Staining of Oligodendroglia with Silver Ammino Tungstate in Unembedded and Embedded Material

Specimens of brain or spinal cord fixed in formalin, Cajal's formol-bromide, or Koenig, Groat and Windle's formalin-acacia can be used to stain oligodendrocytes in frozen, in paraffin, or in celloidin sections. The sections are soaked 3-5 min in 0.02% acetic acid, pH 3.4, then rinsed 2-3 sec in 3% H₂O₂ and transferred to a silver bath prepared as follows: Mix equal parts of 10% AgNO₃ and 10% Na₂WO₄, and dissolve the precipitate with concentrated NH₄OH; avoid an excess of ammonia. Silver at room temperature for 15-20 sec, develop in 1% formalin, dehydrate, and mount. For embedded material, prepare a mixture consisting of 1 part of 10% aqueous Aerosol MA and 4 parts of 10% Aerosol OT in 95% alcohol. Add 5 drops of this mixture to each 50 ml of dilute acetic acid and 3% H₂O₂; 5 drops to each 20 ml of the silver bath.     

Preparation of Large Epoxy Sections for Light Microscopy as an Adjunct to Fine-Structure Studies

Tissue blocks 2 × 2 × 0.4 cm were fixed 6-24 hr in phosphate-buffered 5% glutaraldehyde then sliced to 2 × 2 × 0.1 cm and soaked in 0.1 phosphate-buffer (pH 7.3) for at least 12 hr. Fixation was continued for 2 hr in phosphate-buffered 1-2% OsO₄. The slices were dehydrated, infiltrated with Araldite, and embedded in flat-bottomed plastic molds. Sectioning at 1-8 μ with a sliding microtome was facilitated by addition of 10% dibutylphthalate to the standard epoxy mixture. The sections were spread on warm 1% gelatin and attached to glass slides by drying, baking at 60 C, fixing in 10% formalin or 5% glutaraldehyde and baking again. Sections were mordanted in 5% KMnO₄ (5 min), bleached with 5% oxalic acid (5 min) and neutralized in 1% Li₂CO₃ (1 min). Several stains could then be applied: azure B, toluidine blue, azure B-malachite green, Stirling's gentian violet, MacCallum's stain (modified), tribasic stain (modified) and phosphotungstic acid-hematoxylin. Nuclei, mitochondria, specific granules, elastic tissue or collagen were selectively emphasized by appropriate choice of staining procedures, and cytologic detail in 1-3 μ sections was superior to that shown by conventional methods. Selected areas from adjacent 4-8 μ sections could be re-embedded for ultramicrotomy and electron microscopy.     

Differentiation of Cells in the Hypophysis and in Pancreatic Islets

Deparaffinized, 3-5μ, sections are brought to water, oxidized 3.5 min in an equal-parts mixture of 0.3% H₂SO₄ and 0.3% KMnO₄, and decolorized with 4% K₂S₂O₅. Nuclei are stained with Gomori's (1939) chromium-hematoxylin, and cell granules with Cason's (1950) mixture. The eosinophilic cells of the hypophysis and the alpha cells of pancreatic islets (of Langerhans) stain carmine red; basophilic and beta cells stain dark blue. Heidenhain's _susa is the most suitable fixative for hypophysis, Bouin's fluid for pancreas; but a satisfactory result is obtainable after formalin-sublimate or plain formalin. Besides studying the ratio of the cell types in the hypophysis or in pancreatic islets, it is possible to estimate the granule content of the cells. The method works on human autopsy material provided fixation of hypophysis occurs within 24 hr, and. pancreas, 12 hr post mortem, and it is suitable also for quite fresh organs.     

