i am just getting started using NEURON, and am wondering if there is an easy way to change the duration of transmitter in the synaptic cleft, based on some specific parameters of transmitter clearance. i have looked at NetStim, and the only thing obvious in there that might be useful is to pulse two release events with a very short interval, but this doesn't really seem like what i want to do. specifically, i have made a matlab model of how the synaptic glutamate time constant changes under a couple different conditions, and i am hoping for a trivial way to represent these temporal glutamate profile differences in a simulation.
thanks,
bryan
neurotransmitter time course in the synapse
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The built-in synaptic mechanisms are phenomenological, i.e. they generate conductance
transients that have the same time course as experimentally observed unitary synaptic
inputs.
AlphaSynapse--generates a single conductance transient that starts at a fixed time and
follows an alpha function time course
g = 0 for t < onset and
g = gmax * (t - onset)/tau * exp(-(t - onset - tau)/tau)
for t > onset
No way to emulate changed duration of transmitter action without also affecting onset of
transmitter effect.
ExpSyn--event-driven mechanism whose conductance g decays toward 0 with a single
time constant tau. Arrival of an event with weight w forces g to increase abruptly to g+w
Exp2Syn--event-driven mechanism whose conductance g follows a time course
described by the difference between two decaying exponentials, i.e. the solution of
A->G->bath with rate constants 1/tau1 and 1/tau2
A = a*exp(-t/tau1) and
G = a*tau2/(tau2-tau1)*(-exp(-t/tau1) + exp(-t/tau2))
where tau1 < tau2
The scale factor a is given a value such that, if A and G are initially 0, arrival of an event
with weight w causes G to reach a delayed peak of amplitude w.
Note that neither ExpSyn nor Exp2Syn can emulate saturation. Changing duration of
transmitter, or of transmitter effect, can be emulated by changing ExpSyn's tau or
Exp2Syn's tau2.
If you want a mechanism that displays saturation, and/or want direct control over
"concentration" or persistence of transmitter in the synaptic cleft, see
Example 10.6: Saturating synapses
in The NEURON Book. If you don't have the book, see the relevant portion of this preprint
http://www.neuron.yale.edu/ftp/ted/book ... xedref.pdf
transients that have the same time course as experimentally observed unitary synaptic
inputs.
AlphaSynapse--generates a single conductance transient that starts at a fixed time and
follows an alpha function time course
g = 0 for t < onset and
g = gmax * (t - onset)/tau * exp(-(t - onset - tau)/tau)
for t > onset
No way to emulate changed duration of transmitter action without also affecting onset of
transmitter effect.
ExpSyn--event-driven mechanism whose conductance g decays toward 0 with a single
time constant tau. Arrival of an event with weight w forces g to increase abruptly to g+w
Exp2Syn--event-driven mechanism whose conductance g follows a time course
described by the difference between two decaying exponentials, i.e. the solution of
A->G->bath with rate constants 1/tau1 and 1/tau2
A = a*exp(-t/tau1) and
G = a*tau2/(tau2-tau1)*(-exp(-t/tau1) + exp(-t/tau2))
where tau1 < tau2
The scale factor a is given a value such that, if A and G are initially 0, arrival of an event
with weight w causes G to reach a delayed peak of amplitude w.
Note that neither ExpSyn nor Exp2Syn can emulate saturation. Changing duration of
transmitter, or of transmitter effect, can be emulated by changing ExpSyn's tau or
Exp2Syn's tau2.
If you want a mechanism that displays saturation, and/or want direct control over
"concentration" or persistence of transmitter in the synaptic cleft, see
Example 10.6: Saturating synapses
in The NEURON Book. If you don't have the book, see the relevant portion of this preprint
http://www.neuron.yale.edu/ftp/ted/book ... xedref.pdf