Spontaneous activity of neuron using the complete axon

#1

Hi everyone,

I use the neuron models published by the BBP and available on this portal.
I noticed that some of them show spontaneous firing when including the complete axon while they do not when implementing the stub axon instead.
It happens mostly for cNAC and dNAC neurons.
It is puzzling however that in neurons sharing the same biophysics file (for example one neuron type with 5 different morphologies), some display spontaneous firing while other do not, suggesting that the morphology is critically involved (I believe that is the only variable differing between them).

Is that correct? Or have I again coded a bug? It is anyway quite easy to reproduce (for example: ‘L23_SBC_dNAC222_3’ shows spontaneous firing while ‘L23_SBC_dNAC222_2’ does not (with the complete axon)).
Should the neuron models be used with the complete axon? I am interested in the response of these neurons to various extracellular stimulations. How the implementation of the complete axon can produce such a change?
thanks

#2

Hi,

I would say it’s not ‘completely’ unexpected.

Could you elaborate on what you mean with ‘complete axon’ exactly ? Did you just remove the code that replaces the axon with a stub ? Did you change anything to change the code that puts the channels in the axon. If you didn’t do the latter it means the (fairly high concentration) Na channels will be spread all over the axon. This will not be biophysically correct.

One issue with the current axon stub (which we are fixing in a new version of the modes) is that there are boundary effects due to it’s limited size. To solve this we will add a long section after the stub. But in your case the behaviour of the model might change just because the boundary effect disappears.

Is there a way you can share you code ? I could have a look at it if you want if you’re scared of a bug.

#3

Hi Werner!
Thanks for the info.
With the complete axon I meant the complete morphology, which is indeed “restored” when removing the code that replaces the axon with a stub.
I did not change the

code that puts the channels in the axon. If you didn’t do the latter it means the (fairly high concentration) Na channels will be spread all over the axon. This will not be biophysically correct.

What modifications would you recommend then to have a more biophysically correct axon?
thanks again

#4

All right, so I reduced the conductance of the sodium channels in the axon after an initial segment of 60 um.
I used a factor of 15 to get close to experimental data.
There are now no spontaneously firing neurons in the whole 1035 neuron models.
Thanks for pointing that info.
Is there anything else you would recommend checking up?