National Institute on Drug Abuse
What do drug addiction and Parkinson’s disease have in common? Improper levels of dopamine (DOAP-uh-meen). This chemical acts as a messenger between brain cells. Dopamine is important for many of our daily behaviors. It plays a role in how we move, for instance, as well as what we eat, how we learn and even whether we become addicted to drugs.
Chemical messengers in the brain are called neurotransmitters. They shuttle across the spaces between cells. These messengers then bind to docking-station molecules called receptors. Those receptors relay the signal carried by the neurotransmitter from one cell to its neighbor.
Different neurotransmitters are made in different parts of the brain. Two main brain areas produce dopamine. One is called the substantia nigra (Sub-STAN-sha NY-grah). It’s a tiny strip of tissue on either side of the base of your brain. It sits in a region known as the midbrain. Close by is the ventral tegmental area. It, too, makes dopamine.
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These two brain areas are very thin and tiny. Together they are smaller than a postage stamp. But the dopamine they produce relays signals that travel throughout the brain. Dopamine from the substantia nigra helps us begin movements and speech. When the brain cells that make dopamine in this area start to die off, a person can have trouble initiating movement. It’s just one of the many symptoms ravaging people with Parkinson’s disease (a condition best known for uncontrollable tremors). To move normally, patients with Parkinson’s take a drug that lets them make more dopamine (or they get an implant that stimulates deep regions of the brain).
The dopamine from the ventral tegmental area doesn’t help people move — at least, not directly. Instead, this area usually sends dopamine into the brain when animals (including people) expect or receive a reward. That reward might be a delicious slice of pizza or a favorite song. This dopamine release tells the brain that whatever it just experienced is worth getting more of. And that helps animals (including people) change their behaviors in ways that will help them attain more of the rewarding item or experience.
Dopamine also helps with reinforcement — motivating an animal to do something again and again. Dopamine is what prompts a lab animal, for instance, to repeatedly press a lever to get tasty pellets of food. And it’s part of why humans seek out another slice of pizza. Reward and reinforcement help us learn where to find important things such as food or water, so that we can go back for more. Dopamine even affects moods. Things that are rewarding tend to make us feel pretty good. Lowering dopamine can make animals lose pleasure in activities like eating and drinking. This joyless state is called anhedonia (AN-heh-DOE-nee-uh).
Because of its roles in reward and reinforcement, dopamine also helps animals focus on things. Anything that’s rewarding, after all, is usually well worth our attention.
But dopamine has a more sinister side. Drugs such as cocaine, nicotine and heroin cause huge boosts in dopamine. The “high” people feel when they use drugs comes partly from that dopamine spike. And that prompts people to seek out those drugs again and again — even though they are harmful. Indeed, the brain “reward” associated with that high can lead to drug abuse and eventually to addiction.
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addicted Unable to control the use of a habit-forming drug or to forego an unhealthy habit (such as video game playing or phone texting). It results from an illness triggered by brain changes that occur after using some drugs or engaging in some extremely pleasurable activities. People with an addiction will feel a compelling need to use a drug (which can be alcohol, the nicotine in tobacco, a prescription drug or an illegal chemical such as cocaine or heroin), even when the user knows that doing so risks severe health or legal consequences.
anhedonia A state where animals or people no longer find pleasure in activities they used to enjoy (from favorite hobbies to simply eating tasty food) and are no longer motivated to do those activities. People with some mental illnesses, such as depression and schizophrenia, may experience anhedonia as part of their disease.
behavior The way a person or other organism acts towards others, or conducts itself.
cell The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size. Some organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
chemical A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.
docking The act of bringing together and inserting one thing into another.
dopamine A neurotransmitter, this chemical helps transmit signals in the brain.
heroin A highly addictive and illegal drug derived from morphine, a potent pain killer. People often take heroin as a narcotic — something that dulls the senses, relieves pain and makes them sleepy or unmotivated to do anything other than lay in a slump.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
neurotransmitter A chemical released at the end of a neuron to carry a message to a neighboring cell. This chemical travels across the space between two cells, and then binds to molecules on a neighboring cell to transmit a message. Neurotransmitters are released from neurons, and can bind to neurons or to other types of cell, including those that make up muscles or glands.
nicotine A colorless, oily chemical produced in tobacco and certain other plants. It creates the ‘buzz’ effect associated with smoking. It also is highly addictive, making it hard for smokers to give us their use of cigarettes. The chemical is also a poison, sometimes used as a pesticide to kill insects and even some invasive snakes or frogs.
Parkinson’s disease A disease of the brain and nervous system that causes tremors and affects movement, memory and mood.
receptor (in biology) A molecule in cells that serves as a docking station for another molecule. That second molecule can turn on some special activity by the cell.
reinforcement Some consequence that guides the future behavior of an animal or person. If a rat presses a lever and receives a food pellet, that food pellet becomes a reinforcement of lever-pushing — it’s the reward that will teach the rat to press the lever again.
reward (In animal behavior) A stimulus, such as a tasty food pellet, that is offered to an animal or person to get them to change their behavior or learn a task.
substantia nigra Part of the midbrain. It produces dopamine, a brain signaling chemical, which plays an important role in helping people initiate movements. Death of the dopamine-producing cells in this brain region lead to some of the classic symptoms of Parkinson’s disease.
tissue Any of the distinct types of material, comprised of cells, which make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues. And brain tissue will be very different from bone or heart tissue.
ventral tegmental area Part of the midbrain. It plays an important role in thinking, motivation, emotions and addiction.