed a descending projection, whose development was characterized by the rapid formation of the primary neurite pathway between stages E13 and E15, with the primary neurite of the right ENC1 developing in advance of its contralateral homologue. Secondary neurite branches formed between stages E15 and E30 in a spatiotemporal pattern that closely matched the development of the dorsolateral and pedal bands of cilia. Both dorsolateral and pedal ciliated cells formed basal processes that contacted ENC1 neurites. Finally, gap junction profiles were observed at neurite-neurite, neurite-ciliary cell, and ciliary cell-ciliary cell apposition sites, whereas putative chemical synaptic profiles were observed at neurite-neurite and neurite-ciliary cell apposition sites.

Chemically defined neuron groups and their subpopulations in the glomerular layer of the rat main olfactory bulb: III. Structural features of calbindin D28K-immunoreactive neurons

The present study analyzed three-dimensional structural features and synaptic contacts of morphologically and chemically identified calbindin D28K-immunoreactive neurons in the glomerular layer of the rat main olfactory bulb by means of combined confocal laser scanning light microscopy, high-voltage electron microscopy and electron microscopic serial section/three-dimensional reconstruction. Most of calbindin D28K-immunoreactive neurons were identified as the periglomerular cell type by combined high-voltage electron microscopic and confocal laser scanning light microscopic observations, and the minority were the short-axon cell type and others. The combined confocal laser scanning light microscopic and electron microscopic study revealed that the calbindin D28K-immunoreactive neurons exhibited unique synaptic contact patterns; they received asymmetrical synapses from presumed mitral/tufted dendrites and made conversely symmetrical synapses with them. About 30% of asymmetrical postsynaptic sites and about 40% of symmetrical presynaptic sites formed reciprocal pairs of synapses. Calbindin D28K-immunoreactive dendrites and somata also received synapses from GABA-like-immunoreactive profiles containing numerous pleomorphic, and a few dense-cored, vesicles. On the other hand, surprisingly, calbindin D28K-immunoreactive neurons had almost no synaptic contacts from olfactory nerve terminals. The present study clearly revealed that calbindin D28K-immunoreactive neurons are a type of periglomerular cell involving unique synaptic contacts that have not been reported so far, and thus indicated that so-called periglomerular cells should be heterogeneous in their synaptic connections as well as in their chemical and structural features.

Scanning electron-microscopic lesions in Crohn's disease: relevance for the interpretation of postoperative recurrence

BACKGROUND/AIMS

Endoscopic postoperative recurrence often occurs a few months after surgical therapy for Crohn's disease, even if the resection margins were macroscopically free of disease. Why the disease primarily recurs at the anastomotic site is not known. This study investigated resection margins in Crohn's disease in an attempt to clarify whether early lesions are relevant to the interpretation of postoperative recurrence.

METHODS

Specimens of surgically resected bowel from 29 patients with Crohn's disease and tissue from 11 controls were studied with a scanning electron microscope.

RESULTS

In Crohn's disease, a triad of early lesions occurring in both histopathologically unaffected and affected mucosa was revealed; the triad consisted of mucosal architectural alterations, epithelial bridge formation, and goblet-cell hyperplasia or hypertrophy or both. Seventy-three percent of patients showed early alterations within histopathologically unaffected margins in the small bowel, and 71% had such alterations in the large bowel.

CONCLUSIONS

The findings provide further evidence for the concept of diffuse involvement of the whole gastrointestinal tract by the disease process. The endoscopic recurrence rate in the first year after the operative procedure is almost identical to the number of early lesions present during surgery. The term "postoperatively recurrent disease" should be used only if relevant clinical parameters change.

