Staining of depolymerised DNA in mammalian tissues with methyl violet 6B and crystal violet

The paper contains an account of DNA staining with basic dyes; methyl violet 6B and crystal violet in mammalian tissue sections after RNA extraction with cold concentrated phosphoric acid. The study shows that the best staining is obtained at pHs 2.5 and 3.5. Dehydration of stained nuclei is perfect when a mixture of absolute ethanol and n-butanol is used followed by treatment of sections in isoamyl or amyl alcohol. The in situ absorption data of nuclei stained with aqueous solution of methyl violet 6B as well as with crystal violet are also presented. Possible mechanism of staining as well as an explanation for dye-leaching when sections are dehydrated through ethanol are discussed.     

Gram staining and lectin binding properties of Myxosporea and Sporozoea

The staining method developed by Christian Gram was introduced as a simple and highly selective tool for demonstrating myxosporean and coccidian sporogonic stages. When using standard blood staining procedures for those enigmatic parasites it is sometimes difficult to distinguish them from fish host tissue. They clearly exhibit a partial Gram-positive reaction in histological sections, but staining is variable in air dried fish organ imprints. To visualize the Gram-negative background of different host tissue components in histological sections, the conventional safranin counterstain of the Gram protocol may be modified as follows: after application of 2% crystal violet (basic violet 3) and Lugol's solution, sections are stained with 0.1% nuclear fast red-5% aluminum sulfate and 0.35% aniline blue (acid blue 22) dissolved in saturated aqueous picric acid. Replacement of the Gram-specific dye crystal violet with 2% malachite green gave similar results in organ imprints containing myxospores or coccidia, but only in sections containing myxosporea. Staining for 1 min with an aqueous solution of 0.5% malachite green and followed 1 min washing was sufficient for rapidly demonstrating the parasite spores in organ imprints of both myxosores and oocysts. With regard to the role of acid mucopolysaccharides and other carbohydrates in the Gram reaction of spores, alcian blue 8GX staining was compared to the binding of FITC-labeled WGA, GS I and GS II. Each lectin was applied at 20 μl/ml PBS, HEPES for 1 hr. Whereas WGA yielded a nonspecific pattern like the alcian blue staining, GS II resulted in a pattern similar to the Gram staining results. This binding was weak in untreated specimens, but was significantly enhanced when digested first within trypsin overnight in a humid chamber at 37 °C. The binding of GS II to both myxosporidian and coccidian spores suggests that they are both composed of polymers containing N-acetyl-D-glucosamine residues. Furthermore, the results suggest that this hexosamine plays a key role in the Gram reaction.     

The staining of Brunner's gland and other neutral mucins by carmine, hematoxylin and orcein in alkaline solutions.

Brunner's glands and other neutral mucins may be stained red, brownish red, and violet, respectively, by carmine, hematoxylin, and orcein from appropriate alkaline solutions. Carmine and hematoxylin in concentrations of 0.2-1% are dissolved in 60-70% alcohol containing 1% potassium carbonate; orcein is used in a 0.2% alcoholic solution of sodium hydroxide. Staining times are 15 to 30 minutes. The stained sections are rinsed in 95% or absolute alcohol prior to xylene and mounting. The staining of these mucins is blocked by mild bromine oxidation. By using alcian blue 0.1% in 3% acetic acid for 5 minutes prior to the above stains, mucins may be characterized in the same preparation as acid, neutral or mixed.     

Studies in gram staining.

Gram-negative bacteria stained with crystal violet are decolorized by 95% alcohol within 2 min, whereas Gram-positive bacteria require at least 3 min treatment. Aqueous solutions of safranin, neutral red, and fuschsin replace crystal violet from stained Gram-positive bacteria more quickly than alcohol alone, and alcoholic solutions of these counterstains are in most cases still more effective. Treatment of crystal violet-stained organisms with alcoholic safranin (0.25%) for 15 sec will distinguish Gram-positive bacteria (violet) from Gram-negative bacteria (pink). Alcohol containing very low concentrations of iodine generally decolorizes crystal violet-stained Gram-positive bacteria more quickly than alcohol alone. Increasing concentrations of iodine in alcohol reduce the rate of decolorization of stained bacteria, but stained Gram-negative bacteria are still readily decolorized. The addition of 0.1% iodine to alcohol increases the rate of extraction of crystal violet by alcohol from Gram-negative organisms, but delays extraction of dye from Gram-positive organisms, and this applies when counterstain is also present. A two-solution modification of Gram staining is described in which crystal violet-stained bacteria are treated with an alcoholic solution of safranin, fuchsin, and iodine.     

