Dorsal root ganglion (DRG) neuronal model (Kovalsky et al. 2009)

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This model, diverged from oscillatory parameters seen in live cells and failed to produce characteristic ectopic discharge patterns. Here we show that use of a more complete set of Na+ conductances--which includes several delayed components--enables simulation of the entire repertoire of oscillation-triggered electrogenic phenomena seen in live dorsal root ganglion (DRG) neurons. This includes a physiological window of induction and natural patterns of spike discharge. An INa+ component at 2-20 ms was particularly important, even though it represented only a tiny fraction of overall INa+ amplitude. With the addition of a delayed rectifier IK+ the singlet firing seen in some DRG neurons can also be simulated. The model reveals the key conductances that underlie afferent ectopia, conductances that are potentially attractive targets in the search for more effective treatments of neuropathic pain.
1 . Kovalsky Y, Amir R, Devor M (2009) Simulation in sensory neurons reveals a key role for delayed Na+ current in subthreshold oscillations and ectopic discharge: implications for neuropathic pain. J Neurophysiol 102:1430-42 [PubMed]
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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): Dorsal Root Ganglion (DRG) cell;
Channel(s): I K; I Sodium; Late Na;
Gap Junctions:
Simulation Environment: NEURON;
Model Concept(s): Bursting; Ion Channel Kinetics; Pathophysiology;
Implementer(s): Devor, Marshall [marshlu at];
Search NeuronDB for information about:  I K; I Sodium; Late Na;
TITLE inter.mod
:v1/2 of minf is -25.29 and the slope factor is 9.052
        (mA) = (milliamp)
        (mV) = (millivolt)
	(S) = (siemens)
? interface
        SUFFIX inter
        USEION na READ ena WRITE ina
        RANGE gnabar, gna, ina
        GLOBAL minf, mtau, hinf, htau
        gnabar = 0 (S/cm2)	<0,1e9>            
        m h
        v (mV)
        celsius (degC)
        ena (mV)
	gna (S/cm2)	
	ina (mA/cm2)
        minf hinf
	mtau (ms) htau (ms)
LOCAL mexp, hexp
? currents
        SOLVE states METHOD cnexp
        m = minf
        gna = gnabar*m*h
	ina = gna*(v - ena)	
	m = minf
	h = hinf

? states
DERIVATIVE states {  
        h' = (hinf-h)/htau      

? rates
PROCEDURE rates(v(mV)) {  :Computes rate and other constants at current v.
                      :Call once from HOC to initialize inf at resting v.
        LOCAL  alpha, beta, sum
        TABLE minf, mtau, hinf, htau DEPEND celsius FROM -100 TO 100 WITH 200

	q10 = 3^((celsius - 6.3)/10)
                :"m" sodium activation system
        alpha = .1 * vtrap(-(v+25),10)
        beta =  4 * exp(-(v+50)/18)
        sum = alpha + beta
        minf = alpha/sum
                :"h" sodium inactivation system 
	htau = 0.2218*exp(-0.06883*v)  :Caffrey
        hinf = (1+exp((v+72.5)/8))^-1  :numbers from page 286 + shift
FUNCTION vtrap(x,y) {  :Traps for 0 in denominator of rate eqns.
        if (fabs(x/y) < 1e-6) {
                vtrap = y*(1 - x/y/2)
                vtrap = x/(exp(x/y) - 1)