Effects of scaphognathite nerve stimulation on the acutely deafferented crab ventilatory central pattern generator

1. Sensory axons from crab (Carcinus maenas) scaphognathites enter the thoracic ganglion primarily via the LNb branch of the levator nerve. The LNa branch of the levator nerve and the depressor nerve each contain relatively few sensory axons. 2. Acutely deafferented ventilatory central pattern generators show a free running burst rate which is lower than that observed in intact crabs. Electrical stimulation of the levator nerve, or of its LNb branch, increases the burst rate in a frequency dependent manner. Stimulation at high enough intensity to recruit afferents will restart a paused motor rhythm. Stimulation of the levator nerve with short pulse trains phase resets and can entrain the rhythm. 3. In addition to increasing the burst rate, LNb stimulation also causes a progressive elimination of motor neurons from the bursts as the stimulating frequency increases, probably due to depolarization of the 3 oval organ 'giant' afferent axons in this branch. Intracellular depolarization of single oval organ afferents will also inhibit some motor neurons as well as slow or stop the rhythm. 4. Continuous stimulation of the depressor nerve does not affect the ganglionic burst rate and this nerve contains only a few small diameter afferent axons; however, brief trains of stimuli can reset the rhythm in a phase-dependent manner.

Development of the liver in the chicken embryo. I. Hepatic cords and sinusoids

Hemopoiesis in the liver of the chicken embryo begins on day 7 of incubation (Hamburger and Hamilton Stage 30) and peaks on day 14 (Stage 40). During this time frame, the differentiation of hepatic cells was examined by light microscopy, transmission and scanning electron microscopy, and morphometry. The avian liver is a closely packed mass of dendriform cords and discontinuous sinusoids. Hepatocytes are pyramidal in shape, and they ring the bile canaliculi which run through the centers of the cords. Semithin sections, made possible by infiltration and embedding in glycol methacrylate, were stained with hematoxylin and eosin to assess the general architecture of the organ and the lipid content of the hepatocytes and by the periodic acid-Schiff reaction and hematoxylin to visualize the cytoplasmic stores of glycogen. The number of hepatocytes with demonstrable glycogen fluctuates erratically in early hemopoiesis, and the proportion of glycogen-containing cells progressively increases as hemopoiesis climbs to a peak. Most differentiating hepatocytes are devoid of lipid droplets until Stages 39 and 40. From Stage 30 to 35, hepatocyte volume falls to its lowest value. Subsequently (Stages 36 to 40), cell volume increases and hepatocytes achieve a relatively uniform size. Ultrastructural changes in the differentiating hepatocytes, including alterations to the mitochondria, endoplasmic reticulum, and Golgi apparatus, are documented. These morphological and morphometric findings on the prehepatocyte population and hepatic vasculature cover 2 of the 3 elements deemed critical to hepatic hemopoiesis in many vertebrates.

Correlation of ultrastructural aberrations with dysplasia and flow cytometric abnormalities in Barrett's epithelium

Barrett's esophagus develops as a complication of chronic gastroesophageal reflux and predisposes patients to the development of dysplasia and adenocarcinoma of the esophagus. Because light microscopy of dysplasia in Barrett's esophagus shows diminished or absent mucus, we used transmission electron microscopy to compare cytoplasmic organelles required for mucus production in dysplastic and nondysplastic esophageal columnar epithelium. These observations of the rough endoplasmic reticulum, Golgi apparatus, and secretory granules were correlated with histologic interpretations and flow cytometric measurements of abnormalities of DNA content. Ultrastructural abnormalities included depletion and alteration of organelles required for mucus biosynthesis. These abnormalities often were accompanied by cells with markedly distended rough endoplasmic reticulum and massive accumulation of cytoplasmic glycogen aggregates. All 9 patients who had Barrett's dysplasia with or without early adenocarcinoma had ultrastructural abnormalities, as did 3 of 8 patients whose biopsy histology was indefinite for dysplasia. Abnormalities measured by flow cytometry correlated well with the presence of these ultrastructural aberrations. All 9 patients with Barrett's dysplasia with or without early adenocarcinoma had abnormalities observed by electron microscopy and aneuploidy or increased G2/tetraploid fractions measured by flow cytometry. Two of the 3 patients whose biopsies were indefinite for dysplasia and who had ultrastructural abnormalities also had aneuploidy or increased G2/tetraploid fractions. Neither ultrastructural nor flow cytometric abnormalities were found in the remaining 5 patients whose biopsies were indefinite for dysplasia, in 19 of 22 patients with Barrett's specialized metaplasia, or in any of the 7 patients with gastroesophageal reflux disease without Barrett's specialized metaplasia. Two of the 22 patients with Barrett's specialized metaplasia had distended rough endoplasmic reticulum in rare cells, and one other had an aneuploid cell population. We conclude that neoplastic progression in Barrett's esophagus is associated with abnormalities of cytoplasmic organelles required for mucus production. With few exceptions, these ultrastructural aberrations correspond to the presence of dysplasia or of aneuploidy or increased G2/tetraploid fractions. Electron microscopy and flow cytometery detect abnormalities associated with the development of dysplasia and cancer in Barrett's esophagus that may be biologically significant.

