Spatially resolved absolute quantitation in thin tissue by mass spectrometry

Mass spectrometry (MS) has become the de facto tool for routine quantitative analysis of biomolecules. MS is increasingly being used to reveal the spatial distribution of proteins, metabolites, and pharmaceuticals in tissue and interest in this area has led to a number of novel spatially resolved MS technologies. Most spatially resolved MS measurements are qualitative in nature due to a myriad of potential biases, such as sample heterogeneity, sampling artifacts, and ionization effects. As applications of spatially resolved MS in the pharmacological and clinical fields increase, demand has become high for quantitative MS imaging and profiling data. As a result, several varied technologies now exist that provide differing levels of spatial and quantitative information. This review provides an overview of MS profiling and imaging technologies that have demonstrated quantitative analysis from tissue. Focus is given on the fundamental processes affecting quantitative analysis in an array of MS imaging and profiling technologies and methods to address these biases.Graphical abstract.

4D-Printed Transformable Tube Array for High-Throughput 3D Cell Culture and Histology

3D cell cultures are rapidly emerging as a promising tool to model various human physiologies and pathologies by closely recapitulating key characteristics and functions of in vivo microenvironment. While high-throughput 3D culture is readily available using multi-well plates, assessing the internal microstructure of 3D cell cultures still remains extremely slow because of the manual, laborious, and time-consuming histological procedures. Here, a 4D-printed transformable tube array (TTA) using a shape-memory polymer that enables massively parallel histological analysis of 3D cultures is presented. The interconnected TTA can be programmed to be expanded by 3.6 times of its printed dimension to match the size of a multi-well plate, with the ability to restore its original dimension for transferring all cultures to a histology cassette in order. Being compatible with microtome sectioning, the TTA allows for parallel histology processing for the entire samples cultured in a multi-well plate. The test result with human neural progenitor cell spheroids suggests a remarkable reduction in histology processing time by an order of magnitude. High-throughput analysis of 3D cultures enabled by this TTA has great potential to further accelerate innovations in various 3D culture applications such as high-throughput/content screening, drug discovery, disease modeling, and personalized medicine.

Tissue clearing and its applications in neuroscience

State-of-the-art tissue-clearing methods provide subcellular-level optical access to intact tissues from individual organs and even to some entire mammals. When combined with light-sheet microscopy and automated approaches to image analysis, existing tissue-clearing methods can speed up and may reduce the cost of conventional histology by several orders of magnitude. In addition, tissue-clearing chemistry allows whole-organ antibody labelling, which can be applied even to thick human tissues. By combining the most powerful labelling, clearing, imaging and data-analysis tools, scientists are extracting structural and functional cellular and subcellular information on complex mammalian bodies and large human specimens at an accelerated pace. The rapid generation of terabyte-scale imaging data furthermore creates a high demand for efficient computational approaches that tackle challenges in large-scale data analysis and management. In this Review, we discuss how tissue-clearing methods could provide an unbiased, system-level view of mammalian bodies and human specimens and discuss future opportunities for the use of these methods in human neuroscience.

Antecedents, development, adoption, and application of Duchenne's trocar for histopathologic studies of neuromuscular disorders in the nineteenth century

Duchenne de Boulogne was one of the founders of clinical neurology. His name has been eponymically linked to the most common form of muscular dystrophy, originally described by him as pseudo-hypertrophic muscular paralysis or myo-sclerotic paralysis. Obtaining muscle biopsy specimens was essential to gain insight about the etiopathogenensis of the disease. Duchenne invented a novel instrument: l'emporte-pièce histologique, also known as "Duchenne's trocar," to perform muscle biopsies. Following Duchenne's design and instructions, a Parisian company, Charrière, constructed the first instrument probably in 1864. That instrument was essential for Duchenne's description of the histopathological abnormalities typical of pseudo-hypertrophic muscular paralysis. The innovative needle-biopsy technique enabled physicians to analyze the spectrum of pathological changes at varying stages of different neuromuscular diseases. Duchenne's trocar was a forerunner of several types of modern muscle-biopsy needles. His invention was instrumental in the development of the disciplines of muscle pathology and clinical myology.

Interesting Gross Case Workshop to Remedy Disconnect in Surgical Pathology Curriculum

INTRODUCTION

This workshop was created by pathologists' assistants (PAs) who undertake specialized training programs heavily focused on grossing, which is the macroscopic inspection, evaluation, and sampling of pathology specimens for histologic evaluation by a surgical pathologist. Typically, pathologists or their trainees, during training, focus upon microscopic features, with less emphasis on the macroscopic appearance of disease.

METHODS

We developed monthly hour-long "interesting gross case workshops" (IGCWs) led by PAs to aid in the process of educating and refining pathology residents' grossing skills and abilities to diagnose at a macroscopic level. Our workshops include gross photography, grossing vocabulary, reference to standardized sampling manuals, and viewing of a specimen library to reinforce subject matter. This workshop was designed to train multilevel pathology providers including PA students, residents, fellows, and medical students, in addition to actively practicing PAs. This resource offers the audience preparation materials to host a workshop in any medical training facility.

