Showing papers by "University of Fribourg published in 1993"

Responses of monkey dopamine neurons to reward and conditioned stimuli during successive steps of learning a delayed response task

Abstract: The present investigation had two aims: (1) to study responses of dopamine neurons to stimuli with attentional and motivational significance during several steps of learning a behavioral task, and (2) to study the activity of dopamine neurons during the performance of cognitive tasks known to be impaired after lesions of these neurons Monkeys that had previously learned a simple reaction time task were trained to perform a spatial delayed response task via two intermediate tasks During the learning of each new task, a total of 25% of 76 dopamine neurons showed phasic responses to the delivery of primary liquid reward, whereas only 9% of 163 neurons responded to this event once task performance was established This produced an average population response during but not after learning of each task Reward responses during learning were significantly more numerous and pronounced in area A10, as compared to areas A8 and A9 Dopamine neurons also showed phasic responses to the two conditioned stimuli These were the instruction cue, which was the first stimulus in each trial and indicated the target of the upcoming arm movement (58% of 76 neurons during and 44% of 163 neurons after learning), and the trigger stimulus, which was a conditioned incentive stimulus predicting reward and eliciting a saccadic eye movement and an arm reaching movement (38% of neurons during and 40% after learning) None of the dopamine neurons showed sustained activity in the delay between the instruction and trigger stimuli that would resemble the activity of neurons in dopamine terminal areas, such as the striatum and frontal cortex Thus, dopamine neurons respond phasically to alerting external stimuli with behavioral significance whose detection is crucial for learning and performing delayed response tasks The lack of sustained activity suggests that dopamine neurons do not encode representational processes, such as working memory, expectation of external stimuli or reward, or preparation of movement Rather, dopamine neurons are involved with transient changes of impulse activity in basic attentional and motivational processes underlying learning and cognitive behavior

Wortmannin is a potent phosphatidylinositol 3-kinase inhibitor: the role of phosphatidylinositol 3,4,5-trisphosphate in neutrophil responses

Abstract: Phosphatidylinositol 3,4,5-trisphosphate (PtdInsP3) is rapidly produced upon exposure of neutrophils to the chemoattractant N-formylmethionyl-leucylphenylalanine (fMLP), and has been proposed to act as a second messenger mediating actin polymerization and respiratory-burst activity. Here we present evidence that wortmannin, a known inhibitor of respiratory-burst activity, acts on PtdIns 3-kinase, the enzyme producing PtdInsP3 from PtdIns(4,5)P2. Pretreatment of 32P-labelled human neutrophils with 100 nM wortmannin totally abolished fMLP-mediated PtdInsP3 production, raised PtdInsP2 levels, and did not affect cellular PtdInsP and PtdIns contents. The inhibitory effect on PtdInsP3 formation in intact cells was dose-dependent, with an IC50 of approximately 5 nM. Similar results were obtained with PtdIns 3-kinase immunoprecipitated by antibodies against the p85 regulatory subunit: wortmannin totally inhibited PtdIns3P production in immunoprecipitates at concentrations of 10-100 nM (IC50 approximately 1 nM). These results illustrate the direct and specific inhibition of PtdIns 3-kinase by wortmannin. Since agonist-mediated respiratory-burst activation is most sensitive to wortmannin (IC50 = 12 nM), this suggests that agonist-mediated PtdInsP3 formation is indispensable for this cell response. Neutrophils pretreated with wortmannin develop oscillatory changes in F-actin content, but actin polymerization in response to fMLP is not inhibited. This, and the absence of PtdInsP3 under these conditions, are in agreement with a modulatory role for PtdInsP3 in cytoskeletal rearrangements, but imply that PtdInsP3 production is not a primary event triggering elongation of actin filaments in neutrophils.

Calcium-binding proteins: selective markers of nerve cells.

Abstract: A characteristic of nerve cells is their ability to propagate an action potential and to communicate through specialized contact zones, called synapses. Synapses have received much attention from neurobiologists over the last 40 years, after their existence was ascertained by electron microscopy (De Robertis and Bennett 1954; Palade and Palay 1954). At the synapse, information is transferred from one cell to the contiguous one by neurotransmitters, viz. acetylcholine, biogenic amines and amino acids, or neuromodulators. These are mostly small peptides acting either alone or in combination (Furness et al. 1988; H6kfelt 1992). Thus, nerve cells communicate mostly by the intermediary of chemical signals. These important concepts have had a tremendous impact on the \"Zeitgeist\" of the neurosciences and have led many scientists to try to unravel the exact mechanisms of synaptic transmission. Furthermore, the discovery that the symptoms in Parkinson's disease are the consequence of a decrease in the concentration of the neurotransmitter dopamine in the basal ganglia, and that an improvement can be achieved by a dopamine precursor that passes through the blood-brain barrier (Hornykiewicz 1966), has helped to shape the opinion that many neurological and psychiatric diseases can be explained as defects in neurotransmitter systems. In the meantime, major efforts have been directed at understanding the way in which neurotransmitters

