Simulations of motor unit discharge patterns (Powers et al. 2011)

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Accession:143671
" ... To estimate the potential contributions of PIC (Persistent Inward Current) activation and synaptic input patterns to motor unit discharge patterns, we examined the responses of a set of cable motoneuron models to different patterns of excitatory and inhibitory inputs. The models were first tuned to approximate the current- and voltage-clamp responses of low- and medium-threshold spinal motoneurons studied in decerebrate cats and then driven with different patterns of excitatory and inhibitory inputs. The responses of the models to excitatory inputs reproduced a number of features of human motor unit discharge. However, the pattern of rate modulation was strongly influenced by the temporal and spatial pattern of concurrent inhibitory inputs. Thus, even though PIC activation is likely to exert a strong influence on firing rate modulation, PIC activation in combination with different patterns of excitatory and inhibitory synaptic inputs can produce a wide variety of motor unit discharge patterns."
Reference:
1 . Powers RK, Elbasiouny SM, Rymer WZ, Heckman CJ (2012) Contribution of intrinsic properties and synaptic inputs to motoneuron discharge patterns: a simulation study. J Neurophysiol 107:808-23 [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):
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Activity Patterns; Bursting; Action Potentials;
Implementer(s): Powers, Randy [rkpowers at u.washington.edu];
Search NeuronDB for information about:  Spinal cord lumbar motor neuron alpha ACh cell;
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PowersEtAl2012
code
Gfluctdv.mod *
ghchan.mod *
kca2.mod *
kdrRL.mod *
L_Ca.mod *
mAHP.mod *
na3rp.mod *
naps.mod *
synss.mod
ana_FI.hoc
ana_G.hoc
ana_passive.hoc
ana_vc.hoc
ana_vc_synss.hoc
AP_AHP.ses
FIgraph.hoc
FRcablepas.hoc
FRmnrampcc.ses
FRmnrampvc_synss.ses
FRMotoneuronNaHH.hoc
gramp.ses
GUI_FR_analysis.hoc
inhibdist
makebiramp.hoc *
passive.ses
RecActive.hoc
re-init.hoc
SetConductances.hoc
test.hoc
twobirampsdel.hoc *
vramp
vrampdel
vrampdel.hoc
                            
 COMMENT
 
 mAHP.mod
 
 Calcium-dependent potassium channel responsible for mAHP in motoneurons
 Simplified calcium channel that provides Ca for the KCa conductance is included
 	
 ENDCOMMENT

 NEURON {
 	SUFFIX mAHP
 	USEION k READ ek WRITE ik
 	USEION ca READ eca WRITE ica
 	RANGE n, gkcamax,gcamax,ik,cai,ica,depth,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
 	taur	= 20		(ms)		: rate of calcium removal
								
  	fKCa   = 0.1		: max act rate  
 	bKCa   = 0.1		: max deact rate 
 
 	celsius		(degC)
 } 
 
 
 ASSIGNED {
 	ik 		(mA/cm2)
 	v 		(mV)
	ica 		(mA/cm2)
 	ek		(mV)
	eca		(mV)
 	ninf
 	ntau 		(ms)
	minfca	
	drive_channel
 }
  
 
 STATE {
 mca 
 n 
 cai (mM)
}
 
 INITIAL { 
	cai=cainf
 	rates(cai)
	mcarate(v)
 	n = ninf
	mca=minfca
 }
 
 BREAKPOINT {
         SOLVE states METHOD cnexp
	ica = gcamax*mca*(v - eca)
 	ik =  gkcamax *n* (v - ek)
 } 
 

DERIVATIVE states { 
	 
 	drive_channel =  - (10000) * ica/ (2 * FARADAY * depth)
 	if (drive_channel <= 0.) { drive_channel = 0. }	: cannot pump inward
 	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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