RESULTS

Our use of the IGCWs has been evaluated positively over a 3-year period, with 78 of 150 participants stating they have increased confidence and capabilities to accurately assess and diagnose at the macroscopic level.

DISCUSSION

Utilizing this workshop can be valuable to teach the importance of a thorough gross description and tissue sampling for the diagnostic process. Future work includes expansion to additional pathology learners, improving photography database quantity and quality, and incorporating microscopic correlation when necessary.

High-refractive index of acrylate embedding resin clarifies mouse brain tissue

Biological tissue transparency combined with light-sheet fluorescence microscopy is a useful method for studying the neural structure of biological tissues. The development of light-sheet fluorescence microscopy also promotes progress in biological tissue clearing methods. The current clarifying methods mostly use liquid reagent to denature protein or remove lipids first, to eliminate or reduce the scattering index or refractive index of the biological tissue. However, denaturing protein and removing lipids require complex procedures or an extended time period. Therefore, here we have developed acrylate resin with a high refractive index, which causes clearing of biological tissue directly after polymerization. This method can improve endogenous fluorescence retention by adjusting the pH value of the resin monomer.

Modulated-Alignment Dual-Axis (MAD) Confocal Microscopy Optimized for Speed and Contrast

Modulated-alignment dual-axis (MAD) confocal microscopy combines the benefits of dual-axis confocal (DAC) microscopy and focal-modulation microscopy (FMM) for rejecting out-of-focus and multiply scattered light in tissues. The DAC architecture, which utilizes off-axis and separated beam paths for illumination and detection, has previously been shown to be superior to single-axis confocal (SAC) microscopy for the spatial filtering (rejection) of unwanted background light. With the MAD approach, a modulation of the alignment between the illumination and collection beam paths tags ballistic photons emanating from the focal volume with a characteristic radio frequency that can be extracted and separated from background signal using lock-in detection. We report here an optimized form of MAD confocal microscopy where we have fully mitigated tradeoffs in performance in an initial proof-of-concept system in order to recover the imaging speed of DAC microscopy while retaining contrast enhancement of 6 dB (signal-to-background ratio) with a secondary improvement in optical-sectioning and in-plane resolution. Validation is demonstrated with light-scattering tissue phantoms and freshly excised tissues.

Microwave-aided binding of gold-protein-ligand (GPL) complexes. Light microscopic observations in the rat brain

We describe a rapid method for the preparation and binding site labeling of cryostat sections for use in light microscopy. Instead of using antibodies to bind to specific sites, substance P, delta-sleep-inducing peptide, oxytocin, and dopamine were covalently attached to BSA and then the BSA-ligand complex was adsorbed on 5-nm colloidal gold particles. Bioassays carried out on isolated organs indicated that the physiological activity of the ligand GPL complex was maintained. Most of the technical steps included use of an ordinary microwave oven (MWO), with tissues exposed for less than 1 min in any given step. Cryostat sections of unfixed rat brain were pre-incubated for 50 sec in the MWO in a Tris-buffered solution (pH 7.4) containing 1.5% BSA, then further incubated for 50 sec in the MWO in Tris-buffered solution containing 1% gelatin and the diluted colloidal gold suspension. After washing, the preparations were postfixed for 30 sec in the MWO in 5% formaldehyde solution, pH 7.4. Finally, the cell-bound gold particles were enlarged by a silver-enhancing process and counterstained. Preparations observed at high magnification provided excellent resolution of the cell binding sites. Positive and negative controls performed by addition of BSA-conjugated ligands to the pre-incubation and incubation medium, and displacement of the markers by an excess of unbound ligand in the pre-incubation or the incubation medium, showed the specificity of the tissue labeling.

Systematic optimization of multiplex zymography protocol to detect active cathepsins K, L, S, and V in healthy and diseased tissue: compromise among limits of detection, reduced time, and resources

Cysteine cathepsins are a family of proteases identified in cancer, atherosclerosis, osteoporosis, arthritis, and a number of other diseases. As this number continues to rise, so does the need for low cost, broad use quantitative assays to detect their activity and can be translated to the clinic in the hospital or in low resource settings. Multiplex cathepsin zymography is one such assay that detects subnanomolar levels of active cathepsins K, L, S, and V in cell or tissue preparations observed as clear bands of proteolytic activity after gelatin substrate SDS-PAGE with conditions optimal for cathepsin renaturing and activity. Densitometric analysis of the zymogram provides quantitative information from this low cost assay. After systematic modifications to optimize cathepsin zymography, we describe reduced electrophoresis time from 2 h to 10 min, incubation assay time from overnight to 4 h, and reduced minimal tissue protein necessary while maintaining sensitive detection limits; an evaluation of the pros and cons of each modification is also included. We further describe image acquisition by Smartphone camera, export to Matlab, and densitometric analysis code to quantify and report cathepsin activity, adding portability and replacing large scale, darkbox imaging equipment that could be cost prohibitive in limited resource settings.

