All dams bred for gestational stress studies were virgin, experimentally naïve C57Bl/6:129 F1 hybrid 5 wk old mice purchased from the Jackson laboratory. Offspring from these breedings were used to generate the second-generation (F2) litters for transgenerational studies. Justification for using a hybrid background strain in these studies is related to stress responsivity phenotypes and physiology. C57Bl/6 are extremely low stress responders and display low levels of maternal care, making them poor choices for studies focusing on neurodevelopment. While 129 mice are great stress responders and show high levels of quality maternal care, they frequently lack a fully formed corpus callosum and are poor performers in behavioral tests, especially learning and memory tasks. However, the combination of these two strains produces a hybrid vigor that has served our research well with predictable stress responses, behavioral outcomes, and sex differences in stress physiology and behavioral tests (Mueller and Bale, 2006 (link), 2007 (link), 2008 (link)). Pregnancy was established by confirmation of a copulation plug (checked for each morning between 7–8 am). Presence of a copulation plug denoted experimental day 1 for early prenatal stress exposure. The pregnant female was individually housed, given a cotton nestlet, and randomly assigned to a stress treatment or control group. Food (Purina Rodent Chow; 28.1% protein, 59.8% carbohydrate, 12.1% fat) and water was provided ad libitum throughout the study. All studies were performed according to experimental protocols approved by the University of Pennsylvania Institutional Animal Care and Use Committee, and all procedures were conducted in accordance with institutional guidelines.