**Question:** All of the following acts on GABA receptor except:-

A. Benzodiazepine
B. Opioids
C. NMDA receptors
D. Cholinergic receptors

**Core Concept:** GABA receptors are inhibitory neurotransmitter receptors found in the central nervous system (CNS) that play a crucial role in regulating neuronal excitability, sleep, and anxiety. GABA acts as a neurotransmitter, binding to GABA receptors to modulate neuronal activity. The four types of GABA receptors are GABA-A, GABA-B, GABA-C, and GABA-D (which is not yet fully characterized).

**Why the Correct Answer is Right:**

Option A (Benzodiazepine) is incorrect because benzodiazepines are a class of drugs that enhance the inhibitory effect of GABA on GABA-A receptors. By binding to the benzodiazepine site on GABA-A receptors, benzodiazepines potentiate the chloride ion conductance, leading to increased inhibitory activity.

Option B (Opioids) is incorrect because opioids, like morphine or codeine, are a class of drugs that primarily act on mu-opioid receptors (μ-OR) and delta-opioid receptors (δ-OR), which are involved in pain modulation, reward, and addiction. Opioids have no direct interaction with GABA receptors.

Option C (NMDA receptors) is incorrect because NMDA receptors (N-methyl-D-aspartate receptors) are a subtype of glutamate receptors involved in excitatory neurotransmission. NMDA receptors are distinct from GABA receptors and do not act on the same neurotransmitter system.

Option D (Cholinergic receptors) is incorrect because cholinergic receptors are mainly involved in the modulation of acetylcholine neurotransmission, which is excitatory (increases neuronal activity) rather than inhibitory like GABA receptors. Cholinergic receptors are not related to the GABAergic system.

**Why Each Wrong Option is Incorrect:**

1. **Option A (Benzodiazepine):** Benzodiazepines are a different class of drugs that act on GABA receptors, not opioid receptors. Benzodiazepines potentiate GABA-A receptors, enhancing the inhibitory effects of GABA on the postsynaptic neuron.
2. **Option B (Opioids):** Opioids are primarily involved in modulating pain, reward, and addiction via mu (μ), delta (δ), and kappa (κ) opioid receptors. They primarily act on excitatory neurotransmitters such as glutamate and not inhibitory neurotransmitters like GABA.
3. **Option C (NMDA receptors):** NMDA receptors are excitatory receptors that mediate neuronal excitability through glutamate neurotransmission. They have no relationship with the GABAergic system, which is inhibitory in nature.
4. **Option D (Cholinergic receptors):** Cholinergic receptors are involved in modulating acetylcholine neurotransmission, which is excitatory and contributes to increased neuronal activity. Cholinergic receptors are unrelated to the GABAergic system