Showing papers by "University of Würzburg published in 1974"

Eine Befriedigende Darstellungsmethode für Trimethylphosphin

Abstract: An improved high-yield synthesis of trimethylphosphine from the reaction of triphenylphosphite with methylmagnesium iodide is described. This route has been extended to prepare triethyl-, tripropyl-, and triisobutylphosphine.

The role of air humidity and leaf temperature in controlling stomatal resistance of Prunus armeniaca L. under desert conditions : I. A simulation of the daily course of stomatal resistance.

Abstract: Experiments with Prunus armeniaca were carried out under conditions of constant temperature but varying air humidity. Experiments were also contucted with a constant water vapor difference between the evaporating sites in a leaf and the air, but with varying leaf temperature. These served as a basis for predicting the daily course of total diffusion resistance under the natural climatic conditions of a desert. For the simulation, the rsults of the experiments at constant conditions with only one variable factor are fitted with empirical equations which serve as "calibration curves" to predict the change in diffusion resistance caused by a change in humidity and temperature calculated from the meteorological data of a desert day. The simulation shows that for P. armeniaca humidity and temperature are the dominating factors in controlling the daily course of diffusion resistance. For meteorologically very different days the simulation allows the increase in diffusion resistance in the morning to be predicted with an accuracy of 90%-105% as compared to directly observed measurements. In the afternoon, especially after extreme climatic conditions during the morning, the deviation between predicted and observed values of diffusion resistance may be greater, but not more than -20% to -30%. This possibly indicates the existence of an additional factor of significance which was not included in the simulation. The two peaked curves of net photosynthesis and transpiration characteristic of plants living under arid conditions can be explained in this species by the humidity-and temperature-controlled stomatal response. This stomatal regulation leads to a decreasing total daily transpirational water loss on a dry day as compared to a moist one. The significance of this controlling mechanism for the primary production and the water relations of P. armeniaca is discussed.

The effect of hydrocortisone on the sensitivity of the isolated nictitating membrane to catecholamines: Relationship to extraneuronal uptake and metabolism.

Abstract: On the isolated nictitating membrane of the cat the supersensitivity to catecholamines induced by hydrocortisone was compared with the ability of hydrocortisone to block the extraneuronal uptake and metabolism of catecholamines.

Analysis of the compartments involved in the extraneuronal storage and metabolism of isoprenaline in the perfused heart

Abstract: 1. Rat hearts were perfused with various concentrations of 3H-(±)-isoprenaline, and initial rates were determined for the removal of the amine from the perfusion fluid and for its O-methylation. Both removal and O-methylation obeyed Michaelis-Menten kinetics, Km and Vmax being 21 μM and 38 nmoles · g−1 · min−1 for the former, and 2.9 μM and 1.7 nmoles · g−1 · min−1 for the latter. After block of COMT the kinetic constants for removal (which equals accumulation under these conditions) were about the same as before. The kinetics of O-methylation seem to differ strikingly from those of accumulation of unchanged amine. 2. Corticosterone and 3-O-methylisoprenaline were about equipotent in antagonizing the accumulation and O-methylation of isoprenaline in the rat heart during perfusion with 3H-isoprenaline. 3. U-0521 (dihydroxy-2-methyl propiophenone; 100 μM) was used as a blocker of COMT. In addition it was found to be a weak inhibitor of the extraneuronal uptake of isoprenaline (Ki=230 μM). 4. After block of COMT and subsequent to perfusion of the heart with 0.95 μM 3H-isoprenaline, efflux curves were determined during wash out with amine-free solution. Four compartments were detected (in order of increasing half time of efflux): I represented the fluid in dead space, cardiac cavities and large vessels; II equalled the extracellular space; III and IV represented extraneuronal storage sites. Corticosterone impaired the filling of compartments III and IV when present during filling. Both corticosterone and 3-O-methylisoprenaline (OMI) delayed the efflux from compartment III when present in the wash out solution only. 5. Experiments with guinea-pig hearts showed qualitative similarities between these and rat hearts. However, the storage and the O-methylating capacity of the guinea-pig heart was considerably smaller than that of the rat heart. 6. Rat ventricle slices (exposed to 0.95 μM 3H-(±)-isoprenaline for 30 min) were compared with perfused hearts. While the accumulation of 3H-isoprenaline was about 1/4, the total formation of 3H-OMI was only 1/50 of that determined for the perfused heart. This low rate of formation of 3H-OMI was also observed for slices of aorta, vas deferens and spleen, while slices of salivary glands had a high O-methylating capacity. Apparently, perfusion of the heart provides optimal access to the O-methylating compartment which may be located in vascular smooth muscle.

