It plays a number of different roles throughout the body. It seems to act both as a neurotransmitter within the central nervous system and as a hormone acting on the anterior pituitary gland and on the cardiovascular system (in the latter, it helps to regulate blood pressure and blood volume). It is believed to serve an important role in brain function, particularly in regions involved with movement (the extrapyramidal system) and with emotional and memory behavior (the limbic system). The brains of people with schizophrenia, Alzheimer's disease and Parkinson's disease have been found to have abnormally low quantities of it.