Long-lasting stress sensitisation

Activation of NOS-cGMP pathways promotes stress-induced sensitization of behavioral responses in zebrafish

Nitric oxide (NO) is a molecule involved in plasticity across levels and systems. The role of NOergic pathways in stress-induced sensitization (SIS) of behavioral responses, in which a particular stressor triggers a state of hyper-responsiveness to other stressors after an incubation period, was assessed in adult zebrafish. In this model, adult zebrafish acutely exposed to a fear-inducing conspecific alarm substance (CAS) and left undisturbed for an incubation period show increased anxiety-like behavior 24 h after exposure. CAS increased forebrain glutamate immediately after stress and 30 min after stress, an effect that was accompanied by increased nitrite levels immediately after stress, 30 min after stress, 90 min after stress, and 24 h after stress. CAS also increased nitrite levels in the head kidney, where cortisol is produced in zebrafish. CAS-elicited nitrite responses in the forebrain 90 min (but not 30 min) after stress were prevented by a NOS-2 blocker. Blocking NOS-1 30 min after stress prevents SIS; blocking NOS-2 90 min after stress also prevents stress-induced sensitization, as does blocking calcium-activated potassium channels in this latter time window. Stress-induced sensitization is also prevented by blocking guanylate cyclase activation in both time windows, and cGMP-dependent channel activation in the second time window. These results suggest that different NO-related pathways converge at different time windows of the incubation period to induce stress-induced sensitization.

Effects of oral administration of ondansetron, a 5-HT3 receptor antagonist, on anxiety-related behaviors and colonic hypercontractility in repeated stress-induced mice

PURPOSE

Chronic psychological stress develops and exacerbates irritable bowel syndrome (IBS). 5-hydroxytryptamine (5-HT) via activation of intestinal 5-HT3 receptors involves impairment of intestinal functions. This study aimed to investigate the effects of ondansetron, a 5-HT3 receptor antagonist, on locomotor activity, anxiety-related behaviors, and colonic functions in repeated water avoidance stress.

MATERIALS AND METHODS

Food intake and fecal pellet output (FPO) of sham stress (SS), water avoidance stress (WS), and water avoidance stress with oral administration of ondansetron (1 mg/kg BW) (WA) groups were monitored along the water avoidance stress protocol for 10 consecutive days. On day 11, locomotor activity and anxiety-related behaviors were determined using an open field test. Contractile properties of colonic tissues in response to KCl and a cumulative dose of carbachol (CCh) were determined using in vitro organ bath technique.

RESULTS

FPO was significantly increased in the WS group after 7 days of water avoidance stress, which was reversed in WA group. WS group decreased unsupported rearing behavior compared to WS group, which was not altered in the WA group. The colon of the WS group had a higher tonic contraction in response to CCh than the SS and WA groups, which was reversed with ondansetron pre-incubation.

CONCLUSIONS

Oral administration of ondansetron prevented increased FPO but did not affect anxiety-related behavior in repeated stress model. Colonic hypercontractility in the stressed mice was related to increased responses to cholinergic-induced contractions, which involved 5-HT3 receptors. Our findings suggest the modulatory roles of 5-HT3 receptors to mediate stress-induced colonic dysfunction.

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

Auditory deviance detection and involuntary attention allocation in occupational burnout-A follow-up study

Here, we investigated the central auditory processing and attentional control associated with both recovery and prolongation of occupational burnout. We recorded the event-related brain potentials N1, P2, mismatch negativity (MMN) and P3a to nine changes in speech sounds and to three rarely presented emotional (happy, angry and sad) utterances from individuals with burnout (N = 16) and their matched controls (N = 12). After the 5 years follow-up, one control had acquired burnout, half (N = 8) of the burnout group had recovered, and the other half (prolonged burnout) still had burnout. The processing of acoustical changes in speech sounds was mainly intact. Prolongation of the burnout was associated with a decrease in MMN amplitude and an increase in P3a amplitude for the happy stimulus. The results suggest that, in the absence of interventions, burnout is a persistent condition, associated with alterations of attentional control, that may be amplified with the prolongation of the condition.

Delineating the Psychic Structure of Substance Use and Addictions, from Neurobiology to Clinical Implications: Ten Years Later

The diagnosis of substance use disorder is currently based on the presence of specifically identified behavioral symptoms. In addition, other psychiatric signs and symptoms accompany addictive behavior, contributing to the full picture of patients’ psychopathologic profile. Historically, such symptoms were confined within the framework of “comorbidity”, as comorbid psychiatric disorders or personality traits. However, an alternative unitary view of the psychopathology of addiction, inclusive of related psychiatric symptoms, has been claimed, with the support of epidemiological, neurobiological, and neuropsychological evidence. In the present article, we highlight the research advancements that strengthen this unified perspective. We then give an account of our group’s definition of a specific SCL-90-based construct of the psychopathology of addiction. Lastly, we discuss the benefits that can be expected to be acquired in the evaluation and treatment of patients with a longitudinal approach including psychological/psychiatric predisposing features, addictive behavior, and psychiatric manifestations.

Endocannabinoid modulating drugs improve anxiety but not the expression of conditioned fear in a rodent model of post-traumatic stress disorder

The endocannabinoid (eCB) system is a potential target for the treatment of symptoms of post-traumatic stress disorder (PTSD). Similar to clinical PTSD, approximately 25-30% of rats that undergo cued fear conditioning exhibit impaired extinction learning. In addition to extinction-resistant fear, these "weak extinction" (WE) rats show persistent anxiety-like behaviors. The goal of the present study was to test the hypothesis that behavioural differences between WE animals and those presenting normal extinction patterns (strong extinction; SE) could be mediated by the eCB system. Rats undergoing fear conditioning/extinction and fear recall sessions were initially segregated in weak and strong-extinction groups. Two weeks later, animals underwent a fear recall session followed by a novelty-suppressed feeding (NSF) test. In acute experiments, WE rats were injected with either the fatty acid amide hydrolase (FAAH) inhibitor URB597 or the CB1 agonist WIN55,212-2 1 h prior to long-term recall and NSF testing. SE animals were injected with the inverse CB₁ receptor agonist AM251. In chronic experiments, WE and SE rats were given daily injections of URB597 or AM251 between short and long-term recall sessions. We found that acute administration of WIN55,212-2 but not URB597 reduced anxiety-like behaviour in WE rats. In contrast, AM251 was anxiogenic in SE animals. Neither treatment was effective in altering freezing expression during fear recall. The chronic administration of AM251 to SE or URB597 to WE did not alter fear or anxiety-like behaviour or changed the expression of FAAH and CB₁. Together, these results suggest that systemic manipulations of the eCB system may alter anxiety-like behaviour but not the behavioural expression of an extinction-resistant associative fear memory.