Confocal microscopy with strip mosaicing for rapid imaging over large areas of excised tissue

Confocal mosaicing microscopy is a developing technology platform for imaging tumor margins directly in freshly excised tissue, without the processing required for conventional pathology. Previously, mosaicing on 12-×-12  mm² of excised skin tissue from Mohs surgery and detection of basal cell carcinoma margins was demonstrated in 9 min. Last year, we reported the feasibility of a faster approach called "strip mosaicing," which was demonstrated on a 10-×-10  mm² of tissue in 3 min. Here we describe further advances in instrumentation, software, and speed. A mechanism was also developed to flatten tissue in order to enable consistent and repeatable acquisition of images over large areas. We demonstrate mosaicing on 10-×-10  mm² of skin tissue with 1-μm lateral resolution in 90 s. A 2.5-×-3.5  cm² piece of breast tissue was scanned with 0.8-μm lateral resolution in 13 min. Rapid mosaicing of confocal images on large areas of fresh tissue potentially offers a means to perform pathology at the bedside. Imaging of tumor margins with strip mosaicing confocal microscopy may serve as an adjunct to conventional (frozen or fixed) pathology for guiding surgery.

Improved detectability of neuronal connectivity on mechanical sectioning setup by using confocal detection

A recently reported micro-optical sectioning tomography system has great potential to draw the neuronal circuits of large brain volume with submicron resolution by combining fine mechanic sectioning with simultaneous optical imaging. However, sectioning the fluorescence sample sometimes induces tears between adjacent tiles and causes difficulties in continuous fiber tracing from fluorescence imaging. A confocal detection to recover the interruptions of the nerve fiber is introduced. With a 50-μm-width confocal slit, the signal-to-background ratio is increased 16- to 49-fold more than that without the slit, which effectively improves the detectability of the signal in the interruptions and enables continuous tracing of the neuronal circuits.

Direct imaging of single cells and tissue at sub-cellular spatial resolution using transmission geometry MALDI MS

The need of cellular and sub-cellular spatial resolution in laser desorption ionization (LDI)/matrix-assisted LDI (MALDI) imaging mass spectrometry (IMS) necessitates micron and sub-micron laser spot sizes at biologically relevant sensitivities, introducing significant challenges for MS technology. To this end, we have developed a transmission geometry vacuum ion source that allows the laser beam to irradiate the back side of the sample. This arrangement obviates the mechanical/ion optic complications in the source by completely separating the optical lens and ion optic structures. We have experimentally demonstrated the viability of transmission geometry MALDI MS for imaging biological tissues and cells with sub-cellular spatial resolution. Furthermore, we demonstrate that in conjunction with new sample preparation protocols, the sensitivity of this instrument is sufficient to obtain molecular images at sub-micron spatial resolution.

Student perceptions of digital versus traditional slide use in undergraduate education

Digitized slides provide a number of intriguing benefits for educators. Before their implementation, however, educators should consider student opinion related to their use. This mixed-methods study directly compared Medical Laboratory Science (MLS) student perceptions of learning experiences in both digital and traditional slide laboratory settings. Results suggested that the majority of students preferred learning with digital slides, and numerous reasons for this preference were identified. Survey responses indicated that students using digital slides tended to view their performances, instructor feedback, and their learning environment more positively than students using traditional slides. Apprehensions about digital slide use were also detected from students preferring traditional slides. These findings provide a guide on how best to exploit both digital and traditional slides in an educational setting.

In situ characterization of the brain-microdevice interface using device-capture histology

Accurate assessment of brain-implantable microdevice bio-integration remains a formidable challenge. Prevailing histological methods require device extraction prior to tissue processing, often disrupting and removing the tissue of interest which had been surrounding the device. The Device-Capture Histology method, presented here, overcomes many limitations of the conventional Device-Explant Histology method, by collecting the device and surrounding tissue intact for subsequent labeling. With the implant remaining in situ, accurate and precise imaging of the morphologically preserved tissue at the brain/microdevice interface can then be collected and quantified. First, this article presents the Device-Capture Histology method for obtaining and processing the intact, undisturbed microdevice-tissue interface, and imaging using fluorescent labeling and confocal microscopy. Second, this article gives examples of how to quantify features found in the captured peridevice tissue. We also share histological data capturing (1) the impact of microdevice implantation on tissue, (2) the effects of an experimental anti-inflammatory coating, (3) a dense grouping of cell nuclei encapsulating a long-term implant, and (4) atypical oligodendrocyte organization neighboring a long term implant. Data sets collected using the Device-Capture Histology method are presented to demonstrate the significant advantages of processing the intact microdevice-tissue interface, and to underscore the utility of the method in understanding the effects of the brain-implantable microdevices on nearby tissue.

Spectral characterization and unmixing of intrinsic contrast in intact normal and diseased gastric tissues using hyperspectral two-photon microscopy

Background

Living tissues contain a range of intrinsic fluorophores and sources of second harmonic generation which provide contrast that can be exploited for fresh tissue imaging. Microscopic imaging of fresh tissue samples can circumvent the cost and time associated with conventional histology. Further, intrinsic contrast can provide rich information about a tissue's composition, structure and function, and opens the potential for in-vivo imaging without the need for contrast agents.

