Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Stress is known to impair spatial navigation in rat models of declarative memory, and declarative memory in humans, but the effects on spatial navigation in humans are unclear. At least four models have been proposed to account for the cognitive effects of stress, based on the two different physiological stress response systems (the sympathetic-adrenal-medullary (SAM) and the hypothalamic-pituitary-adrenal (HPA) systems) and the effects of these responses on the hippocampus and (sometimes) other subcortical structures. In this dissertation, I examined the effects of an acute (experimental) stressor on human spatial navigation in three variations of virtual Morris water mazes designed to dissociate between hippocampus-dependent (allocentric) and hippocampus-independent (egocentric) forms of navigation. Results were considered in the light of all 4 models. Experiment 1 used a dual-strategy Morris water maze to test whether acute stress influences navigational strategy selection and whether this effect is mediated by the activation of the HPA or the SAM system. Surprisingly, stress increased hippocampus-based strategy selection, and did so in the presence of SAM but not HPA activation. Experiment 2 used new dual-strategy and place mazes to examine the effects of acute stress on both strategy selection and allocentric navigational performance. It also attempted to contrast the effects of stress at a short delay, which would favour mediation by the SAM system, and a longer, 30 minute delay (from stressor onset), which would favour mediation by the HPA system. Contrary to expectations, results revealed no effect of stress when tested immediately and sex-dependent impairments of performance (in females) and allocentric strategy selection (in males) at the delay. Experiment 3 used the same mazes as Experiment 2, plus a new cue maze to examine the effects of acute stress on strategy selection and both allocentric and egocentric navigational performance after a 30 minute delay. Results confirmed that stress reduces allocentric strategy selection and impairs allocentric performance, but also has sex-dependent effects on egocentric performance: in females, stress enhanced navigation (as expected) but in males, stress impaired it. None of the 4 models provided a good explanation for these results, suggesting that current accounts of the cognitive effects of stress may be inadequate. / Graduate

Disturbance can provoke a chronic (long-term) stress response in wildlife, and can contribute to population declines. I examined the stress response of boreal woodland caribou, moose, and wolves to disturbance in eastern Manitoba by measuring cortisol concentrations in hair. Caribou cortisol concentrations were greatest for the three most southern populations, and increased with decreasing home range size. Intermediate logging (6-21 years) provided the best explanation for individual variation in caribou cortisol concentrations. Disturbance did not affect moose cortisol concentrations, but cortisol concentrations were higher in moose killed by wolves than moose collected by humans, suggesting that chronic stress in moose is linked to poor body condition and increased vulnerability to wolf predation. Wolf cortisol concentrations increased in 2012 and 2013 compared to 2011 following increased harvest pressure, and were higher in females. However, neither winter severity nor variation in wolf diet affected wolf cortisol concentrations. / October 2016

Sturgeon species (family Acipenseridae) are threatened globally due to habitat destruction, pollution, and overfishing. The Atlantic sturgeon Acipenser oxyrinchus oxyrinchus was listed as a federally endangered species in 2012. Atlantic sturgeon have a complex life history that utilizes a wide range of habitats. Timing of life history varies in different areas requiring each population to be studied. Very little work has been published on Atlantic sturgeon reproduction in the James River, Virginia. To aid the recovery of James River Atlantic sturgeon, aspects of life history need to be addressed. To increase understanding of Atlantic sturgeon life history a length at age model was created to show population structure and age of sexual maturity. Telemetry experiments were conducted to determine what types of boats are likely to cause boat strike mortalities of adult fish during a spawning season. Morphometrics, sperm characteristics, and telemetry data were used to determine if Atlantic sturgeon have a fall spawning season. Strontium/calcium ratio analysis was conducted on Atlantic sturgeon fin spines to better understand migration patterns. Cortisol levels were examined in Atlantic sturgeon exposed to MS222, electronarcosis or no anesthetic 1 and 24 hr after a small incision mimicking tag implantation. I also determined the feasibility of using electronarcosis in the field and the effect of salinity on electronarcosis. The length at age data show male Atlantic sturgeon beco,e sexually mature at age 10 y and females around age 15 y. Telemetry data showed that deep draft ocean-cargo ships are most likely responsible for boat strike mortalities and there is a greater chance of Atlantic sturgeon being hit in the narrow portion of the river. Electronarcosis is an effective anesthetic and has various attributes that make it better suited for field applications then frequently used chemical anesthetics. The data generated from this research will help management produce effective recovery plans and create a safer research environment for both the fish and researcher.

