GABA:

Watch this 2-Minute Neuroscience video to learn more about GABA.

gamma-aminobutyric acid. GABA is considered the primary inhibitory neurotransmitter in the nervous system. GABA can decrease the likelihood that action potentials will occur, and thus decreases neuronal signaling. The net effect of GABA, however, is not always inhibitory.

Further reading: The many sides of GABA