Background

In addition to the “fight, flight, or freeze” response, rats were reported to engage in a specific defensive behavior in response to an aversive stimulus by Hudson in 1950, termed “defensive burying”. This burying behavior was determined to be an innate response of rodents (including rats, mice, hamsters, and ground squirrels) to threats in their burrows (see De Boer and Koolhaas, 2003). Additionally, it was found that rats that are allowed to bury a shock-associated stimulus have less HPA axis activation than rats who were prevented from burying and forced to adopt a passive (immobile) response, suggesting that defensive burying is more adaptive compared with passive responses (De Boer et al., 1990; Korte et al., 1992; Bondi et al., 2007). Originally described by Pinel and Treit in 1978, we have adopted the shock-probe defensive burying test in our lab to model central components of stress-related psychiatric illness, i.e., preference for passive, avoidant coping strategies versus adaptive, active coping strategies. Using the protocol described here, we have shown that chronic unpredictable stress induces a shift from active to passive coping in adult Sprague-Dawley rats in this test (Jett et al., 2015; Hatherall et al., 2017; Fucich et al., 2016 and 2018), modeling the maladaptive, avoidant coping strategies adopted by patients across many stress-related psychiatric illnesses (Koolhaas et al., 1999; Bondi et al., 2007). We have previously described the validity of this test as a measure of anxiety-like responding (see Lapiz-Bluhm et al., 2008), and have more recently shown the efficacy of novel antidepressant drugs as well as behavioral therapy in reversing chronic stress-induced shifts in coping style choice (Jett et al., 2015; Hatherall et al., 2017; Fucich et al., 2016 and 2018). Thus, measuring coping style and aversive stimulus reactivity with the shock-probe defensive burying test in rats is useful in characterizing animal models of stress-related psychiatric illnesses like depression and posttraumatic stress disorder as well as testing novel therapeutic interventions and their mechanisms. Variations of the shock-probe defensive burying test have been used to test mice (e.g., Sluyter et al., 1996 and 1999; López-Rubalcava et al., 2000; Paez-Martinez et al., 2003) as well as various rat strains (as reviewed in De Boer et al., 2003), therefore the protocol described here may feasibly be adapted to any rodent model which displays innate defensive burying.