Neuropeptides (when they're located at the pre-synapse) are usually secreted
after intense stimulation such as tetanic trains. Is it possible that they
represent a sort of "over-flow" situation? When the synapse runs out of
"space", then it tries to encode information in the time domain by releasing
peptides? The effects of peptides are usually *long-lasting* changes in
synaptic dynamics, such as altering the shape of later action potentials.
I've read a recent article by H Markram which argues that synapses are highly
*dynamic* and that they may encode information in the time domain with
internal parameters determining the degrees of facilitation / depression in
response to a train of spikes.
I guess (I'm not sure about this) many neuropeptides evolved *after* the
emergence of the action potential. If this is true then it makes sense that
neuropeptides may serve an auxiliary function (ie information "overflow").
Any comments? =)