Spiny versus stubby: 3D reconstruction of human myenteric (type I) neurons

The autonomic nervous system from a morphofunctional perspective: Historical overview and current concepts over the last two centuries highlighting contributions from Eastern Europe

The present contribution comprises both an introductory comment and an overview of the contributions within this special issue on historical and current research on the autonomic nervous system from Eastern European colleagues, particularly focusing on the autonomic innervation of the gastrointestinal tract and of the cardiovascular system. It also gives a selected overview of interesting and seminal papers on these topics that appeared in The Anatomical Record since its foundation in 1906.

Morphological, Immunohistochemical, and Ultrastructural Studies of the Donkey's Eye with Special Reference to the AFGF and ACE Expression

The donkey is mainly used as a working animal for riding and pack transport, as well as for dairy and meat production. Eye afflictions are common in donkeys, thus requiring a detailed study. A few studies had focused on the donkey's eye, and most of them had considered it, merely, a horse's eye. This study aimed to investigate the anatomy, histology, ultrastructure, and immunohistochemical features of the donkey's eye. The results were recorded and compared to those of horses in certain dimensions. Unlike horses, the donkey's eye is more circular in the contour of the cornea, has smaller lenticular thickness, and has longer anterior and vitreous chambers. Positive immunoreactivity to acidic fibroblast growth factor in the basal cell layers of the cornea was observed, indicating their role in cell differentiation and the renewal of the epithelium. Moreover, the corneal keratocytes expressed angiotensin-converting enzyme, which plays a role in corneal homeostasis and wound healing. Additionally, telocytes, hyalocytes, and other immune cells were observed within the iris and ciliary processes. Hence, this work is an updated detailed study of the morphology and ultrastructure of the donkey's eye and reveals some similarities and dissimilarities to the horse's eyes, which should be considered in clinical practice.

Classification of human enteric neurons

Major advances in our understanding of the functional heterogeneity of enteric neurons are driven by the application of newly developed, innovative methods. In contrast to this progress, both animal and human enteric neurons are usually divided into only two morphological subpopulations, “Dogiel type II” neurons (with several long processes) and “Dogiel type I” neurons (with several short processes). This implies no more than the distinction of intrinsic primary afferent from all other enteric neurons. The well-known chemical and functional diversity of enteric neurons is not reflected by this restrictive dichotomy of morphological data. Recent structural investigations of human enteric neurons were performed by different groups which mainly used two methodical approaches, namely detecting the architecture of their processes and target-specific tracing of their axonal courses. Both methods were combined with multiple immunohistochemistry in order to decipher neurochemical codes. This review integrates these morphological and immunohistological data and presents a classification of human enteric neurons which we believe is not yet complete but provides an essential foundation for the further development of human gastrointestinal neuropathology.

Morphological and Immunohistochemical Characterization of Human Intrinsic Gastric Neurons

Our knowledge about human gastric enteric neuron types is even more limited than that of human intestinal types. Here, we immunohistochemically stained wholemounts and sections of gastric specimens obtained from 18 tumor-resected patients. Myenteric wholemounts were labeled for choline acetyl transferase (ChAT), neuronal nitric oxide synthase (NOS), and the human neuronal protein HuC/D (as pan-neuronal marker for quantitative analysis) or alternatively for neurofilament (for morphological evaluation). ChAT-positive neurons outnumbered NOS-positive neurons (56 vs. 27%), and neurons negative for both markers accounted for 17%. Two larger groups of neurons (each between 12 and 14%) costained for ChAT and vasoactive intestinal peptide (VIP) or for NOS and VIP, respectively. Clear morphochemical correlation was found for uniaxonal stubby type I neurons (ChAT+; putative excitatory inter- or motor neurons), for uniaxonal spiny type I neurons (NOS+/VIP+; putative inhibitory motor or interneurons), and for multiaxonal type II neurons (ChAT+; putative afferent neurons; immunostaining of additional wholemounts revealed their coreactivity for somatostatin). Whereas these latter neuron types were already known from the human intestine, the morphology of gastric myenteric neurons coreactive for ChAT and VIP was newly described: they had numerous short, extremely thin dendrites and resembled, together with their cell bodies, a "hairy" head. In our sections, nerve fibers coreactive for ChAT and VIP were commonly found only in the mucosa. We suggest these myenteric ChAT+/VIP+/hairy neurons to be mucosal effector neurons. In contrast to myenteric neurons, the much less common submucosal neurons were not embedded in a continuous plexus and did not display any clear morphochemical phenotypes.

