G.F. Gebhart, R.F. Schmidt (eds.), Encyclopedia of Pain, DO # Springer-Verlag Berlin Heidelberg 2013 receptors, which inhibit neuronal excitability through activation of K (potassium) channels and synaptic transmitter release through inhibition of presynaptic Ca channels. In most parts of the brain, GABA is the only fast inhibitory neurotransmitter, while GABA and glycine act in concert in the spinal cord, the brain stem, and selected areas of the brain, such as the cerebellum.