Spiny neuron model with dopamine-induced bistability (Gruber et al 2003)

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These files implement a model of dopaminergic modulation of voltage-gated currents (called kir2 and caL in the original paper). See spinycell.html for details of usage and implementation. For questions about this implementation, contact Ted Carnevale (ted.carnevale@yale.edu)
1 . Gruber AJ, Solla SA, Surmeier DJ, Houk JC (2003) Modulation of striatal single units by expected reward: a spiny neuron model displaying dopamine-induced bistability. J Neurophysiol 90:1095-114 [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): Neostriatum medium spiny direct pathway GABA cell;
Channel(s): I K,leak; I h; I A, slow;
Gap Junctions:
Receptor(s): D1; Dopaminergic Receptor;
Gene(s): Cav1.3 CACNA1D; D1 DRD1A;
Transmitter(s): Dopamine;
Simulation Environment: NEURON;
Model Concept(s): Intrinsic plasticity;
Implementer(s): Carnevale, Ted [Ted.Carnevale at Yale.edu];
Search NeuronDB for information about:  Neostriatum medium spiny direct pathway GABA cell; D1; Dopaminergic Receptor; I K,leak; I h; I A, slow; Dopamine;

  A single compartment model contains the biophysical properties.
  ExpSyn provides the "excitatory cortical inputs" 
    (tonic background "context" and phasic "visual stimulus").

  Two NetStims drive the ExpSyn--Bkgd and Stim.
  A third NetStim called Stop turns off Stim.

  DAsyn is activated and deactivated by hoc-generated events, 
  which take care of setting its time constant and steady state 
  to the desired values (70 ms and 1.4 during the "on" phase, 
  100 ms and 1.0 during the "off" phase).

ExpSyn's gs = gmax exp(-t/tau), which has area gmax tau.
If this occurs at a mean interval of T, 
mean synaptic conductance is gmax tau/T.
If gmax is 1 pS, tau = 1 ms, T = 10 ms, 
then mean synaptic conductance is 0.1 pS.

This model has surface area of 100 um2, 
so a synaptic conductance density of 1 uS/cm2 
is equivalent to a total conductance of 
1 (uS/cm2) * 100 um2 * (1 cm2/1e8 um2) = 1e-6 uS = 1 pS.

For Fig. 10, Gruber et al. use 
baseline synaptic conductance density = 10.5 uS/cm2.
If gmax is 10.5 pS, tau 3 ms, then T = gmax tau / meangs = 3 ms.
So Bkgd_NetStim[0] fires with mean interval of 3 ms, 
starting at 50 ms, with noise 0.15.

For Fig. 10, Gruber et al. use two different test stimuli:
weak, which produces gt 2.4 uS/cm2 (total meangs 12.9 uS/cm2)
strong, which produces gt 3.8 uS/cm2 (total meangs 14.3 uS/cm2).
The weak stimulus therefore is represented by events with weight 
2.4 pS occurring at a mean interval of 3 ms, 
and the strong stimulus by events with weight
3.8 pS occurring at a mean interval of 3 ms.
In both cases, noise is 0.15.
This is the NetCon from Stim_NetStim[0] to ExpSyn[0] on C_Cell[0]

load_file("fig10syn.hoc")	// link the POINTER vars in caL and kir2 to DAsyn[0].msg

load_file("exptl_conditions.hoc")  // strong vs. weak, rewarded vs. unrewarded

celsius = 20
forall {
  if (ismembrane("k_ion")) ek = -90
  if (ismembrane("ca_ion")) {
    cai0_ca_ion = 1e-5
    cai = 1e-5
    cao0_ca_ion = 2
    cao = 2

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