Excitability of PFC Basal Dendrites (Acker and Antic 2009)

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Accession:117207
".. We carried out multi-site voltage-sensitive dye imaging of membrane potential transients from thin basal branches of prefrontal cortical pyramidal neurons before and after application of channel blockers. We found that backpropagating action potentials (bAPs) are predominantly controlled by voltage-gated sodium and A-type potassium channels. In contrast, pharmacologically blocking the delayed rectifier potassium, voltage-gated calcium or Ih, conductance had little effect on dendritic action potential propagation. Optically recorded bAP waveforms were quantified and multicompartmental modeling (NEURON) was used to link the observed behavior with the underlying biophysical properties. The best-fit model included a non-uniform sodium channel distribution with decreasing conductance with distance from the soma, together with a non-uniform (increasing) A-type potassium conductance. AP amplitudes decline with distance in this model, but to a lesser extent than previously thought. We used this model to explore the mechanisms underlying two sets of published data involving high frequency trains of action potentials, and the local generation of sodium spikelets. ..."
Reference:
1 . Acker CD, Antic SD (2009) Quantitative Assessment of the Distributions of Membrane Conductances Involved in Action Potential Backpropagation Along Basal Dendrites. J Neurophysiol 101:1524-1541 [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: Neocortex;
Cell Type(s): Neocortex V1 L6 pyramidal corticothalamic cell;
Channel(s): I Na,t; I L high threshold; I T low threshold; I A; I K; I h; I Potassium;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Activity Patterns; Dendritic Action Potentials; Parameter Fitting; Active Dendrites; Detailed Neuronal Models; Calcium dynamics;
Implementer(s): Acker, Corey [acker at uchc.edu];
Search NeuronDB for information about:  Neocortex V1 L6 pyramidal corticothalamic cell; I Na,t; I L high threshold; I T low threshold; I A; I K; I h; I Potassium;
load_file("nrngui.hoc")
load_file("Model/PFC_L5Pyramid_AckerAntic06.hoc")
load_file(1,"LocalSpikes.ses")
load_file(1,"Tools.hoc")
load_file(1,"LocalSpikes.ses")

celsius = 32
v_init=-67
print celsius
Dt = 0.1 // ms time step, for graphical output and output to files
dt = Dt
steps_per_ms=1/Dt
tstop = 200+Dt/2
Nstep = int(tstop/Dt)+1

somaCa = 10
distCa() // somatic calcium channel conductance was 10 instead of 8pS/um2 here, makes little difference

strdef dendname
dendname = "basal[34]"

/* Activate variable time step solver */
cvode.active(1)
cvode.rtol(1e-4)
cvode.atol(1e-5)
cvode.maxstep(1)

xpanel("Typical dendrite - Na boosting")
xlabel("     Best fit model, without and with sodium boosting.     ")
xbutton("Run best fit model (Figure 9A Control)","RunBestFit()")
xbutton("Run best fit, Na boosted (Figure 9B)","RunBestFitNaBoosted()")
xpanel(7,350)

xpanel("Typical dendrite - A-type block")
xlabel("     Best fit model, without and with block of A-type current.    ")
xbutton("Run best fit model (Figure 10A Control)","RunBestFit()")
xbutton("Run best fit, IA blocked (Figure 10A IA Blocked)","RunBestFitIABlocked()")
xpanel(7,512)

xpanel("Special case dendrite - A-type block")
xlabel("     Special case dendrite, without and with block of A-type current.    ")
xlabel("          Branch Strength Potentiation in a Model Basal Dendrite.    ")
xbutton("Run special case dend (Figure 10B Control)","RunSpecial()")
xbutton("Run special case, IA blocked (Figure 10B, IA Blocked)","RunSpecialIABlocked()")
xpanel(7,675)

proc RunBestFit() {
   distNaSD(dendname,basalNa)
   distKASD(dendname,somaKA)
   run()
}

proc RunBestFitNaBoosted() {
   distNaSD(dendname,375)
   distKASD(dendname,somaKA)
   run()
}

proc RunBestFitIABlocked() {
   distNaSD(dendname,basalNa)
   distKASD(dendname,0)
   run()
}

proc RunSpecial() {
   distNaSD(dendname,375)
   distKASD(dendname,1200)
   run()
}

proc RunSpecialIABlocked() {
   distNaSD(dendname,375)
   distKASD(dendname,0)
   run()
}

proc distNaSD() {local x,dist,gNalin
  forsec $s1 for (x,0) {
     dist=distance(x)
     gNalin=$2-mNa*dist
     if (gNalin>gNamax) {
         gNalin=gNamax
         print "Setting basal Na to maximum ",gNamax," at distance ",dist," in basal dendrite ",secname()
     } else {
         if (gNalin<0) {
            gNalin=0
            print "Setting basal Na to zero at distance ",dist," in basal dendrite ",secname()
         }
     }
     gbar_na(x)=gNalin
  }
}

proc distKASD() {local x, dist, gkalin, ratiolin, ratio  // distribute IA channels
   forsec $s1 for (x,0) {
      dist=distance(x)
      gkalin=$2+mgka*dist // continuous with soma
      ratiolin=1-mgkaratio*dist
      if (ratiolin<0) {
         ratio=0
      } else ratio=ratiolin
      if (gkalin>gkamax) {
         gkabar_kap(x)=gkamax*ratio/1e4
         gkabar_kad(x)=gkamax*(1-ratio)/1e4
      } else {
         gkabar_kap(x)=gkalin*ratio/10000
         gkabar_kad(x)=gkalin*(1-ratio)/1e4
      }
   }
}


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