In the brain, OCN binds to G protein-coupled receptor 158 (Gpr158) and can cross the blood-brain barrier (BBB) to regulate transcription factors in the ventral tegmental area (VTA), dorsal raphe nucleus, middle raphe nucleus, and hippocampal CA3 neurons, thereby increasing the release of serotonin, dopamine, and norepinephrine, inhibiting the release of γ-aminobutyric acid (148, 149), and reducing depression and anxiety-like behaviors. Here, GPR158 is linked to major depressive disorder.