Acceleration of Mallory's Phosphotungstic Acid-Hematoxylin Staining for Skeletal Muscle Fixed in Formalin

The staining time for mammalian skeletal muscle fixed in neutral phosphate-buffered formalin was shortened from 12-24 hr to 10-30 min. The permanganate-oxalate sequence was omitted although oxidation by periodic acid or with iodine was found to be necessary. The material was embedded in paraffin and cut 6 μ or less. Deparaffinized sections were treated with 1% alcoholic iodine for 10 rain followed by 5% Na₂S₂O₃ for 2 min and placed in an oven at 60 C for 10-30 min to stain in a preheated mixture of 50 ml of ripened Mallory's phosphotungstic acid-hematoxylin and 1 ml of 2% phosphomolybdic acid. Experiments with fixation showed that the staining procedure followed Zenker's fluid successfully but not Bouin's fluid. Oxidation by KMnO₄ was effective only after Zenker fixation; oxidation by CrO₃ was unsuccessful.     

A Consistent Phosphotungstic Acid Hematoxylin Stain for Glial Fibers

After deceration, celloidinization and hydration, oxidize 10 micron paraffin sections for 15 min in a solution containing 0.3 g KMnO₄, and 0.1 ml conc. H₂SO₂, per 100 ml distilled water. Wash in water and reduce in 5% oxalic acid until the sections are colorless. Wash thoroughly in water and place in 4% iron alum solution for two hours. Wash briefly in water and stain for two hours in phosphotungstic acid hematoxylin. Rinse briefly in 95% ethanol and dehydrate in n-butyl alcohol or absolute ethanol for 4 min with two changes, clear and mount. Glial fibers, myofibrils, red blood cells, etc. are stained blue while astrocyte cell bodies, collagen, etc. are stained red. This stain has proven highly consistent in a wide variety of astrocytic derangements. Despite the intensity of this PTAH modification, false positive staining was not observed.     

A Protargol Method for Staining Nerve Fibers in Frozen or Celloidin Sections

Extensive experimentation with protargol staining of neurons in celloidin and frozen sections of organs has resulted in the following technic: Fix tissue in 10% aqueous formalin. Cut celloidin sections IS to 25 μ, frozen sections 25 to 40 μ. Place sections for 24 hours in 50% alcohol to which 1% by volume of NH₄OH has been added. Transfer the sections directly into a 1% aqueous solution of protargol, containing 0.2 to 0.3 g. of electrolytic copper foil which has been coated with a 0.5% solution of celloidin, and allow to stand for 6 to 8 hours at 37° C. Caution: In this and the succeeding step the sections must not be allowed to come in contact with the copper. From aqueous protargol, place the sections for 24 to 48 hours at 37° C. directly into a pyridinated solution of alcoholic protargol (1.0% aqueous solution protargol, 50 ml.; 95% alcohol, 50 ml.; pyridine, 0.5 to 2.0 ml.), containing 0.2 to 0.3 g. of coated copper. Rinse briefly in 50% alcohol and reduce 10 min. in an alkaline hydroquinone reducer (H₃BO₃, 1.4 g.; Na₂SO₃, anhydrous, 2.0 g.; hydroquinone, 0.3 g.; distilled water, 85 cc; acetone, 15 ml.). Wash thoroly in water and tone for 10 min. in 0.2% aqueous gold chloride, acidified with acetic acid. Wash in distilled water and reduce for 1 to 3 min. in 2% aqueous oxalic acid. Quickly rinse in distilled water and treat the sections 3 to 5 min. with 5% aqueous Na₂S₂O₃+5H₂O. Wash in water and stain overnight in Einarson's gallocyanin. Wash thoroly in water and place in 5% aqueous phosphotungstic acid for 30 min. From phosphotungstic acid transfer directly to a dilution (stock solution, 20 ml.; distilled water, 30 ml.) of the following stock staining solution: anilin blue, 0.01 g.; fast green FCF, 0.5 g.; orange G, 2.0 g.; distilled water, 92.0 ml.; glacial acetic acid, 8 ml.) and stain for 1 hour. Differentiate with 70% and 95% alcohol; pass the sections thru butyl alcohol and cedar oil; mount.     

