Showing papers by "University of Fribourg published in 1980"

Dopaminergic activation of reticulata neurones in the substantia nigra

Abstract: Dendritic release of dopamine (DA) in substantia nigra (SN) is well established in various experimental situations. Morphological substrates for DA storage exist in dendrites, as do dendro-dendritic and dendro-axonic contacts. DA receptors in SN are located on both cells and striato-nigral terminals. DA is thought to regulate the activity of neighbouring dopaminergic neurones through its dendritic release by a local feedback mechanism. However, dendrites of DA neurones also ramify close to the neuropil of non-dopaminergic reticulata neurones in SN. The question has arisen whether dendritically release DA might also influence these neurones which, to a large extent, project to ventromedial thalamus (VM) and superior colliculus. A necessary condition would be that they are sensitive to DA. In the experiments reported here this was found to be the case--a considerable proportion of nigrothalamic neurones were activated by iontophoretically applied DA. This contrasts with its known depressant effect on pars compacta DA neurones which we confirmed.

Glucan synthesis by intact cotton fibres fed with different precursors at the stages of primary and secondary wall formation.

Abstract: Seed clusters of individual locules from fruit capsules of Gossypium arboreum L. with adhering intact fibres were fed with radioactive uridinediphosphoglucose (UDPG), guanosinediphosphoglucose (GDPG), glucose and sucrose. The incorporation into high molecular weight glucans of the fibres was studied. For primary wall fibres, UDPG at 1 mM was by far the best precursor, whereas sucrose was the best precursor for secondary wall fibres. No competition was observed between the incorporation of glucose from UDPG and from sucrose when the two were fed simultaneously to secondary wall fibres, indicating that their metabolic pathways are well separated when they are fed from the apoplast. Inhibitors of respiratory ATP-formation strongly inhibited incorporation of sucrose but not that of UDPG. Sucrose incorporation was studied at five different stages of development of the cotton fibres. At the stage of most intense secondary wall formation the incorporation rate was about 300 times that during primary wall formation (24 days post anthesis (DPA)). Incorporation from 1 mM UDPG or GDPG by secondary wall fibres (35 DPA) was less than twice that of primary wall fibres (22 DPA), indicating that the two sugar nucleotides are not readily used as precursors for secondary wall cellulose when they are fed to the exterior of intact cells. The high molecular weight non-cellulosic glucans formed from UDPG and sucrose at 5 and 1,000 μM were solubilized in strongly alkaline solutions or dimethyl-sulfoxide (DMSO) and were partially characterized by degradation with an exo-β-1,3-glucanase. After feeding for one hour, at most 1/3 of the radioactivity in high molecular weight material was found in cellulose and at least 2/3 in β-1,3-glucan. The proportions varied little for fibres in the age range of 30 to 48 DPA when sucrose was the precursor although the total incorporation varied by a factor of about four. The fact that at all stages of secondary wall formation β-1,3-glucan is synthesized at a very high rate, but that the total amount in the cell wall does not exceed 2% in the later stages of wall formation, can be interpreted in terms of a high turnover of this polysaccharide if it is assumed that wound effects are negligible in the system under study.

On the stability of holomorphic foliations

Abstract: In 1978 D.B.A. Epstein and E. Vogt succeeded in constructing an unstable real-analytic periodic flow on a 4-dimensional compact real-analytic manifold. This cannot be generalized to the complex-analytic case:

Aromatic Radical Anions in Neat Aromatic Hydrocarbons as Solvents. Direct evidence of through space spin‐density transfer to the ligand of the counter ion

Abstract: Contact ion pairs of aromatic radical anions, with a crown ether complex of potassium as cation in a neat aromatic hydrocarbon, can be obtained by reducing the aromatic hydrocarbon in which a small amount of crown ether is dissolved. The unpaired electron stays attached to one aromatic molecule during a time interval which is long on the ESR. time scale. The radicals are stabilized by ion-pair formation in the low polarity solvent. As a consequence of this stabilization, radicals of compounds with low electron affinities, e.g. mesitylene, can be prepared. Mesitylene, m-xylene, and toluene show additional hyperfine splitting in the ESR. spectra of their anion radical pairs of the order of 18 μT. The proton ENDOR. spectra have signals at the corresponding frequencies, indicating a hyperfine coupling with protons of the crown ether ligand. Using mixtures of two aromatic compounds, their relative electron affinities can be determined by studying the temperature dependence of the radical concentrations.

