[An electron microscopic study of neocortex of Syrian hamsters (Mesocricetus auratus) infected with SARS-CoV-2 (Coronaviridae: Coronavirinae: Betacoronavirus: Sarbecovirus)].

INTRODUCTION: Convalescent COVID-19 patients have various signs of central nervous system damage, including those directly associated with SARS-CoV-2. Hence, studies of SARS-COV-2 related morphological changes in neocortex are particularly relevant for understanding the mechanisms of their formation and development of approaches to preclinical evaluation of the effectiveness of antiviral drugs. The purpose of the research is a longitudinal study of the ultrastructural alterations in Syrian hamsters neocortex after experimental SARS-CoV-2 infection. MATERIALS AND METHODS: Male Syrian hamsters weighing 80100 g, aged 4 to 6 weeks, were infected with 26 l SARS-CoV-2 intranasally with 4104 TCD50/ml of viral particles. The animals were euthanized on days 3, 7 or 28 post-infection, the brain was extracted with the cortex excision. The material analysis was performed using transmission electron microscopy. RESULTS AND DISCUSSION: On day 3 post-infection, the number of moderately hyperchromic neurons in neocortex increased, while by the day 7 the number of apoptotic cells significantly increased. Simultaneously, an increased signs of neuronophagy and representation of atypical glia were observed. Increased number of altered oligodendrocytes was observed on day 28 post-infection. Viral invasion was accompanied by changes in neocortical cells since day 3 post-infection, such as transformation of their nucleus, the rough endoplasmic reticulum and the Golgi vesicles as well as microvascular spasm with perivascular edema. CONCLUSION: As a result of electron microscopic study, the ultrastructural alterations in neocortex were described in an experimental model of SARS-CoV-2 infection. The findings can be used to identify the mechanisms of infection pathogenesis and to search for the new directions in development of medicines.

[Pathological changes in human brain biopsies from patients with idiopathic normal pressure hydrocephalus]. / Patologicheskie izmeneniia v bioptatakh golovnogo mozga patsientov pri idiopaticheskoi normotenzivnoi gidrotsefalii.

AIM: To analyze specific changes in brain tissue of patients with idiopathic normal pressure hydrocephalus at cellular and subcellular levels. MATERIAL AND METHODS: Brain biopsies from 32 patients with idiopathic normal pressure hydrocephalus were investigated by light and electron microscopy. Biopsies were made in 3 points (the cortex, subcortical and periventricular white matter during ventricular catheter positioning). RESULTS: A number of pathological features of idiopathic normal pressure hydrocephalus were identified. Most frequent were the exhaustion of brain tissue, enlargement of perivascular spaces, aseptic necrosis, and amyloid and Lewy body's formation. CONCLUSION: The changes in brain tissue of patients with idiopathic normal pressure hydrocephalus transform our views on its mechanisms. It becomes clear that idiopathic normal pressure hydrocephalus is part of common neurodegenerative process that has characteristic features affecting clinical manifestations of the disease.

[Two-nuclear neurons: sincitial fusion or amitotic division].

In the review the history of research two-nuclear neurons is stated and two hypotheses about mechanisms of their formation are analysed: by sincitial fusion or amytotic divisions. The facts of discrepancy of the former orthodox cellular theory categorically denying possibility sincitial of communications in nervous system and of sincitial fusion neurons are mentioned. As an example results of ultrastructural researches of occurrence sincitium in a cortex of the big brain of rats, in autonomic ganglions, in hypocampus and a cerebellum of adult animals are presented. The video data of the sincitial fusion of live neurons and the mechanism of formation multinuclear neurons in tissue culture are analyzed. Existing data about amytotic a way of formation two-nuclear neurons are critically considered. The conclusion becomes, that the mechanism of formation two-nuclear neurons is cellular fusion. Simultaneously the review confirms our representations about existence in nervous system sincitial interneural communications.

Interneuronal membrane contacts and syncytial perforations in CA2 hippocampal area after brain trauma.

Membranes of pyramid neuron bodies located in CA2 hippocampal area were studied by electron microscopy after gunshot craniocerebral injury. In control group, asynaptic contacts and interneuronal syncytial perforations forming from tight junctions were observed. Contacts and perforations increased in size after trauma. Their number was maximum after severe gunshot injury. They reached their maximal size on days 5-7 after the injury.

Neuron changes in a mollusk in response to proteolytic enzymes.

