The underlying molecular mechanism of depression is not understood, but the activation of CREB, which drives the expression of brain-derived neurotrophic factor (BDNF) to promote neuronal survival and other growth factors that promote neurogenesis, is a core signalling pathway that is suppressed in mouse models of depression and up-regulated in response to anti-depressants [95,96]. This evidence concerns the gene CREB1 and depressive disorder.