Synthese und Reaktivität von Silicium-Übergangsmetallkomplexen, V. Die modifizierte Alkalisalz-Eliminierungsmethode — ein genereller Weg zu Komplexen mit Silicium-Übergangsmetall-Struktureinheiten

Abstract: Die Umsetzung der komplexen Metallate Na[Fe(CO)2π-C5H5], Na[M(CO)3π-C5H5] (MMo, W) und Na[Mn(CO)5] mit verschiedenen Halogen- und Organohalogensilanen fuhrt in heterogener Reaktion zu den Silylkomplexen dieser Metalle. Die neuen Verbindungen werden spektroskopisch charakterisiert und ihre chemischen Eigenschaften beschrieben. Die Ergebnisse einer Zerfallsstudie der Trimethylsilyl-VIB-Ubergangsmetallkomplexe werden im Zusammenhang mit fruheren Syntheseversuchen diskutiert. Der Verlauf von Austauschreaktionen der gleichen Verbindungen mit Heterosiloxanen (Ge, Sn) ermoglicht eine qualitative Abschatzung der Reaktivitat der Metall- Metalloideinheit. Synthesis and Reactivity of Silicon Transition Metal Complexes, V. The Modified Alkali Salt Elimination Method — a General Procedure for the Synthesis of Silicon Transition Metal Compounds The heterogeneous reaction of the sodium carbonylmetallates Na[Fe(CO)2π-C5H5], Na[M(CO)3π-C5H5] (MMo, W), and Na[Mn(CO)5] with various halo- and organohalosilanes leads to the formation of the corresponding silyl complexes. The new compounds are characterized by spectroscopy and the chemical properties are described. The results of a decomposition study of the trimethylsilyl-VIB transition metal complexes are discussed in connection with former synthetic experiments. Exchange reactions of these species with heterosiloxanes can be used for a qualitative estimation of relative metal-metalloid bond reactivity.

Extraneuronal removal, accumulation and O-methylation of isoprenaline in the perfused heart

Abstract: 1. Isolated rat and guinea-pig hearts were perfused with 0.95 μM (±)-isoprenaline or 3H(±)-isoprenaline, a catecholamine which is taken up by extraneuronal mechanisms only. From measurements of the arterio-nevous difference (by fluorimetry and by scintillation counting, respectively) the rate of removal of the amine from the perfusion fluid was measured; in addition, the rate of appearance of its metabolite (3-O-methyl-3H-isoprenaline; 3H-OMI) was determined in the venous effluent as well as the accumulation of 3H-isoprenaline and 3H-OMI in the heart. 2. Experiments with sodium thiocyanate and 14C-sorbitol showed that these agents distributed into the extracellular space (about 350 μl/g; t/2 for efflux of about 1.2 min) and into ventricular and atrial cavities (about 1500 μl/g; t/2 for efflux of 0.1 to 0.2 min). 3. The removal of 3H-isoprenaline from the perfusion fluid declined biphasically with time; after an initial rapid decline the rate of removal approached steadystate levels within about 30 min. After block of COMT (by the presence of 100 μM U-0521) the second phase of decline approached zero. In the absence of U-0521 the steady-state rate of removal was 10 times higher in rat than in guinea-pig hearts; in the presence of U-0521 the approach to zero was faster for guinea-pig than for rat hearts. 4. When COMT was intact, 3H-OMI appeared in the venous effluent, first at a rapidly increasing rate, from the 9th minute of perfusion onward at a steady rate which was identical with the steady-state rate of removal of 3H-isoprenaline. No 3H-OMI was detected after block of COMT. 5. The accumulation of 3H-isoprenaline in the heart reached a steady level within about 30 min; block of COMT increased the time required for approach to steady levels and increased the accumulation of 3H-isoprenaline in the rat (but not in the guinea-pig) heart. When COMT was intact, the accumulation of 3H-OMI in the heart reached steady-state levels within 10 min. 6. The time-dependent decline of the rate of removal of 3H-isoprenaline by hearts whose COMT had been inhibited was due to a time-dependent increase of the rate of efflux of the amine from the stores; there did not seem to be any change in the rate of gross influx. 7. Isoprenaline-induced ventricular fibrillation reduced the rate of O-methylation of 3H-isoprenaline significantly. 8. Perfusion of hearts with 0.095 μM (±)-isoprenaline resulted in a significantly greater accumulation of the amine in rat than in guinea-pig and rabbit hearts.

