<prompt> Which of the following neurotransmitter is having only inhibitory action?GABAGlutamineAspaateAll of the above  <response>: 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, Ganongs Review of Medical Physiology, 24e. 