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Effects of KIR current inactivation in NAc Medium Spiny Neurons (Steephen and Manchanda 2009)

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"Inward rectifying potassium (KIR) currents in medium spiny (MS) neurons of nucleus accumbens inactivate significantly in ~40% of the neurons but not in the rest, which may lead to differences in input processing by these two groups. Using a 189-compartment computational model of the MS neuron, we investigate the influence of this property using injected current as well as spatiotemporally distributed synaptic inputs. Our study demonstrates that KIR current inactivation facilitates depolarization, firing frequency and firing onset in these neurons. ..."
1 . Steephen JE, Manchanda R (2009) Differences in biophysical properties of nucleus accumbens medium spiny neurons emerging from inactivation of inward rectifying potassium currents. J Comput Neurosci 27:453-70 [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: Basal ganglia;
Cell Type(s): Nucleus accumbens spiny projection neuron;
Channel(s): I Na,p; I L high threshold; I T low threshold; I p,q; I A; I h; I K,Ca; I CAN; I A, slow; I Krp; I R;
Gap Junctions:
Receptor(s): AMPA; NMDA; Gaba;
Gene(s): Cav1.3 CACNA1D; Cav1.2 CACNA1C; IRK;
Simulation Environment: NEURON;
Model Concept(s): Action Potential Initiation; Ion Channel Kinetics; Action Potentials; Synaptic Integration; Delay;
Implementer(s): Steephen, John Eric [johneric at];
Search NeuronDB for information about:  AMPA; NMDA; Gaba; I Na,p; I L high threshold; I T low threshold; I p,q; I A; I h; I K,Ca; I CAN; I A, slow; I Krp; I R;
TITLE    AMPA synapse for nucleus accumbens model
: see comments below

	RANGE gbar, tau_r, tau_d, scale, spkcnt, countflag, i, t1, ca_ratio, ical, itmp, qfact


	(nA) = (nanoamp)
	(mV) = (millivolt)
	(umho) = (micromho)

	gbar = 8.5e-4   (umho) 	: approx 0.5:1 NMDA:AMPA ratio (Myme 2003)
							:   with mg = 0, vh = -70, one pulse, NMDA = 300 pS
							:   here AMPA = 593 pS (NMDA set to Dalby 2003)
	tau_r = 2.2 	(ms)   	: Gotz 1997, Table 1 - rise tau
	tau_d = 11.5  	(ms)   	: Gotz 1997, Table 1 - decay tau
	Erev = 0    	(mV)   	: reversal potential, Jahn 1998
	saturate = 1.2 			: causes the conductance to saturate - matched to 
							:    Destexhe's reduced model in [1]
	qfact = 2				: convert 22 degC to 35 degC
:	ca_ratio = 0.005			: ratio of calcium current to total current
}							: Burnashev/Sakmann J Phys 1995 485:403-418
							: with Carter/Sabatini Neuron 2004 44:483-493

	g (umho)
	v (mV)   		: postsynaptic voltage
	itmp	(nA)	: temp value of current
	i (nA)   		: nonspecific current = g*(v - Erev)
	iCa (nA)		: calcium current through AMPA synapse (Carter/Sabatini)
	t1 (ms)
	y1_add (/ms)    : value added to y1 when a presynaptic spike is registered
	y1_loc (/ms)

	countflag		: start/stop counting spikes delivered
	spkcnt			: counts number of events delivered to synapse
	scale			: scale allows the current to be scaled by weight
}					: so NetCon(...,2) gives 2*the current as NetCon(...,1)

	y1 (/ms) 
	y2    			: sum of beta-functions, describing the total conductance

  	y1_add = 0
	scale = 0
	spkcnt = 0
	countflag = 0
	t1 = 0
	y1_loc = 0

  	SOLVE betadyn METHOD cnexp
	g = gbar * y2
  	itmp = scale * g * (v - Erev)
  	i = 0.995 * itmp
  	iCa = 0.005 * itmp

DERIVATIVE betadyn {
	: dynamics of the beta-function, from [2]
	y1' = -y1 / (tau_d/qfact)
	y2' = y1 - y2 / (tau_r/qfact)

NET_RECEIVE( weight, y1_loc (/ms) ) {
	: updating the local y1 variable
	y1_loc = y1_loc*exp( -(t - t1) / (tau_d/qfact) )

	: y1_add is dependent on the present value of the local
	: y1 variable, y1_loc
	y1_add = (1 - y1_loc/saturate)

	: update the local y1 variable
	y1_loc = y1_loc + y1_add

	: presynaptic spike is finaly registered
	y1 = y1 + y1_add

	: store the spike time
	t1 = t

	spkcnt = spkcnt + 1

	scale = weight

Author Johan Hake (c) spring 2004
:     Summate input from many presynaptic sources and saturate 
:     each one of them during heavy presynaptic firing

: [1] Destexhe, A., Z. F. Mainen and T. J. Sejnowski (1998)
:     Kinetic models of synaptic transmission
:     In C. Koch and I. Segev (Eds.), Methods in Neuronal Modeling

: [2] Rotter, S. and M. Diesmann (1999) Biol. Cybern. 81, 381-402
:     Exact digital simulation of time-invariant linear systems with application 
:     to neural modeling

Dalby, N. O., and Mody, I. (2003). Activation of NMDA receptors in rat
dentate gyrus granule cells by spontaneous and evoked transmitter
release. J Neurophysiol 90, 786-797.

Gotz, T., Kraushaar, U., Geiger, J., Lubke, J., Berger, T., and Jonas,
P. (1997). Functional properties of AMPA and NMDA receptors expressed in
identified types of basal ganglia neurons. J Neurosci 17, 204-215.

Jahn K, Bufler J, Franke C (1998) Kinetics of AMPA-type glutamate
receptor channels in rat caudate-putamen neurones show a wide range of
desensitization but distinct recovery characteristics. Eur J Neurosci

Myme, C. I., Sugino, K., Turrigiano, G. G., and Nelson, S. B. (2003).
The NMDA-to-AMPA ratio at synapses onto layer 2/3 pyramidal neurons is
conserved across prefrontal and visual cortices. J Neurophysiol 90,

Gutfreund H, Kinetics for the Life Sciences, Cambridge University Press,
1995, pg 234.  (suggested by Ted Carnevale)

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