The effect of the thymus cells of the C57BL/6 mice on the colony forming ability of the stem hemopoietic cells of the embryonic liver and bone marrow of young (3 months) and old (2 years) mice was studied their joint transplantation into the mice (CBAXXC57BL/6) F1. The stimulating effect of the thymus cells on the colony forming ability of the stem hemopoietic cells of different age depends both on the dose of the stem hemopoietic cells of embryonic liver and the dose of T-lymphocytes. A suggestion is put forward that the stimulating effect of the thymus cells on the colony formation is due to their interaction with the stem cells in the G2 phase of the mitotic cycle.

The model of heterotopic transplantation of the mixture of bone marrow and thymus fragments was used to study the interaction of hemopoietic and lymphoid tissues under their direct contact. The bone marrow and thymus fragments of adult mice F1 (CBAXXC57BL) were transplanted separately or in the mixture under the kidney capsule of mice of the same strain. During the whole period of observation (from 10 days up to 14 months), the development of bone marrow and thymus fragments in the joint transplants proceeded independently, no "mixed" stroma appeared, and the stroma of each organ ensured the differentiation characteristic of its organ. The development of joint transplants somewhat differs from that of isolated transplants: on the 10th day a greater amount of hemopoietic tissues was noted in the former; the bone marrow component increases continuously up to 6 months (vs. 1--2 months in the isolated transplants); the bone and hemopoietic tissues predominate in the joint transplants by 14 months, the amount of thymic tissue markedly decreases but it does not disappear completely.

Poly-A:U, dextran sulfate and yeast RNA were shown to increase the number of endogenous (CFU) in sublethally (525 r.) irradiated mouse spleens seemingly as a result of their mutagenic effect on proliferating CFU. The preparations had no effect on the number of exogenous colonies when injected together with bone marrow syngeneic cells transfer from intact donors. Dextran sulfate led to a 2.7 time increase in the number of endogenous colonies in unevenly irradiated mouse spleens mostly due to the CFU migration from the protected sites of the bone marrow. Poly-A:U and yeast RNA complex was ineffective in such an experiment. It is quite possible that the ability of dextran sulfate to increase the migrational potencies of the stem hematogenic cells served as one of the essential factors in the mechanism of its adjuvant activity.

A rise of the functional activity of the immune system was noted during reparative processes in the liver Resection of the liver was accompanied by sharp changes in the thymus and spleen structure. The thymus-dependent parts of the spleen were particularly reactive. Resection of the liver in rats was accompanied by an elevation in the bone marrow of the stem cell count (determined by the splenic colony method). The number of the colony-forming cells was significantly greater in the spleen of the recipients of lymphoid cells taken from the operated animals than in the spleen of the recipients of lymphoid cells from intact rats. In screening the limb the capacity to form endogenous colonies proved to be greater in partially hepatectomized rats as compared to the unoperated animals. In rabbits resection of the liver was accompanied by a significant increase of the immunological reactivity on the 1st-3rd postoperative days. Leukergia and leukocytolysis reaction displayed a marked intensification at this period.

A mathematical model of cell population with cooperatively controlled mitotic activity is analysed. The mitotic activity of stem cells is activated by the cells themselves and is inhibited by differentiated cells. Analysis of the model shows that steady-state oscillations in the mitotic activity are possible in such populations. The appearance of self oscillations is due to a delay in the negative feedback loop. The oscillation period, determined to a linear approximation, is greater than a quadruplicate delay.

The authors studied the influence of synthetic polyelectrolytes of polyacrylic acid and poly-2-methyl-5-vinylpyridine and of complete Freund's adjuvant on the migration of stem cells and B-lymphocytes from mouse bone marrow. The stem cell count was evaluated by the number of splenic colonies; as to B-cell migration--it was assessed by the accumulation of the antibody-forming cells forming from B-lymphocytes migrating in the spleen in the transfer of fixed number of T-lymphocytes. As revealed the synthetic substances under study intensified the migration of stem cells and of B-lymphocytes to a much greater extent than Freund's adjuvant. The mechanisms of the influence of the adjuvants used on cell migration processes are discussed.

During first 3 days after mice irradiation and syngeneic bone marrow transplantation in them the number of CFUs (about 0,5% of the injected cells) was stable, although the proliferation induction began 24 hours after transplantation. As it was shown by the method of "thymidine self-distruction". Twenty four hours later all the CFUs entered the mitotic cycle. On the contrary, the commited cells (granulopoesis precursors) compartment (CFUc) enters the logarithmic growth phase since the first day. The exponential growth of the CFUs number was observed from the 4th day simultaneously with the increasing of the proliferation rate of CFUc and the beginning of the recovery of the bone marrow cells total number. In late radiation chimeras (1 month after radiation and reconstitution) the total number of CFUs was 50--70% of the initial. The other hemopoetic parameters were in the normal limits.

Experiments were conducted on CBA mice and albino rats. A study was made of the effect of erythrocyte destruction products (EDP) on the content of hemopoietic colony-forming units (CFU), differentiation of stem cells and the erythropoietin production. It was shown that 3 or 4 EDP injections to normal mice or to lethally irradiated (1000 rad) mice after the transplantation of bone marrow cells caused no changes in the CFU level of stem cells differentiation. In case of a daily (for 3 days) administration of EDP to mice before the irradiation (1000 rad) and bone marrow transplantation there was observed an increase of the colonies count in the recipients' spleen on account of the erythroid colonies. EDP injection caused no changes in the erythropoietic activity of the blood serum. A possible role of erythrocyte destruction products in the mechanism of erythropoiesis autoregulation is discussed.

To ascertain the mechanisms of the locus coeruleus (LC) function the response of the locus coeruleus neurons to the experimental sharp asphyxia was investigated by the light and electron microscope techniques. Apart from the specific nervous effect (directly through the LC axons and through the stem reticular formation), LC produced humoral influence on the brain structures. There are two possible mechanisms by which catecholamines synthesized in the LC cells could reach the blood; 1) through the cell membrane and then through the basal membrane of the capillary bed and the cytoplasm of the endothelial cell; 2) by virtue of the glia cells.

In experiments carried out on albino mice daily heparin injections (250 units/kg) for two weeks resulted in 30% increase of leukocyte count in the venous blood. The femur bone marrow kariocyte count remained unchanged, while the leukoerythroblastic ratio rose from 4.1 to 7.6. Autoradiography demonstrated that the duration of the mitotic cycle and its phases in myeloid cells underwent no change, constituting: T--13 hrs, ts--8 hrs, tG2--1 hour, t(G1+M)--4 hrs. In heparinized animals the curve of labeled mitoses was nearly ideal. It is suggested that there occurred a change in the stem cells differentiation towards the myeloid type in the bone marrow under the effect of heparin.