Angiotensin type 1a receptors on corticotropin-releasing factor neurons contribute to the expression of conditioned fear

Abstract

Although generally associated with cardiovascular regulation, angiotensin II receptor type 1a (AT1a R) blockade in mouse models and humans has also been associated with enhanced fear extinction and decreased post-traumatic stress disorder (PTSD) symptom severity, respectively. The mechanisms mediating these effects remain unknown, but may involve alterations in the activities of corticotropin-releasing factor (CRF)-expressing cells, which are known to be involved in fear regulation. To test the hypothesis that AT1a R signaling in CRFergic neurons is involved in conditioned fear expression, we generated and characterized a conditional knockout mouse strain with a deletion of the AT1a R gene from its CRF-releasing cells (CRF-AT1a R((-/-)) ). These mice exhibit normal baseline heart rate, blood pressure, anxiety and locomotion, and freeze at normal levels during acquisition of auditory fear conditioning. However, CRF-AT1a R((-/-)) mice exhibit less freezing than wild-type mice during tests of conditioned fear expression-an effect that may be caused by a decrease in the consolidation of fear memory. These results suggest that central AT1a R activity in CRF-expressing cells plays a role in the expression of conditioned fear, and identify CRFergic cells as a population on which AT1 R antagonists may act to modulate fear extinction.

Keywords: Amygdala; PTSD; angiotensin II; angiotensin II receptor type 1; blood pressure; cardiovascular; corticotropin-releasing factor; extinction; fear; paraventricular nucleus.

Conflict of interest statement

Conflicts of Interest: The authors declare no competing financial interests.

© 2015 John Wiley & Sons Ltd and International Behavioural and Neural Genetics Society.

Figures

Figure 1. AT1aR and CRF co-localize in subsets of PVN and CeA neurons

Dense AT1aR and CRF expression is observed in the PVN and CeA of AT1aR-GFP mice. Arrows in (d) and (h) indicate co-localization.

Figure 2. Autoradiographic analysis of AT1R binding

AT1R autoradiography revealed a decrease in AT1R expression in the PVNs of CRF-AT1aR(−/−) mice compared to controls. Data are presented as mean ± SEM. * p<0.05.

Figure 3. AT1aR knockout from CRFergic cells has no effect on acquisition of conditioned fear, but leads to decreased fear expression and enhanced extinction retention

(a) AT1aR(+/+) and CRF-AT1aR(−/−) mice show similar levels of freezing during fear acquisition (n=15–17). (b and c) During extinction, CRF-AT1aR(−/−) mice show significantly less freezing than AT1aR(+/+) mice overall and during the last 10 CS presentations (n=15–17).

Figure 4. AT1aR knockout from CRFergic cells does not affect baseline levels of anxiety, locomotion, blood pressure, or heart rate

(a) AT1aR(+/+) and CRF-AT1aR(−/−) mice spend similar amounts of time on the open arms of an elevated plus maze (n=15–16) and (b) travel similar total distances during an open field test (n=15–17). Both groups also have similar (c) mean arterial pressure and (d) heart rate at baseline (n=8–10). Data are presented as mean ± SEM.