**Question:** Ammonia in brain is trapped by -

A. Glutamine synthetase
B. Glutamate
C. Glutamate transporter-1 (GLT-1)
D. Glial cells

**Core Concept:** Ammonia is a waste product generated during the breakdown of proteins, nucleic acids, and other nitrogenous compounds in the body. In the brain, ammonia is eliminated primarily through the urea cycle, which produces urea, a less toxic compound that can be transported out of the brain. Ammonia removal from the brain is essential to prevent ammonia toxicity, which can lead to encephalopathy and brain damage.

**Why the Correct Answer is Right:** The correct answer, Glutamine synthetase (option A), plays a crucial role in ammonia detoxification within the brain. Glutamine synthetase is an enzyme located in astrocytes, which is the primary site for ammonia detoxification in the brain. It catalyzes the formation of glutamine from ammonia and aspartate, converting ammonia into a less toxic compound (glutamine) that can be transported out of the brain via the urea cycle.

**Why Each Wrong Option is Incorrect:**

A. Glutamate (option B) is a neurotransmitter involved in the excitatory signaling within the brain. While glutamate plays a role in the ammonia detoxification process, the primary enzyme involved is glutamine synthetase, not glutamate.

B. Glutamate transporter-1 (GLT-1) (option C) plays a role in regulating extracellular glutamate levels, ensuring proper neurotransmission. Although GLT-1 contributes to ammonia clearance, it is not the primary enzyme responsible for detoxifying ammonia in the brain.

D. Glial cells (option D) are supportive cells in the brain that include astrocytes, oligodendrocytes, and microglia. While glial cells are involved in ammonia detoxification, the primary enzyme responsible is glutamine synthetase, not glial cells as a whole.

**Clinical Pearl:** Glutamine synthetase is the primary enzyme responsible for detoxifying ammonia in the brain by converting ammonia into glutamine, which can be transported out of the brain via the urea cycle. Understanding the role of glutamine synthetase is essential for preventing ammonia toxicity and its associated neurological complications.