# G-protein synapse

## Physical System

Synaptic conductance modulated by activation of postsynaptic G-protein.

## Model

Alpha function approximation to both a conductance change and G-protein change on occurrence of event. An event does two things,

1) An amount of material is introduced at the beginning of the G-protein cascade which produces a peak change of Ginc in the G-protein concentration (relative to its steady state value of 1) approximately Gtau1 after the event (assuming Gtau1 is nearly the same as Gtau2).

2) An amount of transmitter is released which is proportional to the weight of the event and the G-protein concentration and produces a peak change in g of weight*G approximately tau1 after the event (assuming tau1 is nearly the same as tau2).

    	Ginc increase in A -> G ->
    	weight*G increase in a -> g ->
    	i = g*(v - e)

## Simulation

gsyn.mod

text of gsyn.hoc file

The simulation differs from the previous example only in that it uses a different synapse model.

These files are copies of the gsyn example files (along with pregen.mod) in nrn/examples/nrniv/netcon. By running

    	special gsyn.hoc -

the example will start with a PointProcessGroupManager that allows you to vary the parameters for the three spike train generators and the synapse. Another panel shows the weight and delay for the three connections.

## Exercises

1) When Ginc=1 does the g-protein for a single spike double? Is the maximum conductance change for a single spike equal to the weight?

2) When a second spike arrives at the peak of the g-protein pulse from the same network connection, is the increment in the conductance twice as much? What if the second spike arrives on a different network connection?

3) It is impossible to plot the real value of G in this model because it is computed only when an event occurs. Does it make sense to move the computation out of the NET_RECEIVE block and into the DERIVATIVE block? How would that change the behavior with regard to multiple input lines?

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Copyright © 1998, 1999 by N.T. Carnevale and M.L. Hines, all rights reserved.