New investigations on hematoxylin, hematein, and hematein-aluminium complexes. II. Hematein-aluminium complexes and hemalum staining.

The absorption spectra of hematein-aluminium solutions have been recorded at various concentrations and pH values; the solutions were prepared using analytically pure hematein and potassium alum as aluminium source. In aqueous solution, four different hematein-aluminium complexes could be distinguished by absorption spectroscopy. In weakly acidic media we observed the violet 1:1 and 1:2 complexes HmAl (VII) and HmAl2(3) (VIII), and in strongly acidic solution the red 1:1 complex HmAl2 (IX). Whereas, in weakly alkaline solution the blue 1:1 complex HmAl0 (X) was detected. By change of the pH value the complexes were mutual interconverted. The dye complexes were characterized by their absorption spectra and molar extinction coefficients. We have stained HeLa cells with the complex solutions under different experimental conditions. In all cases the nuclear staining was intense whereas the staining of the cytoplasm was weak. The microspectra of the stained nuclei were recorded and compared with the absorption spectra of the complexes in solution. Thus it was possible to identify the bound dye species. After staining in acidic media, the cells were red to red-violet depending on the reaction conditions. The three cationic dye species VII, VIII, and IX were bound in varying amounts. After blueing in weakly acidic media or in water, only the violet dye complex VII was detected whereas, after blueing in weakly alkaline media, only the blue complex X has been observed. Enzymatic digestion experiments have shown that the dye complexes in the nuclei were bound to DNA while those in the cytoplasm and nucleoli were bound to RNA. The binding between the dye complexes and the nucleic acids is discussed.     

The Mechanism of the Gram Reaction. III. Solubilities of Dye-Iodine Precipitates and Further Studies of Primary Dye Substitutes

Solubilities of dye-iodine precipitates in alcohol and in aqueous safranin solution were determined by direct solubility methods and by photocolorimetric methods. It was found that, increasing precipitate solubility in alcohol or safranin solution gave decreasing differentiation between Gram-positive and Gram-negative bacteria. Dyes which did not stain the cells well as a primary stain did not give good Gram stains, regardless of the solubilities of their precipitates. Some dyes (typified by methylene blue) which gave relatively alcohol-insoluble iodine precipitates gave inferior Gram differentiation because these precipitates were readily soluble in the safranin counterstain.

Solubilities of precipitates of crystal violet and various iodine substitutes were determined photocolorimetrically. The ability of a substance to replace iodine in the Gram stain correlated with its ability to give a precipitate which was only slightly soluble in alcohol and relatively insoluble in aqueous safranin solution.

It was concluded that the usual Gram reagents are not truly specific for the differentiation. Any dye and mordant could be used if the dye was deeply colored, stained the cells well, and if the precipitate of dye and mordant was only slightly soluble in alcohol and relatively insoluble in the counterstain. These factors, combined with those influencing differences in cell membrane permeability, constitute the most important factors in the Gram stain differentiation.

Studies were made concerning the ability of dyes to substitute for crystal violet in the Gram procedure. Of 29 dye samples reported on here for the first time none proved to be good substitutes for crystal violet.     

The Staining of Brunner's Gland and Other Neutral Mucins by Carmine, Hematoxylin and Orcein in Alkaline Solutions

Brunner's glands and other neutral mucins may be stained red, brownish red, and violet, respectively, by carmine, hematoxylin, and orcein from appropriate alkaline solutions. Carmine and hematoxylin in concentrations of 0.2-1% are dissolved in 60-70% alcohol containing 1% potassium carbonate; orein is used in a 0.2% alcoholic solution of sodium hydroxide. Staining times are 15 to 30 minutes. The stained sections are rinsed in 95% or absolute alcohol prior to xylene and mounting. The staining of these mucins is blocked by mild bromine oxidation. By using alcian blue 0.1% in 3% acetic acid for 5 minutes prior to the above stains, mucins may be characterized in the same preparation as acid, neutral or mixed.     

