The study was performed on 30 male rats of Wistar line (weight 330-360 g, age 3.5 months).In an experimental model of damage to the femur bone in the hip joint studied the effect of low frequency electrical stimulation of the damaged area on the rate of regeneration of bone. The animals were divided into two groups. Control (15 rats) and experienced (15 rats). In the experimental animals underwent stimulation of the injury site for 5 min daily for 7 days, 14 days and 21 days. Stimulation was carried out using a device "Osteon-1" generating a mixed signal of two voltage pulse of varying duty cycle, one of which is modulated to a higher frequency. Signals were not synchronized with respect to each other, unipolar with varying frequencies and amplitudes. The obtained results show the effectiveness of the electrical stimulation currents of low frequency in the restoration of bone tissue after damage. Morphological studies showed that electrical stimulation to accelerate the regeneration of damaged bone at all stages of the study (7, 14, 21 day), causes a more pronounced integration of newly formed bone with the old intact bone and promote the formation of more powerful periosteal calluses in comparison with the control.

Mesenchymal stromal cells (MSC) represent a heterogeneous population of cells that differ in morphology, phenotype, ability to grow and differentiate, and other properties. Differences between MSC are related in part to the influence of their microenvironment. However, the heterogeneity of these cells also is due to their parent-progeny relationship. Hierarchical organization of the MSC population that comprises different categories of oligopotent and multipotent cells, is complicated and poorly understood. This review includes data on morphological, phenotypic and functional heterogeneity of MSC and its possible connection with the population structure.

Hematopoietic differentiation and formation of hepatic tissue both take place in mammalian liver during its prenatal development. Hematopoietic and hepatic stem cells self-renew, proliferate and differentiate within specific microenvironment that is organized by stromal elements. Stroma of developing liver consists of different cell populations such as mesenchymal stromal cells, Ito cells, portal fibroblasts and myofibroblasts, vascular endothelial and smooth muscle cells, cells undergoing epithelial-to-mesenchymal transition. In this review, their phenotypical and functional properties, possible derivation and role in the regulation of hematopoiesis and hepatogenesis are discussed.

Mesenchymal stem cells present in the bone marrow and some other organs are primitive pluripotent precursors of osseous, cartilaginous, adipose, and other mesenchymal tissues. The recently revealed capacity of these cells for differentiation into nonmesenchymal derivatives is of considerable theoretical and practical interest. However, many aspects of the biology of these cells remain obscure despite active research. This review considers possible sources and methods for the isolation of mesenchymal stem cells, their potential for proliferation and differentiation in different directions, and outlooks of their therapeutic application. A model of parent-progeny relationships of stromal cells is proposed, and the problems of regulation of proliferation and differentiation of mesenchymal precursors as well as their role in the maintenance of regeneration and tissue functioning are discussed.

Effects of ten day long exposure to gamma-irradiation at low doses (mean dose rate of 1.5-2.0 m Gy/day, total dose of 15 m Gy) on hemopoietic (CFU-S) and stromal (CFU-F) progenitor cells from murine bone marrow were examined. The CFU-F content measured as in vitro fibroblastic colony number showed 1.5-4.5-fold increase. Additionally, the size of ectopic marrow transplants evaluated by counting myelokariocytes and CFU-S numbers also increased. No significant changes of CFU-S proliferation rate were found.

It was shown for the first time that when the liver of 14 day-old mouse fetuses was transplanted under the renal capsule or in the subcutaneous connective tissue of adult recipients, successive de novo formation of hyaline cartilage, bone, and hemopoietic foci took place. We propose that the liver mesenchyme, which preserves wider differentiation potencies in fetuses, is the cellular source of different types of mechanocytes: cartilaginous, bone, and reticular cells.