Methodology/Principal Findings

In this study, we used hyperspectral two-photon microscopy to explore the characteristics of both normal and diseased gastrointestinal (GI) tissues, relying only on their endogenous fluorescence and second harmonic generation to provide contrast. We obtained hyperspectral data at subcellular resolution by acquiring images over a range of two-photon excitation wavelengths, and found excitation spectral signatures of specific tissue types based on our ability to clearly visualize morphology. We present the two-photon excitation spectral properties of four major tissue types that are present throughout the GI tract: epithelium, lamina propria, collagen, and lymphatic tissue. Using these four excitation signatures as basis spectra, linear unmixing strategies were applied to hyperspectral data sets of both normal and neoplastic tissue acquired in the colon and small intestine. Our results show that hyperspectral unmixing with excitation spectra allows segmentation, showing promise for blind identification of tissue types within a field of view, analogous to specific staining in conventional histology. The intrinsic spectral signatures of these tissue types provide information relating to their biochemical composition.

Conclusions/Significance

These results suggest hyperspectral two-photon microscopy could provide an alternative to conventional histology either for in-situ imaging, or intraoperative ‘instant histology’ of fresh tissue biopsies.

[Logistic support and ways for reducing costs in a pathological laboratory]

The paper provides a comparative technical-and-economical assessment of the basic reagents that are most commonly used for histological processing of tissue specimens in terms of cost optimization. The presented data may be useful to experts to make decisions on the current logistical support of pathology laboratories.

[Impact of technical characteristics of histological equipment on the research costs]

The paper provides a comparative technical-and-economical assessment of manual and hardware-based methods for histological tissue processing in terms of cost optimization. The presented data may be useful to experts to make decisions on the logistical support of pathology laboratories.

A simple and inexpensive method for investigating microbiological, enzymatic, or inorganic catalysis using standard histology and microbiology laboratory equipment: assembly, mass transfer properties, hydrodynamic conditions and evaluation

We introduce a generic, simple, and inexpensive method for performing microbiological, enzymatic, or inorganic catalysis with solids using standard histology and microbiology laboratory equipment. Histology cassettes were used to standardize hydrodynamic conditions and to protect the catalysts and their solid supports. Histology cassettes have the following advantages: they are readily available, inexpensive, solvent and acid resistant, automatable, and the slots in the cassette walls allow liquid to circulate freely. Standard Erlenmeyer flasks were used as reaction vessels. We developed a new camera to observe the movement and position of the histology cassettes as well as the liquid in the Erlenmeyer flasks. The camera produces a stable image of the rotating liquid in the Erlenmeyer flask. This visualization method revealed that in a 250 ml Erlenmeyer flask, stable operating conditions are achieved at a shaking frequency of 300 rpm and a fill volume of 30 ml. In vessels with vertical walls, such as beakers or laboratory bottles, the movement of the histology cassette is not reproducible. Mass transfer characterization using a biological model system and the chemical sulfite-oxidation method revealed that the histology cassette does not influence gas-liquid mass transfer.

A procedure for tissue freezing and processing applicable to both intra-operative frozen section diagnosis and tissue banking in surgical pathology

Different methods for snap freezing surgical human tissue specimens exist. At pathology institutes with higher work loads, solid carbon dioxide, freezing sprays, and cryostat freezing are commonly used as coolants for diagnosing frozen tissue sections, whereas for tissue banking, liquid nitrogen or isopentane cooled with liquid nitrogen is preferred. Freezing tissues for diagnostic and research purposes are therefore often time consuming, laborious, even hazardous, and not user friendly. In tissue banks, frozen tissue samples are stored in cryovials, capsules, cryomolds, or cryocassettes. Tissues are additionally embedded using freezing media or wrapped in plastic bags or aluminum foils to prevent desiccation. The latter method aggravates enormously further tissue handling and processing. Here, we describe an isopentane-based workflow which concurrently facilitates tissue freezing and processing for both routine intra-operative frozen section and tissue banking and satisfies the qualitative demands of pathologists, cancer researchers, laboratory technicians, and tissue bankers.

A novel method for three-dimensional observation of the vascular networks in the whole mouse brain

A novel method for acquiring serial images suitable for three-dimensional reconstruction of vascular networks in the whole brain of mouse was developed. The brain infused with a White India ink-gelatin solution was fixed and embedded in paraffin containing Sudan Black B through xylene also containing Sudan Black B. Each sliced surface of the paraffin block was coated with liquid paraffin and its image was serially acquired. Coating with liquid paraffin extremely improved the quality of the image. The series of serial images was free of distortion and a three-dimensional image was reconstructed without the problem of the alignment and registration of adjacent images. The volume-rendered image indicated three-dimensional distribution of blood vessels in a whole brain. No ghost or shadow was observed on a volume-rendered image of the White India ink-gelatin infused brain. The z-axial resolution examined on the orthogonal sections reconstituted from serial images obtained at an interval of 5 mum showed no cross talk, indicating that the z-axial resolution was no larger than 5 mum. A proper understanding of the vascular system in a whole brain is indispensable to reveal the development of the vascular system in the brain of normal and genetically manipulated mouse and vascular alterations in pathological situation, such as stroke and neurodegenerative disease. Although simple and inexpensive, this method will provide fundamental information on the vascular system in a whole brain.