Antagonism of corticotropin releasing factor in the basolateral amygdala of resilient and vulnerable rats: Effects on fear-conditioned sleep, temperature and freezing

The basolateral nucleus of the amygdala (BLA) plays a significant role in mediating individual differences in the effects of fear memory on sleep. Here, we assessed the effects of antagonizing corticotropin releasing factor receptor 1 (CRFR1) after shock training (ST) on fear-conditioned behaviors and sleep. Outbred Wistar rats were surgically implanted with electrodes for recording EEG and EMG and with bilateral guide cannulae directed at BLA. Data loggers were placed intraperitoneally to record core body temperature. The CRFR1 antagonist, antalarmin (ANT; 4.82 mM) was microinjected into BLA after shock training (ST: 20 footshocks, 0.8 mA, 0.5 s duration, 60 s interstimulus interval), and the effects on sleep, freezing and the stress response (stress-induced hyperthermia, SIH) were examined after ST and fearful context re-exposure alone at 7 days (CTX1) and 21 days (CTX2) post-ST. EEG and EMG recordings were scored for non-rapid eye movement sleep (NREM), rapid eye movement sleep (REM) and wakefulness. The rats were separated into 4 groups: Vehicle-vulnerable (Veh-Vul; n = 10), Veh-resilient (Veh-Res; n = 11), ANT-vulnerable (ANT-Vul; n = 8) and ANT-resilient (ANT-Res; n = 8) based on whether, compared to baseline, the rats showed a decrease or no change/increase in REM during the first 4 h following ST. Post-ST ANT microinjected into BLA attenuated the fear-conditioned reduction in REM in ANT-Vul rats on CTX1, but did not significantly alter REM in ANT-Res rats. However, compared to Veh treated rats, REM was reduced in ANT treated rats on CTX2. There were no group differences in freezing or SIH across conditions. Therefore, CRFR1 in BLA plays a role in mediating individual differences in sleep responses to stress and in the extinction of fear conditioned changes in sleep.

Effect of lairage time, behaviour and gender on stress and meat quality parameters in pigs

The objective of this study was to determine the effects of lairage time (short vs. long), behavior (aggressive vs. non-aggressive) and gender (gilts, barrows and boars) on stress and meat quality parameters in pigs (n = 100). In the group with short lairage, aggressive behavior of gilts and boars was observed. At exsanguination, blood samples were collected and levels of blood lactate and plasma cortisol were determined. Post mortem pH value, temperature, drip loss, sensory and instrumental color and meat quality class were determined on the muscle Longissimus dorsi. Higher blood lactate concentration (P < 0.05) and skin blemish score (P <0.001), lower temperature (P < 0.05) and drip loss (P < 0.01), as well as darker, less red and yellow meat color (P < 0.001) were found after long lairage compared to short lairage. Gilts had higher plasma cortisol concentrations than barrows (P < 0.05), while barrows had lower skin blemish scores (P < 0.05) than gilts and boars after long lairage. The highest incidence of PSE (pale, soft and exudative) meat was observed in barrows (100.00%) and boars (91.67%) after short lairage, while the lowest incidence of PSE meat was found in barrows (28.89%) after long lairage. Aggressiveness affected meat temperature, as aggressive pigs had higher meat temperature (P < 0.05) than non-aggressive pigs.

Towards a better preclinical model of PTSD: characterizing animals with weak extinction, maladaptive stress responses and low plasma corticosterone

Most of the available preclinical models of PTSD have focused on isolated behavioural aspects and have not considered individual variations in response to stress. We employed behavioural criteria to identify and characterize a subpopulation of rats that present several features analogous to PTSD-like states after exposure to classical fear conditioning. Outbred Sprague-Dawley rats were segregated into weak- and strong-extinction groups on the basis of behavioural scores during extinction of conditioned fear responses. Animals were subsequently tested for anxiety-like behaviour in the open-field test (OFT), novelty suppressed feeding (NSF) and elevated plus maze (EPM). Baseline plasma corticosterone was measured prior to any behavioural manipulation. In a second experiment, rats underwent OFT, NSF and EPM prior to being subjected to fear conditioning to ascertain whether or not pre-stress levels of anxiety-like behaviours could predict extinction scores. We found that 25% of rats exhibit low extinction rates of conditioned fear, a feature that was associated with increased anxiety-like behaviour across multiple tests in comparison to rats showing strong extinction. In addition, weak-extinction animals showed low levels of corticosterone prior to fear conditioning, a variable that seemed to predict extinction recall scores. In a separate experiment, anxiety measures taken prior to fear conditioning were not predictive of a weak-extinction phenotype, suggesting that weak-extinction animals do not show detectable traits of anxiety in the absence of a stressful experience. These findings suggest that extinction impairment may be used to identify stress-vulnerable rats, thus providing a useful model for elucidating mechanisms and investigating potential treatments for PTSD.

Elevated dopamine D2 receptor in prefrontal cortex of CUMS rats is associated with downregulated cAMP-independent signaling pathway

Because depression is associated with significant morbidity and functional disability, it is important to reveal the mechanism of action. A variety of studies have suggested the involvement of dopaminergic receptors in the pathophysiological mechanism of non-stress-associated depression-like behavior in rodents. Nevertheless, controversy exists about whether chronic stress acts on dopaminergic receptors in the prefrontal cortex. Thus, we investigated the level of dopamine D2 receptors (DRD2) and the possible mechanisms involved in a chronic unpredictable mild stress (CUMS) rat model of depression. The results showed CUMS-induced, depression-like symptoms in the rat, characterized by reduced sucrose consumption and body mass, and increased duration of immobility in a forced swimming test. Moreover, chronic stress upregulated the expression of DRD2 but downregulated protein kinase A (PKA), transcription factor cAMP response element binding protein (CREB), and phospho-CREB (p-CREB) in the prefrontal cortex, as demonstrated by Western blot. Notably, in the rat model of depression, decreased cyclic adenine monophosphate (cAMP) levels and PKA activity were present at the same time, which is consistent with clinical findings in depressed patients. Our findings suggested that dopaminergic system dysfunction could play a central role in stress-related disorders such as depression.

