Active dendrites and spike propagation in a hippocampal interneuron (Saraga et al 2003)

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Accession:28316
We create multi-compartment models of an Oriens-Lacunosum/Moleculare (O-LM) hippocampal interneuron using passive properties, channel kinetics, densities and distributions specific to this cell type, and explore its signaling characteristics. We find that spike initiation depends on both location and amount of input, as well as the intrinsic properties of the interneuron. Distal synaptic input always produces strong back-propagating spikes whereas proximal input could produce both forward and back-propagating spikes depending on the input strength. Please see paper for more details.
Reference:
1 . Saraga F, Wu CP, Zhang L, Skinner FK (2003) Active Dendrites and Spike Propagation in Multi-compartment Models of Oriens-Lacunosum/Moleculare Hippocampal Interneurons. J Physiol 552(3):673-689 [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): Hippocampus CA1 interneuron oriens alveus cell;
Channel(s): I Na,t; I A; I K; I h;
Gap Junctions:
Receptor(s): AMPA;
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Action Potential Initiation; Dendritic Action Potentials; Active Dendrites; Influence of Dendritic Geometry; Detailed Neuronal Models; Action Potentials;
Implementer(s): Saraga, Fernanda [Fernanda.Saraga at utoronto.ca];
Search NeuronDB for information about:  Hippocampus CA1 interneuron oriens alveus cell; AMPA; I Na,t; I A; I K; I h;
COMMENT

Sodium current for the axon

Conductances taken from Traub & Miles 1995 paper where ratio of Na for 
soma:axon is 1:5

References:

1.	Martina, M., Vida, I., and Jonas, P.  Distal initiation and active
	propagation of action potentials in interneuron dendrites,
	Science, 287:295-300, 2000.

			soma	axon-lacking dend	axon-bearing dend
Na+	gmax	    107 ps/um2	   117 ps/um2		   107 ps/um2
	slope 	    10.9 mV/e	   11.2 mV/e		   11.2 mV/e
	V1/2        -37.8 mV       -45.6 mV                -45.6 mV



2.	Marina, M. and Jonas, P.  Functional differences in Na+ channel
	gating between fast-spiking interneurons and principal neurones of rat
	hippocampus, J. Physiol., 505.3:593-603, 1997.

*Note* The interneurons here are basket cells from the dentate gyrus.

Na+	Activation V1/2				-25.1 mV
	slope			 		11.5
	Activation t (-20 mV)	 		0.16 ms
	Deactivation t (-40 mV)	 		0.13 ms
 	Inactivation V1/2			-58.3 mV
	slope			 		6.7
	onset of inactivation t (-20 mV)	1.34 ms
	onset of inactivation t (-55 mV)	18.6 ms
	recovery from inactivation t		2.0 ms
	(30 ms conditioning pulse)
	recovery from inactivation t		2.7 ms
	(300 ms conditioning pulse)

ENDCOMMENT
UNITS {
        (mA) = (milliamp)
        (mV) = (millivolt)
}
 
NEURON {
        SUFFIX Naaxon
        USEION na READ ena WRITE ina
        NONSPECIFIC_CURRENT il
        RANGE gnaaxon, gl, el, ina
        GLOBAL minf, hinf, hexp, mtau, htau
}
 
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
 
PARAMETER {
        v (mV)
        celsius = 24 (degC)
        dt (ms)
        gnaaxon = .0107 (mho/cm2)
        ena = 90 (mV)
        gl = .00005 (mho/cm2)
        el = -70 (mV)
}
 
STATE {
        m h 
}
 
ASSIGNED {
        ina (mA/cm2)
        il (mA/cm2)
        minf 
	mexp 
	hinf 
	hexp
	mtau (ms)
	htau (ms)
}
 
INITIAL {
	m = minf
	h = hinf
}

BREAKPOINT {
        SOLVE states
	ina = gnaaxon*minf*minf*minf*h*(v - ena)    
        il = gl*(v - el)
}

PROCEDURE states() {	:exact when v held constant
	evaluate_fct(v)
	h = h + hexp*(hinf - h)
	VERBATIM
	return 0;
	ENDVERBATIM 
}
UNITSOFF
PROCEDURE evaluate_fct(v(mV)) {  :Computes rate and other constants at 
		      :current v.
                      :Call once from HOC to initialize inf at resting v.
        LOCAL q10, tinc, alpha, beta
        TABLE minf, hinf, hexp, mtau, htau DEPEND dt, celsius FROM -200 TO 
100 WITH 300
		q10 = 3^((celsius - 24)/10)
		tinc = -dt*q10
		alpha = 0.1*vtrap(-(v+38),10)
		beta = 4*exp(-(v+63)/18)
		mtau = 1/(alpha + beta)
		minf = alpha*mtau
		alpha = 0.07*Exp(-(v+63)/20)
		beta = 1/(1+Exp(-(v+33)/10))
		htau = 1/(alpha + beta)
		hinf = alpha*htau
		hexp = 1-Exp(tinc/htau)
}
FUNCTION vtrap(x,y) {	:Traps for 0 in denominator of rate eqns.
		if (fabs(x/y) < 1e-6) {
			vtrap = y*(1 - x/y/2)
		}else{
			vtrap = x/(Exp(x/y) - 1)
		}
}
FUNCTION Exp(x) {
		if (x < -100) {
			Exp = 0
		}else{
			Exp = exp(x)
		}
}
UNITSON

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