Electron Microscope Observations of the Melanocyte of the Human Epidermis

Using standard osmium fixation and methacrylate embedding techniques, a study has been made of the melanocyte of human biopsy skin removed under general and local anaesthesia. Melanogenesis was easily observable in the melanocytes, but immature pigment granules were rarely seen in the Malpighian cells. The passage of melanin from melanocyte to Malpighian cell—cytocrine secretion—is thought to have been observed. Phagocytes near the dermal-epidermal junction seem to have their pigment granules in vacuoles, rather than surrounded directly by the cytoplasmic matrix as in the melanocytes. This, together with the failure to observe "effete" melanocytes, prompts the suggestion that the phagocytes are melanocytes which have migrated from the epidermis into the dermis. A melanin granule is shown with alternating dark and lighter transverse striations, concerning which structure little can at present be said.     

Electron Microscope Studies of the Human Epidermis : The Cell Boundaries and Topography of the Stratum Malpighii

The thin skin of the left upper quadrant of the human abdomen has been studied by electron microscopy. Tissue removed with a high speed rotary punch was fixed in osmium tetroxide or potassium permanganate. The latter fixative in our preparations is superior to osmium for the demonstration of epidermal cell membranes and certain other membranous structures of the epidermis. The cytoplasmic membranes of basal cells and cells of the stratum granulosum have been found to be relatively straight, while those of most spinous cells are sharply scalloped. The deep cells of the stratum spinosum in the rete ridge area show cell membranes and cytoplasmic structure intermediate between true basal cells and most cells of the stratum spinosum. The extracellular material of the desmosome has been found to consist of alternate dark and light laminae similar to those described by Odland (13) and Horstmann and Knoop (7).     

Electron Microscope Studies on Eimeria perforans (Sporozoa)

SYNOPSIS. By means of electron microscopy, a study has been made of the fine structure of the macrogametocytes, microgametocytes and oocysts of Eimeria perforans from the intestine of the wild rabbit (Oryctolagus cuniculus). The parasites lie in a vacuole within the host cell. The surface of the gametocytes is not plain, but displays irregular protrusions. A large intranuclear body can be detected within the macrogametocytes. Similar structures are also found within the cytoplasm. Within the latter there exists a large spread out reticulum, the channels and vesicles of which concentrate especially close to the nuclear membrane. Tubuli are seen in the numerous mitochondria, which often have a dumb-bell shape.
In most of the gametocytes irregular, strongly osmiophilic lipid inclusions are observed, which always are surrounded by the endoplasmic reticulum. Strange folded ovoid bodies are found within the cytoplasm of the oocysts. Nothing can be told with certainty of their nature and function. Probably they represent specific storage bodies.     

Electron Microscope Study of the Human Neuromuscular Junction

A preliminary electron microscope study of human neuromuscular junction is presented. The biopsy material was taken from the palmarus longus, and fixed routinely in osmium tetroxide and embedded in methacrylate. The structure of the motor endings and the relationship of the synaptic vesicles to the axolemmal membrane are described. The synaptic clefts are filled with an homogeneous material in continuity with the basement membrane covering the muscle fiber. The subneural apparatus is described, and special attention is paid to a vesicular component present in the sarcoplasm of the junctional area, which differs from synaptic vesicles and is presumed to be a derivate of the sarcoplasmic reticulum.     

Studies of Small-intestinal Mucosa with the Scanning Electron Microscope

Preliminary observations indicate that scanning electron microscopy is a useful method for studying the surface of the small intestine.     

Cell Communication in the Basal Cells of the Human Epidermis

Electrotonic spread can be measured in the basal cells of the human epidermis. The communication between neighboring cells is high, whereas no leak to the intercellular spaces could be detected. The specific resistance of the membranes between the cells is about 10 Ωcm². This finding suggests that for those particles that are able to pass the cell membrane the intracellular path through the epidermis is at least as suitable as the path through the intercellular spaces.     

Synchronized Growth In Human Epidermis Following Tape-Stripping: Its Implication For Cell Kinetic Studies

Abstract. A after stimulation A recent investigation of the hyperproliferative activity of human epidermis following sellotape stripping showed a wave of cell divisions with a maximal percentage of cells in mid-S phase at about 39 h after stripping. Here we present a study over the period of 52-76 h following stripping, showing a second wave of cell divisions with a maximal percentage of cells in mid-S at about 63 h. This indicates an average cell cycle time of about 23 h. Human epidermis after tape-stripping provides us with a useful model of synchronized growth, allowing us to study drug influences on cell kinetics accurately.     

