Chronic stress alters behavior in the conditioned defensive burying test: role of the posterior paraventricular thalamus.

In the present studies, we examined the effects of chronic restraint on behavior in the conditioned defensive burying paradigm, a well-validated test of anxiety. This test is based on the findings that rodents tend to cover or bury the source of a noxious or aversive stimulus. However, little is known about whether prior chronic stress exposure can alter this anxiety-related behavior. In the present study, we examined whether chronic restraint affects indices of behavior in the conditioned defensive burying paradigm. Furthermore, since the posterior division of the paraventricular thalamus (pPVTh) regulates neuroendocrine activity specifically in chronically stressed but not control rats, we hypothesized that the pPVTh may also regulate any chronic stress-induced changes in behavior observed in the defensive burying test. Chronically stressed rats (30-min restraint per day for seven consecutive days) exhibited decreased latency to bury compared to control rats regardless of the presence of lesions suggesting increased reactivity to the shock in these animals. Importantly, pPVTh-lesioned chronically stressed rats exhibited increased duration and height of burying compared to control rats with pPVTh lesions, whereas no differences existed between sham-lesioned control and chronically stressed rats. Since both burying height and duration of burying are considered indices of anxiety in the defensive burying test, the present results suggest that the intact pPVTh may be important in dampening behaviors related to anxiety in chronically stressed rats.