The Effects of Stress Inoculation on Anxiety-related Behaviors in a Rodent Model

Problem. Humans may face psychological stressors in their everyday life due to their ability to contemplate future events. While long-term stress exposure may be detrimental to health, this study examines the possibility that exposure to unpredictable/controllable, moderate stress may cause resilience against future stressors. This is referred to as the stress inoculation hypothesis. The effects of unpredictable/controllable stress can be illustrated as a rightward shift in an inverted U-shaped curve, where optimal performance (the top of the curve) can be maintained at higher stress levels. -- Method. Thirty-three male Sprague-Dawley rats were tested on the elevated-plus maze (EPM) for trait anxiety. Rats were then placed in housing platforms; 15 rats were exposed to unpredictable/controllable stress (UST) in the housing platform, and 18 rats were used as a control group (CT). After 21 days in the UST or CT housing, spatial memory and anxiety-related behaviors were tested under aversive conditions on the Barnes maze. -- Results. Spatial memory: UST rats took less time to reach the goal box on the Barnes maze (p\u3c0.05), and made fewer errors (p\u3c0.05). General locomotor activity: No significant effect was seen for mobility, which is a measure of general locomotor behavior, on the Barnes maze (p=0.100). The UST rats took less time to approach the first hole on the Barnes maze (p\u3c0.05). There was no significant effect for the number of holes jumped over in the Barnes maze (p=0.599). There was no significant effect for the number of times the rats looked over the edge (p=0.431). No correlations were seen between Barnes maze data and EPM behaviors (all p\u3e0.05). -- Conclusion. These data are consistent with the stress inoculation hypothesis. As humans, exposure to stress is unavoidable and unpredictable. The results of this study, however, indicate that stress does not always lead to negative consequences, but can be helpful. By causing a rightward shift in the inverted U-shaped curve, stress can better prepare us to face stressful situations in the future and reduce our anxiety about facing those stressors