Transmission And Scanning Electron Microscope Preparations Of The Same Cell Culture

A technique has been developed which allows transmission electron microscopy and scanning electron microscopy to be performed on the same cell culture sample. The technique uses the Costar 3393 Leighton Tube containing a plastic insert, which does not stick to epoxy, for transmission electron microscopy. A cut piece of the plastic insert can be critical point dried, sputter coated and viewed under high vacuum with the scanning electron microscope.     

Electron microscope studies of the human epidermis: the clear cell of Masson (dendritic cell or melanocyte)

The human epidermis has been studied by electron microscopy following osmium tetroxide and potassium permanganate fixation. An anatomically distinct cell in the human epidermis has been demonstrated with features similar to the melanocyte of the hair bulb described by Barnicot, Birbeck and Cuckow (3). It is dendritic in form and does not contain tonofilaments. "Intercellular bridges" are not formed. The mitochondria are larger and more numerous than those of other epidermal cells and the endoplasmic reticulum is more complex. Some of these cells contain melanin but others are melanin-free. The cell has been interpreted as being identical with the dopa-positive, clear cell of Masson (dendritic cell of Bloch or melanocyte). We have found that many membranous structures in the human epidermis are better preserved by permanganate fixation than by osmium tetroxide fixation.     

Light and Electron Microscope Studies of Some Annelid Setae

An account of a light and electron microscope study of the setae of Disoma multisetosum, Pectinaria belgica (Polychaeta sedentaria) and Echiurus echiurus (Echiuroidea) is given. The results are compared with those of previous researchers, and the possibility of using the ultrastructure of the “annelid seta” as a phylogenetic-systematic instrument is preliminarily discussed.     

Cell Kinetic Studies In the Epidermis of Mouse. Iii. the Percent Labelled Mitosis (Plm) Technique

Full PLM curves have been obtained for four sites in the mouse. the first peaks have been analysed by computer and the duration of the G₂+ M and S phases determined together with their standard deviations. the full curves showed a general similarity for all four sites with no clear second peak. the data are compared with the published data for mouse and human epidermis using the in vivo PLM technique. the timing and shape of the first peak can vary considerably even for one site in mice. Hence, both G₂+ M and S can vary in their durations. Cells labelled at one time of day exhibit different kinetic properties to those labelled at another time of day. the duration of G₂+ M is shortest in dorsum labelled at 03.00 hours (3.2 hr) and longest in tail (up to 7.5 hr). the S-phase is shortest in dorsum (6.3–7.2 hr) and longest in tail or ear (13.3–14.1 hr). There is also a very large standard deviation in tail and foot. There is little general variability when the psoriatic human data are considered, which is surprising. the general variability amongst the data from experimental mice might also be expected amongst humans which might make comparisons between the cell kinetics of normal and diseased skin difficult.     

The Development of the Cnidoblasts of Hydra : An Electron Microscope Study of Cell Differentiation

The general histological organization of Hydra is reviewed and electron microscopic observations are presented which bear upon the nature of the mesoglea, the mode of attachment of the contractile processes of the musculo-epithelial cells, and the cytomorphosis of the cnidoblasts. Particular attention is devoted to the changes in form and distribution of the cytoplasmic organelles in the course of nematocyst formation. The undifferentiated interstitial cell is characterized by a small Golgi complex, few mitochondria, virtual absence of the endoplasmic reticulum, and a cytoplasmic matrix crowded with fine granules presumed to be ribonucleoprotein. These cytological characteristics persist through the early part of the period of interstitial cell proliferation which leads to formation of clusters of cnidoblasts. With the initiation of nematocyst formation in the cnidoblasts, numerous membrane-bounded vesicles appear in their cytoplasm. These later coalesce to form a typical endoplasmic reticulum with associated ribonucleoprotein granules. During the ensuing period of rapid growth of the nematocyst the reticulum becomes very extensive and highly organized. Finally, when the nematocyst has attained its full size, the reticulum breaks up again into isolated vesicles. The Golgi complex remains closely applied to the apical pole of the nematocyst throughout its development and apparently contributes to its enlargement by segregating formative material in vacuoles whose contents are subsequently incorporated in the nematocyst. The elaboration of this complex cell product appears to require the cooperative participation of the endoplasmic reticulum and the Golgi complex. Their respective roles in the formative process are discussed.     

