The effects of estradiol on different stages of memory extinction in post-traumatic stress disorder

One of the main symptoms of post-traumatic stress disorder (PTSD), as an anxiety disorder, is a disability to forget the traumatic event. The aim of this study was to evaluate the effects of estradiol on different stages of conditioned fear memory extinction in PTSD. For PTSD induction, combination of Shock and Single Prolonged Stress model (S+SPS) was used. In order to assess conditioned fear memory extinction, 7 days after PTSD induction, animals were placed back into the shock chamber for 9 minutes without receiving any electric shock and their freezing behavior was measured in this time (3 sections, each section 3 min). The first test is an index of extinction learning. The second test, as same as the first one, was performed one day after the first test. During the second test, retrieval and reconsolidation of memory extinction were occurred. Estradiol injection (90, 180 and 360 mg/kg) in treated groups or vehicle injection (the control group) was done half an hour before the tests. Results showed that estradiol administration, at the dose of 180 mg/kg, significantly decreased the freezing behaviors in all three sections of the two tests. Estradiol has a dose-dependent effect on acquisition, retrieval and consolidation of fear memory extinction in PTSD animals. Subcutaneous injection of 180mg/kg estradiol can enhance all three phases, acquisition, consolidation and retrieval of fear memory extinction.