The influence of fixation on the relative amount of cytoplasmic ribosomes in mouse epidermal basal keratinocytes. A morphometric study of so-called "dark cells" and their putative role in epidermal carcinogenesis

The nature and significance of so-called dark keratinocytes in the epidermis during chemical carcinogenesis is still a matter of concern and debate. Based on ultrastructural observations it has been suggested that dark cells most often are shrunken cells. Reports on skin carcinogenesis, however, claim that dark cells are a sign of ongoing tumor promotion and represent those stem cells in the epidermis from which the tumors originate. It is therefore important to find out whether these cells are simply injured and shrunken cells, or vital cells of great importance for carcinogenesis. Dark cells are assumed to be rich in ribosomes. There is evidence, however, that the observed number of dark cells is highly dependent on tissue fixation. In the present ultrastructural study, morphometric methods were used to compare the effects of two different fixation procedures on the amount of cytoplasmic ribosomes in dark cells from both untreated and carcinogen-treated hairless mouse epidermis. The results show that the ultrastructural features of both dark and clear cells vary considerably with different fixation procedures. In acetone-treated controls typical dark cells are only observed when the fixative has a lower osmotic activity than the plasma. With iso-osmolal fixation typical dark cells are not observed. After an abortive two-stage carcinogenesis treatment, in which a single application of 9,10-dimethyl-1,2-benzanthracene (DMBA) in acetone was followed by a single application of 12-O-tetradecanoyl-13-acetate (TPA) in acetone, signs of cell injury could be found after both fixation procedures. With DMBA/TPA and hypo-osmolal fixation the number of dark cells seemed to increase, whereas only signs of cell injury with occurrence of some heavily altered "clear cells" dominated the picture with iso-osmolal fixation. Morphometry showed that both the numerical and the volumetric densities of cytoplasmic ribosomes in basal keratinocytes varied most significantly with the fixation procedure used. The cytoplasmic volumes did not vary in a way that could explain these differences. One might therefore assume that the number of ribosomes depends on the fixative. Large swelling artifacts occurred when a fixative with low osmotic activity was used, leading to compression of neighboring cells. Hence, an increased ribosomal density reported previously in dark cells is probably related to such cell volume artifacts and does not reflect an actually increased quantity of ribosomes.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of human jejunal and ileal fat absorption by electron microscopy