Cycle times of the neural epithelial cells of various types of neuron in the rat. An autoradiographic study.

Abstract: Cell kinetic studies of the proliferation of the neural epithelium during the embryonic development of the rat brain are described Pregnant rats received a single injection of 3H-thymidine (3H-TdR) between the tenth and twenty-first day of pregnancy Autoradiographs of the brains of the 25-day-old offspring were prepared For a number of different cell types (table 1, II) the percentage of labeled neurons as a function of time of prenatal 3H-TdR injection was determined The end of the proliferating period of the neural epithelial cells of certain cell types can be derived from these percentages of labeled cells (table 1, V) Further-more, it can be demonstrated that the percentage of labeled neurons is equal to the labeling index of the neural epithelial cells of these cell types at the time of prenatal 3H-TdR injection Based on the labeling index of the neural epithelial cells and their S phase, cycle times can be calculated This way it is possible for the first time to determine the cycle times of those neural epithelial cells that later on differentiate into a certain type of neuron (table 1, IV) The calculated cycle times show that up to the sixteenth prenatal day the neural epithelial cells behave like a homogeneous cell population which proliferates with an approximately constant cycle time of about half a day The cycle time seems to increase with increasing fetal age From the total number of a certain type of neuron the number of mitotic divisions or cycle times respectively can be derived which is necessary to produce the number of neural epithelial cells providing these neurons With regard to the mean cycle time of the neural epithelial cells it can be concluded that the beginning of proliferation of the neural epithelial cells coincides with the formation of the neural plate on the ninth day of embryonic development or starts even shortly before this time

The temperature-related photosynthetic capacity of plants under desert conditions : I. Seasonal changes of the photosynthetic response to temperature.

Abstract: Temperature dependence of net photosynthesis under conditions of light saturation and maximum air humidity was measured throughout the season in the Central Negev Desert (Israel). Experimental plants were the wild growing Hammada scoparia and Prunus armeniaca cultivated in the runoff farm of Avdat.The optimum temperature for net photosynthesis and the upper temperature compensation point of CO2 exchange showed a characteristic seasonal variation with low values in spring and fall and high values in mid-summer. This shift was exhibited by plants growing under conditions of normal soil-water stress as well as by irrigated plants. There was no general correlation between the changes in temperature dependence of net photosynthesis of the plants, their maximum photosynthetic capacity under the experimental conditions, their daily photosynthesis maximum under natural conditions, and their rate of dark respiration. The seasonal shift of the photosynthetic response to temperature cannot be explained by changes in the temperature sensitivity of the stomata. It may be caused by seasonal changes of biochemical and/or biophysical properties.A number of observations made on other wild plants also showed, in all cases, seasonal shifts of the upper temperature compensation point, with an amplitude of 6.0°C-13.7°C.

CO2-Gaswechsel-Untersuchungen zur SO2-Resistenz von Flechten.

