Long-term behavioral and cognitive changes following stress in adolescence

Open Access
Author:
Chaby, Lauren Evelyn
Graduate Program:
Neuroscience
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 21, 2015
Committee Members:
  • Victoria Anne Braithwaite Read, Dissertation Advisor
  • Victoria Anne Braithwaite Read, Committee Chair
  • Sonia Angele Cavigelli, Committee Member
  • David John Vandenbergh, Committee Member
  • Charles Geier, Committee Member
  • David Peter Hughes, Special Member
Keywords:
  • Adolescence
  • cognitive bias
  • coping
  • decision making
  • chronic unpredictable stress
  • Rattus norvegicus
  • developmental stress
Abstract:
This dissertation focuses on understanding the potential for exposure to stress during adolescent development to shape adult phenotype. Chapter 1 summarizes and reviews current hypotheses addressing the effects of developmental stress, including models formulated by primarily human or biomedical researchers (i.e. the differential susceptibility and biological sensitivity to context theories) and hypotheses proposed by researchers spanning the fields of ecology, biology, and neurophysiology (i.e. the mismatch hypothesis, and allostasis and reactive scope models). Subsequent chapters (2-6) empirically assess the long-term effects of exposure to chronic unpredictable stress during adolescence (e.g. isolation, crowding, damp bedding) on adult phenotype in laboratory rats (Rattus norvegicus). These adolescent-stressed rats were compared to unstressed, control animals that were maintained in standard, predictable conditions throughout development. Chapter 2 investigates the lasting effects of exposure to chronic unpredictable stress in adolescence on adult decision making, coping response, cognitive bias, and exploratory behavior in rats. The results showed that exposure to adolescent-stress can have long-term impacts on behavior and cognition by shaping the interpretation of ambiguous stimuli, behavioral response to adverse events, and how animals make decisions. It was also found that adolescent-stress can induce short-term changes in the way animals interact with novel stimuli and explore an environment. Chapter 3 examines the effects of adolescent-stress on learning (both associative and reversal) and memory (both reference and working) starting 110 days after completion of the adolescent-stress treatment. Adolescent-stressed rats exhibited enhanced reversal learning, an indicator of behavioral flexibility, but showed no change in associative learning and reference memory abilities compared to rats reared without stress. Chapter 4 assesses the lasting effects of adolescent-stress on anxiety in a novelty suppressed feeding test and found elevated anxiety levels 6.5 months after exposure to stress ceased, which is after the median lifespan of wild Norway rats. In Chapter 5, I test the mismatch hypothesis, described in Chapter 1, by quantifying the effect of adolescent-stress on foraging behavior and performance in adulthood, under both low and high-threat conditions. The results suggest that adolescent-stress exposure enabled rats to forage more effectively under novel threat in adulthood and that phenotypic changes resulting from stressful experiences during adolescence may enhance function in future high-threat conditions, supporting the mismatch hypothesis. Chapter 6 investigates whether adolescent-stress alters the allocation of time between foraging and vigilance behaviors in low and high-threat conditions in adulthood. I found no evidence of a tradeoff between foraging and vigilance, but under low-threat conditions adolescent-stressed rats spent more time foraging and being vigilant than unstressed rats, suggesting that adolescent-stress may enhance anticipation of threat in adulthood. Finally, Chapter 7 integrates the prior chapters by contextualizing the findings of this thesis in modern theories of developmental stress and introducing the arousal-shift hypothesis to explain the lasting effects of developmental stress on cognition. Together the results described in this thesis suggest that stress in adolescence can cause lasting changes in phenotype that persist into adulthood and serve some functional role that is dependent upon the environmental conditions an animal experiences later in life.