Morphology

One of the pressing challenges in modern neuromorphology is the comprehensive study of the morphofunctional characteristics of various parts of the human cerebral cortex. Of particular interest are the associative areas of the neocortex. The need to study these areas is dictated by their significant role in mediating the most complex manifestations of brain activity associated with the control of higher mental functions and human behavior.

Currently, a significant amount of information has been accumulated on the cyto- and fibroarchitectonics of associative cortical areas, and numerous data have been obtained on their neuronal organization and connections with various brain structures. However, determining the localization of functions to specific associative cortical areas of the human brain faces difficulties stemming from differences in the cytoarchitectonic maps used by Russian and foreign researchers.

The aim of this review is to analyze and systematize current data on the morphofunctional organization of the temporo-parieto-occipital subarea of the neocortex, represented by cytoarchitectonic area 37 in the posterior associative cortex, which plays a crucial role in human cognitive brain activity. The article provides a detailed description of the structural features of area 37 according to existing atlases of neocortical cyto- and fibroarchitectonics, as well as atlases of human brain connectomics. It is demonstrated that the use of modern neuromorphological techniques and in vivo brain imaging methods allows a more accurate and complete identification of the structural and functional organization of area 37, as well as the development of a deeper understanding of its role in mediating complex cognitive functions and the systemic processes of multisensory analytical-synthetic activity of the human brain.

Endothelial cells, which form the lining of blood vessels, lymphatic vessels, and heart chambers, are located in the body's internal environment but do not separate it from the external environment. They have an epitheliomorphic organization, and, therefore, are often classified as part of the epithelial tissue system.

This work aimed to update current data on the molecular, genetic, and morphofunctional organization, reactivity, and regeneration of the endothelium, which influence understanding of its systematic affiliation.

The accumulated evidence shows that, based on the combined data on the molecular signature of differentiation that occur during histogenesis, including the expression of cytoskeletal proteins (vimentin), proteins of intercellular adhesion (CD31, CD34 and others), components of intercellular signaling, and products of specialized synthesis (von Willebrand factor), as well as on the characteristics of reactivity and regeneration, endothelial cells correspond to representatives of tissues of the internal environment. The review presents data on the functioning of transcription factors that differ between epithelial and endothelial cells and on inducers of their activity. Information on postnatal physiological and reparative regeneration, the presence of dispersed cambial cells, including those extending beyond the cell layer (bone marrow, the subendothelial layer of loose connective tissue), further supports this conclusion.

Thus, in current interpretations of the physiological and reparative histogenesis of the endothelium, as well as in the educational process, the histological phenomena associated with it should be interpreted taking into account the general patterns characteristic of tissues of the internal environment.

BACKGROUND: The human forefoot, despite its fundamental role in bipedalism, is the least studied part of the foot in most biomechanical and clinical models, where it is often considered a rigid structure. Evolutionary adaptations associated with upright walking have led to a complex morphological structure of the forefoot. Existing concepts of morphological modularity and integration are often limited by the complexity of analyzing multiple relationships. This study suggests solving this problem by applying anatomical network analysis (AnNA) to study the structural organization of the forefoot. AnNA enables formalization of the connections between the components of the foot, revealing patterns of its integration and modularity.

AIM: To study the structural organization of the metatarsal bones and toe phalanges of the human foot using AnNA.

METHODS: As part of this study, the igraph library in the R programming environment was used to analyze the AnNA network. Modeling and visualization of the network structure were carried out using the Fruchterman–Reingold algorithm, which ensures the optimal placement of nodes. Structural characteristics, including modularity and integration of the AnNA network, were analyzed using the Spinglass algorithm. Osteometric parameters — the length of the metatarsal bones and phalanges of toes I–V of the right foot from 100 middle-aged men — were used as input data for the AnNA analysis.

