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Evaluation of Kinetic Properties of Dendritic Potassium Current in Ghostbursting Model of Electrosensory Neurons  [PDF]
Takaaki Shirahata
Applied Mathematics (AM) , 2015, DOI: 10.4236/am.2015.61013
Abstract: A ghostbursting model is a mathematical model (a system of coupled nonlinear ordinary differential equations) that is based on the Hodgkin-Huxley formalism. The ghostbursting model describes bursting similar to the in vitro bursting of electrosensory neurons of weakly electric fish. Doiron and coworkers have focused on two system parameters of the model: maximal conductance of the dendritic potassium current \"\" and the current injected into the somatic compartment\"\" . They performed bifurcation analysis and revealed that the \"\" -parameter space was divided into three dynamical states: quiescence, periodic tonic spiking, and bursting. The present study focused on a third system parameter: the time constant of dendritic potassium current inactivation\"\" . A computer simulation of the model revealed how the dynamical states of the \"\" -parameter space changed in response to variations of \"\" .
Characterization of Voltage-Gated Ca2+ Conductances in Layer 5 Neocortical Pyramidal Neurons from Rats  [PDF]
Mara Almog, Alon Korngreen
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0004841
Abstract: Neuronal voltage-gated Ca2+ channels are involved in electrical signalling and in converting these signals into cytoplasmic calcium changes. One important function of voltage-gated Ca2+ channels is generating regenerative dendritic Ca2+ spikes. However, the Ca2+ dependent mechanisms used to create these spikes are only partially understood. To start investigating this mechanism, we set out to kinetically and pharmacologically identify the sub-types of somatic voltage-gated Ca2+ channels in pyramidal neurons from layer 5 of rat somatosensory cortex, using the nucleated configuration of the patch-clamp technique. The activation kinetics of the total Ba2+ current revealed conductance activation only at medium and high voltages suggesting that T-type calcium channels were not present in the patches. Steady-state inactivation protocols in combination with pharmacology revealed the expression of R-type channels. Furthermore, pharmacological experiments identified 5 voltage-gated Ca2+ channel sub-types – L-, N-, R- and P/Q-type. Finally, the activation of the Ca2+ conductances was examined using physiologically derived voltage-clamp protocols including a calcium spike protocol and a mock back-propagating action potential (mBPAP) protocol. These experiments enable us to suggest the possible contribution of the five Ca2+ channel sub-types to Ca2+ current flow during activation under physiological conditions.
Effects of lithium chloride on outward potassium currents in acutely isolated hippocampal CA1 pyramidal neurons
Chaofeng Zhang,Huizhi Du,Pin Yang
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-2076-2
Abstract: Although lithium possesses neuroprotective functions, the molecular mechanism underlying its actions has not been fully elucidated. In the present paper, the effects of lithium chloride on voltage-dependent potassium currents in the CA1 pyramidal neurons acutely isolated from rat hippocampus were studied using the whole-cell patch-clamp technique. Depolarizing test pulses activated two components of outward potassium currents: a rapidly activating and inactivating component, I A and a delayed component, I K. Results showed that lithium chloride increased the amplitude of I A in a concentration-dependent manner. Half enhancement concentration (EC 50) was 22.80±5.45 μmol·L 1. Lithium chloride of 25 μmol·L 1 shifted the steady-state activation curve and inactivation curve of I A to more negative potentials, but mainly affected the activation kinetics. The amplitude and the activation processes of I K were not affected by lithium chloride. The effects of lithium chloride on potassium channel appear to possess neuroprotective properties by Ca2+-lowing effects modulate neuronal excitability by activating I A in rat hippocampal neurons.
Cholinergic Neuromodulation Changes Phase Response Curve Shape and Type in Cortical Pyramidal Neurons  [PDF]
Klaus M. Stiefel, Boris S. Gutkin, Terrence J. Sejnowski
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003947
Abstract: Spike generation in cortical neurons depends on the interplay between diverse intrinsic conductances. The phase response curve (PRC) is a measure of the spike time shift caused by perturbations of the membrane potential as a function of the phase of the spike cycle of a neuron. Near the rheobase, purely positive (type I) phase-response curves are associated with an onset of repetitive firing through a saddle-node bifurcation, whereas biphasic (type II) phase-response curves point towards a transition based on a Hopf-Andronov bifurcation. In recordings from layer 2/3 pyramidal neurons in cortical slices, cholinergic action, consistent with down-regulation of slow voltage-dependent potassium currents such as the M-current, switched the PRC from type II to type I. This is the first report showing that cholinergic neuromodulation may cause a qualitative switch in the PRCs type implying a change in the fundamental dynamical mechanism of spike generation.
