Ulrich Welsch

The fine structure of the digital pads of rhacophorid tree frogs

SummaryThe digital pads of three tree-frogs (genus Rhacophorus) have been studied by transmission and scanning electron microscopy. The distal parts of the outermost epidermal cells are separated by wide gaps. The surface of these cells is characterized by stout microvillus-like processes. The apical plasma membrane is reinforced by a layer of electron-dense material attached to its inner side. The cytoplasm contains bundles of tonofilaments extending into the apical cellular processes, numerous ribosomes and abundant granular and vesicular inclusions. In the connective tissue under the epidermis mucous glands — characterized by granule-containing, mitochondria-rich and smooth muscle cells — and an extensive nerve plexus occur. The latter innervates the mucous glands and in addition consists of sensory fibres which have been found in connection with lamellated sensory corpuscles. In respect of the degree of adaption towards a tree-dwelling life, the excluvisely tree inhabiting species (Rhacophorus reinwardti) appears to be particularly advanced.

Electron microscopical observations on Kölliker's and Hatschek's pit and on the wheel organ in the head region of Amphioxus (Branchiostoma lanceolatum)

SummaryKöllikers and Hatscheks pit and the wheel organ in the head region of Amphioxus have been studied with the electron microscope. Köllikers pit is lined by ciliated cells lacking specific ultrastructural characteristics which might suggest an olfactory function. No nerve terminals have been found near this structure. The wheel-organ consists of tall ciliated cells, which occasionally have been found to be innervated and which are clearly marked off the rest of the epithelial lining of the oral cavity. The epithelium of Hatscheks pit again is ciliated and possesses markedly euchromatin rich nuclei. In the area of Hatscheks pit numerous epithelial cells have been observed which possess accumulations of small granules and vesicles in their basal cytoplasm. Such basally granulated cells occur in the immediate neighbourhood of blood spaces of the glomus and other vessels; the connective tissue between blood and epithelium is loosened up or has completely disappeared. The question of homology of the structures investigated with the olfactory groove and hypophysis of vertebrates is briefly discussed.

The fine structure of the stomochord of the enteropneusts Harrimania kupfferi and Ptychodera flava.

SummaryThe stomochord of Harrimania kupfferi and Ptychodera flava. a tubular structure which extends from the oral cavity into the presoma, consists of two cell types:a)epithelial cells interconnected by desmosomes, which bear at their apical pole a brush-border and cilia. The largest part of these cells is occupied by a voluminous vacuole;b)mucus cells. In addition, at the base of the epithelium numerous nerve fibres occur, which are characterized by electron dense granules of about 1,500 Å diameter. The whole stomochord is surrounded by a basement lamina and connective tissue fibres.The question of homology between stomochord and notochord is discussed.ZusammenfassungDas Stomochord von Harrimania kupfferi und Ptychodera flava, eine Ausbuchtung des Darmkanals der Enteropneusten, welche in das Präsoma hineinragt, besteht aus zwei Zelltypen:a)Epithelzellen, die durch Desmosomen verbunden sind und große Vakuolen besitzen; ihr distaler Zellsaum ist mit Mikrovilli und Zilien ausgestattet.b)Schleimzellen. An der Basis des Epithels kommen zahlreiche Nervenfasern vor, die Granula (Durchmesser etwa 1,500 Å) enthalten.Das Stomochord wird von einer Basallamina und Bindegewebsfasern umschlossen.Die Frage der Homologie des Stomochords mit der Chorda dorsalis wird diskutiert.

Epitheliomuscular cells in Lingula unguis (Brachiopoda) and Branchiostoma lanceolatum (Acrania).

SummaryEpitheliomuscular cells largely corresponding to those of cnidarians have been found in the mesenteria of Lingula and in various coelomic channels of Branchiostoma. They are characterized by basal extensions containing thin and thick myofilaments. In Lingula they also bear an apical cilium.

Septate junctions in the cephalic epidermis of turbellarians (Bipalium)

SummaryIn the epidermis of turbellarians septate junctions of the pleated sheet type have been demonstrated in conventional thin sections and freeze fractured preparations. The structure of these junctions entirely agrees with that found in molluscs and arthropods.

Ultrastructural changes in lactating tissue related to the suppression of milk secretion by concanavalin A

SummaryThe plant lectin, concanavalin A (Con A) suppresses milk secretion when infused into the mammary gland or when incubated with lactating tissue in vitro. Toward defining its mode of action, we infused Con A into rat and goat mammary glands via the teats and observed effects on lactating cells. Lectin dosages were 2 and 25 mg per gland for rats and goat, respectively. Tissue samples were taken 1 and 3 h post infusion for rats and at 24 h for the goat. Control and Con A-treated tissues were observed by light microscopy and by both thin section and freeze fracture electron microscopy. In comparison to controls, Con A-treated tissues of both species exhibited alveoli with enlarged cells and relatively empty lumina; cells were distended with secretory vesicles and fat droplets. Apical plasma membranes of lectin-affected cells of the rat displayed a marked reduction in the number of microvilli, and exhibited an atypical branching and folded structure. Morphometry was employed to quantitate changes in cell and secretory product parameters in both rat and goat tissue. Microtubule numbers and distribution did not appear to be altered by Con A but considerable changes were noted in the arrangement of microfilaments associated with the secretory surface of lectin-treated epithelial cells. Various related ultrastructural changes and the role of Con A in perturbing the microfilament system are discussed.

Histological and histochemical observations on the neurosecretory cells in the diencephalon of Chthonerpeton indistinctum and Ichthyophis paucisulcus (Gymnophiona, Amphibia).

SummaryIn the diencephalon of two species of Gymnophiona (Amphibia) two neurosecretory nuclei were examined with histological (Alcian Blue, Aldehyde Fuchsin, Brookes Trichrome stain) and enzyme histochemical techniques (acid phosphatase, α-naphthyl acetate esterase, acetylcholinesterase (AChE)). In the preoptic nucleus two categories of secretory neurons were distinguished: large and medium sized neurons. The perikarya of both cell types contain very little neurosecretory material. The Alcian Blue method stained the medium sized neurons faintly but selectively. The tractus praeopticohypophyseus is marked by the presence of Herring bodies, which, however, are relatively scarce. The neurohypophysis, in contrast, contains large amounts of neurosecretory material. Both cell types of the preoptic nucleus are characterized by their very strong AChE and α-naphthylacetate esterase activity. The AChE also marks the tractus praeoptico-hypophyseus. In the large neurons acid phosphatase is present around the nucleus; in the medium sized neurons this enzyme is concentrated close to the origin of the axon. In the dorso-caudal hypothalamus a small group of neurons is stained with Alcian-Blue. These neurons, which also contain AChE, are located immediately under the ependyma which seems to be specialized in this region.

Freeze-fracture study of the turtle lung

SummaryThe air-blood barrier in the lung of the turtle Pseudemys scripta was studied by means of freeze-fracture replicas in an attempt to give a detailed account on the structural organization of the intercellular junctions. Between the pneumocytes, zonulae occludentes containing 4–19 strands in the apico-basal direction are present; they are considered to be physiologically very tight. In the endothelium, fasciae occludentes, i.e., discontinuous occluding junctions can be found, composed of up to 4 strands. These junctions are regarded to be very leaky. The findings are discussed in relation to recent physiological results, suggesting that in comparison with ‘dry’ mammalian lungs, the turtle lung is a rather wet lung based on its much larger transcapillary fluid filtration into the interstitium. In addition, small maculae communicantes are demonstrated between the pneumocytes; they possibly serve for metabolic coupling.