Recent advances in high-pressure freezing: equipment- and specimen-loading methods

This chapter is an update of material first published by McDonald in the first volume of this book. Here, we discuss the improvements in the technology and the methodology of high-pressure freezing (HPF) since that article was published. First, we cover the latest innovation in HPF, the Leica EM PACT2. This machine differs significantly from the BAL-TEC HPM 010 high-pressure freezer, which was the main subject of the former chapter. The EM PACT2 is a smaller, portable machine and has an optional attachment, the Rapid Transfer System (RTS). This RTS permits easy and reproducible loading of the sample and allows one to do correlative light and electron microscopy with high time resolution. We also place more emphasis in this article on the details of specimen loading for HPF, which is considered the most critical phase of the whole process. Detailed procedures are described for how to high-pressure freeze cells in suspension, cells attached to substrates, tissue samples, or whole organisms smaller than 300 microm, and tissues or organisms greater than 300 microm in size. We finish the article with a brief discussion of freeze substitution and recommend some sample protocols for this procedure.

High-throughput zebrafish histology

The morphological effects of mutation and disease are often critical to our understanding of normal and abnormal function. The power and popularity of zebrafish as a forward and reverse genetic vertebrate model system, combined with its small size, have made it an ideal model in which to study the genetics of histologically scorable phenotypes. The presence of multiple tissue types in this organism's small larvae also makes it a potentially important model for toxicological analysis. Studying histological phenotypes is greatly enhanced by high-throughput methods of histology. Here, we describe details of high-throughput histology of the zebrafish using larval arrays, along with recent advances in mold design and discussion of work in progress that will lead to easier ways for people in the field to more rapidly score phenotypes in arrays. These detailed descriptions, together with the troubleshooting guide, should enable any laboratory with ties to a histology facility to perform high-throughput histology of zebrafish.

A simple device to rapidly prepare whole mounts of murine intestine

Many mouse models of neoplasia and pre-neoplasia require the examination of whole mounts of the gastrointestinal tract. A simple device has been produced to facilitate the rapid preparation of mouse intestines for subsequent quantification of tumours and pre-neoplastic lesions such as aberrant crypt foci. The device greatly speeds up the production of whole mounts and also provides far more consistent and better-quality preparations.

Critical comparison of 31 commercially available digital slide systems in pathology

Advances in new technologies for complete slide digitization in pathology have allowed the appearance of a wide spectrum of technologic solutions for whole-slide scanning, which have been classified into motorized microscopes and scanners. This article describes technical aspects of 31 different digital microscopy systems. The most relevant characteristics of the scanning devices are described, including the cameras used, the speed of digitization, and the image quality. Other aspects, such as the file format, the compression techniques, and the solutions for visualization of digital slides, (including diagnosis-aided tools) are also considered. Most of the systems evaluated allow a high-resolution digitization of the whole slide within about 1 hour using a x40 objective. The image quality of the current virtual microscopy systems is suitable for clinical, educational, and research purposes. The efficient use of digital microscopy by means of image analysis systems can offer important benefits to pathology departments.

Técnicas endoscópicas emergentes. La llegada de la histología virtual

Endoscopic technology has evolved in such a way that gastroenterologists can now visualize and store high-resolution images of the gastrointestinal tract. This has improved the approach to precancerous and cancerous lesions of the gastrointestinal tract and biliary tree. However, certain difficulties remain, especially in relation to diagnosis. In the last few years, multiple techniques have been developed that, using the properties of light, enable an instantaneous histologic diagnosis to be made while endoscopy is being performed. What has been called the "optical biopsy" allows highly exact information to be obtained, both from the morphological and functional point of view. Some of these techniques, such as chromoendoscopy and magnification, are already being performed in clinical practice while others are still under investigation. The aim of the present article is to review the underlying principles and applications of these emerging techniques.

Methods for cartilage and subchondral bone histomorphometry

This chapter presents the histological assessment of cartilage and bone of tibial plateaus, by procedures that have been applied and validated in two animal models of osteoarthritis: meniscectomized rats and guinea pigs. It starts from bone sampling, followed by all the steps of sample preparation from embedding to sectioning (without prior decalcification), staining, and mounting. Depending on the cartilage or bone components to be visualized, two dyes are described: safranin O and Goldner's trichrome. On these stained sections, various histomorphometric parameters are then quantified using the dedicated programs of an image analyzer. The following parameters are evaluated at the medial side of the tibia and are described at the levels of both cartilage (cartilage thickness, fibrillation index, proteoglycan content ratio based on safranin-O staining intensities and chondrocyte density) and bone (subchondral bone plate thickness).

Constructing tissue microarrays without prefabricating recipient blocks: a novel approach

Tissue microarray (TMA) is a powerful research tool and is applied in such diverse areas as tumor marker validation and laboratory quality control. Existing TMA construction techniques require an essential step of prefabricating recipient paraffin blocks on which holes are punched so that tissue cores can be inserted. This procedure has several disadvantages, such as accidental block breakage during hole punching and difficulty ensuring that the cores are flush with the block surface. We developed a novel TMA construction technique without prefabricating recipient blocks. We used double-sided adhesive tape attached to x-ray film as an adhesive platform on which the tissue cores were placed securely. The array of tissue cores then was embedded in an embedding mold. We have been making high-quality TMAs with up to 220 cores within 2 to 3 hours using this highly dependable, efficient, versatile, and cost-effective technique, which can be adopted by pathology laboratories and researchers with minimal investment.

