shyam_u2 wrote:I want subsequent spikes to produce a "summating" effect on the IPSC of post synaptic cell instead of just prolonging the effect for a specific duration.
The key question is whether your code does what you intend it to do. What is needed is an explicit and clear statement of your intent, either in unambiguous human language (ambiguity is hard to expunge) or in the form of equations and conditional statements (has an inherent clarity advantage).
With regard to temporal summation, any synaptic mechanism whose conductance is governed by one or more ODEs gives you that for free. Even ExpSyn and Exp2Syn do that, and they don't involve second messenger effects. But maybe you're not talking about summation of synaptic conductance.
If there were no "G protein" effect, how should your synaptic mechanism respond to a single activation (what is the time course of the resulting conductance change)? What should happen if it is activated repeatedly (should there be temporal summation of conductance)? Should temporal summation be linear or should it saturate, i.e. if the synapse is activated 10, 100, or 1000 times in rapid succession, should each activation cause the same increase of conductance, or should successive events in a train of activations produce a smaller and smaller response (as would occur for any real synapse that has a finite number of ligand-gated channels on the postsynaptic side)?
If there is a "G protein" effect, is it homosynaptic (i.e. caused by activation of the same presynaptic terminal that releases the transmitter that binds to the receptor associated with the postsynaptic channels)? In this case, repeated activation of presynaptic cell A would do two things:
direct action on postsynaptic ion channels
perturbation of postsynaptic G protein that in turn affects the postsynaptic ion channels
Or is it heterosynaptic (caused by activation of some other presynaptic cell)? In which case:
activation of presynaptic cell A would affect the postsynaptic ion channels but not the G protein
activation of presynaptic cell B would affect postsynaptic G protein but wouldn't by itself open the ion channels
What is the time course of the G protein effect?
If a synaptic activation occurs at t0, is there immediate potentiation of the opening of ligand-gated channels, or is the potentiating effect revealed only by a train of activations or a "paired pulse" type of experiment (conditioning pulse followed by a test pulse after some interval, in which case the conditioning pulse would elicit an unpotentiated response but the test pulse would elicit a potentiated response).
In either case, what are the equations that govern the temporal dynamics of the potentiation, does it show saturation or not, and is potentiation additive or multiplicative (does each activation add a constant amount to the G protein signal, or does it increase the G protein signal by some percentage)?