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It has been suggested that cognitive impairments exhibited by people with post-traumatic stress disorder (PTSD) result from intrusive, flashback memories transiently interfering with ongoing cognitive processing. Researchers have further speculated that females are more susceptible to developing PTSD because they form stronger traumatic memories than males, hence females may be more sensitive to the negative effects of intrusive memories on cognition. We have examined how the reminder of a naturalistic stress experience would affect rat spatial memory and if sex was a contributing factor to such effects. Male and female Sprague-Dawley rats were exposed, without contact, to an adult female cat for 30 min. Five weeks later, the rats were trained to locate a hidden platform in the radial-arm water maze and given a single long-term memory test trial 24 h later. Before long-term memory testing, the rats were given a 30-min reminder of the cat exposure experienced 5 weeks earlier. The results indicated that the stress reminder impaired spatial memory in the female rats only. Control manipulations revealed that this effect was not attributable to the original cat exposure adversely impacting learning that occurred 5 weeks later, or to merely exposing rats to a novel environment or predator-related cues immediately before testing. These findings provide evidence that the reminder of a naturalistic stressful experience can impair cognitive processing in rats; moreover, since female rats were more susceptible to the memory-impairing effects of the stress reminder, the findings could lend insight into the existing sex differences in susceptibility to PTSD.

SOJ Psychology Open Access Research Articlepituitary-adrenal (HPA) axis response to a traumatic event could affect his or her likelihood of developing PTSD [8][9][10]. In these studies, researchers showed that individuals who developed PTSD exhibited significantly lower levels of cortisol after the traumatic event than those individuals who did not develop PTSD. Preclinical work has provided similar results by examining the development of PTSD-like behaviors in different strains of rats. For instance, Cohen and colleagues [11] reported that Lewis rats, which exhibit a significantly blunted corticosterone response to stress, are more prone to developing PTSD-like behaviors following an acute stressor than Fischer or SpragueDawley rats. However, the studies conducted on this topic thus far have not been able to determine whether it is the HPA axis response to an acute stressor that affects PTSD / PTSD-like behavior development or if reduced HPA axis activity is merely a baseline characteristic of the people / rats that are more likely to develop PTSD / PTSD-like behaviors.Only one study of which we are aware has utilized an experimental inhibition of a rat's HPA axis response to stress in order to assess whether or not it would facilitate the development of PTSD-like behaviors. In that study, the investigators found that the combination of a blunted corticosterone and parasympathetic nervous system response to stress resulted in significantly greater anxiety on an elevated plus maze three weeks following a single stress exposure [12]. However, these results were observed when comparing the experimental groups to their respective controls only, and the effects of the manipulations on cognitive performance were not examined. This latter point is especially important because PTSD can be considered a disorder of memory, as individuals suffering from the disorder show marked impairments of learning and memory, a phenomenon that may be a result of intrusive memories transiently interfering with these individuals' ability to process new information [13][14][15][16][17]. Thus, the purpose of the present study was to determine whether or not a blunted HPA axis response to acute predator