Karin Gorgas

Fine structure of baroreceptor terminals in the carotid sinus of guinea pigs and mice

SummaryA light and electron microscopic study was undertaken on the baroreceptor axon terminals in the carotid sinus of guinea pigs and mice, using serial semithin and thin sections.Together with their enveloping Schwann cells, numerous lanceolate axon terminals are organized into a well-defined discoid end organ, referred to as the ‘baroreceptor unit’. Baroreceptor units measure 100 to 150 μm in diameter and are arranged in a hexagonal pattern. These end organs represent free branched lanceolate mechanoreceptors of complex type (Andres and von Düring, 1973) which belong to the main group of stretch receptors.In the guinea pig the lanceolate terminals enter the media and approach the innermost layers near the intima. In the mouse the terminals are seen to spread in the adventitia and along the medio-adventitial border. Only a few of them penetrate the external elastic layer. Species differences concerning the localization and extent of these visceral mechanoreceptors are discussed, as well as the modified architecture of the sinus wall in the receptor area (‘elastic segment’).Lanceolate terminals form beaded varicosities which are equipped with finger-like or lamellar axoplasmic protrusions. These projections contain a well-differentiated receptor matrix. They are attached to collagen and elastic fibers. The varicosities include densely packed mitochondria, neurotubules, profiles of axoplasmic reticulum, clear and granular vesicles, and striking accumulations of glycogen particles, lamellated bodies and lysosomes. Four types of varicosities are discerned according to their main axoplasmic components. Various types of these varicosities occur within an individual lanceolate terminal.The adrenergic innervation of the carotid sinus was studied by fluorescence histochemistry. In guinea pigs a multilayered wide-meshed plexus of fluorescent fibers occurs in the adventitia where it is closely related to baroreceptor stem fibers. However, adrenergic axons do not enter the media. In mice fluorescent fibers are extremely rare in the adventitia of the carotid sinus.

Morphology and histochemistry of the adrenal medulla

SummarySemithin sections (Araldite) of mouse adreno-medullary tissue were examined in the light microscope after perfusion fixation with glutaraldehyde, glutaraldehyde/formaldehyde or after freeze-drying followed by a treatment with hot formaldehyde gas. The following methods were employed: (i) aldehyde-induced fluorescence of catecholamines, (ii) Schmorls ferric ferricyanide reaction, (iii) argentaffin reaction, and (iiii) staining with alkaline lead citrate followed by Timms silver sulphide reaction. The correspondence of results obtained by the various methods was proven in consecutive sections or by successively applying different methods to identical sections.Four types of primary catecholamine-storing cells were identified. NA1 cells contain cytoplasmic granules up to 0.3 μm in diameter which stain black with ammoniacal silver and display a bright white to yellow fluorescence. NA2 cells show smaller cytoplasmic granules which stain brown with the argentaffin method and give white catecholamine fluorescence. NA3 cells appear yellow-earth after applying the argentaffin reaction and show greenish fluorescence. NA4 cells are hardly identified in the light microscope. These cells are significantly smaller than the above mentioned cells and characterized by a high nucleo-cytoplasmic ratio. They become straw coloured with ammoniacal silver and show greenish fluorescence.The argentaffin reaction was also used to identify these cells in semithin sections of glutaraldehyde/osmium tetroxide fixed material. The fine structure of the various noradrenalin-storing cells was studied in consecutive thin sections. NA1 cells were found to contain two populations of granules, the larger ones measuring between 300 and 350 nm, the smaller ones about 175 nm. The granules in NA2 cells correspond to this latter population (175 nm). NA3 cells contain an uniform granule population with a main diameter of 120 nm. The smallest granules are seen in NA4 cells being in the dimension of 80 nm. Granules in NA1 and NA2 cells show uniformly high electron density, whereas those in NA3 and NA4 cells display cores of varying density. Granules with moderately dense cores in NA3 and NA4 cells may represent partially emptied sites of noradrenalin storage or dopamin containing particles.