Recently, with the development of new technology, researchers have focused on physiological predictors of aggressive behavior, specifically cortisol and alpha amylase. Gordis, Granger, Susman, and Trickett (2006) found the interaction between cortisol and alpha-amylase significantly predicted parent reports of aggression indicating that low levels of physiological reactivity was associated with higher levels of problem behavior. While this research has provided valuable information about aggressive behavior, a major limitation is the majority of research focuses on males, or has not examined gender differences explicitly. This study expanded on work by Gordis et al. (2006) and other researchers on the HPA axis and sympathetic nervous system responses and aggression by using a larger sample, focusing on female adolescents, examining both physical and relational aggression, and utilizing parent and adolescent reports of aggressive behavior. Based on prior literature, I expected that lower levels of salivary cortisol taken at the beginning of the interview and the beginning of the stress task would be associated with higher levels of physical and relational aggression in girls. I also hypothesized that lower levels of cortisol and α-amylase reactivity will be associated with higher levels of physical and relational aggression. Finally, I hypothesized that lower levels of cortisol reactivity coupled with higher levels of α-amylase reactivity will be associated with lower levels of aggressive behavior. Participants in the current study live in moderate- to high-violence areas in Richmond, VA. Participants were 146 adolescent females who were enrolled in a larger longitudinal study on coping with exposure to violence. Most of the adolescents were African-American (91.1%) with a mean age of 13.9 years old (range from 11-17). The changes in physiological responses were monitored during the interview process which included the administration of the Social Competence Interview (SCI). Aggression was measured using the Child Behavior Checklist and Problem Behavior Frequency Scales. In the analyses, I controlled for pubertal status, medication usage, race, and time of day which are all factors that can influence the level of cortisol and alpha-amylase. Results indicated that higher levels of basal cortisol were associated with higher levels of aggressive behavior. In contrast to previous research and prediction, results indicated that symmetry in α-amylase and cortisol predicted lower levels of self-reported physical aggression in girls. Asymmetry in the two systems was associated with higher levels of self-reported physical aggression. These results contribute to the mixed results on female physiological responses and aggression. It also provides support for symmetry in cortisol and α-amylase as a predictor of lower levels of aggressive behavior. Studying a child’s physiological reactions to stress can give insight into behavior regulation, help identify adolescents for prevention/intervention, and serve as markers of treatment progress. These data suggest that physiological associations with aggression may not be the same for males and females, or for youth living in extremely stressful circumstances. Further research is needed to replicate these finding, and specifically to compare these patterns of associations across gender.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

We attempted to identify the psychobiological mechanisms that mediate the process by which the sensation seeking trait culminates in behavior. We used the Sensation Seeking Scales to assess the SS trait in individuals who expressed a desire to skydive. We obtained measures of autonomic (heart rate) and endocrine (salivary cortisol) activity before, during and after skydiving. To distinguish the contribution of novelty, we compared novices (N=29) to experienced jumpers (N=15). All jumpers exhibited HPA-axis activation; novices exhibited a prolonged response and more extreme peak in cortisol compared to experienced jumpers, suggesting that novelty contributes to an intense pattern of stress responding. Both groups displayed increases in heart rate; there were no significant differences between the groups, indicating that repeated exposure to the stressor did not habituate this system. We provided evidence that the stress response systems instantiate novelty and risk to motivate and reward behavioral expressions of the SS trait.

Callous-unemotional (CU) traits have been shown to designate a particular subgroup of antisocial youth that are particularly violent, recidivistic, and more likely to continue offending in adulthood. Disordered neuroendocrine function may be a mechanism for the development of CU traits. We examined whether altered stress responsivity served as a mechanism linking stress exposure and the expression of CU traits. Participants were 15 incarcerated adolescent girls with CU traits. Measures of CU traits, stress exposure, and salivary cortisol were collected. Results revealed girls with CU traits had higher morning levels of cortisol, an intact cortisol awakening response (CAR), and flatter diurnal rhythms. Results indicated the type of stressor being measured and time since stressor onset are crucial to the interpretation of neuroendocrine function. We also found support for a neurobiological model for the development of CU traits drawing on the Adaptive Calibration Model. Implications of the study and directions for further research are discussed.

The Hypothalamic-Pituitary-Adrenal (HPA) and –Gonadal (HPG) axes have been considered mutually inhibitory; however, emerging evidence supports the proposition that this might not necessarily be the case. This idea is termed “coupling,” in which the HPA-HPG axis are mutually activated or deactivated. Coupling is examined across three data sets with different time-courses of stress exposure, and results demonstrate HPA-HPG co-activation occurs. Furthermore, stress exposure influences this relationship. The discussion shows how it is physiologically possible to have positive coupling or co-activation between these axes according to complex regulatory feedback systems and overlapping neural structures. Findings are interpreted developmentally, because adolescence may be a critical time for this co-activation to occur. Finally, the discussion emphasizes an individual difference perspective because each individual differs in the duration and type of stress they experience, and these exerted individualized effects on HPA-HPG coupling.

Ten to 15% of the population is temperamentally shy and have elevated physiological stress responses to novel social situations. Yet, the neural mechanisms underlying this personality trait are not fully understood (Beaton et al., 2009; Schmidt et al., 1997). Efficiently attending to, acting on, and remembering relevant stimuli and filtering out less important information is critical given the sheer volume of sensory and perceptual stimuli the brain is exposed to. Relevant stimuli that garner attention are remembered and consolidated with existing memories. Stimuli that do not warrant extended attention are ignored or habituated to in a process underpinned by cortical and subcortical inhibitory brain networks that reduce processing load on finite attentional resources (Freedman et al., 1991; Adler et al., 1998). Inefficient filtering of irrelevant stimuli could underpin anxiety in those with temperamental shyness and anxiety (Aron, Aron, & Davies, 2005). We measured the P50 auditory event-related potential (ERP) using a paired auditory click paradigm, as well as self-reported social anxiety and shyness, and salivary cortisol in two groups of healthy young adults selected for being very shy or very gregarious. While shy and gregarious groups demonstrated a similar P50 ERP to sound one (S1), the shy group showed elevated P50 amplitudes in response to the second sound (S2) compared to the gregarious group. Participants categorized as being lower or higher on social anxiety displayed a reverse pattern: those higher in social anxiety had a reduced response to S1 compared to those lower in social anxiety, yet a similar response to S2. Further, higher salivary cortisol predicted smaller differences and larger ratios in the P50 ERP from S1 to S2.