Acute stress disrupts risk assessment behavior in mice

Impact of the Sound of Magnetic Resonance Imaging Pulse Sequences in Awake Mice

Magnetic resonance imaging (MRI) is a research field of high interest as the implementation of new imaging modalities can significantly improve clinical diagnosis of several human pathologies. Awake nonhuman animals in the laboratory are being used in MRI pre-clinical systems for the validation of new imaging techniques, but animal welfare concerns emerge as MRI pulse sequences produce extremely loud sounds, up to 120 dB. Consequently, it is unclear how stressful these sounds are to the animals. Here, the impact of these sounds in the rodent behavior and physiology was evaluated. To achieve this, C57BL6/J mice were divided into two groups: a group exposed to sounds of typical pulse sequences used in imaging and a control group that was not exposed to those sounds. Mice have been tested in the open field and elevated plus maze to monitor baseline behavior and a hormonal stress biomarker was assayed to assess acute stress. The results indicate that the pulse sequences used in MRI are transient stressors that overall do not impact the behavioral status of the animals.

Acute stress differentially affects grooming subtypes and ultrasonic vocalisations in the open-field and home-cage test in rats

Grooming behaviour in rodents has been associated with emotional distress, especially in unfamiliar and aversive contexts. However, the biological function of grooming in such situations is still unclear. We hypothesised that particular grooming subtypes are differentially associated with the stress response. Here, we investigated the effects of an acute stress exposure on grooming and ultrasonic vocalisations (USVs) assessed on different testing contexts varying in the level of familiarity. To this aim, footshocked and non-footshocked rats were tested for 20 min on one of the following conditions: an unfamiliar open-field test, a familiar open-field test, and an individual home cage filled with bedding. We found that footshock stress slightly decreased complex grooming sequences while increased cephalic grooming. Stress induced a negative affective state inferred from an increase and decrease of 22-kHz and 50-kHz calls, respectively. The latter USVs correlated positively with the complex grooming subtypes. Altogether, a detailed analysis of grooming seems necessary for elucidating its diverse biological functions. Nevertheless, footshock stress and testing conditions produced weaker-than-expected effects, possibly because the time elapsed between footshocks and behavioural testing was too short for eliciting a full stress response, and because the simple footshock-chamber experience may have impeded detecting stronger effects of familiarity.

First experimental evidence for olfactory species discrimination in two nocturnal primate species (Microcebus lehilahytsara and M. murinus)

Olfactory communication is highly important for nocturnal mammals, especially for solitary foragers, but knowledge is still limited for nocturnal primates. Mouse lemurs (Microcebus spp.) are nocturnal solitary foragers with a dispersed lifestyle and frequently use chemo-sensory signalling behaviour for governing social interactions. Different mouse lemur species can co-occur in a given forest but it is unknown whether olfaction is involved in species recognition. We first screened 24 captive mouse lemurs (9 M. murinus, 15 M. lehilahytsara) for their olfactory learning potential in an experimental arena and then tested the species discrimination ability with urine odour in an operant conditioning paradigm in four individuals. The majority of the screened animals (75%) did not pass the screening criteria within a 2-week test period. However, all four final test animals, two M. murinus and two M. lehilahytsara, were successfully trained in a 5-step-conditioning process to reliably discriminate conspecific from heterospecific urine odour (requiring an overall median of 293 trials). Findings complement previous studies on the role of acoustic signalling and suggest that olfaction may be an important additional mechanism for species discrimination.

Acute stress worsens the deficits in appetitive behaviors for social and sexual stimuli displayed by rats after long-term withdrawal from morphine

RATIONALE

Negative affective states, e.g., anhedonia, are suggested to be involved in the long-lasting motivational processes associated with relapse. Here, we investigated whether anhedonic behaviors could be elicited by an acute stress after protracted abstinence from morphine.

OBJECTIVES

The behavioral responses to natural stimuli following exposure to an acute stress were examined after 14 days of withdrawal from morphine. Male rats were pretreated with either a binge-like morphine regimen or daily saline injections for 5 days. The motivation for two natural stimuli, i.e., a social stimulus (male rat) and a sexual stimulus (estrous female rat), was measured, following exposure to an acute stress (intermittent foot shock, 0.5 mA * 0.5 s * 10 min; mean inter-shock interval 40 s), under three conditions: free approach and effort- and conflict-based approaches.

