**Core Concept**
The detoxification of ammonia in the brain involves the urea cycle, also known as the ornithine cycle, which is a series of biochemical reactions that convert ammonia into urea. This process is crucial for maintaining the brain's acid-base balance and preventing neurotoxicity.

**Why the Correct Answer is Right**
Ammonia is detoxified in the brain by the enzyme glutamine synthetase, which catalyzes the conversion of glutamate and ammonia into glutamine. This reaction is a key step in the urea cycle, allowing the brain to safely eliminate ammonia. The glutamine synthetase enzyme is found in astrocytes, which are specialized glial cells in the brain that play a crucial role in maintaining the brain's environment.

**Why Each Wrong Option is Incorrect**
**Option A:** Glutamate dehydrogenase is an enzyme that catalyzes the conversion of glutamate to α-ketoglutarate, but it does not play a direct role in ammonia detoxification.
**Option B:** Aspartate aminotransferase is an enzyme involved in the metabolism of aspartate, but it is not directly involved in ammonia detoxification.
**Option C:** Urea is the end product of the urea cycle, but it is not the enzyme responsible for ammonia detoxification in the brain.

**Clinical Pearl / High-Yield Fact**
The urea cycle is a complex process that involves multiple enzymes and steps, but it is critical for maintaining the brain's acid-base balance and preventing neurotoxicity. Glutamine synthetase is a key enzyme in this process, and its dysfunction can lead to neurological disorders.

**Correct Answer:** C.