Morphologic and physiologic experiments in rodents have demonstrated differences between jejunal and ileal fat absorption. Compared with the rat jejunum, absorbed lipid particles within rat ileal absorptive cells are larger and exit at a slower rate. To evaluate the relevance of these observations to humans, we studied jejunal and ileal ultrastructure in 3 volunteers, each of whom had an intact small intestine and an ileostomy postcolectomy for ulcerative colitis. Proximal jejunal biopsy specimens were obtained via a hydraulic tube after an overnight fast and again after a 20-min intrajejunal lipid infusion. On a separate day, terminal ileal biopsy specimens were taken via the stoma with a small steerable suction biopsy tube after an overnight fast and again after a 20-min intraileal infusion of the same lipid mixture. One volunteer underwent biopsy after a 60-min ileal infusion of a digested meal of higher lipid content. Electron microscopy of fasting human jejunal absorptive cells revealed obvious smooth endoplasmic reticulum in the extreme apical region beneath the terminal web; very low density lipoprotein particles were observed within smooth endoplasmic reticulum and Golgi cisternae. In contrast, fasting human ileal absorptive cells contained less apical smooth endoplasmic reticulum and fewer or no very low density lipoprotein particles. After the 20-min infusion of lower-lipid content, human jejunal and ileal absorptive cells were indistinguishable because they contained fat particles of the same size and number within smooth endoplasmic reticulum, Golgi cisternae, and extracellular spaces. After the 60-min ileal infusion of higher-lipid content, human ileal absorptive cells appeared to be the same as those of the human jejunum after similar lipid infusions. Our observations of the ultrastructural similarity in human jejunal and ileal absorptive cells after lipid infusions contrasts with those in rodents and may reflect species-specific differences in mechanisms of fat absorption.

Evaluation of different procedures for the dissociation of retinal pigmented epithelium into single viable cells

Retinal pigmented epithelium (RPE) from 7-day-old chicken embryos (stages 29 to 31) was isolated and dissociated into single cells using different procedures. The results were assessed in two ways. (1) The yield of single RPE cells per embryo was determined, and their ability to form pigmented colonies in clonal culture was tested. The most efficient and gentle procedure included isolation of the RPE in EDTA solution, trypsinization at low temperature and low enzyme concentration in the presence of EDTA, followed by incubation in culture medium for up to 4 hr. The completely dissociated cells thus obtained had a much higher plating efficiency and more uniform pattern of colony growth and differentiation than those obtained under any other conditions tested. (2) The effects of different treatments on cell junctions and morphological integrity of the cells were determined by transmission electron microscopy. EDTA solution yielded excellent separation of the epithelial sheet from the mesenchyme by dissociating it from Bruch's membrane, but had little effect on the junctions between adjacent RPE cells. Trypsinization of the epithelium under various conditions separated the basal lateral cell borders and caused loss of gap junctions, but left many cells still joined by apical tight junctions. Final disruption of the tight junctions occurred during recovery of the trypsinized cells in culture medium and was accompanied by dedifferentiation of the RPE cells.

Application of frozen thin sectioning immunogold staining to the study of the developing neuroepithelial basal lamina

In order to examine the deposition of basal lamina components in the developing neuroepithelium, a technique for frozen thin sectioning and immunogold staining of early embryonic tissue was developed. Different fixatives and buffer systems were evaluated to determine which best retained immunoreactivity and satisfactory ultrastructure of day 9 and 10 mouse embryos. Fixation in sodium phosphate and sodium bicarbonate buffers did not retain antigenicity, and incubations in TBS (trishydroxymethyl-aminomethane buffered saline) in an effort to 'restore' immunoreactivity were similarly unsuccessful. Fixation in sodium cacodylate buffer, however, did retain the antigenicity of basal lamina components; the pattern of type IV collagen and laminin distribution was clearly determined. These results represent the first report of on-grid immunocytochemistry of early embryonic material.

The influence of different fixatives and a tumor promoter, 12-0-tetradecanoyl-phorbol-13-acetate (TPA), on the induction of so-called dark cells in mouse epidermis. A light microscopical study

