GAD2 and major depressive disorder: The pathological changes in markers related to this system, such as decreased parvalbumin mRNA in the dorsolateral prefrontal cortex (DLPFC) [37] and reduced density of glutamic acid decarboxylase 65/67-immunoreactive (GAD 65/67-ir) neurons in DLPFC and temporal cortical areas [7] specific for BD, differentiated this diagnostic entity from MDD.