23,24 The stressful event consists of cither brief exposure to intermittent tailshocks or brief swim stress (20 min), both of which are common methods for inducing behavioral depression in laboratory animals. As a measure of learning, we again used the classically conditioned eyeblink response. These opposite responses to

stress are not limited to simple associative learning as occurs during classical conditioning with overlapping stimuli. As illustrated in Figure 1, they are also evident during trace conditioning, a more difficult task in which the conditioning stimuli are separated in time. This task critically involves the hippocampal formation, and some have Inhibitors,research,lifescience,medical even suggested that it involves conscious awareness.25-27 Figure 1. Percentage of conditioned responses measured over training in male rats and female rats tested during proestrus. They were Inhibitors,research,lifescience,medical exposed to the acute stressor and 24 hours later were trained on the trace-conditioned eyeblink response. If these effects of uncontrollable stressful experience on learning in rats are relevant, to the human condition, they should possess some characteristics of mental illness, particularly those associated with stressful experience. One that Inhibitors,research,lifescience,medical comes to mind is posttraumatic stress

disorder (PTSD). After experiencing a traumatic stressful event, some humans develop a series of behaviors that are maladaptive and cause distress and dysfunction,28 such as avoidance, reduced responsiveness, increased arousal, anxiety, and guilt. Of those that develop PTSD, more

than twice as Inhibitors,research,lifescience,medical many are women.29 Often-times, they reexperience frightening aspects of the traumatic event, particularly if presented with cues that are associated with the event. To determine whether the effects of stress on learning in rats were sensitive to these factors, we exposed rats to cues associated with the stressful event days after it had ceased and at a time when the effects of stress would have dissipated. Inhibitors,research,lifescience,medical Indeed, days after the stressor, males Enzalutamide concentration reintroduced to the stress context, were further enhanced in their performance, whereas females were further impaired.10,30 Minimally, these others results suggest that, the effects of acute stress on learning are not. entirely dependent on sensory stimulation, but rather can be stimulated by associations that were established during stressful environment. More generally, they suggest that the effects of acute stress on later learning in rats may model some disrupting effects of trauma on cognitive processes in humans such as occurs during PTSD. Stress hormones and stress effects on memory formation There are numerous examples of sex differences in behavior, but few demonstrating an opposite response to the same stimulus between sexes.