This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Psychiatry
[{'content': 'Which drug acts through alpha subunit of GABA? \nSelect and explain. \nA. Benzodiazepine, B. Barbiturate, C. Haloperidol, D. TCA', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The exact subunit structures of native GABA receptors are still unknown, but it is thought that most GABA receptor are composed of α, β and γ subunits that coassemble with some uncertain stoichiometry.\nBinding site of GABA is on β -subunit.\nBenzodiazepine site is located on the a subunit but the stabilization or completion of that site in the assembled\xa0structure requires also the γ subunit.\n\n"The photo - affinity labeling of the benzodiazepine site has confirmed, using isoform - antibodies, to be on an α\xa0and not a γ subunit".\n\nSo, BZD binding site is present on α subunit at α - γ interface, and both α & γ units are required for BZDs action.\nBarbiturates act on Picrotoxin site that is located usually on β- subunit at α -β interface. Both α & β subunit are required for barbiturates action.\n\n\n\nGABA → β - subunit.\nBZD\xa0→\xa0α subunit at α - γ interface, i.e. α / γ site.\nBarbiturate\xa0→ β subunit at α\xa0-\xa0β interface, i.e. α / β site.', 'role': 'assistant'}]