### Single node with McIntyre equations fires without stimulus

Posted:

**Mon Sep 17, 2018 11:30 am**Hi,

I am new to NEURON and want to reproduce a model found in a paper by Mercadal et al (2017) http://stacks.iop.org/0031-9155/62/i=20/a=8060. They say they use a model for a myelinated axon where the behaviour of the nodes is described by the equations by McIntyre (2002). I have found the corresponding NEURON model in the ModelDB (No. 3810). In the paper, they say they just use the modified HH equations together with the cable equation by McNeal (1976). So I tried to make just a node with those equations, the next step would be to make more nodes and add an extracellular stimulus.

The problem I have is that the node is firing continuously without a stimulus, although I have initialized the potential to the value given in the model (-80 mV).

Here is the NEURON code I use. The parameters for the node are taken from the McIntyre model file.

axnode is the .mod file from the McIntyre model containing the modified HH equations. I just compiled it without change.

If I comment out the celsius statement, change v_init to -65 mV and use hh instead of axnode, I get the expected flat line at -65 mV.

[EDIT] I have added a stimulus (using the code from the McIntyre model) to verify that with hh, it fires if I give some current stimulus, and it doesn't if I set the current to zero. With axnode, it fires all the time, the shape of the first spike just changes a bit if I add a stimulus.[/EDIT]

What do I do wrong?

Thanks for a pointer or hint,

Matthias

I am new to NEURON and want to reproduce a model found in a paper by Mercadal et al (2017) http://stacks.iop.org/0031-9155/62/i=20/a=8060. They say they use a model for a myelinated axon where the behaviour of the nodes is described by the equations by McIntyre (2002). I have found the corresponding NEURON model in the ModelDB (No. 3810). In the paper, they say they just use the modified HH equations together with the cable equation by McNeal (1976). So I tried to make just a node with those equations, the next step would be to make more nodes and add an extracellular stimulus.

The problem I have is that the node is firing continuously without a stimulus, although I have initialized the potential to the value given in the model (-80 mV).

Here is the NEURON code I use. The parameters for the node are taken from the McIntyre model file.

Code: Select all

```
proc globals(){
celsius=37
v_init=-80 //mV//
dt=0.005 //ms//
tstop=20
nodeD=3.3
nodelength=1.0
rhoa=0.7e6 //Ohm-um//
}
globals()
create node
access node
proc initialize(){
node {
nseg=1
diam=nodeD
L=nodelength
Ra=rhoa/10000
cm=2
insert axnode
//insert hh
}
}
initialize()
```

axnode is the .mod file from the McIntyre model containing the modified HH equations. I just compiled it without change.

If I comment out the celsius statement, change v_init to -65 mV and use hh instead of axnode, I get the expected flat line at -65 mV.

[EDIT] I have added a stimulus (using the code from the McIntyre model) to verify that with hh, it fires if I give some current stimulus, and it doesn't if I set the current to zero. With axnode, it fires all the time, the shape of the first spike just changes a bit if I add a stimulus.[/EDIT]

What do I do wrong?

Thanks for a pointer or hint,

Matthias