“Peptides operate on multiple scales: they have feedback effects on the cells of origin that modulate activity patterning, and local effects on neighboring cells to coordinate the behavior of a population; and the hormone-like release of peptides from cell populations can have organizational effects on distant targets. It's a mode of communication quite different from neurotransmitter release. Oxytocin, as we have seen, by its priming actions, can affect how oxytocin cells communicate with each other. How common such priming actions are we don't know. But all peptides can affect gene expression and can alter the behavior of neurons by changing what receptors they express and what they secrete. These actions of peptides together underlie what we might see as a reprogramming of communication in the brain.”