Developmental differences in stress responding after repeated underwater trauma exposures in rats

Abstract

Adolescence is a distinct developmental period characterized by behavioral and physiological maturation. Rapid ongoing changes during neurodevelopment in particular present potential opportunities for stress to have lasting effects on longitudinal outcomes of behavioral and neuroendocrine function. While adult stress effects on outcomes during adulthood have been characterized, little is known about the lasting effects of adolescent repeated stressor exposure on outcomes during adolescence. We have previously reported different stress responses in adolescent rats relative to adult rats, including a blunted fear response outcome in adulthood in rats stressed during adolescence. The present study characterized the ontogeny of behavioral and neuroendocrine responses to eight underwater trauma (UWT) exposures in rats over a two week poststress time period during adolescence (P34) or adulthood (P83) relative to age-matched control groups that underwent eight swimming episodes without UWT. Repeated UWT exposures starting in adolescence, but not adulthood, resulted in adverse behavioral responses on the elevated plus maze 1 day post-stress. Corticosterone responses did not differ between UWT-exposed and controls for either age group at 1 day or at 7 days poststress, although there was an effect of age on corticosterone levels. We conclude that repeated UWT stress events have a lasting, negative behavioral effect on adolescent rats that is not observed in adult rats after the two-week exposure window. These results suggest that neurophysiological mechanisms underlying recovery from a repeated stressor are immature in adolescence relative to adulthood in rats.

Keywords:

• Development
• adolescence
• stress
• homeostasis
• behavior
• underwater trauma

Ethical approval

Studies were conducted in compliance with the Animal Welfare Act and other Federal statutes and regulations relating to animals and experiments involving animals and adhere to principles stated in the Guide for the Care and Use of Laboratory Animals, NRC Publication, 2011 edition. All procedures were reviewed and approved by the Walter Reed Army Institute of Research/Naval Medical Research Center Institutional Animal Care and Use Committee, and performed in facilities fully accredited by the Association for Assessment and Accreditation of Laboratory Animal Care, International.

The opinions or assertions contained herein are the private views of the author, and are not to be construed as official, or as reflecting true views of the Department of the Army or the Department of Defense.

Acknowledgements

The authors thank Stefania Dobre and Christina Johnson for laboratory assistance, Dr. Emily G. Lowery-Gionta for helpful comments on the manuscript, and Dr. Raymond F. Genovese.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Military Operational Medicine Research Program, US Army Medical Research and Materiel Command.