Raphe nuclei of medulla oblongata

The raphe nuclei are a moderate-size cluster of nuclei found in the brain stem. Their main function is to release serotonin to the rest of the brain. Selective serotonin reuptake inhibitor antidepressants are believed to act in these nuclei, as well as at their targets.

The raphe nuclei are traditionally considered to be the medial portion of the reticular formation, and appear as a ridge of cells in the center and most medial portion of the brain stem.