McCormick CM, Mathews IZ
Pharmacol. Biochem. Behav. 2007 Feb;86(2):220-33
The hypothalamic-pituitary-adrenal (HPA) axis is one of the physiological systems involved in coping with stressors. There are functional shifts in the HPA axis and its regulation by sex hormones over the lifespan that allow the animal to meet the challenges of the internal and external environment that are specific to each stage of development. Sex differences in HPA function emerge over adolescence, a phenomenon reflecting the concomitant initiation of regulatory effects of sex hormones. The focus of this review is recent research on differences between adolescents and adults in HPA function and the enduring effects of exposure to stressors in adolescence. During adolescence, HPA function is characterized by a prolonged activation in response to stressors compared to adulthood, which may render ongoing development of the brain vulnerable. Although research has been scarce, there is a growing evidence that exposure to stressors in adolescence may alter behavioural responses to drugs and cognitive performance in adulthood. However, the effects reported appear to be stressor-specific and sex-specific. Such research may contribute toward understanding the increased risk for drug abuse and psychopathology that occurs over adolescence in people.
McCormick CM, Mathews IZ, Thomas C, Waters P
Brain Cogn 2010 Feb;72(1):73-85
Developmental differences in hypothalamic-pituitary-adrenal (HPA) axis responsiveness to stressors and ongoing development of glucocorticoid-sensitive brain regions in adolescence suggest that similar to the neonatal period of ontogeny, adolescence may also be a sensitive period for programming effects of stressors on the central nervous system. Although research on this period of life is scarce compared to early life and adulthood, the available research indicates that effects of stress exposure during adolescence differ from, and may be longer-lasting than, effects of the same stress exposure in adulthood. Research progress in animal models in this field is reviewed including HPA function and the enduring effects of stress exposures in adolescence on sensitivity to drugs of abuse, learning and memory, and emotional behaviour in adulthood. The effects of adolescent stress depend on a number of factors, including the age, gender, the duration of stress exposure, the type of stressor, and the time between stress exposure and testing.
Mathews IZ, Wilton A, Styles A, McCormick CM
Behav. Brain Res. 2008 Jun;190(1):33-40
We previously reported that males undergoing chronic social stress (SS) (daily 1h isolation and new cage partner on days 30-45 of age) in adolescence habituated (decreased corticosterone release) to the homotypic stressor, but females did not. Here, we report that adolescent males exposed to chronic social stress had potentiated corticosterone release to a heterotypic stressor (15 min of swim stress) compared to acutely stressed and control males. The three groups of males did not differ in depressive-like behaviour (time spent immobile) during the swim stress. Corticosterone release in socially stressed females was elevated 45 min after the swim stress compared to acutely stressed and control females, and socially stressed females exhibited more depressive behaviour (longer durations of immobility and shorter durations of climbing) than the other females during the swim stress. Separate groups of rats were tested as adults several weeks after the social stress, and there were no group differences in corticosterone release after the swim stress. The only group difference in behaviour among the adults was more time spent climbing in socially stressed males than in controls. Thus, there are sex-specific effects of social stress in adolescence on endocrine responses and depressive behaviour to a heterotypic stressor, but, unlike for anxiety, substantial recovery is evident in adulthood in the absence of intervening stress exposures.