Multiple choice Which is the chief inhibitory neurotransmitter in the mammalian central nervous system? Adrenaline Androgen GABA Nitric oxide Purine Reveal answer Fill a bubble to check yourself C Correct answer Explanation Gamma aminobutyric acid (GABA) plays a role in regulating neuronal excitability throughout the nervous system. Neurons in every region of the brain use GABA to fine tune neurotransmission.