Abstract: Es wurde die SO2-Resistenz von 12 Flechtenarten verschiedener Wuchsformen und Standorte untersucht. Hierzu wurden die Thalli einerseits mit SO2 begast (Konzentrationsstufen am Eingang der Begasungskuvette 0,5; 1,0; 2,0 und 4,0 mg SO2/m3 Luft) oder andererseits mit Na2S2O5-Losungen unterschiedlicher Konzentrationen und pH-Werte behandelt. Als Vitalitatskriterium wurde der CO2-Gaswechsel der Thalli vor der SO2-Begasung, unmittelbar danach und darauffolgend in Abstanden im Verlauf von mehreren Wochen mit dem Ultrarotabsorptionsschreiber verfolgt. Auserdem wurden in einigen Fallen die Chlorophyllgehalte bestimmt. Die Ergebnisse werden in Anlehnung an das Resistenz-Konzept Levitts unter dem Gesichtspunkt diskutiert, das die Gesamt-Resistenz der Flechten gegen SO2 im Luftraum von 2 Komponenten bestimmt wird, der „avoidance” und der „tolerance” (vgl. Abb. 15). Einerseits hangt die Widerstandsfahigkeit bei gegebener Ausenkonzentration davon ab, wieviel SO2 in den Thallus aufgenommen wird, was u. a. durch die Thallusorganisation (Lebensform, Oberflachenbeschaffenheit) und durch den augenblicklichen Quellungsgrad des poikilohydren Organismus bestimmt wird. Auserdem kann die Toxizitat des aufgenommenen SO2 erniedrigt werden, wobei der pH-Wert im Thallus und seine Pufferkapazitat (bedingt u.a. durch Standort und Substrat) eine ausschlaggebende Rolle spielen. Neben diesen „avoidance”-Faktoren wird die Gesamtresistenz der Flechten andererseits von der plasmatischen Widerstandsfahigkeit der empfindlichen Systeme gegen das aufgenommene SO2 bestimmt („tolerance”). Auch diese durch Einwirkung der Na2S2O5-Losungen bestimmte Resistenz ist gewissen Schwankungen, z.B. mit dem Entwicklungszustand der Flechten, unterworfen. Die Unterschiede in der Abstufung der untersuchten Arten nach Gesamt-Resistenz (SO2-Begasung) und plasmatischer Resistenz (Na2S2O5-Losungen) zeigen die Bedeutung der „avoidance”-Komponente fur die Gesamt-Resistenz der Organismen. In okologischer Hinsicht bestatigen die Untersuchungen die hohe Empfindlichkeit von Flechten gegenuber SO2-Belastung, auch in Konzentrationen, wie sie bei tatsachlichen Immissionen auftreten konnen. Andererseits zeigt sich die Kompliziertheit der okologischen Interpretation experimentall ermittelter Resistenzphanomene.

Deoxyribonucleic acid polymerases from yeast. Further purification and characterization of DNA-dependent DNA polymerases A and B.

Abstract: Yeast DNA polymerases A and B were purified 5000 – 10000-fold by chromatography on DEAE-cellulose, phosphocellulose, DNA-agarose and DEAE-Sephadex. In acrylamide gel electrophoresis in the presence of sodium dodecylsulfate, both enzymes give rise to three main bands. The enzymes are equally susceptible to inhibition by the – SH reagents N-ethylmaleimide and p-chloromercuri-benzoate but differ in their sensitivity to cytosine-arabinoside triphosphate, polymerase A being considerably more sensitive to this nucleotide analog. Whereas DNA polymerase A prefers nicked DNA and poly[d(A-T)] as template-primer, polymerase B is most active with poly(dA) · (dT)10. Km values for deoxyribonucleoside triphosphates were determined as 3.7–3.9 μM for enzyme A and 1.8–2.4 μM for enzyme B. During active growth of cells polymerase activity increases about 1.4-fold over the amount found in resting cells, which is mainly if not exclusively due to an increased level of DNA polymerase A. This together with other properties suggests a role of this enzyme in DNA replication.