The aims of the present work were to investigate the structure of neurons after treatment with proteases and to identify possible recovery of interneuronal syncytial connections. In the first series of experiments, phase-contrast microscopy studies of live dissociated neurons from ganglia of the mollusk Lymnaea stagnalis treated with 0.4% pronase solution demonstrated retraction of nerve processes and biphasic changes in cell body volume. At stage I, at an average of 82.5 min, neuron body volume decreased by 12.1%, after which it increased by a mean of 14.1%. Signs of neuron viability in Ringer's solution were seen for an average of 828 min; survival time in pronase solution was 1.4 times shorter. In the second series of experiments, studies of neuron ultrastructure showed many cases of persistence of mitochondria, the rough and smooth endoplasmic reticulum (ER), Golgi complex, light and granular vesicles, nuclear structure, and neuroplasm optical density. Cells coming close together after centrifugation formed intracellular clefts of uniform width (about 20 nm). There were very rare cases of points at which membranes came into contact. There were no signs of syncytial connections. Lengthening and fusion of smooth ER cisterns separated fragments of neuron bodies from relatively undamaged cells. Some neurons were damaged, with multiple vacuoles formed form swollen mitochondria and ER cisterns. Fragments of nerve processes formed on dissociation were surrounded by a normal outer cell membrane.

[Cytoplasmic syncytial connection--one of three forms of interneuronal connection].

The paper is a review of the current state of the important theoretical problem of neurophysiology about the principal possibility of the existence in the nervous system, apart from the major synaptic and contact connections, also of the cytoplasmic syncytial interneuronal connection. Also analyzed are electron microscopy data and results of observation on behavior of living neurons in tissue culture, which allow suggesting the existence in some loci of the nervous system and under certain conditions of the third form of syncytial interneuronal interactions. Regular signs of syncytial perforations are their formation on the ground of membrane contacts and the presence of rounded layers of fused membranes in the zone of defect and of residual membrane structures in the lumen of the perforations. Syncytial connections are formed only in the places, in which glia is absent. In other areas of neuronal bodies or processes, such perforations have never been revealed. The appearance of the cytoplasmic connections in some parts of the nervous system and at certain periods of its development undoubtedly produces an essential effect on functional properties of these parts.

Cytoplasmic syncytial connections between neuron bodies in the CNS of adult animals.

Studies of neurons in the dentate gyrus and hippocampal fields CA1 and CA2 and cerebellar granule cells were performed to test the hypothesis that there are syncytial connections between the bodies of neurons in adult higher vertebrates. Electron microscopic investigations showed that these cells were densely packed and had incomplete glial coatings. The outer cell membranes of these cells were found to be in contact, and membrane contacts in the form of tight junctions and gap junctions were seen. These areas showed membrane perforation and the establishment of syncytial connections between neurons, with all the expected ultrastructural characteristics. These connections could form between several contacting neurons, resulting in a unified functional cell cluster. These studies support the hypothesis that cytoplasmic syncytial interneuronal connections, along with synaptic and contact-type electrical connections, form not only in tissue cultures and the autonomic nervous system during early postnatal ontogenesis, but also in the CNS in adult vertebrates.

[Changes in molluscan neurons under the influence of proteolytic enzymes].

The goal of the work was to study the structure of neurons treated with proteases and to elucidate if this could lead to the formation of the interneuronal syncytial connections. In the first series of experiments, phase contrast observation of the living dissociated ganglionic neurons of the mollusc Lymnaea stagnalis treated with 0.4% pronase, demonstrated a retraction of nerve processes and a two-phase change of the cell body volume. At the first stage, the soma volume decreased, on the average, for 82.5 min by 12.1%; subsequently, the volume increased, on average, by 14.1%. Signs of neuronal vital activity in Ringer's solution were observed, on the average, for 828 min, while in pronase solution their duration was 1.4 times shorter. In the second series of experiments, the study of neuronal ultrastructure has demonstrated in many cases the integrity of mitochondria, rough and smooth endoplasmic reticulum (ER), Golgi complex, light and granular vesicles, nuclear structure, and the preservation of the optical density of neuroplasm. The cells making contacts after centrifugation form uniform intercellular clefts of about 20 nm. Point approaches of membranes were very rare. No signs of syncytial connections were detected. Elongation and fusion of smooth ER cisterns separated the fragments of soma from relatively undamaged cells. Some neurons were damaged, they contained numerous vacuoles formed by swollen mitochondria and ER cisterns. The nerve process fragments, detached during the dissociation, were surrounded by the normal plasma membrane.

[Cytoplasmic syncytial connections between the cell bodies of the central nervous system neurons in adult animals].

The neurons of the gyrus dentatus, hippocampal area CA1-2, and the cerebellar granular cells were examined to test the hypothesis of the possibility of the syncytial connections between neuron cell bodies in the adult individuals of higher vertebrates. As a result of electron microscopic studies, the dense disposition of these neurons was shown together with their incomplete glial coverage. These cells were shown to establish the contacts with their cell membranes and to form interneuronal tight and gap membrane junctions. In these contact regions, the membrane perforations were found and the formation of cytoplasmic interneuronal syncytial connections with all their typical ultrastructural signs. Such connections could be established between several contacting neurons forming the common functional cellular cluster. These investigation confirm the hypothesis that the cytoplasmic syncytial interneuronal connections were possible, in addition to chemical synaptic and contact electrical connections, not only in the tissue culture and in the autonomic nervous system during the early postnatal ontogenesis, but also in CNS of the adult vertebrates.