Chagasic megacolon: enteric neurons and related structures

Megacolon, the irreversible dilation of a colonic segment, is a structural sign associated with various gastrointestinal disorders. In its hereditary, secondary form (e.g. in Hirschsprung's disease), dilation occurs in an originally healthy colonic segment due to an anally located, aganglionic zone. In contrast, in chronic Chagas' disease, the dilated segment itself displays pathohistological changes, and the earliest and most prominent being found was massive loss of myenteric neurons. This neuron loss was partial and selective, i.e. some neurons containing neuronal nitric oxide synthase and/or vasoactive intestinal peptide (VIP) were spared from neuron death. This disproportionate survival of inhibitory neurons, however, did not completely correlate with the calibre change along the surgically removed, megacolonic segments. A better correlation was observed as to potentially contractile muscle tissue elements and the interstitial cells of Cajal. Therefore, the decreased densities of α-smooth muscle actin- and c-kit-immunoreactive profiles were estimated along resected megacolonic segments. Their lowest values were observed in the megacolonic zones itself, whereas less pronounced decreases were found in the non-dilated, transitional zones (oral and anal to dilation). In contrast to the myenteric plexus, the submucosal plexus displayed only a moderate neuron loss. Neurons co-immunoreactive for VIP and calretinin survived disproportionately. As a consequence, these neurons may have contributed to maintain the epithelial barrier and allowed the chagasic patients to survive for decades, despite their severe disturbance of colonic motility. Due to its neuroprotective and neuroeffectory functions, VIP may play a key role in the development and duration of chagasic megacolon.

What neurons hide behind calretinin immunoreactivity in the human gut?

Calretinin (CALR) is often used as an immunohistochemical marker for the histopathological diagnosis of human intestinal neuropathies. However, little is known about its distribution pattern with respect to specific human enteric neuron types. Prior studies revealed CALR in both myenteric and submucosal neurons, most of which colabel with choline acetyl transferase (ChAT). Here, we specified the chemical code of CALR-positive neurons in small and large intestinal wholemounts in a series of 28 patients. Besides other markers, we evaluated the labeling pattern of CALR in combination with vasoactive intestinal peptide (VIP). In colonic submucosa, CALR and VIP were almost completely colocalized in about three-quarters of all submucosal neurons. In the small intestinal submucosa, both the colocalization rate of CALR and VIP as well as the proportion of these neurons were lower (about one-third). In the myenteric plexus of both small intestine and colon, CALR amounted to 11 and 10 %, respectively, whereas VIP to 5 and 4 % of the whole neuron population, respectively. Colocalization of both markers was found in only 2 and 3 % of myenteric neurons, respectively. In section specimens, nerve fibers coreactive for CALR and VIP were found in the mucosa but not in the muscle coat. Summarizing the present and earlier results, CALR was found in at least one submucosal and two myenteric neuron populations. Submucosal CALR+/VIP+/ChAT± neurons innervate mucosal structures. Furthermore, CALR immunoreactivity in the myenteric plexus was observed in morphological type II (supposed primary afferent) and spiny type I (supposed inter- or motor-) neurons.

Development of a method for the measurement of primary cilia length in 3D

Background

Primary cilia length is an important measure of cell and tissue function. While accurate length measurements can be calculated from cells in 2D culture, measurements in tissue or 3D culture are inherently difficult due to optical distortions. This study uses a novel combination of image processing techniques to rectify optical distortions and accurately measure cilia length from 3D images.

Methods

Point spread functions and experimental resolutions were calculated from subresolution microspheres embedded in 3D agarose gels for both wide-field fluorescence and confocal laser scanning microscopes. The degree of axial smearing and spherical aberration was calculated from xy:xz diameter ratios of 3D image data sets of 4 μm microspheres that had undergone deconvolution and/or Gaussian blurring. Custom-made 18 and 50 μm fluorescent microfibers were also used as calibration objects to test the suitability of processed image sets for 3D skeletonization. Microfiber length in 2D was first measured to establish an original population mean. Fibers were then embedded in 3D agarose gels to act as ciliary models. 3D image sets of microfibers underwent deconvolution and Gaussian blurring. Length measurements within 1 standard deviation of the original 2D population mean were deemed accurate. Finally, the combined method of deconvolution, Gaussian blurring and skeletonization was compared to previously published methods using images of immunofluorescently labeled renal and chondrocyte primary cilia.

Results

Deconvolution significantly improved contrast and resolution but did not restore the xy:xz diameter ratio (0.80). Only the additional step of Gaussian blurring equalized xy and xz resolutions and yielded a diameter ratio of 1.02. Following image processing, skeletonization successfully estimated microfiber boundaries and allowed reliable and repeatable measurement of fiber lengths in 3D. We also found that the previously published method of calculating length from 2D maximum projection images significantly underestimated ciliary length.

