The effects of altered heat stress on voluntary pacing strategies during prolonged cycling

Central Governor Model (CGM) suggests that perturbations in the rate of heat storage (AS) are centrally integrated to regulate exercise intensity in a feed-forward fashion to prevent excessive thermal strain. We directly tested the CGM by manipulating ambient temperature (Tam) at 20-minute intervals from 20°C to 35°C, and returning to 20°C, while cycling at a set rate of perceived exertion (RPE). The synchronicity of power output (PO) with changes in HS and Tam were quantified using Auto-Regressive Integrated Moving Averages analysis. PO fluctuated irregularly but was not significantly correlated to changes in thermo physiological status. Repeated measures indicated no changes in lactate accumulation. In conclusion, real time dynamic sensation of Tam and integration of HS does not directly influence voluntary pacing strategies during sub-maximal cycling at a constant RPE while non-significant changes in blood lactate suggest an absence of peripheral fatigue.

The effects of thermal stress on glucoregulation during exercise in participants with Type 1 Diabetes Mellitus

Type 1 Diabetes Mellitus (T1DM) is an autoimmune disease that destroys pancreatic beta cells, affecting glucose homeostasis. In T1DM, glucoregulation and carbohydrate oxidation may be altered in different ambient temperatures; however, current literature has yet to explore these mechanisms. This study examines the effects of 30 minutes of exercise at 65% VO2max in 5ºC, 20ºC and 35ºC in individuals with T1DM. No significant differences were observed for blood glucose across the 3 conditions (p = 0.442), but significance was found for core temperature, heat storage, and sweat rate (p < 0.01). Blood glucose was also shown to vary greatly between individuals among conditions. The mechanisms behind the differences in blood glucose may be due to the lack of significant glucagon production among conditions. These findings suggest that T1DM individuals may exercise submaximally for 30 minutes in different ambient temperatures without significant differences in glucoregulation.

Disambiguating the Effects of Social Instability Stress in Adolescence on Learning and Memory Tasks that Involve the Medial Prefrontal Cortex and Hippocampus

Exposure to chronic stress can alter the structure and function of brain regions involved in learning and memory, and these effects are typically long-lasting if the stress occurs during sensitive periods of development. Until recently, adolescence has received relatively little attention as a sensitive period of development, despite marked changes in behaviour, heightened reactivity to stressors, and cognitive and neural maturation. Therefore, the purpose of the present study was to investigate the long-term effects of chronic stress in adolescence on two spatial learning and memory tasks (Morris water maze and Spatial Object Location test) and on a working memory task (Delayed Alternation task). Male rats were randomly assigned to chronic social instability stress (SS; daily 1 hour isolation and subsequent change of cage partner between postnatal days 30 and 45) or to a no-stress control group (CTL). During acquisition learning in the Morris water maze task, SS rats demonstrated impaired long-term memory for the location of the hidden escape platform compared to CTL rats, although the impairment was only seen after the first day of training. Similarly, SS rats had impaired long-term memory in the Spatial Object Location test after a long delay (240 minutes), but not after shorter delays (15 or 60 minutes) compared to CTL rats. On the Delayed Alternation task, which assessed working memory across delays ranging from 5 to 90 seconds, no group differences were observed. These results are partially in line with previous research that revealed adult impairment on spatial learning and memory tasks after exposure to chronic social instability stress in adolescence. The observed deficits, however, appear to be limited to long-term memory as no group differences were observed during brief periods of retention.

Effects of Cerebral Blood Flow and PETCO2 on Cognitive Function During Passive Heat Stress

This thesis tested whether cognitive performance during passive heat stress may be affected by changes in cerebrovascular variables as opposed to strictly thermally-induced changes. A pharmacological reduction in cerebral blood flow (CBF) using indomethacin along with a hypocapnia-induced CBF reduction during passive heat stress (Tre ~1.5°C above baseline) were used to investigate any cerebrovascular-mediated changes in cognitive performance. Repeated measures analysis of variance indicated that One-Touch Stockings of Cambridge (OTS) performance was not affected by a significant reduction in CBF during passive heat stress. More specifically, OTS accuracy measures did not change as a result of either a reduction in CBF or increasing passive heat stress. However, it was found that OTS response time indices improved with increasing passive heat stress independent of CBF changes. In conclusion, a significant reduction in CBF does not cause additional changes in performance of an executive functioning task during severe passive heat stress.

