Occurrence of lymphohaemopoietic tissue in the meninges of the stingray Dasyatis akajei (Elasmobranchii, chondricthyes)

The cytoarchitecture of the lymphohaemopoietic masses occurring in the "meninx primitiva" of the stingray Dasyatis akajei (Elasmobranchii, Chondricthyes) has been analyzed by light and scanning and transmission electron microscopy. Lymphohaemopoietic aggregates showing similar morphologies occurred along all the central nervous system, but they were more frequent in the telencephalon, diencephalon, and mesencephalon. In each aggregate, the granulopoietic tissue appeared in a fibroblastic stroma surrounding the large blood vessels, and the lymphoid components were present in a reticular network. Developing and mature eosinophils and heterophils--as well as lymphocytes, monocytes, macrophages, and plasma cells--are the main free cells present in these meningeal aggregates. The remarkable intimate association between macrophages and lymphoid cells to form close cell clusters suggests some immunological capacity for the meningeal lymphohaemopoietic tissue. According to their capacities, presence of lymphoid tissue, and histological organization, the meningeal lymphohemopoietic aggregates of Dasyatis akajei resemble other lymphomyeloid aggregates associated with cranium and choroid plexuses in Holocephali and Ganoidei. The phylogenetical relationships of these aggregates with mammalian bone marrow are discussed.     

Intravital-microscopic observations on the intravascular behavior of blood cell components during dietary-induced hyperlipidemia in the male rabbit

In normal male rabbits loaded dietary cholesterol, intravital-microscopy revealed a marked acceleration of intravascular adhesiveness of white blood cells and aggregability of red blood cells and a swarming of lipid-laden macrophages in connective tissue space concurrently with a systemic hyperlipidemia and anemia. Possible roles of the microcirculatory changes in the atherogenesis were discussed.     

Simulation analysis of excitation conduction in the heart: Propagation of excitation in different tissues

The normal excitation and conduction in the heart are maintained by the coordination between the dynamics of ionic conductance of each cell and the electrical coupling between cells. To examine functional roles of these two factors, we proposed a spatially-discrete model of conduction of excitation in which the individual cells were assumed isopotential. This approximation was reasoned by comparing the apparent space constant with the measured junctional resistance between myocardial cells. We used the four reconstruction models previously reported for five kinds of myocardial cells. Coupling coefficients between adjacent cells were determined quantitatively from the apparent space constants. We first investigated to what extent the pacemaker activity of the sinoatrial node depends on the number and the coupling coefficient of its cells, by using a one-dimensional model system composed of the sinoatrial node cells and the atrial cells. Extensive computer simulation revealed the following two conditions for the pacemaker activity of the sinoatrial node. The number of the sinoatrial node cells and their coupling coefficients must be large enough to provide the atrium with the sufficient electric current flow. The number of the sinoatrial node cells must be large so that the period of the compound system is close to the intrinsic period of the sinoatrial node cell. In this simulation the same sinoatrial node cells produced action potentials of different shapes depending on where they were located in the sinoatrial node. Therefore it seems premature to classify the myocardial cells only from their waveforms obtained by electrical recordings in the compound tissue. Second, we investigated the very slow conduction in the atrioventricular node compared to, for example, the ventricle. This was assumed to be due to the inherent property of the membrane dynamics of the atrioventricular node cell, or to the small value of the coupling coefficient (weak intercellular coupling), or to the electrical load imposed on the atrioventricular node by the Purkinje fibers, because the relatively small atrioventricular node must provide the Purkinje fibers with sufficient electric current flow. Relative contributions of these three factors to the slow conduction were evaluated using the model system composed of only the atrioventricular cells or that composed of the atrioventricular and Purkinje cells. We found that the weak coupling has the strongest effect. In the model system composed of the atrioventricular cells, the propagation failure was not observed even for very small values of the coupling coefficient.(ABSTRACT TRUNCATED AT 400 WORDS)     

Electron spin resonance studies on a flavoprotein in neutrophil plasma membranes. Redox potentials of the flavin and its participation in NADPH oxidase

Plasma membrane fractions of stimulated and resting cells were isolated from pig blood neutrophils. The midpoint redox potential (Em) of the membrane-bound flavin was determined potentiometrically by analysis of the flavin free-radical signal by electron spin resonance (ESR) spectroscopy. In both stimulated and resting cells, a peak position of the titration curve gave an Em value of -280 mV at pH 7.0 (Em7). The flavin free radical showed an ESR spectrum at g = 2.004 with a peak to peak width of 19 G, which indicates that the redox intermediate is a neutral semiquinone. Redox titrations were anaerobically examined at 25 degrees C with NADPH in place of dithionite. Addition of NADPH to plasma membranes of stimulated cells resulted in a rapid change in potential, accompanied by the formation of the ESR signal of flavin free radical. Computer simulation of the titration points gave an ambient midpoint potential of -280 mV (Em7). In contrast, those of resting cells showed a very slow change in potential and no g = 2.00 signal formation. Power saturation behavior of the ESR signal showed a marked difference between those of stimulated and resting cells. ESR characteristics of the flavin are discussed in relation to the membrane-bound NADPH oxidase.     

