Immunohistochemical conditions for staining choline acetyltransferase-containing axon terminals in the rat

Immunohistochemical conditions for staining cholinergic axon terminals using a commercially available anticholine acetyltransferase (anti-ChAT) monoclonal antibody were determined in the rat. A number of variations of procedures including fixative composition, fixation time, and incubation time and temperature in the anti-ChAT antibody solution were tested. Optimal procedures for minimizing the chance of negative staining of ChAT-containing axon terminals consisted of perfusion with a mixture of 4% paraformaldehyde and 0.2% glutaraldehyde for 3 min followed by a fixative containing only 4% paraformaldehyde for 10 min, and reaction with the anti-ChAT antibody for 2 days at 37 C. The distribution patterns of axon terminals stained in the cerebral cortex and the hippocampal formation were comparable to those reported by other investigators using different monoclonal antibodies.     

Localization of choline acetyltransferase-expresing neurons in the larval vissual system of Drosophila melanogaster

Choline acetyltransferease (ChAT) is the enzyme catalyzing the biosynthesis of acetylcholine and is considered to be a phenotypically specific marker for cholinergic neurons. We have examined the distribution of ChAT-expressing neurons in the larval nervous system of Drosophila melanogaster by three different but complementary techniques: in situ hybridization with a cRNA probe to ChAT messenger RNA, immunocytochemistry using a monoclonal anti-ChAT antibody, and X-gal staining of transformed animals carrying a reporter gene composed of 7.4 kb of 5 flanking DNA from the ChAT gene fused to a lacZ reporter gene. All three techniques demonstrated ChAT-expressing neurons in the larval visual system. In embryos, the photoreceptor organ (Bolwig's organ) exhibited strong cRNA hybridization signals. The optic lobe of late third-instar larvae displayed ChAT immunoreactivity in Bolwig's nerve and a neuron close to the insertion site of the optic stalk. This neuron's axon ran in parallel with Bolwig's nerve to the larval optic neuropil. This neuron is likely to be a first-order interneuron of the larval visual system. Expression of the lacZ reporter gene was also detected in Bolwig's organ and the neuron stained by anti-ChAT antibody. Our observations indicate that acetylcholine may be a neurotransmitter in the larval photoreceptor cells as well as in a first-order interneuron in the larval visual system of Drosophila melanogaster.This work was supported by a grant from the National Institute of Neurological Disorders and Stroke.     

Immunohistochemical detection of human epidermal growth factor in submandibular glands and their tumors using a polyclonal antiserum and a monoclonal antibody

Summary We applied immunohistochemical procedures to detect hEGF in salivary glands and pleomorphic adenomas of salivary-gland origin using a polyclonal hEGF antiserum and a monoclonal antibody against hEGF synthesized by applying the synthetic gene technique using Escherichia coli. In normal salivary glands, hEGF was mainly localized in the ductal system (i.e., intercalated, striated, and excretory ducts). The staining intensity and intracellular localization exhibited some variation depending on the fixative used. When a polyclonal hEGF antiserum was used for immunostaining, slight background staining was observed in sections prepared using the fixatives tested. Therefore, precise localization of hEGF was obtainable only in formalin-fixed sections using the monoclonal antibody against hEGF. In pleomorphic adenomas, positive hEGF staining was seen on the luminal side of tumors and in cells of ductal origin; no reactivity was present on the outer side of tumors or in cells of myoepithelial origin. Occasionally, long, spindleshaped tumor cells and chondroidally changed tumor cells also exhibited positive staining for hEGF.     

Comparison of LR white resin, Lowicryl K4M and Epon postembedding procedures for immunogold staining of actin in the testis

The efficiency of various postembedding procedures for actin immunogold detection was compared using testicular tissue as a model. Whatever the fixative, testes embedded in LR White resin or in Lowicryl K4M showed few differences as regard ultrastructural preservation and gave similar actin antigenicity preservation. A purified polyclonal antibody (IgG) and a monoclonal antibody (IgM) visualized with gold secondary antibody yielded high labeling intensity whereas the IgG-protein-A gold association was less efficient. Crude antisera gave a low specific staining/background ratio. Samples of testes, fixed in different conditions, were also embedded in Epon, omitting propylene oxide and lowering polymerization temperature to 40 degrees-50 degrees C. This slight modification improved ultrastructural preservation which was better than with hydrophilic resins, as well as made possible immunogold detection of actin though antigenicity preservation was lesser than with these resins. Thus, in Epon embedded samples actin labeling, using IgG antiactin-gold secondary antibody, was similar to that observed after hydrophilic resin-protein-A gold procedures. In addition to actin labeling of various somatic cells it was confirmed that actin is a consistent component of the subacrosomal space of spermatids during the greater part of spermiogenesis in rat.     

