Situation specific effects of stressor controllability on plasma corticosterone changes in mice

Interactions Between Experience, Genotype and Sex in the Development of Individual Coping Strategies

Coping strategies, the first line of defense against adversities, develop through experience. There is consistent evidence that both genotype and sex contribute to the development of dysfunctional coping, leading to maladaptive outcomes of adverse experiences or to adaptive coping that fosters rapid recovery even from severe stress. However, how these factors interact to influence the development of individual coping strategies is just starting to be investigated. In the following review, we will consider evidence that experience, sex, and genotype influence the brain circuits and neurobiological processes involved in coping with adversities and discuss recent results pointing to the specific effects of the interaction between early experiences, genotype, and stress in the development of functional and dysfunctional coping styles.

Animal models of liability to post-traumatic stress disorder: going beyond fear memory

In this review, we advocate a dimensional approach on the basis of candidate endophenotypes to the development of animal models of post-traumatic stress disorder (PTSD) capable of including genetic liability factors, variations in symptoms profile and underlying neurobiological mechanisms, and specific comorbidities. Results from the clinical literature pointed to two candidate endophenotypes of PTSD: low sensory gating and high waiting impulsivity. Findings of comparative studies in mice of two inbred strains characterized by different expressions of the two candidate endophenotypes showed different strain-specific neural and behavioral effects of stress experiences. Thus, mice of the standard C57BL/6J strain show stress-induced helplessness, stress-learned helplessness, and stress-extinction-resistant conditioned freezing. Instead, mice of the genetically unrelated DBA/2J strain, expressing both candidate endophenotypes, show stress-induced extinction-resistant avoidance and neural and behavioral phenotypes promoted by prolonged exposure to addictive drugs. These strain differences are in line with evidence of associations between genetic variants and specific stress-promoted pathological profiles in PTSD, support a role of genotype in determining different PTSD comorbidities, and offer the means to investigate specific pathogenic processes.

Changes in Monoamine Levels in BALB/c and 57Bl/6N Mice in Response to Acute Stress with Different Controllability

The severity and specificity of CNS disturbances resulting from negative psychoemotional experience are determined by not only genetically determined stress sensitivity, but also epigenetic factors; among the latter, the context of stress exposure, e.g. stress controllability is considered. We examined the effect of controllability factor on behavioral and neurochemical parameters of acute stress in the elevated plus maze test. The situations of controllable and uncontrollable stress were modeled by allowing or restricting mice in their choice for closed arms during testing in the maze. The anxiety level of inbred BALB/c and C57Bl/6N mice was assessed and the levels and monoamine turnover in the medial prefrontal cortex, hippocampus, amygdala, and hypothalamus were measured. It was found that the decrease in stress controllability suppresses explorative activity in mice; the behavioral and neurochemical differences between the two strains are not constant feature and depend on stress controllability; serotoninergic and dopaminerigic neurotransmission in the hypothalamus can be a signal to discriminate stress controllability in the brain.

Environmental Programming of Susceptibility and Resilience to Stress in Adulthood in Male Mice

Epidemiological evidence identifies early life adversity as a significant risk factor for the development of mood disorders. Much evidence points to the role of early life experience in susceptibility and, to a lesser extent, resilience, to stress in adulthood. While many models of these phenomena exist in the literature, results are often conflicting and a systematic comparison of multiple models is lacking. Here, we compare effects of nine manipulations spanning the early postnatal through peri-adolescent periods, both at baseline and following exposure to chronic social defeat stress in adulthood, in male mice. By applying rigorous criteria across three commonly used measures of depression- and anxiety-like behavior, we identify manipulations that increase susceptibility to subsequent stress in adulthood and other pro-resilient manipulations that mitigate the deleterious consequences of adult stress. Our findings point to the importance of timing of early life stress and provide the foundation for future studies to probe the neurobiological mechanisms of risk and resilience conferred by variation in the early life environment.

Controllability affects endocrine response of adolescent male rats to stress as well as impulsivity and behavioral flexibility during adulthood

Exposure to stress during adolescence exerts a long-term impact on behavior and might contribute to the development of several neuropsychiatric disorders. In adults, control over stress has been found to protect from the negative consequences of stress, but the influence of controllability at early ages has not been extensively studied. Here, we evaluated in a rodent model the effects of repeated exposure in adolescent male rats to controllable versus uncontrollable foot-shock stress (CST or UST, respectively). Rats were assigned to three groups: non-stress (stress-naïve), CST (exposed to 8 sessions of a two-way shuttle active avoidance task over a period of 22 days) and UST (receiving the same amount of shocks as CST, regardless of their actual behavior). During adulthood, different cohorts were tested in several tasks evaluating inhibitory control and cognitive flexibility: 5-choice serial reaction time, delay-discounting, gambling test and probabilistic reversal learning. Results showed that the hypothalamic-pituitary-adrenal response to the first shock session was similar in CST and UST animals, but the response to the 8^th session was lower in CST animals. In adulthood, the UST animals presented impaired motor (but not cognitive) impulsivity and more perseverative behavior. The behavioral effects of UST were associated with increased number of D2 dopamine receptors in dorsomedial striatum, but not in other striatal regions. In summary, UST exposure during adolescence induced long-term impairments in impulsivity and compulsivity, whereas CST had only minor effects. These data support a critical role of stress uncontrollability on the long-lasting consequences of stress, as a risk factor for mental illnesses.

