Abstract
Repeated stress can trigger a range of psychiatric disorders, including anxiety. The propensity to develop abnormal behaviors after repeated stress is related to the severity, frequency and number of stressors. However, the pattern of stress exposure may contribute to the impact of stress. In addition, the anxiogenic nature of repeated stress exposure can be moderated by the degree of coping that occurs, and can be reflected in homotypic habituation to the repeated stress. However, expectations are not clear when a pattern of stress presentation is utilized that diminishes habituation. The purpose of these experiments is to test whether interrupted stress exposure decreases homotypic habituation and leads to greater effects on anxiety-like behavior in adult male rats. We found that repeated interrupted restraint stress resulted in less overall homotypic habituation compared to repeated daily restraint stress. This was demonstrated by greater production of fecal boli and greater corticosterone response to restraint. Furthermore, interrupted restraint stress resulted in a lower body weight and greater adrenal gland weight than daily restraint stress, and greater anxiety-like behavior in the elevated plus maze. Control experiments demonstrated that these effects of the interrupted pattern could not be explained by differences in the total number of stress exposures, differences in the total number of days that the stress periods encompased, nor could it be explained as a result of only the stress exposures after an interruption from stress. These experiments demonstrate that the pattern of stress exposure is a significant determinant of the effects of repeated stress, and that interrupted stress exposure that decreases habituation can have larger effects than a greater number of daily stress exposures. Differences in the pattern of stress exposure are therefore an important factor to consider when predicting the severity of the effects of repeated stress on psychiatric disorders.
Highlights
Repeated stress exacerbates depression and anxiety, and can trigger post-traumatic stress disorder
The acute response to homotypic stress is strongly attenuated with repeated exposures, while the long-lasting outcomes of the effects of stress are enhanced with repeated exposures
This study tested whether the stress exposure pattern exerted parallel modification of homotypic habituation and longer lasting outcomes
Summary
Repeated stress exacerbates depression and anxiety, and can trigger post-traumatic stress disorder. The pattern of stress exposure may play a role in its effects [13,14]. Common patterns of stress exposure include 1) continuous over an extended period of time (chronic), 2) daily acute episodes over an extended period (daily), or 3) sporadic acute episodes over an extended period. Two types of sporadic exposures include intermitent, when the stressor is not a frequent occurrence over a given period of time, or interrupted, when the stressor occurs frequently over a given period of time with occassional interuptions. Stress exposure in humans is often in an interrupted pattern. There have been few studies to test whether interrupted stressors exert the same effects on physical and behavioral manifestations of repeated stress
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