RESULTS

Foot-shock-induced stress did not influence free-approach behavior (sniffing time) towards the social or sexual stimulus. However, in the effort-based approach task, the stressed morphine-withdrawn rats demonstrated an attenuated motivation to climb over a partition to approach the social stimulus while the stressed saline-pretreated rats showed an increased motivation to approach the social stimulus. When an aversive stimulus (pins) was introduced in order to induce an approach-avoidance conflict, both drug-withdrawn and drug-naïve groups exhibited a bimodal distribution of approach behavior towards the sexual stimulus after the stress was introduced, i.e., the majority of rats had low risky appetitive behaviors but a minority of them showed rather highly "risky" approach behavior.

CONCLUSIONS

The acute stress induces differential motivational deficits for social and sexual rewards in protracted drug-abstinent rats.

Acute stress in adulthood impoverishes social choices and triggers aggressiveness in preclinical models

Adult C57BL/6J mice are known to exhibit high level of social flexibility while mice lacking the β2 subunit of nicotinic receptors (β2(-/-) mice) present social rigidity. We asked ourselves what would be the consequences of a restraint acute stress (45 min) on social interactions in adult mice of both genotypes, hence the contribution of neuronal nicotinic receptors in this process. We therefore dissected social interaction complexity of stressed and not stressed dyads of mice in a social interaction task. We also measured plasma corticosterone levels in our experimental conditions. We showed that a single stress exposure occurring in adulthood reduced and disorganized social interaction complexity in both C57BL/6J and β2(-/-) mice. These stress-induced maladaptive social interactions involved alteration of distinct social categories and strategies in both genotypes, suggesting a dissociable impact of stress depending on the functioning of the cholinergic nicotinic system. In both genotypes, social behaviors under stress were coupled to aggressive reactions with no plasma corticosterone changes. Thus, aggressiveness appeared a general response independent of nicotinic function. We demonstrate here that a single stress exposure occurring in adulthood is sufficient to impoverish social interactions: stress impaired social flexibility in C57BL/6J mice whereas it reinforced β2(-/-) mice behavioral rigidity.

Chronic mild stress-induced changes of risk assessment behaviors in mice are prevented by chronic treatment with fluoxetine but not diazepam

As an important part of risk-related defensive behavior and central element of anxiety, risk assessment in rodents is particularly sensitive to psychosocial stress and may consequently influence the following decision-making and behavioral output. In this study, using a mouse-test battery, we evaluated the possible impacts of chronic mild stress (CMS) on risk assessment behaviors and action selections. For non-stressed control animals, a close relationship between risk assessment and choice behavior was observed in EPM and LDT. For stressed animals, however, 5 weeks of CMS exposure not only increased risk assessment behaviors, but also abolished the correlations between risk assessment and action selection. Pharmacological intervention with GABA-A receptor modulator diazepam (0.25-4 mg/kg) blocked the alterations of conventional spatiotemporal behaviors in response to CMS, but had no effect on the CMS-induced risk assessment behavioral changes. In contrast, 4-weeks of chronic treatment with fluoxetine (4-20mg/kg), a selective serotonin reuptake inhibitor, not only ameliorated the CMS-affected risk-assessment behaviors, but also restored the CMS-impaired correlations between risk assessment and decision making-related action selection. The present findings may shed new light on the better understanding of emotional reactivity and decision making under stressful situations. These results also indicate a differential pharmacological sensitivity in CMS-affected emotional response and risk-assessment behaviors.

Inheritable effect of unpredictable maternal separation on behavioral responses in mice

The long-term impact of early stress on behavior and emotions is well documented in humans, and can be modeled in experimental animals. In mice, maternal separation during early postnatal development induces poor and disorganized maternal care, and results in behavioral deficits that persist through adulthood. Here, we examined the long-term effect of unpredictable maternal separation combined with maternal stress on behavior and its transmissibility. We report that unpredictable maternal separation from birth to postnatal day 14 in C57Bl/6J mice has mild behavioral effects in the animals when adult, but that its combination with maternal stress exacerbates this effect. Further, the behavioral deficits are transmitted to the following generation through females, an effect that is independent of maternal care and is not affected by cross-fostering. The combined manipulation does not alter basic components of the hypothalamic-pituitary-adrenal axis but decreases the expression of the corticotropin releasing factor receptor 2 (CRFR2) in several nuclei of the amygdala and the hypothalamus in the brain of maternal-separated females. These results suggest a non-genomic mode of transmission of the impact of early stress in mice.

