The NeuN protein is localized in nuclei and perinuclear cytoplasm of most of the neurons in the central nervous system of mammals. Monoclonal antibodies to the NeuN protein have been actively used in the immunohistochemical research of neuronal differentiation to assess the functional state of neurons in norm and pathology for more than 20 years. Recently, NeuN antibodies have begun to be applied in the differential morphological diagnosis of cancer. However, the structure of the protein, which can be revealed by antibodies to NeuN, remained unknown until recently, and the functions of the protein are still not fully clear. In the present mini-review, data on NeuN accumulated so far are summarized and analyzed. Data on the structure and properties of the protein, its isoforms, intracellular localization, and hypothesized functions are reported. The application field of immunocytochemical detection of NeuN in scientific and clinical studies, as well as the difficulties in the interpretation of the obtained experimental data and their possible causes, is described in details.

Neuromelanin (NM) is a dark polymer pigment produced in certain populations of catecholaminergic neurons in the brain. It is present in various areas of the human brain, most often in the substantia nigra (SN) pars compacta and the locus coeruleus, the main centers of dopaminergic and noradrenergic innervation, respectively. Interest in NM has revived in recent years due to the alleged link between NM and the particular vulnerability of neuromelanin-containing neurons to neurodegeneration. The aim of this work was to study the structural, cytochemical, and localization features of cytoplasmic and extracellular neuromelanin in the human SN pars compacta during normal aging. Sections of human SN from young/middle-aged adults (25 to 51 years old, n=7) and older adults (60 to 78 years old, n=5), all of which had no neurological disorders, were stained histochemically for metals (Perls’ reaction, Mayer's hematoxylin) and immunohistochemically for tyrosine hydroxylase (TH) and Iba-1. It was shown that dopaminergic neurons in SN pars compacta differ in the amount of neuromelanin and the intensity of TH-immunoreactivity. The number of neuromelanin-containing neurons with decreased TH-immunoreactivity positively correlates with age. Extracellular NM is present in SN pars compacta in both young/middle-aged and older adults. The number of extracellular NM accumulations increases with aging. Cytoplasmic and extracellular NM are predominantly not stained using histochemical methods for detecting metals in people of all ages. We did not detect the appearance of amoeboid microglia in human SN pars compacta with aging, but we found an age-related increase in microglial phagocytic activity. The absence of pronounced microgliosis, as well as a pronounced loss of neuromelanin-containing neurons, indicate the absence of neuroinflammation in human SN pars compacta during normal aging.

In neurobiological studies, crucial is the selection of most appropriate and informative experimental methods, one of which is immunohistochemistry. This review briefly summarizes the experience of adaptation of immunohistochemical methods to nervous system studies accumulated over years the Laboratory of Functional Morphology of the Central and Peripheral Nervous System (Institute of Experimental Medicine). The aim of this work was to determine the most effective and reliable immunomarkers for neurobiological studies. The article contains theoretical basis and practical recommendations for use of key cytospecific and functional markers used in studies of structural and functional organization of brain and spinal cord of mammalian animals and human. In particular, the results of immunohistochemical reactions to neural markers (NeuN, neurofilament proteins, alpha-tubulin, alpha-synuclein), neurotransmitter synthesizing enzymes (tyrosine hydroxylase, glutamate decarboxylase, choline acetyltransferase, NO synthase) and glial markers (GFAP, glutamine synthetase, Iba-1, vimentin) are demonstrated. The presented methodology is useful for experimental neurobiology and clinical morphological diagnostics.

Amyloidosis is a group of diseases that occurs when amyloid proteins are deposited in tissues and organs. The traditional way of identifying amyloid in tissue sections is staining with Congo red. However, this method has a number of limitations including background staining (background fluorescence), low fluorescence intensity and false-positive staining. Therefore, a complex of fluorescence-based methods should be applied to characterize tissue localization of amyloid deposits. The aim of this study was to identify amyloid deposits in the kidneys of dystrophin-deficient mdx mice using different fluorescent dyes. We examined 8 cases of renal amyloidosis in aged mdx mice. In all cases, we used traditional methods for amyloid detection (Congo red and Thioflavin T), as well as a new fluorescent dye, disodium salt of 2,7- (1-amino-4-sulfo-2-naphthylazo) fluorene (DSNAF). In our study, we confirmed the amyloid structure of protein deposits in kidneys of aging mdx mice by several fluorescence-based staining methods. We found that fixation method has profound effects on downstream staining procedures, and demonstrated that the application of specific fixative, zinc-ethanol-formaldehyde (ZEF), instead of traditional NBF allow to reduce the background fluorescence. We also illustrated the usefulness of novel fluorescent dye DSNAF for detection of amyloid deposits in mouse tissues. Our results confirmed the strong affinity and high specificity of this dye for amyloid fibrils. The verification of DSNAF for detecting amyloid in human tissues will provide a conclusion on the applicability of the developed staining method in clinical research practice.