The revolution of counting “tops”: Two decades of the disector principle in morphological research

Twenty years have passed since the publication of the seminal paper enunciating the disector principle by an author using the pseudonym D.C. Sterio. During this time, methods based on the revolutionary principle of counting "tops" have become progressively better known and have been included in several commercially available systems for quantitative morphology. Analysis of the number of published studies citing Sterio's paper on the ISI Web of Knowledge database showed that its scientific "impact factor" has almost continuously risen since its publication, indicating the growing knowledge about disector-based methods in the various scientific fields where morphological quantification is required. This report briefly reviews the first two decades of disector use, pointing to its advantages as well as to shortcomings that have recently been addressed in critical papers and have given rise to a lively debate on the role of counting tops in quantitative morphology today.

A simple, low-cost device for processing and embedding tissues at sub-zero temperatures

A simple apparatus to maintain tissues samples at sub-zero temperatures during dehydration, infiltration, and polymerization is described. The device uses a conventional siphon-type carbon dioxide gas cylinder to maintain an aluminum block at temperatures as low as -35 degrees C for over 15 hours/cylinder.

Traumatic brain injury in piglets of different ages: techniques for lesion analysis using histology and magnetic resonance imaging

Quantitation of lesions in large gyrencephalic brains presents a variety of technical challenges. Specific techniques are required when comparing lesions in subjects of different ages in order to assess maturational effects. We have modified existing techniques to attain reliable, consistent and reproducible paraffin-embedded histological sections for volumetric lesion analysis and correlation with magnetic resonance imaging (MRI) in piglets of different ages following focal traumatic brain injury. Twenty-four Yorkshire domestic piglets at three different ages (5 days, 1 month, and 4 months old) underwent scaled cortical impact injury to the fronto-parietal cortex. This contusion model utilizes a rapid volume of indentation scaled proportionally to the growth of the brain, allowing for examination of maturational influences on the brain's response to focal mechanical trauma. To overcome problems with differential processing and embedding of brains ranging from 43 to 107 g, we developed a piglet parallel brain slicing apparatus. Along with specific methods for processing, embedding, mounting, and slide preparation, these techniques enabled excellent quality 10-microm serial coronal sections to be obtained for histology and immunohistochemical analysis. Accurate co-registration of histologic, immunohistochemical and radiologic images at different ages was possible, which may enhance understanding of developmental aspects of brain injury pathophysiology.

Microdissection of histologic sections: past, present, and future

Histologic and cytologic changes are central to the diagnosis and classification of many disease processes, particularly neoplasms. The correlation of these changes with genomics, proteomics, and molecular pathways entails refined microdissection techniques that are frequently used to procure a pure population of cells from complex tissue. Here we review the past, present, and future of some of these new advances in microdissection techniques including manual techniques, laser microdissection, laser capture microdissection, and laser catapulting.

Preparation of autogenous bone grafts in two different bone mills

The purpose of this study was to evaluate the performance of two bone mills (R Quetin Bone Mill and Micro Knochenmühle, Aesculap) for the grinding of autogenous bone (intraoral, cortical) according to the following criteria: (1) loss of bone during the grinding process, (2) particle size of the chips, (3) variability in chip size, (4) technical handling, and (5) cost-benefit ratio. The amount of material loss was determined by harvesting 30 bone cores from the mandibular symphysis of a pig. Each specimen was weighed before and after the grinding procedure on scales with an accuracy of 0.1 mg. The size and variability of the bone particles were determined histomorphometrically. Twenty-seven bone specimens from different patients were analyzed. Eight were ground with the Aesculap and 12 with the Quetin mill. Seven specimens harvested with a Brånemark implant bur served as controls. A histologic section was prepared from each specimen, and 10 bone particles per section were subjected to histomorphometric analysis. The Quetin mill was superior in all points to the Aesculap mill for the requirements of a periodontal practice.

Amplification of tissue by construction of tissue microarrays

Tissue microarrays are a method of relocating tissue from conventional histologic paraffin blocks in a manner that tissue from multiple patients or blocks can be seen on the same slide. This is done by using a needle to biopsy a standard histologic section and placing the core into an array on a recipient paraffin block. This technique allows maximization of tissue resources by analysis of small core biopsies of blocks, rather than complete sections. Using this technology, a carefully planned array can be constructed using cases from pathology tissue block archives, and a 20-year survival analysis can be done on a cohort of 600 or more patients using only a few microliters of antibody in a single experiment. Furthermore, this cohort can be analyzed thousands of times with different reagents as a result of judicious sectioning of the array block. This review describes this process and discusses the issues of representative sampling in heterogeneous lesions, the issue of antigen preservation, and some technical strategies and methods of array construction. In summary, this technique can provide a highly efficient, high-throughput mechanism for evaluation of protein expression in large cohorts. It has the potential for allowing validation of new genes at a speed comparable to the rapid rate of gene discovery afforded by DNA microarrays.