Recent X-ray Diffraction and Electron Microscope Studies of Striated Muscle

The sliding filament model for muscular contraction supposes that an appropriately directed force is developed between the actin and myosin filaments by some process in which the cross-bridges are involved. The cross-bridges between the filaments are believed to represent the parts of the myosin molecules which possess the active sites for ATPase activity and actin-binding ability, and project out sidewise from the backbone of the thick filaments. The arrangement of the cross-bridges is now being studied by improved low-angle X-ray diffraction techniques, which show that in a resting muscle, they are arranged approximately but not exactly in a helical pattern, and that there are other structural features of the thick filaments which give rise to additional long periodicities shown up by the X-ray diagram. The actin filaments also contain helically arranged subunits, and both the subunit repeat and the helical repeat are different from those in the myosin filaments. Diffraction diagrams can be obtained from muscles in rigor (when permanent attachment of the cross-bridges to the actin subunits takes place) and now, taking advantage of the great increase in the speed of recording, from actively contracting muscles. These show that changes in the arrangement of the cross-bridges are produced under both these conditions and are no doubt associated in contraction with the development of force. Thus configurational changes of the myosin component in muscle have been demonstrated: these take place without any significant over-all change in the length of the filaments.     

Scanning Electron Microscope Studies of Steinernema anomali Kozodoi, 1984

This paper presents SEM micrographs of portions of the male, female, and infective-stage juvenile of Steinernema anomali. Included are micrographs of the cephalic and caudal region, spicules, and gubernaculum of the male, the cephalic and vulval region of the female, and the cephalic region of the infective-stage juvenile. Males have six labial and four prominent cephalic papillae and small amphids. There are 11-14 pairs and one single genital papillae; of these, 6-9 pairs are preanal and subventral, one pair preanal, lateral, one pair adanal, and three pairs postanal. Spicules have a short head, a long blade, and a reduced shaft. The distal end is enlarged and bears a dorsal aperture. Gubernaculum much shorter than spicules; cuneus of gubernaculum short and bifurcate anteriorly. Females have six labial and four cephalic papillae and small amphids. Vulva with a thickened posterior lip. Infective juveniles have a smooth head, prominent amphids, and four cephalic papillae. Labial papillae, if present, are not evident.     

Observations of the Leaf Cell Vacuole of Stevia rebaudiana Bertani Under the Electron Microscope

By applying electron microscopic technique, we aimed to observe the morphology of leaf cell vacuole of Stevia rebaudiana Bertani, and the change of inclusion during its different stages of growth. We ascertain that the size of vacuoles is small in younger leaf cell, that the number of vacuoles is more than that in other stages, and that vacuoles appear translucent, either round or elliptical in form. Also those leaf cells that are at the stage of active growth appear to have many morphologically specialized vacuoles containing a lot of inclusions in different forms of granule and vesicle. Furthermore, the inclusion of the vacuols in the elder leaf cells decompose gradually, eventually disappear. Comparing with the substructural observation of chloroplast, by PAS reaction, and with different content of steviaside, we discover that there exists corresponding relationship. Thus, we may infer that steviaside is stored mainly in the vacuoles and it is relevant with the function of production.     

The Membrane Method of Electron Microscope Autoradiography

Thin sections of methacrylate and Araldite embedded tissues labelled with radioactive isotopes were transferred with a wire loop or brush from the knife edge onto thin formvar membranes which covered 7 mm holes in 76 × 25 × 1.5 mm or 76 × 38 × 1.5 mm plastic slides. To facilitate the mounting of sections, a platform supported the plastic slides close to the ultramicrotome knife. Photographic emulsion diluted 1:5 or 1:10 with water was applied with a pipette to the upper surface of each formvar membrane to cover the mounted sections. Excess emulsion was drained off and the remaining thin film was dried on a warm plate at 45 C to produce a uniform layer over the sections. After storing in the dark for several weeks, preparations were processed in photographic solutions and washed, and sometimes stained, before applying electron microscope grids to the underside of each formvar membrane. To detach each grid with its adherent formvar, section and emulsion, the membrane was pierced around the perimeter of the grid. Grain counts made over nuclei of cells labelled with tritiated thymidine indicate that emulsion is uniformly distributed over each section and that quantitative comparison is possible between labelled areas.