A role for ZnR/GPR39 in the regulation of the CREB/BDNF/TrkB (cyclic AMP response element binding protein/brain-derived neurotrophic factor/tyrosine receptor kinase B) pathway, and thereby in depression, has also been postulated, though it is not clear at present how Gαq signaling activates this pathway or whether these effects are lost in ZnR/GPR39 deficient mice [166,167]. This evidence concerns the gene NTRK2 and major depressive disorder.