Showing papers by "University of Freiburg published in 1984"

Human express saccades: extremely short reaction times of goal directed eye movements

Abstract: Human subjects were asked to execute a saccade from a central fixation point to a peripheral target at the time of its onset. When the fixation point is turned off some time (≈ 200 ms) before target onset, such that there is a gap where subjects see nothing, the distribution of their saccadic reaction times is bimodal with one narrow peak around 100 ms (express saccades) and another peak around 150 ms (regular saccades) measured from the onset of the target. Express saccades have been described earlier for the monkey.

Transcription of plant defence genes in response to UV light or fungal elicitor

Abstract: The synthesis of secondary metabolites in response to stress conditions has been implicated as a major defence response of higher plants1. Cell suspension cultures of parsley (Petroselinum hortense) have been studied extensively as a model system and shown to respond to UV irradiation and treatment with fungal elicitor by the synthesis of flavonoids and furanocoumarins, respectively2,3. The induced synthesis of these compounds might afford the plant protection against the respective environmental hazards, because flavonoids strongly absorb UV light and furanocoumarins possess fungitoxic properties4. The production of each class of compound is preceded by the induction of groups of coordinately regulated enzymes2,5–8, based on rapid changes in amounts and activities of the corresponding messenger RNAs9,10. We now report that these changes are due to transient increases in the transcription rates of the respective genes, which indicates that gene activation has an important role in UV and disease resistance in higher plants.

The role of prostaglandins in the endothelium-mediated vasodilatory response to hypoxia.

Abstract: The effect of intraluminal hypoxia on vascular tone and the release of prostaglandins (PG) I2 and E2 were investigated in intact isolated segments of canine femoral and coronary arteries as well as in the rat tail artery. Perfusion with hypoxic Tyrode's solution (pO2: 20-40 mm Hg) evoked a marked vasodilation of the segments, precontracted with norepinephrine or serotonin. Simultaneously, a 2-3-fold increase in the release of 6-keto-PGF1 alpha (the stable hydrolysis product of PGI2) could be observed. In parallel to 6-keto-PGF1 alpha, smaller quantities of PGE2 were released. Removal of the endothelium as well as pretreatment with indomethacin abolished both, the dilatory response and the PG-release. After administration of verapamil as well as 3,4,5-trimethoxybenzoic acid 8-diethylaminooctylester (TMB-8) (which binds intracellular calcium) the PG-increase was abolished and hypoxic dilatation could no longer be elicited, although the vessel had still a capacity to dilate. Exogenous administration of PGI2 and PGE2 showed that in canine femoral and coronary arteries PGI2 was the most effective vasodilating prostaglandin, while in the rat tail artery PGE2 had a 10-fold higher dilating potency compared to PGI2. At very high concentrations both PGI2 and PGE2 caused vasoconstriction. Our experiments suggest that the hypoxic endothelium-dependent dilatation may be mediated by an increased PG-release. Hypoxia-induced transmembrane calcium influx into the endothelial cells seems to be the trigger reaction.

Protein Single Crystal Growth Under Microgravity

Abstract: The preparation of suitably large protein single crystals is essentially the rate-determining step of protein x-ray structure determinations. Attempts to produce single crystals with two model compounds—β-galactosidase and lysozyme—under conditions of microgravity were successful. Crystals formed by salting out from solutions kept free of convection were 27 and 1000 times larger in volume, respectively, than those produced in the same apparatus but exposed to terrestrial gravitation.