The capacity of CFU-S-11, which formed colonies in the spleen on day 11 after transplantation to an irradiated recipient for self-maintenance, was studied. The indices for self-renewal of individual CFU-S from the spleen, bone marrow, and peripheral blood were compared in the same sexually mature donor mice by retransplanting the colonies isolated from the spleen parenchyma to secondary recipients. The number of secondary CFU-S-11 per primary CFU-S-11 originating from the liver hardly differed from that originating from the peripheral blood, but is almost twice less than for the bone marrow CFU-S-11. The conclusion was drawn that compartment CFU-S of the liver of adult animals contains the cells migrating from blood flow, which, apparently, are not dormant embryonic cells.

We studied the effect of a single injection of 5-fluorouracil (5-FU) (150 mg/kg) on the numbers of stromal precursor cells (CFU-F) in the bone marrow and spleen and their capacity for formation of hemopoietic foci after ectopic transplantation under the renal capsule. 5-FU decreased the number of CFU-F in the bone marrow and spleen of mice and rats to 30 - 50% of the control values. The size of transplants, as estimated according to the number of hemopoietic clonogenic (CFU-S) and nucleated cells, diminished within the first two months after transplantation. Within four months after transplantation the size of the bone marrow transplants approached the control level, while that of the spleen transplants markedly exceeded the control level. Differences in the growth rate of regenerating transplants of the hemopoietic organs are discussed with special reference to the organ specific features of populations of the stromal cells.

We studied sensitivity of various types of clonogenic hemopoietic cells (CFU-S-7, CFU-S-11, and CFU-ep) on the liver of 14-days embryos and from the bone marrow and spleen of adult mice to the cytotoxic agent 5-fluorouracil (5-FU) in vitro and in vivo. We discovered that different types of CFU-S of the embryos and adult mice has similar sensitivity to 5-FU in vitro. At the same time in vivo the bone marrow CFU-S-7 display a higher sensitivity to 5-FU than CFU-S-11, thus agreeing with the published data (Hodgson and Bradley, 1979). The differences between the 5-FU effects in vitro and in vivo are related to the hemopoietic microenvironment, which modulates the cytotoxic 5-FU effect in vivo.

The effects of space flight factors (SFF) on the peripheral blood in Pleurodeles waltlii were assessed after 12-day flight on board of the biosatellite "Kosmos-2229". These animals were also used to study regeneration of the limb, tail and lens. The corresponding control groups of animals allowed to distinguish between the effects of the operation, non-specific and specific SFFs: (1) basal control-operated animals; (2) synchronous control-operated animals kept on the Earth under the same conditions as the flight group, and (3) intact animals. It has been shown that the relative content of neutrophils (mostly, young forms) increased and the proportion of lymphocytes and eosinophils decreased under the influence of SFFs, while the capacity of blood cells for DNA synthesis was not affected. A conclusion has been drawn that the Spanish newts can be used for adequate studies of the SFF effects on the hemopoietic tissue.

: Content of three classes of clonogenic haemopoietic cells (CFU-S-7, CFU-S-11 and CFU-S-ep) was determined in haemopoietic organs of mouse during embryogenesis (10, 14 and 18 day) and postnatal ontogenesis (2, 3 and 7 day, 1, 2, 3 and 18 month). CFU-S-7 and CFU-S-11 that from big splenic colonies on 7th and 11th days of transplantation are present in liver, spleen and bone marrow at all developmental stages. However their concentration and CFU-S-7 CFU-S-11 ratio change in haemopoietic organs. CFU-S-ep that form small colonies on 11th day are observed before birth in liver and spleen and 1 week after birth there and also in bone marrow but are practically absent from haemopoietic organs of older animals. Thus, CFU-S compartment structure is characterized by definite ratio of its subpopulations. It seems to reflect functional state of haemopoietic system during development.

Histological analysis was carried out on the hemopoietic spleen colonies within 7 and 11 days after transplantation of the embryonic liver cells. Large superficial colonies were always present and were, predominantly, erythroid and mixed. Small superficial colonies consisted of undifferentiated cells and, unlike large colonies, appeared on the 11th day only. In the spleen thickness erythroid colonies predominated. The possibility of formation of small superficial 11 day colonies at the expense of pre-CFU-S is discussed.