RESULTS: The structural organization of the metatarsal bones and toe phalanges of the human foot consists of several modules: a proximal module (includes metatarsals I–V) and a distal module (includes the phalanges of toes I–V) relative to the longitudinal axis of the foot, and a medial module (includes metatarsals I–III and the phalanges of toes I–III) and a lateral module (includes metatarsals IV–V and the phalanges of toes IV–V) relative to the transverse axis of the foot. Network analysis showed that the distal and medial modules are more complex and less anisomeric than the proximal and lateral modules. The distal module is more complex than the proximal one, while the medial and lateral modules show greater similarity in organizational complexity. Overall, the medial and lateral modules are more similar to each other than are the distal and proximal modules.

CONCLUSION: Morphological modularity and integration are organizing principles of the bone architecture of the foot. The structural organization of the metatarsal bones and toe phalanges of the human foot is a system of four modules — a proximal (metatarsal bones) and a distal (toe phalanges) module relative to the longitudinal axis of the foot, and a medial (metatarsals I–III and phalanges of toes I–III) and a lateral (metatarsals IV–V and phalanges of toes IV–V) module relative to the transverse axis of the foot.

BACKGROUND: Newborns experience activation of the hypothalamic-pituitary-testicular axis, known as minipuberty. In preterm boys, sex hormone imbalance has been observed during the neonatal period. However, whether preterm birth affects testicular development has not been adequately studied.

AIM: To morphologically analyze the spermatogenic and steroidogenic compartments of the testes in immature rats born 24 hours preterm.

METHODS: We studied the testes of full-term and preterm Wistar rats (n = 10 per group) on postnatal days 14 and 28, with 5 animals at each time point. Full-term offspring (gestation length 22 days) were obtained via natural delivery. Preterm offspring (gestation length 21 days) were obtained by inducing preterm labor with mifepristone. Histological, immunohistochemical (detection of activated caspase-3), and morphometric analyses of the testes of full-term and preterm rats were performed.

RESULTS: The testicular microstructure of preterm and full-term rats on postnatal days 14 and 28 was similar. However, the diameter of the seminiferous tubules in preterm rats on day 14 was smaller than in full-term rats (p = 0.000); these differences resolved by day 28. At day 28, the number of testicular interstitial endocrinocytes showing morphological signs of functional activity was higher in preterm rats than in full-term animals (p = 0.000). Preterm birth led to an increase in the number of caspase-3-positive spermatogenic cells on day 28 (p = 0.000), as well as in caspase-3-positive interstitial endocrinocytes on days 14 (p = 0.000) and 28 (p = 0.000).

CONCLUSION: Preterm birth affects testicular structure in immature rats. The rate of spermatogenesis in preterm animals was unchanged; however, their testes showed a higher number of spermatogenic and steroidogenic cells undergoing apoptosis compared with full-term animals.

BACKGROUND: Graves ophthalmopathy (GO) is characterized by pathological expansion of the retrobulbar adipose tissue and fibrosis, which are based on the dysregulation of stromal cell differentiation. A key aspect of the pathogenesis is the competition between adipogenic and myofibroblastic differentiation. It was previously suggested that these pathways are associated with distinct stromal cell subpopulations expressing (CD90⁺) or not expressing (CD90^–) the membrane protein CD90 (Thy-1). It was hypothesized that the secretome of CD90⁺ cells could inhibit adipogenesis in CD90^– cells, but the specific mechanisms of this interaction, including the potential role of extracellular vesicles (EVs), remained unclear.

AIM: To clarify the mechanisms of paracrine interaction between CD90⁺ and CD90^– stromal cell subpopulations isolated from the retrobulbar adipose tissue of patients with different forms of GO.

METHODS: Stromal cells were isolated from the orbital adipose tissue of patients with GO (lipogenic, myogenic, and mixed forms) and a control group (n = 12 cell lines). Cells were separated into CD90⁺ and CD90^– subpopulations using fluorescence-activated cell sorting. Directed differentiation into myofibroblasts (using TGF-β) and adipocytes (using a commercial adipogenic cocktail) was performed. Differentiation was assessed using immunocytochemistry (markers: αSMA, vimentin, collagens, and Nile Red for lipids) and western blotting (αSMA and FAPα). To study paracrine effects, conditioned medium (CM) from CD90⁺ cells was used, along with fractions enriched for extracellular vesicles (EVs) and soluble factors (SFs).

