What neurotransmitter is deficient in Parkinson's disease?

The neurotransmitter most characteristically deficient in Parkinson's disease is dopamine. The main loss occurs in dopamine-producing neurons in the substantia nigra, a region of the midbrain that helps regulate movement.

These neurons normally send dopamine to the striatum, a group of structures involved in initiating and coordinating purposeful motion. As dopamine levels fall, brain circuits controlling movement become imbalanced. This contributes to Parkinson's classic motor symptoms: resting tremor, slowness of movement, muscle rigidity, and problems with balance.

Dopamine deficiency is central to Parkinson's disease, but the condition is more than a simple single-chemical shortage. Other neurotransmitter systems, including noradrenaline and acetylcholine, can also be affected, and non-motor symptoms may appear years before movement problems. Levodopa is the most effective medicine for replacing dopamine signaling because the dopamine molecule itself does not cross the blood-brain barrier efficiently. In the brain, levodopa is converted into dopamine.