The titers and the clearance of ecdysteroids from the blood of last instar larvae ofGalleria mellonella L.

Abstract: Mesothoracal ligations of young last instar larvae ofGalleria mellonella cause the abdominal ecdysteroid blood titer, as determined by radioimmunoassays, to decrease from 48 to 11–17 ng/ml. External application of 13 μg/g, the ecdysterone dose needed to stimulate normal wing growth, raises the titer to 360–1140 ng/ml for 2 days.

Cardiogenic hypertension: experimental evidence from a comparison between intravenous and intracoronary administration of dobutamine in conscious dogs

Abstract: 1. We have studied whether the progressive rise in peripheral resistance observed in response to chronic intracoronary administration of dobutamine in conscious dogs could have resulted from extracardiac or non-β-adrenergic cardiac effects of the drug. 2. Six conscious dogs received dobutamine, 1.56 × 10 −8 mol min −1 kg −1 , intravenously for a 7 day period and seven conscious dogs were given dobutamine, 1.51 × 10 −8 mol min −1 kg −1 , into the left coronary artery under oral propranolol treatment for the same period while arterial pressure, cardiac output (electromagnetic flowmeter) and heart rate were measured. 3. Intravenous dobutamine produced no increase in arterial pressure, but a decrease in peripheral resistance and an increase in cardiac output which persisted until the end of the infusion. 4. With propranolol treatment intracoronary dobutamine induced no significant haemodynamic changes but a short-lasting increase in mean arterial pressure and peripheral resistance. 5. It is concluded that β-adrenergic cardiac effects of dobutamine are essential to the development of hypertension and increased peripheral resistance after prolonged intracoronary infusion of this drug.

Embryonic development of NMRI mice: relationship between the weight, age and ossification of embryos

Abstract: Summary The time and the order of the appearance of the ossification centres were found to be similar in C3H and NMRI mice. Bodyweight comparisons confirmed these results. Location in the right as opposed to the left uterine horn, or in the upper, middle or lower part, was not found to influence the weight of the embryo. Significant differences in the weight of embryos within the same litter were used in investigating the sequence of ossification in embryos. This should prove useful in comparative morphology and teratology. Johnson (1933) determined the chronology of appearance of ossification centres in the skull, face, axial and appendicular skeleton in a white mouse of an unknown strain. Wirtschafter (1960) studied the genesis of the skeleton in the C3H mouse, as did Hoshino (1967) for the strain CF 1. The relationship between endogenous and exogenous factors (Griineberg, 1937) and between genetic and non-genetic factors (Green, 1941), as well as the effects of uterine environment (Green & Green, 1946; Munro & Barnett, 1969; Noel & Wright, 1970) have been studied. Embryonic development may be influenced by the position of the foetus in the uterus, which would explain the significant weight differences between embryos of the same litter. This difference led Heinecke (1972) to use the embryo's weight as a criterium for estimating the age and stage of development.

Processes in photogalvanic cells and their possibilities in solar energy storage

Abstract: A photochemical electron transfer reaction with large positive ΔG, a slow homogeneous back reaction and selective electrodes for two redox couples are the main requirements for solar energy conversion and storing in photogalvanic cells. In the present paper, some possibilities and difficulties of photogalvanic cells are discussed. Photogalvanic cells may be used to convert solar energy into electriciry. For this purpose storage of chemical energy is necessary. The general scheme of a photogalvanic cell may be demonstrated in the following way:

New Developments in the Study of Mesic Chemistry

Abstract: Experiments and calculations seem today to establish that the atomic capture of exotic particles proceeds predominantly through Auger electron ejection and that, in comparison, the radiative atomic capture is negligible. This fact gives a priori the possibility of an influence of the chemical structure of matter in the Coulomb capture mechanism of exotic particles.