A modified roller method for organotypic brain cultures: free-floating slices of postnatal rat hippocampus

We describe a novel procedure for organotypic cultivation of free-floating brain sections of postnatal rats with a modified roller technique. Three hundred to 350-microm-thick sections of hippocampus are cultured for 13-15 days at 35.5 degrees C in 10-15 ml of feeding medium in 50-100 ml bottles under constant rotation on a horizontal high-speed mini-roller (60 rpm). Histological analysis (paraffin sections, Nissl Cresyl Violet and Hematoxylin/Eosin staining) demonstrates good survival of neuronal and glial cells and complete preservation of the neuronal organization of cultivated hippocampus with minimal central necrosis. This novel protocol permits not only survival and development of long-term three-dimensional organotypic postnatal brain tissue but also allows simultaneous cultivation of any number of brain sections in one bottle (up to 50 and even more) and therefore is useful for high throughput study of neurocytotoxic and hypoxic/ischemic neuronal damage with subsequent histological, immunocytochemical, biochemical, and molecular analysis.

[Creating low-power photomicrographs by digital scanning of histological sections]

The recent introduction of digital film scanners in the medical-scientific field provided everyone dealing with light-microscopy an easy method to obtain low-power photomicrographs from entire histological sections. Direct scanning of the common microscope slide allows the easy creation of high quality images. The digital images obtained may be improved or retouched using dedicated software and then printed on paper or film. The required instrumentation is relatively unexpensive and neither skilled staff nor expertise of photographic techniques is required. This reduces costs and saves time. The obtained images may be employed in histopathology, embryology, histochemistry, image analysis and telepathology, and are suitable for scientific papers, educational purposes and lecturing, as well as for daily reporting. The authors bring their personal experience in this field, making also a complete literature review on the topic.

A developmental time line in a retinal slice from rainbow trout

The retina in teleost fish continues to grow throughout much of the life of the animal, in part by the continuing differentiation of new tissue at the retinal margin, an area termed the peripheral growth zone (PGZ) (Lyall, Q J Micros Sci, 1957:98:101-110). We have developed a retinal slice preparation--including the PGZ--from juvenile rainbow trout (Onchorynchus mykiss), a species in which retinal growth is rapid and the PGZ is correspondingly pronounced. The PGZ slice preparation contains a time line of retinal development, with cells at different stages of maturation present side by side. We present evidence that the birth sequence of the various retinal cell types in the PGZ recapitulates the sequence during embryonic development. We also report data on the rate of growth of the PGZ in juvenile trout in vivo. Finally, we have used the PGZ slice preparation to make whole-cell voltage clamp recordings from individual retinal GCs at both early and late stages of maturation. We report that the amplitude of delayed rectifier and A-type potassium currents increases during GC maturation.

Cardiac muscle tissue engineering: toward an in vitro model for electrophysiological studies

The objective of this study was to establish a three-dimensional (3-D) in vitro model system of cardiac muscle for electrophysiological studies. Primary neonatal rat ventricular cells containing lower or higher fractions of cardiac myocytes were cultured on polymeric scaffolds in bioreactors to form regular or enriched cardiac muscle constructs, respectively. After 1 wk, all constructs contained a peripheral tissue-like region (50-70 micrometer thick) in which differentiated cardiac myocytes were organized in multiple layers in a 3-D configuration. Indexes of cell size (protein/DNA) and metabolic activity (tetrazolium conversion/DNA) were similar for constructs and neonatal rat ventricles. Electrophysiological studies conducted using a linear array of extracellular electrodes showed that the peripheral region of constructs exhibited relatively homogeneous electrical properties and sustained macroscopically continuous impulse propagation on a centimeter-size scale. Electrophysiological properties of enriched constructs were superior to those of regular constructs but inferior to those of native ventricles. These results demonstrate that 3-D cardiac muscle constructs can be engineered with cardiac-specific structural and electrophysiological properties and used for in vitro impulse propagation studies.

Double embedding broad thin leaves in paraffin

Paraffin pellets were melted in 24x24x5 mm stainless steel base molds. Specimens of leaves, 18x18 mm, were fixed, dehydrated and infiltrated with paraffin. Two specimens were transferred into molten paraffin on their laminar surfaces in a base mold and moved quickly onto a cold surface to cast them in a shallow block of paraffin. Each block was then scored with a razor blade, broken into two primary blocks, and trimmed to 20x9 mm with 5 mm flat edges. Each primary block was immersed upright on its long edge in a 22x22x20 mm Peel-A-Way embedding mold containing molten paraffin. The leaf edge was held centrally in the mold while moving the double embedment onto a cold surface. In this secondary block, the leaf specimen stood perpendicular to the sectioning surface in perfect orientation for transverse ribbon sectioning. The two phases of paraffin bonded well.

[Histologic tissue processing in an automated microwave histoprocessor]

A new vacuum histoprocessor has been tested as well as new more effective protocols to work with this processor. The device allows histoprocessing of 50 samples simultaneously of surgery, biopsy or autopsy material during 1-1.5 h. Apart from the standard protocols, new protocols with a much lower (5-10 times) expenditure of the chemicals can be implemented due to combination of microwaves and vacuum. Each protocol was tested repeatedly (20 and more times) with stable good quality of microscopic image.