The Staining of Brunner's Gland and Other Neutral Mucins by Carmine,Hematoxylin and Orcein in Alkaline Solutions

Brunner's glands and other neutral mucins may be stained red, brownish red, and violet, respectively, by carmine, hematoxylin, and orcein from appropriate alkaline solutions. Carmine and hematoxylin in concentrations of 0.2-1% are dissolved in 60-70% alcohol containing 1% potassium carbonate; orein is used in a 0.2% alcoholic solution of sodium hydroxide. Staining times are 15 to 30 minutes. The stained sections are rinsed in 95% or absolute alcohol prior to xylene and mounting. The staining of these mucins is blocked by mild bromine oxidation. By using alcian blue 0.1% in 3% acetic acid for 5 minutes prior to the above stains, mucins may be characterized in the same preparation as acid, neutral or mixed.     

Staining of keratin and keratohyalin with the reactive dye levafix red violet E-2BL.

Demonstration of keratin in Zenker-fixed skin and in tissues stored in formalin can be difficult because such material is unsuitable for histochemical studies. A reactive dye, Levafix red violet E-2BL, proved useful for demonstration of keratohyalin and some types of keratin. Formalin-, Zenker- and methacarn-fixed sections were pretreated with alkaline alcohol, stained one hour at 60 C in an aqueous solution containing 0.25% Levafix red violet E-2BL plus 0.25% NaCl, rinsed in buffer solution pH 9, dehydrated and mounted. Keratohyalin granules and stratum corneum were colored red violet; hair and tonofibrils remained unstained. In sections prestained with Mayer's acid hemalum, keratohyalin was dark blue. Sulfonated monoazo dyes without reactive groups colored no tissue structures under the conditions of this technic; apparently, Levafix red violet E-2BL is bound via its reactive group. Polarization microscopic studies suggest binding of Levafix red violet E-2BL by an amorphous matrix of keratin. Correlations with chemical data indicate that the staining patterns parallel the distribution of proteins formed in the stratum granulosum.     

Contribution to the Staining of Neuroglia

The chemistry of Weigert's glia staining method is critically discussed. An investigation of the Heidelberger Victoria blue staining method has shown that Victoria blue may be replaced by other phenylmethane dyes as methyl violet, ethyl violet, and crystal violet. It was found that the exposure of the stained section to sunlight is an oxidation process. Artificial ultra violet rays or chemical oxidation agents give the same effect. Frozen sections fixed in formalin or alcohol may be stained in a concentrated aqueous solution of any of the above mentioned phenylmethane dyes, dried, and exposed to ultra violet rays for 30 minutes, then treated with 1/10 N. iodine solution, differentiated in xylol anilin and cleared in xylol. The glia cell body as well as the fibrils are clearly differentiated from the nervous elements and connective tissue.     

A Tribasic Stain for Thin Sections of Plastic-Embedded, OsO4-Fixed Tissues

Thin (0.5-1 μ) sections of plastic-embedded, OsO₄-fixed tissues were attached to glass slides by heating to 70 C for 1 min. A saturated solution combining toluidine blue and malachite green was prepared in ethanol (8% of each dye) or water (4% of each dye). Methacrylate or epoxy sections were stained in the ethanol solution for 2-5 min. The water solution was more effective for some epoxy sections (10-80 min). Epoxy sections could be mordanted by 2% KMnO₄, in acetone (1 min) before use of the aqueous dye, reducing staining time to 5-10 min and improving contrast. Aqueous basic fuchsin (4%) was used as the counter-stain in all cases; staining time varied from 1-30 min depending upon the embedding medium and desired effects, methacrylate sections requiring the least time. In the completed stain, nuclei were blue to violet; erythrocytes and mitochondria, green; collagen and elastic tissue, magenta; and much and cartilage, bright cherry red. Sections were coated with an acrylic resin spray and examined or photographed with an oil-immersion lens.     