Action of dextran sulfate as a direct and general b cell mitogen.

Abstract: Dextran sulfate (DS-500) significantly stimulates the in vitro immune response against thymus-dependent antigens in the absence of T cells. The stimulation of antibody production takes place both in the presence and absence of antigens. Dextran sulfate leads to increased cell division as measured by [3H]thymidine incorporation; the amount of TCA precipitable radioactivity is greater in the absence of T cells than in their presence. It is suggested that the stimulatory effect of DS-500 is due to its function as a general and direct B cell mitogen.

Optically Active Lattice Vibrations in Bi2Se3

Abstract: The preparation of Bi2Se3 single crystals with low free carrier densities allowed an investigation of the lattice vibrations to be carried out from the reflectivity of cleavage planes at nearly normal incidence of the radiation (E ⟂ c). The experimental results can be explained with two classical oscillators, whose eigenfrequencies occur at 92 and 69.5 cm−1. The static dielectric constant was determined to be 100 ± 10 for E ⟂ c. Die Praparation von Bi2Se3-Einkristallen mit niedriger Konzentration freier Ladungstrager erlaubte die Untersuchung der Gitterschwingungen aus dem Reflexionsvermogen von Spaltflachen bei nahezu senkrechter Inzidenz der Strahlung (E ⟂ c). Die Mesergebnisse konnen mit zwei klassischen Dispersionsoszillatoren erklart werden, deren Eigenfrequenzen bei 92 und 69,5 cm−1 liegen. Die statische Dielektrizitatskonstante wurde zu 100 ± 10 fur E ⟂ c bestimmt.

The differentiation function of T cell-replacing factor in nu-nu spleen cell cultures.

Abstract: The effect of T cell-replacing factor (TRF) on B cells was studied in spleen cell cultures from athymic nu/nu mice with particular emphasis on its possible role in proliferation and/or differentiation of precursor cells. In contrast to B cell mitogens, such as lipopolysaccharide, TRF does not significantly increase thymidine incorporation nor does it lead to the development of an increased number of plaque-forming cells in the absence of test antigen. It was found that under conditions of maximal induction of plaque-forming cells by TRF, i.e. TRF administration 1–2 days following commencement of tissue culture and antigenic stimulation, there was a proportional increase in levels of IgM production relative to total protein synthesis by the cells. In such cultures, Ig formation represented up to 37 % of total protein synthesis. Although the background level of Ig production varied in different cultures, TRF reproducibly led to a 1.5 to 4-fold increase in proportional Ig synthesis. The results suggest that some proliferation takes place before TRF is added and indeed before it can act. This is supported by the finding that conditions of reduced cell proliferation (lowered temperature) before the addition of TRF prevent subsequent plaque responses. In contrast, the same treatment applied later on and simultaneously with TRF addition still permits a significant increase in the number of PFC. X-irradiation of the culture on day 2, immediately prior to TRF addition, still permits an increase in proportional Ig synthesis. Thus, it appears that a major component of the function of TRF, i.e. the nonantigen-specific soluble T cell factor, is a differentiation signal favoring Ig production. Mitosis is required before the differentiation signal can be received, and some controlled concomitant proliferation is not excluded.

