Willy Humbert

The midgut of Tomocerus minor lubbock (Insecta, Collembola): Ultrastructure, cytochemistry, ageing and renewal during a moulting cycle

SummaryThe midgut cells of Tomocerus minor (Insecta, Collembola) were examined with the electron microscope and cytochemically. The midgut epithelium consists of a series of cells characterised by numerous mineral concretions scattered throughout the cytoplasm. Mitochondria are abundant; microvilli are well developed at the apical surface of the cell. A zonula continua (continuous junction) characterises the apical contact region of these cells. Polysaccharides, glycoproteins and carbohydrate components have been demonstrated on the surface of microvilli. Peritrophic membranes surround the food bolus and preserve midgut cells from mechanical abrasion. Lysosomes are present during the alimentary period and show strong acid phosphatase activity. During an intermoulting cycle, two stages can be observed: (1) the postexuvial feeding period during which cytoplasmic extrusions appear at the apical part of the cell: lysosomes increase in number and autophagic vacuoles appear. (2) The preexuvial fasting period; a new epithelium grows beneath the old one and pushes it into the lumen. Degeneration processes can be observed in the old epithelium. This excretory reactivity of the midgut epithelium has been compared to the cycle of the cuticle.

Calcium content and concretions of pineal glands of young and old rats

SummaryCalcium content and pineal concretions were studied in young (2–3 months) and old (28 months) Wistar rats. Samples, deep-frozen by liquid propane/isopentane and freeze-dried were analysed by means of X-ray microanalysis in a scanning electron microscope. Total semi-quantitative measurements revealed that pineals of old rats showed a marked increase of calcium compared with the pineals of young rats. It is thus suggested that a calcium-rich environment is responsible for the growth of pineal concretions, which only appear in old rats. Pineal calcifications in rats could thus be an indicator of aging and/or of a degenerating state.

The pineal gland of the aging rat: Calcium localization and variation in the number of pinealocytes

Abstract: In the present study, we investigated the population of pinealocytes in the pineal gland of aging rats. Dark and light pinealocytes were analyzed as to their calcium content. Calcium localization was realized in dark and light cells by means of cytochemistry and X‐ray microanalysis. Calcium was mainly localized in dark pinealocytes characterized by many ultrastructural signs of degeneration. The number of pinealocytes per square surface of aged rats (28 months) was com‐pared to young ones (3–4 months). While there is a significant increase in the number of dark pinealocytes there is a decrease in the total number of pinealo‐cytes in aged rats. This age‐related loss of pinealocytes may explain the age‐related functional decline of the pineal gland activity (e.g., the decrease of the nocturnal melatonin production).

Calcium concretions in the pineal gland of aged rats: an ultrastructural and microanalytical study of their biogenesis

The genesis of calcium concretions in aged rats was studied by means of transmission and scanning electron microscopy. The potassium pyroantimonate method, combined with X-ray microanalysis, allowed us to study the distribution of cations and calcium. Notable accumulations of calcium (associated with phosphorus) were localized in vesicles, vacuoles, lipid droplets, lipopigments, and mitochondria of dark pinealocytes. The results obtained in the present investigation suggest that these organelles are involved in the genesis of the concretions. The presence of sulfur indicates the existence of an organic matrix. We propose that genesis takes place in dark pinealocytes, which contain more calcium than light pinealocytes. Mineralization foci are some-times associated with cellular debris and enlarge by further apposition of material. Two types of concretions, as determined by electron microscopy and confirmed by electron diffraction, could be observed: the “amorphous” type with concentric layers and the crystalline type with needle-shaped crystals. Once formed, the concretions reach the extracellular space and the cell breaks down. Possible extracellular calcification is suggested in the extracellular calcium-rich floculent material. The mineralization process is interpreted as being an age-related phenomenon and mainly a consequence of the degeneration of pinealocytes.

The role of mucus in ion absorption by the oesophagus of the sea-water eel (Anguilla anguilla L.)