Conclusions

This study used commercial and public domain image processing software to rectify a long-standing problem of 3D microscopy. We have shown that a combination of deconvolution and Gaussian blurring rectifies optical distortions inherent in 3D images and allows accurate skeletonization and length measurement of microfibers and primary cilia that are bent or curved in 3D space.

Three-dimensional image quantification as a new morphometry method for tissue engineering

Morphological analysis is an essential step in verifying the success of a tissue engineering strategy where the presence of a desired cellular phenotype must be determined. While morphometry has transitioned from observational grading to computational quantification, established quantitative methods eliminate information by relying on two-dimensional (2D) analysis to describe three-dimensional (3D) niches. In this study, we demonstrate the validity and utility of 3D morphological quantification using two common angiogenesis assays in our fibrin-based in vitro model: (1) the microcarrier bead assay with human mesenchymal stem cells and (2) the rat aortic ring outgrowth assay. The quantification method is based on collecting and segmenting fluorescent confocal z-stacks into 3D models with 3D Slicer, an open-source magnetic resonance imaging/computed tomography analysis program. Data from 3D models are then processed into biologically relevant metrics in MATLAB for statistical analysis. Metrics include descriptive parameters such as vascular network length, volume, number of network segments, and degree of network branching. Our results indicate that 2D measures are significantly different than their 3D counterparts unless the vascular network exhibits anisotropic growth along the plane of imaging. Additionally, the statistical outcomes of 3D morphological quantification agreed with our initial qualitative observations among different test groups. This novel quantification approach generates more spatially accurate and objective measures, representing an important step toward improving the reliability of morphological comparisons.

Quantitative estimation and chemical coding of spiny type I neurons in human intestines

Previous studies have shown that most human myenteric neurons co-staining for vasoactive intestinal peptide (VIP), neuronal nitric oxide synthase (nNOS) and neurofilaments (NF) display the morphology of spiny type I neurons displaying a descending projection pattern. Here, we estimated the proportions of spiny neurons in human intestines, the amount of congruence of VIP/nNOS-immunoreactive with spiny neurons and whether galanin (GAL) is co-localized with VIP. Three sets of colchicine-pretreated and fixed whole mounts of 21 patients or body donors (median age 65 years; 10 female, 11 male) were stained for VIP, nNOS and NF, for VIP, nNOS and the human neuronal protein Hu C/D (HU) as well as for VIP, nNOS and GAL. The majority of VIP/nNOS-co-reactive neurons were spiny neurons (79/80% in small/large intestine, respectively) and the majority of spiny neurons co-stained for VIP and nNOS (82/69%). Neurons co-immunoreactive for VIP/nNOS/HU amounted to 7 and 4%, respectively. GAL/VIP-co-immunoreactivity was demonstrated in 69 and 27% of spiny neurons, respectively. We conclude that the number of neurons displaying co-reactivity for VIP and nNOS is a quantitative indicator of spiny neurons in both small and large intestine and that the proportion of spiny neurons is about 7% in small and 4% in large intestines. Since nerve fibres co-staining for NF/VIP/nNOS were found mainly in the circular muscle layer but not the surrounding perikarya of spiny neurons, we suggest that they may represent inhibitory motor neurons rather than descending interneurons.

Visualization of image data from cells to organisms

Advances in imaging techniques and high-throughput technologies are providing scientists with unprecedented possibilities to visualize internal structures of cells, organs and organisms and to collect systematic image data characterizing genes and proteins on a large scale. To make the best use of these increasingly complex and large image data resources, the scientific community must be provided with methods to query, analyze and crosslink these resources to give an intuitive visual representation of the data. This review gives an overview of existing methods and tools for this purpose and highlights some of their limitations and challenges.

Extending the knowledge in histochemistry and cell biology

Central to modern Histochemistry and Cell Biology stands the need for visualization of cellular and molecular processes. In the past several years, a variety of techniques has been achieved bridging traditional light microscopy, fluorescence microscopy and electron microscopy with powerful software-based post-processing and computer modeling. Researchers now have various tools available to investigate problems of interest from bird's- up to worm's-eye of view, focusing on tissues, cells, proteins or finally single molecules. Applications of new approaches in combination with well-established traditional techniques of mRNA, DNA or protein analysis have led to enlightening and prudent studies which have paved the way toward a better understanding of not only physiological but also pathological processes in the field of cell biology. This review is intended to summarize articles standing for the progress made in "histo-biochemical" techniques and their manifold applications.