Serotonin is a monamine neurotransmitter that is biosynthesized in the human body from the amino acid tryptophan. The substance can also be consumed orally and is present in foods such as meat, fruit, nuts, and a variety of vegetables. However, serotonin taken into the body through dietary sources remains solely in the bloodstream, never entering into the serotonin pathways of the brain. Within the brain, serotonin is associated with a variety of important centers, including those that control appetite, memory, sleep, and learning. Serotonin is also closely associated with feelings of well being, acting in conjunction with endorphins, GABA, and dopamine to generate the biological process known as the reward cascade. In fact, many pharmaceuticals designed to fight depression, bipolar disorder, and a number of other mood-related conditions function by stimulating serotonin production or inhibiting its uptake.