Stabile Kupfer- und Silberverbindungen von Phosphor-yliden

Abstract: Trimethylmethylenphosphoran bildet mit (CH3)3PCuCl einen ionogenen 2:1-Komplex der Formel [(CH3)3PCH2CuCH 2P(CH3)3]Cl (1), mit (CH3)3SiCH2Cu die Molekulverbindung (CH3)3SiCH2CuCH 2P(CH3)3 (4) und mit CuCl unter Umylidierung den neuartigen achtgliedrigen Heterocyclus [(CH3)2P(CH2)2Cu]2(5). Die Zusammensetzung und Konstitution dieser kupferorganischen Verbindungen mit stabilisierendem Oniumzentrum wurden mit analytischen und spektroskopischen Methoden sichergestellt. Fur 5 liegt von anderer Seite eine Rontgenstrukturanalyse vor. – Aus (CH3)3PCH2 und (CH3)3PAgCl entsteht nur die zu 5 analoge Silberverbindung 6, in deren NMR-Spektren die uber echte Ag-C-σ-Bindungen vermittelten Spin-Spin- Wechselwirkungen 1H-C-107,109Ag und 31P-C-107,109Ag beobachtet werden konnen. Auch die Ylide C6H5(CH3)2PCH2 und CH3(C6H5)2PCH2 bilden derartige Cu- und Ag- Heterocyclen, die jedoch im Gegensatz zu 5 und 6 nur geringe thermische und chemische Bestandigkeit aufzuweisen haben (7a, b, 8a, b). Stable Copper and Silver Derivatives of Phosphorus Ylides Trimethylmethylenephosphorane has been shown to form an ionic 2:1 complex with (CH3)3PCuCl, of the formula [(CH3)3PCH2CuCH 2P(CH3)3]Cl (1). With (CH3)3SiCH2Cu, the molecular species (CH3)3SiCH2CuCH2P(CH3)3 (4) has been isolated, while with CuCl a novel eight-membered heterocycle [(CH3)2P(CH2)2Cu]2 (5)ist formed in a trans-ylidation reaction. The composition and structure of these unusual organocopper compounds have been proved by analytical and spectroscopic methods. The crystal structure of compound 5 has been determined elsewhere. - A silver analogue of 5 (6) is obtained from (CH3)3PAgCl (or AgCl) and (CH3)3PCH2. The detection of 1H-C-107, 109Ag and 31P-C-107,109Ag spin-spin-interactions in the n. m. r. spectra of 6 provided direct evidence for covalent C-Ag bonding in these molecules. The ylides C6H5(CH3)2PCH2 and CH3(C6H5)2PCH2 are forming similar Cu- and Ag-heterocycles (7a, b, 8a, b), but these compounds are of a markedly reduced thermal and chemical stability if compared with 5 and 6.

Untersuchungen über den Nahrungserwerb der Waldameisen (Formica polyctena foerster) im Eichenwald : III. Jahresbilanz.

Abstract: During a year, the workers of a medium-sized nest of red wood ants, which is characterized by a territory of 0.27 ha and a number of 10 workers running out per sec at 15°C, collected on average 6.1 million prey pieces with a Volume of 28 l, a nitrogen content of 280 g, and an energy content of 6.2×104 kcal, as well as 155 l honey-dew with a sugar content of 41 kg, a nitrogen content of 100 g, and an energy content of 16.4×104 kcal. In the years of an outbreak of Tortrix viridana L. the annual amount of prey was not considerably higher than during the time of latency of this insect. About one third of the prey volume was brought into the nest in the crop. Only 0.2% of the annual amount of crop liquid consisted of bleeding sap, which is collected in early spring. The annual input from nest territory is estimated at 81 kcal/m2 (23 kcal/m2 from prey, 58 kcal/m2 from honey-dew).

Effects of light, temperature, pH, and inhibitors on the ATP level of the blue-green alga Anacystic nidulans.

Abstract: The dependence of the ATP level of the blue-green alga Anacystis nidulans on light intensity (300–20000 erg·cm-2·s-1 white light) and on temperature (0–50°), pH (6.5–9.0), and phosphate concentration (up to 10-1 M) in light (20000 lx) and dark was measured. In contrast to a low ATP level in darkness the level in light remains high and constant with each treatment in a broad range of the respective scales. DCMU [3-(3′,4′-dichlorophenyl)-l,1-dimethyl-urea)] (5×10-6 M) has no effect on the ATP pool in light, supporting the view that the ATP level is maintained by cyclic photophosphorylation. Dio-9, an inhibitor of energy transfer, lowers the ATP level according to concentration in light and dark. The unchanged ATP level after transitions from N2 to N2+CO2 under different conditions indicates an intensive regulation of the ATP pool. The ADP level, where measured, was found to be inverse to the ATP level. These results are discussed in comparison with data collected by other authors using different organisms.

