Dopamine is one of the brain’s neurotransmitters—a chemical
that ferries information between neurons. Dopamine helps regulate movement,
attention, learning, and emotional responses. It also enables us not only to
see rewards, but to take action to move toward them. Since dopamine contributes
to feelings of pleasures and satisfaction as part of the reward system, the
neurotransmitter also plays a part in addiction.
Neurotransmitters are chemicals made by nerve cells called
neurons. They’re used to communicate messages across different parts of the
brain and between the brain and the rest of the body.
Dopamine is involved mainly in controlling movement. An
insufficient production of dopamine in part of the brain can lead to
Parkinson’s disease. Parkinson’s diseases is a noncurable nervous system
disorder that affects movement. It may cause stiffness, tremors, shaking, and
other symptoms. How Dopamine Works Inside the Brain’s Reward System
Dopamine plays a role in the brain’s reward system, helping
to reinforce certain behaviors that result in reward. A surge of dopamine, for
instance, is what prompts a laboratory rat to repeatedly press a lever to get a
pellet of food, or a human to take a second slice of pizza.
Recently, scientists have shown that dopamine can help with
unlearning fearful associations. In a study published in June 2018 in the
journal Nature Communications, researchers uncovered the role of dopamine in
lessening fearful reactions over time, an important component of therapy for
people with anxiety disorders, such as phobias or post-traumatic stress
disorder (PTSD).
More on the Brain and Dopamine
Dopamine also helps to aid the flow of information to the
brain regions responsible for thought and emotion. According to the National
Institute of Mental Health, too little dopamine — or problems in the way the
brain uses dopamine — may play a role in disorders such as schizophrenia or
attention deficit hyperactivity disorder (ADHD).
Dopamine and the Body’s Stress Response
In other parts of the body, dopamine acts as type of hormone
called a catecholamine. Catecholamines are made in the adrenal glands — small
hormone production factories that sit on top of the kidneys.
There are three main catecholamines:
Dopamine
Epinephrine
(adrenaline)
Norepinephrine
These hormones get released into the bloodstream when the
body is physically or mentally stressed. They cause biochemical changes that
activate the so-called fight-or-flight response. That’s the body’s natural
reaction to a real or perceived stress.
Dopamine has many functions outside the brain. It acts as a
vasodilator, helping to widen blood vessels. It helps to increase urine output
in the kidneys, and in the pancreas it reduces the production of insulin, a
hormone involved in blood sugar regulation.
Dopamine and Digestion
Dopamine also plays a role in the digestive system, helping
to make sure the contents of the gastrointestinal tract don’t pass through too
quickly. In the immune system, dopamine dampens inflammation, normally helping
to prevent the sort of runaway immune response seen in autoimmune diseases.
What Are Dopamine Receptors?
Dopamine receptors are proteins found in the brain and
nerves throughout the body. If neurotransmitters are the nerve cells’ chemical
messengers, then receptors are the nerve cells’ chemical receivers.
As a dopamine signal approaches a nearby neuron, it attaches
to that neuron’s receptor. The receptor and neurotransmitter work like a lock
and key. The dopamine attaches to the dopamine receptor, delivering its
chemical message by causing changes in the receiving nerve cell.
Why Dopamine Receptors Are Key for Neurological and Physical
Functions
Dopamine receptors play an important role in many
neurological processes, including movement coordination and fine motor control,
pleasure, cognition, memory, and learning.
Abnormally functioning dopamine receptors may play a role in
several neurological and psychiatric illnesses. Therefore, dopamine receptors
are a natural target for many drug therapies.
Some street drugs, including heroin, cocaine, and
methamphetamine, also act on dopamine receptors in the brain. They can cause
nerve cells to release too much dopamine or prevent the nervous system from
recycling dopamine once it’s done its job, highjacking the brain’s reward
system.
Euphoric Effects, Pleasure, and Dopamine
Dopamine creates feelings of pleasure. Certain drugs, such
as cocaine, can cause large amounts of dopamine to flood the system, producing
euphoric effects or a “high” that leave the user wanting more.
