γ-amidobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system and mediates fast synaptic inhibition through GABAA and GABAC ionotropic receptors as well as slow and prolonged synaptic inhibition through the metabotropic GABAB receptors.GABAB receptors mediate both presynaptic inhibition of neurotransmitter release and post-synaptic inhibition of neuronal excitability.