A comparison of the normal and regenerated retinotectal pathways of goldfish

Abstract: This is a light and electron microscopic study of the retinotectal pathway: intact and after regeneration of the optic nerve. The spatiotemporal pattern of axonal outgrowth and termination was studied with the methods of proline autoradiography, horseradish peroxidase (HRP) labeling, and fiber degeneration. The spatial order of optic fibers in the normal and regenerated pathways was assessed by labeling small groups intraretinally with HRP and then tracing them to the tectum. The labeled fibers occupied a greater fraction of the cross section of the regenerated than the normal optic tract. At the brachial bifurcation, roughly 20% of the regenerated fibers chose the incorrect brachium vs. less than 1% of the normals. In tectum, the regenerated optic fibers reestablished fascicles in stratum opticum, but they were less orderly than in the normals. The retinal origins of the fibers in the fascicles were established by labeling individual fascicles with HRP and then, following retrograde transport, finding labeled ganglion cells in whole-mounted retinas. Labeled cells were more widely scattered over the previously axotomized retinas than over the normal ones. A similar result was obtained when HRP was applied in the tectal synaptic layer. All of these results indicate that the pathway of the regenerated optic fibers is less well ordered than the intact pathway. Both autoradiography and HRP showed that the regenerating optic fibers invaded the tectum from the rostral end, and advanced from rostral to caudal and from peripheral to central tectum, along a front roughly perpendicular to the tectal fascicles. Synapses of retinal origin were noted electron microscopically in the tectum at the same sites where autoradiography indicated that the fibers had arrived. No retinal terminals were seen where grain densities were at background levels. Fiber ingrowth and synaptogenesis apparently occurred simultaneously. The synapses were initially smaller and sparser than in normals, but were in the normal tectal strata and contacted the same classes of post synaptic elements as in normals.

Mass Spectra of Negatively Charged Water and Ammonia Clusters

Abstract: Slow electrons are mixed into a heavily clustered supersonic expansion of water and ammonia. The resulting negatively charged cluster ions are mass analyzed. Mass spectra for (H2O)n−, (D2O)n−, and (NH3)n− are presented. The smallest cluster ions observed contain 11, 12, and 36 water, heavy water and ammonia molecules per clusters, respectively.

Interlimb coordination of posture in patients with spastic paresis. Impaired function of spinal reflexes.

Abstract: Activation of leg musculature on both sides following a unilateral displacement was studied during stance on separate see-saws, or on stable force-measuring platforms, in patients with spastic hemiparesis and paraparesis. During balancing the movements on the spastic side were damped and the degree of muscle activation reduced. Whereas in healthy subjects the tibialis anterior muscles of both sides were activated, following a unilateral displacement, with the same strength and latency (see-saws 55 ms, platforms 85 ms), in hemispastic patients the EMG responses were delayed (by about 20 to 30 ms) and of reduced strength on the spastic leg, irrespective of whether the unaffected or the spastic side was displaced. In addition, the compensatory movements on the spastic side were damped in both conditions, although the amplitude of displacement was the same bilaterally. Although there was no correlation between the delay and the reduction in EMG response, the latter was correlated with the severity of paresis. In patients with spastic paraparesis quite similar results were obtained with delayed and reduced EMG responses on both sides. It is concluded that in spasticity the impaired regulation of quick compensatory movements is due to a dysfunction of a spinal interneuronal system by which the early EMG responses are mediated. This could be explained by loss of supraspinal control. In addition to the impaired neural activation of leg muscles, changes in the mechanical properties of muscle can be assumed to contribute to the damped movements on the spastic side.

Express-saccades of the monkey: reaction times versus intensity, size, duration, and eccentricity of their targets.

Abstract: Monkeys were trained to fixate a small spot of light (fixation spot) and to saccade to a peripheral target if and only if the fixation spot was turned off. If the offset of the fixation spot preceded the onset of the peripheral target by a temporal gap of more than 140 ms the animals could change their direction of gaze after saccadic reaction times of no more than 70-80 ms (express-saccades). The reaction times of the express-saccades depend on the luminance and the size of the target and decrease from about 120 ms for near threshold targets by about 50 ms in a range of 2,5 log units above threshold (gap duration 200 ms). The minimum reaction time and the target size for which the minimum is reached are functions of the retinal eccentricity of the target. Comparison with response latencies of afferent visual neurons suggests that the dependence of the reaction times of express- as well as regular-saccades on the physical parameters of the target is mostly determined by retinal factors. The short reaction times of the express-saccades are discussed in relation to the reaction times of other visually-guided goal-directed movements.

Express-saccades of the monkey: effect of daily training on probability of occurrence and reaction time.