Corticosterone Blocks Ovarian Cyclicity and the LH Surge via Decreased Kisspeptin Neuron Activation in Female Mice

Stress elicits activation of the hypothalamic-pituitary-adrenal axis, which leads to enhanced circulating glucocorticoids, as well as impaired gonadotropin secretion and ovarian cyclicity. Here, we tested the hypothesis that elevated, stress-levels of glucocorticoids disrupt ovarian cyclicity by interfering with the preovulatory sequence of endocrine events necessary for the LH surge. Ovarian cyclicity was monitored in female mice implanted with a cholesterol or corticosterone (Cort) pellet. Cort, but not cholesterol, arrested cyclicity in diestrus. Subsequent studies focused on the mechanism whereby Cort stalled the preovulatory sequence by assessing responsiveness to the positive feedback estradiol signal. Ovariectomized mice were treated with an LH surge-inducing estradiol implant, as well as Cort or cholesterol, and assessed several days later for LH levels on the evening of the anticipated surge. All cholesterol females showed a clear LH surge. At the time of the anticipated surge, LH levels were undetectable in Cort-treated females. In situ hybridization analyses the anteroventral periventricular nucleus revealed that Cort robustly suppressed the percentage of Kiss1 cells coexpressing cfos, as well as reduced the number of Kiss1 cells and amount of Kiss1 mRNA per cell, compared with expression in control brains. In addition, Cort blunted pituitary expression of the genes encoding the GnRH receptor and LHβ, indicating inhibition of gonadotropes during the blockage of the LH surge. Collectively, our findings support the hypothesis that physiological stress-levels of Cort disrupts ovarian cyclicity, in part, through disruption of positive feedback mechanisms at both the hypothalamic and pituitary levels which are necessary for generation of the preovulatory LH surge.

Differential Effects of Controllable Stress Exposure on Subsequent Extinction Learning in Adult Rats

Deficits in fear extinction are thought to be related to various anxiety disorders. While failure to extinguish conditioned fear may result in pathological anxiety levels, the ability to quickly and efficiently attenuate learned fear through extinction processes can be extremely beneficial for the individual. One of the factors that may affect the efficiency of the extinction process is prior experience of stressful situations. In the current study, we examined whether exposure to controllable stress, which is suggested to induce stress resilience, can affect subsequent fear extinction. Here, following prolonged two-way shuttle (TWS) avoidance training and a validation of acquired stress controllability, adult rats underwent either cued or contextual fear-conditioning (FC), followed by an extinction session. We further evaluated long lasting alterations of GABAergic targets in the medial pre-frontal cortex (mPFC), as these were implicated in FC and extinction and stress controllability. In cued, but not in contextual fear extinction, within-session extinction was enhanced following controllable stress compared to a control group. Interestingly, impaired extinction recall was detected in both extinction types following the stress procedure. Additionally, stress controllability-dependent alterations in GABAergic markers expression in infralimbic (IL), but not prelimbic (PL) cortex, were detected. These alterations are proposed to be related to the within-session effect, but not the recall impairment. The results emphasize the contribution of prior experience on coping with subsequent stressful experiences. Moreover, the results emphasize that exposure to controllable stress does not generally facilitate future stress coping as previously claimed, but its effects are dependent on specific features of the events taking place.

Neonatal tactile stimulation alleviates the negative effects of neonatal isolation on novel object recognition, sociability and neuroendocrine levels in male adult mandarin voles (Microtus mandarinus)

Neonatal isolation results in long-lasting negative alterations to the brain and behavior. Some of these changes include effects on non-spatial learning and memory, sociability and neuroendocrine levels. Theoretically, neonatal tactile stimulation should reverse the impacts of neonatal isolation; however, this remains unknown for changes relating to learning, memory, sociability and hormones in social animals. Using socially monogamous mandarin voles (Microtus mandarinus), the long-lasting effects of these early manipulations on anxiety-like behavior, novel object recognition, sociability, and neuroendocrine levels were investigated. Compared with neonatal-isolated males, males subjected to the same manipulation but accompanied with tactile stimulation had heavier body weights across PND4-18 and displayed significantly less anxiety-like behavior in an open field test. In addition, tactile stimulation increased the preference index for novel object recognition reduced by neonatal isolation. Compared with control males, neonatal-isolated males engaged in less body contact with unfamiliar same-sex individuals and this effect was reversed by neonatal tactile stimulation. Tactile stimulation enhanced aggressive behavior in neonatal-isolated males and increased the levels of AVP and OT in the paraventricular nucleus (PVN) which were decreased by neonatal isolation. This early manipulation also reduced serum CORT levels that were significantly up-regulated by neonatal isolation in both neonatal and adult offspring. These results indicate that adequate tactile stimulation in early life plays an important role in the prevention of behavioral disturbances induced by neonatal isolation, possibly through the alteration of central OT, AVP and the serum corticosterone levels.