Comparison of SHR, WKY and Wistar rats in different behavioural animal models: effect of dopamine D1 and alpha2 agonists

Spontaneously hypertensive rats (SHR) and its counterpart, the Wistar-Kyoto rats (WKY), are probably the most often used animal model of ADHD. However, SHR as model of ADHD have also been criticised partly because of not differing to outbred rat strains. In the present study, adolescent SHR, WKY and Wistar rats from Charles River were tested in open-field, elevated plus maze and novel object recognition and on gastrointestinal transport to more intensively evaluate the strain characteristics. Non-habituated SHR and Wistar rats were more active than WKY rats but contrary to Wistar rats SHR stay hyperactive in a familiar environment. SHR were more sensitive to the alpha2-adrenoceptor agonist guanfacine and the dopamine D1 agonist A-68930 than WKY and Wistar rats, whereas amphetamine, the D1/D5 agonist ABT431 and the D2 agonist quinpirole, similarly affected open-field activity in all strains. In the elevated plus maze, SHR and Wistar rats showed less anxiety-related behaviour than WKY rats. Guanfacine and amphetamine induced an anxiolytic-like activity in SHR but not in WKY and Wistar rats. SHR showed the highest long-term memory in the novel object recognition. Gastrointestinal transport was similar and comparably affected by guanfacine in all rat strains. The present study shows clear differences in the behaviour of SHR and Wistar rats but also of WKY and Wistar rats. The use of SHR as animal model of ADHD is supported.

The relationship between anxiety and sleep-wake behavior after stressor exposure in the rat

Disturbed sleep is a common subjective complaint among individuals diagnosed with anxiety disorders. In rodents, sleep is often recorded after exposure to various foot-shock paradigms designed to induce an anxiety state. Although differences in sleep-wake architecture are noted, the relationship to specific level of anxiety is often assumed or absent. Utilizing the elevated plus-maze (EPM) after exposure to escapable shock (ES), inescapable shock (IS) or fear conditioning (FC), resulting differences in sleep architecture were compared to an objective measure of anxiety. Male Wistar rats were implanted with EEG, EMG and hippocampal theta electrodes to record sleep-wake behavior. After recovery and recording of baseline sleep, rats were exposed to one of five manipulations: ES, IS, FC or control (CES or CIS; utilizing either chamber with no shock exposure). Shortly after experimental manipulation, the EPM was employed to quantify traditional and ethological measures of anxiety and polygraphic signs of sleep-wake behavior were recorded continuously for 6 h. Although no significance was observed in EPM measurements across groups, profound differences in sleep architecture were present. Individual correlation analysis revealed no differences in anxiety level and total percentage of time spent in sleep-wake states. These results indicate that differences in sleep architecture after foot-shock exposure may not be simply due to increased anxiety. Rather, individual anxiety may be exacerbated by disrupted sleep. To fully understand the relationship between anxiety and sleep-wake behavior, a more objective analysis of anxiety after stressor exposure is mandated.

Modelling facets of mania--new directions related to the notion of endophenotypes

The lack of appropriate animal models is a major limitation in research of bipolar disorder (BPD): at this time there are very few models for this devastating disease. Whereas limited attempts have been made to develop comprehensive models for BPD, the new notion of endophenotypes encourages us to explore the possibility of developing separate models for separate facets of the disorder. Since more models are available for depression, there is a dire need for models for mania that will be relatively easy and simple to induce and test and will therefore be practical for purposes of screening possible new drugs or mutant mice that are developed based on novel molecular theories. Such models may already be tentatively available as they were developed in the context of other disorders, but there is a need to validate them for mania. The present paper proposes such models for most of the facets of mania including: increased energy, activity or restlessness; extreme irritability; reduced sleep; provocative, intrusive or aggressive behaviour; increased sexual drive; abuse of drugs; distractibility, reduced ability to concentrate; and unrealistic beliefs in one's abilities and powers resulting in poor judgement. Validating these models may demand a major research effort but it may be worthy as validated models for the different facets of mania could then be used efficiently and may be utilized to construct a standard battery of tests that can serve to explore the various components of manic-like behaviour in rodents.

