**Question:** Drug used to halt the process of degeneration of dopaminergic neurons in nigrostriatal pathway is -

A. Levodopa
B. Risperidone
C. Amantadine
D. Methylphenidate

**Core Concept:**
The nigrostriatal pathway is a crucial component of the central nervous system (CNS) involved in the regulation of movement, mood, and cognition. It consists of dopaminergic neurons originating from the substantia nigra and projecting to the striatum. Degeneration of these neurons is associated with Parkinson's disease, characterized by motor symptoms like tremors, rigidity, bradykinesia, and non-motor symptoms.

**Why the Correct Answer is Right:**
The correct answer, C. Amantadine, is an antipsychotic drug primarily used to treat Parkinson's disease. Its mechanism of action involves blocking the action of the neurotransmitter acetylcholine at the motor end plate, thereby increasing dopamine levels in the striatum. This helps in improving motor symptoms, such as tremors, rigidity, and bradykinesia in Parkinson's disease.

**Why Each Wrong Option is Incorrect:**
A. Levodopa (L-DOPA) is a precursor to dopamine and is commonly used in the treatment of Parkinson's disease. However, it does not halt the degeneration of dopaminergic neurons in the nigrostriatal pathway.

B. Risperidone is an atypical antipsychotic drug used to treat schizophrenia and bipolar disorder. It does not specifically target the degeneration of dopaminergic neurons in Parkinson's disease.

D. Methylphenidate is an amphetamine-like stimulant used in the treatment of attention-deficit/hyperactivity disorder (ADHD) and narcolepsy. It does not address the degeneration of dopaminergic neurons in Parkinson's disease.

**Clinical Pearl:**
In Parkinson's disease, the loss of dopaminergic neurons contributes to the motor symptoms and overall progression of the disease. Although L-DOPA and dopamine agonists can alleviate symptoms, they do not halt the degeneration of these neurons. Amantadine, on the other hand, specifically targets the motor symptoms by increasing dopamine levels in the striatum, improving motor function and reducing shaking in Parkinson's disease patients. However, it does not prevent the degeneration of dopaminergic neurons, which is crucial for long-term management of the disease.