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L-DOPA is an amino acid involved in the synthesis of the neurotransmitter dopamine.
When dopamine is produced in the brain, the amino acid tyrosine is first converted to
L-DOPA and then L-DOPA is converted to dopamine.
While dopamine administered as a drug cannot pass the blood-brain barrier to enter the
brain, L-DOPA can, and this characteristic has helped to make L-DOPA the most common
treatment for Parkinson’s disease.
Parkinson’s disease is characterized by the death of dopamine neurons in a region
of the brainstem called the substantia nigra, and a subsequent deficiency of dopamine in
a group of structures known as the basal ganglia.
This dopamine deficiency is thought to contribute to the problems Parkinson’s patients experience
with movement.
L-DOPA has a remarkable ability to reduce the symptoms of Parkinson’s disease in some
patients.
The generally accepted mechanism for this action is that the brain is able to use L-DOPA
to synthesize more dopamine and replenish its depleted dopamine stores.
While this does seem to be a main characteristic of L-DOPA’s mechanism, however, it is thought
that L-DOPA may exert a therapeutic effect through other mechanisms as well, such as
by acting as a neurotransmitter on its own.
While L-DOPA can effectively treat the symptoms of Parkinson’s disease, it is not able to
stop the neurodegeneration caused by the disease.
Thus, Parkinson’s disease continues to progress even with L-DOPA treatment.
Additionally, over time L-DOPA’s effectiveness begins to decrease and eventually movement
problems, known as L-DOPA dyskinesias, may occur in response to L-DOPA treatment.
L-DOPA dyskinesias typically involve quick involuntary movements, but may also include
a number of other complications like uncontrolled muscle contractions or writhing movements.
The mechanisms underlying L-DOPA dyskinesias are still not completely understood, and may
involve factors like the continued death of dopamine neurons in the substantia nigra and
fluctuations in dopamine levels caused by L-DOPA treatment.