Comparison of the Connectional Properties of the Two Forelimb Areas of the Rat Sensorimotor Cortex: Support for the Presence of a Premotor or Supplementary Motor Cortical Area

Abstract: The existence of multiple motor cortical areas that differ in some of their properties is well known in primates, but is less clear in the rat. The present study addressed this question from the point of view of connectional properties by comparing the afferent and efferent projections of the caudal forelimb area (CFA), considered to be the equivalent of the forelimb area of the primary motor cortex (MI), and a second forelimb motor representation, the rostral forelimb area (RFA). As a result of various tracing experiments (including double labeling), it was observed that CFA and RFA had reciprocal corticocortical connections characterized by preferential, asymmetrical, laminar distribution, indicating that RFA may occupy a different hierarchical level than CFA, according to criteria previously discussed in the visual cortex of primates. Furthermore, it was found that RFA, but not CFA, exhibited dense reciprocal connections with the insular cortex. With respect to their efferent projection to the basal ganglia, it was observed that CFA projected very densely to the lateral portion of the ipsilateral caudate putamen, whereas the contralateral projection was sparse and more restricted. The ipsilateral projection originating from RFA was slightly less dense than that from CFA, but it covered a larger portion of the caudate putamen (in the medial direction); the contralateral projection from RFA to the caudate putamen was of the same density and extent as the ipsilateral projection. The reciprocal thalamocortical and corticothalamic connections of RFA and CFA differed from each other in the sense that CFA was mainly interconnected with the ventrolateral thalamic nucleus, while RFA was mainly connected with the ventromedial thalamic nucleus. Altogether, these connectional differences, compared with the pattern of organization of the motor cortical areas in primates, suggest that RFA in the rat may well be an equivalent of the premotor or supplementary motor area. In contrast to the corticocortical, corticostriatal, and thalamocortical connections, RFA and CFA showed similar efferent projections to the subthalamic nucleus, substantia nigra, red nucleus, tectum, pontine nuclei, inferior olive, and spinal cord.

Some difficulties of ecological thinking, considered from a critical systems perspective: A plea for critical holism

Abstract: We probably have simplified matters too much. We tend to talk about systems thinking and practice as if we knew what they are. The fashionable call for “holistic” or “systems” thinking in ecological issues provides a major example. This much is certain: the quest for comprehensiveness, although it represents an epistemologically necessary idea, is not realizable. If we assume that it is realizable, the critical idea underlying the quest will be perverted into its opposite, i.e., into a false pretension to superior knowledge and understanding—a danger of which the environmental movement does not always appear to be sufficiently aware. My question, therefore, is this: How can we deal critically with the fact that our thinking, and hence our knowledge, designs, and actions, cannot possibly be comprehensive, in the sense that we never “comprehend” all that ought to be understood before we pass to judgment and action? What consequences does this fact imply for a critical systems approach to ecological concerns and, ultimately, for our concepts of rationality in general?

Reward-related activity in the monkey striatum and substantia nigra.

Abstract: Publisher Summary The basal ganglia are often considered as parts of the motor system. This concept is derived from the movement disorders arising in Parkinsonism, choreaand hemiballism, from the projections of the primary motor and somatosensory cortex to the putamen and subthalamic nucleus, and from movement-related neuronal activity in several basal ganglia nuclei. The motor role of the basal ganglia can be extended to include preparatory activity preceding the execution of limb and eye movements, which reflects neuronal access to stored information about forthcoming events and thus constitutes a higher function than primary movement processes. However, there are a number of indications suggesting a larger involvement of the basal ganglia in behavioral processes. In particular, the basal ganglia, notably the striatum, receive input from several limbic structures, such as the amygdala and the orbitofrontal and cingulate cortex. In addition, results from lesioning and psychopharmacological experiments indicate that the functions of the nigrostriatal, mesolimbic and mesocortical dopamine systems encompass a larger spectrum of behavioral processes than a primary motor role suggested by the movement disorders. In particular, they appear to participate in motivational processes determining behavioral activity. In order to assess the involvement of the basal ganglia in motivational processes, this chapter discusses the activity of neurons in the dorsal and ventral striatum and of dopamine neurons in the substantia nigra in relation to the delivery of primary rewards. Examples of primary rewards are food objects or fluids that are approached by subjects through innate or instinctive behavior, or are learned very early during ontogenesis. Primary rewards may serve to establish and sustain learned appetitive behavior, in which case they are called positive reinforcers. Thus, primary rewards are key components in the motivational control of behavior.

