Cell volume preservation and the reflection coefficient in chemical fixation

Glutaraldehyde - A Subtle Tool in the Investigation of Healthy and Pathologic Red Blood Cells

Glutaraldehyde is a well-known substance used in biomedical research to fix cells. Since hemolytic anemias are often associated with red blood cell shape changes deviating from the biconcave disk shape, conservation of these shapes for imaging in general and 3D-imaging in particular, like confocal microscopy, scanning electron microscopy or scanning probe microscopy is a common desire. Along with the fixation comes an increase in the stiffness of the cells. In the context of red blood cells this increased rigidity is often used to mimic malaria infected red blood cells because they are also stiffer than healthy red blood cells. However, the use of glutaraldehyde is associated with numerous pitfalls: (i) while the increase in rigidity by an application of increasing concentrations of glutaraldehyde is an analog process, the fixation is a rather digital event (all or none); (ii) addition of glutaraldehyde massively changes osmolality in a concentration dependent manner and hence cell shapes can be distorted; (iii) glutaraldehyde batches differ in their properties especially in the ratio of monomers and polymers; (iv) handling pitfalls, like inducing shear artifacts of red blood cell shapes or cell density changes that needs to be considered, e.g., when working with cells in flow; (v) staining glutaraldehyde treated red blood cells need different approaches compared to living cells, for instance, because glutaraldehyde itself induces a strong fluorescence. Within this paper we provide documentation about the subtle use of glutaraldehyde on healthy and pathologic red blood cells and how to deal with or circumvent pitfalls.

What do the synaptic vesicles contain?

The intersynaptic membranes of the rat brain cortex were found to remain firmly attached to one another after perfusion of strongly anisotonic solutions. Brains perfused with depolarizing and excitotoxic agents showed abundant, apparent intermingling of mitochondria and synaptic vesicles. The results suggest (i) that the intersynaptic membranes are not separated from one another by an essentially fluid intersynaptic medium as it is commonly assumed, but rather firmly attached to one another by a layer of faintly osmiophilic yet remarkably stable, water-insoluble material; and (ii) that the synaptic vesicles may be involved in adenosine triphosphate carriage. Well established multidisciplinary data are presented which appear to be in line with both possibilities.

Dimensional changes in cells and tissues during specimen preparation for the electron microscope

Studies on dimensional changes incurred during preparation of tissue specimens for the transmission and scanning electron microscopes are reviewed, with emphasis on quantitative measurements pertinent to morphometry and three-dimensional reconstruction. The scope of the review includes fixation, dehydration, plastic embedment, critical-point drying, and freeze-drying. Recommendations are presented for monitoring dimensional changes; a strategy for the choice of method of specimen preparation is outlined.

Alignment and intracytoplasmic disintegration of synaptic vesicles in the brain cortex

Perfusion fixation with highly concentrated aldehydes suggests that the synaptic vesicles undergo disintegration within the presynaptic ending upon touching the presynaptic membrane rather than being released by exocytosis into the intersynaptic cleft. Three factors have been explored in order to inquire further into the possible significance of the findings: (a) fixative concentration; (b) physiological activity; (c) cell depolarization. The transformation of the vesicles into amorphous, electron-dense material was observed in all experiments in all synapses, including those fixed with the lowest concentration of aldehydes. Besides, after acute ischemia and perfusion of excitatory and depolarizing pharmacological agents, the synaptic vesicles were seen to conflue upon the intersynaptic cleft in well-aligned rows. It was also found that the vesicles flow post mortem towards the intersynaptic cleft with absolute specificity.

Synaptic vesicle relationships with the presynaptic membrane as shown by a new method of fast chemical fixation

Brief vascular perfusion of the rat brain with a mixture of concentrated aldehydes completely insolubilized the brain protein in less than 30 s and yielded excellent ultrastructural preservation. Abundant synaptic vesicles closely and specifically attached to the presynaptic membrane were constantly detected. These vesicles appeared to undergo progressive transformation into amorphous, electron-dense material. No evidence of vesicle exocytosis was detected in the brains perfused in vivo but fixations performed 1 h after death showed abundant exocytotic-like images. The results suggest that the vesicles may not be exocytotically released to the intersynaptic cleft but disintegrate intracytoplasmically in the immediate vicinity of the presynaptic membrane.

