Differential effects of chronic restraint stress on two active avoidance tasks in rats

Although avoidance can serve an adaptive function in daily life, excessive or persistent avoidance can form a debilitating symptom of anxiety-related disorders. The transition from adaptive to maladaptive avoidance remains poorly understood, but stress is a potential contributing factor. We investigated the effects of chronic restraint stress on two active avoidance procedures: two-way active avoidance (2WAA) and platform-mediated avoidance (PMA). Whereas 2WAA entails a low-cost response, avoidance in the PMA task comes with a cost, i.e., no access to food. We hypothesized that chronic restraint stress would hinder avoidance acquisition in the 2WAA task, but increase avoidance acquisition in the PMA task. In two experiments, male and female rats underwent either chronic restraint stress or a control procedure. In Experiment 1, all rats (N = 31) were then trained in a 2WAA acquisition and extinction procedure, in two contexts. Stressed rats showed significantly reduced avoidance acquisition, while extinction was unaffected. In Experiment 2 (N = 32), stressed rats and controls were trained in a PMA acquisition and extinction procedure. Contrary to our hypothesis, we did not find effects on avoidance acquisition, although we found group and sex differences in lever press suppression. All rats gradually extinguished defensive behaviors during extinction. Overall, chronic restraint stress had limited effects on PMA, but significantly impaired avoidance acquisition in the 2WAA task without affecting its extinction. These divergent effects may relate to differences in response cost or differences in safety of the context (i.e., a permanent safe area in PMA, but not in 2WAA).