A Simplified Nissl Stain with Thionin

Recently two articles on the use of thionin as a cell stain for neurological materials have appeared. One utilizes a solution buffered in the acid range³; the other uses a “steaming” staining solution⁴. For some time we have been using thionin as a routine stain after either formalin or alcohol fixation and our method is so simple and has given such satisfactory results with a variety of brands of thionin that it seemed to be worthy of more general use. Briefly the method consists of placing the celloidin sections in a 0.05% solution of Li₂CO₃ (the percentage of Li₂CO₃ is non-critical) for about 5 minutes and then grossly overstaining in a 0.25% solution of thionin in a 0.05% solution of Li₂CO₃ in distilled water. The overstaining is necessary if all the stain is to be removed from the background. The sections are then passed through distilled water, 70 or 80% alcohol, two changes of butyl alcohol, two changes of xylene and mounted with Clarite. For most material, split mica cover-slips are quite satisfactory. The time of differentiation may be considerably lessened by the use of the differentiator recommended by Neumann (1942) except that we find the chloroform superfluous and transfer the sections to the aniline solution from 95% alcohol. Less fading seems to occur if the aniline differentiator is followed by a saturated solution of Li₂CO₃ in 95% alcohol.     

Staining with Chromoxane Cyanine R

Since Pearse in 1957 introduced chromoxane cyanine R as a dual nuclear and cytoplasmic stain there have appeared numerous procedures for use of this dye. These have differed widely, sharing in common mainly the implication that each is best. A defendable procedure has been developed on an experimental basis and is reported here. Four stock solutions are needs. (1) a 0.2% solution of chromoxane cyanine R in 0.5% aqueous H₂SO₄ (v/v); boil this solution for 5 min, (2) 10% FeCl₃ in 3% HCI, (3) 1% aqueous NH₄OH, and (4) 1% HCI in 70% ethanol. The staining solution: 40 ml of dye solution, 2 ml of FeCl₃ solution, 8 ml H₂O. Dewax and hydrate sections and stain for 10 min. If a myelin sheath stain is desired differentiate for 1 min in solution (3). For a nuclear stain differentiate for 1 min in solution (4). The nuclear stain when counterstained with eosin closely resembles the routine hematoxylin and win. Histochemical tee show that the functional pup for myelin staining contains nitrogen, and probably hydrogen bonding is involved. The nuclear stain involves a different functional group and possibly neither electrostatic nor hydrogen bonding.     

Differential Staining of Yeast for Purified Cell Walls, Broken Cells, And Whole Cells

Intact yeast cells are Gram positive but broken or disrupted cells are Gram negative. A counterstain with methyl green provides differential staining between cell wall and cytoplasm. The cells and cell fragments are dried on a slide and stained by a standard Gram stain. The preparation is then treated for 5 min with 1% phosphomolybdic acid, washed, and stained 0.5 min with 1% aqueous methyl green (unpurified by CHCl₃ extraction). Under these conditions whole, intact cells are dark purple or black, walls of broken cells and purified walls are light green, and the exposed cytoplasm stains light purple. All fractions can be easily differentiated.     

The Histochemical Detection of Thallium in Paraffin-Embedded Tissues by the Sulfide-Selenium-Silver Method

Thallium can be histochemically localized in formalin-fixed, paraffin-processed tissues by treating sections, after passing them through xylene and graded alcohols to water, with gaseous H₂S for 15 min and with 20% ammonium sulfide saturated with powdered selenium for 10 min. Sections are then washed, treated 10 min with 20% H₂O₂, and incubated in darkness for 20-30 min in the following mixture: 25% gum acacia, 10 ml; 2% hydroquinone in 5% citric acid, 1 ml; and 10% AgNO₃, 0.1 ml. Tissues and cells, which contain thallium, are demonstrated by small black granules of silver.     