The permeability of blood vessels in the guinea pig cochlea

SummaryHorseradish peroxidase (HRP) has been injected intravenously in order to study its transport across endothelia of modiolar blood vessels. Fixation was performed by vascular perfusion at timed intervals after injection of the trace (1/2, 1, 2, 3, 5, 8, 10, 15, 20, 25, 30, 45 and 60 min).Fenestrated capillaries are found in the cochlear plexus only. In this region, diffusion of HRP into extracapillary spaces occurs already 1/2 min after the injection. It is possible to demonstrate the outflow of HRP across endothelial fenestrae.Vesicular transport of HRP across nonfenestrated endothelia (capillaries of the spiral ganglion, cochlear nerve, spiral limbus and the spiral vessel) does not reach significant amounts in the time intervals studied. Although HRP is found in membrane bound endothelial vesicles already 1 min after its injection, its concentration in extravasal spaces never attains amounts necessary for its histochemical demonstration. Thus these endothelia represent a blood-perilymph barrier to HRP.

Studies on intra-arterial cushions

SummaryThe distribution of horseradish peroxidase (HRP) in intraarterial cushions at the origins of intercostal arteries was studied in mice 30 min after intravenous injection of the tracer.HRP is found to be evenly distributed in the extracellular space of the entire arterial wall. Basal lamina material is penetrated by the tracer protein. This is not the case with collagenic fibrils, elastic material and intercellular granular deposits which occur regularly in cushions of adult mice but not in those of newborn animals (granules 300 to 800 Å in diameter, probably cell debris). However, the elastic sheets do not act as diffusion barriers. HRP is not phagocytized in significant amounts by ramified smooth muscle cells within the time intervals tested. It is therefore assumed that granular deposits are also not phagocytized by smooth muscle cells.

Formaldehyde induced catecholamine fluorescence in the mouse inferior laryngeal paraganglion

SummaryThe presence of high concentrations of catecholamines is shown in the mouses inferior laryngeal paraganglion by means of fluorescence histochemistry. In mice, the entire organ is composed of 20 to 25 small, intensely fluorescent cells of oval shape (about 15 μm in diameter). The paraganglion is well provided with capillaries. The identification of catecholamines in the inferior laryngeal paraganglion, originally described as nonchromaffin (parasympathetic) paraganglion, presents additional evidence that all paraganglia store biogenic amines, are related to the sympathetic nervous system, and belong to the APUD cell series.

Alkaline lead citrate: a selective stain for glutaraldehyde precipitates of indolamines and primary catecholamines in electron microscopy.

SummaryTest-tube experiments proved that alkaline lead citrate (Reynolds, 1963), which is generally used as an electron-opaque stain, specifically reacts with precipitates formed by glutaraldehyde and biogenic amines (indolamines, primary catecholamines). Glutaraldehyde/osmium tetroxide fixation and staining of thin sections with alkaline lead citrate is recommended as an optimal preparation method of studying the above-mentioned amines at a fine structural level.

Material und Methodik

Zur Untersuchung der inneren Rindenschichten der Nebenniere standen 3, 7 (♂, ♀) Sumpfbiber (Myocastor coypus Molina) zur Verfugung. Die Praparation der Tiere erfolgte stets zur gleichen Tageszeit (9.00–11.00), da die Nebennierenrinde in Abhangigkeit tagesrhythmischer Schwankungen der ACTH-Ausschuttung einem stetigen Funktionswandel unterliegt (Winkler et al., 1962; Retienne et al., 1964; u.a.).

The Ultrastructure of the Zona reticularis of the Adrenal Cortex from Nutria, Myocastor coypus Molina, with Special Reference to the So-Called Dark Cells

The main feature of the inner region of the nutria adrenal cortex (Myocastor coypus Molina) is a striking variety of cell types which differ essentially in the differentiation of their organelles and reflect the extreme plasticity of smooth ER and mitochondria in distribution and structure.