Exposure to juvenile stress exacerbates the behavioural consequences of exposure to stress in the adult rat

TLDR

The study investigates how a brief juvenile stress exposure influences anxiety and cognition when rats later face adult stress. Rats were subjected to stress at juvenile (26–28 d) and adult (60 d) ages, or only at adult ages, to test age‑dependent effects. Juvenile plus adult stress produced the greatest anxiety and the best spatial learning, indicating that early stress has lasting, enhancing effects on coping with later stress.

Abstract

To examine the effects of exposure to post-weaning pre-puberty (juvenile) stress on the emotional and cognitive abilities in response to exposure to stress in adulthood, we first exposed rats to a platform stress at the age of 28 d. Two months later the rats were exposed to acute swim stress. Rats exposed to both stressors showed a higher level of anxiety (as measured both in open-field and startle response tests) than controls or rats exposed to either the juvenile or the adulthood stressor. In the Morris water-maze, rats that were exposed to both juvenile and adulthood stress performed better than the other groups. In a second experiment we verified that the effect of the juvenile stress was indeed age-dependent. One group was exposed at the age of 26–28 d and again at the age of 60 d (juvenile+adulthood stress); the other group was exposed to the first stressor at the age of 60–62 d and to the second at the age of 90 d [adulthood (60)+adulthood (90) stress]. Juvenile+adulthood stress had a significantly greater effect than exposure to stress twice in adulthood, on anxiety level and on the performance in the water-maze. Finally, in a third experiment we found that the juvenile+adulthood stress group swam faster and tended to explore the central area more than the other groups – a finding that could explain their better performance on the first trial of the spatial task. These results indicate that an exposure to a relatively brief juvenile stressful experience has profound and long-lasting effects on the ability to cope with stress in adulthood.