Selective Staining of Neurosecretory Material in Semithin Epoxy Sections by Gomori's Aldehyde Fuchsin

The epoxy resin was removed from semithin (1 μm) sections by immersing them for 30 sec in sodium methoxide (Mayor et al., J. Biophys. Biochem. Cytol., 9: 909-10, 1961) and then processed as follows: (1) left for 1-3 hr at 60 C in a mixture of formalin, 25 ml; glacial acetic acid, 5 ml; CrO₃, 3 gm; and distilled water, 75 ml: (2) oxidized 10 min in a 1:1:6 v/v mixture of 2.5% KMnO₄, 5% H₂SO₄ and distilled water: (3) bleached in 1% oxalic acid, and (4) stained for 15 min in aldehyde fuchsin, 0.125% in 70% alcohol, or in a 1% aqueous solution of toluidine blue. The neurosecretory material is selectively stained.     

Differentiated Staining of Osmium Tetroxide-Fixed, Vestopal-w-Embedded Tissue in thin Sections

Tissues were fixed at 20° C for 1 hr in 1% OsO₄, buffered at pH 7.4 with veronal-acetate (Palade's fixative), soaked 5 min in the same buffer without OsO₄, then dehydrated in buffer-acetone mixtures of 30, 50, 75 and 90% acetone content, and finally in anhydrous acetone. Infiltration was accomplished through Vestopal-W-acetone mixtures of 1:3, 1:1, 3:1 to undiluted Vestopal. After polymerisation at 60° C for 24 hr, 1-2 μ sections were cut, dried on slides without adhesive, and stained by any of the following methods. (1) Mayer's acid hemalum: Flood the slides with the staining solution and allow to stand at 20°C for 2-3 hr while the water of the solution evaporates; wash in distilled water, 2 min; differentiate in 1% HCl; rinse 1-2 sec in 10% NH,OH. (2) Iron-trioxyhematein (of Hansen): Apply the staining solution as in method 1; wash 3-5 min in 5% acetic acid; restain for 1-12 hr by flooding with a mixture consisting of staining solution, 2 parts, and 1 part of a 1:1 mixture of 2% acetic acid and 2% H₂SO₄ (observe under microscope for staining intensity); wash 2 min in distilled water and 1 hr in tap water. (3) Iron-hematoxylin (Heidenhain): Mordant 6 hr in 2.5% iron-alum solution; wash 1 min in distilled water; stain in 1% or 0.5% ripened hematoxylin for 3-12 br; differentiate 8 min in 2.5%, and 15 min in 1% iron-alum solution; wash 1 hr in tap water. (4) Aceto-carmine (Schneider): Stain 12-24 hr; wash 0.5-1.0 min in distilled water. (5) Picrofuchsin: Stain 24-48 hr in 1% acid fuchsin dissolved in saturated aqueous picric acid; differentiate for only 1-2 sec in 96% ethanol. (6) Modified Giemsa: Mix 640 ml of a solution of 9.08 gm KH₂PO₄ in 1000 ml of distilled water and 360 ml of a solution of 11.88 gm Na₂HPO₄-2H₂O in 1000 ml of distilled water. Soak sections in this buffer, 12 hr. Dissolve 1.0 gm of azur I in 125 ml of boiling distilled water; add 0.5 gm of methylene blue; filter and add hot distilled water until a volume of 250 ml is reached (solution “AM”). Dissolve 1.5 gm of eosin, yellowish, in 250 ml of hot distilled water; filter (solution “E”). Mix 1.5 ml of “AM” in 100 ml of buffer with 3 ml of “E” in 100 ml of buffer. Stain 12-24 hr. Differentiate 3 sec in 25 ml methyl benzoate in 75 ml dioxane; 3 sec in 35 ml methyl benzoate in 65 ml acetone; 3 sec in 30 ml acetone in 70 ml methyl benzoate; and 3 sec in 5 ml acetone in 95 ml methyl benzoate. Dehydrated sections may be covered in a neutral synthetic resin (Caedax was used).     

Direct Staining of Reticular Fibers with Gold Chloride

Reticular fibers are selectively stained in paraffin sections of formalin-fixed or Bouin's-fixed tissue as follows: 1% aqueous solution of gold chloride for 20 min, followed by a 10 min immersion in an aqueous solution containing 5% Na₂CO₃ and 0.5% KOH. The sections then are placed in a 5% aqueous solution of KI for 2 min. Counterstaining with a 0.25% aqueous solution of methylene blue chloride is optional. The reticular fibers stain dark pink; the collagen bundles are a light pink to straw color without the counterstain, or a light blue color when the methylene blue is used.     

