Demonstration of gap junction coupling

gapdemo.g is a simple demo of the effect of gap junctions on synchronization of firing. It is a modification of the Tutorials/cells/simplecell simulation in the GENESIS Neural Modeling Tutorials package, with two copies of the simple two-compartment cell having a random background activation frequency for the dendrite Ex_channel, and a gap junction between the the dendrites of the two cells. The cells are defined in cell.p and protodefs.g.

The GUI allows the frequency and the resistance of the gap junction to be varied. The latter is performed by the function in graphics.g:

function set_R_gap(dialog)
    str dialog

    R_gap = {{getfield {dialog} value}*1e6}  // sets it globally
    // get rid of the original messages
    deletemsg /cell2/dend 0 -incoming -find /cell1/dend RAXIAL
    deletemsg /cell1/dend 0 -incoming -find /cell2/dend RAXIAL
    addmsg /cell1/dend /cell2/dend RAXIAL {R_gap} Vm
    addmsg /cell2/dend /cell1/dend RAXIAL {R_gap} Vm
end

With the default R_gap of 200 Mohm and a frequency of 200 Hz, the synchronization is nearly perfect. The firing begins to desynchronize for larger values.

Of course, the synchronization is aided by the fact that the two cells are identical, although they have independent set of random activations at the same average frequency. The setrandfield command can be used to the genesis prompt in order to explore the effect of introducing random variations in the cell passive parameters or the channel dynamics. For example:

setrandfield /cell1/soma Rm -gaussian 117891384 50e6
setrandfield /cell2/soma Rm -gaussian 117891384 50e6

This is causes some obvious decrease in synchronization when R_gap = 300 Mohm.

Dave Beeman Wed Jun 18 18:05:36 MDT 2008

Links to files in the gapdemo directory:

cell.p
gapdemo.g
graphics.g
protodefs.g
xtools.g
README