CACNB4 and major depressive disorder: Impaired synaptic GABAergic function of CRH+ interneurons of MDD patients was implied from gene expression changes suggesting (1) cellular hyperpolarization (low SLC12A2 expression; also known as NKCC1), (2) less GABA release [downregulated voltage-gated calcium channels (CACNA1B, CACNB4)], less synaptic vesicle docking and fusion (decreased SNPH) and (3) less GABA reuptake (reduced expression of SLC6A1, also known as GAT1); (Figure 3C).