Lymphocyte membrane antigens in glycol methacrylate embedded tissue

The use of formalin or Michel's solution either alone or in combination with acetone, and acetone, methanol or ethanol alone as fixatives, and glycol methacrylate as embedding medium were evaluated for their suitability in procedures to detect lymphocyte membrane antigens by OKT and Leu monoclonal antibodies in human tonsils. No staining was detected in sections fixed in 70% or absolute ethanol and embedded in glycol methacrylate with either the direct immunofluorescence or avidin-biotin methods. Fixation in Michel's solutions plus acetone at room temperature revealed staining by both. Neither method resulted in staining after fixation in Michel's solution plus acetone at 4 C presumably due to the slow action of the fixative. Staining was enhanced using a combination of primary and secondary biotinylated antibodies. Dual staining allowed concurrent detection of two antigens in the same section. Glycol methacrylate embedding is a possible replacement for ultracold storage in the preservation of tissue for immunofluorescent staining.     

Lymphocyte Membrane Antigens in Glycol Methacrylate Embedded Tissue

The use of formalin or Michel's solution either alone or in combination with acetone, and acetone, methanol or ethanol alone as fixatives, and glycol methacrylate as embedding medium were evaluated for their suitability in procedures to detect lymphocyte membrane antigens by OKT and Leu monoclonal antibodies in human tonsils. No staining was detected in sections fixed in 70% or absolute ethanol and embedded in glycol methacrylate with either the direct immunofluorescence or avidin-biotin methods. Fixation in Michel's solutions plus acetone at room temperature revealed staining by both. Neither method resulted in staining after fixation in Michel's solution plus acetone at 4 C presumably due to the slow action of the fixative. Staining was enhanced using a combination of primary and secondary biotinylated antibodies. Dual staining allowed concurrent detection of two antigens in the same section. Glycol methacrylate embedding is a possible replacement for ultracold storage in the preservation of tissue for immunofluorescent staining.     

Production and characterization of a novel monoclonal antibody against neurotensin: immunohistochemical localization in the midbrain and hypothalamus

We developed a mouse monoclonal antibody against neurotensin (NT), termed NT8, for applications in immunohistochemistry and for ELISA analysis of NT. The antibody's paratope was determined by competitive ELISA using several peptide fragments of NT. That paratope requires intact peptide bonds between NT residues proline-7, arginine-8, and arginine-9. The antibody is of the IgG2B sub-isotype, having an IC50 for intact NT of approximately 3 nM when measured by competitive ELISA. Light microscopic immunohistochemical studies in the periaqueductal gray (PAG) and hypothalamus demonstrated staining patterns that agreed well with previous reports. Neuron perikarya were visualized even in the absence of colchicine pre-treatment, indicating that NT8 antibody is very sensitive in immunohistochemical applications. At the EM level, the antibody stained axon terminals, dendrites, and perikarya in the PAG. In lightly immunoreactive perikarya, rough endoplasmic reticula were visualized, suggesting that biosynthetic precursors to NT might be recognized by NT8.     

Immunolocalization of choline acetyltransferase in 2 types of efferent synapses of the organ of Corti

The efferent (olivo-cochlear) innervation of the organ of Corti was studied using a monoclonal antibody against choline acetyltransferase (ChAT). In the inner spiral bundle (ISB), below the inner hair cells (IHCs), the anti-ChAT immunoreactivity was observed within unvesiculated fibers and vesiculated varicosities. Unreactive varicosities, at least as numerous as the immunoreactive ones, were also detected. Both types of vesiculated varicosities synapsed with the dendrites of the primary auditory neurons (afferent fibers) connected to the IHCs. At the outer hair cell (OHC) level, nearly all the vesiculated terminals making axo-somatic synapses with the OHCs were anti-ChAT immunoreactive. Only few terminals synapsing with the OHCs were unreactive. These findings allowed the differentiation of at least three types of efferent synapses in the organ of Corti. In the ISB, a first population of axo-dendritic synapses seems to be cholinergic whereas a second population might use another neurotransmitter. At the OHC level, our results support the hypothesis that acetylcholine is the neurotransmitter of nearly all the large axo-somatic synapses. The rare unreactive axo-somatic synapses could constitute a fourth and minor type of efferent synapse. Thus, it would be helpful to subclassify the efferent innervations of the organ of Corti according to their neurochemical nature. A re-evaluation of the whole body of available electrophysiological data would be also necessary, as until now, acetylcholine was considered as being the only efferent cochlear neurotransmitter.     

