Escitalopram reduces increased hippocampal cytogenesis in a genetic rat depression model

Hippocampal neurogenesis is potentially implicated in etiology of depression and as the final common mechanism underlying antidepressant treatments. However, decreased neurogenesis has not been demonstrated in depressed patients and, in animals, reduced cytogenesis was shown in healthy rats exposed to stressors, but, so far, not in models of depression. Here we report that the number of BrdU positive cells in hippocampus was (1) significantly higher in a rat model of depression, the Flinders Sensitive Line (FSL) compared to control FRL, (2) increased in both FSL and FRL following maternal separation, (3) reduced by escitalopram treatment in maternally separated animals to the level found in non-separated animals. These results argue against the prevailing hypothesis that adult cytogenesis is reduced in depression and that the common mechanism underlying antidepressant treatments is to increase adult cytogenesis. The results also point to the importance of using a disease model and not healthy animals for testing effects of potential treatments for human depression and suggest other cellular mechanisms of action than those that had previously been proposed for escitalopram.