Effect on Emotional Behavior and Stress by Inhalation of the Essential oil from Chamaecyparis obtusa

Various effects have been reported in the literature for the essential oil from Chamaecyparis obtusa (EOCO), such as antibacterial and antifungal activity. In this study, we examined the effect of EOCO on emotional behavior and stress-induced biomarkers. Male ICR mice, aged 5 weeks at the start of each experiment, were individually housed in cages for 1 week. After placing each mouse in a glass container and exposing it to EOCO for 90 min, we then investigated the influence on emotional behavior using the elevated-plus maze (EPM) test, which is one of the evaluation methods for anxiolytic-like behavior. Significant anxiolytic-like effects were observed for the 7.0 mg/L air EOCO ( P<0.05). After the EPM test, mice were dissected and changes in the stress-induced biomarkers within the brain were investigated by examining the amounts of fast nerve growth factor receptor (NGFR) and activity regulated cytoskeletal-associated protein (Arc) gene expression, and brain-derived neurotrophic factor (BDNF) and galactokinase 1 (GLK1) protein expression. Significant increases were observed in the amount of NGFR after inhalation of 7.0 mg/L air EOCO ( P<0.05). These results indicate that EOCO has both anxiolytic-like and stress mitigation effects.

Maternal prenatal stress in rats influences c-fos expression in the spinal cord of the offspring

Previous studies in humans have reported a link between maternal stress and disturbed infant physiological behavior. The objective of our study was to examine in experimental rats how maternal prenatal stress induced by a forced swim test affects offspring afferent spinal responses mediated by stimulation of vaginocervical receptors. The activation of spinal cord neurons showing c-fos expression was examined following vaginocervical mechanical stimulation in adult rats, which were the offspring of dams exposed to gestational stress from E10 until delivery. Vaginocervical stimulation of both prenatal-stressed and non-prenatal-stressed rats induced an increase in immunoreactive protein in the spinal cord ranging from T12 to S1 segmental levels. However, a significantly higher (40%) increase in the expression of Fos-immunoreactive neurons was observed in vaginocervical stimulated prenatally stressed rats than in non-stimulated prenatally stressed ones. This increase was higher in L5-S1 levels than in T12-L4. When the regional distribution was examined, results showed that up to 80% of activated neurons were located in the dorsal horn in both non-stimulated prenatally stressed and stimulated prenatally stressed groups, with a significantly higher density in the latter. Our results demonstrate that maternal prenatal stress can have consequences on vaginocervical responses conveyed to the spinal cord. The increase in Fos labeled neurons in T12-S1 in prenatally stressed rats induced by vaginocervical stimulation suggests the hypersensitivity of the genital tract associated with activation of spinal circuits spanning multiple segments.

Murine model of repeated exposures to conspecific trained aggressors simulates features of post-traumatic stress disorder

We evaluated repeated exposures of mice to a trained aggressor mouse as a model (adapted from "social stress" models of traumatic stress) for aspects of post-traumatic stress disorder (PTSD). Using a "cage-within-cage resident-intruder" protocol, subject C57BL/6J mice were exposed to aggressors for 6 h daily for 5 or 10 days. At one to three random times during each 6-h session, subjects were exposed directly to aggressor for 1 min or 10 bites, whichever came first. Behavioral, physiological, and histological changes associated with aggressor-exposure were assessed for up to 6 weeks. During aggressor exposure, subjects displayed less territorial behavior, gained weight, and increased body temperature. One day after the last aggressor exposure, inflammatory cardiac histopathologies were prevalent; after 10 days, only mild myocardial degeneration with fibrosis or fibroplasias was evident, while controls showed almost no cardiac abnormalities at any time. After 4 weeks, the medial prefrontal cortex of control mice showed increased dendritic spine density, but aggressor-exposed mice showed no increase. Behaviors affected by aggressor exposure were evaluated in a partition test wherein the subject mouse is separated from the aggressor by a fenestrated partition that permits sensory cues to pass but prevents direct physical interaction. For up to 4-6 weeks after the last aggressor exposure, subjects showed prolonged grooming, freezing, retarded locomotion and no tail rattling. PTSD and its co-morbidities are often consequent to repeated aggravated "social" assaults (e.g., combat) and manifest socially over time, suggesting the relevance of this repeated aggressor-exposure model to clinical aspects of PTSD.

Endocrine response and perceived stress test during an experimental challenge task in adult survivors of a childhood cancer

BACKGROUND

Although long-term implications of cancer in childhood or adolescence with regard to medical conditions are well documented, the impact on mental health and on response to stress, which may be an indicator of psychological vulnerability, is not yet well understood. In this study, psychological and physiological responses to stress were examined.

PROCEDURE

Fifty-three participants aged 18-39 years (n = 25 survivors of childhood or adolescence cancer, n = 28 controls) underwent an experimental stress test, the Trier Social Stress Test (TSST). Participants were asked to provide repeated evaluations of perceived stress on visual-analogical scales and blood samples were collected before and after the TSST to measure plasma cortisol.

RESULTS

The psychological perception of stress was not different between the two groups. However, the cancer survivors group showed a higher global plasma cortisol level as well as higher amplitude in the response to the TSST. The global cortisol level in cancer survivors was increased when depression symptoms were present. The subjective perception of stress and the plasma cortisol levels were only marginally correlated in both groups.

CONCLUSIONS

It is suggested that the exposure to a life-threatening experience in childhood/adolescence increases the endocrine response to stress, and that the presence of depressive symptoms is associated with an elevation of plasma cortisol levels. A better knowledge of these mechanisms is important given that the dysregulations of the stress responses may cause psychological vulnerability.

Effects of acute stress on acquisition of nicotine conditioned place preference in adolescent rats: a role for corticotropin-releasing factor 1 receptors

RATIONALE

Studies indicate that adolescence is a time of increased sensitivity to the rewarding effects of nicotine, and that stress is associated with an increased risk for smoking initiation in this age group. It is possible that stress leads to increased nicotine use in adolescence by augmenting its rewarding properties. Corticotropin-releasing factor type 1 receptors (CRF-R1) mediate physiological and behavioral stress responses. They may also mediate stress-induced potentiation of activity in multiple neural substrates implicated in nicotine reward.

OBJECTIVES

The aim of the present study was to determine the effect of acute stressor exposure on single trial nicotine conditioned place preference (CPP) in adolescent male rats using a biased CPP procedure and the role of CRF-R1 in this effect.

RESULTS

A single episode of intermittent footshock administered 24 h before the start of place conditioning dose-dependently facilitated acquisition of CPP to nicotine (0.2, 0.4, and 0.6 mg/kg). Pretreatment with CP-154,526 (20 mg/kg), a selective CRF-R1 antagonist, 30 min before footshock exposure significantly attenuated the effect of prior stress to facilitate nicotine CPP acquisition. CP-154,526 pretreatment had no effect in animals conditioned with a nicotine dose that produced CPP under non-stress conditions, suggesting a specific role for CRF-R1 following stress.