An investigation into the physical and psychological stress factors that elementary teachers experience : recommendations to boards and personal calming strategies /

The prlmaiy objective of this study was to Identify and describe the physical and psychological stress factors that elementary school teachers experience and how teachers cope with stress. A secondary objective was to offer boards and teachers potential coping strategies counteracting stress and the effects of stress. The sample consisted of 120 elementaiy teachers from southern Ontario. Ten elementaiy schools were randomly chosen. The Teacher Stress Inventory questionnaire (Flmian, 1989) was used. Data were analyzed using a variety of statistics. Test norms and interpretations were performed based on standard results obtained from the author of the questionnaire (Flmian, 1988). Overall, the results indicated that work-related stressors were the main factor for teacher stress. This Included such factors as caseload/class is too big, too much administrative paperwork, and having little time to prepare lessons. Implications for further research and practical suggestions for further reseairch are discussed. Also a variety of recommendations to boards and for individual use are discussed. Some recommendations are having counselling available for teachers, workshops on how to handle stress, and learning how to breathe and using calm visualization.

Linking of stress offset score (SOS), work satisfaction, and organizational commitment to intentions to quit

The purpose of this study was to identify the impact of stressors and offsetting satistiers, measured in this study with Stress Offset Score (SOS), on intentions to quit and examine the mediating and moderating effects of three facets of work satisfaction (job satisfaction, pay satisfaction, and satisfaction with supervisor) and two facets of organizational commitment (affective and nonnative commitment) on this relationship. The sample was composed of 2990 employees from 21 public and private organizations. The interaction of each type of work satisfaction and organizational commitment, with SOS, was tested using Ordinary Least Squares (OLS) procedures. Intentions to quit was the dependent variable. The research questions were determine: (1) Does SOS predict intentions to quit? (2) Does work satisfaction mediate the predictive relationship of SOS on intentions to quit? (3) Does organizational commitment mediate the predictive relationship of SOS on intent to quit? (4) Does work satisfaction moderate the predictive relationship of SOS on intentions to quit? and (5) Does organizational commitment moderate the predictive relationship of SOS on intentions to quit? The results indicated that SOS was negatively correlated with intentions to quit. Each of the types of work satisfaction and organizational commitment variables showed a partial mediated relationship with SOS and each relationship was highly significant, while normative commitment explained more of the relationship then other mediators. The study also tested for interactions but no statistical significant relationships where established between any of the interaction terms (e.g., SOSxJob Satisfaction and SOSxAffcctive Commitment) and intentions to quit.

Relating leadership, thinking styles, self-concept, motivation and stress management in education

Seventy-five principals and vice-.wincipals from public elementary and secondary schools in Hamilton, Ontario, Canada participated in this study. Participants provided ,information concerning their thinking styles, motivations, and the physical effects of stress. This information was examined to find out how satisfaction-oriented, and how security-oriented the thinking styles of the participants were. Second, the data were analysed to see how the thinking style orientations related to life style habits and the effects of stress. The satisfaction-oriented thinking styles scored higher than all of the security-oriented thinking styles by a wide margin with a small preference for the satisfaction-people-oriented styles labelled humanistic-helpful, and affiliative as opposed to the satisfaction-task-oriented styles labeled achievement, and self-actualizing. Although all eight of the security-oriented thinking styles scored well below all of the satisfaction-oriented thinking styles on the Life Styles Inventory, the perfectionistic style scored higher than all of the security-oriented styles by an impressive margin. The next highest scores were recorded by a cluster of three passive-defensive people-oriented thinking styles labeled approval, conventional, and dependent. The competitive style scored lower, and the styles labeled avoidance, oppositional, and power scored the lowest of all the defensive-security-oriented styles. These findings suggest that principals and vice-principals see themselves as relaxed, flexible, and satisfied with their ability to adapt to the stress levels they experience in their lives; however, there was some support for medical research findings that suggest that specific security-oriented thinking styles are associated with emotional stresses that contribute to the development of specific lifestyle habits, physical symptoms, and illnesses. Although the number of females in this study provides very limited generalizability, the findings of this study suggest that high achieving females tend to develop satisfaction-growth styles to a higher level than males, and they tend to use security-oriented styles to a lesser degree than males.

