The content of nucleic acids (DNA and RNA) and proteins in 1 mg of tissue and RNA/DNA and protein/DNA ratio in different brain structures (the neocortex, the hippocampus, the cerebellum, the brain-stem), as well as in the liver was studied in rats at different stages of postnatal ontogenesis (25 to 55 days) in the norm, under ecological deprivation and in an information-enriched medium, involving elaboration of conditioned reflexes. It was shown that intense physiological function of the brain cells in an information-enriched medium is attended with substantial enhancement of the RNA/DNA ratio, i.e. stimulation of transcribing activity of the cells genome. In conditions of ecological deprivation this value at first slightly increases, and the significantly diminishes in all the studied brain structures. Protein content in the nerve tissue is more stable in ontogenesis and changes but slightly at different afferentation levels. No significant changes were observed in any of the studied parameters in the lever tissue.

Effect of polypeptide thymic and bone marrow factors on functional activity of stem cells was studied with the use of two-layer agar system containing human bone marrow hemopoietic cells. Unlike bone marrow factor, thymic factor appreciably increased the cluster- and colony-forming abilities of cells - precursors of granulomonopoiesis. The results indicate that thymic and bone marrow factors regulate different stages of stem cell differentiation.

The only experimental approach to the increase in the body serotonin level is a pharmacological one that has a number of shortcomings. The authors suggest an experimental model with additional source of endogenous serotonin (ASS-model) which occurs after embryonal gastrointestinal tract transplantation beneath the skin of adult syngeneic mice. The developing transplants showed significant amounts of serotonin and serotonin-producing enterochromaffin cells. The ASS-model provides long-term and selective increase in the blood serotonin content (by 40% on the average) with no changes being detected in the brain. This model may be used for studies on the role of serotonin in peripheral regulation of the physiological systems.

A combined cultivation in vitro of the hippocampal and raphe nuclei explants have been performed. Certain conditions and mechanisms on connections formed between them have been analysed. Vital observations by means of a phase-contrast microscope makes it possible to reveal three types of connections between the explants which differ by the degree of development and differentiation. The base of the earliest diffuse type of connection is presented by a fine network of flat multipressed and intercontacting gliocytes. The intermediate type of connection is characterized by aggregation of glial elements and formation of loose cords with anastomoses. Reduction of the fine network results from reduction of the glyocytic processes. The most differentiated type of connections is presented by raphe-hippocampal tracts. They are always rectilinear and develop along the shortest way between the explants. When the explants from the hippocamp and cerebellum, which have no natural intercerebral connections, are cultivated together, no formation of any magistral or intermediate types of connection is observed. An important factor in differentiation of the magistral tracts is the reactive kinetics of the glial cells. Strict straightness of the tracts and selectivity in formation of connections between various explants demonstrate also an important role of the neuro-neuronal mechanisms of chemotaxis. The direction of the connections formed can be correlated by means of some artificial guides-threads.

The cells of syngeneic bone marrow were added in the primary monolayer cultures of bone marrow, thymus and peritoneal fluid of the mouse. Discrete plaques with several dozens to several thousands of myeloid cells developed on the surface of fibroblast colonies within 2--7 days. It was shown that both the size and rate of formation of myeloid plaques were markedly higher in the culture of thymus fibroblasts than in those of bone marrow and peritoneal fluid fibroblasts. Hence, the stromal fibroblasts of different origin differ from each other by their ability to interact in vitro with hemopoietic precursor cells forming myeloid plaques.

Hemopoietic cells at different stages of differentiation were found in the liver imprints of adult thymus-less mutant mice BALB/c nu/nu, thus suggesting the presence of extramedullary hemopoiesis. During the postnatal development the intensity of leucopoiesis in the liver of mutant animals increased reliably and that of erythropoiesis suffered no marked changes. In the liver of adult BALB/c nu/nu mice, a high content of stem hemopoietic cells was found. The subcutaneous implantation of thymus to 2 weeks old BALB/c nu/nu mice resulted in the reliable decrease of leuco- and erythropoiesis in the liver. The neonatal thymectomy of the control mice BALB/c+/+ did not prevent the switching embryonic hemopoiesis in the liver off. A question of regulating influence of thymus on the process of switching hemopoiesis in the mouse liver off is discussed.

Polypotential hemopoietic stem cell numbers were monitored by means of the splenic colony-forming unit (CFU-S) method in bone marrow and spleen of CBA mice in condition of suppressed erythropoiesis (after syngeneic red blood cell hypertransfusion and chronic hypoxia). Erythropoietic activity determined by radioactive isotope 59Fe uptake in erythroid cells of spleen, bone marrow and erythrocytes of peripheral blood sharply decreased after these treatments. CFU-S contents in bone marrow and spleen increased during a week after syngeneic red blood cell hypertransfusion and after chronic hypoxia. It is assumed that the increase in hemopoietic stem cell contents in hemopoietic organs of mice under inhibited erythropoiesis may be interpreted due to the appearance of vacant differentiation potencies of stem cells, which in the normal state is realized in production of erythroid cells.

Glucose-6-phosphate dehydrogenase (G6PD) isozymes were studied in the lens and some tissues of Arctic fox x fox female hybrids at different developmental stages. During the embryonic and early postnatal (till the 2nd day of life) development the lens is characterized by a high degree of individual variation of the ratio between parental G6PD forms. The number of stem cells for the lens was determined to be equal to six by means of binomial method of description of this variation. Taking into account the similarity of G6PD spectra in the right and left lenses, a suggestion was put forward that both the lenses develop from the common pool of stem cells. After the 4th day of postnatal life a hemizygote-like phenotype of maternal type was observed in the lenses of all hybrid females. It is suggested that the formation of pseudohemizygote phenotype is due to the posttranslation chemical modification of G6PD isozymes.