Side effects of control treatment can conceal experimental data when studying stress responses to injection and psychological stress in mice.

Routine laboratory procedures, such as handling or transporting animals or carrying out injections on animals, are stressful for animals but are necessary in many pre-clinical studies. Here, the authors show that multiple injections of the non-toxic vehicle cyclodextrin moderately increased plasma corticosterone concentrations in female BALB/c mice. Additionally, male BALB/c mice that had received a single intraperitoneal injection of harmless saline had an increased glucocorticoid response to a second saline injection.