CONCLUSIONS

Taken together, the results suggest that during adolescence, nicotine reward is enhanced by recent stressor exposure in a manner that involves signaling at CRF-R1. Information from studies such as this may be used to inform efforts to prevent and treat adolescent nicotine dependence.

Repeated pre-exposure to tobacco smoke potentiates subsequent locomotor responses to nicotine and tobacco smoke but not amphetamine in adult rats

These studies investigated if pre-exposure to tobacco smoke affects the locomotor response to tobacco smoke, nicotine, and amphetamine in adult rats. The rats were habituated to an open field for 3-4 days and then exposed to tobacco smoke for 2h/day for 13-14 days. The effect of exposure to tobacco smoke on locomotor activity was investigated after 1, 7, and 14 days of smoke exposure and after one 2-hour exposure session that followed a 3-week off period. The effects of tobacco smoke on the locomotor responses to nicotine (0.04 and 0.4 mg/kg, base) and amphetamine (0.1 and 0.5mg/kg) were investigated on day 14, one day after the last smoke exposure session. The locomotor response to tobacco smoke was increased after 7 and 14 days of smoke exposure and after one exposure session after the 3-week off-period. The acute administration of the high dose of nicotine (0.4 mg/kg) led to a brief period of hypoactivity that was followed by a period of hyperactivity. Pre-exposure to tobacco smoke attenuated the nicotine-induced hypoactivity and potentiated the nicotine-induced hyperactivity. The low dose of nicotine (0.04 mg/kg) did not affect locomotor activity in the control rats but increased the total distance traveled in the tobacco smoke exposed rats. Exposure to tobacco smoke did not affect the locomotor response to amphetamine. These findings indicate that exposure to tobacco smoke leads to tolerance to the depressant effects of nicotine and potentiates the stimulant effects of nicotine and tobacco smoke.

Stress-induced enhancement of fear conditioning and sensitization facilitates extinction-resistant and habituation-resistant fear behaviors in a novel animal model of posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is characterized by stress-induced symptoms including exaggerated fear memories, hypervigilance and hyperarousal. However, we are unaware of an animal model that investigates these hallmarks of PTSD especially in relation to fear extinction and habituation. Therefore, to develop a valid animal model of PTSD, we exposed rats to different intensities of footshock stress to determine their effects on either auditory predator odor fear extinction or habituation of fear sensitization. In Experiment 1, rats were exposed to acute footshock stress (no shock control, 0.4 mA, or 0.8 mA) immediately prior to auditory fear conditioning training involving the pairing of auditory clicks with a cloth containing cat odor. When presented to the conditioned auditory clicks in the next 5 days of extinction testing conducted in a runway apparatus with a hide box, rats in the two shock groups engaged in higher levels of freezing and head out vigilance-like behavior from the hide box than the no shock control group. This increase in fear behavior during extinction testing was likely due to auditory activation of the conditioned fear state because Experiment 2 demonstrated that conditioned fear behavior was not broadly increased in the absence of the conditioned auditory stimulus. Experiment 3 was then conducted to determine whether acute exposure to stress induces a habituation resistant sensitized fear state. We found that rats exposed to 0.8 mA footshock stress and subsequently tested for 5 days in the runway hide box apparatus with presentations of nonassociative auditory clicks exhibited high initial levels of freezing, followed by head out behavior and culminating in the occurrence of locomotor hyperactivity. In addition, Experiment 4 indicated that without delivery of nonassociative auditory clicks, 0.8 mA footshock stressed rats did not exhibit robust increases in sensitized freezing and locomotor hyperactivity, albeit head out vigilance-like behavior continued to be observed. In summary, our animal model provides novel information on the effects of different intensities of footshock stress, auditory-predator odor fear conditioning, and their interactions on facilitating either extinction-resistant or habituation-resistant fear-related behavior. These results lay the foundation for exciting new investigations of the hallmarks of PTSD that include the stress-induced formation and persistence of traumatic memories and sensitized fear.

Do mice habituate to "gentle handling?" A comparison of resting behavior, corticosterone levels and synaptic function in handled and undisturbed C57BL/6J mice

STUDY OBJECTIVES

"Gentle handling" has become a method of choice for 4-6 h sleep deprivation in mice, with repeated brief handling applied before sleep deprivation to induce habituation. To verify whether mice do indeed habituate, we assess how 6 days of repeated brief handling impact on resting behavior, on stress, and on the subunit content of N-methyl-D-aspartate receptors (NMDARs) at hippocampal synapses, which is altered by sleep loss. We discuss whether repeated handling biases the outcome of subsequent sleep deprivation.

DESIGN

Adult C57BL/6J mice, maintained on a 12 h-12 h light-dark cycle, were left undisturbed for 3 days, then handled during 3 min daily for 6 days in the middle of the light phase. Mice were continuously monitored for their resting time. Serum corticosterone levels and synaptic NMDAR subunit composition were quantified.

RESULTS

Handling caused a ∼25% reduction of resting time throughout all handling days. After six, but not after one day of handling, mice had elevated serum corticosterone levels. Six-day handling augmented the presence of the NR2A subunit of NMDARs at hippocampal synapses.

CONCLUSION

Repeated handling induces behavioral and neurochemical alterations that are absent in undisturbed animals. The persistently reduced resting time and the delayed increase in corticosterone levels indicate that mice do not habituate to handling over a 1-week period. Handling-induced modifications bias effects of gentle handling-induced sleep deprivation on sleep homeostasis, stress, glutamate receptor composition and signaling. A standardization of sleep deprivation procedures involving gentle handling will be important for unequivocally specifying how acute sleep loss affects brain function.

Delineating the psychic structure of substance abuse and addictions: should anxiety, mood and impulse-control dysregulation be included?