Establishment of a battery of simple models for facets of bipolar disorder: a practical approach to achieve increased validity, better screening and possible insights into endophenotypes of disease

The lack of appropriate animal models for bipolar disorder (BPD) hinders the translation of novel molecular and genetic findings into the development of new more efficient treatments. Attempts to develop a comprehensive model for BPD did not result in a practical and valid model and at present most studies utilize a limited number of models for specific components of the disorder. Whereas there is a higher availability of models for the depression pole of BPD, only a few models represent the manic pole with the most frequently used being psychostimulant-induced hyperactivity. This last model had been important in studies of the disease and has some validity but it is clear that by itself cannot be considered to represent mania. Additional models for facets of BPD are needed to allow better screening of new drugs and new mutant mice. Such models may also support the exploration of endophenotypes of BPD and the mechanisms of the disease. An advantage of a battery approach is that each model can be only partially valid when used alone but the combination of a few models may result in strong validity. The present study suggests that such a battery can be based on existing models previously developed in the context of studying normal behavior or other disorders after an initial validation in the context of BPD. An example for this idea is described using the resident-intruder test for aggression. Present results show that 3 weeks oral treatment with 1.2-2.4% lithium (increasing doses), or 20 g/kg daily dose of valproate, significantly reduced aggressive behavior in resident mice without affecting non-aggressive social interactions. Accordingly, it is suggested that the simplified resident-intruder paradigm may model the aggression related to mania as part of a test battery for facets of BPD. It is further speculated that, pending further research, this paradigm can be combined with additional methods to explore changes in the LHPA axis that may be linked to an important endophenotype of BPD.

Anxiety-Like Behavior in Mice in Two Apparatuses During Withdrawal From Chronic Ethanol Vapor Inhalation

BACKGROUND

Anxiety during ethanol withdrawal may be a factor in relapse to alcohol abuse and dependence. Animal models of ethanol withdrawal have typically used forced consumption of an ethanol-containing liquid diet to induce dependence. Ethanol vapor inhalation offers an advantage over liquid diet consumption in that the onset of withdrawal can be temporally controlled more precisely, allowing studies of the development of withdrawal symptoms.

METHODS

The purpose of the current study was to induce ethanol dependence in mice using an inhalation procedure and to assess withdrawal anxiety symptoms behaviorally in the elevated zero maze and in the light/dark box. Male and female mice were exposed to 3 days of ethanol vapors. Anxiety-like behavior was measured on the elevated zero maze and light/dark box at multiple time points during withdrawal.

RESULTS

Mice experiencing ethanol withdrawal demonstrated increased anxiety-like behaviors relative to control animals in both apparatuses. However, this finding was specific to the procedure used with the elevated zero maze and was strongly influenced by sex in the light/dark box.

CONCLUSIONS

Ethanol vapor inhalation appears to be a valid tool for the study of withdrawal-induced anxiety.

The Suok ("ropewalking") murine test of anxiety

In the present study, we suggest that long elevated horizontal rod (Suok test, ST) and its light-dark modification (LDST) may be used for behavioral characterization in mice, including simultaneous assessment of their anxiety, activity, and neurological phenotypes. To establish the ST and the LDST as murine models of anxiety, we used several different mouse strains which differ markedly in their anxiety and activity (C57BL/6, 129S1/SvImJ, NMRI, and BALB/c). Here we show that our tests are able to ethologically discriminate between high and low anxiety mouse strains, as assessed by horizontal and directed exploration, stops, and defecation boli. The spatial distribution of the LDST behaviors is also sensitive to these strain-specific anxiety phenotypes, showing clear avoidance of the brightly lit part of the test in stressed (rat exposed) vs. control NMRI mice. In addition, we validated the ST in 129S1/SvImJ and BALB/c mice by assessing the behavioral consequences of acute stress such as rat exposure. Finally, we showed that our test is able to detect high anxiety and poorer motor coordination in 129S1/SvImJ (vs. C57BL/6) mice. The results of our study show that the ST emerges as an experimental tool to analyze anxiety, motor-vestibular anomalies, as well as anxiety-induced motor impairments in mice. Overall, we suggest that the ST can be a useful protocol in neurobehavioral stress research including modeling stress-evoked states, pharmacological screening of potential anti-stress drugs, or behavioral phenotyping of genetically modified animals.