Structural effects of neutral lipids on the divalent cation-induced interactions of phosphatidylserine - containing bilayers

As Ca2+ and phosphatidylserine (PS) are known to induce the adhesion of bilayer vesicles and form collapsed multibilayer structures in vitro, it was the aim of this study to examine how that interaction and the resultant structures might be modified by neutral lipid species. X-ray diffraction data from multilamellar systems suggest that phosphatidylcholine (PC) and diacylglycerol (DG) might be in the collapsed phase up to a concentration of -30 mole % and that above this concentration these neutral lipids may modify Ca2+-induced bilayer interactions. Using large unilamellar vesicles and long incubations in excess Ca2+ to ensure equilibration, similar preliminary results were again obtained with PC, and also with phosphatidylethanolamine (PE). A combination of X-ray diffraction, thin-layer chromatography, density gradient centrifugation and freeze-fracture electron microscopy, used in conjunction with an osmotic stress technique, showed that (i) -30 mole % PC can be accomodated in the Ca(DOPS)2 phase; and (ii) higher PC levels modify Ca2+-induced bilayer interactions resulting in single lamellar phases of larger dimension and reduced tendency for REV collapse. Importantly, the data suggest that PC is dehydrated during the rapid collapse process leading. to Ca(DOPS)2 formation and exists with this dehydrated phase. Similar results were obtained using PS isolated from bovine brain. Preliminary studies using two different phosphatidylethanolamine (PE) species indicated accomodation by Ca(DOPS)2 of -25-30 mole 0/0 PE and bulk phase separation, of species favouring a non-bilayer phase, at higher levels. Significantly, all PS/PE vesicles appear to undergo a complete Ca2+-induced collapse, even with contents of up to 90 mole % PE. These data suggest that PE may have an important role in fusion mechanisms in vivo. In sum the data lend both structural and stoichiometric evidence for th~ existence of laterally segregated neutral lipid molecules within the same bilayers as PS domains exposed to Ca2+.

The effects of temperature on nickel tocicity in goldfish (carassius auratus L.)

Although it is widely assumed that temperature affects pollutant toxicity, few studies have actually investigated this relationship. Moreover, such research as has been done has involved constant temperatures; circumstances which are rarely, if ever, actually experienced by north temperate, littoral zone cyprinid species. To investigate the effects of temperature regime on nickel toxicity in goldfish (Carassius auratus L.), 96- and 240-h LCSO values for the heavy metal pollutant, nickel (NiCI2.6H20), were initially determined at 2DoC (22.8 mg/L and 14.7 mg/L in artificially softened water). Constant temperature bioassays at 10°C, 20°C and 30°C were conducted at each of 0, 240-h and 96-h LCSO nickel concentrations for 240 hours. In order to determine the effects of temperature variation during nickel exposure it was imperative that the effects of a single temperature change be investigated before addressing more complex regimes. Single temperature changes of + 10°C or -10°C were imposed at rates of 2°C/h following exposures of between 24 hand 216 h. The effects of a single temperature change on mortality, and duration of toxicant exposure at high and low temperatures were evaluated. The effects of fluctuating temperatures during exposure were investigated through two regimes. The first set of bioassays imposed a sinewave diurnal cycle temperature (20.±.1DOC) throughout the 10 day exposure to 240-h LeSO Ni. The second set of investigations approximated cyprinid movement through the littoral zone by imposing directionally random temperature changes (±2°C at 2-h intervals), between extremes of 10° and 30°C, at 240-h LC50 Ni. Body size (i.e., total length, fork length, and weight) and exposure time were recorded for all fish mortalities. Cumulative mortality curves under constant temperature regimes indicated significantly higher mortality as temperature and nickel concentration were increased. At 1DOC no significant differences in mortality curves were evident in relation to low and high nickel test concentrations (Le., 16 mg/L and 20 mg/L). However at 20°C and 30°C significantly higher mortality was experienced in animals exposed to 20 mg/L Ni. Mortality at constant 10°C was significantly lower than at 30°C with 16 mg/L and was significantly loWer than each of 2DoC and 39°C tanks at 20 mg/L Ni exposure. A single temperature shift from 20°C to 1DoC resulted in a significant decrease in mortality rate and conversely, a single temperature shift from 20°C to 30°C resulted in a significant increase in mortality rate. Rates of mortality recorded during these single temperature shift assays were significantly different from mortality rates obtained under constant temperature assay conditions. Increased Ni exposure duration at higher temperatures resulted in highest mortality. Diurnally cycling temperature bioassays produced cumulative mortality curves approximating constant 20°C curves, with increased mortality evident after peaks in the temperature cycle. Randomly fluctuating temperature regime mortality curves also resembled constant 20°C tanks with mortalities after high temperature exposures (25°C - 30°C). Some test animals survived in all assays with the exception of the 30°C assays, with highest survival associated with low temperature and low Ni concentration. Post-exposure mortality occurred most frequently in individuals which had experienced high Ni concentrations and high temperatures during assays. Additional temperature stress imposed 2 - 12 weeks post exposure resulted in a single death out of 116 individuals suggesting that survivors are capable of surviving subsequent temperature stresses. These investigations suggest that temperature significantly and markedly affects acute nickel toxicity under both constant and fluctuating temperature regimes and plays a role in post exposure mortality and subsequent stress response.

