No-stress Control Research Articles

High-intensity stress elicits robust cortisol increases, and impairs working memory and visuo-spatial declarative memory in Special Forces candidates: A field experiment

While running a selection procedure, 27 male Belgian Special Forces candidates, with a mean age of 27.4 years (SD = 5.1), were randomly assigned to a no-stress control (n = 14) or a high-intensity stress group (n = 13). Participants in the latter group were exposed to an extremely strenuous mock prisoner of war (POW) exercise. Immediately after stress or control treatment, working memory and visuo-spatial declarative memory performances were measured by the digit span (DS) test and the Rey–Osterrieth complex figure (ROCF), respectively. Concurrently, stress levels were assessed by obtaining salivary cortisol measurements and subjectively by the NASA Task Load Index (TLX). As expected, exposure to high-intensity stress led to both robust cortisol increases and significant differences in TLX scores. Stress induction also significantly impaired DS and ROCF performances. Moreover, delta cortisol increases and ROCF performance in the POW stress group showed a significant negative correlation, while DS performances followed the same tendency. Summarizing, the current findings complement and extend previous work on hormonal stress effects, and the subsequent performance deterioration on two memory tests in a unique high-intensity stress environment.

Acute Stress Modulates Risk Taking in Financial Decision Making

People's decisions are often susceptible to various demands exerted by the environment, leading to stressful conditions. Although a goal for researchers is to elucidate stress-coping mechanisms to facilitate decision-making processes, it is important to first understand the interaction between the state created by a stressful environment and how decisions are performed in such environments. The objective of this experiment was to probe the impact of exposure to acute stress on financial decision making and examine the particular influence of stress on decisions with a positive or negative valence. Participants' choices exhibited a stronger reflection effect when participants were under stress than when they were in the no-stress control phase. This suggests that stress modulates risk taking, potentially exacerbating behavioral bias in subsequent decision making. Consistent with dual-process approaches, decision makers fall back on automatized reactions to risk under the influence of disruptive stress.

Stress-induced changes in corticosteroid receptor expression in primate hippocampus and prefrontal cortex

Neurobiological studies of stress often focus on the hippocampus where cortisol binds with different affinities to two types of corticosteroid receptors, i.e., mineralocorticoid receptor (MR) and glucocorticoid receptor (GR). The hippocampus is involved in learning and memory, and regulates the neuroendocrine stress response, but other brain regions also play a role, especially prefrontal cortex. Here, we examine MR and GR expression in adult squirrel monkey prefrontal cortex and hippocampus after exposure to social stress in infancy or adulthood. In situ hybridization histochemistry with (35)S-labeled squirrel monkey riboprobes and quantitative film autoradiography were used to measure the relative distributions of MR and GR mRNA. Distinct cortical cell layer-specific patterns of MR expression differed from GR expression in three prefrontal regions. The relative distributions of MR and GR also differed in hippocampal Cornu Ammonis (CA) regions. In monkeys exposed to adult social stress compared to the no-stress control, GR expression was diminished in hippocampal CA1 (P=0.021), whereas MR was diminished in cell layer III of ventrolateral prefrontal cortex (P=0.049). In contrast, exposure to early life stress diminished GR but not MR expression in cell layers I and II of dorsolateral prefrontal cortex (P's<0.048). Similar reductions likewise occurred in ventrolateral prefrontal cortex, but the effects of early life stress on GR expression in this region were marginally not significant (P=0.053). These results provide new information on regional differences and the long-term effects of stress on MR and GR distributions in corticolimbic regions that control cognitive and neuroendocrine functions.