Staining Scab Actinomyces in Potato Tuber Tissues

Actinomyces hyphae imbedded in the middle lamellae of potato tuber cells may be stained in sections by the use of a modified Gram's stain. The modifications are: a very strong (5%) solution of crystal violet in anilin oil; a 24-hour exposure to both the dye and the iodine solution; and a slow decolorization in absolute alcohol until no more color flows.     

The Site of Action of the Crystal Violet Nuclear Stain

Enzymatic treatment of bacterial cells prior to staining revealed that the crystal violet nuclear stain reacts with protein components of the nucleus as contrasted to the desoxyribonucleic acid specificity of some nuclear stains.     

The Mechanism of the Gram Reaction I. The Specificity of the Primary Dye

Dyes of all major types were tested for their suitability as the primary dye in the Gram stain. When a counterstain was not used, some dyes of all types were found to differentiate Gram-positive from Gram-negative organisms. When a counterstain was used, these dyes were found to vary greatly in their suitability. Those dyes found to be good substitutes for crystal violet were: Brilliant green, malachite green, basic fuchsin, ethyl violet, Hoffmann's violet, methyl violet B, and Victoria blue R. All are basic triphenylmethane dyes. Acid dyes were generally not suitable. Differences in the reaction of Gram-positive and Gram-negative cells to Gram staining without the use of iodine were observed and discussed but a practical differentiation could not be achieved in this manner. Certain broad aspects of the chemical mechanism of dyes in the gram stain are discussed.     

Neuron Staining by Basic Dyes Versus Basic Metal-Dye Complexes; Differences Shown by Histochemical Blocking Reactions

Various blocking procedures were applied to sections of paraffin-embedded, formalin-fixed cat spinal cord. Treated sections and untreated controls were stained with cresyl violet acetate or gallocyanine-chrome alum. Although both dyes have been said to stain by simple salt formation it was found that staining was affected differently for each dye by the blocking procedures, and also that staining of neuron nuclei differed in the controls. In these, the cresyl violet acetate stained only the nucleoli within the nucleoplasm whereas gallocyanine-chrome alum stained much more material of unknown composition and function. It is proposed that if cresyl violet acetate and other basic dyes stain by salt linkage, and can be specific for nucleic acid and other highly acid materials, then gallocyanine and other basic metal dye complexes can not be specific for nucleic acid and do not stain by a simple salt linkage.     

Staining of Keratin and Keratohyalin with the Reactive Dye Levafix Red Violet E-2BL

Demonstration of keratin in Zenker-fired skin and in tissues stored in formalin can be difficult because such material is unsuitable for histochemical studies. A reactive dye, Levafix red violet E-PBL, proved useful for demonstration of keratohyalin and some types of keratin. Formalin-, Zenker- and methacarn-fired sections were pretreated with alkaline alcohol, stained one hour at 60 C in an aqueous solution containing 0.25% Levafix red violet E-2BL plus 0.25% NaC1, rinsed in buffer solution pH 9, dehydrated and mounted. Keratohyalin granules and stratum corneum were colored red violet; hair and tonofibrils remained unstained. In sections prestained with Mayer's acid hemalum, keratohyalin was dark blue. Sulfonated monoazo dyes without reactive groups colored no tissue structures under the conditions of this technic; apparently, Levafix red violet E-2BL is bound via its reactive group. Polarization microscopic studies suggest binding of Levafix red violet E-2BL by an amorphous matrix of keratin. Correlations with chemical data indicate that the staining patterns parallel the distribution of proteins formed in the stratum granulosum.     

Studies in Gram Staining

Gram-negative bacteria stained with crystal violet are decolorized by 95% alcohol within 2 min, whereas Gram-positive bacteria require at least 3 min treatment. Aqueous solutions of safranin, neutral red, and fuchsin replace crystal violet from stained Gram-positive bacteria more quickly than alcohol alone, and alcoholic solutions of these counterstains are in most cases still more effective. Treatment of crystal viokt-stained organisms with alcoholic safranin (0.25%) for 15 scc will distinguish Gram-positive bacteria (viokt) from Gram-negative bacteria (pink).