Acid Orcein-Iron and Acid Orcein-Copper Stains for Elastin

Paraffin sections of formol-fixed tissues stained 4-18 hr in 70% alcohol containing 1% orcein and 1% of concentrated (12 N) HCl by volume yield the familiar purple brown elastin and red nuclei on a pink background. When sections so stained are transferred directly from the stain to 70% alcohol containing 0.02% ferric chloride (FeCl₃·6 H₂O) or 0.02% copper sulfate (CuSO₄·5 H₂O) for a 15 sec to 3 min period, elastin coloration is changed to black or reddish black and chromatin staining to reddish black. The procedure can be counterstained with picro-methyl blue to yield blue collagen and reticulum or with our flavianic acid, ferric chloride, acid fuchsin mixture to give deep yellow background and deep red collagen.     

Preferential In Vivo Incorporation of [3H]Arachidonic Acid from Blood into Rat Brain Synaptosomal Fractions Before and After Cholinergic Stimulation

Abstract: Awake adult male rats were infused intravenously with [³H]arachidonic acid for 5 min, with or without prior administration of an M1 cholinergic agonist, arecoline (15 mg/kg i.p.). Methylatropine was also administered (4 mg/kg s.c.) to control and arecoline-treated animals. At 15 min postinfusion, the animals were killed, brains were removed and frozen, and subcellular fractions were obtained from homogenates of whole brain. Total radioactivity and radioactivity in various lipid classes were determined for each fraction following normalization for exposure by use of a unidirectional incorporation coefficient, k ^⋆_brain. In control animals, incorporation was greatest in synaptosomal and microsomal fractions, accounting for 50 and 30% of total label incorporated into membrane lipids, respectively. Arecoline increased incorporation in these two fractions by up to 400% but did not increase incorporation into the myelin, mitochondrial, or cytosolic fractions. Of the incorporated radioactivity, 50–80% was in phospholipid in microsomal and synaptosomal fractions, indicating that phospholipid is the major lipid affected by cholinergic stimulation. These results demonstrate that plasma [³H]arachidonic acid is preferentially incorporated into phospholipids of synaptosomal and microsomal fractions of rat brain. Cholinergic stimulation increases incorporation into these fractions, likely by activation of phospholipase A₂ and/or C in association with acyltransferase activity. Thus, intravenously infused radiolabeled arachidonic acid can be used to examine synapse-mediated changes in brain phospholipid metabolism in vivo.     

Silver Protein Staining of Nerve Fibers in Celloidin Sections

Celloidin sections from formalin-fixed brain and spinal cord of primates are stored in 70% alcohol after cutting, soaked in 2% pyridine in 50% alcohol for 6-8 hr at 37 C, and transferred to 1% concentrated NH₄OH in 50% alcohol 15-18 hr at 20-25 C. After washing and flattening, the sections are transferred to 1% silver protein solution containing 30 ml of 0.2 M H₃BO₃/100 ml. Impregnation is accomplished in 50 ml screw-top jars, 50 mm in diameter, which are filled to a depth of 35 mm, and have 1 gm of copper foil, 0.002 inch thick added. The foil is folded in loose accordion-fashion, pierced and threaded, cleaned in 5% HNO₃, rinsed in distilled water, and suspended in the solution just above the sections by fastening the thread to the jar lid. The sections are impregnated for 24 hr at 37 C, rinsed in distilled water, reduced in a solution of 5% Na₂SO₃ and 1% hydroquinone for 10 min, washed in distilled water and toned in 0.2% gold chloride for 5 min. After rinsing in distilled water, the sections are transferred to 1% oxalic acid for 45-60 sec, washed in distilled water and placed in 5% Na₂S₂O₃ for 5 min. Sections are then washed, dehydrated to 95% alcohol, cleared in terpineol, followed by 3 changes in xylene, and mounted.     

