A modified aldehyde perfusion technique for preventing certain artifacts in electron microscopy of the central nervous system

Processing biological tissues for ultrastructural study

Biological tissues are passed through numerous procedures before they can be studied at the ultrastructural level with the electron microscope. Chemical fixation is widely used as a method for preserving structural detail and can be performed by simple immersion or total body vascular perfusion. A 2 to 4% solution of glutaraldehyde buffered with 0.1 M sodium phosphate, or a combination of similarly buffered glutaraldehyde and paraformaldehyde, can be used successfully to preserve the fine structure of biological tissues. The material next is washed briefly in the buffer vehicle and then secondarily fixed in 1% osmium tetroxide (osmic acid), which also is buffered with sodium phosphate. The tissue then is thoroughly dehydrated in solutions of ethanol at increasing concentrations of 50%, 70%, 95%, and 100%. After dehydration, tissues are infiltrated for a prescribed time interval with an epoxy embedding medium. After infiltration, specimens are transferred into fresh epoxy resin and polymerized at 60 to 70 degrees C for several hours. This orderly process ultimately yields fixed tissues that are encased in hardened blocks that can be thin-sectioned with an ultramicrotome. The thin sections are counterstained with solutions of heavy metals to add contrast. The material then can be subjected to the electron beam in an electron microscope to produce useful images for ultrastructural study. This overall procedure has been used successfully since the advent of biological electron microscopy to define the minute details of cells and tissues.

An antistress and antiaging neurometabolic therapy. Accelerated lipofuscinolysis and stimulated anabolic regeneration by the antagonic-stress synergistic formula

In both stress and aging, an etiopathogenic analysis demonstrates in the brain some common mechanisms and reciprocal accelerating relationships: hypoanabolism (decrease of RNA and protein synthesis), coupled with hypercatabolism (increase of oxidative stress-lipid peroxidation, with waste product accumulation: lipofuscinage pigment and water-insoluble proteins). For therapeutical intervention in these antihomeostatic processes, we successively (1972-1992) developed a neurometabolic antioxidative therapy--finally represented by a specific antistress and antiaging synergistic formula, Antagonic-Stress. Its homeostatic actions have been demonstrated in the stressed aging brains by reestablishing the anabolism/catabolism balance: anabolic regeneration by increasing total RNA, total proteins and water-soluble proteins, coupled with catabolic regulation by accelerated lipofuscinolysis and age pigment elimination (neuronal-->glial-->capillary route) and decreasing of water-insoluble proteins. Specific, synergistic, and superior actions of Antagonic-Stress multiple formula vs. antistress and antiaging monotherapy have been demonstrated by preclinical and clinical studies, confirming our results.

Fine architecture of the splenic terminal vascular bed as revealed by arterial and venous pressure-loading perfusion fixation

The three-dimensional fine architecture of the red pulp of human and animal spleens, which as fixed by a modified version of the arterial and venous pressure-loading perfusion fixation (AVPL perfusion fixation) method, is demonstrated by scanning and transmission electron microscopy. In the human spleen, changes in splenomegalias associated with hereditary spherocytosis and chronic portal hypertension are also introduced in addition to the normal architecture of the red pulp of spleens removed from patients with stomach cancer. The AVPL perfusion fixation of these spleens clearly visualized complicated three-dimensional fine architecture of the red pulp and provided much important information on in situ morphology and dynamic change of the terminal vascular bed, including venous pressure-dependent size change of the stomata and three-dimensional shapes of the capillary terminal, with positive proof of their opening into the cordal reticular tissue. In studies of the spleen associated with portal hypertension, the AVPL perfusion fixation is considered a necessary technique for analysis of the structural deviation closely relating to a very high venous pressure.

