1,113 research outputs found
Passive Electrical Properties of Ventral Horn Neurons in Rat Spinal Cord Slices
No full text Thurbon, David, Hans-R. Lüscher, Thomas Hofstetter, and Stephen J. Redman. Passive electrical properties of ventral horn neurons in rat spinal cord slices. J. Neurophysiol. 79: 2485–2502, 1998. Recordings were made from large neurons located in the ventral horn of transverse spinal cord slices from young rats (7–15 days). Whole cell recordings were made simultaneously with two electrodes from the soma of these neurons, visualized using infra-red differential interference contrast optics. Positive identification of motoneurons could not always be achieved. The response of a neuron to a brief pulse of current delivered by one electrode, and recorded by the other electrode, were matched optimally to responses of a compartmental model of the same neuron with an identical current pulse as input. The compartmental model was based on a reconstruction of the neuron, using Biocytin staining. The compartmental model had three free parameters: specific membrane capacitance ( C m), membrane resistivity ( R m), and cytoplasmatic resistivity ( R i), all assumed to be uniform throughout the neuron. The experimental and model responses could be matched unequivocally for four neurons, giving C m = 2.4 ± 0.5 μF/cm2, R m = 5.3 ± 0.9 kΩ/cm2, and R i = 87 ± 22 Ω/cm. No somatic shunt was required. For the remaining six neurons, a less perfect fit (but still within 95% confidence limits) was indicative of nonhomogeneous membrane properties. The electrotonic length of uncut dendrites was 0.85 ± 0.14 λ. The results resolve the issue of a somatic shunt conductance for motoneurons, relegating it to a microelectrode impalement artifact. They are consistent with previous reports on the electrical compactness of motoneurons to steady state currents and voltages. However, the much higher value of C m (than the previously assumed 1 μF/cm2) implies much greater dendritic attenuation of fast synaptic potentials, and a much enhanced integrative response of motoneurons to synaptic potentials. </jats:p
Timing and Precision of Spike Initiation in Layer V Pyramidal Cells of the Rat Somatosensory Cortex
No full textModeling Action Potential Initiation and Back-Propagation in Dendrites of Cultured Rat Motoneurons
No full text Lüscher, Hans-R. and Matthew E. Larkum. Modeling action potential initiation and back-propagation in dendrites of cultured rat motoneurons. J. Neurophysiol. 80: 715–729, 1998. Regardless of the site of current injection, action potentials usually originate at or near the soma and propagate decrementally back into the dendrites. This phenomenon has been observed in neocortical pyramidal cells as well as in cultured motoneurons. Here we show that action potentials in motoneurons can be initiated in the dendrite as well, resulting in a biphasic dendritic action potential. We present a model of spinal motoneurons that is consistent with observed physiological properties of spike initiation in the initial segment/axon hillock region and action potential back-propagation into the dendritic tree. It accurately reproduces the results presented by Larkum et al. on motoneurons in organotypic rat spinal cord slice cultures. A high Na+-channel density of ḡ Na = 700 mS/cm2 at the axon hillock/initial segment region was required to secure antidromic invasion of the somato-dendritic membrane, whereas for the orthodromic direction, a Na+-channel density of ḡ Na = 1,200 mS/cm2 was required. A “weakly” excitable ( ḡ Na = 3 mS/cm2) dendritic membrane most accurately describes the experimentally observed attenuation of the back-propagated action potential. Careful analysis of the threshold conditions for action potential initiation at the initial segment or the dendrites revealed that, despite the lower voltage threshold for spike initiation in the initial segment, an action potential can be initiated in the dendrite before the initial segment fires a spike. Spike initiation in the dendrite depends on the passive cable properties of the dendritic membrane, its Na+-channel density, and local structural properties, mainly the diameter of the dendrites. Action potentials are initiated more easily in distal than in proximal dendrites. Whether or not such a dendritic action potential invades the soma with a subsequent initiation of a second action potential in the initial segment depends on the actual current source-load relation between the action potential approaching the soma and the electrical load of the soma together with the attached dendrites. </jats:p
Evaluación de características de personalidad de microempresarios eficaces, a través del test de Lüscher
No full textTesis (Licenciado en Psicología)La presente tesis corresponde a una investigación orientada a proponer un perfil de indicadores del Test de los colores de Lüscher asociado a la alta eficacia en una muestra de microempresarios urbanos.
Para tal efecto se revisaron conceptos en torno a las características de la microempresa en Chile, características psicológicas de los microempresarios y la psicología funcional y de los colores del doctor Max Lüscher.
