BDNF and major depressive disorder: The hypothesis that increases in hippocampal volume are a function of an ECT-related neurotrophic effect was suggested by the finding that a regulatory single nucleotide polymorphism (SNP) in the VEGF (but not the BDNF) gene associates with greater hippocampal volume increases following a course of RUL ECT in 61 older adults (55 years and older) with major depressive disorder [145].