An acetylcholinesterase inhibitor, 3-benzidino-5-methyl-6-phenylpyridazine, blocking outward potassium currents in acutely isolated rat hippocampal pyramidal neurons
HuiZhi Du,MiaoYu Li,Pin Yang
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-008-0569-x
Abstract: 3-benzidino-5-methyl-6-phenylpyridazine (BMP) inhibited electric eel acetylcholinesterase (AChE), with IC50 being 0.58 μmol·L 1. As an AChE inhibitor, the effects of BMP on delayed rectifier potassium current (I K(DR)) and transient outward potassium current (I K(A)) in acutely isolated rat hippocampal pyramidal neurons were studied using the whole cell patch-clamp technique. BMP (0.1–50 μmol·L 1) inhibited I K(DR) and I K(A) in a concentration-dependent and voltage-independent manner. The IC50 value for the blocking action of BMP on I K(DR) and I K(A) was calculated to be 2.92 and 2.11 μmol·L 1, respectively. At the concentration of 10 μmol·L 1, BMP shifted the activation curve of IK(DR) to negative potential by 8.85 mV. Meanwhile, at the concentration of 10 μmol·L 1, BMP also shifted the activation and the steady-state inactivation curve of IK(A) to negative potential by 5.82 mV and 10.02 mV, respectively. In conclusion, BMP potently inhibits I K(DR) and I K(A) in rat hippocampal pyramidal neurons, which may contribute to restore the damaged central nervous system.
An acetylcholinesterase inhibitor, 3-benzidino-5-methyl-6-phenylpyridazine, blocking outward potassium currents in acutely isolated rat hippocampal pyramidal neurons

HuiZhi Du,MiaoYu Li,Pin Yang,

科学通报(英文版) , 2009,
Abstract: 3-benzidino-5-methyl-6-phenylpyridazine (BMP) inhibited electric eel acetylcholinesterase (AChE), with IC50 being 0.58 μmol·L 1. As an AChE inhibitor, the effects of BMP on delayed rectifier potassium current (I K(DR)) and transient outward potassium current (I K(A)) in acutely isolated rat hippocampal pyramidal neurons were studied using the whole cell patch-clamp technique. BMP (0.1–50 μmol·L 1) inhibited I K(DR) and I K(A) in a concentration-dependent and voltage-independent manner. The IC50 value for the blocking action of BMP on I K(DR) and I K(A) was calculated to be 2.92 and 2.11 μmol·L 1, respectively. At the concentration of 10 μmol·L 1, BMP shifted the activation curve of IK(DR) to negative potential by 8.85 mV. Meanwhile, at the concentration of 10 μmol·L 1, BMP also shifted the activation and the steady-state inactivation curve of IK(A) to negative potential by 5.82 mV and 10.02 mV, respectively. In conclusion, BMP potently inhibits I K(DR) and I K(A) in rat hippocampal pyramidal neurons, which may contribute to restore the damaged central nervous system. Supported by National Natural Science Foundation of China (Grant No. 20637010)
Effect of temperature on spiking patterns of neocortical layer 2/3 and layer 6 pyramidal neurons  [PDF]
Tristan Hedrick,Jack Waters
Frontiers in Neural Circuits , 2012, DOI: 10.3389/fncir.2012.00028
Abstract: The spiking patterns of neocortical pyramidal neurons are shaped by the conductances in their apical dendrites. We have previously shown that the spiking patterns of layer 5 pyramidal neurons change with temperature, probably because temperature modulates the electrical coupling between somatic and dendritic compartments. Here we determine whether temperature has similar effects on the spiking patterns of layer 2/3 and layer 6 pyramidal neurons in acute slices of mouse primary motor cortex. In both cell types, decreasing temperature led to more irregular spiking patterns. Our results indicate that a decrease in spiking regularity with decreasing temperature, probably mediated by increased electrical coupling between soma and dendrites, is common to all pyramidal neurons in motor cortex.
