Figure 1. Neuropeptide activation requires multiple processing steps in the cell.

A representative neuropeptide is shown with sequential processing steps within the neuron beginning in the endoplasmic reticulum, followed by endoproteolytic cleavages in the trans-Golgi network (TGN) or secretory vesicles. Further processing in the vesicles at the C-terminus removes amino acids and adds a C-terminal amide group. The vesicles are transported down the axon and are stored at varicosities (not shown) and near the synapse. Neuropeptides are stored in dense core vesicles, which are larger and functionally distinct from the small, clear synaptic vesicles.