Epidermal "dark cells" (DC) are believed to play a specific role in the so-called promotion phase of experimental skin carcinogenesis. They are recognized by their morphological features both at the light and the electron microscopical level. The possible effects of fixation on the morphology of epidermal cells and hence on the number of DC have not yet been thoroughly studied. In the present light microscopical study we used a semiquantitative method together with simple cell counting to evaluate the influence of fixation on the specific cellular morphology which is traditionally used to determine the number of DC. The use of cacodylate vehicled prefixatives, either formaldehyde or glutaraldehyde, led to a higher incidence of DC, and furthermore both to an increased width of the intercellular spaces (ICS) and a more heavy staining of the keratinocytes than when s-collidine vehicled glutaraldehyde was used. Differences in yield of DC solely due to the prefixative itself (formaldehyde or glutaraldehyde) were not detected. Exposure to TPA or the use of a hyperosmolal prefixative vehicle both yielded higher DC numbers than did controls or conventional prefixative vehicles, respectively. After prefixation with hyperosmolal vehicles, however, TPA treatment did not induce higher DC yield than in a control series. Phenomena usually accompanying exposure to TPA, such as intercellular oedema (widening of the ICS) and cytoplasmic vacuolization, varied in parallel to the number of DC. Hence, there is reason to believe that the induction of epidermal DC is mainly associated with volume reduction of keratinocytes. Such shrinkage may be due to the cytotoxic properties of TPA and degenerative phenomena appearing during tissue processing.

Fine structure of the doliolaria larva of the feather star Florometra serratissima (Echinodermata: Crinoidea), with special emphasis on the nervous system

The epidermis of the doliolaria larva of the Florometra serratissima is differentiated into distinct structures including an apical organ, adhesive pit, ganglion, ciliary bands, nerve plexus, and vestibular invagination. All these structures possess unique cell-types, suggesting that they are functionally specialized in the larva, except the vestibular invagination that becomes the postmetamorphic stomodeum. The epidermis also contains yellow cells, amoeboid-like cells, and secretory cells. The enteric sac, hydrocoel, axocoel, and somatocoels have differentiated but are probably not functional in the doliolaria stage. Mesenchymal cells, around the enteric sac and coeloms, appear to be actively secreting the endoskeleton and connective tissue fibers. The nervous system is composed of a nerve plexus, ganglion, and sensory receptor cells in the apical organ. The apical organ is a larval specialization of the anterior end; the ganglion is located in the base of the epidermis at the anterior dorsal end of the larva. The nerve plexus underlies most of the epidermis, although it is more prominent in the anterior region. Here, processes from sensory receptor cells of the apical organ, as well as those from nerve cells, contribute to the plexus. These processes contain one or a combination of organelles including vesicles, vacuoles, microtubules, and mitochondria. The configuration of glyoxylic acid-induced fluorescence, revealing catecholamine activity, correlates to the apical organ, nerve cells, and nerve plexus. Morphological evidence suggests that the nervous system may function in initiation and control of settlement, attachment, and metamorphosis. The crinoid larval nervous system is discussed and compared to that found in other larval echinoderms.

Alterations in the volume of the intercellular space between epithelial cells of the hamster cheek-pouch: quantitative studies of normal and carcinogen-treated tissues

The present report investigated the extent of the epithelial dysplastic feature known as "loss of cellular adherence" at the ultrastructural level by quantifying the volume of the intercellular space during hamster cheek-pouch carcinogenesis. Following topical application of DMBA to cheek-pouches, lesions were classified as hyperplasia, dysplasia and carcinoma, with untreated pouches serving as a control. Stereological point counting procedures were used to determine the volume density of intercellular space in defined basal, spinous and granular layers for each group. In general, progressive increases in volume density were detected within each stratum during carcinogenesis. These results indicate that increasing separation of epithelial cells occurs during carcinogenesis, although it is not yet known whether this results from loss of cohesion between specialised (i.e., desmosomal) or nonspecialised membrane areas. In addition, a simple indicator of pathological alteration, the Pathological Alteration Ratio (PAR), is described and was used to evaluate existing published data for intercellular spaces in various oral mucosal conditions. Values of the PAR were found to be substantially higher in carcinogen-treated epithelia than in reports describing changes in wound healing, lichen planus and leukoplakia simplex. These objective techniques are of value for investigating the pathogenesis of diseased epithelium and may find applications in the diagnosis of oral premalignant lesions.