Alcohol containing very low concentrations of iodine generally decolorizes crystal violet-stained Gram-positive bacteria more quickly than alcohol alone. Increasing concentrations of iodine in alcohol reduce the rate of decolorization of stained bacteria, but stained Gram-negative bacteria are still readily dccolorized. The addition of 0.1% iodine to alcohol increases the rate of extraction of crystal violet by alcohol from Gram-negative organisms, but delays extraction of dye from Gram-positive organisms, and this applies when counterstain is also present. A two-solution modification of Gram staining is described in which crystal violet-stained bacteria are treated with an alcoholic solution of safranin, fuchsin, and iodine.     

A Tri-Basic-Dye Stain for Nerve Cells

A new staining method has been developed for the study of nerve cells and Nissl granules which combines three basic dyes, cresylecht violet, toluidine blue and thionin. The use of this tri-basic-dye stain results in finished preparations that are critically stained and permanent. Paraffin sections (4 μ sections preferably) are mounted on slides by the starch medium, deparaffinized and stained by the tribasic staining solution. After differentiation in acidified distilled water, sections are dehydrated, returned to stain solution and again dehydrated, then cleared and mounted in Clarite. Various vertebrate material including normal and pathological human tissues have been stained with this triple dye solution. Especially for pathological material, re-immersion of slides in the staining and 80% alcohol solutions before mounting, differentially intensifies the staining reaction. Fixatives used were 10% formalin, 95% alcohol, Bouin and formalin-Bouin (10% formalin followed by Bouin).     

Use of acridine orange for histologic analysis of the central nervous system

The application of the fluorescent dye acridine orange (AO) to the staining of histologic sections of the brain, and its use for automatic cyto- and histophotometric evaluation are described and compared with the results obtained using cresyl violet. The most suitable procedure for aldehyde-fixed brain tissue, embedded in paraffin and sectioned at 5 micron, proved to be treatment of the sections with an aqueous solution of AO (1:50,000) at pH 1.2 for 30 min, followed by rinsing in distilled water for 10 min. This procedure revealed the morphology in a highly acceptable manner, clearly differentiating various cell components; its characteristics included exact reproducibility and high contrast. The degree of fading was calculable, with a very gradual decrease in fluorescent intensity. The AO procedure appears to be compatible with most other staining procedures that do not rely on the same binding mechanisms. Thus, AO staining has two advantages over the classical cytoarchitectural staining methods: first, it is more suitable for automated morphometric analysis, and second, it can be used in conjunction with immunologic and other techniques.     

Basic Two-Dye Stains for Epoxy-Embedded 0.3-1 μ Sections

Dyes used in the 3 methods recommended are: I, thionin and acridine orange (T-AO); II, Janus green and Darrow red (JG-DR); III, methyl green and methyl violet (MG-MV). The first 2 methods were two-solution stains, applied in sequence; the third, required only one solution since methyl violet is present in commercial methyl green. Staining solution and timing was as follows: Method I. 0.1% thionin in a 45% ethanolic solution of 0.01 N NaOH, 5 min at 70 C; rinsing in water and followed by 1 min in a 1% aqueous solution of acridine orange made up in 0.02 N NaOH, also at 70 C, then washed, and dried on slides. Method II. 0.5% Janus green in aqueous 0.05 N NaOH, 5 min at 70 C; rinsing in water then into 0.5% Darrow red in 0.05 N NaOH (aq.), 2 min at 70 C., washing, and drying on slides. Method III. 1% methyl green (commercial, unpurified) in 1% aqueous borax for 15-20 min at 20-25 C, washing and attaching to slides. All staining was performed by floating the sections on the staining solutions, all drying at 70 C, and mounting in a resinous medium. T-AO gave blue to violet cytoplasmic structures, darker nuclei which contrasted strongly with yellow connective tissue and the secretion of goblet cells. JG-DR resembled a hematoxylineosin stain, but by shortening the staining time in DR to 0.5-1 min, collagenous and elastic tissue retained more of the green dye. MG-MV gave dark green nuclei in light green cytoplasm, with collagenous and elastic tissues in blue to violet. As with most methods for staining ultrathin sections, thicknesses of less than 1 μ required longer staining times.