Current "official" nosology (e.g. DSM IV) is largely limited to physical manifestations of addiction that can be objectively observed and are suited to the maintaining of an "atheoretical" perspective. However, addicted subjects display additional psychiatric symptoms that affect their well-being and social functioning and, in accordance with DSM IV, are typically relegated to the domain of psychiatric "comorbidity." We contend that the relationship of these psychiatric symptoms with addiction is very close, as demonstrated by the high frequency of association observed. We further assert that substance use may modify pre-existing psychic structures such as temperament and related subthreshold conditions and lead to addiction as a specific mental disorder, inclusive also of symptoms pertaining to mood/anxiety, or impulse-control dimensions. The present contribution addresses the weaknesses of the current DSM-based nosology of addiction-related mental comorbidity. We highlight the overlap of the biological substrates and the neurophysiology of addictive processes and psychiatric symptoms associated with addiction, and propose the inclusion of specific mood, anxiety, and impulse-control dimensions in the psychopathology of addictive processes. We postulate that addiction reaches beyond the mere result of drug-elicited effects on the brain and cannot be peremptorily equated only with the use of drugs despite the adverse consequences produced. We infer that mood, anxiety and impulse-control dysregulation is at the very core of both the origins and clinical manifestations of addiction and should be incorporated into the nosology of the same, emphasising how addiction is a relapsing chronic condition in which psychiatric manifestations play a crucial role. To conclude, addictionology cannot be severed from its psychopathological connotations, in view of the undeniable presence of symptoms, of their manifest contribution to the way addicted patients feel and behave, and to the role they play in maintaining the continued use of substances.

Social modulation of learning in rats

It is well known that emotions participate in the regulation of social behaviors and that the emotion displayed by a conspecific influences the behavior of other animals. In its simplest form, empathy can be characterized as the capacity to be affected by and/or share the emotional state of another. However, to date, relatively little is known about the mechanisms by which animals that are not in direct danger share emotions. In the present study, we used a model of between-subject transfer of fear to characterize the social interaction during which fear is transmitted, as well as the behavioral effects of socially transmitted fear. We found that (1) during social interaction with a recently fear-conditioned partner, observers and demonstrators exhibit social exploratory behaviors rather than aggressive behaviors; (2) learning and memory in a shock-motivated shuttle avoidance task are facilitated in rats that underwent a social interaction with a partner that had been fear conditioned; and (3) a brief social interaction with a recently fear-conditioned partner immediately before fear conditioning increases conditioned freezing measured on the next day. The observed effects were not due to a stress-induced increase in pain sensitivity or analgesia. Collectively, these data suggest that a brief social interaction with a cage mate that has undergone an aversive learning experience promotes aversive learning in an otherwise naïve animal. We argue that socially transferred fear is an adaptation that promotes defensive behavior to potentially dangerous situations in the environment.

Oxytocin response to an experimental psychosocial challenge in adults exposed to traumatic experiences during childhood or adolescence

Long-term implications of the exposure to traumatizing experiences during childhood or adolescence, such as sexual abuse, or cancer, have been documented, namely the subjects' response to an acute stress in adulthood. Several indicators of the stress response have been considered (e.g. cortisol, heart rate). Oxytocin (OT) response to an acute stress of individuals exposed to trauma has not been documented. Eighty subjects (n=26 women who had experienced episodes of child abuse, n=25 men and women healthy survivors of cancer in childhood or adolescence, and 29 controls) have been submitted to a laboratory session involving an experimental stress challenge, the Trier social stress test. Overall, there was a clear OT response to the psychosocial challenge. Subjects having experienced a childhood/adolescence life-threatening illness had higher mean levels of OT than both abused and control subjects. There was a moderate negative relationship between OT and salivary cortisol. It is suggested that an acute stress stimulates OT secretion, and that the exposure to enduring life-threatening experiences in childhood/adolescence has long-lasting consequences regarding the stress system and connected functions, namely the activation of OT secretion. Better knowledge of such long-term implications is important so that to prevent dysregulations of the stress responses, which have been shown to be associated to the individual's mental health.

The influence of attachment on perceived stress and cortisol response to acute stress in women sexually abused in childhood or adolescence

The long-term implications of sexual abuse in childhood or adolescence (CSA) have been relatively well documented regarding attachment (disorganized attachment in childhood, unresolved trauma in adulthood), stress reactions (altered patterns of stress reactivity under experimental conditions), and psychopathology. Attachment has been shown to mediate the implications of CSA, namely on psychopathology. The implication of attachment on stress responses of abused persons has not been documented. Twenty-seven 20-46 years old women who had experienced episodes of CSA, and 17 controls have been interviewed using the Adult Attachment Interview. Sixty-three percent of abused women presented an unresolved trauma (12% for the controls). Thirty-six women (14 controls and 22 abused) came again to the laboratory for a session involving an experimental stress challenge (TSST). Subjects provided repeated appreciations of perceived stress on visual analogue scales and saliva samples were collected to assay cortisol levels. Whereas abused women with unresolved trauma showed the highest levels of perceived stress, they simultaneously presented the most suppressed cortisol reactions (there were significant post hoc differences between "unresolved abused" and controls on the increase of perceived stress and on cortisol recovery after the acute stress). It is suggested that important stressful experiences (such as CSA), especially when they have not been psychologically assimilated, may cause a disconnection, during subsequent mildly stressful circumstances, between the perception of stress and natural defensive body reactions.

Involvement of septal Cdk5 in the emergence of excessive anxiety induced by stress

The aim of the present study was to evaluate whether the activation of Cdk5, a protein that has been suggested to participate in higher cognitive functions, is required for the onset of a sensitized anxiety-related behavior induced by stress. The exposure to restraint enhanced both Cdk5 expression in certain subareas of the septohippocampal system, principally in the lateral septum (LS) and septal Cdk5 kinase activity in rats. Behaviorally, restrained wild type mice showed a behavior indicative of enhanced anxiety in the elevated plus maze (EPM). In contrast, unstressed mice and stressed knockout mice, which lacked the p35 protein, the natural activator of Cdk5, displayed similar anxiety-like behavior in the EPM. Finally, the intra-LS infusion of olomoucine - a Cdk5 inhibitor - blocked the enhanced anxiety in the EPM induced by prior stress in rats. All these data provide evidence that septal Cdk5 is required in the emergence of a sensitized emotional process induced by stress.

