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]
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 k channel channel
: Hodgkin - Huxley k channel


NEURON {
	SUFFIX B_DR
	USEION k READ ek WRITE ik
	RANGE gkbar, ik
	GLOBAL inf
}

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

INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
PARAMETER {
	v (mV)
	dt (ms)
	gkbar=.036 (mho/cm2) <0,1e9>
	ek = -84 (mV)
	celsius = 6.3 (degC)
}
STATE {
	n
}
ASSIGNED {
	ik (mA/cm2)
	inf
}
LOCAL	fac

INITIAL {
	rate(v*1(/mV))
	n = inf
}

BREAKPOINT {
	SOLVE states
	ik = gkbar*n*n*n*n*(v - ek)
}

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

UNITSOFF
FUNCTION alp(v(mV)) { LOCAL q10
	v = v
	q10 = 3^((celsius - 6.3)/10)
	alp = q10 * .0075*expM1(-v - 30, 10)
}

FUNCTION bet(v(mV)) { LOCAL q10
	v = v
	q10 = 3^((celsius - 6.3)/10)
	bet = q10 * .1*exp((-v - 46)/31)
}

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
		a = alp(v)  b=bet(v)
		tau = 1/(a+b)
		inf = a/(a + b)
		fac = (1 - exp(-dt/tau))
}
UNITSON

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