Which of the following neurotransmitter is having only inhibitory action?

GABA is the major inhibitory mediator in the brain and mediates both presynaptic and postsynaptic inhibition. GABA, which exists as -aminobutyrate in the body fluids, is formed by decarboxylation of glutamate by the enzymeglutamate decarboxylase (GAD), which is present in nerve endings in many pas of the brain. Glutamate is the main excitatory transmitter in the brain and spinal cord and has been calculated to be responsible for 75% of the excitatory transmission in the CNS. Glycine has both excitatory and inhibitory effects in the CNS. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 7. Neurotransmitters & Neuromodulators. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.