The Experts below are selected from a list of 153 Experts worldwide ranked by ideXlab platform
S. A. Greenfield - One of the best experts on this subject based on the ideXlab platform.
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Possible intermixing of neurons from the subthalamic nucleus and substantia nigra pars compacta in the guinea-pig
Experimental Brain Research, 1995Co-Authors: P. G. Overton, J. F. X. O'callaghan, S. A. GreenfieldAbstract:A population of cells in the anterior substantia nigra pars compacta (SNPc) of the guinea-pig have been reported previously that differ from classical dopaminergic neurons in terms of their active and passive membrane properties. To investigate this population further, anterior nigral neurons ( n =17) were compared with neurons in the adjacent subthalamic nucleus (STN; n =26). The anterior nigral neurons were found to be indistinguishable from STN neurons in their action potential characteristics, firing rate, resting membrane potential and input resistance. A low-threshold Calcium Conductance and anomalous rectification could be demonstated in cells from both groups. Furthermore, the gross morphological characteristics of anterior nigral neurons and STN neurons were very similar, as assessed following the intracellular injection of biocytin. A further similarity was seen in the response of the two cell groups to cyanide (200 μM) and apomorphine (500 μM). Cyanide hyperpolarised the membrane potential of all STN neurons and the majority (77.8%) of anterior nigral neurons, in both cases producing a concomitant reduction in firing rate. These changes were accompanied by an increase in membrane Conductance for potassium ions. Apomorphine depolarised the membrane potential of all STN neurons and anterior nigral neurons, in most cases increasing the input resistance (83.3% of STN neurons and 100% of anterior nigral neurons). In both groups of cells, when firing rate was affected, an increase was usually seen. Given the physiological, morphological and pharmacological similarities of STN and anterior nigral neurons, the most parsimonious interpretation is that the anterior nigral neurons belong to the STN. However, the anterior nigral neurons were found in slices that, when resectioned, contained tyrosine hydroxylase (TH)-immunoreactive cell bodies in every section, in a location corresponding to the SNPc. The implication is that in the guinea pig the SNPc and STN (usually considered to be anatomically distinct nuclei) intermix at this level for several hundred microns. This close association of the STN and the compacta was further demonstrated by the presence of TH-positive varicose and non-varicose neuronal processes within the STN.
Thierry Grisar - One of the best experts on this subject based on the ideXlab platform.
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Increased Synchrony with Increase of a Low-Threshold Calcium Conductance in a Model Thalamic Network: A Phase-Shift Mechanism
Neural computation, 2000Co-Authors: Elizabeth Thomas, Thierry GrisarAbstract:A computer model of a thalamic network was used in order to examine the effects of an isolated augmentation in a low-threshold Calcium current. Such an isolated augmentation has been observed in the reticular thalamic (RE) nucleus of the genetic absence epilepsy rat from the Strasbourg (GAERS) model of absence epilepsy. An augmentation of the low-threshold Calcium Conductance in the RE neurons (gTs) of the model thalamic network was found to lead to an increase in the synchronized firing of the network. This supports the hypothesis that the isolated increase in gTs may be responsible for epileptic activity in the GAERS rat. The increase of gTs in the RE neurons led to a slight increase in the period of the isolated RE neuron firing. In contrast, the low-threshold spike of the RE neuron remained relatively unchanged by the increase of gTs. This suggests that the enhanced synchrony in the network was primarily due to a phase shift in the firing of the RE neurons with respect to the thalamocortical neurons. The ability of this phase-shift mechanism to lead to changes in synchrony was further examined using the model thalamic network. A similar increase in the period of RE neuron oscillations was obtained through an increase in the Conductance of the Calcium-mediated potassium channel. This change was once again found to increase synchronous firing in the network.
Randall K. Powers - One of the best experts on this subject based on the ideXlab platform.
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A variable-threshold motoneuron model that incorporates time- and voltage-dependent potassium and Calcium Conductances.