A Sensitive Myelin-Sheath Stain Particularly Useful for Small Mammals and Neonatal Cats

Staining of myelinated fibers including the delicate myelin sheaths of infantile animals is as follows: perfuse the anesthetized animal with a pH 7.4 posphate-buffered fixative, either 10% formalin, 6% gluteraldehyde or a mixture containing 3% gluteraldehyde and 2% acrolein. Dissect out the brain or spinal cord and continue fixation for at least 24 hr. Cut larger brains to 1 cm in at least one dimension. Wash in running tap water 2-3 hr and soak in 2.5% potassium dichromate in 1% acetic acid (the primary mordant) for 3-5 days in darkness. Wash at least 12 hr in running tap water. Dehydrate and embed in celloidin and store in 80% ethanol. Section at 25-60 μ into 80% ethanol. Wash 1-2 min in distilled water and then immerse in 1-2% ferric alum at 50 C for at least 1 hr (the secondary mordant). Wash in tap water and stain at least 1 hr at 50-60 C in 0.5% unripened hematoxylin in 1% acetic acid. Wash well in tap water and differentiate in a mixture containing 0.5% ferrityanide, 0.5% borax and 0.5% Na₂CO₃; 2 changes. Wash well in distilled water, then in tap water, and dehydrate, clear and mount. Myelin stains black, cell bodies stain tan, and the background is pale yellow. With minor modifications in timing, the method is applicable to frozen and to paraffin sections; the primary mordant being omitted in the freezing technique.     

Orthochromatic, Species-Limited Staining of Mast Cells With Night Blue

Night blue will stain the mast cells of rat, mouse and hamster selectively if alcohol differentiation is controlled. The technical steps are: Dewax paraffin sections with xylene, 2 changes; air dry; 2% Na₂SO₄, 3-5 sec; 0.5% night blue in 10% ethanol, 1 hr at 60°C; rinse in water; 9% HNO₃, 15 sec; water 1-5 min; 70% ethanol, 2 changes, 30 sec each; wash; 0.01% safranin, 3-5 sec; rinse, blot, air dry, mount in synthetic resin. A clear orthochromatic stain of the mast-cell granules occurs. Acid fixation prevents the staining reaction.     

A HYDROXYL-DEPENDENT SILVER METHOD FOR NERVE AXOPLASM

Axoplasm is selectively impregnated by the following steps: (1) fixation in 10% formalin or in 10% formalin with added sucrose, 15%, and concentrated NH₄OH, 1%, for 1-7 days; (2) frozen sections; (3) extraction of the sections in 95% ethyl alcohol, absolute alcohol, xylene, and 95% ethyl alcohol and absolute alcohol, 1 hr each; (4) distilled water, 3 changes of 10 min each; (5) 20% AgNO₃ (aq.) at 25°C, 30 min; (6) distilled water, 3 changes of 1-2 sec each; (7) 6.9% K₂CO₃, 1 hr; (8) water, 3 changes of about 1 min each; (9) 0.2%AuCl₃, 2 min; (10) distilled water; (11) 5% Na₂S₂O₃, 2 min; (12) washing, clearing and mounting. This procedure is proposed as a simplified stain for axoplasm, with other tissue components remaining unstained. The few reagents necessary suit this method for histochemical investigation of the mechanism of silver staining.     

A Mordanting Fixation for Intense Staining of Small Chromosomes

A combination iron-mordant fixative in which propionic acid is substituted for acetic acid has been found useful in preparing small plant chromosomes for carmine stained squashes. Propionic acid is better than acetic acid because it holds more iron in stable solution. The fixative is a 3:1 mixture of 95% alcohol and pure propionic acid which contains 400 mg. of Fe(OH)₃ per 100 ml. of propionic acid. The latter is previously prepared by dissolving the dry freshly prepared Fe(OH)₃ in it. To each 10 ml. vial of fixative is added a few drops of carmine stain. Standard aceto-carmine squashes of material fixed in this mixture show quick intense staining and are especially useful for differentiated chromosomes at mitotic prophase.