Comparison of LR white resin,lowicryl K4M and Epon postembedding procedures for immunogold staining of actin in the testis

Summary The efficiency of various postembedding procedures for actin immunogold detection was compared using testicular tissue as a model. Whatever the fixative, testes embedded in LR White resin or in Lowicryl K4M showed few differences as regard ultrastructural preservation and gave similar actin antigenicity preservation. A purified polyclonal antibody (IgG) and a monoclonal antibody (IgM) visualized with gold secondary antibody yielded high labeling intensity whereas the IgG-protein-A gold association was less efficient. Crude antisera gave a low specific staining/background ratio. Samples of testes, fixed in different conditions, were also embedded in Epon, omitting propylene oxide and lowering polymerization temperature to 40°–50° C. This slight modification improved ultrastructural preservation which was better than with hydrophilic resins, as well as made possible immunogold detection of actin though antigenicity preservation was lesser than with these resins. Thus, in Epon embedded samples actin labeling, using IgG antiactin-gold secondary antibody, was similar to that observed after hydrophilic resin-protein-A gold procedures. In addition to actin labeling of various somatic cells it was confirmed that actin is a consistent component of the subacrosomal space of spermatids during the greater part of spermiogenesis in rat.     

Fixation of cryo-sections under HIV-1 inactivating conditions: integrity of antigen binding sites and cell surface antigens

Summary Cryostat-sections of biopsies from HIV-infected patients or HIV/SIV-infected experimental animals pose a biohazard risk to laboratory workers. The objective of this study was to select a procedure that appropriately fixes cryo-sections and reduces the risk of HIV-1 infectivity. This inactivation procedure should preserve antigen binding capacity of host-produced antibodies and the antigenic structure of epitopes present in these tissues, while retaining sufficient morphologic detail. We tested the effect of seven different established fixation-inactivation procedures for HIV-1 on the detection of specific antibodies and membrane markers, compared to acetone fixation as a reference. Frozen sections of spleens from mice immunized with trinitrophenyl (TNP)-Ficoll were incubated with TNP-alkaline phosphatase to detect specific antibody-forming cells and follicular immune complexes containing TNP-specific antibodies. In addition, sections were stained with monoclonal antibodies directed against IgM (187-1), T-cells (anti Thy-1), and marginal metallophilic macrophages (MOMA-1). Five procedures proved useful as they gave results similar to regular acetone fixation. In contrast, two procedures with a methanol-containing fixative obscured both antigen binding sites and membrane antigens. Subsequently, these five selected procedures were tested on glass slide preparations of HIV-1 infected cell lines, expressing HIV-1 determinants defined by monoclonal antibodies. Finally, the procedures were tested on sections of an HIV-1 infected human lymph node. for detection of HIV-specific B-cells. We show that fixation-inactivation in 0.37% (v/v) formaldehyde in PBS for 10 min at room temperature and 0.5% paraformaldehyde (w/v) in PBS for 10 min at room temperature are the methods of choice, combining preservation of antigen binding sites (Fab), membrane antigens, and HIV-1 determinants with good tissue morphology.Abbreviations AFC antibody forming cell - AP alkaline phosphatase - MAb monoclonal antibody - HIV-1 human immunodeficiency virus type 1 - HRP horseradish peroxidase - TNP trinitrophenyl     

The type of chemical fixative affects the immunohistochemical localization of transforming growth factor alpha in rat colon crypts

The effects of the different fixation agents, Omnifix, 10% neutral-buffered formalin, 70% ethanol, acetone, 10% neutral-buffered formalin, for 2 h followed by 70% ethanol for 10 h or 40% paraformaldehyde on the immunohistochemical localization of transforming growth factor alpha in rat colon crypts were studied. Segments of rat descending colon were fixed and then processed for immunohistochemistry using a monoclonal antibody to the growth factor. The results showed that the pattern of transforming growth factor alpha staining in the colonic crypts differed and was distinct for each fixative. © 1998 Chapman & Hall     