Measuring emotional processes in animals: the utility of a cognitive approach

Contemporary researchers regard emotional states as multifaceted, comprising physiological, behavioural, cognitive and subjective components. Subjective, conscious experience of emotion can be inferred from linguistic report in humans, but is inaccessible to direct measurement in non-human animals. However, measurement of other components of emotion is possible, and a variety of methods exist for monitoring emotional processes in animals by measuring behavioural and physiological changes. These are important tools, but they have limitations including difficulties of interpretation and the likelihood that many may be sensitive indicators of emotional arousal but not valence-pleasantness/unpleasantness. Cognitive components of emotion are a largely unexplored source of information about animal emotions, despite the fact that cognition-emotion links have been extensively researched in human cognitive science indicating that cognitive processes-appraisals of stimuli, events and situations-play an important role in the generation of emotional states, and that emotional states influence cognitive functioning by inducing attentional, memory and judgement biases. Building on this research, it is possible to design non-linguistic cognitive measures of animal emotion that may be especially informative in offering new methods for assessing emotional valence (positive as well as negative), discriminating same-valenced emotion of different types, identifying phenotypes with a cognitive predisposition to develop affective disorders, and perhaps shedding light on the issue of conscious emotional experiences in animals.

Differential effects of infralimbic vs. ventromedial orbital PFC lidocaine infusions in CD-1 mice on defensive responding in the mouse defense test battery and rat exposure test

The ventromedial prefrontal cortex (vmPFC) is extremely sensitive to a variety of stressful situations and threatening events, and has been suggested to be an associative cortical brain system processing the integration of anxiety-related cognitive, affective and motivated behavior in rodents, primates and humans. In addition, recent evidence suggests that (a) anxiety-related affective processing appears to be lateralized to the right hemisphere vmPFC; and (b) there appears to be functional heterogeneity within the rodent vmPFC. The present study evaluated the possibility that distinct sub-areas of the right hemisphere ventral PFC might differentially influence anxiety-like defensive responding in two different predator stress situations following transient inactivation of the ventromedial orbital (vMO) or infralimbic (IL) vmPFC in CD-1 mice. In week 1, IL vmPFC lidocaine infusions reduced anxiety-like defensive responding in mice (enhanced approach and contact) confronted with a hand-held anesthetized rat stimulus in the mouse defense test battery (vMO inactivation exerted minimal effects). In week 2, vMO lidocaine infusions enhanced anxiety-like defensive responding (enhanced avoidance and protected risk assessment) toward a barricaded live rat in the rat exposure test (IL inactivation exerted minimal effects). Although it is unclear whether week 1 mouse defense test battery testing influenced week 2 rat exposure test results, these preliminary data suggest functional differences within the mouse right hemisphere ventral PFC related to cautious evaluation of predator threat. Given the dense unilateral reciprocal connectivity between the IL and vMO subregions of the PFC, both associative ventromedial cortical areas may exert complimentary yet dissociable roles in the processing of threat stimuli. This suggests that while the IL vmPFC may mediate cautious evaluation of threat situations (risk assessment), the vMO PFC may inhibit prepotent avoidance responses to facilitate such IL-mediated adaptive behavioral responses.

Deletion of the 5-HT3 receptor differentially affects behavior of males and females in the Porsolt forced swim and defensive withdrawal tests

The central serotonin (5-HT) system is important in regulating behaviors associated with anxiety and depression. While a fair amount is known about the role of 5-HT1 and 5-HT2 receptor subtypes in regulating these behaviors, much less is known about the involvement of the 5-HT3 receptor, especially with regards to its role in sex differences in behavior. Our goal in the present studies was to examine whether deletion of the 5-HT3 receptor produces different effects in adult male and female mice on performance in three behavioral tests. We examined behavior of male and female mice lacking the 5-HT3 receptor (knock-out or KO) and their wild-type (WT) littermates in the Porsolt forced swim test because of its importance in reliably detecting anti-depressant efficacy. In addition, we examined behavior in the defensive withdrawal test and repeated exposure to an open field because behavior in these two tests provides measures of anxiety. In the Porsolt swim test, sex differences were eliminated by deletion of the 5-HT3 receptor while deletion had no effect in the habituation of locomotor activity to repeated exposure to an open field. In the defensive withdrawal test, deletion of the 5-HT3 receptor had more complex effects though these effects tended to be in the opposite direction in males and females. Together these results suggest that the 5-HT3 receptor regulates behavior-related to depression and anxiety differently in males and females. Whether these effects are due to the interaction of 5-HT3 receptor with gonadal hormones requires further examination.