Human prostatic carcinoma in cell culture: preliminary report on the development and characterization of an epithelial cell line (EB 33).

Abstract: The permanent epithelial cell-line EB 33 was developed from a human prostatic carcinoma. First attempts were made to characterize this strain by functional, morphological and kinetic parameters. The doubling time was found to be quite slow and to remain constant at 50.0 h during the exponential phase of growth over many passages. High acid phosphatase activity in the cytoplasma was found by histochemical means in comparison to HeLa cells. Electron microscopic studies suggested the epithelial origin of the cell-line. The karyotype was near triploid. Successful heterotransplantation into “nude mice” was achieved reproducibly. Histological examination of the heterotransplants revealed solid epithelial tumors with a rapid rate of growth. The findings reported suggest the prostatic epithelial origin of the cell-line EB 33. Their origin from the carcinomatous part of the explanted tissue remains still unproven. Future aspects for the development of an experimental model for human prostatic carcinoma are discussed.

Effects of centrally applied drugs on pressor responses to hypothalamic stimulation.

Abstract: The posterior hypothalamus of anaesthetized cats was superfused through a push-pull cannula with artificial cerebrospinal fluid and electrically stimulated with the non-insulated tip of the cannula. The hypothalamus was superfused with drugs, and their effects on the pressor responses to hypothalamic stimulation were studied. Superfusion with low concentrations of clonidine (1×10−5 M or 5×10−5 M) enhanced the pressor responses to hypothalamic stimulation, while the rise of blood pressure caused by stimulation of the hypothalamus was reduced during superfusion with high concentrations of clonidine (1×10−3 M or 1×10−2 M). A moderate concentration of clonidine (1×10−4 M) was ineffective. Superfusion with carbachol or DMPP (1×10−3 M or 1×10−2 M) elicited a dose-dependent enhancement of the pressor responses to hypothalamic stimulation. Hexamethonium (1×10−2 M) did not affect the rise of blood pressure but abolished the enhancing effects of carbachol and DMPP. In some experiments the nucleus of the solitary tract was superfused with the push-pull cannula and the posterior hypothalamus was stimulated electrically with a monopolar electrode. Superfusion of the nucleus of the solitary tract with tolazoline (1×10−1 M) enhanced the pressor responses to hypothalamic stimulation. The present results are compatible with the following views: 1. Low concentrations of clonidine enhance the pressor responses to hypothalamic stimulation by activating the alpha-adrenoceptors of the hypothalamic area; high concentrations of clonidine inhibit the pressor responses by reducing the noradrenaline release via a feed-back mechanism and/or by inhibiting the release of acetylcholine from cholinergic nerve endings of the hypothalamus. 2. Nicotine agents enhance the rise of blood pressure caused by hypothalamic stimulation; their effects are mediated by nicotinic receptors. 3. More than one neurotransmitter seems to be involved in the central modulation of the arterial blood pressure.

Burstein Shift of the Absorption Edge of nBi2Se3

Abstract: The spectral position of the absorption edge of n-type Bi2Se3, single crystals was determined from reflectivity measurements on cleavage planes at nearly normal incidence of the radiation (E ⊥ c). A small reflectivity peak yields a maximum of the real part n2 - k2 of the dielectric constant, which is correlated to the critical photon energy of the direct absorption edge. A direct optical gap of 160 me V at 77 K is extrapolated for an empty conduction band. The temperature coefficient between 77 and 300 K is -2 × 10−4 eV/K. Assuming a linear temperature dependence down to T = 0 a gap of 175 me V at T = 0 and of 115 me V at 300 K is derived. For E ⊥ c a parabolic ϵ(k) relation of the valence band of Bi2Se3 is deduced with m = 0.125 m0 ± 10%. Die spektrale Lage der Eigenabsorptionskante von nBi2Se3-Einkristallen wurde aus Reflexionsmessungen an Spaltflachen bei nahezu senkrechter Inzidenz der Strahlung (E ⊥ c) bestimmt. Ein kleines Reflexionsmaximum ergibt ein Maximum des Realteils n2 - k2 der Dielektrizitatskonstante, das mit der Einsatzenergie fur direkte Interbandanregungen korreliert ist. Ein direktes optisches Gap von 160 me V bei 77 K wird fur ein unbesetztes Leitungsband extrapoliert. Der Temperaturkoeffizient zwischen 77 und 300 K betragt -2 × 10−4 eV/K. Mit der Annahme einer linearen Temperaturabhangigkeit bis T = 0 wird eine Energieliicke von 175 meV fur T = 0 und von 115 me V bei 300 K abgeleitet. Fur E ⊥ c ergibt sich ein parabolischer ϵ(k)-Zusammenhang fur das Valenzband mit m = = 0,125 m0 ± 10%.

