Understanding Dopamine and Parkinson’s Disease

What is dopamine, and why does it matter in Parkinson’s disease?

Todd M. Herrington, MD, PhD, a neurologist and movement disorders specialist with the Mass General Brigham Neuroscience Institute, has answers that shed light on many people’s experiences living with Parkinson’s. As part of a leading research team at Mass General Brigham developing cell therapy for Parkinson’s, Dr. Herrington studies ways to replace lost dopamine in the brain and improve disease care. He explains the connection between Parkinson’s disease and dopamine, what dopamine therapies can help, and what treatments are on the horizon.

What is dopamine?

Dopamine is a chemical messenger, called a neurotransmitter, in the brain. The brain has many types of neurotransmitters that control different functions by helping cells talk to each other. Dopamine plays an important role in movement, motivation, learning, mood, and pleasure.

Almost all the dopamine in your brain is made by cells in the midbrain called dopamine neurons. The midbrain sits at the base of your brain and is part of the brainstem, which connects your brain to your spinal cord.

How does Parkinson’s affect dopamine?

Parkinson’s disease causes dopamine neurons to become dysfunctional and die off over time. It especially impacts neurons in the part of the midbrain that connects to the motor system, which controls your body’s movement. As this connection changes, people experience a range of movement-related symptoms. Scientists don’t know exactly why Parkinson’s leads to dopamine loss or what causes the disease to develop in the first place.

“We think now that Parkinson’s may more commonly begin in the peripheral nervous system (nerve cells outside of your brain and spinal cord)” says Dr. Herrington. “From there, gradually—potentially even over decades—it may spread through the brain and end up affecting dopamine neurons.”

Parkinson’s symptoms caused by dopamine loss

Low dopamine can cause a range of movement-related symptoms, affecting each person differently. For some, dopamine loss can cause pain or discomfort and make it hard to do everyday activities.

On one or both sides of your body, you may experience:

• Resting tremor (uncontrollable, rhythmic shaking of a relaxed body part, such as your hand)
• Shuffling when you walk
• Slowness
• Stiffness

You may also have difficulty making:

• Fine movements, like fastening buttons or writing
• Large movements, such as getting dressed and putting your arm into a jacket sleeve
• Repetitive movements, such as when washing your hair or brushing your teeth

Does dopamine loss cause mood symptoms in Parkinson’s?

Dopamine loss may play a role in causing mood symptoms of Parkinson’s, such as depression, anxiety, and apathy (a loss of motivation or lack of interest in activities). Medications that increase dopamine can sometimes help treat these symptoms. However, other disease-related changes to the brain also influence mood in people with Parkinson’s.

How to measure dopamine levels in Parkinson’s

No blood test or spinal fluid test can measure dopamine levels directly. The main way to measure dopamine in the brain is through an imaging test called a dopamine transporter scan (DaTscan). DaTscans can show your doctor whether your dopamine system has declined, but they can’t tell your doctor why.

“A DaTscan can be useful to distinguish Parkinson’s from conditions that can sometimes mimic it, like essential tremor, or when there’s some question as to whether these symptoms are a side effect of medications that block dopamine signaling in the brain,” says Dr. Herrington.

In most cases, however, neurologists don’t use DaTscans to diagnose Parkinson’s. Instead, they complete a clinical exam to identify signs and symptoms of Parkinson’s. They may also assess whether medications that increase dopamine help relieve your movement symptoms.

How to increase dopamine with Parkinson’s treatment

Various types of Parkinson’s medication help restore the brain’s dopamine system and increase dopamine levels. These medications aim to improve movement symptoms, such as stiffness, slowness, and tremor.

Levodopa to boost dopamine production

The most effective treatment for dopamine loss in Parkinson’s is a medication called levodopa, which brain cells use to make dopamine. Levodopa medication is considered the gold standard treatment for movement symptoms of Parkinson’s.

“Your brain takes levodopa and converts it into dopamine,” says Dr. Herrington. “Essentially, it’s a way of boosting your brain’s remaining dopamine system and making it work more effectively.”

Extended-release levodopa and infusions

Some forms of levodopa release medication slowly over time, helping to avoid “off” periods—when symptoms worsen in between doses. You can also receive low doses of levodopa continuously through a small wearable pump. The pump connects to your intestine or just under your skin and helps keep symptoms steady throughout the day.

Dopamine agonists to mimic dopamine

A dopamine agonist is a medication that mimics dopamine in the brain. It acts like dopamine, rather than causing your brain to make more dopamine.

Your neurologist may recommend a dopamine agonist if you experience mild movement symptoms or in addition to levodopa. This medication can help control symptoms between levodopa doses or “off” periods.

When should I start Parkinson’s medication?

Not everyone with Parkinson’s needs medication. If you have mild movement symptoms that don’t interfere with daily activities, your neurologist and Parkinson’s care team may recommend waiting.

“It makes sense to start medication when motor symptoms are impairing your day-to-day quality of life,” says Dr. Herrington.

Learn about how Parkinson’s progresses.

New advances in Parkinson’s disease treatment

Scientists are actively working on methods to preserve dopamine neurons in Parkinson’s disease, from new medications to gene and cell therapies. If you’re interested in contributing to research to improve care, ask your neurologist about clinical trials for novel Parkinson’s treatments near you.

Dr. Herrington, neurosurgeon Jeffrey S. Schweitzer, MD, PhD, and colleagues at Mass General Brigham Neuroscience Institute are testing a groundbreaking stem cell-based therapy for Parkinson’s disease. “The hope is that we’ll improve the treatment of dopamine-related symptoms by replacing in a restorative way some of the dopamine signaling in the brain,” he says.

Stem cell therapy for Parkinson’s

Stem cell therapy for Parkinson’s disease involves growing cells in the laboratory that will become dopamine neurons and transplanting them into the brain. These cells may help treat bothersome or severe movement symptoms, especially when medication no longer works consistently.

 Stem cell therapy approaches include:

• Allogeneic cell therapy, which involves growing cells that can be transplanted into many different people’s brains to become dopamine neurons
• Autologous cell therapy, which turns samples from each individual patient into cells that will become dopamine neurons when transplanted back into their brain

“Both these approaches are moving forward in clinical trials here at Mass General Brigham and around the world,” says Dr. Herrington. “We’re hopeful that they can meaningfully improve quality of life for people with Parkinson’s.”