Anxiety as a predictor of alcohol preference in rats?

Many clinical studies based on retrospective self-reports indicate a relationship between anxiety and increased alcohol consumption or relapse in individuals with alcohol abuse or dependence. However, by these retrospective studies it cannot be definitely concluded whether the alcohol abuse or the anxiety was first. In the present study, alcohol-consuming behaviour was determined in three rat strains showing different anxiety-related behaviour but being not genetically selected for high or low alcohol consumption. The innate anxiety of the three rat strains (Harlan-Fischer, Wistar-BgVV and Wistar-Harlan) was measured by the elevated plus maze test. Thereafter voluntary ethanol intake was measured for 3 months followed by a progressive ratio paradigm, in which the number of responses required to obtain alcohol was successively increased during session. The point at which rats ceased to respond (breaking point) was taken as a measure of their motivation to obtain ethanol. The study revealed that Harlan-Fischer rats showing most anxiety-related behaviour in the elevated plus maze test displayed the lowest ethanol intake [g/kg/d b.w.] and the lowest breaking points in the progressive ratio paradigm. The Wistar-Harlan rats with least anxiety-related behaviour and the Wistar-BgVV rats with medium anxiety-related behaviour drank more alcohol and showed higher breaking points than the Harlan-Fischer rats. Thus, in the present study, a distinct relationship between innate anxiety and alcohol-consuming behaviour in rat strains not genetically selected for high and low ethanol intake could not be shown.

Infralimbic D2 receptor influences on anxiety-like behavior and active memory/attention in CD-1 mice

Ventromedial prefrontal cortical (vmPFC) dopamine (DA) influences attentional aspects of cognition and anxiety-like behavioral responding in rodents. The present study investigated the role of D2 receptors on spontaneous alternation in the Y-maze and anxiety-like behavior in a two-trial elevated plus-maze (EPM) procedure in CD-1 mice following vmPFC infusions of the D2 antagonist, sulpiride, and the D2 agonist, quinpirole. Pretrial 1 quinpirole infusions did not influence any anxiety measure (with the exception that the lowest dose increased protected stretch attends), but reduced protected exploration activity (closed-arm entry/time ratios and wall rearing). In Trial 2 24 h later (no injection), quinpirole exerted an anxiolytic behavioral profile relative to Trial 2 control mice (enhanced open-arm entry/time ratios, unprotected head dips), with no effects on protected exploration or risk assessment activity. Pretrial 1 sulpiride infusions enhanced unprotected exploration (open-arm entry/time ratios, unprotected stretch attend, and head dips), but did not influence protected exploration or risk assessment in the EPM. In Trial 2, 24 h later (no injection), sulpiride extended this anxiolytic profile to reduced protected exploration and risk assessment activity (closed-time ratio, protected stretch attend, and head dips). In the Y-maze, whereas quinpirole disrupted alternation performance (5- and 10-nmol dose) concomitant with marked repetitive same-arm returns (SAR) at the highest dose, sulpiride disrupted alternation performance concomitant with marked repetitive SAR behavior at the lowest dose only. These data indicate that although infralimbic (IL) quinpirole and sulpiride infusions similarly disrupted alternation performance in the Y-maze and reduced Trial 2 anxiety-like responding in the EPM, these drugs differentially produced these effects.

Neurochemical and behavioral alterations elicited by a chronic intermittent stressor regimen: implications for allostatic load

Although stressors induce a series of adaptive neurochemical changes, sustained physiological activation associated with protracted stressor exposure may engender adverse effects (allostatic load). In the present investigation CD-1 mice exposed to a series of different stressors, twice a day over 54 days, exhibited increased signs of depression and anxiety, including increased passivity in a forced swim test, reduced aggression in a social interaction test, and delayed approach to food in a novel environment. Consistent with the view that a chronic stressor regimen affects immune-related processes, sickness behavior elicited by the proinflammatory cytokine, interleukin-1beta, was augmented in response to a chronic but not an acute stressor. Relative to nonstressed mice, median eminence serotonin was augmented by the cytokine treatment administered 24 h after chronic stressor exposure. Treatment with IL-1beta diminished plasma growth hormone levels and increased circulating corticosterone levels irrespective of the animals stressor history. It is suggested that chronic stressor exposure may instigate relatively protracted neurochemical effects, thereby influencing the behavioral responses to later psychological and systemic challenges.