Determinants of environmental action with regard to climatic change

Abstract: The study of human dimensions of global climatic change is still in the initial stage of development. Several attempts have been undertaken to define sensible research strategies in the field but until now relatively little empirical work has been undertaken and there is a lack of sound theoretical arguments. The present paper presents a theory-based empirical study of determinants influencing the probability that somebody takes climate-relevant environmental action. Important methodological differences between current models of climate dynamics and models of human reality are discussed in order to build three models of climate-related environmental action. A model focussed on the information transfer from science to the public at large is compared with a model focussed on sociodemographic characteristics and with a model focussed on socio-cultural variables like interpersonal rules and social networks. The hypothesis that the latter model is strongly superior to the former ones is tested and confirmed. Some implications for interdisciplinary cooperation and for policy making are discussed.

Long range correlation in human writings

Abstract: We study long range correlation in various human writings by mapping them into a simple 1d random walk model. This approach allows us to obtain better quality scaling data than the traditional power spectrum methods. Optimally written computer programs seem to have the highest scaling exponent, i.e., close to that of ideal 1/f noise. Literature, on the other hand, leads to smaller exponents. The Bible, however, has the strongest correlation among the Roman letter writings examined.

Magnetic‐Field‐Dependent Electronic Relaxation of Gd3+ in Aqueous Solutions of the Complexes [Gd(H2O)8]3+, [Gd(propane‐1,3‐diamine‐N,N,N′,N′‐tetraacetate)(H2O)2]−, and [Gd(N,N′‐bis[(N‐methylcarbamoyl)methyl]‐3‐azapentane‐1,5‐diamine‐3,N,N′‐triacetate)(H2O)] of interest in magnetic‐resonance imaging

Abstract: EPR Spectra have been measured for aqueous solutions of a series of Gd3+ complexes at variable temperature and a range of magnetic fields; S-band (0.14 T), X-band (0.34 T), Q-band (1.2 T), and 2-mm-band (5.0 T). The major contribution to the observed line widths is magnetic-field-dependent and is interpreted as being due to the modulation of the zero-field splitting produced by distortion of the complexes from perfect symmetry. The transverse and longitudinal relaxation matrices for an 8S ion with such an interaction have been calculated using Redfield theory with vector-coupling methods, and diagonalised numerically to obtain relaxation rates and intensities for the degenerate transitions which contribute to the multiplet. The observed line width, which is inversely proportional to the magnetic field at low temperatures, is best described by the intensity-weighted mean transverse relaxation time for the four transitions with non-zero intensity. A least-squares fit of the data yields the square of the zero-field splitting tensor, Δ2, and a correlation time, τv, with activation energy, Ev. The physical significance of these parameters and the extent of validity of the theoretical approach are considered. The parameters are used to predict the magnetic-field dependence of the longitudinal and transverse electronic relaxation times, which are discussed in the context of their relevance to 1H-NMR relaxivity.

Neuronal morphology and efferent projections of the dorsal nucleus of the lateral lemniscus in the rat.

Abstract: The dorsal nucleus of the lateral lemniscus (DLL) is the main source of inhibitory influence in the auditory brainstem of mammals. The cytoarchitecture and connectional properties of DLL were established in the cat in contrast to the rat. The goal of the present study was to establish to what extent the anatomical properties of the rat DLL compare to those of the cat, thus providing a basis of interpretation for future functional studies in the rat, an animal model used more and more in the auditory system. DLL of the rat contains four well-differentiated neuronal types, as seen in Nissl-stained material. Type I neurons are large and multipolar with abundant cytoplasm and darkly stained Nissl substance. Type II neurons are large, bipolar and darkly stained in Nissl material. Type III neurons are medium in size and their soma is round or ovoid. Type IV neurons are small and round with scant cytoplasm; they seem to be also the least common neuronal type of the DLL. After Phaseolus vulgaris-leucoagglutinin or biocytin injections in the DLL, fibers and terminals labeled by orthograde transport were observed in the corresponding region of the contralateral DLL and in the inferior colliculus, bilaterally. A few labeled fibers and terminal fields were seen in the deep layers of the superior colliculus bilaterally, as well as in the medial division of the medial geniculate body and, even more rostrally, in the posterior nucleus of the thalamus. Descending projections from DLL terminated in the periolivary regions of the ipsilateral superior olivary complex. Retrograde tracing based on injections of horseradish peroxidase in the various targets of the DLL confirmed the connections established with orthograde labeling.

