Reducing reconsolidation of reactivated traumatic memories may offer a novel pharmacological treatment for posttraumatic stress disorder (PTSD). Preclinical research is needed to identify candidate drugs. We evaluated the ability of postreactivation mifepristone (RU38486, a glucocorticoid antagonist), alone and in combination with propranolol (a beta-adrenergic blocker), both given systemically, to reduce cue-conditioned fear in rats. On Day 1, a 30-s tone conditioned stimulus (CS) was paired with an electric shock unconditioned stimulus (US). On Day 2, the CS was presented without the US (reactivation), and the freezing conditioned response (CR) was measured. This was immediately followed by subcutaneous injection of vehicle, mifepristone 30 mg/kg, propranolol 10 mg/kg, or both. On Day 3, the CR was again measured as a test of postreactivation long-term memory (PR-LTM). On Day 10, the CR was again measured to evaluate spontaneous recovery. On Day 11, the US was presented alone (reinstatement). On Day 12, the CR was again measured. A fifth group received mifepristone without the CS presentation (nonreactivation) on Day 2. A sixth group was tested four hours after the Day 2 mifepristone injection to measure postreactivation short-term memory. Postreactivation, but not nonreactivation, mifepristone produced a decrement in the CR that did not undergo spontaneous recovery and underwent only modest reinstatement. Mifepristone did not exert its effect when administered concurrently with propranolol. Postreactivation mifepristone did not impair short-term memory. Systemic mifepristone blocks the reconsolidation of cue-conditioned fear in rats. Concurrent administration of propranolol prevents this effect. Postreactivation mifepristone may be a promising treatment for PTSD, but not necessarily in combination with propranolol.

A common treatment for anxiety disorders is chronic administration of selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine. Recent data suggest that SSRIs modulate fear responses after conditioned fear extinction and that gonadal hormones influence fear extinction. In this study we investigated the influence of sex and the estrous cycle on the effects of acute (experiment 1) and chronic (experiment 2) fluoxetine treatment on fear extinction. In experiment 1, rats received tone-footshock pairings during day 1. On day 2, rats received either fluoxetine (10mg/kg in 0.5mL) or vehicle prior to extinction learning. On day 3, extinction memory was assessed during extinction recall. In experiment 2, rats were exposed to a similar behavioral protocol, except that fluoxetine and vehicle were administered for 14 consecutives days after conditioning (days 2–15). Extinction learning and extinction recall occurred on days 15 and 16, respectively. Acute administration of fluoxetine increased fear responses equally in males and females during extinction learning and extinction recall. Chronic administration of fluoxetine reduced fear responses during extinction learning and extinction recall in female but not in male rats and this effect seems to be modulated by the estrous cycle. The SSRI-induced reduction of freezing during extinction learning and recall suggest a general anxiolytic effect of the drug treatment rather than a specific effect on extinction learning per se. Our data show evidence of sex-specific anxiolytic effects of 14-day treatment of fluoxetine while the acute anxiogenic effect of SSRI seems independent of sex effects.