Sorry I have made some mistake earlier. I said that fast synaptic
trasnmission evolved before neuropeptide signaling, but that was
probably incorrect or at best uncertain. In the most primitive
nerve nets such as that of the Hydra, peptides as well as fast
Taking one step back to the sponges, they lack a nerve net but
probably use peptide signaling for signaling purposes. But I'm
not sure if this kind of signaling continues in the nervous
systems of higher organisms; or just remain "housekeeping"