Showing papers by "University of Fribourg published in 1987"

Neuronal activity preceding self-initiated or externally timed arm movements in area 6 of monkey cortex

Abstract: Several lines of evidence suggest that the supplementary motor area (SMA) and the premotor cortex (PM) may participate in neuronal mechanisms for the initiation of movements. We recorded the impulse activity of single neurons in monkeys that were trained in two behavioral tasks employing, respectively, self-initiated and externally timed movements. Neurons in both areas were activated up to 2.6 s in advance of self-initiated, reward-related arm reaching movements. In the externally timed task, changes occurred during light instructions that preceded movements by 2 s. Neurons also responded to the trigger stimulus for movement. In view of similar premovement activity in the basal ganglia, these cortical regions appear to be parts of a distributed neuronal system for movement initiation.

Spatial median and directional data

Abstract: SUMMARY We introduce the normalized spatial median as an estimator of location for rotationally symmetric distributions on the hypersphere. We investigate some of its asymptotic properties and use them to obtain confidence regions for the modal direction of a distribution on the hypersphere. These results are then applied to the von Mises-Fisher distribution and to a contamination model. It is seen that the normalized spatial median can perform more efficiently than the normalized mean in presence of outliers.

Input and output organization of the supplementary motor area

Abstract: Recent work on the supplementary motor area (SMA) in Macaca fascicularis led to the conclusion that this area is involved mainly in the preparation of self-paced movements. Results are presented indicating that the posterior portion of the SMA is also directly involved in movement execution and that it receives various sensory inputs. The main results are as follows: (1) The SMA has direct access to the spinal cord by way of corticospinal neurons, but the density of these neurons is lower than in the primary motor cortex (MI). (2) Intracortical microstimulation effects can be elicited in the SMA. Facilitatory effects on ongoing EMG activity can even be produced by single micropulses (8/s). The shortest latencies are compatible with an oligosynaptic or monosynaptic transmission. (3) SMA neurons respond (as do MI neurons) to external perturbations. (4) Anatomical tracing studies revealed that basal ganglia outflow to the SMA via the thalamus is important; our results suggest that dentate outflow contributes as well. (5) Many cells of the SMA may covary with conditioned movements in the same way as MI neurons do. It is argued that it is difficult to compare the lead-time of MI and SMA neurons since 'early' discharges may be coupled with anticipatory postural events.

The role of iron in the activation of mannoni and altronic acid hydratases, two Fe-requiring hydro-lyases

Abstract: d-Altronate hydratase and d-mannonate hydratase belong to a class of Fe2+-requiring enzymes, but the function of iron in these enzymes is largely unknown. Methods are described for the convenient preparation of both these hydratases from Escherichia coli and studies related to metal activation are presented. The enzymes are inactive in the absence of a bivalent metal and a reducing agent such as dithiothreitol. Fe2+ at low concentrations activates the enzymes efficiently, but inhibits them over 2 mM. Furthermore Mn2+ is also capable of activating aldonic acid hydratases and appears to be a constituent of the enzyme active center. A marked synergistic activation is observed in the presence of both ions, raising the possibility that the enzyme has two binding sites for ions. Upon activation, the two aldonic acid hydratases incorporate a single Fe atom and contain no Fe-S core, in contrast to other characterized Fe-hydratases, such as aconitase or maleic acid hydratase. The incorporated iron is losely bound (with Kd about 4.5 mM and 20 mM for mannonate and altronate hydratase, respectively) and can be readily removed with EDTA. The enzymes exhibit no requirement for sulphide ions and are insensitive to thiol reagents. A first-order inhibition is observed with iron chelators and can be removed by competition with excess metal ions. No change in the absorption spectra is observed upon oxidation-reduction or activation with metals. The activated enzymes exhibit no electron paramagnetic (EPR) spectrum under anaerobic conditions; in the presence of oxygen, an intense EPR spectrum develops in Fe2+-activated samples with signal at g= 1.98, which upon reaction of the enzyme with the substrate moves into a species with signals at g= 4.15 and g= 9.07, with EPR parameters very similar to those of oxidized rubredoxins.

Photoionization of Naphthalene and Anthracene in Acetonitrile

Abstract: Naphthalene and anthracene undergo a monophotonic ionization process in MeCN to produce the radical cations in low quantum yields (around 0.06 for anthracene). This reaction originates from the relaxed singlet excited state S1, and it is not due to traces of H2O in the solvent.

Sensory projection patterns of supernumerary legs and aristae in D. melanogaster

Abstract: The central projection patterns of afferents from normal and duplicated legs and antennal aristae in D. melanogaster were established by horseradish peroxidase or cobalt labelling. Duplications were obtained genetically, by using l(1)ts726 and engrailed mutants, which are known to produce supernumerary legs and aristae, respectively. In normal legs, afferents from singly innervated mechanoreceptive (M-) bristles terminate in the lateral and medial periphery of the corresponding leg neuromere. The medial periphery is also occupied by terminals of multiply innervated chemoreceptive (C-) bristles; another target of C-bristles is the anterior margin of the neuromere. The sensory projection patterns of homologous M-bristles on different leg segments are overlapping, suggesting that terminals are not ordered according to the proximo-distal location of their cell bodies on the leg. The sensory projections of duplicated legs or aristae overlap the corresponding normal projections. However, when stimulating supernumerary legs in the proboscis extension paradigm, the frequency and intensity of reflex activity are significantly reduced compared to normal legs. These data suggest that normal and supernumerary afferents compete with one another in a subtle way which is not accompanied by gross morphological changes of the projection patterns.

