Action of which anaesthetic agent is through NMDA receptors?
**Core Concept**
The question is testing the understanding of the molecular mechanism of action of certain anaesthetic agents on N-methyl-D-aspartate (NMDA) receptors. NMDA receptors are a subtype of glutamate receptors involved in synaptic plasticity and memory formation.
**Why the Correct Answer is Right**
Ketamine, a dissociative anaesthetic agent, exerts its effects by acting as a non-competitive antagonist of NMDA receptors. This action is distinct from other anaesthetics that act on GABA receptors or other ion channels. By blocking NMDA receptors, ketamine prevents the excessive release of glutamate, thereby reducing excitatory neurotransmission and leading to anaesthesia.
**Why Each Wrong Option is Incorrect**
**Option A:** Propofol, a commonly used intravenous anaesthetic agent, primarily acts on GABA_A receptors to enhance inhibitory neurotransmission. It does not have a significant effect on NMDA receptors.
**Option B:** Etomidate, another intravenous anaesthetic agent, also acts on GABA_A receptors to produce its anaesthetic effects. It does not have a notable action on NMDA receptors.
**Option C:** Midazolam, a benzodiazepine, enhances the activity of GABA at GABA_A receptors, leading to sedation and amnesia. It does not have a significant effect on NMDA receptors.
**Clinical Pearl / High-Yield Fact**
Ketamine's unique mechanism of action on NMDA receptors makes it a useful agent for treating pain and reducing the risk of opioid-induced respiratory depression in certain clinical scenarios.
**Correct Answer:** C. Ketamine.