Abstract: Two monkeys learned to make saccadic eye movements from a central fixation point to a peripheral target, when there was a temporal gap between fixation point offset and target onset. Under these conditions the animals made saccades after extremely short reaction times (< 100 ms), so called express-saccades. With ongoing training the rate of occurrence increased (10 to 100%) and the reaction time of the express-saccades decreased (95 to 75 ms). The training effects were mediated by the amount of previously executed express-saccades and they were also spatially selective for express-saccades to that target position that had been used during training. The training effects on the express-saccades can be saturated after less than 7 days of daily training and are reversible after another 7 days of no training. The results indicate the existence of a fast-operating visuo-to-oculomotor pathway which can be quickly and reversibly modified by daily exercise.

Testing of chemicals for genetic activity with Saccharomyces cerevisiae: a report of the U.S. Environmental Protection Agency Gene-Tox Program.

Abstract: The yeast Saccharomyces cerevisiae is a unicellular fungus that can be cultured as a stable haploid or a stable diploid . Diploid cultures can be induced to undergo meiosis in a synchronous fashion under well-defined conditions. Consequently, yeasts can be used to study genetic effects both in mitotic and in meiotic cells. Haploid strains have been used to study the induction of point mutations. In addition to point mutation induction, diploid strains have been used for studying mitotic recombination, which is the expression of the cellular repair activities induced by inflicted damage. Chromosomal malsegregation in mitotic and meiotic cells can also be studied in appropriately marked strains. Yeast has a considerable potential for endogenous activation, provided the tests are performed with appropriate cells. Exogenous activation has been achieved with S9 rodent liver in test tubes as well as in the host-mediated assay, where cells are injected into rodents. Yeast cells can be recovered from various organs and tested for induced genetic effects. The most commonly used genetic end point has been mitotic recombination either as mitotic crossing-over or mitotic gene conversion. A number of different strains are used by different authors. This also applies to haploid strains used for monitoring induction of point mutations. Mitotic chromosome malsegregation has been studied mainly with strain D6 and meiotic malsegregation with strain DIS13 . Data were available on tests with 492 chemicals, of which 249 were positive, as reported in 173 articles or reports. The genetic test/carcinogenicity accuracy was 0.74, based on the carcinogen listing established in the Gene-Tox Program. The yeast tests supplement the bacterial tests for detecting agents that act via radical formation, antibacterial drugs, and other chemicals interfering with chromosome segregation and recombination processes.

Calmodulin and calmodulin‐mediated processes in plants

Abstract: . The Ca2+ -binding protein calmodulin is found in all plants investigated so far. The comparison of the biochemical and functional properties reveals that it is structurally conserved and functionally preserved throughout the plant and animal kingdom. Among the plant enzymes so far known to be dependent on the Ca2+ -calmodulin complex are NAD kinase(s), Ca2+ -transport ATPase, quinate: NAD+ oxidoreductase, soluble and membrane bound protein kinases, and H+ -transport ATPase. Calmodulin may play also an important role in the regulation of other cellular reactions, such as hormone-mediated processes, secretion of enzymes, and contractile mechanisms. On the basis of the NAD kinase and its regulation by light and Ca2+ -calmodulin, it is suggested that changes in the cellular, free Ca2+ concentration following stimulation may alter the metabolism of a plant cell. According to this suggestion free Ca2+ may act as a second messenger in plants much as it does in animal cells.

DNA sequence requirements for the accurate transcription of a protein-coding plastid gene in a plastid in vitro system from mustard (Sinapis alba L.).

Abstract: A nuclease-treated plastid extract from mustard (Sinapis alba L.) allows efficient transcription of cloned plastid DNA templates. In this in vitro system, the major runoff transcript of the truncated gene for the 32 000 mol. wt. photosystem II protein was accurately initiated from a site close to or identical with the in vivo start site. By using plasmids with deletions in the 5'-flanking region of this gene as templates, a DNA region required for efficient and selective initiation was detected 28-35 nucleotides upstream of the transcription start site. This region contains the sequence element TTGACA, which matches the consensus sequence for prokaryotic ;-35' promoter elements. In the absence of this region, a region 13-27 nucleotides upstream of the start site still enables a basic level of specific transcription. This second region contains the sequence element TATATAA, which matches the consensus sequence for the ;TATA' box of genes transcribed by RNA polymerase II (or B). The region between the ;TATA'-like element and the transcription start site is not sufficient but may be required for specific transcription of the plastid gene. This latter region contains the sequence element TATACT, which resembles the prokaryotic ;-10' (Pribnow) box. Based on the structural and transcriptional features of the 5' upstream region, a ;promoter switch' mechanism is proposed, which may account for the developmentally regulated expression of this plastid gene.

