Figure 1. A timetable for different experimental procedures relative to the animals’ light-dark cycle.

Female mice were injected with eCG at 15∶30. Mice in the experimental group were subjected to predatory stress for 24 h from 24 h (15∶30 the next day) to 48 h after eCG injection. To ensure continuity of stress, the predator cat was replaced every 6 h during the 24-h stress period with an individual to which the mice had not been exposed. Blood collection and 5-min behavior tests (B&B) were conducted at 0.25 (15∶45), 1 (16∶30), 12 (03∶30), 17 (08∶30), 19 (09∶30) and 24 (15∶30) h of stress. At 48 h after eCG injection, oocytes at the germinal vesicle (GV) stage were collected for maturation in vitro, and some females were injected with hCG and caged with males to produce oocytes for subsequent evaluation of development in vivo.