Angiotensin Type 1 Receptor Inhibition Enhances the Extinction of Fear Memory

Background: The current effective treatment options for posttraumatic stress disorder (PTSD) are limited, and therefore the need to explore new treatment strategies is critical. Pharmacological inhibition of the renin-angiotensin system is a common approach to treat hypertension, and emerging evidence highlights the importance of this pathway in stress and anxiety. A recent clinical study from our laboratory provides evidence supporting a role for the renin-angiotensin system in the regulation of the stress response in patients diagnosed with PTSD. Methods: With an animal model of PTSD and the selective angiotensin receptor type 1 (AT(1)) antagonist losartan, we investigated the acute and long-term effects of AT(1) receptor inhibition on fear memory and baseline anxiety. After losartan treatment, we performed classical Pavlovian fear conditioning pairing auditory cues with footshocks and examined extinction behavior, gene expression changes in the brain, as well as neuroendocrine and cardiovascular responses. Results: After cued fear conditioning, both acute and 2-week administration of losartan enhanced the consolidation of extinction memory but had no effect on fear acquisition, baseline anxiety, blood pressure, and neuroendocrine stress measures. Gene expression changes in the brain were also altered in mice treated with losartan for 2 weeks, in particular reduced amygdala AT(1) receptor and bed nucleus of the stria terminalis c-Fos messenger RNA levels. Conclusions: These data suggest that AT(1) receptor antagonism enhances the extinction of fear memory and therefore might be a beneficial therapy for PTSD patients who have impairments in extinction of aversive memories.