**Question:** Which of the following agents do not act via GABAA – Cl– channel complex receptors?

**Core Concept:** GABAA receptors are neurotransmitter receptors found primarily in the central nervous system, which play a crucial role in modulating neuronal excitability. GABA (gamma-aminobutyric acid) is the inhibitory neurotransmitter that binds to GABAA receptors, leading to the opening of chloride channels and hyperpolarization of the neuron. The GABAA – Cl– channel complex receptors are responsible for the chloride influx and the generation of inhibitory postsynaptic potentials.

**Why the Correct Answer is Right:** The correct answer, **Option D**, is **"Diazepam"**, a benzodiazepine. Benzodiazepines, unlike GABA, do not directly interact with the chloride channel complex of the GABAA receptors. Instead, they act by enhancing the GABA action on the receptors, leading to increased chloride influx and neuronal hyperpolarization. This results in a heightened inhibitory response but does not involve direct interaction with the chloride channel complex.

**Why Each Wrong Option is Incorrect:**

A. **"Buspirone"**: Although buspirone is a serotonin-specific 5-HT1A receptor agonist, it does not directly interact with the chloride channel complex. Buspirone primarily acts on serotonin receptors, enhancing serotonergic neurotransmission.

B. **"Methotrimeprazine"**: Methotrimeprazine is a selective serotonin reuptake inhibitor (SSRI), and its main action involves inhibiting the reuptake of serotonin, thereby increasing its concentration in the synaptic cleft. As it does not directly interact with the chloride channel complex, methotrimeprazine is incorrect.

C. **"Loperamide":** Loperamide is an opioid receptor agonist, primarily targeting the mu-opioid receptors. It does not directly modulate the chloride channel complex of the GABAA receptors, making it an incorrect choice.

**Clinical Pearl:** Benzodiazepines, such as diazepam, are commonly used as anxiolytics and sedatives due to their ability to increase the inhibitory effect of GABA in the brain. However, their mechanism of action does not involve direct interaction with the chloride channel complex of the GABAA receptors.