Chronic intermittent hypoxia sensitizes acute hypothalamic-pituitary-adrenal stress reactivity and Fos induction in the rat locus coeruleus in response to subsequent immobilization stress

Obstructive sleep apnea (OSA) is associated with several pathophysiological conditions, including hypertension, obesity, insulin resistance, hypothalamic-pituitary-adrenal (HPA) dysregulation, and other endocrine and metabolic disturbances comprising the "metabolic syndrome." Repeated episodes of hypoxia in OSA may represent a chronic intermittent stress, leading to HPA dysregulation. Alterations in HPA reactivity could then contribute to or exacerbate other pathophysiological processes. We showed previously that another metabolic stressor, chronic intermittent cold stress, enhanced noradrenergic facilitation of acute HPA stress reactivity. In this study, we investigated whether chronic intermittent hypoxia (CIH), a rat model for the arterial hypoxemia that accompanies OSA, similarly sensitizes the HPA response to novel acute stress. Rats were exposed to CIH (alternating cycles of normoxia [3 min at 21% O(2)] and hypoxia [3 min at 10% O(2)], repeated continuously for 8 h/day during the light portion of the cycle for 7 days). On the day after the final CIH exposure, there were no differences in baseline plasma adrenocorticotropic hormone (ACTH), but the peak ACTH response to 30 min acute immobilization stress was greater in CIH-stressed rats than in controls. Induction of Fos expression by acute immobilization stress was comparable following CIH in several HPA-modulatory brain regions, including the paraventricular nucleus, bed nucleus of the stria terminalis, and amygdala. Fos induction was attenuated in lateral hypothalamus, an HPA-inhibitory region. By contrast, acute Fos induction was enhanced in noradrenergic neurons in the locus coeruleus following CIH exposure. Thus, similar to chronic cold stress, CIH sensitized acute HPA and noradrenergic stress reactivity. Plasticity in the acute stress response is important for long-term adaptation, but may also contribute to pathophysiological conditions associated with states of chronic or repeated stress, such as OSA. Determining the neural mechanisms underlying these adaptations may help us better understand the etiology of such disorders, and inform the development of more effective treatments.

Social defeat-induced contextual conditioning differentially imprints behavioral and adrenal reactivity: a time-course study in the rat

The present experiments were based on the rat resident-intruder paradigm and aimed at better understanding the long-term conditioning properties of this social stress model. Intruders were exposed to aggressive conspecifics residents. During 3 daily encounters, intruders were either defeated or threatened by residents, providing the defeated-threatened (DT) and threatened-threatened (TT) groups respectively, or exposed to a novel empty cage (EC). The effect of such exposures was assessed in 3 separate experiments 8, 14, or 21 days following the last session on both behavior and hypothalamus-pituitary-adrenal (HPA) axis parameters. A specific and persistent behavioral conditioning due to social defeat but also to the sole social threat experience was observed as defensive behaviors and anxiety-like behaviors were observed respectively in DT and TT rats, highlighting a lack of habituation for the conditioning properties of this social stressor. On the other hand, at the earlier time points examined a less specific activation of the HPA axis parameters was found, starting to show habituation at day 21 in EC but not in DT or TT rats. These data give further support to the lasting effects of this social stress model, bestowing a special emphasis upon the impact of its psychological component and upon the relevance of its development and maintenance over time.

Involvement of group II metabotropic glutamate receptors in stress-induced behavioural sensitization

RATIONALE

A short session of repeated foot shocks in rats causes long-lasting sensitization of behavioural, hormonal and autonomic responses to novel stressful challenges. The behavioural sensitization can be reduced by anxiolytics and mimics aspects of stress-induced changes in patients with post-traumatic stress disorder.

OBJECTIVES

The aim of this study was to test the efficacy of a group II metabotropic glutamate receptor (mGluR) agonist and assess altered brain mGluR receptor expression in shock-sensitized rats.

MATERIALS AND METHODS

Male Wistar rats were exposed to a 15-min session with ten 6-s foot shocks (preshocked). One and 2 weeks later, rats were intraperitoneally injected with the group II metabotropic glutamate receptor agonist (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (APDC) or vehicle, and 30 min later exposed to 5 min of 85 dB noise. For in situ hybridization with probes for mGluR1, mGluR2, mGluR3 and mGluR5, preshocked and control rats were killed under basal conditions 2 weeks after foot shocks and their brains cryosectioned.

RESULTS

APDC had no clear effect in controls, but dose-dependently reduced high immobility and increased low locomotion and rearing seen in preshocked rats to the levels of controls. mGluR3 expression was increased in the basolateral nucleus of the amygdala, and mGluR2 expression was increased in the agranular insular cortex of preshocked rats compared to controls.

CONCLUSIONS

Shock-induced behavioural sensitization in rats is reduced by acute treatment with a group II metabotropic glutamate receptor agonist. This effect may depend on the increased expression of amygdala mGluR3, which could be hypothesized as an endogenous mechanism to counteract stress-induced neuronal sensitization.

Functional neuroimaging studies in posttraumatic stress disorder: review of current methods and findings

Posttraumatic stress disorder (PTSD) is an anxiety disorder associated with changes in neural circuitry involving frontal and limbic systems. Altered metabolism in these brain structures after a traumatic event is correlated to PTSD. Developments in the field of neuroimaging have allowed researchers to look at the structural and functional properties of the brain in PTSD. Despite the relative novelty of functional imaging and its application to the field of PTSD, numerous publications have brought to light several of the circuits implied in this disorder. This article summarizes the findings with regard to PTSD in the functional imaging techniques of single-photon emission computed tomography (SPECT), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI). Furthermore, we discuss strengths and weaknesses of the various techniques and studies. Finally, we explore the future potential of functional neuroimaging studies in PTSD.

Elevated pCREB in the PAG after exposure to the elevated plus maze in rats previously exposed to a cat

The elevated plus maze (EPM) is an ethologically based test of anxiety-like behavior. In addition, exposure to the maze itself is stressful and anxiogenic. One of the goals of this study was to examine if the stress of EPM exposure increased pCREB-like-immunoreactivity (lir). The second goal of this study was to determine if prior stress impacted expression of pCREB-lir in animals exposed to the EPM. Toward this end, pCREB-lir was examined after exposure to the EPM in young adult male rats that had been exposed to a cat 7 days earlier. Brain areas investigated included the amygdala, periaqueductal gray (PAG), and bed nucleus of the stria terminalis (BNST), all areas considered to be part of the "fear circuit". Results show that there were no pCREB-lir differences between control rats and rats exposed to the EPM only. However, exposure to the EPM in predator stressed rats showed elevated pCREB-lir in the right lateral column of the PAG and bilaterally in the dorsal column of the PAG. In contrast, EPM exposure did not elevate pCREB-lir in the amygdala or BNST in predator stressed rats. Findings suggest mechanisms associated with neuroplasticity may be engaged by relatively mild stresses in animals with a history of severe stress exposure. This may be clinically relevant, as a key feature of posttraumatic stress disorder (PTSD) is the exaggerated reaction to a mild stressor in which the response is more appropriate to the original traumatic situation than the current conditions. If what happens in animals also occurs in humans, the findings of this study suggest that neural mechanisms of prior traumatic stress may interact with subsequent stress to reinforce psychopathology.

