**Core Concept**
The detoxification of ammonia in the brain involves the conversion of ammonia into a less toxic compound, which is essential for maintaining brain function and preventing neurotoxicity. This process is mediated by the enzyme glutamine synthetase, which catalyzes the condensation of glutamate and ammonia to form glutamine.

**Why the Correct Answer is Right**
Glutamine synthetase is a key enzyme in the brain that catalyzes the conversion of glutamate and ammonia to form glutamine. This reaction is essential for detoxifying ammonia, which is a toxic byproduct of protein metabolism. The formation of glutamine is a critical step in the regulation of ammonia levels in the brain, and it helps to prevent neurotoxicity. Glutamine synthetase is highly expressed in astrocytes, which are specialized glial cells that play a key role in maintaining the brain's internal environment.

**Why Each Wrong Option is Incorrect**
**Option A:** Glutamate is an excitatory neurotransmitter that plays a key role in neurotransmission, but it is not involved in the detoxification of ammonia.
**Option B:** Uric acid is a waste product of purine metabolism, but it is not directly involved in the detoxification of ammonia.
**Option D:** Urea is a waste product of protein metabolism, but it is primarily produced in the liver and kidneys, not in the brain.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the brain's ability to detoxify ammonia is limited, and excessive ammonia levels can lead to neurotoxicity and neurological dysfunction. This is why patients with liver disease or other conditions that impair ammonia metabolism may experience neurological symptoms.

**✓ Correct Answer: C. Glutamine**