Trust in Advance: on the professional morality of teachers

Abstract: This article introduces an understanding of professional morality that evolves around the notions of discourse and discursive conflict solutions. After a sketch of the basic ideas, a typology of decision‐making strategies is described and particular elements of discursive procedures in conflict solving are highlighted. In the second part of the paper, major goals and results of a series of empirical studies are delineated. The question whether the fundamental ethical orientations of teachers can be influenced and changed was addressed in an intervention study of which the design and selected results are reported.

Modulation of Sustained Electromyographic Activity by Single Intracortical Microstimuli: Comparison of Two Forelimb Motor Cortical Areas of the Rat

Abstract: In rats, a rostral and a caudal forelimb motor area (RFA and CFA, respectively) have been distinguished on the basis of intracortical microstimulation effects (see Neafsey et al., 1986, for a review). The goal of the present study was to assess and compare their relative connectional strength with target motor units of the forelimb. This was achieved by averaging modulation responses of sustained electromyographic (EMG) activity triggered by single intracortical microstimuli (S-ICMS) of relatively low intensity (mostly below 35 μA) to minimize both direct and transsynaptic current spread. In chronically prepared and ketamine-sedated rats, this method produced prominent peaks and troughs in the averaged EMG at short latencies with S-ICMS currents as low as 5 μA. S-ICMS at 30–50 μA in CFA sometimes even elicited visible twitches and an EMG burst of the contralateral wrist or digits following each stimulation pulse. Increasing S-ICMS currents to about 1.5 mA revealed a sudden shortening of EMG response laten...

Central retinal area is not the site where ganglion cells are generated first.

Abstract: The development of retinal ganglion cells (RGC) was studied in the chick from stage 18 to adulthood. Our main objectives were to identify the retinal site where the first RGCs differentiate, to locate this site relative to the optically defined central retinal area, and to map the spatial arrangement of the RGC field at different stages in development. The eyes of the experimental animals were fixed and serially sectioned. The borders of RGC fields were determined from the presence of either ganglion cell perikarya or ganglion cell axons. In seven cases between stages 21 and 26, the borders of the RGC fields were confirmed electron microscopically. The serial sections together with the RGC fields were then reconstructed in three dimensions. The reconstructed retinae were projected onto a plane by using the radially equidistant polar azimuthal projection. First, RGCs appear dorsal to the apex of the optic fissure. Ganglion cell development then initially spreads out symmetrically with respect to the optic fissure. However, from stage 29 on, the nasal half of the retina expands much more than the temporal half. This asymmetrical growth entails that the optic fissure is eventually located in the temporal half of the retina in the mature animal. The RGC fields of the embryonic stages were superimposed on the retina of a visually active animal according to their real size and position. It turned out that the central retinal area was at least 2 mm away from the site where the first RGCs were generated. It is not before stage 28 that the prospective central retinal area is included into the expanding ganglion cell field. The fact that RGCs at the central retinal area are generated 2.5 days later than first RGCs near the apex of the optic fissure has important implications for the formation of the retinotectal projection. © 1993 Wiley-Liss, Inc.

Non-linear Langevin model of geomorphic erosion processes

Abstract: SUMMARY Recent spectral studies of vertical transect profiles of landscapes and mountains have shown them to be self-affine fractals, i.e. the rms height fluctuation Ah(L) averaged over a distance L scales as Ah(L) - Lx with x = 0.5 f 0.1, related to the fractal dimension Df = 2 - x = 1.5 of the horizontal contours. We propose that self-affine rough landscapes are created by the interplay of non-linearity and noise. To illustrate this idea and model the formation of such structures, we suggest a non-linear stochastic equation ahla? = DV*h + A(Vh)' + ~(r, t), which is the generalization of the deterministic Culling's linear equation. The non-linear term h(Vh)* comes from the requirement that erosion is proportional to the exposed area of the landscape; the noise term ~(r, t) accounts for the fact that erosion is locally irregular, as a result of the heterogeneity of soils and distribution of storms. Using this general framework, we recover the scaling law Ah(L) - Lx with x 2 0.4. Several novel avenues of research emerge from this analysis to further quantify geological data.