High-resolution study of heavy-ion-induced K α x-ray spectra of molybdenum atoms

Abstract: The K\ensuremath{\alpha} x-ray spectra of molybdenum bombarded with 6.7-MeV/u $^{4}\mathrm{He}$ and 5.5-MeV/u $^{16}\mathrm{O}$ ions were recorded with an on-line curved-crystal spectrometer in the DuMond geometry. The instrumental resolution was approximately 10.5 eV. K${\ensuremath{\alpha}}_{1}$${L}^{n=0}$,1,2,3 and K${\ensuremath{\alpha}}_{2}$${L}^{n=0}$,1 principal and satellite lines were observed and resolved for the first time for an atom in the mid-Z region. The relative yields, energies, and linewidths were determined. The yields in the $^{16}\mathrm{induced}$ spectrum deviate significantly from the binomial distribution. The width and energy shifts indicate additional multiple M-shell ionization.

Topography of the corticofugal projection to the lateral reticular nucleus in the monkey.

Abstract: The cortical projection to the lateral reticular nucleus (LRN) was explored in monkeys prepared for autoradiography and horseradish peroxidase (HRP) histochemistry. An unambiguous projection was revealed only in cases with injections of the precentral forelimb and hindlimb areas. The forelimb area projection occupied centromedial segments, the hindlimb area projection occupied ventrolateral segments of the LRN with very little overlap. Some sparse labeling was also seen with injections of the supplementary motor area (SMA), but only when the lectin-bound tracer HRP was injected and not when autoradiography was used. Retrogradely labeled cortical cells occupied a larger cortical area in one case with injection of free HRP into the LRN. Since the additional expanse of cortex, however, was not examined in anterograde cases, and since the injected marker substance had diffused to neighboring structures, the significance of the labeled cells outside the precentral motor cortex is questionable. There was no evidence for a projection from the precentral face area with either anterograde tracing method. The corticoreticular projection was bilateral and only slightly more marked contralateral to the injection. The labeling was largely confined to the magnocellular division with minor amounts in the parvicellular division (especially in the hindlimb cases). The subtrigeminal portion was spared in all cases. It is concluded that the LRN constitutes another somatotopically organized precerebellar nucleus relaying signals from the motor cortex to the cerebellum. Compared with the corticopontocerebellar pathway in monkeys, however, the LRN is only a minor component of the corticocerebellar transmission system.

Cortical and peripheral effects on single neurons of the lateral reticular nucleus in the monkey.

Abstract: The aim of this study was to extend the anatomical study of the cortico-reticular organization in the monkey by means of microelectrophysiological techniques. Considering the relatively modest projection (see companion paper, Wiesendanger and Wiesendanger, '87), it was surprising to see that over 70% of the investigated LRN neurons were influenced from at least one cortical stimulation site. Many neurons responded, however, with long latencies suggesting an indirect transmission line. In line with the anatomical tracing study, most short-latency responses were obtained from the motor cortex. Postcentral cortex and the SMA were, in general, less effective sites for evoking responses in the LRN. LRN neurons with similar cortical inputs tended to be clustered together suggesting that the corticoreticular projection is discretely organized with an “intermingled somatotopy.” The majority of the 87 tested LRN neurons were not reactive to any peripheral stimulus (33%) or responded only to nociceptive peripheral stimulation (31%). Very large receptive fields were seen in 8% of the units. However, a significant proportion of LRN neurons (10%) had restricted receptive fields and reacted to gentle cutaneous stimuli, and others (17%) responded to discrete passive rotations of one or more joints. There was often a somatotopical correspondence between the peripheral and the cortical inputs. It is concluded that the LRN in monkeys is under the influence of the motor cortex, which, however, may be exerted to a major extent via indirect pathways. The electrophysiological data suggest a discrete rather than a diffuse relationship with the LRN.

Nuclear structure of 170Tm from neutron-capture and (d,p)-reaction measurements.

Abstract: The nuclide /sup 231/Th was investigated with the reactions /sup 230/Th(n,..gamma..) /sup 231/Th, /sup 230/Th(n,..gamma..e)/sup 231/Th, and /sup 230/Th(d,p)/sup 231/Th. Gamma rays from average resonance capture were measured, in addition to the usual thermal neutron capture spectroscopy. From these data, 70 excited levels in /sup 231/Th were identified and, of these, 57 were placed in 18 rotational bands with assigned configurations. Candidates have been proposed for all expected Nilsson states below 750 keV, albeit with varying degrees of confidence, including the (5/2)/sup +/(622), (7/2)/sup +/(624), (3/2)/sup -/(761), (1/2)/sup -/(770), (1/2)/sup +/(640), and (5/2)/sup -/(503) configurations. Several vibrational states have been identified; a special feature of these is the observation of greater fragmentation of single-particle-0/sup +/ phonon-mixed states than expected theoretically. Assuming degenerate parity doublets indicate the existence of stable octupole deformation, no evidence was found for a tendency toward this phenomenon in /sup 231/Th. The neutron binding energy was determined to be 5118.13 +- 0.20 keV.