Bursts and Isolated Spikes Code for Opposite Movement Directions in Midbrain Electrosensory Neurons  [PDF]
Navid Khosravi-Hashemi, Maurice J. Chacron
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040339
Abstract: Directional selectivity, in which neurons respond strongly to an object moving in a given direction but weakly or not at all to the same object moving in the opposite direction, is a crucial computation that is thought to provide a neural correlate of motion perception. However, directional selectivity has been traditionally quantified by using the full spike train, which does not take into account particular action potential patterns. We investigated how different action potential patterns, namely bursts (i.e. packets of action potentials followed by quiescence) and isolated spikes, contribute to movement direction coding in a mathematical model of midbrain electrosensory neurons. We found that bursts and isolated spikes could be selectively elicited when the same object moved in opposite directions. In particular, it was possible to find parameter values for which our model neuron did not display directional selectivity when the full spike train was considered but displayed strong directional selectivity when bursts or isolated spikes were instead considered. Further analysis of our model revealed that an intrinsic burst mechanism based on subthreshold T-type calcium channels was not required to observe parameter regimes for which bursts and isolated spikes code for opposite movement directions. However, this burst mechanism enhanced the range of parameter values for which such regimes were observed. Experimental recordings from midbrain neurons confirmed our modeling prediction that bursts and isolated spikes can indeed code for opposite movement directions. Finally, we quantified the performance of a plausible neural circuit and found that it could respond more or less selectively to isolated spikes for a wide range of parameter values when compared with an interspike interval threshold. Our results thus show for the first time that different action potential patterns can differentially encode movement and that traditional measures of directional selectivity need to be revised in such cases.
Integration of Subthreshold and Suprathreshold Excitatory Barrages along the Somatodendritic Axis of Pyramidal Neurons  [PDF]
Hysell V. Oviedo, Alex D. Reyes
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0033831
Abstract: Neurons integrate inputs arriving in different cellular compartments to produce action potentials that are transmitted to other neurons. Because of the voltage- and time-dependent conductances in the dendrites and soma, summation of synaptic inputs is complex. To examine summation of membrane potentials and firing rates, we performed whole-cell recordings from layer 5 cortical pyramidal neurons in acute slices of the rat's somatosensory cortex. We delivered subthreshold and suprathreshold stimuli at the soma and several sites on the apical dendrite, and injected inputs that mimic synaptic barrages at individual or distributed sites. We found that summation of subthreshold potentials differed from that of firing rates. Subthreshold summation was linear when barrages were small but became supralinear as barrages increased. When neurons were discharging repetitively the rules were more diverse. At the soma and proximal apical dendrite summation of the evoked firing rates was predominantly sublinear whereas in the distal dendrite summation ranged from supralinear to sublinear. In addition, the integration of inputs delivered at a single location differed from that of distributed inputs only for suprathreshold responses. These results indicate that convergent inputs onto the apical dendrite and soma do not simply summate linearly, as suggested previously, and that distinct presynaptic afferents that target specific sites on the dendritic tree may perform unique sets of computations.
The effects of estrogen on the morphology of the pyramidal neurons of the parietal cortex of female rats
Dreki? Dmitar,Lozan?e Olivera,Milovanovi? N.,Kerkez M.
Acta Veterinaria , 2006, DOI: 10.2298/avb0603215d
Abstract: In this study the effects of a neonatally (3rd day of life) administered single dose (1 mg) of estradiol dipropionate (E2) on the parietal cortex of juvenile (16 days of life) female rats were investigated. The morphology the volume of the soma and the thickness of the apical dendrite were studied in Golgi impregnated pyramidal neurons from both the external and internal pyramidal layers. In the treated female rats the volume of the soma and the thickness of the apical dendrite of pyramidal neurons was increased surpassing the values in the corresponding controls. These findings indicated significant and prolonged effects of a single dose of estrogen administered in the neonatal period, on the parietal neocortical pyramidal neurons of female rats.
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