Electrotonic distance negative values

[afc]

Dear all,

I have a quick question that I could not answer myself: when I compute the electrotonic distance of some cells sometimes a number of dendritic branches of these cells show negative values (these cells have active conductances). Does this mean that there was no attenuation, and instead (probably due to the active properties) there was an "amplification"?

Thank you all in advance!

[ted]

when I compute the electrotonic distance of some cells

How are you doing this calculation?

[afc]

Thank you for the prompt reply!

I am computing it as:

Code: Select all

log(1/(zz.ratio(1)))

What I want to compute is the electrotonic distance (L) described here: http://www.neuron.yale.edu/neuron/stati ... l#citation.

Thank you!

[ted]

What do you see if you use the Log(A) vs. x Impedance tool to plot log(Attenuation)? Any negative electrotonic distances in that plot, either for Vin or Vout, with or without using "include dstate/dt contribution"?

[afc]

When I do not use the "include dstate/dt contribution" the plot only has positive values, either for Vin or Vout. When I use the "include dstate/dt contribution" the plot shows negative values for both Vin and Vout.

[ted]

At what frequency is it negative?

[afc]

From 0 to ~20 Hz. Afterwards the results become positive.

[ted]

I bet your model has a big persistent inward current, e.g. sodium, and not much of an h current or even much of a delayed rectifier. To diagnose this further, you might consider changing the channel density of each active current, individually, to 0 and seeing what happens to the negativity that you're observing in the log(Attenuation) plot.

[afc]

Even if this is the case (I am checking it now), how can one interpret the negative values?

[afc]

You were right, it seems that was the case! Thank you very much.

But still I wanted to keep analyzing the electrotonic structure of the cell, and I wanted to compare the active and passive electrotonic structure of it. Do you know how can I compute the passive electrotonic structure of the cell without taking into account the impedance contributions of gating state differential equations? Because I am using:

Code: Select all

proc calcZ() {
  soma zz.loc(WHERE) 
  zz.compute(FREQ, 1) 
  forall {
        fprint("%s\%s\%g\n", secname(),"L=", log(1/(zz.ratio(1))))
  }

but I would like to compare it with the passive electrotonic structure.

Thank you once more!

[afc]

Nevermind, I just found out how to do that:

Code: Select all

proc calcZ() {
  soma zz.loc(WHERE) 
  zz.compute(FREQ) 
  forall {
        fprint("%s\%s\%g\n", secname(),"L=", log(1/(zz.ratio(1))))
  }

Thank you!

[ted]

Even if this is the case (I am checking it now), how can one interpret the negative values?

Amplification by regenerative membrane properties that produce phenomenological negative slope conductance.

[ted]

Nevermind, I just found out how to do that

doubtless by applying the time-honored practice of RTFM.