Stress-induced impairment of fear extinction recall is associated with changes in neuronal activity patterns in PVT

Treatment resistance of anxiety-related disorders often arises from an inappropriate fear expression, impairment in fear extinction, and spontaneous return of fear. Stress exposure is considered a high risk factor for neuropsychiatric disorders, but understanding of the long-term consequences of stress is limited, particularly when it comes to treatment outcome. Therefore, studying the consequences of acute stress would provide critical information on the role of stress in psychopathology. In the present study, we investigated the effect of acute immobilization stress on anxiety-like behavior and on conditioned fear memory. Our results demonstrate that prior stress exposure had no effect on anxiety-related behavior, fear acquisition, as well as fear extinction compared to non-stressed controls, but resulted in significantly higher rates of freezing during recall of extinction, indicating a consolidation failure. Further, immunohistochemical analysis of the expression of the immediate early gene c-Fos after recall of extinction revealed increased neuronal activity in the posterior paraventricular nucleus of the thalamus (PVT) in previously stressed animals compared to non-stressed controls. These results indicate, firstly, that acute stress affects long-term fear memory even after successful extinction training, and secondly, a strong involvement of the PVT in maladaptive fear responses induced by prior stress. Thus, stress-induced changes in PVT neuronal activity might be of importance for the pathophysiology of stresssensitive anxiety-related psychiatric disorders, since exposure to an earlier acute stressor could counteract the success of therapy.