Neurotrophins are proteins secreted in the nervous system. They are essential for the survival, differentiation, growth, and apoptosis of nerve cells. Dysregulation of neurotrophin signaling has been linked to neurological and psychiatric disorders, including Alzheimer's disease, depression, and anxiety. There are several types of neurotrophins, such as NGF, BDNF, and NT-3, which exert specific functions in different circumstances.