Acute exposure to a novel stressor further reduces the habituated corticosterone response to restraint in rats

The present study sought to identify dishabituation of the hypothalamic-pituitary-adrenal(HPA) axis response to different psychological stressors. Young adult male Sprague Dawley rats were exposed to five, 1 h sessions of restraint stress on five consecutive days. On the sixth day, and 2 h before additional exposure to restraint, animals were subjected to 30 min of a small (27cm square), elevated open field stressor (pedestal), which served as the dishabituating stimulus. We predicted HPA axis response dishabituation in chronically restrained rats exposed to the novel pedestal. Rats which underwent five days of restraint stress showed significantly blunted plasma corticosterone levels to restraint (habituation) as compared to restraint-nai've rats. However, rats which underwent five sessions of restraint responded with an enhanced habituation response when confronted with restraint shortly after exposure to the novel pedestal. Instead of HPA axis response dishabituation, we observed enhanced habituation. Subsequent experiments determined that a 1.25 mgkg corticosterone injection could substitute for pedestal exposure to produce enhanced restraint habituation.Combined treatment with both the glucocorticoid receptor antagonist RU40555 (30 mgkg)and the mineralocorticoid receptor antagonist RU283 18 (50 mgkg) blocked the expression of enhanced habituation after pedestal exposure. Thus, the delayed corticosterone negative feedback produced by novel stress led to enhanced expression of corticosterone response habituation.     

Posttraumatic stress disorder and retrospectively reported stressor exposure: a longitudinal prediction model

There has been recent concern about the degree to which posttraumatic stress disorder (PTSD) symptomatology influences reports of prior exposure to highly stressful life events. In this longitudinal study of 2,942 male and female Gulf War veterans, the authors documented change in stressor reporting across 2 occasions and the association between change and PTSD symptom severity. A regression-based cross-lagged analysis was used to examine the relationship between PTSD symptom severity and later reported stressor exposure. Shifts in reporting over time were modestly associated with PTSD symptom severity. The cross-lagged analysis revealed a marginal association between Time 1 PTSD symptom severity and Time 2 reported stressor exposure for men and suggested that later reports of stressor exposure are primarily accounted for by earlier reports and less so by earlier PTSD symptomatology.     

Children's natural conversations following exposure to a rumor: Linkages to later false reports

Previous research has shown that children naturally propagate overheard false rumors and that the circulation of such information can induce children and their peers to wrongly recall actually experiencing rumored-but-nonexperienced events. The current study extends this work by recording 3- to 6-year-olds' naturally occurring conversations following exposure to an erroneous rumor. Results indicate that, compared with children who overhear rumors spread by adults, those who pick up rumors from peers during natural interactions engage in deeper and more inventive rumor mongering. Moreover, the degree and originality of rumor propagation was linked with various qualities of children's subsequent recollections at both 1-week and 4-week delayed interviews. Furthermore, compared with 3- and 4-year-olds, 5- and 6-year-olds naturally transmitted more novel and coherent embellishments of the rumor to their peers, and more of their false narrative reports during the interviews overlapped with their own and their peers' utterances transmitted soon after the rumor was planted.     

Genetic and environmental effects on daily life stressors: more evidence for greater variation in later life

People vary in the occurrence and perceived severity of stressors experienced in their daily lives. In the current study, the authors examined the extent to which individual differences in these relatively minor occurrences are determined by genetic endowment as well as environmental influences and how these effects vary by age. Identical (n-sub(pairs) = 111) and fraternal (n-sub(pairs) = 99) twin adults ranging from 25 to 73 years old reported the occurrence and severity of their daily stressors on 8 consecutive evenings. Both genetic and unique environmental effects accounted for the variance in stressor occurrence, whereas shared family and unique environmental effects accounted for the variance in the perceived severity of these stressors. In addition, the influence of unique environment on perceived stress exerted a stronger influence among the older adults than the younger adults.     