Expression of transferrin receptors and intracellular ferritin during terminal differentiation of human monocytes

Abstract: Human blood monocytes when cultured on hydrophobic Teflon membranes differentiate into mature macrophages. The expression of transferrin receptors was monitored by monoclonal antibody (OKT9) binding as detected by immunoperoxidase staining. Whereas monocytes were negative, an increasing percentage of macrophages, starting from day 2 in culture, labelled with the antitransferrin receptor antibody as these cells undergo differentiation. After completion of maturation more than 90% of macrophages expressed transferrin receptors. While 90-95% of macrophages from broncho-alveolar lavage fluids labelled with the OKT9 antibody, only a minor portion of macrophages obtained from peritoneal and pleural cavities did so. In parallel, intracellular ferritin in cells of the monocyte-macrophage lineage increased from 10 ng/10(6) cells to 350-1,500 ng/10(6) cells during maturation in vitro. Alveolar macrophages proved to have the highest ferritin content which ranged from 355-8,400 ng/10(6). The results may indicate that iron uptake and storage is a function of cells at late stages of macrophage maturation and that the occurrence of surface receptors for transferrin can be regarded as differentiation dependent marker.

Endogenous adenosine as a modulator of hippocampal acetylcholine release.

Abstract: Modulation of acetylcholine release via adenosine receptors was studied in rabbit hippocampal slices, which were preincubated with 3H-choline and then continuously superfused. Electrical field stimulation of the slices elicited a release of acetylcholine, which was inhibited in a concentration-dependent manner by various adenosine receptor agonists. The effects of the agonists were antagonized by the methylxanthines. From the order of potency: cyclohexyladenosine > (−)phenylisopropyl-adenosine ((−)PIA) > 5′-N-ethylcarboxamideadenosine (NECA) > 2-chloradenosine > (+)phenylisopropyladenosine > adenosine, the inhibitory adenosine receptor may be classified as A1-(R1-)receptor. In experiments on rabbit caudate nucleus slices, adenosine receptor agonists only slightly decreased the evoked acetylcholine release. The presence of an inhibitory tone of endogenous adenosine on hippocampal acetylcholine release is supported by the following findings: 1) the methylxanthines theophylline, 8-phenyltheophylline and 3-isobutylmethyl-xanthine (IBMX) increased the evoked acetylcholine release in concentrations below those required for phosphodiesterase inhibition. 2) Adenosine uptake inhibitors, in contrast, decreased the evoked transmitter release. 3) Deamination of endogenous adenosine by addition of adenosine deaminase to the medium enhanced the acetylcholine release. In conclusion, acetylcholine release in the hippocampus is depressed at the level of the cholinergic nerve terminals by endogenous adenosine via A1-(Ri-)receptors.

Synthesis of prostanoids and cyclic nucleotides by phagocytosing rat Kupffer cells

Abstract: Rat Kupffer cells in monolayer culture were allowed to phagocytose unopsonized zymosan granules. They responded with a strongly stimulated synthesis and release of prostanoids, mainly the immunologically determined prostaglandins PGE2 and PGF2 alpha. The same response could be obtained by treatment with the calcium ionophore A23187. The effects of the ionophore and the zymosan particles were of the same magnitude but not additive. The rapid uptake of Ca2+ after contact with phagocytosable material recently described by us [(1983) Eur. J. Biochem. 131, 539-543] appears to mediate the enhanced prostaglandin synthesis. That response was suppressed not only by indomethacin but also by trifluoperazine which does not inhibit Ca2+ entry in the Kupffer cells. Similar effects by R24571 and 4-bromophenacyl bromide support the participation of calcium-calmodulin and of phospholipase A2. The calcium channel blocker Verapamil did not influence the zymosan-provoked production of prostaglandin PGE2 nor were any indications obtained for a feedback inhibition by PGE1 or PGE2. Contact with zymosan resulted in a rapid but transient rise of the intracellular levels of cAMP and cGMP: 10 nM indomethacin completely blocked the increase of both cyclic nucleotides while trifluoperazine elicited different responses in the cAMP and cGMP levels. The stimulated release of prostaglandin E2 was inhibited in a dose-dependent manner by nordihydroguaiaretic acid, an inhibitor of 5-lipoxygenase and by FPL 55712, known as a receptor antagonist for some leukotrienes. This suggests a regulatory role for its metabolites on prostaglandin synthesis.