Postnatal development of the feline lateral cervical nucleus: I. A quantitative light and electron microscopic study

With the aim of obtaining some basic information for future developmental studies, the lateral cervical nucleus (LCN) was investigated in 32 kittens of different ages by electron microscopic and stereologic methods. Corresponding light microscopic measurements of neuronal and nuclear profiles and of the total LCN volume were also performed. The total LCN volume increased sixfold between the ages of 12 hours and 120 days, the most rapid increase occurring during the first month. The neuronal size was fairly constant up to the age of 9 days, whereafter it showed greater variation. The mean profile area increased rapidly during the second week and then more slowly. The relative volume of boutons increased significantly between birth and the age of 34 days and then decreased slightly up to 120 days postnatally. The total bouton volume showed a steady increase, which was most pronounced between the ages of 9 and 34 days. The relative dendritic volume decreased during the 120 days of observation, whereas the total volume of dendrites increased up to the age of 92 days and then decreased. The total volume of glial cells increased during the 120-day observation period, as did both the relative and total volumes of myelinated axons. The changes in the relative volumes of mitochondria in boutons and dendrites were very similar, with increases that were most marked between the ages of 9 and 34 days and between 92 and 120 days.

Changes in transcapillary exchange induced by perfusion fixation with glutaraldehyde, followed by measurements of capillary filtration coefficient, diffusion capacity and albumin clearance

The isolated, maximally vasodilated rat hindquarter preparation was used to determine how fixation of the vascular bed (glutaraldehyde, 2.5% in 0.05 M Na-cacodylate with dextran 40 g X 1-I) affected transcapillary filtration and diffusion events, as well as macromolecular transfer, measured as transport of water (CFC), of small solutes (PS) and of 125I-albumin. Vascular conductance to flow was decreased by 52% after fixation. The three capillary permeability-surface area parameters were reduced almost equally to 50% of control after fixation, i.e. the relative flux rates of water, small and large molecules were similar in the living and in the fixed vascular bed. As this fall in transendothelial exchange was larger than the calculated degree of wall shrinkage of the resistance vessels, it could not be ascribed simply to a uniform shrinkage which also involved the capillaries. Rather, the fixation appears to have induced closure of entire capillaries. As a consequence, the surface area for exchange is reduced, with no apparent changes in membrane 'permselectivity'.

Validation of cell volume determination for stereological studies of adrenocortical cells: comparison of values from semifine sections with those of dissociated zona fasciculata cells

The average cell volume of rat adrenocortical zona fasciculata cells, determined using three different stains on semifine sections, was compared to that of dissociated, unfixed zona fasciculata cells. The maximum number of nuclei per area (NA) was obtained by counting nuclear profiles in semifine sections from nonosmicated adrenocortical tissue stained with toluidine blue. In osmicated adrenocortical tissue on the other hand, fewer nuclear profiles were seen and more of the small size classes were missing from the distribution of profiles. The skewness of the nuclear-profile distribution was much greater in osmicated than in nonosmicated tissue, reflecting the missing small profiles. Although the average diameter of nuclei (D) in nonosmicated tissue was smaller than that for osmicated tissue, profiles were in all likelihood more readily identified because they stained quite intensely. Three different methods for correcting nuclear-size profile distribution and determining nuclei per volume (NV) (Giger-Riedwyl, Cruz-Orive, and Weibel-Gomez) were generally in agreement for nonosmicated tissue. Considerable shrinkage occurred during preparation for electron microscopy, with the greater change occurring in nonosmicated tissue. Cell volume in osmicated tissue corrected for shrinkage varied considerably among the different methods, producing significantly greater values for cell volume than those in nonosmicated tissue. The cell volume of nonosmicated tissue, corrected for shrinkage during processing and for missing small nuclear profiles, did not differ significantly from that of freshly dissociated zona fasciculata cells. The one exception was nonosmicated tissue stained by Feulgen-methylene blue and corrected for missing small nuclear profiles by the method of Cruz-Orive. Use of nonosmicated adrenocortical tissue in stereological studies with an appropriate correction for shrinkage for each experiment is recommended for determining cell volume, although osmicated tissue should also be included to facilitate identification of intracellular membranes when electron microscopy is required.

Electron staining of the cell surface coat by osmium-low ferrocyanide

In aldehyde-fixed liver and renal cortex of rat and mouse several variations of postfixation with osmium tetroxide plus potassium ferrocyanide ( FeII ) were tried. Depending on the ferrocyanide concentration different staining patterns were observed in TEM. -Osmium-High Ferrocyanide [40 mM (approximately 1%) OsO4 + 36 mM (approximately 1.5%) FeII , pH 10.4], stains membranes and glycogen. Cytoplasmic ground substance, mitochondrial matrices and chromatin are partially extracted, cell surface coats remain unstained. Membrane contrast, but extraction too, are higher with solutions containing cacodylate- than phosphate-buffer. -Osmium-Low Ferrocyanide [40 mM (approximately 1%) OsO4 + 2 mM (approximately 0.08%) FeII , pH 7.4], stains cell surface coats and basal laminae, but not glycogen, except for special cases. The trilaminar structure of membranes is poorly delineated. Signs of cytoplasmic extraction are not visible. The surface coat staining is stronger and more widespread with solutions containing phosphate- instead of cacodylate-buffer; it is enhanced by section staining with lead citrate. The cell surface coat stain does not traverse tight junctions nor permeate membranes.