Which of the following antiparkinsonian drugs directly activates dopaminergic D2 receptors in the striatum?
## **Core Concept**
The question tests understanding of antiparkinsonian drugs and their mechanisms of action, specifically those that directly stimulate dopaminergic D2 receptors in the striatum. Parkinson's disease is characterized by the degeneration of dopaminergic neurons in the substantia nigra, leading to decreased dopamine levels in the striatum. Antiparkinsonian drugs aim to either increase dopamine levels or mimic its action.
## **Why the Correct Answer is Right**
The correct answer, , directly activates dopaminergic D2 receptors in the striatum. This class of drugs, known as dopamine agonists, mimics the action of dopamine by directly stimulating dopamine receptors. By activating D2 receptors, these drugs help to alleviate the symptoms of Parkinson's disease, such as tremors, rigidity, and bradykinesia, without the need for increasing dopamine levels through other means like levodopa.
## **Why Each Wrong Option is Incorrect**
- **Option A:** is incorrect because it is a COMT (catechol-O-methyltransferase) inhibitor. COMT inhibitors work by blocking the enzyme responsible for the breakdown of dopamine, thereby increasing its availability and duration of action but not directly stimulating D2 receptors.
- **Option B:** is incorrect because it is a MAO-B (monoamine oxidase B) inhibitor. MAO-B inhibitors work by blocking the action of an enzyme that breaks down dopamine, thereby increasing dopamine levels but not directly stimulating D2 receptors.
- **Option D:** is incorrect because it primarily acts by inhibiting the NMDA receptor and has some anticholinergic effects but does not directly activate dopaminergic D2 receptors.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that dopamine agonists like can have a lower risk of dyskinesias and motor fluctuations compared to levodopa therapy, making them valuable in the management of Parkinson's disease, especially in early stages.
## **Correct Answer:** .