An experimental ligand binds the benzodiazepine site of the GABA-A receptor and, when applied alone to cells showing constitutive receptor activity, pushes chloride channel opening below the baseline level seen without any ligand present. How should this ligand be classified?

• A Neutral antagonist
• B Partial agonist
• C Positive allosteric modulator
• D Inverse agonist ✓

Explanation

Some receptors show constitutive activity even without a ligand. An inverse agonist stabilizes the inactive receptor conformation and reduces signaling below the basal level, whereas a neutral antagonist simply occupies the receptor without changing activity. Beta-carbolines at the benzodiazepine site are classic examples. Option C is wrong because positive allosteric modulators enhance GABA effects and raise activity above baseline, the opposite of the described finding.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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