The results presented here confirm earlier reports on the relationship between stress in the early stages of development and the associated impairments in adult hippocampal neurogenesis [39–41]. In addition, further evidence is provided to establish a critical developmental period when aNSCs are mainly generated. The present work also identifies a critical period of aNSC formation in mice around postnatal day 6. This time window can be considered an especially relevant stage to be protected from stress for functional adult hippocampal neurogenesis to develop correctly.