Discharge hysteresis in motoneurons (Powers & Heckman 2015)

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Accession:183949
"Motoneuron activity is strongly influenced by the activation of persistent inward currents (PICs) mediated by voltage-gated sodium and calcium channels. ... It has recently been suggested that a number of factors other than PIC can contribute to delta F (firing rate differences between motoneurons) values, including mechanisms underlying spike frequency adaptation and spike threshold accommodation. In the present study, we used a set of compartmental models representing a sample of 20 motoneurons with a range of thresholds to investigate how several different intrinsic motoneuron properties can potentially contribute to variations in F values. ... Our results indicate that, although other factors can contribute, variations in discharge hysteresis and delta F values primarily reflect the contribution of dendritic PICs to motoneuron activation.
Reference:
1 . Powers RK, Heckman CJ (2015) Contribution of intrinsic motoneuron properties to discharge hysteresis and its estimation based on paired motor unit recordings. A simulation study. J Neurophysiol 114:184-198 [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 L motor neuron alpha;
Channel(s): I Na,p; I Na,t; I L high threshold; I K; I M; I K,Ca; I_AHP; I Calcium; I Sodium;
Gap Junctions:
Receptor(s):
Gene(s): Kv1.2 KCNA2; Kv1.9 Kv7.1 KCNQ1;
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Spike Frequency Adaptation;
Implementer(s): Powers, Randy [rkpowers at u.washington.edu];
Search NeuronDB for information about:  Spinal cord L motor neuron alpha; I Na,p; I Na,t; I L high threshold; I K; I M; I K,Ca; I Sodium; I Calcium; I_AHP;
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Discharge_hysteresis
Model hoc files and output
README.txt
Gfluctdv.mod *
ghchan.mod *
kca2.mod *
KCNQ.mod *
kdrRL.mod *
km_hu.mod
kv1_gp.mod *
L_Ca.mod *
L_Ca_inact.mod *
mAHP.mod *
mAHPvt.mod
na3rp.mod *
naps.mod *
napsi.mod *
AHPlen.csv
FasterMis.csv
FR3cablepas.hoc
FRMot3dendNaHH.hoc
gramp.ses
HiDKCa.csv
init_3dend_gramp.hoc
LCai.csv
Napi.csv
pars2manyhocs.py *
ProxCa.csv
SetConductances2.hoc *
SlowM.csv
standard.csv
twobirampsdel.hoc *
                            
 COMMENT
 
 mAHPvt.mod
 
 Calcium-dependent potassium channel responsible for mAHP in motoneurons
 Simplified calcium channel that provides Ca for the KCa conductance is included
 This version has a slowly incrementing Ca decay time constant to mimic
 Wienecke, Zhang and Hultborn
 	
 ENDCOMMENT

 NEURON {
 	SUFFIX mAHPvt
 	USEION k READ ek WRITE ik
 	USEION ca READ eca WRITE ica
 	RANGE n, gkcamax,gcamax,ik,cai,ica,depth,taurmin,tauinc,taur
 	GLOBAL fKCa, bKCa, caix
 }

 
 UNITS {
 	(mA) = (milliamp)
 	(mV) = (millivolt)
 	(S) = (siemens)
 	(um) = (micron)
 	(molar) = (1/liter)			: moles do not appear in units
 	(mM)	= (millimolar)
 	(msM)	= (ms mM)
 	FARADAY = (faraday) (coulomb)
 } 
 
 PARAMETER {
 	gkcamax = 0.03   	(S/cm2)	
	gcamax = 3e-5		(S/cm2)
	mvhalfca = -30		(mV)
	mslpca = 4 		(mV)
	mtauca = 1		(ms)	
 	caix = 2	
  	cainf=0.0001		(mM)
 	depth	= .1		(um)		: depth of shell
 	taurmin	= 20		(ms)		: minimum decay time constant of calcium removal
	tauinc  = 10		(ms)
								
  	fKCa   = 0.1		: max act rate  
 	bKCa   = 0.1		: max deact rate
	ftau   = 0.002		:rate of increasing time constant
	btau   = 0.0005		:rate of decreasing time constant
 
 	celsius		(degC)
 } 
 
 
 ASSIGNED {
 	ik 		(mA/cm2)
 	v 		(mV)
	ica 		(mA/cm2)
 	ek		(mV)
	eca		(mV)
 	ninf
 	ntau 		(ms)
 	sinf
 	stau 		(ms)
	taur		(ms)
	minfca	
	drive_channel
 }
  
 
 STATE {
 mca 
 n 
 s
 cai (mM)
}
 
 INITIAL { 
	cai=cainf
 	rates(cai)
	mcarate(v)
 	n = ninf
	s=0
	mca=minfca
 }
 
 BREAKPOINT {
         SOLVE states METHOD cnexp
	ica = gcamax*mca*(v - eca)
 	ik =  gkcamax *n* (v - ek)
 } 
 

DERIVATIVE states { LOCAL a,b
	 
 	drive_channel =  - (10000) * ica/ (2 * FARADAY * depth)
 	if (drive_channel <= 0.) { drive_channel = 0. }	: cannot pump inward
	a=n*ftau
	b=btau
	stau=1/(a+b)
	sinf=a*stau
	s'=(sinf-s)/stau
	taur=taurmin+s*tauinc
 	cai' = drive_channel + (cainf-cai)/taur

         rates(cai)    
         n' = (ninf-n)/ntau
         mcarate(v)    
         mca' = (minfca-mca)/mtauca
}
PROCEDURE rates(cai(mM)) {  LOCAL a,b
							UNITSOFF
         a = fKCa * (1e3*(cai  -cainf))^caix		: rate constant depends on cai in uM
         b = bKCa
         ntau = 1/(a+b)
         ninf = a*ntau
					UNITSON
 }

PROCEDURE mcarate(v (mV)) {
	TABLE minfca
	DEPEND mvhalfca,mslpca 
	FROM -100 TO 100 WITH 200
	
	minfca = 1/(1+exp(-(v-mvhalfca)/mslpca))
}

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