"Monoamines" is a term used to describe neurotransmitters that act to transmit signals of a nerve or neuron to a cell. They play a significant role in the metabolism or processing of the brain and elicit many different behaviors. Monoamines fall under two categories — catecholamines and indolamines — and within each class are different neurotransmitters. Catecholamines consist of neurotransmitters such as epinephrine, norepinephrine and dopamine, and indolamines include the neurotransmitter serotonin.
Chemical substances called catecholamines are created within the body from amino acids such as phenylalanine and tyrosine. Amino acids are a vital building block for proteins within the body. Proteins are produced within the human body by 20 different amino acids, nine of which have been classified as "essential" or indispensable amino acids. They are given this label because the body alone is unable to produce them but is very dependent upon them. These amino acids are provided to the body via food.
Catecholamines are a class of monoamines consisting of epinephrine, norepinephrine and dopamine. These neurotransmitters usually operate within the sympathetic and central nervous system and have many different roles. Under a microscope, the chemical structure of a catecholamine consists of a benzene ring with amine and hydroxyl side chains.
Epinephrine is released from the adrenal glands and stimulates the sympathetic nervous system, creating feelings such as excitement, shock and fear. Norepinephrine is the precursor of epinephrine and functions to mediate the signaling of such nerve impulses. Dopamine is the precursor of norepinephrine. The greatest concentration of dopamine is found within the basal ganglia, an area of the brain involved in regulating subconscious voluntary movement.
Indolamines are another class of monoamines and consist of the neurotransmitter serotonin. This chemical substance is extensively spread throughout the body's tissue. It is particularly found within the brain, in the lining of the gastrointestinal tract and in platelets located in blood. Serotonin has the role of controlling states of consciousness and mood, and it functions to inhibit gastric secretions from the gastrointestinal tract.
Monoamines are neuromodulators, which means they are able to stimulate many neurons that are located far away from each other. As a result of this, monoamines are able to produce many different behavioral outcomes. Monoamines are broken down by naturally occurring enzymes called monoamine oxidases (MAOs).