Improved procedures for pineal gland fixation for electron microscopy

The common procedures used for preparing some organs and tissues for electron microscopy, in which a fixative with the buffer portion adjusted to near-isotonicity to plasma is perfused in vivo, causes intolerable shrinkage of rat pineal cells. The present study was undertaken to optimize the parameters involved in the fixation of the pineal gland. The buffer and its concentration and the aldehyde or aldehydes used were among the variables investigated. The buffers tried were phosphate, cacodylate, PIPES, and HEPES. Decreasing the buffer concentration prevented shrinkage with all four buffers. The optimum concentrations were 0.05 M phosphate, 0.07 M cacodylate, 0.05 M or 0.057 M PIPES, and 0.1 M HEPES. PIPES and HEPES were clearly superior in retaining cytoplasmic density when compared with phosphate or cacodylate. The use of lithium PIPES and HEPES instead of the sodium equivalents enhanced membrane detail. A small volume of more concentrated aldehyde fixative perfused ahead of the main perfusate (a strong prewash) definitely helped prevent shrinkage. Using a mixture of aldehydes consisting of glutaraldehyde, formaldehyde, and acrolein reduced the tendency for shrinkage when compared with glutaraldehyde only. Some of the shrinkage space artefacts could be easily misinterpreted as normal features. Since the pineal gland commonly contains degenerating structures, a dependable fixation procedure is particularly needed. Also, accurate preservation is essential in the evaluation of physiological changes.

Membrane alterations in cerebral cortex when using PIPES buffer

When used for vascular perfusion of brain, 0.1 M PIPES-buffered 3% glutaraldehyde resulted in the formation of expanded, vesicle-filled cell processes limited by multiple membrane layers. These structures, termed multivesicular myelin figures and interpreted as artefacts, were most common in layer 2 of the cerebral cortex. When cacodylate or phosphate buffer was used instead of PIPES buffer in the primary fixative, such structures were not seen. The use of a more concentrated initial aldehyde fixative, PIPES-buffered, markedly reduced the size and numbers of these artefacts when compared to PIPES-buffered 3% glutaraldehyde only. Slowing the initial perfusion rate increased the size and frequency of occurrence of multivesicular myelin figures with PIPES buffer when compared to optimum perfusions. Prolonged initial exposure to PIPES buffer by using it to wash out the blood and then perfusing with fixative 5 min later did not increase the number or size of multivesicular myelin figures but did reduce the multivesicular nature of the artefacts. We suggest that the non-toxic nature of PIPES buffer allowed the formation of these membranous artefacts, while phosphate and cacodylate interfered with the cellular activity during the process of fixation.

Quantitative analyses of axonal endings in the central nucleus of the inferior colliculus and distribution of 3H-labeling after injections in the dorsal cochlear nucleus

Quantitative analyses of electron microscopic (EM) autoradiographs were used to identify the afferents from the dorsal cochlear nucleus in the central nucleus of the inferior colliculus (IC) in the cat. In order to localize the sources of radioactivity, material from axonal transport experiments was analyzed by means of a hypothetical grain procedure which takes the cross-scatter of beta particles into account. Measurements of the synaptic vesicles in axonal endings and a cluster analysis were used to identify different groups of endings. In order to determine which types of endings arise in the dorsal cochlear nucleus, axonal endings labeled after axonal transport and unlabeled endings were characterized and compared to the groups defined by the cluster analysis. Axonal endings with round synaptic vesicles were labeled with more than 2 grains/micron2 which was about 30% of the radioactivity in the central nucleus of the IC. This was six to seven times greater than if the radioactivity had been randomly distributed. Other tissue compartments usually had less radioactivity. Some myelinated and unmyelinated axons were labeled, but, as a group they had lower amounts of radioactivity than predicted by random labeling. In most cases, only low levels of activity were found in glial and postsynaptic structures. Five groups of axonal endings in the medial part of the central nucleus were identified by an analysis which clustered similar types of endings. The variance of the longest axis, the mean diameter, the variance of area, and the mean area of the synaptic vesicles were the variables most useful in distinguishing these five groups. Axonal endings with round synaptic vesicles were classified as either small, or large, or very large, while endings with pleomorphic vesicles were either large or small. Using measurements of the cross-sectional diameter of dendritic microtubules, samples of digitized axonal endings from normal and experimental cases were normalized and could be compared directly to the groups defined by the cluster analysis. Microtubules were 21.7 nm (+/- 1.6) in average diameter. After injections of 3H-leucine and/or proline in the dorsal cochlear nucleus, most of the labeled endings in the IC contained small, round vesicles (less than 47 nm in diameter) although a very small number of endings with large, round vesicles also were labeled.(ABSTRACT TRUNCATED AT 400 WORDS)