Information processing of an acquaintance rape scenario among high- and low-dissociating college women

To assess the impact of dissociation on information processing, 66 college women with high and low levels of trait dissociation were studied with regard to how they unitized videotape segments of an acquaintance rape scenario (actual assault not shown) and a nonthreatening control scenario. Unitization is a paradigm that measures how actively people process stimuli by recording how many times they press a button to indicate that they have seen a significant or meaningful event. Trait dissociation was negatively correlated with participants' unitization of the acquaintance rape videotape, unitization was positively correlated with danger cue identification, and state dissociation was negatively correlated with dangerousness ratings.

Social status in mice: behavioral, endocrine and immune changes are context dependent

The aim of the present study was to investigate the effect of social status on the endocrine, immune and behavior response of male mice. We found that in mice reared in a group of siblings since weaning, no difference exists between dominants and subordinates in basal corticosterone level, in behavior in the open-field test (OFT) and in a series of immune parameters. These results suggest that living with siblings is not a stressful condition for either dominant or subordinate mice. Therefore, group-housed siblings can be regarded as a valid control group in social stress studies. When mice were subjected to chronic psychosocial stress for 21 days, four types of social outcome occurred: residents becoming dominants, intruders becoming subordinates, residents becoming subordinates and intruders becoming dominants. Interestingly, the behavioral profile in the OFT revealed a status-dependent effect, with resident dominants (RD) and intruder dominants (InD) showing the highest locomotor and exploratory activity, whereas the corticosterone level was higher than control for all four categories. In addition, a context-dependent effect emerged at the immune level: resident subordinates (RS) had a reduced splenocyte proliferation and IL-4 and IL-10 production. Mice in all the other three social ranks showed no immune alterations. Therefore, the loss of an individual's social rank position seems a promising field of study to investigate the psychological impact of stressful events.

The effects of restraint on ventilatory responses to hypercapnia and hypoxia in adult mice

The aim of this experiment was to determine whether ventilatory measurements in adult restrained mice provide a valid assessment of chemosensitivity. We used whole-body plethysmography to compare breathing patterns in eight restrained and eight unrestrained outbred Swiss mice during air breathing, hypercapnia, and hypoxia. The mice in the restrained group were each placed in a loosely restraining wire-mesh cage. The unrestrained mice could move freely inside the plethysmograph. All the mice received three hypercapnic stimuli (8.5% CO2) and three hypoxic isocapnic stimuli (10% O2, 3.5% CO2). As compared to unrestrained mice, restrained mice had significantly lower breath durations (TT, 445+/-110 ms vs. 323+/-32 ms) and higher ventilation (VE) levels (15.7+/-2.6 microl/(sec x g) vs. 22.2+/-4.5 microl/(sec x g)), whereas no difference was observed for tidal volume (VT). The increases in frequency and ventilation from baseline to hypercapnia were not significantly different in restrained and unrestrained mice. The VE response to hypoxia was marginally higher in restrained mice. We conclude that chemosensitivity to hypercapnia, and to a lesser extent to hypoxia, can be measured in restrained adult mice, but that the baseline breathing pattern cannot.

Blockade of effect of stress on risk assessment behavior in mice by a beta-1 adrenoceptor antagonist

Previous studies have shown that acute stress impairs risk assessment behavior in mice. The present study was undertaken to determine the role of beta adrenoceptors, which are known to be stimulated by stress, in this effect. Mice were treated with either a beta-1 antagonist, betaxolol, a beta-2 antagonist, ICI 118551, an alpha-1 antagonist, prazosin, or an alpha-2 antagonist, yohimbine, and 30 min later were subjected to a 1-h session of restraint stress. Thirty minutes after the stress the animals were tested for the entry latency, number of headpokes prior to entry, and the path of entry into a white open field from a small dark box. In agreement with previous findings, stress was found to markedly reduce risk assessment behaviors as reflected by a reduced entry latency, a reduced number of headpokes and a changed entry path from wall hugging to central entry. Betaxolol was found to prevent all of the above effects of stress dose dependently, whereas ICI 118551, prazosin, and yohimbine had no reversal effects. It is concluded that beta-1 receptor activation and possibly brain glycogen depletion is involved in the effects of stress on risk assessment behavior.