A study of acid mucopolysaccharides in cold microtome sections of normal and experimentally hydrated bovine corneas

Summary Acid mucopolysaccharides were investigated in cold microtome sections of normal and experimentally hydrated bovine corneas. Staining methods using cationic dyes were used for the detection.A 10 min fixation of cold microtome sections in absolute alcohol did not change the stainability of acid mucopolysaccharides substantially. The staining was only a little fainter (as against unfixed sections). After 10 min fixation with formol-cetylpyridinium chloride the staining of sections was diminished and after 30 min fixation in this fluid completely abolished. After formol-calcium chloride fixative the staining was decreased in dependence on the time of fixation due to the elution of acid mucopolysaccharides in the fixative (acid mucopolysaccharides in the fixative were demonstrated by means of paper electrophoresis). Formolcalcium chloride is likewise unsuitable.Experimental hydration of corneas in distilled water did not substantially alter the staining properties of acid mucopolysaccharides in cold microtome sections. Only quantitative differences were found in comparison with untreated corneas. These differences were due to hydration causing an increase in the distance of acidic groups among individual molecules of acid mucopolysaccharides.     

Large-scale purification of choline acetyltransferase and production of highly specific antisera

Choline acetyltransferase (ChAT) was purified by immunoaffinity chromatography using a covalently immobilized monoclonal antibody. In a two-step procedure, 10 kg porcine brain yielded 750 micrograms active enzyme of apparent homogeneity. This amount of ChAT was purified routinely. The purification factor was 18,000 and the yield of activity 4.3%. The affinity resin was stable under the experimental conditions applied and was used many times. The highly purified enzyme was subsequently employed to obtain a specific anti-ChAT antiserum of high titer.     

Immunogold electron microscopic demonstration of glutamate and GABA in normal and deafferented cerebellar cortex: correlation between transmitter content and synaptic vesicle size

Selective labeling of mossy fiber terminals and parallel fibers was obtained in rat cerebellar cortex by a glutamate antibody produced and characterized by Hepler et al. The high-resolution electron microscopic immunogold demonstration of this amino acid offered the possibility of determining the size and shape of synaptic vesicles in glutamate-positive mossy endings. Mossy terminals that stained with the glutamate antibody formed two distinct populations, one with spherical synaptic vesicles with an average diameter of 34.0 nm (more than 90% of all mossy fiber endings) and one with pleomorphic and smaller synaptic vesicles which had an average diameter of 28.5 nm. We present experimental evidence that the mossy terminals with large round vesicles are of extracerebellar origin, whereas those with small pleomorphic synaptic vesicles are endings of nucleocortical fibers. The presence of two distinct classes of gamma-aminobutyric acid (GABA)-containing axon terminals within cerebellar glomeruli has also been demonstrated; those originating from the cerebellar nuclei contain large (36.2 nm) synaptic vesicles, whereas the majority of GABA-stained axon terminals that are of local (cortical) origin contain small (29.1 nm) synaptic vesicles. It therefore appears that, at least in the case of glutamate and GABA, morphological characterization of the axon terminals based on the size and shape of synaptic vesicles is not a reliable indicator of their functional nature (i.e., whether they are excitatory or inhibitory); convincing evidence for the identity of the transmitter can be obtained only by electron microscopic immunostaining procedures. Our results also suggest the existence of both inhibitory and excitatory feedback from cerebellar nuclei to cerebellar cortex.     

Simultaneous immunohistochemical demonstration of antigen expression and 5-bromodeoxyuridine incorporation in plastic embedded sections

Summary In this study a double immunohistochemical staining procedure is described for the simultaneous demonstration of antigen expressing cells and replicating cells in rat thymus. As markers for cell surface antigen expression a monoclonal antibody against Ia-expressing cells (His 19) and a monoclonal antibody against cells of the monocyte-macrophage lineage (ED2) were used. Replicating cells were demonstrated by the incorporation of 5-bromodeoxyuridine (BrdUrd). Tissue pieces were fixed in a periodate-lysine-paraformaldehyde fixative and embedded in glycol methacrylate. To demonstrate Ia-expressing cells or ED2-positive macrophages in plastic embedded sections a digestion with trypsin is necessary. The staining procedure was applied sequentially and was performed with a peroxidase and an alkaline phosphatase labeled reagent yielding respectively a brown and a blue reaction product. Results with this staining procedure on plastic embedded sections of rat thymus, an organ with a high DNA synthesizing capacity, showed incorporation of BrdUrd predominantly in the cortex. ED2-positive macrophages were only found in the cortex. The la-positive epithelial reticular cells demonstrated extremely well their stellate form.     