Summary1.The structure of mucus in the oesophagus of the sea-water adapted eel, consists of a framework of fibers decreasing in density and thickness from the anterior to the posterior oesophagus.2.With seawater in the lumen the mucus layer supports, in vitro, about 45% of the lumen to serosa gradient of sodium ion activity along the whole oesophagus. It supports different chloride ion activity gradients: about 80% in the anterior and about 45% in the middle and posterior oesophagus. These results are confirmed by X-ray micro-analysis.3.Experiments without lumen-to-serosa gradients demonstrate a linked sodium and chloride active absorption appearing in the middle oesophagus and increasing towards the posterior oesophagus.4.Na+−K+-ATPase is cytochemically demon-strated but could not be inhibited by ouabaïn during in vitro experiments, due to its particular localization.

Mucus and intestinal ion exchanges in the sea-water adapted eel, Anguilla anguilla L.

Summary1.Scanning electron microscopy of the intestinal epithelium in the cel showed an important mucus layer over the middle intestine.2.Ion-selective microelectrodes (Na+, Cl−, K+) demonstrated several standing gradients of ion activities in the mucus layer.3.The Na+ and Cl− gradients were identical and related to transepithelial NaCl absorption. They were cancelled by ouabain application on the serosal side.4.Symmetrical substitution of Na+ or Cl− in the luminal and serosal Ringer solution gave results in agreement with the presence of an apical Na+−K+−2Cl− cotransport system, and of K+ channels.5.The intestinal mucus appeared, at least in the middle part of the intestine, to act as a diffusion barrier essential to K+ recycling.

Role of intestinal mucus in crystal biogenesis: an electron-microscopical, diffraction and X-ray microanalytical study

SummaryIn the posterior intestine of the sea-water eel, mucus plays an important role in biocrystallization of calcium ions. By means of transmission and scanning electron microscopy associated with X-ray microanalysis and X-ray diffraction it has been possible to determine the role of mucous fibers as nucleation sites. Biocrystallization occurs in 2 steps: (1) Calcification of mucus. As soon as mucus is excreted in the intestinal lumen, it is loaded with calcium, as shown by lanthanum affinity and X-ray microanalysis on freeze-dried tissues. (2) Genesis of crystals. Needleshaped crystallites build up in coalescent spherites in the intestinal lumen near the microvilli. Genesis occurs as follows: (a) crystallite mineralization by nucleation in an organic matrix composed of glycoproteinaceous mucous fibers, followed by the appearance of spherites; (b) coalescence in spherites and association of spherites in rhombohedra; (c) extrusion of organic material during the final step of crystallization.

Permeability of the pineal gland of the rat to lanthanum: Significance of dark pinealocytes

Abstract: The permeability of the pineal gland to lanthanum was investigated by means of transmission electron microscopy and X‐ray microanalysis. Different pineal cell populations were studied. Light pinealocytes as well as glial cells were not permeated by the tracer lanthanum, which normally stays extracellularly. Dark pinealocytes showing different degrees of degenerative changes are permeated by lanthanum. The loss of plasma membrane integrity explains the entry of lanthanum into these cells. We conclude: (1) the lanthanum tracer can be used as an indicator of an alteration in membrane permeability, (2) dark pinealocytes appear as cells in the state of degeneration and represent a different physiological state than light pinealocytes.

Is mucus involved in biocrystallization

SummaryFreeze-dried intestinal mucus of sea-water-adapted eels was analysed by scanning electron microscopy (SEM) and X-ray microanalysis. Calcite crystals were observed in the mucus fibres; their concentration increased along the hindgut. Random SEM observations made in situ indicated that mucus fibres were involved in the genesis of these crystals. Calcium-rich mucus globules were found fused inside crystal matrices. Single typical rhombohedric crystals of various complexity appeared within the mucus framework. The steps of crystal biogenesis were reconstituted in in-vitro conditions.

A POSSIBLE ROLE OF COLLAGEN FIBRILS IN THE PROCESS OF CALCIFICATION OBSERVED IN THE CAPSULE OF THE PINEAL GLAND IN AGING RATS

Abstract.The relationship between collagen fibrils and calcified concretions exclusively appearing in the pineal gland of adult/aging rats has been investigated. Deposits of lanthanum, which replace calcium ions are distributed along collagen fibrils with a repeating period of about 70 nm. Calcium has been detected histochemically between collagen bundles surrounding extracellular concretions by means of the pyroantimonate method and by X-ray microanalysis. It is associated with phosphorus. The data presented here suggest that collagen fibrils are involved in the genesis and growth of extracellular concretions located in the connective tissue surrounding the pineal gland of aging rats.