Tonic neuron in spinal lamina I: prolongation of subthreshold depol. (Prescott and De Koninck 2005)

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Accession:53569
Model demonstrates mechanism whereby two kinetically distinct inward currents act synergistically to prolong subthreshold depolarization. The important currents are a persistent Na current (with fast kinetics) and a persistent Ca current (with slower kinetics). Model also includes a slow K current and transient Ca current, in addition to standard HH currents. Model parameters are set to values used in Fig. 8A. Simulation shows prolonged depolarizations in response to two brief stimuli.
Reference:
1 . Prescott SA, De Koninck Y (2005) Integration time in a subset of spinal lamina I neurons is lengthened by sodium and calcium currents acting synergistically to prolong subthreshold depolarization. J Neurosci 25:4743-54 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type: Neuron or other electrically excitable cell;
Brain Region(s)/Organism:
Cell Type(s): Spinal cord lamina I neuron;
Channel(s): I Na,p; I K,Ca; I Calcium;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Action Potential Initiation; Nociception; Delay; Calcium dynamics;
Implementer(s): Prescott, Steven [steve.prescott at sickkids.ca]];
Search NeuronDB for information about:  I Na,p; I K,Ca; I Calcium;
Files displayed below are from the implementation
Readme for model associated with the paper

Prescott SA, De Koninck Y. (2005) Integration time in a subset of
spinal lamina I neurons is lengthened by sodium and calcium currents
acting synergistically to prolong subthreshold depolarization. 
J Neurosci. 25(19):4743-54. 

Abstract:
Lamina I of the spinal dorsal horn plays an important role in 
processing and relaying nociceptive information to the brain. 
It comprises physiologically distinct cell types that process 
information in fundamentally different ways: tonic neurons fire 
repetitively during stimulation and display prolonged EPSPs, 
suggesting operation as integrators, whereas single-spike neurons
act like coincidence detectors. Using whole-cell recordings from a 
rat spinal slice preparation,weset out to determine the basis for 
prolonged EPSPs in tonic cells and the implications for signal 
processing. Kinetics of synaptic currents could not explain 
differences in EPSP kinetics. Instead, tonic neurons were found to 
express a persistent sodium current, INa,P , that amplified and 
prolonged depolarization in response to brief stimulation. Tonic 
neurons also expressed a persistent calcium current, ICa,P , that 
contributed to prolongation but not to amplification. Simulations
using NEURON software demonstrated that INa,P was necessary and 
sufficient to explain amplification, whereas INa,P and ICa,P acted
synergistically to prolong depolarization: initial activation of the
slower current (ICa,P) depended on the faster current (INa,P) but
maintained activation of the faster current likewise depended on the
slower current. Additional investigation revealed that INa,P and 
ICa,P could dramatically increase integration time (>30X) and 
thereby encourage temporal summation but at the expense of spike 
time precision. Thus, by prolonging subthreshold depolarization, 
intrinsic inward currents allow tonic neurons in spinal lamina I
to specialize as integrators that are optimally suited to encode
stimulus intensity.

Model Notes:
Model demonstrates mechanism whereby two kinetically distinct 
inward currents act synergistically to prolong subthreshold 
depolarization.  The important currents are a persistent Na current
(with fast kinetics) and a persistent Ca current (with slower 
kinetics).  Model also includes a slow K current and transient Ca 
current, in addition to standard HH currents.  Model parameters are
set to values used in Fig. 8A.  Simulation shows prolonged 
depolarizations in response to two brief stimuli.

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mswin:
Expand the archive.  Run mknrndll and traverse to the newly created
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Then double click the mosinit.hoc file in windows explorer.

Unix:
Expand the archive with 
unzip *.zip
Compile the NEURON mod files by running nrnivmodl in the newly created directory.  
Type 
nrngui mosinit.hoc
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The mod files are automatically compiled and the simulation starts automatically.

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Note:  The voltage-gated mechanisms have been revised to allow 
adaptive integration, rather than fixed time step integration 
with dt = 0.01 ms as was done in the paper.  This allows the 
simulation to run faster without loss of accuracy.  Also, the 
initial membrane potential has been changed from -63 to -62.65 mV, 
which is the resting potential for this particular model 
implementation.

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