A small protein used by neurons to communicate—unlike fast electrical signals, neuropeptides provide slower, longer-lasting modulation of brain circuits.Neuropeptides are small proteins (3–100 amino acids) synthesized in neuronal cell bodies, packaged in dense-core vesicles, and released from axon terminals to modulate neural circuits. Unlike classical neurotransmitters, neuropeptides act at nanomolar concentrations, have longer durations of action, and signal through GPCRs. Key neuropeptides on Peptidings include orexin (wakefulness), galanin (sleep/cognition), NPY (appetite/stress), cortistatin (sleep), PACAP (neuroprotection), ghrelin (appetite/GH), and cholecystokinin (satiety). Neuropeptide signaling is volumetric—not confined to synapses.