Vascular reactions to perfusion fixation

Vascular reactions to fixation with a 2 x 5% w/v glutaraldehyde fixative were studied in a constant flow perfusion system on isolated rabbit intestines and hind limb preparations. Reactions induced by the fixative were compared to reactions induced by noradrenaline in each single preparation. Changes in vascular resistance were assessed from continuous recordings of arterial and venous pressures and perfusion flow. Changes in vascular filtration and macromolecular permeability during fixation were approximated from recordings of flow and measurements of concentrations of dextran in the perfusate at the arterial inlet and at the venous outlet. Our results indicate that the vascular bed of the preparations studied can be reliably fixed in a high resistance state of smooth muscle activity induced by noradrenaline as well as in a low resistance state in the absence of noradrenaline, provided that hydrodynamic parameters are strictly controlled. The vascular filtration decreases during fixation. In optimally perfused preparations 5-10 min are required to fully saturate the binding capacity of the tissue for glutaraldehyde. Data on viscosity and colloid osmotic pressure of Tyrode solution containing dextran T-70 in various concentrations, and of various aldehyde-containing fixatives in 0 . 1 M sodium phosphate buffer with and without dextran added, are given.

Transmitter histochemistry of the rat olfactory bulb III. Autoradiographic localization of [3H]GABA

The distribution of [3H]gamma-aminobutyric acid (GABA) labeled elements in rat olfactory bulb was studied by light and electron microscopic autoradiography. [3H]GABA was strongly taken up into glial cells and pericytes in all layers of the bulb. The neuronal uptake of [3H]GABA was mainly seen in certain types of nerve terminals. About one-third of the granule dendritic terminals, some nerve endings of short axon cells, and certain nerve endings of extrabulbar origin showed a strong labeling. Labeling was seen in a small population of the periglomerular, short axon and granule cell bodies. Most cell bodies of these 3 types as well as the mitral cells did not, however, accumulate any appreciable amo9nt of [3H]GABA. The labeling pattern seen after injection of [3H]glycine and [3H]leucine was clearly different from the pattern seen after [3H]GABA injection. The labeling was more uniformly distributed over the components of the neuropil with a considerably higher activity over certain cell somata such as the mitral cells. The present results demonstrate that neuronal uptake and accumulation of [3H]GABA occur into populations of olfactory bulb cells and processes, which from neurophysiological and/or immunohistochemical studies are supposed to use GABA as a neurotransmitter.

Transmitter histochemistry of the rat olfactory bulb. II. Fluorescence histochemical, autoradiographic and electron microscopic localization of monoamines

The rat olfactory bulb was studied with the Falck-Hillarp formaldehyde fluorescence technique, including recent modifications, autoradiography and electron microscopic cytochemistry (permanganate fixation). Some periglomerular cells and few superficial tufted cells take up and accumulate catecholamines and precursors. They probably represent dopamine cells. In the glomeruli, probable 5-hydroxy-tryptamine nerve terminals could be identified. In the granular and external plexiform layers, noradrenaline axon terminals were present. At the ultrastructural level, monoamine boutons were in synaptic contact with dendritic spines of granule cells and in the glomeruli, probable 5-hydroxytryptamine boutons formed synapses with periglomerular cell dendrites. Therefore, monoamine afferents to the bulb may exert their influence via interneurons.

The ultrastructure of the sheath around chronically implanted electrodes in brain