Stimulated rat T cell-derived inhibitory factor for cellular DNA synthesis (STIF). III. Effect on cell proliferation and immune responses

Stimulated T cell-derived inhibitory factor for cellular DNA synthesis (STIF), a lymphokine produced from concanavalin A (Con A)-stimulated rat suppressor T cells, was examined for its inhibitory effect on various cultured cells and on in vitro immune reactions. STIF could inhibit the DNA synthesis of a variety of normal and neoplastic cells from rats, mice, and humans in a dose-dependent fashion. Kinetics studies revealed that STIF selectively inhibited cellular DNA synthesis after incubation for 12 hr, but after 36 hr, it also inhibited RNA and protein syntheses. The inhibited cellular DNA synthesis by 12-hr incubation with STIF was recovered after culturing the cells in STIF-free medium. The inhibitory effect of STIF on the DNA synthesis was not blocked by addition of a sugar (alpha-methyl-D-mannoside, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, L-fucose, or L-rhamnose) in culture, as determined by using rat bone marrow cells. STIF inhibited proliferative responses of rat lymphocytes to T cell mitogens, Con A and phytohemagglutinin, and a B cell mitogen, lipopolysaccharide, as well as IL 2-dependent growth of cloned T572 cells. It could also inhibit both blastogenesis and cytotoxic T cell generation in allogeneic mixed lymphocyte reaction. The release of IL 2 from Con A-stimulated T cells was also inhibited by the added STIF in culture, as demonstrated from the finding that IL 2 activity was not detected in the supernatants even after an anion-exchange column chromatography. These results indicate that STIF could inhibit cellular DNA synthesis in a species-unrestricted manner and thus inhibits the proliferation of various normal and neoplastic cells, and that it could also inhibit lectin- or IL 2-dependent T cell proliferation as well as IL 2 production from T cells in in vitro immune reactions.     

Long-term effect of postnatal hypoxia on the seizure susceptibility in rats

The effects of postnatal hypoxia at ten days of age on the pentylenetetrazol (PTZ)-induced seizure and amygdaloid kindling were investigated in male adult rats. The rats with postnatal hypoxia were significantly more susceptible to PTZ and had a significantly more easily induced amygdaloid kindling with a rapid propagation of afterdischarges to the contralateral amygdala than the control group. Light microscopic examination in one adult rat brain with postnatal hypoxia revealed no abnormal histopathological changes. The present study suggests that the consequences of postnatal hypoxia in rats remain for a long time as enhancement in seizure susceptibility.     

Studies directed toward testing the "channeling" hypothesis--ribonucleotides----DNA in leukemia L1210 cells

Experiments were carried out to test for the presence of "channeling" in L1210 cells. L1210 cells were incubated in culture in the presence of labeled cytidine and "cold" deoxycytidine and conversely, in the presence of labeled deoxycytidine and "cold" cytidine. Cytidine did not inhibit the incorporation of [14C]deoxycytidine into DNA while deoxycytidine decreased the incorporation of [14C]cytidine into DNA. Further, in L1210 cells there was not a coordinate inhibition of thymidylate synthetase when either DNA polymerase was inhibited (aphidicolin) or ribonucleotide reductase was inhibited (hydroxyurea). These data indicate that leukemia L1210 cells do not selectively channel ribonucleotides to DNA through a tightly coupled enzyme complex.     

Effect of absolute and relative changes of hematocrit on erythropoiesis in mice

The serial changes of peripheral reticulocytes and marrow erythroid progenitor cells (CFU-e) in mice were monitored under the conditions of absolute or relative changes in red cell mass to study the regulatory mechanism of erythropoiesis. A decreased number of marrow CFU-e and peripheral reticulocytes was observed in the mice with relative polycythemia induced by dehydration as well as in the mice with absolute polycythemia induced by hypertransfusion. On the other hand, a transient increase in the number of marrow CFU-e followed by a gradual increase in the number of peripheral reticulocytes was seen after a considerable amount of exsanguination. Similar stimulatory effects on marrow CFU-e were also observed either by rehydrating the dehydrated mice or by overhydrating the untreated mice to relatively decrease the level of hematocrit. The results suggested that in addition to factors relating to the balance between oxygen supply and requirement, which has been well known, erythropoiesis is greatly affected by hematocrit.