Repeated threat (without harm) in a living environment potentiates defensive behavior

• An ethologically relevant model of psychological stress was developed and tested.
• Threat without harm was delivered to selectively induce psychological stress without physical stress.
• Threats during foraging increased avoidance of threat, risk assessment behaviors, and adrenal gland weight.
• Responses to threat lasted the full 21 days of the manipulation.
• After experimental conditions, threat exposed rats were more likely to defensively bury and spent more time burying.

Children exposed to neighborhood violence have higher rates of aggression, but it is unclear whether aggression is associated with threat, harm or the combination of factors. All animals, including humans, experience threat as they leave the safety of home and risk harm to gather resources (foraging). To better understand how selective environmental variables drive behavioral tendencies, we developed a semi-naturalistic living environment that includes the need to navigate across space to obtain resources. Rats were housed for three weeks in two tub cages, one with food and the other with water, both consistently available, but separated by a 91 cm long tunnel. After habituating for three days, half the rats (threat stress condition) received unpredictable threats (simultaneous puff of air with ferret dander, abrupt flash of light, and an abrupt sound) when crossing the central position of the tunnel (random order with p = 0.25) for 21 days. During the manipulation, the threat stress rats crossed the tunnel less and exhibited risk assessment behaviors. After cessation of the treatment conditions, the threat stress group spent more time burying a rag with ferret dander odor and was more likely to bury, and spent more time burying a highly novel stimulus. There were no group differences in symptoms of depression, avoidance, or exploration. The results suggest that repeated threats without harm increase pre-emptive defense behaviors, a form of active coping, without affecting passive forms of coping.