Stress-induced changes in primate prefrontal profiles of gene expression

Stressful experiences that consistently increase cortisol levels appear to alter the expression of hundreds of genes in prefrontal limbic brain regions. Here, we investigate this hypothesis in monkeys exposed to intermittent social stress-induced episodes of hypercortisolism or a no-stress control condition. Prefrontal profiles of gene expression compiled from Affymetrix microarray data for monkeys randomized to the no-stress condition were consistent with microarray results published for healthy humans. In monkeys exposed to intermittent social stress, more genes than expected by chance appeared to be differentially expressed in ventromedial prefrontal cortex compared to monkeys not exposed to adult social stress. Most of these stress responsive candidate genes were modestly downregulated, including ubiquitin conjugation enzymes and ligases involved in synaptic plasticity, cell cycle progression and nuclear receptor signaling. Social stress did not affect gene expression beyond that expected by chance in dorsolateral prefrontal cortex or prefrontal white matter. Thirty four of 48 comparisons chosen for verification by quantitative real-time polymerase chain reaction (qPCR) were consistent with the microarray-predicted result. Furthermore, qPCR and microarray data were highly correlated. These results provide new insights on the regulation of gene expression in a prefrontal corticolimbic region involved in the pathophysiology of stress and major depression. Comparisons between these data from monkeys and those for ventromedial prefrontal cortex in humans with a history of major depression may help to distinguish the molecular signature of stress from other confounding factors in human postmortem brain research.

Context-dependent enhancement of declarative memory performance following acute psychosocial stress

Studies on how acute stress affects learning and memory have yielded inconsistent findings, with some studies reporting enhancing effects while others report impairing effects. Recently, Joëls et al. [Joëls, M., Pu, Z., Wiegert, O., Oitzl, M.S., Krugers, H.J., 2006. Learning under stress: how does it work? Trends in Cognitive Sciences, 10, 152–158] argued that stress will enhance memory only when the memory acquisition phase and stressor share the same spatiotemporal context (i.e., context-congruency). The current study tested this hypothesis by looking at whether context-congruent stress enhances declarative memory performance. Undergraduates were assigned to a personality stress group ( n = 16), a memory stress group ( n = 18), or a no-stress control group ( n = 18). While being exposed to the acute stressor or a control task, participants encoded personality- and memory-related words and were tested for free recall 24 h later. Relative to controls, stress significantly enhanced recall of context-congruent words, but only for personality words. This suggests that acute stress may strengthen the consolidation of memory material when the stressor matches the to-be-remembered information in place and time.

Time course and mechanisms of mental stress‐induced changes and their recovery: Hematocrit, colloid osmotic pressure, whole blood viscosity, coagulation times, and hemodynamic activity

The mechanisms for stress-induced changes in hematocrit and blood viscosity are unclear. Twenty-two males completed experimental (30 min baseline, 10 min mental stress, 30 min recovery) and no-stress control conditions (70 min). Hemostatic and hemodynamic activity were measured throughout. Hematocrit, colloid osmotic pressure, and blood viscosity displayed parallel patterns: a progressive increase with stress, followed by a gradual recovery. Correlational and covariance analyses indicated that the increase in hematocrit may be mediated by arterial pressure whereas recovery may be mediated by colloid osmotic pressure. Analyses also indicated that acute changes in blood viscosity may depend on hematocrit. These data suggest that stress disturbs hematocrit, colloid osmotic pressure, and blood viscosity through arterial pressure. Poststress, elevated colloid osmotic pressure may drive its own recovery and that of hematocrit and blood viscosity.

Effects of Drink‐Stress Sequence and Gender on Alcohol Stress Response Dampening in High and Low Anxiety Sensitive Drinkers

This study tested the appraisal disruption hypothesis of alcohol stress response dampening (SRD) in male and female high or low anxiety sensitive (AS) undergraduates. The hypothesis predicts that alcohol SRD will be greater when drinking occurs before versus after stress exposure. High AS males' predominant social-evaluative concerns further implied that alcohol SRD to a social stressor (i.e., a speech) would be relatively stronger in high AS males than in high AS females. Male and female (n=90/gender) high and low AS participants (>or=70th; <or=30th percentile on Anxiety Sensitivity Index-Revised) were matched on drinking habits and randomly assigned to 1 of 9 experimental cells. Drink type--alcohol (0.7 g/kg males; 0.63 g/kg females), placebo, soda--was fully crossed with stress condition--drink before stress (DBS), drink after stress (DAS), and no stress control (NSC). Stress was induced by telling participants they would be required to make a self-revealing speech. Stress response dampening was assessed for state anxiety on the Spielberger scale and Stroop interference to threat-related words. Subjective desire for alcohol was also assessed. Relative to placebo, alcohol (peak blood alcohol concentration, 0.064%) reliably reduced state anxiety in high AS but not in low AS participants. Alcohol decreased STAI scores and Stroop interference to social threat words significantly more in the DBS than the DAS condition in high AS males; high AS females displayed the exact opposite pattern of effects. In contrast to other participants, high AS males also reported relatively strong desire scores under alcohol. Overall, the results do not support the appraisal disruption hypothesis as a general mechanism of alcohol SRD in undergraduate drinkers. The findings for high AS males do support the hypothesis, while the opposing profile for high AS females implies that the nature of the stressor (i.e., social challenge) may contribute to gender differences in alcohol SRD in high AS individuals.

