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
All of the following are excitatory neurotransmitters except 
Select and explain. 
A. Gamma-aminobutyric acid, B. Acetylcholine, C. Dopamine, D. Serotomin
A: Gamma-aminobutyric acid
Answer: A: Gamma-aminobutyric acid 
Explanation: 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