Investigating the effects of arousal state on cognitive performance in individuals with and without mild head injury

We examined the cognitive and emotional sequelae following mild head injury (MHI; e.g., concussion) in high-functioning individuals and whether persons with MHI pre~ent, both physiologically and via self-report, in a manner different from (i.e., underaroused) that of persons who have no history of head injury. We also investigated the effect arousal state ~as on the cognitive performance of this population. Using a quasiexperimental research design (N = 91), we examined changes in attention, working memory, and cognitive flexibility (subtests ofthe WAIS-III, 1997,WMS-III, 1997, & DKEFS, 2002) as a function of manipulated arousal (i.e., induced psychosocial stress/activation; reduced activation/relaxation). In addition to self-reported arousal and state anxiety (State-Trait Anxiety Inventory; Speilberger, 1983a) measures, physiological indices of arousal state (i.e., electrodermal responsivity, heart rate, and respiration activity) were recorded (via Polygraph Professional Suite, 2008) across a 2.5 hour interval while completing various cognitive tasks. Students also completed the Post-concussive Symptom Checklist (Gouvier et aI., 1992). The results demonstrate that university students who report a history ofMHI (i.e., "altered state of consciousness") experience significantly lower levels of anxiety, were physiologically underaroused, and were less responsive to stressors in their environment, compared to their non-~HI cohorts. As expected, cognitive flexibility (but not other neuropsychological measures of cognition) was advantaged with increased stress, and disadvantaged with reduced stress, in persons with reported MHI, but not for those without reported MHI which provided limited support for our hypothesis. Further, university students who had no complaints related to their previous MHI endorsed a greater number of traditional post-concussive symptoms in terms of intensity, duration and frequency as compared to students who did not report a MHI. The underarousal in traumatic brain injury has been associated with (ventromedial prefrontal cortex) VMPFC disruption and may be implicated in MHI generally. Students who report sustaining a previous MHI may be less able to physiologically respond and/or cognitively appraise, stressful experiences as compared to their no-MHI cohort and experience persistent, long-lasting consequences despite the subtle nature of a history of head injury.