Preferential integration of yeast transposable element Ty into a promoter region.

Abstract: Mobile genetic elements have been identified in several eukaryotic organisms and some classes have been found to share common structural features with the proviral forms of animal retroviruses1–7. The representatives of this class of mobile elements in the yeast Saccharomyces cerevisiae are called Ty elements8, which could be a useful model system for studying the transposition of retrovirus-like elements. Here we have attempted to answer two questions often raised in discussions of the biological importance of transposition: what is the frequency of spontaneous Ty transposition, and are there certain chromosomal regions into which Ty elements preferentially integrate? We chose the LYS2 gene to investigate these questions because it allows direct selection of both mutants and revertants9. We have found that 2% of spontaneous lys2 mutants are caused by Ty transposition with a preferential integration into the transcription initiation region.

The importance of endogenous prostaglandins other than prostacyclin, for the modulation of contractility of some rabbit blood vessels

Abstract: Helically cut strips of rabbit aorta, extrapulmonary artery, coeliac artery, and femoral artery were set up in organ baths. Contractions of the strips by noradrenaline and angiotensin II were recorded isotonically. The release of prostaglandins 6-keto-PGF1 alpha, E2, F2 alpha, D2 and thromboxane B2 from the strips was measured by means of sensitive and specific radioimmunoassays. All blood vessels released a characteristic pattern of cyclo-oxygenase products. Prostacyclin (PGI2, measured as 6-keto-PGF1 alpha) was the major compound formed, followed by smaller amounts of PGE2 and traces of PGF2 alpha, PGD2 and thromboxane A2 (measured as thromboxane B2). The pulmonary and the femoral artery had comparatively high abilities to synthesize PGE2. Contractions induced by noradrenaline increased prostaglandin release from the pulmonary artery but not from the other blood vessels. Angiotensin II-induced contractions were accompanied by a marked prostaglandin release from the coeliac artery. After angiotensin II, prostaglandin release was also enhanced in the pulmonary artery, but remained essentially unchanged in the aorta and femoral artery. Arachidonic acid markedly increased the levels of all prostaglandin formed. Indomethacin inhibited the formation of all prostaglandins below the detection limits of the respective radioimmunoassays. Indomethacin treatment induced a qualitatively similar shifting of the concentration-response curves of noradrenaline and angiotensin II in some vessels: the concentration-response curves remained unchanged for the aorta, were slightly shifted to the left of the pulmonary artery, were markedly shifted to the left for the coeliac artery, and were shifted to the right for the femoral artery. 7 Exogenous PGI2 strongly and concentration-dependently inhibited contractions induced by the approximate EC50 of noradrenaline in the coeliac artery, but was without effect on the other three preparations. PGE2 had no effect on noradrenaline-induced contractions of the aorta, inhibited those of the pulmonary and the coeliac artery, but markedly potentiated those of the femoral artery. PGF2 alpha significantly enhanced contractions of the femoral artery, but increased contractions of the other preparations were not significant. PGD2 was without effect on any preparation. 8 In conclusion, the contractility of the aorta does not seem to be modulated substantially by prostaglandins. The major prostanoid regulating the tone of the coeliac artery was found to be PGI2. The contractility of the pulmonary and especially the femoral artery is probably not modulated by PGI2 but rather by PGE2. 9 These observations suggest that in certain blood vessels, prostaglandins other than PGI2 are important endogenous modulators of contractility.