CN pyramidal fusiform cell (Kanold, Manis 2001)

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Accession:37856
Pyramidal cells in the dorsal cochlear nucleus (DCN) show three characteristic discharge patterns in response tones: pauser, buildup, and regular firing. Experimental evidence suggests that a rapidly inactivating K+ current (I(KIF)) plays a critical role in generating these discharge patterns. To explore the role of I(KIF), we used a computational model based on the biophysical data. The model replicated the dependence of the discharge pattern on the magnitude and duration of hyperpolarizing prepulses, and I(KIF) was necessary to convey this dependence. Experimentally, half-inactivation voltage and kinetics of I(KIF) show wide variability. Varying these parameters in the model ... suggests that pyramidal cells can adjust their sensitivity to different temporal patterns of inhibition and excitation by modulating the kinetics of I(KIF). Overall, I(KIF) is a critical conductance controlling the excitability of DCN pyramidal cells. (See readme.txt and paper for details). Any questions regarding these implementations should be directed to: pmanis@med.unc.edu 2 April 2004 Paul B Manis, Ph.D.
References:
1 . Kanold PO, Manis PB (2001) A physiologically based model of discharge pattern regulation by transient K+ currents in cochlear nucleus pyramidal cells. J Neurophysiol 85:523-38 [PubMed]
2 . Kanold PO, Manis PB (1999) Transient potassium currents regulate the discharge patterns of dorsal cochlear nucleus pyramidal cells. J Neurosci 19:2195-208 [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): Cochlear nucleus pyramidal/fusiform GLU cell;
Channel(s): I K; I h; I Sodium; I Potassium;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Activity Patterns; Temporal Pattern Generation; Synaptic Integration;
Implementer(s): Manis, Paul B [PManis at med.unc.edu];
Search NeuronDB for information about:  Cochlear nucleus pyramidal/fusiform GLU cell; I K; I h; I Sodium; I Potassium;
// --------------------------------------------------------------
// Redefinition of the standard hoc procedure for initialization
// that allows for pre-equilibration of currents and translation
// of "rho" and "kappa" parameters into proper dendrite L and Ra
// --------------------------------------------------------------
// Taken from Zach Mainen's init routine - finds the initial RMP
// at the "steady state" with zero current
// 1/25/99 P. Manis
// Note that this is no longer a "redefinition".

proc findrmp() {

  st_amp_save = istim.amp1   // preserve stimulus amplitude
  istim.amp1 = 0             // turn stimulus off
  old_el = el_pyr
  el_pyr = $1 // try a new leak value and get the v...

  t = -1e5               // back up in time
  finitialize(v_init)    // initialize
  fcurrent()
  temp_dt = dt           
  dt = 200                // take a few very large steps (allow Ih to settle)
  for i=0,50 fadvance()  // to allow currents to reach steady state

  t = 0                  // restore t,dt
  dt = temp_dt

  finitialize(v)         // initialize again
  fcurrent()

  istim.amp1 = st_amp_save   // restore stimulus
  el_pyr = old_el  // restore old leak
}


// adjust leak to set cell at rmp as specified
// 2/9/99 P. Manis
// Uses current balance eq'n (per NEURON manual), better choice than interative method
proc adjleak() {
	finitialize($1) // sets v to target rmp, init's state variables to inf values
	fcurrent()	// set all assigned variables consistent with states
	// use current balance: 0 = ina + ik + ih + ica + gl_pyr*(v - el_pyr)		
	el_pyr = (ina + ik + ih + gl_pyr*v)/gl_pyr
	finitialize($1)
	fcurrent()	// recalculate currents (il_hh)
}

// set Rin at V to a particular value by adjusting gl_pyr
// requires 2 input values: v and Rin (in Mohm!)
// 2/9/99 P. Manis
proc setrin() {
	ar=L*1E-4*diam*1E-4*3.14159 /* area of soma in cm2 */
	finitialize($1)
	fcurrent()
	gtarget = 1/($2*ar*1e6) // make g from Rin, but assume input uints are Mohm
	gtest = gtarget - (gna_pyr + gk_pyr + gkif_pyr + gkis_pyr + gh_pyr)
	if(gtest < 0) {
		printf("setRin: R=%7.1f requires negative gl_pyr (of %7.1f)\n", $2, 1/gtest)
		return
	}
	gl_pyr = gtest
	// verify by calling the standard routine
	findRin($1)
}

// compute Rin and Tau_m by summing all conductances at rest and inverting result 
// Tau_m is calculated as Rin*Cm, assuming 1 uF/cm2 (could specify cm to get actual value?)
//
proc findRin() {
	finitialize($1)	/* make sure parameters are set for the new voltage */
	fcurrent()
	gin = gna_pyr + gk_pyr + gkif_pyr + gkis_pyr + gl_pyr + gh_pyr
	ar=L*1E-4*diam*1E-4*3.14159 /* area of soma in cm2 */
	rin = 1/(gin*ar)
	cm_soma = ar*1E-6	/* in farads, assuming 1 uF/cm2 */
	taum = rin * cm_soma * 1E3 /* convert to msec */
}

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