Which among the following is an excitatory amino acid receptor antagonist?

Appeared in: AIIMS Raipur - 2017 (shift-2)

Explanation

Excitatory Amino Acid (EAA) receptors, also known as glutamate receptors, are a class of receptors that mediate excitatory neurotransmission.
The main types are NMDA, AMPA, and Kainate receptors.
Phencyclidine (PCP) is a well-known non-competitive antagonist of the NMDA receptor.
It works by blocking the receptor's ion channel, thereby inhibiting the excitatory effects of glutamate.
This mechanism classifies it as an EAA receptor antagonist.

Option B: Quisqualate is an agonist, not an antagonist. It specifically activates AMPA receptors, a subtype of glutamate receptors.
Option C: Homocysteate is an agonist. It is an excitatory amino acid that can activate glutamate receptors, particularly NMDA receptors.
Option D: Kainite (or Kainic acid) is the specific agonist for which the Kainate receptor subtype is named. It is a potent excitatory agent.

Visual 1: Diagram - A diagram of the NMDA receptor, showing the binding site for glutamate (agonist) and the separate site within the ion channel where phencyclidine (non-competitive antagonist) binds and blocks ion flow. This visual helps differentiate between agonist and antagonist actions.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacology of Excitatory Amino Acid (EAA) Receptors as background academic context rather than a clinical decision trigger.
Understanding the difference between EAA receptor agonists and antagonists is critical in pharmacology and toxicology.
NMDA receptor antagonists have clinical applications. For example, Ketamine (related to PCP) is used for dissociative anesthesia, and Memantine is used to treat Alzheimer's disease.
Phencyclidine (PCP) is a drug of abuse known for causing hallucinations, delirium, and psychosis due to its potent effects on NMDA receptors. Nurses may encounter patients with PCP intoxication in emergency settings.

How to Approach the Question

First, identify the core concept of the question: 'excitatory amino acid receptor antagonist'. This means you are looking for a drug that blocks the action of excitatory amino acids like glutamate.
Recall the main types of EAA (glutamate) receptors: NMDA, AMPA, and Kainate.
Systematically evaluate each option to determine its action (agonist or antagonist) on these receptors.
Phencyclidine is a classic NMDA receptor antagonist. Quisqualate and Kainite are the defining agonists for their respective receptors (AMPA and Kainate). Homocysteate is also an agonist.
Based on this classification, conclude that Phencyclidine is the only antagonist in the list.

Concept Tested & Keywords

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Practise the full AIIMS Raipur - 2017 (shift-2)

Attempt every question from this paper in a timed mock, then review the full solution for each one.