system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
All of the following are excitatory neurotransmitters except
assistant
The correct answer is  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