Mental stress‐induced hemoconcentration and its recovery: A controlled study of time course and mechanisms

Hemoconcentration to mental stress has been implicated in acute cardiovascular events. Participants were exposed to a 30-min baseline, a 4-min stress task, and a 40-min recovery; they also undertook a 74-min no-stress control session. Hemodynamic activity was recorded and blood sampled regularly and analyzed for hematocrit, colloid osmotic pressure, and coagulation time. Hematocrit increased with stress and fully recovered after 20 min. Colloid osmotic pressure showed a similar time course. No such changes occurred in the control session. Coagulation time was not perturbed by stress. The pattern of increase in hematocrit correlated with contemporary colloid osmotic pressure and blood pressure. In recovery, only colloid osmotic pressure was strongly associated with hematocrit. The mechanisms of stress-induced hemoconcentration may differ from those responsible for recovery, which may depend primarily on colloid osmotic pressure.

The effect of psychological stress on symptom severity and perception in patients with gastro-oesophageal reflux

Objective Using an experimental paradigm this investigation explored whether exposure to psychological stress would produce a significant increase in acid-reflux episodes or modify subjective perceptions of gastro-oesophageal reflux (GOR) symptoms. Methods Forty-two patients presenting with heartburn and acid regurgitation underwent 24-h oesophageal pH monitoring. During the last 90 min of this monitoring period, 21 patients received a psychological stressor, while the remaining participants were randomly assigned to a no-stress control condition. State anxiety and subjective GOR symptom ratings were obtained 1 min pretest, 1 min posttest, and 40 min posttest. Cortisol samples were collected at 10-min intervals. Results The stressor induced a significant increase in cortisol and state anxiety; however, this was not associated with any increase in reflux. Instead, the experimental group reported a dissociation between objectively measured reflux episodes and subjective symptom ratings. A similar pattern was established for participants who reported greater state anxiety, produced larger cortisol responses, or exhibited certain stress-related personality characteristics. Conclusion The perception of symptoms in the absence of increased reflux when one is stressed may account for low response rates to traditional treatments. This highlights a need to bridge the gap between psychosomatic research and clinical practice to develop more successful GOR therapies.

Differential effects of chronic escapable versus inescapable stress on male syrian hamster ( Mesocricetus auratus) reproductive behavior

Stress decreases sexual activity, but it is uncertain which aspects of stress are detrimental to reproduction. This study used an escapable/inescapable stress paradigm to attempt to dissociate physical from psychological components of stress, and assess each component’s impact on reproductive behavior in the male Syrian hamster ( Mesocricetus auratus). Two experiments were completed using this protocol where two animals receive the same physical stressor (an electric footshock) but differ in the psychological aspect of control. One group (executive) could terminate the shock for themselves as well as a second group (yoked) by pressing a bar. Experiment 1 demonstrated a significant increase in plasma glucocorticoids at the end of a single 90-min stress session with no difference in glucocorticoid levels between the executive and yoked groups at any time point. Experiment 2 quantified male reproductive behavior prior to and immediately following 12 days of escapable or inescapable stress in executive, yoked, and no-stress control hamsters ( n = 12/group). Repeated-measures analysis of variance revealed a number of significant changes in reproductive behavior before and after stress in the three treatment groups. The most striking difference was a decrease in hit rate observed only in the animals that could not control their stress (yoked group). Hit rate in the executive males that received the exact same physical stressor but could terminate the shock by pressing a bar was nearly identical to control animals that never received any foot shock. Therefore, we conclude that coping or control can ameliorate the negative effects of stress on male reproductive behavior.

