This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
[{'content': 'All of the following are excitatory neurotransmitters except \nSelect and explain. \nA. Gamma-aminobutyric acid, B. Acetylcholine, C. Dopamine, D. Serotomin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: GABA is the major inhibitory mediator in the brain, including being responsible for presynaptic inhibition. GABA, which exists as b-aminobutyrate in the body fluidsReference: Ganong review of medical physiology 23rd edition Page no; 141', 'role': 'assistant'}]