Our results confirm and extend previous findings showing the enrichment of expression signals in excitatory and inhibitory neurons. Importantly, the increased power in this genetic analysis provided additional evidence for involvement of amygdala and hippocampal excitatory neurons, including granule cells and medium spiny neurons. The amygdala and hippocampus have been previously implicated from a wide range of human imaging24,25 and animal studies of depression26–28 and medium spiny neurons have also been previously implicated in animal studies of reward and are linked to depressive behaviors.29,30 The enrichment of expression signals in granule cells is of particular interest given the renewal of this cell type throughout adult life in the dentate gyrus,31 its role in stress resilience,32 and the increased hippocampal granule cell expansion associated with antidepressant treatment.33 Together, these findings underline the mechanistic insights provided by the expansion of GWAS to over half a million depressed individuals.