We studied the intranuclear localization of protein nucleophosmin (B23) and ubiquitin in the dopaminergic neurons of human substantia nigra (n = 6, age of 25-87 years) using immunohistochemistry and confocal laser microscopy. Intranuclear ubiquitin-immunopositive bodies that morphologically correspond to Marinesco bodies were found to be present in substantia nigra dopaminergic (tyrosine hydroxylase-immunopositive) neurons but absent in non-dopaminergic neurons. The number of bodies varied from 0 to 6 per cell nucleus. Nucleophosmin (B23) was found in the neuronal nucleolus, with the nucleolus size being constant in the nigral neurons of each individual brain. All the observed neurons had only one large nucleolus with intense nucleophosmin immunoreactivity and a lightly stained region (1-2 m in diameter) that apparently represents the giant fibrillar center (GFC). An intensely immunostained nucleophosmin-containing granule was often observed at the GFC periphery. Double labeling demonstrated that nucleophosmin-immunoreactive nucleolus and ubiquitin-immunoreactive Marinesco bodies can occur both closely to and remotely from each other. Three-dimensional reconstruction indicates that rounded Marinesco bodies are polymorphic and often have a complex shape, with some flattening and concavities, which may be associated with contact not only with the nucleolus, but also, presumably, with other intranuclear structures free of ubiquitin or nucleophosmin. Ubiquitin-immunoreactive structures with a relatively small size (up to 1 m in length) and various clastosome-like shapes (Lafarga et al., 2002) often occur near Marinesco bodies. There were no cases of detection of ubiquitin in the nucleoli of dopaminergic neurons and nucleophosmin/B23 in typical Marinesco bodies. The obtained information may be helpful in unraveling the molecular mechanisms of the selective vulnerability of substantia nigra dopaminergic neurons to damaging factors.

In the study we used brain samples from Wistar rats at different ages: 7 days of postnatal development (n=18), 14 days of postnatal development (n=18), 4–6 months (n=22); the brain samples from 3–6-month-old SHR (spontaneously hypertensive rats) male rats (n=4); human cerebral cortex samples (n=10). Rabbit polyclonal antibodies against calcium-binding protein Iba-1 (Biocare Medical, USA) were used to detect microglia immunohistochemically followed by light and confocal laser microscopy. A previously developed original technique was applied to simultaneously detect microglial cells and amyloid plaques. Iba-1 protein in microglial cells was shown to be present in grey and white matter in all cerebral regions under study. Microglial cells in different regions were noted to be characterized by pronounced structural and functional features when stained for Iba-1. In addition to microglial cells, in the rat brain there were found other Iba-1-immunopositive macrophages, which were tissue cerebral macrophages differing from microgliocytes by specific morphology and localization. Iba-1 protein was demonstrated to be present in microglial cells in all investigated stages of postnatal development that makes Iba-1 an appropriate marker for comparative ontogenetical studies of microglial cells. The localization of Iba-1 in the bodies and processes of microgliocytes enables to more clearly identify the complex ramified cell morphology and make three-dimensional reconstructions. In the brain of spontaneously hypertensive rats (SHR line rats) the Iba-1-immunopositive microglia were shown to have a number of structural and functional features indicating the moderate activation of microglia. 48 h after ischemic injury, an anomalously great number of large Iba-1-immunopositive cells with amoeboid morphology were detected in the gray matter of the striatum in an ipsilateral hemisphere near the injured area in the rat brain. Microglial cells in human cerebral cortex were noted to be localized in the majority of the detected amyloid plaques and characterized by amoeboid morphology indicating their severe activation. The presented findings suggest Iba-1 protein to be a reliable and universal microglial marker. The immunohistochemical detection of the protein enables to identify and analyze qualitatively and quantitatively microglial cells in different brain regions in human and laboratory animals under normal and pathological conditions. The limitations of using Iba-1 as a marker of microglia include the inability to determine the microglial activation vector and the difficulty in distinguishing between microglia and infiltrating macrophages of the brain in pathology. In such cases, it is necessary to improve the technology for detecting microglia that can be based on using a multi-marker analysis.