The activity of the hypothalamo-neurohypophysial system in response to acute stressor exposure: neuroendocrine and electrophysiological observations

The present mini review focuses on stress-induced alterations of the electrical and secretory activity of vasopressin (AVP) and oxytocin (OXT) neurones originating within the supraoptic nucleus (SON) and constituting the hypothalamo-neurohypophysial system (HNS) in the male rat. Previously, it was thought that SON neurones are predominantly activated by osmotic and reproductive stimuli. However, recent findings also suggest a selective activation of AVP and/or OXT neurones in response to specific stressors. Inhibitory amino acids seem to participate at the level of the SON in the control of HNS activity during stress. Taurine, probably of glial origin, selectively inhibits the secretory activity of AVP neurones. In contrast, GABA, probably of neuronal origin, interferes with the release of OXT both from axon terminals into blood and from somata/dendrites into the extracellular fluid of the SON. Depending upon whether a defined stressor triggers taurine and/or GABA release within the SON the secretion of AVP and/or OXT from HNS neurones will be inhibited. These observations shed new light on the neurone-neurone and glial-neurone interactions that ensure an appropriate neuroendocrine stress response.     

Impact of stressors in a natural context on release of cortisol in healthy adult humans: a meta-analysis

Increased hypothalamic-pituitary-adrenal (HPA) activation, culminating in elevated circulating cortisol levels is a fundamental response to stressors. In animals, this neuroendocrine change is highly reliable and marked (approximately 5-10-fold elevations), whereas in humans, the increase of cortisol release is less pronounced, and even some potent life-threatening events (anticipation of surgery) only elicit modest cortisol increases. Meta-analysis of factors that influenced the increase of cortisol release in a laboratory context pointed to the importance of social evaluative threats and stressor controllability in accounting for the cortisol rise. The present meta-analysis, covering the period from 1978 through March 2007, was undertaken to identify the factors most closely aligned with cortisol increases in natural settings. It appeared that stressor chronicity was fundamental in predicting cortisol changes; however, this variable is often confounded by the stressor type, the stressor's controllability, as well as contextual factors, making it difficult to disentangle their relative contributions to the cortisol response. Moreover, several experiential factors (e.g. previous stressor experiences) may influence the cortisol response to ongoing stressors, but these are not readily deduced through a meta-analysis. Nevertheless, there are ample data suggesting that stressful events, through their actions on cortisol levels and reactivity, may influence psychological and physical pathology.     

Environmental enrichment in male CD-1 mice promotes aggressive behaviors and elevated corticosterone and brain norepinephrine activity in response to a mild stressor

Housing rodents in an enriched environment (EE) has been typically considered to have positive effects on well-being and cognitive functioning of the animals. However, in some strains of mice, EEs have also been reported to elicit aggression and to promote stress-related outcomes. In the current investigation, we examined whether environmental enrichment would elicit aggression among CD-1 male mice and thus sensitize responses to a subsequent mild stressor. It was first observed that mice housed in an EE for 2 weeks displayed more aggressive behaviors than did mice that had been housed in a standard environment (SE). In the second experiment, it was noted that after 4 weeks of EE or SE housing, mice exhibited comparable plasma corticosterone concentrations as well as levels of brain norepinephrine and its metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), in the absence of a challenge. However, upon exposure to mild stressor (placement in a novel cage), relative to their SE counterparts, EE mice were more active and displayed higher plasma corticosterone concentrations and enhanced MHPG accumulation in the prefrontal cortex and hippocampus. It seems that enrichment in male CD-1 mice promotes aggression, and may sensitize biological processes, possibly increasing vulnerability to stressor-related outcomes.     

Cigarette smoking and chewing gum: response to a laboratory-induced stressor.

The current study examined the anxiolytic effects of cigarette smoking and chewing gum on urge to smoke, withdrawal, and anxiety in response to a public speaking task in 45 undergraduate smokers. Participants were asked to smoke, chew gum, or do nothing in response to the stressor. Participants completed measures of anxiety, withdrawal symptoms, and urge to smoke pre- and poststressor. The smoke group reported fewer urges to smoke pre- and poststressor than the other groups. The smoke and gum groups reported fewer withdrawal symptoms than did the control group poststressor. Chewing gum was helpful in managing levels of withdrawal symptoms compared with the control group. Groups did not differ on measures of anxiety. Results suggest that smoking in response to a stressor may not reduce levels of affective stress. Furthermore, chewing gum may be helpful in managing withdrawal symptoms in response to a stressor.     

