GAD1 and schizophrenia: The GABA hypothesis is also supported by human post-mortem tissue from individuals with schizophrenia showing markedly reduced GAD67 expression [10,11], an enzyme that synthesizes GABA, in addition to reduced GAT1 [12], the membrane transporter of GABA, somatostatin (SOM) [13] and parvalbumin (PV) [14], a calcium buffer expressed within FSINs in the dorsolateral prefrontal cortex (dlPFC).