Insulated, bipolar stainless steel electrodes were chronically implanted in various regions of the cat brain and the long-term structural changes in the tissue surrounding the electrodes were studied by light and electron microscopy. A sheath surrounded and separated the electrode from normal grey or white matter. A layer of foreign body giant cells of variable thickness was formed adjacent to the electrode. This layer was attenuated in some places so that it was unrecognizable by light microscopy. The bulk of the sheath structure consisted of collagen fibrils, leptomeningeal cells and hypertrophied astrocytes. Areas consisting of modified leptomeningeal cells with long thin processes we designated as spongy areas. These have not been previously reported using the electron microscope. Glycogen bodies were seen in leptomeningeal cells. Astrocytes became greatly enlarged and were more numerous in and around the sheath. Oligodendrocytes contained lamellar bodies, and direct continuity was shown between a lamellar body and an adjacent myelin sheath. Myelin was seen in abnormal sites (around oligodendrocytes and neurons) and in unusual configurations. Neuronal changes near the sheath included whorls and stacks of modified endoplasmic reticulum and the presence of cytoplasmic nucleolus-like bodies. Reactive, regenerative and degenerative axons were observed. Blood vessels were more numerous in the sheath and surrounding tissue than normal. Perivascular spaces were prominent even around capillaries and often plasma cells and monocytes were in these spaces. As compared to normal tissue the extracellular space is noticeably increased. Electrodes passing through ventricles were surrounded with a sheath covered with ependymal cells. This sheath was comparable in structure to the sheath present around the electrode in other locations.

The function of the retina in the perfused eye

The data show that the enucleated eye of the cat can be maintained in apparently physiologically functioning condition by appropriate arterial perfusion. Under appropriate conditions, photically evoked electrical mass responses can be recorded from various parts of the isolated, perfused eye for 8 to 10 hours. ERGs as well as responses from axonal bundles of the optic nerve exhibit shapes, amplitudes and time courses comparable to their counterparts in vivo. Homeostasis of the perfusion ensures the stability of these light-evoked electrical responses. Transient changes in biophysical parameters of the perfusate rapidly induce marked, although reversible, changes in the amplitudes of b-waves of the ERGs. Increases or decreases in the flow rate of the perfusate induce parallel increases or decreases in the amplitudes of the b-waves as well as of the optic nerve responses. Similar alterations in the oxygen concentration of the perfusate induce similar and proportional changes in the amplitudes of the b-waves. It is concluded, that low flow rates of hemoglobin-free perfusate induce hypoxia; consequently, acceleration of the flow can compensate for hypoxia in a certain range. Previous studies on the effects of and recovery after transient hypoxia in mammalian retina are in concordance with the present data. Progressive decrease of temperature induces gradual and reversible reductions in the amplitudes of the b-waves and increases their latencies and peak-times. It is suggested, that initial hypothermia, which occurs during the period of cannulation, reduces the deliterious effects of the coincident unavoidable hypoxia on retinal neuronal elements. Since light-evoked electrical responses can be maintained for many hours in these preparations and since movements of cardiovascular and respiratory origin, invariably present to varying extent in the in vivo experiments, are eliminated, this preparation is suitable for intracellular recordings from neuronal elements of the retina. Potentials were recorded from cells in various layers of the retina of the cat; intracellular recordings from horizontal cells (S-potentials) are described in detail. Spectral analysis of S-potentials allowed to distinguish between three types according to their inputs: a mixed, rod-cone type, which was most frequently encountered, a pure cone- and a pure rod-type. Light- and electronmicroscopic investigation of the retina after perfusion revealed that (1) the extent of cellular damage depends on the flow rate of the perfusate; (2) little cellular damage is observed if medium flow rates, which maintain physiologic responsiveness of the isolated eye to light, were applied for two hours; (3) high flow rates applied for two hours, or medium flow rates applied for 7 hours appear to induce cystic changes in the pigment epithelium, but only minor changes in the cells of the inner nuclear layer.

The avian erythrocyte: a study of fixation for electron microscopy

The quality of ultrastructural preservation of the avian erythrocyte achieved using various fixation techniques is evaluated. Different combinations of initial fixatives, buffers and post-fixation procedures were tested as well as variations in fixative osmolarity, pH and temperature. Of the commonly used initial fixatives (glutaraldehyde, acrolein and formaldehyde), 2% glutaraldehyde, alone in a slightly hypertonic buffer containing divalent ions, produced optimum erythrocyte preservation. The osmolarity was balanced using a non-electrolyte such as a sucrose. The addition of 12% hexylene glycol to the buffer solutions also improves erythrocyte preservation, as evidenced by the increased stability of the marginal microtubules, microfilaments and proteinaceous material. The use of Spurr low-viscosity epoxy resin enables the cells to be collected using low gravitational centrifugation.