Journal of neurophysiology, 1993Co-Authors: Randall K. PowersAbstract:1. A "threshold-crossing" motoneuron model was developed to relate recently described biophysical features of cat alpha-motoneurons to motoneuron discharge behavior. This model incorporated three features not included in precedent models: 1) a low-threshold, persistent Calcium current; 2) realistic voltage dependencies of the major ionic Conductances; and 3) a variable spike threshold. The effects of these additional biophysical features on model behavior were investigated by successively adding them to a fixed threshold model with a single potassium Conductance. 2. Fixed-threshold models with either one or two potassium Conductances could not produce appropriate discharge behavior. Steady-state frequency-current (F-I) relations were characterized by a continuously increasing slope, unlike the piecewise linear relations observed in real motoneurons. These models also produced unrealistically high discharge rates at the highest levels of "injected" current. 3. The addition of a variable spike threshold, which was made to increase linearly with the magnitude of injected current, could limit maximum discharge rates to more realistic levels. However, steady-state F-I relations still did not exhibit the appropriate shape. 4. The incorporation of a low-threshold Calcium current led to a good quantitative agreement between the steady-state F-I relations produced by the model and those obtained in real motoneurons. In addition, the steady-state relation between total membrane current and membrane voltage (I-V relation) of the model was very similar to those measured in real motoneurons. The model's I-V and F-I relations were both very sensitive to the exact form of the steady-state relation between the magnitude of the Calcium Conductance and membrane voltage. 5. Additional modifications, which included a second Calcium Conductance and a factor relating spike threshold to membrane voltage, helped to produce more realistic afterhyperpolarizations and first-interval F-I relations. 6. Bistable discharge behavior could be produced by reducing the slow potassium Conductance and increasing the time constants governing the activation and deactivation of the low-threshold Calcium Conductance. 7. The final model thus reproduces a wide range of motoneuron behaviors including subthreshold rectification, piecewise linear first interval and steady-state F-I relations, and, with appropriate modifications, bistable discharge behavior. Nonetheless, by simplifying the representation of fast spike Conductances as well as the kinetics of the other ionic Conductances, the model remains simple enough to be incorporated into a larger neural network.
Dirk L. Ypey - One of the best experts on this subject based on the ideXlab platform.
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The block of total and N-type Calcium Conductance in mouse sensory neurons by the local anesthetic n-butyl-p-aminobenzoate.
Anesthesia and analgesia, 2005Co-Authors: Jeroen P. Beekwilder, Daniel L. B. Winkelman, Gertrudis Th. H. Van Kempen, Rutgeris J. Van Den Berg, Dirk L. YpeyAbstract:To contribute to the understanding of the mechanism underlying selective analgesia by epidural application of suspensions of the local anesthetic butamben (n-butyl-p-aminobenzoate; BAB), we investigated the effect of dissolved BAB on Calcium channels in sensory neurons. Small-diameter dorsal root ganglion neurons from newborn mice were used to measure whole-cell barium or Calcium currents through Calcium channels upon voltage-clamp stimulation. BAB suppressed the voltage-step-evoked barium current of these cells in a concentration-dependent manner with a 50% inhibitory concentration of 207 +/- 14 microM (n = 40). A similar concentration dependency was found for the pharmacologically isolated N-type component of the whole-cell barium current. The time constants of inactivation and deactivation of the N-type current became smaller in the presence of BAB, thus suggesting that kinetic changes are involved in the inhibition of this current. BAB caused a similar inhibition of the total Calcium current and its N-type component when these currents were evoked by command potentials with the shape of an action potential. This inhibition of Calcium currents by BAB should be considered in the search for the mechanism of selective analgesia by epidural suspensions of this local anesthetic.
A. Den Hertog - One of the best experts on this subject based on the ideXlab platform.
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Generation of slow-wave-type action potentials in canine colon smooth muscle involves a non-L-type Ca2+ Conductance.
The Journal of physiology, 1991Co-Authors: Jan D. Huizinga, Laura Farraway, A. Den HertogAbstract:1. The hypothesis was addressed that a non-L-type Calcium Conductance is involved in the generation of the initial part of the slow-wave-type action potential in the canine colon. 2. In the absence of a sodium and chloride gradient (NaCl replaced by glucamine), and in the presence of nitrendipine (in 'glucamine-nitrendipine' Krebs solution), a major portion of the upstroke potential of the slow wave persists at unchanged frequency. 3. In 'glucamine-nitrendipine' Krebs solution, the rate of rise and amplitude of the upstroke potential is reduced by removal of extracellular Calcium in a concentration-dependent manner. 4. The rate of rise and the amplitude of the upstroke potential is in a concentration-dependent manner reduced by Ni2+ greater than Cd2+ greater than Co2+ greater than Mg2+. 5. In 'glucamine-nitrendipine' Krebs solution, Ba2+ cannot replace Ca2+ in the generation of the upstroke potential. 6. Positive evidence was obtained for the hypothesis that a non-L-type Calcium Conductance is involved in the initiation of the slow-wave-type action potential in colonic smooth muscle.
