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: Pharmacology
All acts through GABAA receptors except - 
Select and explain. 
A. Benzodiazepines, B. Barbiturates, C. Zopiclone, D. Promethazine
D: Promethazine
Answer: D: Promethazine 
Explanation: Ans. is 'd' i.e., Promethazine GABA RECEPTORS o There are two types of GABA receptors:? 1) GABAA receptors :- These are intrinsic CI channels and when open cause increase in CI conductance and CNS depression. Drugs acting on these receptors are - i) Agnoists :- barbiturates, benzodiazepines, zopiclone, zolpidem, zoleplon, muscimol ii) Inverse agonist:- 0-carboline iii) Antagonist :- Flumazenil. iv) Other drugs :- Alphaxalone, alcohol, anticonvulsants (Gabapentine, vigabaterine), Picrotoxin 2) GABAB receptors :- These are G-protein coupled receptors. Baclofen is agonist and saclofen is antagonist on these receptors.