Posttraumatic stress disorder symptoms might be destroying your intimacy : a test of mediational models in a community sample of couples

The present research focused on the pathways through which the symptoms of posttraumatic stress disorder (PTSD) may negatively impact intimacy. Previous research has confirmed a link between self-reported PTSD symptoms and intimacy; however, a thorough examination of mediating paths, partner effects, and secondary traumatization has not yet been realized. With a sample of 297 heterosexual couples, intraindividual and dyadic models were developed to explain the relationships between PTSD symptoms and intimacy in the context of interdependence theory, attachment theory, and models of selfpreservation (e.g., fight-or-flight). The current study replicated the findings of others and has supported a process in which affective (alexithymia, negative affect, positive affect) and communication (demand-withdraw behaviour, self-concealment, and constructive communication) pathways mediate the intraindividual and dyadic relationships between PTSD symptoms and intimacy. Moreover, it also found that the PTSD symptoms of each partner were significantly related; however, this was only the case for those dyads in which the partners had disclosed most everything about their traumatic experiences. As such, secondary traumatization was supported. Finally, although the overall pattern of results suggest a total negative effect of PTSD symptoms on intimacy, a sex difference was evident such that the direct effect of the woman's PTSD symptoms were positively associated with both her and her partner's intimacy. I t is possible that the Tend-andBefriend model of threat response, wherein women are said to foster social bonds in the face of distress, may account for this sex difference. Overall, however, it is clear that PTSD symptoms were negatively associated with relationship quality and attention to this impact in the development of diagnostic criteria and treatment protocols is necessary.

Immediate and enduring effects of corticosterone administration during adolescence and adulthood on anxiety and depressive behavior in male rats

Previous research has shown that the stress hormone corticosterone can increase depressive and anxiety-like behavior in rats as well as dampen the HPA response to a novel stressor (Kalynchuk et aI., 2004; Johnson et aI., 2006). Several studies have also shown that adolescence is a period of increased sensitivity to the negative effects of stressors (reviewed in McCormick et aI., 2010), which are often the result of exposure to corticosterone, and yet there is no research to date examining the effects of corticosterone administration during adolescence. The purpose of these experiments is to determine both the immediate and enduring effects of prolonged exposure to corticosterone in adolescence and adulthood on anxiety-like behavior, depressive behavior, and the HPA response. In Experiment 1 adolescent and adult rats were administered an injection of 40 mg/kg of corticosterone or vehicle daily for 16 days. Ha l f of the rats were then tested on the elevated plus maze (EPM) one day after their last injection, and the following day were tested on the forced swim test (FST). After the FST, which is a stressor, blood samples were collected at three time points, and the plasma concentrations of corticosterone were determined using a radioimmunoassay. The remaining rats were left undisturbed for three weeks, and then underwent the same testing as the first group. Corticosterone treatment had little effect on anxiety-like and depressive behavior, but it did alter the HPA response to the FST. In those rats tested soon after the period of injections, corticosterone dampened the HPA response as compared to vehicle treated rats in both adolescent and adult treated rats. For the adolescent treated rats that were tested several weeks later, corticosterone treatment increased HPA response as compared to the vehicle treated rats, but the same was not true for the adult treated rats. I t was hypothesized that the lack of behavioral effects of the corticosterone treatment may be the result of the vehicle injections inducing a stress response and thereby both groups would have similarly altered behavior. In Experiment 2 rats were administered corticosterone dissolved in their drinking water with 2.5% ethanol, or jus t the 2.5% ethanol or plain water, to determine the effects of corticosterone treatment without a stressor present. The regular drinking water was replaced with treated water for 16 days either during adulthood or adolescence, and as before, rats were either tested in the FST one day after the water was removed or three weeks later. Again there was no effect of treatment on depressive behavior. Similar to what was observed in Experiment 1, corticosterone treatment dampened the HPA response to a stressor for the rats tested soon after the treatment period. However, in Experiment 2 there was no effect of treatment on HPA response in those rats tested several weeks after they were treated. These results indicate that corticosterone can have a lasting effect on the HPA when administered in adolescence by injections but not in drinking water, which is likely because of the different schedules of exposure and rates of absorption between the two administration methods.

