Excitability of the soma in central nervous system neurons (Safronov et al 2000)

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Accession:62266
The ability of the soma of a spinal dorsal horn neuron, a spinal ventral horn neuron, and a hippocampal pyramidal neuron to generate action potentials was studied using experiments and computer simulations. By comparing recordings ... of a dorsal horn neuron with simulated responses, it was shown that computer models can be adequate for the study of somatic excitability. The modeled somata of both spinal neurons were unable to generate action potentials, showing only passive and local responses to current injections. ... In contrast to spinal neurons, the modeled soma of the hippocampal pyramidal neuron generated spikes with an overshoot of +9 mV. It is concluded that the somata of spinal neurons cannot generate action potentials and seem to resist their propagation from the axon to dendrites. ... See paper for more and details.
Reference:
1 . Safronov BV, Wolff M, Vogel W (2000) Excitability of the soma in central nervous system neurons. Biophys J 78:2998-3010 [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): Spinal cord lumbar motor neuron alpha ACh cell;
Channel(s): I Na,t; I A; I K;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Action Potential Initiation; Ion Channel Kinetics; Action Potentials;
Implementer(s): Safronov, Boris [safronov at ibmc.up.pt];
Search NeuronDB for information about:  Spinal cord lumbar motor neuron alpha ACh cell; I Na,t; I A; I K;
TITLE HH sodium channel
: Hodgkin - Huxley squid sodium channel

NEURON {
	SUFFIX B_Na
	USEION na READ ena WRITE ina
	RANGE gnabar, ina
	GLOBAL inf
}

UNITS {
	(mA) = (milliamp)
	(mV) = (millivolt)
}

INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
PARAMETER {
	v (mV)
	celsius = 6.3	(degC)
	dt (ms)
	gnabar=.120 (mho/cm2) <0,1e9>
	ena = 53 (mV)
}
STATE {
	m h
}
ASSIGNED {
	ina (mA/cm2)
	inf[2]
}
LOCAL	fac[2]

INITIAL {
	rate(v*1(/mV))
	m = inf[0]
	h = inf[1]
}

BREAKPOINT {
	SOLVE states
	ina = gnabar*m*m*m*h*(v - ena)
}

PROCEDURE states() {	: exact when v held constant
	rate(v*1(/mV))
	m = m + fac[0]*(inf[0] - m)
	h = h + fac[1]*(inf[1] - h)
	VERBATIM
	return 0;
	ENDVERBATIM
}

UNITSOFF
FUNCTION alp(v(mV),i) { LOCAL a,b,c,q10 :rest = -70  order m,h
	v = v :convert to hh convention
	q10 = 3^((celsius - 6.3)/10)
	if (i==0) {
		alp = q10*.182*expM1(-v - 35, 9)
	}else if (i==1){
		alp = q10*.024*expM1(-v - 50, 5)


	}
}

FUNCTION bet(v,i) { LOCAL a,b,c,q10 :rest = -70  order m,h
	v = v 
	q10 = 3^((celsius - 6.3)/10)
	if (i==0) {
		bet = q10*.124*expM1(v + 35, 9)
	}else if (i==1){
		bet = q10*.0091*expM1(v + 75, 5)
	}
}

FUNCTION expM1(x,y) {
	if (fabs(x/y) < 1e-6) {
		expM1 = y*(1 - x/y/2)
	}else{
		expM1 = x/(exp(x/y) - 1)
	}
}

PROCEDURE rate(v) {LOCAL a, b, tau :rest = -70
	TABLE inf, fac DEPEND dt, celsius FROM -150 TO 100 WITH 200
	FROM i=0 TO 1 {
		a = alp(v,i)  b=bet(v,i)
		tau = 1/(a + b)
		if (i==0) {		
		inf[i] = a/(a+b)
	}else if (i==1) {
		inf[i] = 1/(1+exp((v+75)/9))
	} 
		fac[i] = (1 - exp(-dt/tau))
	}
}
UNITSON