Individual reactivity to the open-field predicts the expression of cardiovascular and behavioural sensitisation to novel stress

Posttraumatic stress disorder (PTSD) is the fourth most common psychiatric disorder. It is associated with cardiovascular disorders and irritable bowel syndrome (IBS). Besides stressful life-events, a prior history of gastrointestinal infection is a predisposing factor for the development of IBS. Only a proportion of persons exposed to traumatic events develop PTSD. Several factors, like genetic predisposition, stressor intensity, cognitive appraisal mechanisms and coping processes influence the likelihood of developing PTSD after exposure to a trauma. We used a single session of footshocks in rats, an animal model with a high degree of validity for PTSD, to study whether transient colonic inflammation alters local and distal visceral sensitivity, and whether reactivity to the open-field (low (LA) or high (HA) active) predicts long-term stress-induced behavioural and cardiovascular sensitisation and altered visceral pain sensitivity. A distention series and noise challenge were given 2 weeks after foot-shocks, followed by a transient colonic inflammation period and a second distention series and noise challenge 4 weeks after foot-shocks. During exposure to noise, both before and after inflammation, footshocked rats showed increased immobility compared to controls, which was significantly greater in LA rats than in HA rats. LA preshocked rats also showed a greater blood pressure response to the noise test, but this only became evident in the second noise-test. Neither footshocks nor colonic inflammation affected duodenal pain sensitivity. The results provide additional evidence for long-lasting cardiovascular hyperresponsivity after a stressful event and indicate that its degree is predicted by personality traits or coping style.

Glucocorticoid receptors in lateral septum are involved in the modulation of the emotional sequelae induced by social defeat

The current research studied the behavior adopted in the elevated plus maze (EPM) of rats previously subjected to a social defeat using the resident-intruder paradigm. One day after defeat, intruder animals exhibited an anxiogenic-like behavior in the EPM. In addition, we also evaluated the role of the corticosteroid receptor system (minerlocorticoid - MR - and glucocorticoid - GR - receptors) from the lateral septum (LS) on the anxiety generated by social defeat. The LS is an area of the aversive circuitry that is preferentially activated in passive defensive postures, and participates - together with other brain areas - in the modulation of aversive states. Intruder animals were infused into the LS with the MR or GR antagonist (ZK 91587 and RU 38486, respectively) and then submitted to social stress. All rats were tested in the EPM 1 day later. Only the administration of the GR antagonist, but not the MR antagonist, into the LS normalized the anxiogenic response induced by defeat. Furthermore, we examined whether a single injection of corticosterone (CS) could induce the same influence on the behavior in the EPM as that observed after social defeat. Moreover, we explored the effect of local infusions of MR or GR antagonists into the LS on the behavior exhibited by CS-treated rats in a subsequent EPM exposure. CS administration also exerted an increased anxiogenic-like behavior, which was normalized only by the local infusion of the GR antagonist. Based on these findings, we suggest that CS secreted by emotionally relevant stimuli acting via GR in LS plays an important role in the modulation of the emotional sequelae induced by social defeat.

Effects of stress on catecholamine stores in central and peripheral tissues of long-term socially isolated rats

Both the peripheral sympatho-adrenomedullary and central catecholaminergic systems are activated by various psycho-social and physical stressors. Catecholamine stores in the hypothalamus, hippocampus, adrenal glands, and heart auricles of long-term socially isolated (21 days) and control 3-month-old male Wistar rats, as well as their response to immobilization of all 4 limbs and head fixed for 2 h and cold stress (4 degrees C, 2 h), were studied. A simultaneous single isotope radioenzymatic assay based on the conversion of catecholamines to the corresponding O-methylated derivatives by catechol-O-methyl-transferase in the presence of S-adenosyl-l-(3H-methyl)-methionine was used. The O-methylated derivatives were oxidized to 3H-vanilline and the radioactivity measured. Social isolation produced depletion of hypothalamic norepinephrine (about 18%) and hippocampal dopamine (about 20%) stores and no changes in peripheral tissues. Immobilization decreased catecholamine stores (approximately 39%) in central and peripheral tissues of control animals. However, in socially isolated rats, these reductions were observed only in the hippocampus and peripheral tissues. Cold did not affect hypothalamic catecholamine stores but reduced hippocampal dopamine (about 20%) as well as norepinephrine stores in peripheral tissues both in control and socially isolated rats, while epinephrine levels were unchanged. Thus, immobilization was more efficient in reducing catecholamine stores in control and chronically isolated rats compared to cold stress. The differences in rearing conditions appear to influence the response of adult animals to additional stress. In addition, the influence of previous exposure to a stressor on catecholaminergic activity in the brainstem depends on both the particular catecholaminergic area studied and the properties of additional acute stress. Therefore, the sensitivity of the catecholaminergic system to habituation appears to be tissue-specific.

Protein expression profile in the striatum of acute methamphetamine-treated rats

PURPOSE

Methamphetamine (MAP) is an addictive drug with psychostimulant effects. It is known that MAP induces behavioral changes, including hyperlocomotion and stereotypical movements in rodents. These behavioral changes induced by MAP have been compared with behavioral changes in patients with MAP addiction and MAP psychosis. However, little is known about the underlying mechanisms of MAPs effects on global protein expression. 2-DE proteomics allows us to examine global changes in protein expression in complex biological systems and to propose possible hypotheses of the underlying mechanisms in various pathological conditions. In the present study, we aim to identify protein expression profiles in the striatum (ST) of acute low dose MAP (1 mg/kg)-treated rats using 2-DE proteomics.

MATERIALS AND METHODS

Rats were given an intraperitoneal injection of MAP (1 mg/kg) or saline. Locomotor activity was monitored. Proteins were extracted from the ST of MAP-treated and saline-treated control rats then separated and analyzed using 2-DE. RESULTS. Low dose MAP administration significantly increased locomotor activity. 2-DE analysis revealed 36 protein spots differentially regulated in the ST of acute MAP-treated rats compared to a vehicle-treated control. 26 protein spots have been identified using MALDI-TOF, including phosphoglycerate kinase 1, Dihydrolipoamide dehydrogenase, Voltage-dependent anion-selective channel protein 1, Rho GDP dissociation inhibitor alpha, peroxiredoxin 2, ubiquitin carboxy-terminal hydrolase L1, and actin beta, N-tropomodulin.

DISCUSSION

These proteins could be related to underlying mechanisms of acute low dose MAP effects, indicating mitochondrial dysfunction, oxidative damages, lysosomal degradation, degenerative processes, and neuronal modification.

