Which of the following is an inhibitory neurotransmitter found exclusively in the central nervous system?

Serotonin (5-hydroxytryptamine) is an impoant regulatory amine in the CNS. Serotonin-containing neurons are present in the raphe nuclei in the pons and medulla. Serotonin is a generally inhibitory monoamine type neurotransmitter found in the CNS. Acetylcholine can be excitatory or inhibitory and is found in the CNS, neuromuscular junction, and many autonomic nervous system (ANS) synapses.Glutamate is found in the brain and spinal cord and is excitatory. Norepinephrine, such as serotonin, is a monoamine neurotransmitter but can be excitatory or inhibitory found in the CNS, sympathetic ANS synapses, and nearly all tissues. Ref: Katzung B.G. (2012). Chapter 16. Histamine, Serotonin, & the Ergot Alkaloids. In B.G. Katzung, S.B. Masters, A.J. Trevor (Eds), Basic & Clinical Pharmacology, 12e.