<prompt> Which drug acts through alpha subunit of GABA ?BenzodiazepineBarbiturateHaloperidolTCA  <response>: Ans. is a i.e., Benzodiazepine o The exact subunit structures of native GABA receptors are still are unknown, but it is thought that most GABA receptor are composed of a, b and y subunits that Coassemble with some unceain stoichiometry. o Binding site of GABA is on beta-subunit. o Benzodiazepine site is located on the alpha subunit but the stabilization or completion of that site in the assembled structure also requires the y subunit. The photo-affinity labelling of the benzodiazepine site has confirmed, using isoform - antibodies, to be on an alpha and not a y subunit. -- Receptor subunit complexes. o So, BZD binding site is present on a subunit at alpha - y interface, and both a y units are required for BZDs action. o Barbiturates act on picrotoxin site that is located usually on beta- subunit at alpha - beta interface. Both alpha beta subunit are required for barbiturates action. GABA --- beta - subunit BZD --- alpha subunit at a - y interface, i.e. ag site Barbiturate - --- beta subunit at alpha - beta interface, i.e. ab site 