On the Orbital Nature of the Luminescent Excited State of Orthometalated Transition Metal Complexes

Abstract: The study of the photochemical and photophysical properties of transition metal complexes is of great interest for theoretical reasons (i.e., for a better understanding of the “excited state dimension” of chemistry) as well as for practical applications (luminescent materials, photocatalytic processes etc.). In the last few years the attention of numerous research groups has been focussed on the search and characterization of transition metal complexes that can play the role of light absorption sensitizers (LAS) and/or light emission sensitizers (LES) for the interconversion between light energy and chemical energy via electron transfer reactions involving electronically excited states (Balzani 1983). To perform systematic experiments in this field as well as to arrive at practical devices we need a series of compounds covering a broad range of excited state energies, lifetimes, and oxidation-reduction potentials. The family of Ru(II)-polypyridine compounds, having as a prototype the famous \({\text{R}\text{u} (\text{b}\text{p}\text{y})_3}^{2+}\) complex, has proved to be very interesting for these purposes, and some hundreds Ru(II)-polypyridine compounds have been synthetized and studied in the last few years (Kalyanasundaram; Juris). Polypyridine complexes of Cr(III) (Jamieson), Rh(III) (De Armond), Ir(III) (Watts), and Os(II) (Sutin) have also been studied, but an ideal LAS and/or LES has not yet been found (Balzani 1986).

Classes of neurons in relation to the laminar organization of the lateral geniculate nucleus in the tree shrew, Tupaia belangeri.

Abstract: We used the rapid Golgi and horseradish peroxidase (HRP) techniques to study the dendritic spread of relay neurons in functionally distinct laminae of the tree shrew dorsal lateral geniculate nucleus (LGNd). On the basis of their dendritic spread in relation to laminar and interlaminar zones, we describe three classes of relay neurons. (1) Unilaminar neurons with multipolar radiate, bitufted, and intermediate types of dendrites. Dendrites of these neurons are confined to one lamina only, but also can have some of their segments in adjacent interlaminar zones. (2) Multilaminar neurons with multipolar radiate, bitufted, and intermediate types of dendrites. Independent of the site of their cell bodies in a laminar or interlaminar zone, these neurons spread their dendrites over two or more laminae. (3) Interlaminar neurons whose cell bodies and dendrites are confined to a single interlaminar zone. Unilaminar neurons are found in all the laminae. In the medial three laminae, they are more of the radiate type, whereas in laminae 4 and 5 their dendrites tend to be more of a tufted nature. Lamina 6 shows a preponderance of the elongated bitufted type. Multilaminar neurons, although less common as compared to the unilaminar, are also observed in all the laminae. Some neurons have their dendrites confined to an interlaminar zone. By retrograde transport of HRP injected into the visual cortex, we have shown that these neurons are, in fact, relay neurons. In addition to relay neurons, there are small interneurons with “axoniform” dendrites and an unmyelinated axon whose arborization is confined within the limits of the neuron's dendritic spread. Neurons of this type are not labeled with HRP injected into the visual cortex. We conclude that although each lamina is functionally specialized by input from ipsilateral or contralateral retina and by segregation of neurons responding to on or off stimuli, some multilaminar neurons can be found in each lamina. Thus, laminar as well as interlaminar zones contain a class of neurons that could provide a cross-talk between the functionally specialized laminae. Most relay neurons in all the laminae, however, confine their dendrites to their home lamina. Thus, the dendritic architecture of relay neurons allows for processing of information both within channels and between channels.

Localization of the in vivo and in vitro transcription initiation site and comparative analysis of the flanking sequences in the two main size classes of Ascaris lumbricoides rDNA

Abstract: An accurate in vitro transcription system which utilizes the cloned 8.8 and 8.4 kb size classes of Ascaris rRNA genes (pAlr8 and pAlr13) and two kinds of cellular extracts from Ascaris oogonia has been established. Both rDNA containing plasmids are efficiently transcribed in vitro by RNA polymerase I from a unique site of rDNA which corresponds to the in vivo initiation site. The in vitro transcription product has a triphosphorylated 5'-end and starts on a G localized 414 bp (pAlr8) upstream of the beginning of the mature 18S rRNA. The promoter region has been delimited by testing the in vitro template activity of a series of restriction fragments. The region essential for the accuracy of initiation is contained within nucleotides -72 to +65, but full efficiency of transcription requires the additional presence of the region from nucleotides +66 to +84. The sequences upstream from position -72 do not appear to modulate the efficiency of specific in vitro initiation. Furthermore, the sequences flanking the transcription initiation site from position -1500 to +570 have been determined in the two cloned representatives of the two rDNA main size classes.