Simultaneous immunohistochemical demonstration of antigen expression and 5-bromodeoxyuridine incorporation in plastic embedded sections

In this study a double immunohistochemical staining procedure is described for the simultaneous demonstration of antigen expressing cells and replicating cells in rat thymus. As markers for cell surface antigen expression a monoclonal antibody against Ia-expressing cells (His 19) and a monoclonal antibody against cells of the monocyte-macrophage lineage (ED2) were used. Replicating cells were demonstrated by the incorporation of 5-bromodeoxyuridine (BrdUrd). Tissue pieces were fixed in a periodate-lysine-paraformaldehyde fixative and embedded in glycol methacrylate. To demonstrate Ia-expressing cells or ED2-positive macrophages in plastic embedded sections a digestion with trypsin is necessary. The staining procedure was applied sequentially and was performed with a peroxidase and an alkaline phosphatase labeled reagent yielding respectively a brown and a blue reaction product. Results with this staining procedure on plastic embedded sections of rat thymus, an organ with a high DNA synthesizing capacity, showed incorporation of BrdUrd predominantly in the cortex. ED2-positive macrophages were only found in the cortex. The Ia-positive epithelial reticular cells demonstrated extremely well their stellate form.     

Improved staining method for the simultaneous flow cytofluorometric analysis of DNA content, S-phase fraction, and surface phenotype using single laser instrumentation.

We have developed an improved technique for triple staining that permits the simultaneous flow cytofluorometric analysis of cell surface antigens, bromodeoxyuridine incorporation into DNA, and DNA quantification using 7-amino-actinomycin D. PHA-activated human peripheral blood lymphocytes were incubated with bromodeoxyuridine and stained for cell surface phenotype with phycoerythrin-labeled monoclonal antibodies. Stained cells were fixed serially with 1% paraformaldehyde and 45% ethanol. Fixed cells were sequentially stained with an anti-BrdUrd monoclonal antibody followed by a FITC-conjugated goat anti-mouse antibody and incubated with 7-amino-actinomycin D. Hypotonic buffer was employed for all procedures after fixation. Stained-fixed cells were analyzed by flow cytofluorometry for simultaneous green (525 nm), orange (570 nm), and red (greater than 650 nm) fluorescence. Utilizing this staining technique, we were able to analyze simultaneously cell phenotype, DNA synthesis, and total cellular DNA content with single laser excitation.     

A Simple Procedure to Obtain One-Micrometer Sections of Routinely Embedded Paraffin Material

By freezing blocks of paraffin-embedded tissues to a convenient temperature it is possible to obtain routinely 1 µm sections that can be further processed as normal thicker sections. Normal and disposable steel knives can be used and the staining time should be increased in most procedures. Gradual freezing of blocks to the temperature of dry ice is the simplest and safest way to obtain an adequate temperature. The best results were obtained using as fixative 4% paraformaldehyde in phosphate buffered saline solution.     

Immunohistochemical Localization of Prothoracicotropic Hormone-Producing Neurosecretory Cells in the Brain of Bombyx mori

A monoclonal antibody that recognized the Bombyx prothoracicotropic hormone (PTTH) was produced by immunizing mice with a synthetic pentadecapeptide corresponding to the amino-terminal portion of Bombyx PTTH. The antibody recognized both intact and reduced forms of PTTH. Immunohistochemistry with this antibody has demonstrated that PTTH is produced by two pairs of dorso-lateral neurosecretory cells of the brain and transported to the corpora allata by axons running through the contralateral hemisphere of the brain. Immunoreactive axon terminals in the corpora allata were localized between the glandular cells, suggesting that PTTH is released at the inner part of this organ.     

A simple procedure to obtain one-micrometer sections of routinely embedded paraffin material

By freezing blocks of paraffin-embedded tissues to a convenient temperature it is possible to obtain routinely 1 micron sections that can be further processed as normal thicker sections. Normal and disposable steel knives can be used and the staining time should be increased in most procedures. Gradual freezing of blocks to the temperature of dry ice is the simplest and safest way to obtain an adequate temperature. The best results were obtained using as fixative 4% paraformaldehyde in phosphate buffered saline solution.