[An improved method for isolating a section of the rat neocortex]

Neocortical island chronically isolated from surrounding cortical and subcortical structures with preserved pial blood supply has long been a model for research into the mechanisms of cortex functioning. To fully cut the cortex we improved the type of knife by using a retractable tungsten wire. The tip of a syringe needle was bent and cut away all but the beginning of the bend. In anesthetized rats the somatosensory cortex was exposed, the guide needle was lowered down to the desired depth into the cortex avoiding blood vessels. The wire then was pulled out through the curved needle tip until the tip of the wire touched the pia mater. The device was then raised, lowered, rotated to achieve complete separation of the cortical island from the surrounding tissues. The wire was retracted into the needle before withdrawal of the device. Analysis of neocortical slices 8 weeks later showed lesions of the white matter and transcortical cuts.

[A device for demonstrating micropreparations "histoskop"]

A device "Histoscop" for demonstration of histologic preparations is described. The device has a powerful lighting system enabling it to reflect images of histological structures from the microscope objective to a screen. The device is multipurpose (can be used in conferences, teaching, etc.).

Electrophysiological characterization of human distal colon epithelium isolated using a novel technique

Electrophysiological studies of human colonic epithelia traditionally have been hampered by the lack of tissue availability and by poor tissue quality. Human colonic epithelium is usually obtained surgically from individuals with underlying disease, while surgery itself can injure or alter the resected tissue. As a result, a wide range in electrophysiological parameters is reported in previous studies of human colonic epithelium. Such factors may also account for differences in measurements between humans and the few other species studied. We therefore devised a novel and rapid endoscopic technique, endoscopic mucosal resection (EMR), that allows for the removal and study of intestinal mucosal epithelium from normal volunteers. Using EMR we rapidly (7.2+/-2.4 min) isolated surgical-sized epithelial sheets from the distal colon (1.4+/-0.4 by 1.3+/-0.4 cm) that were readily mounted in a 0.64-cm2 Ussing chamber. We observed stable resistance (289+/-30 omega cm2), potential difference (1.6+/-0.6 mV), and I(SC)(24+/-9 microA/cm2) for at least 90 min, after which all experiments were terminated. Exposure to carbachol increased I(SC)2.2+/-0.5-fold, while forskolin increased I(SC) 4.4+/-0.5-fold. These data show that the electrophysiological characteristics of the human distal colon removed by EMR more closely approximate values reported for other mammals than when removed using other techniques. Thus EMR represents a significant advance over traditional techniques for isolating human tissues and will increase the availability of this tissue for future studies.

[Confocal laser scanning microscopy (CLSM) for validation of non-destructive histotomography of healthy bone tissue]

OBJECTIVES

Fixation (formalin), decalcification (sections) or mechanical treatment (grinding) all bear the risk of artifacts occurring during hard-tissue histology. Because studies on the etiology of pathological changes mostly focus on subclinical lesions, artifacts can simulate early changes or even be superimposed on existing changes. The objective of this study was to determine how artifacts can be reduced.

MATERIAL AND METHODS

In confocal laser scanning microscopy (CLSM) a focused laser beam scans the surface of the specimens and penetrates into the tissue. The intensity of the remitted light is recorded. The confocal effect is due to an extremely small aperture (pin-hole), excluding light from out-of-focus planes of the sample. By stepwise movement of the object table, a tomographic series of tomographic images is obtained. Sound cortical bone samples of the lower jaw (n = 20) were studied by light microscopy and by CLSM, visualizing identical areas of a ground sectioned sample after H&E staining. Additionally, embedded and fresh blocks of tissue of the same bone sample were studied histotomographically in the CLSM.

RESULTS

(1) Light microscopic micromorphology of cortical bone can be visualized adequately in the CLSM; (2) many structures that can be visualized by light microscopy only after special staining (e.g., osteozyte processes) can be visualized by the CLSM using sample blocks without pretreatment.

CONCLUSION

(1) Nondestructive subsurface histotomography by CLSM totally excludes mechanical artifacts; (2) physicochemical artifacts can be handled more easily because fresh samples can be studied; (3) pseudo-three-dimensional imaging allows histological interpretation of the tissue that is equivalent to macroscopic tomographic techniques (CT, MRT).

A technique for section thickness evaluation for microphotometry and image analysis of sectioned nuclei

The exact knowledge of the section thickness is a requisite for making the necessary corrections on DNA measurements in tissue sections. Several methods have been proposed to evaluate section thickness, each of them with advantages and disadvantages depending on the type of specimen and equipment available. We herein report another method based on preparation of standard material whose optical density varies as a function of its thickness and is sectioned and measured alongside the tissue specimen. The standards consist of celloidin cylinders stained with the PAS reaction and embedded in paraffin. For prior characterization of the cylinders, sections of different thickness were obtained and mounted. The optical density of each section was measured by direct microphotometry or image analysis. The actual thickness of each section was evaluated following re-embedding of piled groups of sections in a paraffin block and transversal sectioning. The thickness was then measured with a micrometric eye-piece. Optical density and actual thickness of each section were plotted on a normogram curve. Once a given tissue is sectioned alongside with the reference cylinder, the actual thickness is determined by its optical density on the normogram curve.