Se aplicó el Test de Lüscher y se entrevistó a una muestra total de treinta sujetos, siendo dieciséis de ellos de alta eficacia y catorce de eficacia media, en base a un criterio de referencia de crecimiento económico. A partir del análisis y validación concurrente de los resultados, se establecieron cinco indicadores diferenciales en el Test de Lüscher que permitieron predecir razonablemente el nivel de eficacia de los microempresarios estudiados. se discuten aplicaciones y proyecciones de estos resultados, especialmente en su relevancia para mejorar las condiciones de asistencia a este tipo de actividad económica de tanta importancia para la superación de la pobreza en Chile
Top-down dendritic input increases the gain of layer 5 pyramidal neurons
No full textThe cerebral cortex is organized so that an important component of feedback input from higher to lower cortical areas arrives at the distal apical tufts of pyramidal neurons. Yet, distal inputs are predicted to have much less impact on firing than proximal inputs. Here we show that even weak asynchronous dendritic input to the distal tuft region can significantly increase the gain of layer 5 pyram-idal neurons and thereby the output of columns in the primary somatosensory cortex of the rat. Noisy currents injected in ramps at different dendritic locations showed that the initial slope of the frequency–current (f/I) relationship increases with the distance of the current injection from the soma. The increase was due to the interaction of dendritic depolarization with back-propagating APs which activated dendritic calcium conductances. Gain increases were accompanied by a change of firing mode from isolated spikes to bursting where the timing of bursts coded the presence of coinci-dent somatic and dendritic inputs. We propose that this dendritic gain modulation and the timing of bursts may serve to associate top-down and bottom-up input on different time scales
Hyperpolarization-Activated Current Ih Disconnects Somatic and Dendritic Spike Initiation Zones in Layer V Pyramidal Neurons
No full textLayer V pyramidal cells of the somatosensory cortex operate with two spike initiation zones. Subthreshold depolarizations are strongly attenuated along the apical dendrite linking the somatic and distal dendritic spike initiation zones. Sodium action potentials, on the other hand, are actively back-propagating from the axon hillock into the apical tuft. There they can interact with local excitatory input leading to the generation of calcium action potentials. We investigated if and how back-propagating sodium action potentials alone, without concomitant excitatory dendritic input, can initiate calcium action potentials in the distal dendrite. In acute slices of the rat somatosensory cortex, layer V pyramidal cells were studied under current-clamp with simultaneous recordings from the soma and the apical dendrite. A train of four somatic action potentials had to reach high frequencies to induce calcium action potentials in the dendrite (“critical frequency,” CF ∼100 Hz). Depolarization in the dendrite reduced the CF, while hyperpolarization increased it. The CF depended on the presence of the hyperpolarization-activated current Ih: blockade with 20 μM 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyridinium chloride (ZD7288) reduced the CF to 68% of control. If the neurons were stimulated with noisy current injections, leading to in-vivo-like irregular spiking, no calcium action potentials were induced in the dendrite. However, after Ih channel blockade, calcium action potentials were frequently seen. These data suggest that Ih prevents initiation of the dendritic calcium action potential by proximal input alone. Dendritic calcium action potentials may therefore represent a unique signature for coincident somatic and dendritic activation
Dyadic self-regulation in couples
No full textDatafiles asssociated with research article in PLOS ONE: Berli, C., Lüscher, J., Luszczynska, A., Schwarzer, R., & Scholz, U. (2018). Couples' daily self-regulation: The Health Action Process Approach at the dyadic level. PloS One, 13: e0205887. doi: 10.1371/journal.pone.020588
Integration of Excitatory Postsynaptic Potentials in Dendrites of Motoneurons of Rat Spinal Cord Slice Cultures
No full text Larkum, Matthew E., Thomas Launey, Alexander Dityatev, and Hans-R. Lüscher. Integration of excitatory postsynaptic potentials in dendrites of motoneurons of rat spinal cord slice cultures. J. Neurophysiol. 80: 924–935, 1998. We examined the attenuation and integration of spontaneous excitatory postsynaptic potentials (sEPSPs) in the dendrites of presumed motoneurons (MNs) of organotypic rat spinal cord cultures. Simultaneous whole cell recordings in current-clamp mode were made from either the soma and a dendrite or from two dendrites. Direct comparison of the two voltage recordings revealed that the membrane potentials at the two recording sites followed each other very closely except for the fast-rising phases of the EPSPs. The dendritic recording represented a low-pass filtered version of the somatic recording and vice versa. A computer-assisted method was developed to fit the sEPSPs with a generalized α-function for measuring their amplitudes and rise times (10–90%). The mean EPSP peak attenuation between the two recording electrodes was determined by a maximum likelihood analysis that extracted populations of similar amplitude ratios from the fitted events at each electrode. For each pair of recordings, the amplitude attenuation ratio for EPSP traveling from dendrite to soma was larger than that traveling from soma to dendrite. The linear relation between mean ln attenuation and distance between recording electrodes was used to map 1/ e attenuations into units of distance (μm). For EPSPs with typical time course traveling from the somatic to the dendritic recording electrode, the mean 1/ e attenuation corresponded to 714 μm; for EPSPs traveling in the opposite direction, the mean 1/ e attenuation corresponded to 263 μm. As predicted from cable analysis, fast EPSPs attenuated more in both the somatofugal and somatopetal direction than did slow EPSPs. For EPSPs with rise times shorter than ∼2.0 ms, the attenuation factor increased steeply. Compartmental computer modeling of the experiments with biocytin-filled and reconstructed MNs that used passive membrane properties revealed amplitude attenuation ratios of the EPSP traveling in both the somatofugal and somatopetal direction that were comparable to those observed in real experiments. The modeling of a barrage of sEPSPs further confirmed that the somato-dendritic compartments of a MN are virtually isopotential except for the fast-rising phase of EPSPs. Large, transient differences in membrane potential are locally confined to the site of EPSP generation. Comparing the modeling results with the experiments suggests that the observed attenuation ratios are adequately explained by passive membrane properties alone. </jats:p
Renormalisation of one-link quark operators for overlap fermions with Lüscher-Weisz gauge action
No full textWe compute lattice renormalisation constants of one-link quark operators (i.e., operators with one covariant derivative) for overlap fermions and Lüscher-Weisz gauge action in one-loop perturbation theory. Among others, such operators enter the calculation of moments of polarised and unpolarised hadron structure functions. Results are given for β=8.45, β=8.0 and mass parameter ρ=1.4, which are commonly used in numerical simulations. We apply mean field (tadpole) improvement to our results. © 2005 Elsevier B.V. All rights reserved
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