Reduction in hippocampal neurogenesis after social defeat is long-lasting and responsive to late antidepressant treatment

Major depressive disorder is a chronic disabling disease, often triggered and exacerbated by stressors of a social nature. Hippocampal volume reductions have been reported in depressed patients. In support of the neurogenesis theory of depression, in several stress-based animal models of depression, adult hippocampal neurogenesis was reduced and subsequently rescued by parallel antidepressant treatment. Here, we investigated whether repeated social defeat and subsequent individual housing for 3months induces long-lasting changes in adult hippocampal neurogenesis in rats, and whether these can be normalized by late antidepressant treatment, as would match human depression. Neurogenesis was analysed by stereological quantification of the number of immature doublecortin (DCX)-immunopositive cells, in particular young (class I) and more mature (class II) DCX