Positive impact of prior military combat exposure on Terrorism Prevention work: Inoculation to stress

Forty-four Israeli security agents employed by the Israeli Government Terrorism Prevention Agency providing security services for the national Israeli airlines and the Israeli Consulate in Los Angeles were administered the Subjective Stress Experience Scale (SSES). This scale measures stress at terrorism-prevention work, past stress during combat exposure, and subjects’ most stressful life events. Results support the hypothesis that terrorism prevention personnel who are also combat veterans appraise their work as less stressful than their noncombat exposed counterparts. Combat veterans also rated their combat experience as significantly more stressful than prevention team member’s other stressful life events. Subjects presented a uniform stress- inoculation effect but, combat veterans of the prevention team were more stress-inoculated than their noncombat exposed counterparts.     

Reported exposure and emotional reactivity to daily stressors: the roles of adult age and global perceived stress

A central goal of daily stress research is to identify resilience and vulnerability factors associated with exposure and reactivity to daily stressors. The present study examined how age differences and global perceptions of stress relate to exposure and emotional reactivity to daily stressors. Sixty-seven younger (M age = 20) and 116 older (M age = 80) adults completed a daily stress diary and measures of positive and negative affect on 6 days over a 14-day period. Participants also completed a measure of global perceived stress. Results revealed that reported exposure to daily stressors is reduced in old age but that emotional reactivity to daily stressors did not differ between younger and older adults. Global perceived stress was associated with greater reported exposure to daily stressors in older adults and greater stress-related increases in negative affect in younger adults. Furthermore, across days on which daily stressors were reported, intraindividual variability in the number and severity of stressors reported was associated with increased negative affect, but only among younger adults.     

Effect of prior exposure to a lithium- and an amphetamine-paired flavor on the acoustic startle response in rats

The experiments reported here evaluated the hypothesis that an amphetamine-paired flavor elicits conditioned fear-arousal, whereas a lithium-paired flavor elicits conditioned nausea-disgust by examining the effect of prior flavor exposure on an acoustic startle reaction (ASR). Exposure to a lithium-paired flavor by intraoral infusion, either immediately prior to a startle session (Experiment 1) or during a startle session (Experiments 2 and 3), resulted in a blunted ASR. In contrast, intraoral infusion of an amphetamine-paired flavor resulted in a potentiated ASR. The blunted ASR produced by exposure to a lithium-paired flavor dramatically reversed to a potentiated ASR when rats were pretreated with the antiemetic drug ondansetron prior to the saccharin-lithium pairing (Experiment 3). The findings shed light on a mechanism by which rewarding drugs produce conditioned taste avoidance in rats.     

Adaptation to auditory motion in the horizontal plane: Effect of prior exposure to motion on motion detectability

Thresholds for auditory motion detectability were measured in a darkened anechoic chamber while subjects were adapted to horizontally moving sound saurces of various-velocities. All stimuli were 500-Hz lowpass noises presented at a level of 55 dBA. The threshold measure employed was the minimum audible movement angle(MAMA)—that is, the minimum angle a horizontally moving sound must traverse to be just discriminable from a stationary sound. In an adaptive, two-interval forced-choice procedure, trials occurred every 2-5 sec (Experiment 1) or every 10–12 sec (Experiment 2). Intertrial time was “filled” with exposure to the adaptor—a stimulus that repeatedly traversed the subject’s front hemifield at ear level (distance: 1.7 m) at a constant velocity (?150°/secto + 150°/sec)during a run. Average MAMAs in the control condition, in which the adaptor was stationary (0°/sec), were 2.4° (Experiment 1) and 3.0° (Experiment 2). Three out of 4 subjects in each experiment showed significantly elevated MAMAs (by up to 60%), with some adaptors relative to the control condition. However, there were large intersubject differences in the shape of the MAMA versus adaptor velocity functions. This loss of sensitivity to motion that most subjects show after exposure to moving signals is probably one component underlying the auditory motion aftereffect (Grantham, 1989), in which judgmentsof the direction-afmoving sounds are biased in the direction opposite to that of a previously presented adaptor.     

The effects of exposure to an acute naturalistic stressor on working memory, state anxiety and salivary cortisol concentrations

Exposure to an acute naturalistic stressor induces both psychological and physiological changes in humans. The two studies reported here explored the impact of exposure to an acute naturalistic stressor on state anxiety, working memory and HPA axis activation (salivary cortisol). In both experiments, ten healthy male participants were exposed to an acute naturalistic stressor, helicopter underwater evacuation training (HUET), and their physiological and behavioural responses before (first study) and after (second study) the stressor were compared to ten non-stressed controls. The results of both experiments showed that working memory performance was preserved during anticipation of an acute stressor, but impairments were observed immediately after stress exposure. Participants reported significantly higher state anxiety levels during anticipation and following stress exposure, whereas significant elevations in cortisol levels were only observed 25 min post exposure to stress, but not before or immediately after stress exposure. The results of both experiments demonstrated a dissociation between behavioural and biochemical measures and provided evidence for a dissociation of the effects of stress on cognitive and physiological measures depending on the time of testing, with cognitive impairments most evident following stress exposure.     