Protein Turnover in Rat Skeletal Muscle During In Vitro Hypo-Osmotic Stress

Hypo-osmolality influences tissue metabolism, but research on protein turnover in skeletal muscle is limited. The purpose of this investigation was to examine the effects of hypo-osmotic stress on protein turnover in rat skeletal muscle. We hypothesized increased protein synthesis and reduced degradation following hypo-osmotic exposure. EDL muscles (n=8/group) were incubated in iso-osmotic (290 Osm/kg) or hypo-osmotic (190 Osm/kg) modified medium 199 (95% O2, 5% CO2, pH 7.4, 30±2 °C) for 60 min, followed by 75 min incubations with L-U[14C]phenylalanine or cycloheximide to determine protein synthesis and degradation. Immunoblotting was performed to assess signalling pathways involved. Phenylalanine uptake and incorporation were increased by 199% and 169% respectively in HYPO from ISO (p < 0.05). This was supported by elevated phosphorylation of mTOR Ser2448 (+12.5%) and increased Thr389 phosphorylation on p70s6 kinase (+23.6%) (p < 0.05). Hypo-osmotic stress increased protein synthesis and potentially amino acid uptake. Future studies should examine the upstream mechanisms involved.

Chronic mild social stress increases neurogenesis in adolescent male rats

Once thought to occur only during specific periods of development, it is now clear that neurogenesis occurs in the rat hippocampus into adulthood. It is wellestablished that stress during adulthood decreases the rate of neurogenesis, but during adolescence, the effects of stress are much less understood. I investigated the effect of short-term or chronic stress during adolescence (daily lhr isolation and change of cage partner from postnatal day (PND) 30-32 or 30-45) on hippocampal neurogenesis. In experiment 1, rats were administered Bromodeoxyuridine (BrdU) daily on PND 30-32, or 46-48, to mark neurogenesis at the beginning of the stressor or after the stressor had ceased, respectively. Neither short-term nor chronic stress had an effect on proliferation or survival (evidenced by BrdU and Doublecortin (Dcx) immunohistochemistry respectively) of cells born at the beginning of the stress procedure. Compared to controls, BrdU-labeling showed chronic stress significantly increased proliferation of cells generated after the stressor had ceased, but survival of new neurons was not supported (Dcx-Iabeling). However, it may be that BrdU injections are inherently stressful. In experiment 2, the stressor (described above) was applied in the absence of BrdU injections. Ki67 (a marker of proliferation) showed that stress transiently increased cell proliferation. Dcx-Iabeling showed that stress also increased neuron survival into adulthood. Labeling with OX.,.42 (a marker of macro phages) suggested that the immune system plays a role in neurogenesis, as stress transiently decreased the number of activated microglia in the hippocampus. It can be concluded that in the adolescent male rat, chronic mild stress increases neurogenesis.

Effects of social context on endocrine function and Zif268 expression in response to an acute stressor in adolescent and adult rats

There is a paucity of studies comparing social buffering in adolescents and adults, despite their marked differences in social behaviour. I investigated whether greater effects of social buffering on plasma corticosterone concentrations and expression of Zif268 in neural regions after an acute stressor would be found in adolescent compared with adult rats. Samples were obtained before and after one hour of isolation stress and after either one or three hours of recovery back in the colony with either a familiar or unfamiliar cage partner. Adolescent and adult rats did not differ in plasma concentrations of corticosterone at any time point. Corticosterone concentrations were higher after one hour isolation than at baseline (p < 0.001), and rats with a familiar partner during the recovery phase had lower corticosterone concentrations than did rats with an unfamiliar partner (p = 0.02). Zif268 immunoreactive cell counts were higher in the arcuate nucleus in both age groups after isolation (p = 0.007) and higher in the paraventricular nucleus of adolescents compared with adults during the recovery phase irrespective of partner familiarity. There was a significant decrease in immunoreactive cell counts after one hour isolation compared to baseline in the basolateral amygdala, central nucleus of the amygdala, and in the pyramidal layer of the hippocampus (all p < 0.05). An effect of partner familiarity on Zif268 immunoreactive cell counts was found in the granule layer of the dentate gyrus irrespective of age (higher in those with a familiar partner, p = 0.03) and in the medial prefrontal cortex in adolescents (higher with an unfamiliar partner, p = 0.02). Overall, the acute stress and partner familiarity produced a similar pattern of results in adolescents and adults, with both age groups sensitive to the social context.