As these drugs are abused over time, dopamine’s pleasurable
effects on the brain lessen.
To regain these pleasurable effects, a user must increase
the amount of drug taken. This phenomenon is called “tolerance.”
Dopamine Drugs
There are a few classes of medication that work on the
dopamine pathways of the brain to treat disease. They include:
Levodopa (L-dopa) Levodopa is a drug used to treat
Parkinson’s disease. Symptoms of Parkinson’s disease start to show up when
dopamine-producing cells in the brain die. Levodopa, a precursor chemical to
dopamine, helps to boost dopamine levels in the brain. Once levodopa reaches
the brain, it transforms into dopamine.
Dopamine Agonists Dopamine agonists are a class of drugs
that bind to and activate dopamine receptors in the brain. They mimic the
action of naturally-occurring dopamine in the brain, causing the neurons to
react as they would to dopamine.
Dopamine agonists trick the brain into thinking it’s getting
the dopamine it needs.
Dopamine agonists are used to treat low dopamine conditions,
including Parkinson’s disease and restless legs syndrome (RLS). RLS is a sleep
disorder that causes an unpleasant tingling or twitching sensation in the legs
when lying or sitting down, mostly at night, resulting in an irresistible urge
to move them, and in insomnia. Like Parkinson’s disease, it too seems to be
caused by a dopamine shortage in the brain.
Dopamine agonists also are sometimes used to treat
depression and fibromyalgia.
Common dopamine agonist drugs include:
Mirapex
(ramipexole)
Neupro
(rotigotine)
Requip
(ropinirole)
Serious side effects associated with dopamine agonists
include low blood pressure, dizziness when standing up, hallucinations, and
impulse control disorders, such as pathological gambling, compulsive eating,
and hypersexuality.
Dopamine Antagonists Dopamine antagonists are a class of
drugs that bind to and block dopamine receptors. Dopamine antagonists turn down
dopamine activity, which may be useful for the treatment of psychiatric
conditions such as schizophrenia and bipolar disorder, which have been
associated with an overactive dopamine system.
Many antipsychotic drugs are dopamine antagonists, working
to block dopamine receptors in the brain.
Dopamine antagonists that act on dopamine receptors in the
gastrointestinal tract may be used to treat nausea, or as anti-emetics to stop
vomiting.
Dopamine antagonist drugs include:
Thorazine or
Largactil (chlorpromazine)
Reglan
(metoclopramide)
Phenergan
(promethazine)
Invenga
(paliperidone)
Risperdal
(risperidone)
Seroquel
(quetiapine)
Clozaril
(clozepine)
Dopamine Supplements and Supplementation
Dopamine is found in many types of food, but dopamine itself
can’t cross into the brain from the bloodstream, so eating foods that contain
dopamine won’t raise dopamine levels in the brain. But dopamine’s precursor
molecule, tyrosine, can cross the blood-brain barrier, according to a review
published in November 2015 in the Journal of Psychiatric Research.
Tyrosine is an amino acid found naturally in protein-rich
foods, such as cheese, nuts, and meat. Under certain circumstances, tyrosine
supplements can help boost dopamine levels in the brain, leading some to
believe that tyrosine supplementation could help with neurological and mental
health conditions involving low dopamine. In fact, the Parkinson’s disease drug
Levodopa was originally synthesized from one form of tyrosine.
But scientific studies have failed to show that this is the
case. Tyrosine supplements don’t appear to have much — if any — effect on
physiology, thought, or behavior.
Dopamine is heavily involved in the motor system. When the
brain fails to produce enough dopamine, it can result in Parkinson’s disease. A
primary treatment for Parkinson’s disease, therefore, is a drug called L-dopa,
which spurs the production of dopamine. Dopamine has also been implicated in
schizophrenia and ADHD, but its role is not fully understood. People with low
dopamine activity may also be more prone to addiction. The presence of a
certain kind of dopamine receptor is associated with sensation-seeking, more
commonly known as risk taking.
