Role of the AIS in the control of spontaneous frequency of dopaminergic neurons (Meza et al 2017)

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Computational modeling showed that the size of the Axon Initial Segment (AIS), but not its position within the somatodendritic domain, is the major causal determinant of the tonic firing rate in the intact model, by virtue of the higher intrinsic frequency of the isolated AIS. Further mechanistic analysis of the relationship between neuronal morphology and firing rate showed that dopaminergic neurons function as a coupled oscillator whose frequency of discharge results from a compromise between AIS and somatodendritic oscillators.
1 . Meza RC, López-Jury L, Canavier CC, Henny P (2017) Role of the axon initial segment in the control of spontaneous frequency of nigral dopaminergic neurons in vivo. J Neurosci [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: Basal ganglia; Mouse;
Cell Type(s): Substantia nigra pars compacta dopaminergic cell;
Channel(s): Na/K pump; I K,Ca; I K; I L high threshold; I T low threshold; I A; I N; I Na,t;
Gap Junctions:
Simulation Environment: NEURON;
Model Concept(s): Activity Patterns; Temporal Pattern Generation; Oscillations; Pacemaking mechanism;
Implementer(s): Lopez-Jury, Luciana [lucianalopezjury at]; Canavier, CC;
Search NeuronDB for information about:  Substantia nigra pars compacta dopaminergic cell; I Na,t; I L high threshold; I N; I T low threshold; I A; I K; I K,Ca; Na/K pump;
Run mosinit.hoc file
Press the init & run button to generate a figure with the membrane potential simulated in two recording sites: axon-initial-segment (AIS) and soma. You may zoom-in to note the firing delay between two compartments. 

To check how AIS length modify the spontaneous firing rate, use "L" NEURON parameter by typing: ais.L 
Original reconstruction length is  41.45 microns, try changing it to 10 or 100 microns to see the effect on firing rate. 
From our results, the range of AIS length of 16 dopaminergic neuron reconstructions is from 19 to 58 microns.

To check how distance AIS-to-soma modify the spontaneous firing rate, use "L" NEURON parameter by typing: dend[25].L
The section "dend[25]" corresponds to a dendrite between AIS and the soma. 
AIS of dopaminergic neurons origins from a dendrite, consequently AIS distance to the soma is considerably variable (from our results, from 13 to 71 microns.)

To better visualize the effect you may select "Keep Lines" mode before changing the AIS length parameter, by pressing and releasing the option "Keep Lines" in the Graph menu with the right mouse button.

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