[2.2]Paracyclophanes, structure and dynamics

Abstract: Non-planar benzene rings, anomalous bond lengths and angles, and electronic interactions between parallel benzene nuclei are common features of the [2.2]paracyclophane system. This progress report reviews the unusual physical and, in particular, spectroscopic properties of such a strained molecular structure. Chirally substituted [2.2]paracyclophanes offer parallels to the stereochemistry of the metallocenes. Characteristics of the chemical behaviour of [2.2]paracyclophanes and analogous compounds comprise: transannular directing effects in electrophilic substitution, neighboring-group effects of the [2.2]paracyclophanyl moiety, cis-addition at the aliphatic bridges, dynamic intramolecular processes such as isomerization and racemization, and photochemical reactions.

Stability of DNA in Purkinje cell nuclei of the mouse. An autoradiographic study.

Abstract: Neurons of the mouse were labeled with [(3)H]thymidine during their prenatal period of proliferation. The (3)H activity of the Purkinje cell nuclei was then studied autoradiographically 8, 25, 55, and 90 days after birth. The measured grain number per nucleus decreased by about 14% between the 8th and 25th postnatal days and then remained constant up to 90 days. There was no significant decrease of the (3)H activity of the Purkinje cell nuclei after correction of the measured grain number per nucleus for increasing nuclear volume of the growing Purkinje cells and for the influence of [(3)H]beta self-absorption in the material of the sections. Injection of a high dose of [(3)H]thymidine into young adult mice did not result in (3)H labeling of either Purkinje or other neurons in other brain regions. The results agree with the concept of metabolic stability of nuclear DNA. "Metabolic" DNA could not be observed in these experiments.

The O.Methylation of Extraneuronally Stored Isoprenaline in the Perfused Heart

Abstract: 1. Rat hearts were perfused with 0.95 or 23.8 μM 3H-(±)-isoprenaline for 30 min; efflux curves were determined for total radioactivity, 3H-isoprenaline and 3H-O-methylisoprenaline during wash out with amine-free solution. 2. The efflux curves indicated that most or all of the COMT activity was associated with compartment III of Bonisch et al. (1974). Most of the metabolite appearing in the wash out solution was formed during wash out. 3. The efflux curves for the metabolite (3H-OMI) were convex. The convexity was much more pronounced after perfusion with 23.8 μM than after perfusion with 0.95 μM 3H-isoprenaline. 4. On addition of 20 μM corticosterone to the wash out solution, the rate of efflux of 3H-isoprenaline was reduced but not that of 3H-OMI; in addition, the appearance of the convexity of the efflux curve for 3H-OMI was delayed. 5. In order to explain these phenomena, it is suggested that, during perfusion with 0.95 μm or more of catecholamine, the rate of uptake into compartment III is substantially higher than the rate of O-methylation. Consequently, unchanged amine can accumulate in compartment III and saturate COMT. During wash out the enzyme becomes desaturated, and the convex shape of the efflux curve for the product (3H-OMI) ensues. 6. The O-methylating capacity of the guinea-pig hearts is considerably smaller than that of the rat heart.