Differential effects of acute and chronic social defeat stress on hypothalamic-pituitary-adrenal axis function and hippocampal serotonin release in mice

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) stress axis and disturbances in serotonin (5-HT) neurotransmission have been implicated in the pathogenesis of depressive disorder. Repeated social defeat of male NMRI mice has been shown to induce increases in core body temperature and corticosterone, indicative of a state of chronic stress in subordinate animals. The present study further characterised the HPA axis response to social defeat stress, and also examined hippocampal extracellular 5-HT release during the stress. Exposure to an acute social defeat elicits increases in plasma adrenocorticotrophic hormone and corticosterone levels, peaking at 15 and 30 min, respectively, and enhances corticotrophin-releasing factor (CRF) mRNA, but not arginine vasopressin (AVP) mRNA within the medial parvocellular division of the hypothalamic paraventricular nucleus. A concomitant increase in hippocampal corticosterone and 5-HT levels is observed. By contrast, although chronic social defeat is associated with greatly elevated corticosterone levels, the predominant drive appears to be via parvocellular AVP rather than CRF. Furthermore, subordinate animals allowed to recover for 9 days after chronic social defeat display an increase in immobility in the forced swimming model of depression, indicating that animals previously exposed to the homotypic defeat stress are sensitised to the behavioural effects of a novel stressor. These results demonstrate that social defeat induces prolonged activation of the HPA axis and alterations in 5-HT neurotransmission that could be of relevance to some of the pathological abnormalities observed in clinical depression.

Cholecystokinin and endogenous opioid peptides: interactive influence on pain, cognition, and emotion

It is well documented that stressful life experiences contribute to the etiology of human mood disorders. Cholecystokinin (CCK) is a neuropeptide found in high concentrations throughout the central nervous system, where it is involved in numerous physiological functions. A role for CCK in the induction and persistence of anxiety and major depression appears to be conspicuous. While increased CCK has been associated with motivational loss, anxiety and panic attacks, an increase in mesocorticolimbic opioid availability has been associated with coping and mood elevation. The close neuroanatomical distribution of CCK with opioid peptides in the limbic system suggests that there may be an opioid-CCK link in the modulation and expression of anxiety or stressor-related behaviors. In effect, while CCK induces relatively protracted behavioral disturbances in both animal and human subjects following stressor applications, opioid receptor activation may change the course of psychopathology. The antagonistic interaction of CCK and opioid peptides is evident in psychological disturbances as well as stress-induced analgesia. There appears to be an intricate balance between the memory-enhancing and anxiety-provoking effects of CCK on one hand, and the amnesic and anxiolytic effects of opioid peptides on the other hand. Potential anxiogenic and mnemonic influences of site-specific mesocorticolimbic CCK and opioid peptide availability, the relative contributions of specific CCK and opioid receptors, as well as the time course underlying neuronal substrates of long-term behavioral disturbances as a result of stressor manipulations, are discussed.

A Model of Anxious Depression: Persistence of Behavioral Pathology

Chronic psychoemotional stress induced by negative experience of social defeats in intermale confrontations over a period of 30 days was found to lead to the development of anxious-depressive symptomatology in male mice. Cessation of the psychopathogenic conditions and placing of depressed animals in comfortable conditions for 1-2 weeks with females did not lift the pathological state. Individuals continued to show marked anxiety, a behavioral deficit, decreased communicativeness, and a high level of depressivity, as revealed by a variety of behavioral tests. Persistence of the resulting psychoemotional disturbance in these animals is evidence for the development and persistence of the behavioral pathology requiring drug treatment.

Novel stressors affected catecholamine stores in socially isolated normotensive and spontaneously hypertensive rats

Catecholamines in some central (hypothalamus and hippocampus) and peripheral tissues (adrenal glands and heart auricles) of long-term socially isolated normotensive and spontaneously hypertensive rats exposed to novel immobilization stress were determined by a simultaneous single isotope radioenzymatic assay. Long-term isolation (21 days) produced depletion of hypothalamic norepinephrine (NE) stores and hippocampal dopamine (DA) stores in both normotensive and spontaneously hypertensive rats. Acute immobilization stress (2 h) significantly decreased NE and DA stores in hypothalamus and hippocampus of naive normotensive and spontaneously hypertensive rats controls. However, novel immobilization stress applied to normotensive rats previously subjected to long-term isolation produced no changes in catecholamine levels in hypothalamus, while resulting in somewhat higher depletion of NE stores in hypothalamus of spontaneously hypertensive rats treated in the same way. Novel immobilization stress decreased NE and DA stores in hippocampus of normotensive but was without effect on NE and DA stores of spontaneously hypertensive rats. Social isolation did not affect catecholamine stores in peripheral tissues but novel immobilization stress produced a significant decrease in catecholamine content. The results suggest that some central and peripherals tissues of spontaneously hypertensive rats and normotensive rats differ with regard to catecholamine content and that there are certain differences in their responsiveness to stress.

Repeated exposure to water avoidance stress in rats: a new model for sustained visceral hyperalgesia

Chronic stress plays an important role in the development and exacerbation of symptoms in functional gastrointestinal disorders. To better understand the mechanisms underlying this relationship, we aimed to characterize changes in visceral and somatic nociception, colonic motility, anxiety-related behavior, and mucosal immune activation in rats exposed to 10 days of chronic psychological stress. Male Wistar rats were submitted daily to either 1-h water avoidance (WA) stress or sham WA for 10 consecutive days. The visceromotor response to colorectal distension, thermal somatic nociception, and behavioral responses to an open field test were measured at baseline and after chronic WA. Fecal pellets were counted after each WA stress or sham WA session as a measure of stress-induced colonic motility. Colonic samples were collected from both groups and evaluated for structural changes and neutrophil infiltration, mast cell number by immunohistochemistry, and cytokine expression by quantitative RT-PCR. Rats exposed to chronic WA (but not sham stress) developed persistent visceral hyperalgesia, whereas only transient changes in somatic nociception were observed. Chronically stressed rats also exhibited anxiety-like behaviors, enhanced fecal pellet excretion, and small but significant increases in the mast cell numbers and the expression of IL-1beta and IFN-gamma. Visceral hyperalgesia following chronic stress persisted for at least a month. Chronic psychological stress in rats results in a robust and long-lasting alteration of visceral, but not somatic nociception. Visceral hyperalgesia is associated with other behavioral manifestations of stress sensitization but was only associated with minor colonic immune activation arguing against a primary role of mucosal immune activation in the maintenance of this phenomenon.