The emergence test: effects of psychotropic drugs on neophobic disposition in Wistar Kyoto (WKY) and Sprague Dawley Rats

1. The Emergence Test (ET), a variation of the open field test in which the rat is not handled, and is purported to measure neophobia, was applied to Wistar Kyoto (WKY) and Sprague Dawley (S-D) rats. 2. While no-stress control WKY rats were less active in the ET, pre-treatment with shock stress exacerbated strain differences. WKY rats, previously exposed to shock, did not emerge from the home cage start box during repeated testing, whereas previously stressed S-D rats vacated the home cage quickly and revealed increasing behavioral agitation. 3. Diazepam reduced emergence latency only in S-D rats, whereas nomifensine significantly increased head poke responses in WKY rats. 4. WKY rats responded to the ET with characteristically depressive behavior, whereas S-D rats responded to the same ET with behavioral agitation and anxiety. The implications of these behavior patterns for discriminating between anxiety and depressive behavior are presented.

Positive Evaluation as a Strategy for Coping with Stress

The present study evaluated the effectiveness of positive evaluation of stressful experiences as a strategy for coping with stress. Two methods of manipulating positive evaluation (i.e., videotape modeling and writing) were compared with a coping-instructions control condition, a no-instructions control condition, and a no-stress control condition. Measures of physiological arousal indicated that, relative to the control conditions, positive evaluation produced greater rather than less stress during anticipation of and confrontation with electric shock. A postexperimental questionnaire assessing cognitive behaviors indicated that the positive-evaluation manipulations produced increased preoccupation with the stressful aspects of the situation. The results are discussed in relation to other research and theory on the positive evaluation of stressful experiences.

Stress induced suppression of maintenance but not of acquisition of ethanol consumption in rats

Male Wistar rats were given a free-choice between water and increasing concentrations of ethanol from 3% to 11% (v/v) during the acquisition phase. Thereafter, animals were maintained on a choice between water and 11% ethanol for the balance of the experiment. For 5 days prior to and for periods during the acquisition and maintenance phases, the animals were expo exposed to electric footshock, restraint or no stress. The results showed no differences in ethanol drinking patterns among the groups during the acquisition phase. However, in the maintenance phase, both footshock and restraint suppressed the increase in ethanol intake seen in the no-stress control group.

The sensitivity of growth and yield of dwarf wheat to water stress at three growth stages

Response of dwarf wheat (Triticum aestivum L. em Thell) to three different levels of water stress at three growth stages — seeding to maximum tillering, maximum tillering to flowering and flowering to maturity, was studied under field conditions for two seasons. At each of these three stages, plants were subject to three ratios of irrigation water to cumulative pan evaporation (IW/CPE) −0.45, 0.60 and 0.75. During the remaining stages the plants were irrigated with an IW/CPE ratio of 0.9. Thus mild, moderate and severe stress treatments were compared with a no-stress control. At all stages moderate and severe water stress decreased plant height, leaf area, ear number, 1000-grain weight, grain yield and water-use efficiency. In stage 3 the effect of water stress on straw yield was not marked. Wheat was most sensitive to water stress during stage 1 when the reduction in grain yield was caused by a reduction in numbers of ears and grains per ear. In stage 2, grain yield reduction was due to fewer grains perear and a lower 1000-grain weight. On rewatering, mild stressed plants showed recovery of plant height, tiller number and in consequence, yield. Results indicate that under the conditions of this study the wheat crop should be irrigated at a IW/CPE ratio of 0.75 when water resources are limited. With an unlimited water supply the ratio may be increased to 1.2 in stage 2 to maximise the yield.

The effect of evaporative demand on the growth of well-watered kikuyu

A study was made of the effect of evaporative demand (potential evapotranspiration, E t) on the growth of heavily fertilized and well-watered kikuyu pasture. Mean weekly growth rates on an irrigated pasture, adjusted for differences in temperature during the various growth periods, declined significantly when the mean E t increased above 3.5 mm day −1. Using growth rates at lower E t as a no-stress control, the maximum reduction in growth rate (57%) occurred at the highest E t (5.0–5.8 mm day −1). When frequent leaf wetting was used to modify the possible effects of evaporative demand on the internal water status of the plant, the growth rate still declined with increasing E t, but to a lesser extent than on irrigated pasture. The leaf wetting was done at 20-min intervals and evidently this interval was too long to fully ameliorate the evaporative demand effect when mean E t exceeded 4.5 mm day −1. It was concluded that the growth of kikuyu is sensitive to evaporative demand even on wet soil and that cloudy periods enhance growth by reducing E t.