Retinal ganglion cells responses and activity (Tsai et al 2012, Guo et al 2016)

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Accession:260653
From the abstracts: "Retinal ganglion cells (RGCs), which survive in large numbers following neurodegenerative diseases, could be stimulated with extracellular electric pulses to elicit artificial percepts. How do the RGCs respond to electrical stimulation at the sub-cellular level under different stimulus configurations, and how does this influence the whole-cell response? At the population level, why have experiments yielded conflicting evidence regarding the extent of passing axon activation? We addressed these questions through simulations of morphologically and biophysically detailed computational RGC models on high performance computing clusters. We conducted the analyses on both large-field RGCs and small-field midget RGCs. ...", "... In this study, an existing RGC ionic model was extended by including a hyperpolarization activated non-selective cationic current as well as a T-type calcium current identified in recent experimental findings. Biophysically-defined model parameters were simultaneously optimized against multiple experimental recordings from ON and OFF RGCs. ...
Reference:
1 . Guo T, Tsai D, Morley JW, Suaning GJ, Kameneva T, Lovell NH, Dokos S (2016) Electrical activity of ON and OFF retinal ganglion cells: a modelling study. J Neural Eng 13:025005 [PubMed]
2 . Tsai D, Chen S, Protti DA, Morley JW, Suaning GJ, Lovell NH (2012) Responses of retinal ganglion cells to extracellular electrical stimulation, from single cell to population: model-based analysis. PLoS One 7:e53357 [PubMed]
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Model Information (Click on a link to find other models with that property)
Model Type: Synapse; Extracellular;
Brain Region(s)/Organism: Retina;
Cell Type(s): Retina ganglion GLU cell;
Channel(s):
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Oscillations; Activity Patterns; Development;
Implementer(s): Tsai, David [d.tsai at unsw.edu.au];
Search NeuronDB for information about:  Retina ganglion GLU cell;
TITLE decay of submembrane calcium concentration
:
: Internal calcium concentration due to calcium currents and pump.
: Differential equations.
:
: This file contains two mechanisms:
:
: 1. Simple model of ATPase pump with 3 kinetic constants (Destexhe 1992)
:
:       Cai + P <-> CaP -> Cao + P  (k1,k2,k3)
:
:   A Michaelis-Menten approximation is assumed, which reduces the complexity
:   of the system to 2 parameters: 
:       kt = <tot enzyme concentration> * k3  -> TIME CONSTANT OF THE PUMP
:    kd = k2/k1 (dissociation constant)    -> EQUILIBRIUM CALCIUM VALUE
:   The values of these parameters are chosen assuming a high affinity of 
:   the pump to calcium and a low transport capacity (cfr. Blaustein, 
:   TINS, 11: 438, 1988, and references therein).  
:
:   For further information about this this mechanism, see Destexhe, A. 
:   Babloyantz, A. and Sejnowski, TJ.  Ionic mechanisms for intrinsic slow 
:   oscillations in thalamic relay neurons. Biophys. J. 65: 1538-1552, 1993.
:
:
: 2. Simple first-order decay or buffering:
:
:       Cai + B <-> ...
:
:   which can be written as:
:
:       dCai/dt = (cainf - Cai) / taur
:
:   where cainf is the equilibrium intracellular calcium value (usually
:   in the range of 200-300 nM) and taur is the time constant of calcium 
:   removal.  The dynamics of submembranal calcium is usually thought to
:   be relatively fast, in the 1-10 millisecond range (see Blaustein, 
:   TINS, 11: 438, 1988).
:
: All variables are range variables
:
: Written by Alain Destexhe, Salk Institute, Nov 12, 1992
: Modified by TJ Velte, Univ of Minnesota, March 17, 1995

INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}

NEURON {
    SUFFIX cad
    USEION ca READ ica, cai WRITE cai
    RANGE depth,kt,kd,cainf,taur
}

UNITS {
    (molar) = (1/liter)  : moles do not appear in units
    (mM)    = (millimolar)
    (um)    = (micron)
    (mA)    = (milliamp)
    (msM)   = (ms mM)
}

CONSTANT {
    FARADAY = 96489 (coul)  : moles do not appear in units
}

PARAMETER {
    depth  = .1     (um)  : depth of shell
    taur   = 1.5    (ms)  : remove first-order decay
    cainf  = 0.0001 (mM)
    kt     = 1e-5   (mM/ms)
    kd     = 0.0001 (mM)
}

STATE {
    cai  (mM) 
}

INITIAL {
    cai = kd
}

ASSIGNED {
    ica            (mA/cm2)
    drive_channel  (mM/ms)
    drive_pump     (mM/ms)
}
    
BREAKPOINT {
    SOLVE state METHOD euler
}

DERIVATIVE state { 

    drive_channel =  - (10000) * ica / (2 * FARADAY * depth)

    if (drive_channel <= 0.) {
        drive_channel = 0.  : cannot pump below resting level
    }

    drive_pump = -kt * cai / (cai + kd )  : Michaelis-Menten

    if (ica <= kd ) {
        drive_pump = 0.
    }

    cai' = drive_channel + (cainf-cai)/taur
}