Biomedical subjects

R A Steinbrecht

Publications and source records attributed to R A Steinbrecht.

30 records · Page 2Linked to original sources

PubMed1989

Ions and mucoid substances in sensory organs--microanalytical data from insect sensilla.

In insect sensory organs, the receptor endings are surrounded by an extracellular subcuticular matrix, the sensillum lymph. This matrix provides the correct aqueous and ionic milieu around the sensory processes, plays a role in the generation of the receptor current, and is also important for stimulus transport and/or stimulus inactivation in chemoreceptors. Histochemical evidence indicates the presence of proteoglycans (probably hyaluronate and/or chondroitin sulfate) in the sensillum lymph. X-ray micro-analytical studies demonstrate a very low sodium content, whereas potassium is present in high concentrations, comparable to those in intracellular compartments. The total positive charges of cationic elements are not balanced by the negative charges of chlorine, but by polyanions of the mucoid substances present in sensillum lymph. These fixed negative charges probably play a key-role in the establishment of the non-neural transepithelial voltage of insect sensilla, which in turn is a major source of the receptor current. Moreover, the mucoid substances of the sensillum lymph are probably involved in water conservation, since sensilla are prone to water loss, because the overlying cuticle must be permeable to the chemical stimuli. Functional analogies are pointed out between insect sensillum lymph and vertebrate olfactory mucus and, in particular, the endolymph of the vertebrate inner ear.

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PubMed1984

Pheromone receptors in Bombyx mori and Antheraea pernyi. I. Reconstruction of the cellular organization of the sensilla trichodea.

The cellular organization of freeze-substituted antennal sensilla trichodea, which contain the sex pheromone receptors, was studied in male silkmoths of two species (Bombyx mori, Bombycidae; Antheraea pernyi, Saturniidae). The cellular architecture of these sensilla is complex, but very similar in both species. A three-dimensional reconstruction of a sensillum trichodeum of B. mori is presented. Two receptor cells (in A. pernyi 1-3) and three auxiliary cells are present. Of the latter, only the thecogen cell forms a true sheath around the receptor cells. A unique thecogen-receptor cell junction extends over the entire area of contact. Septate junctions occur between all sensillar cells apically, and in the region of the axonal origin basally. Gap junctions are also found between all cells except the receptor cells. The trichogen and tormogen cells show many structural indications of secretory activity and are thought to secrete the receptor lymph. Their apical membrane bordering the receptor-lymph space is enlarged by microvilli and microlamellae, but only those of the trichogen cell show regularly arranged membrane particles (portasomes), indicating secretory specialization among the auxiliary cells. Epidermal cells are found as slender pillars between sensilla, but extend apically along the non-sensillar cuticle and basally along the basal lamina.

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PubMed1984

Pheromone receptors in Bombyx mori and Antheraea pernyi. II. Morphometric analysis.

Sensilla trichodea of the silk moths, Antheraea pernyi and Bombyx mori, were reconstructed from serial sections after freeze substitution. The volume and surface area of the different sensillar cells were calculated from the area and circumference of consecutive section profiles. A. pernyi and B. mori differ largely in the size of the sensory hair and the larger outer dendritic segments as well as in the volume of the receptor lymph within the hair, while there are only small differences regarding inner dendritic segments, receptor-cell somata, trichogen and tormogen cells and the volume of the receptor lymph below the hair base. In each sensillum the two (or three) receptor-cell somata, dendrites, and initial axonal segments differ significantly in volume and surface. The apical cell membranes of the trichogen and tormogen cells, which border the receptor-lymph cavity and which are the presumed site of electrogenic cation pumps, are deeply invaginated and enlarged by microlamellae and microvilli, so that their area is twice that of the remaining basolateral cell membrane. In contrast to mechanoreceptors, the trichogen cell is the largest auxiliary cell and has the largest apical membrane surface. The morphometric data are discussed with regard to recent electrophysiological observations.

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PubMed1984

A cryoembedding method for cutting ultrathin cryosections from small frozen specimens.

A technique is described which allows one to embed small frozen specimens for easy sectioning in a cryoultramicrotome. n-Heptane is recommended as a cryoembedding medium due to its suitable melting point (182.4K), high vapour pressure, chemical inertia, and good sectioning properties when solid. Freeze dried cryosections of cultured muscle cells, slime moulds, insect antennae and unicellular algaee are presented as examples. There is no evidence that the preparation disturbs the distribution of soluble elements in the specimen, since X-ray spectra of muscle cells exposed to heptane do not differ from those of samples not exposed.

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PubMed1983

The effects of salines and fixatives upon the size of an identified neuron.

Because accurate neuronal dimensions are essential for mathematical modeling of neuronal properties, the effects of a number of salines and fixative procedures on neuronal size were compared, including the non-chemical, freeze substitution method. Using an identified neuron we compared diameters and found some of the fixative-saline combinations caused shrinkage by as much as a factor of four from our best estimates of the in vivo size from the quick frozen preparations. A glutaraldehyde based fixation procedure was found which gives results in good agreement with the frozen tissue.

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PubMed1980

Cryofixation without cryoprotectants. Freeze substitution and freeze etching of an insect olfactory receptor.

Antennae of the silk moth, Bombyx mori, were frozen by immersion into propane at -180 degrees C, and further processed by (a) freeze substitution (FS) or (b) freeze etching (FE). Although no cryoprotectant was used, freezing damage was observed in deeper tissue regions only. Data from FS specimens closely resemble those from FE replicas. Therefore, FS usually does not induce noticeable secondary artefacts by the preparation steps subsequent to freezing. When compared with chemically fixed antennae, the superior quality of cryofixation in this tissue is evident, particularly where cell surfaces and processes border the receptor lymph cavity; membranes are smooth following a steady course; dendrites and axons are round in cross-section with evenly distributed microtubules. The value of cryofixation is discussed with special reference to structures of presumed functional significance (e.g. stimulus conducting pore tubules, intramembrane particles of the receptor membrane, the ciliary segment of the dendrites, intercellular dilations, membrane junctions).

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PubMed1976

Fine structure of the antennal receptors of the bed bug, Cimex lectularius L.

Sensilla on the antenna of the bed bug, Cimex lectularius, were studied with the scanning and transmission electron microscope. Those which display a tubular body in the dendrite ending are presumed to have a mechanoreceptor function (bristles of type A, flat plate of type B). Bristles of type A1 contain additional dendrites which terminate at the tip of the bristle and may be gustatory receptors. Sensilla with pores in the hair wall are supposed to have an offactory, humidity and/or temperature receptor function (pegs and hairs of types C, D, E). Hairs of type E contain receptors for the alarm pheromones of the bed bug. Special attention has been paid to the pore structures and epicuticular layers of these sensilla. Possible differences in stimulus conduction are discussed between (i) sensilla with a simple wall and pores with pore tubules (types D and E) and (ii) the ribbed pegs (type C), which have a complex wall structure and spoke channels. The immersed cones of type F have a peculiar innervation, which has not been described previously. Two dendrites are held closely together by a third flat dendrite which wraps around them in the region of the outer segment. Coupling structures were found between the central dendrites, and between these and the third enveloping dendrite. Possible functions of this unique innervation are discussed. The dendrites innervating type D are grouped in three to eight bundles by multiple sheaths. The term thecogen cell is introduced to denote the innermost of the three sheath cells of a sensillum (the outer being the tormogen and the trichogen cell) which builds the dendrite sheath during ontogeny. Comparative morphometry revealed type-specific differences in the length and diameter of the dendrites. Some axons were found to lack any glial or perineurial sheath. Microorganisms were observed in the antennal tissue of several animals.

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PubMed1974