Aggression and heat: mediating effects of prior provocation and exposure to an aggressive model.

Sixty-four undergraduate males participated in an experiment designed to examine the effects of level of prior anger arousal, exposure to an aggressive model, and ambient temperature on physical aggression. On the basis of Bandura's social learning theory of aggression, it was predicted that uncomfortably hot environmental conditions would be most effective in facilitating later aggression when subjects had both witnessed the actions of the model and been exposed to strong provocation from the victim, but least effective in this regard when they had neither witnessed the actions of the model nor been exposed to prior instigation. In contrast to these predictions, results indicated that high ambient temperatures facilitated aggression by nonangered subjects but actually inhibited such behavior by those who had previously been provoked.     

Adaptation to auditory motion in the horizontal plane: effect of prior exposure to motion on motion detectability.

Thresholds for auditory motion detectability were measured in a darkened anechoic chamber while subjects were adapted to horizontally moving sound sources of various velocities. All stimuli were 500-Hz lowpass noises presented at a level of 55 dBA. The threshold measure employed was the minimum audible movement angle (MAMA)--that is, the minimum angle a horizontally moving sound must traverse to be just discriminable from a stationary sound. In an adaptive, two-interval forced-choice procedure, trials occurred every 2-5 sec (Experiment 1) or every 10-12 sec (Experiment 2). Intertrial time was "filled" with exposure to the adaptor--a stimulus that repeatedly traversed the subject's front hemifield at ear level (distance: 1.7 m) at a constant velocity (-150 degrees/sec to +150 degrees/sec) during a run. Average MAMAs in the control condition, in which the adaptor was stationary (0 degrees/sec,) were 2.4 degrees (Experiment 1) and 3.0 degrees (Experiment 2). Three out of 4 subjects in each experiment showed significantly elevated MAMAs (by up to 60%), with some adaptors relative to the control condition. However, there were large intersubject differences in the shape of the MAMA versus adaptor velocity functions. This loss of sensitivity to motion that most subjects show after exposure to moving signals is probably one component underlying the auditory motion aftereffect (Grantham, 1989), in which judgments of the direction of moving sounds are biased in the direction opposite to that of a previously presented adaptor.     

Mug shot exposure prior to lineup identification: interference, transference, and commitment effects.

The effects of viewing mug shots on subsequent identification performance are as yet unclear. Two experiments used a live staged-crime paradigm to determine if interpolated eyewitness exposure to mug shots caused interference, unconscious transference, or commitment effects influencing subsequent lineup accuracy. Experiment 1 (N = 104) tested interference effects. Similar correct decision rates were obtained for the mug shot and no mug shot groups from both perpetrator-present and absent lineups. Experiment 2 (N = 132) tested for commitment and transference effects. Results showed that the commitment group made significantly more incorrect identifications than either the control or the transference group, which had similar false-identification rates. Commitment effects present a serious threat to identification accuracy from lineups following mug shot searches.     

Empathetic perception of emotional displays in films as a function of hedonic and excitatory state prior to exposure

A film clip depicting a young couple in a dysphoric encounter was seen following one of four film segments that were selected and pretested to effect a factorial variation in (a) hedonic tone (positive, negative) and (b) excitatory potential (low, high). Reactions to the subsequent film were assessed via ratings to test predictions from excitation-transfer theory and to determine sequential effects in hedonically valued experiences. In a first experiment, in which the subsequent film was viewed immediately after the antecedent film, a nearly significant distraction effect of excitation occurred, that is, affective responses to the subsequent film were less intense following high-excitation films than following low-excitation films. In a second experiment, in which the procedure employed in the interval between films was changed to foster close attention to the subsequent film, an excitation-transfer effect was observed, with the dysphoric encounter being perceived as sadder after high-excitation films than after low-excitation films. In both experiments, hedonic-set effects were also observed. The role of cognitive adjustment in excitation transfer was discussed.