RESULTS: Orbital stromal cells were successfully separated into CD90⁺ and CD90^– subpopulations; the number of CD90^– cells was significantly higher in patients with the lipogenic form of GO. Both subpopulations were capable of differentiating into both myofibroblasts (under the influence of TGF-β) and adipocytes. However, CD90^– cells demonstrated significantly higher adipogenic potential, accumulating twice as many lipid droplets. Contrary to the initial hypothesis, the secretome of CD90⁺ cells (whole CM, EVs, or SFs) did not inhibit the adipogenic differentiation of CD90^– cells. Conversely, the secretome of CD90⁺ cells, including its vesicular and extravesicular fractions, significantly stimulated adipogenic differentiation within the CD90⁺ subpopulation itself.

CONCLUSION: This study demonstrates that the CD90^– subpopulation of orbital stromal cells has a higher adipogenic potential, which may be associated with the lipogenic form of GO. Paracrine interaction between the subpopulations is complex: the secretome of CD90⁺ cells does not suppress adipogenesis in CD90^– cells but instead stimulates differentiation into adipocytes within CD90⁺ subpopulation. These findings are important for understanding the mechanisms that regulate the balance between fibrosis and adipogenesis in GO and highlight the need for further study of the secretory function of stromal cells to develop new therapeutic strategies.

BACKGROUND: The morphofunctional state of the pinealocytes is closely related to the lighting regimen. Light deprivation is known to lead to increased metabolic activity of these cells and to ultrastructural changes. In contrast, darkness deprivation is associated with decreased pinealocyte activity and reduced numbers of mitochondria and lipid inclusions. Studying the effect of various lighting regimens on the ultrastructure of rat pinealocytes provides deeper insight into the mechanisms underlying pineal gland adaptation to environmental changes and the regulation of circadian rhythms and may be relevant for developing approaches to correcting biorhythm disorders.

AIM: To study the ultrastructure of the pineal gland in Wistar rats under constant light and under a light regimen that models a "one day on, two days off" shift work schedule.

METHODS: The study was conducted on 120 male Wistar rats aged 5 months. The animals were divided into three equal groups (n = 40 per group) based on the light regimen: control group was kept under a fixed light/dark (LD) regimen (10 h light / 14 h dark); experimental group I under constant light (LL); and experimental group II under a light regimen simulating a shift work schedule (1 day of LL followed by 2 days of LD). The experiment lasted 21 days; euthanasia for pineal gland harvesting was performed on day 22 at four time points (9:00 AM, 3:00 PM, 9:00 PM, 3:00 AM). Structural and ultrastructural evaluation of pinealocytes was performed on pineal gland sections using light and transmission electron microscopy. Micromorphometric analysis included measuring the size of pinealocytes and their ultrastructural components. Statistical analysis was performed using GraphPad Prism v8.41 (GraphPad Software, USA).

RESULTS: Constant light leads to vacuolization of pinealocytes, destructive changes in lipid inclusions, the Golgi complex, and the endoplasmic reticulum, the formation of autophagosomes of various sizes, mitochondrial polymorphism, and changes in nuclear structure, including the nuclear envelope. The presence of necrotic cells, perivascular edema, and leukocyte infiltration was also observed. The most pronounced effect of the shift regimen on pinealocytes is changes in mitochondrial ultrastructure, accompanied by relative structural and functional preservation of the endoplasmic reticulum and Golgi complex.

CONCLUSION: Thus, both constant light and the "one day on, two days off" shift regimen are associated with pronounced ultrastructural rearrangements in rat pinealocytes. Constant light causes deep disintegration of the pinealocyte ultrastructure, characterized by oxidative stress, suppression of transcriptional and metabolic activity, mitochondrial dysfunction, and cell death. The alternating lighting regimen causes profound disturbances in the nuclear and mitochondrial apparatus of pinealocytes, likely due to desynchronization of circadian rhythms and dysregulated apoptosis.