HH model with high positive current

[reza_rzm]

Dear Friends,

as a frist step in neuroscience computation i start with HH model with the following simple code

load_file("nrngui.hoc")
//create soma
create soma
access soma
soma{
nseg = 15
diam =18.8
L = 18.8
Ra = 123.0
insert hh
gnabar_hh = 0.12 //(s/cm2)
gkbar_hh = 0.036 //(s/cm2)
gl_hh = 0.0003 //(s/cm2)
el_hh = -54.3 //(mv)
ena=50 //(mv)
ek=-77 //(mv)

//celsius=32.3
}

objectvar stim
stim = new IClamp(0.5)
stim.del = 100
stim.dur = 100
stim.amp = 0.1 //mA [0.1 0.2 0.3 0.5 0.9 1.0 1.5 2 2.5 3 ]

dt=0.0001
tstop = 400



i run this code for positive current and;

when temperature is 6.3 (celsius=6.3,default), i change "stim.amp" from 0.1 to 3.5.
Spikes Frequency(SF) increase as i increase "amp" but for amp>2, (SF) decrease, i have one big spike that starts very fast. even for high temperature (celsius=32.3), for small(0.1) amp i don't have spike and for (stim.amp=0.5)i have one very fast and big spike!!!

is it somthing wrong in my code , and parameters that i have used?
should i add another parameter to have spike in celsius=32.3?!!



thank's in advance,

Have Great Time

[ted]

Good first step, but there are some things you might want to change--
A model with these anatomical and biophysical properties only needs nseg = 1.
The time step is 0.1 microsecond, which is unnecessarily small. 0.025 ms would
be perfectly adequate.
Why wait 100 ms to apply the stimulus current?

Now for your questions.
The HH mechanism is based on experiments from the squid giant axon.
Squid live in cold water, and the giant axon's job is to conduct one or two spikes.
The giant axon is not specialized for repetitive firing, and can only fire over a limited range
of frequencies.
The sodium current is the thing that gets the spike going, and it's always in a race with
its own inactivation and the potassium current, which turn the spike off. At high
temperatures, the sodium current turns on and off too quickly for the axon to make
much of a spike. That's why a weak stimulus, which coud trigger a spike in a cold axon,
may fail to trigger a spike in a warm axon.

A suggestion: learn how to use the GUI. Get the CellBuilder tutorial from
http://www.neuron.yale.edu/neuron/docs

[reza_rzm]

Hi,

Thank you very much for reply!

you have written that HH mechanism works for low temerature. in my simple code, i change temperature by this command : celcisus=32.3
i think this parameter modified the rate constants for HH model by 3^(celsius-6.3)/10 .

but as you said it is not enough, so what should i do to have spike for ( celsius>6.3)?

thank's in advance

[ted]

As temperature increases, squid axon becomes less excitable, so a stronger stimulus
is needed to trigger a spike. To avoid gNa inactivation and gK activation, it is best to
increase stimulus strength by raising the amplitude of the stimulus, rather than
prolonging stimulus duration.