Some factors controlling cell polarity in chick retinal pigment epithelial cells in clonal culture

In clonal culture differentiated chick retinal pigmented epithelial (RPE) cells form a monolayer which shows little or no cellular division. The cells usually rest on a basal and reticular lamina and are polarized with their apical surface towards the medium. The apical surface is characterized by apical protrusions, an extensive apical web of microfilaments and junctional complexes which join the apical-lateral borders. A PA/S positive material with a felt-like appearance from the serum component of the medium coats the surfaces of the tissue culture plates. A similar material is found on any membrane filter which has been exposed to medium containing serum. When such a filter brought in contact with the upper surfaces of the RPE cells, the apical surface characteristics are lost, the cells often accumulate Alcian Blue positive material between the cells and the filter and secrete a reticular and a basal lamina, i.e. they establish a second basal surface. Once this has occurred, the cells appear to either detach from the plate and reverse their polarity, or undergo division forming two cell layers. In the latter case new apical surfaces are created between the cell layers but the cells appear to join to form circular structures rather than sheets. These results suggest that contact with this felt-like material initiates formation of a basal surface. They further suggest that where the apical surface has been converted to a basal one the cell attempts to restore the apical surface either by separating from the plate and reversing its polarity or by creating circular structures and developing new apices oriented toward the center of the circle.

Imidazole-buffered osmium tetroxide: an excellent stain for visualization of lipids in transmission electron microscopy

The usefulness of imidazole-buffered osmium tetroxide as a stain for lipids in transmission electron microscopy has been investigated. Rat liver and other tissues were fixed by perfusion with glutaraldehyde and post-fixed with osmium-imidazole and the appearance of lipid droplets was compared with that after post-fixation in unbuffered aqueous osmium tetroxide or an osmium solution buffered otherwise. Prominent electron-opaque staining of lipid droplets and of lipoprotein particles was noted after post-fixation with 2% osmium-imidazole, pH 7.5, for 30 min. The lipid droplets appeared well circumscribed with no evidence of diffusion. In contrast, the intensity of staining was much less and there was some diffusion around lipid droplets in material post-fixed in aqueous or cacodylate-buffered osmium tetroxide. Spot tests on filter paper revealed that unsaturated fatty acids, especially linolenic and linoleic acids reacted more intensely with osmium-imidazole than with aqueous osmium tetroxide. These findings demonstrate that osmium-imidazole provides an excellent stain for lipids in transmission electron microscopy and that most probably it stains lipids with unsaturated fatty acids.

Fine structure of the larval rhinophores of the nudibranch, Rostanga pulchra, with emphasis on the sensory receptor cells

The rhinophores of the veliger larva of Rostanga pulchra are located in the intravelar field near the base of the velar lobes. Each rhinophore is a cylindrical structure, tapering distally, and covered with a dense meshwork of microvilli. A conspicuous row of ciliary tufts runs along each side of the rhinophore and several stiffer tufts, composed of fewer cilia, are positioned around the tip or at the base. The rhinophoral epithelium consists of supporting cells, ciliated cells (giving rise to the ciliary rows), dendritic terminals (giving rise to the tufts around the apex), and sinuses containing occasional amebocytes. The lumen of the rhinophore is occupied by the rhinophoral ganglion and muscle cells that are oriented in two perpendicular planes. Cells bodies of the dendritic endings are located within the rhinophoral ganglion, which in turn joins into the optic and cerebral ganglia. Rhinophoral ganglionic neurons do not synapse with each other, but numerous neuromuscular synapses are found in the lumen of the rhinophore. Morphological evidence suggests that the dendritic endings are chemoreceptors and the ciliated cells are possibly mechanoreceptors but are not functional at this stage in development. The functional role of the rhinophores is discussed in relation to larval behavior at settlement and metamorphosis.