Coping in an intermittent swim stress paradigm compromises natural killer cell activity in rats

The effects of intermittent swim stress and stressor controllability on natural killer cell activity (NKCA) was examined. Significant decreases in splenic NKCA were observed immediately post-stress, but only when the stress was controllable. Although decreased NKCA was also observed in yoked rats subjected to the same stressor, it failed to attain statistical significance. Previous results suggest these effects are not due to corticosterone. The results suggest a cost of coping on the acute, in vitro immune measure of NKCA.

ERK2 and CREB activation in the amygdala when an event is remembered as "Fearful" and not when it is remembered as "Instructive"

A training protocol was developed based on durable exposure to the two-way shuttle avoidance task, in which the conditioned stimulus (CS), which was fear evoking for both training conditions on the first day of training, becomes instructive at the end of training under controllable conditions but remains fear evoking under the uncontrollable conditions. The protocol was utilized to examine whether, depending on the training regime, the memory formed will result in a different level of involvement of the amygdala. Three groups of rats were tested: controllable, subjected to durable avoidance learning; uncontrollable, subjected to the same training schedule but with no control over the stressor; and naive. Two weeks later, after the introduction of a reminder cue, freezing response, defecation, and blood corticosterone (CORT) of the uncontrollable group were higher than in the controllable and naive groups, indicating that indeed, for this group, the CS remained fear evoking. Significantly higher than chance shuttling responses of the controllable group indicated that, for them, the CS became "instructive." Activation of ERK2 and CREB in the basolateral amygdala (BLA) was highest in the uncontrollable group compared with the controllable and naive groups. Overall, the results indicate that the training procedure succeeded in dissociating between the physical (electric shock) and the psychological (control) attributes of the experience. Also, our findings support the view that an emotionally charged reminder cue activates the amygdala but that, as a previously fear-evoking memory cue becomes instructive, the involvement of the amygdale lessens.

Effects of single episodes of severe stress on the behavior of male and female CBA/Lac and C57BL/6J mice

Experiments were performed to compare the behavior of male and female mice of the inbred strains CBA/Lac and C57BL/6J in the open field test after single episodes of severe stress imposed by forced swimming. Testing was performed 2 h (first test) and one day (second test) after stress. Control animals were intact males and females of these strains, and were also tested in the open field on two sequential days. Both male and female CBA/Lac mice showed increases in the latent period of excursions from the center of the field 2 h after stress. This change persisted to the second test in female CBA/Lac mice. In female C57BL/6J mice, there were changes in four of seven behavioral measures 2 h after stress, though at one day their behavior was as in control individuals. Stress had virtually no effect in males of this strain, only increasing the number of grooming acts in the first test. In addition, detailed analysis of the effects of repeat testing in control and stressed individuals of these mouse strains also revealed interstrain and gender-related differences in the effects of stress. The possible existence of increased basal (trait) and situational (state) anxiety in female C57BL/6J and CBA/Lac mice respectively is discussed.

Endocrine and immunological correlates of behaviorally identified swim stress resilient and vulnerable rats

Animal models of stress-induced depression have identified a bimodal reactivity to stress, namely 'resilience' and 'vulnerability.' Possible corresponding differences in endocrine and immunological responses between these groups have not been delineated. Male Sprague-Dawley rats were divided into three groups: stress (n=25), confined controls (n=7), and home cage controls (n=7). Stress rats were exposed to 80, 5-s inescapable cold water swim trials (15 degrees C). Twenty-four hours later, the stress rats were tested on an instrumental swim escape test (SET) but now they had access to an omnidirectional lever that terminated the stress. Immediately after the SET, trunk blood was collected to assay for serum corticosterone (CORT), and spleens were removed and natural killer cell activity (NKCA) and concanavalin A (CON-A) induced lymphocyte proliferation determined. Subjects in the stress treatment group were divided into distinct 'resilient' and 'vulnerable' categories by a median split for average escape latencies across the last 25 trials of the SET. Stress rats secreted more CORT than controls and vulnerable rats secreted greater levels than resilient rats. NKCA was greatest in control rats, and was decreased in the stress rats although the resilient and the vulnerable groups did not differ. Conversely, CON-A-induced lymphocyte proliferation was greatest in stress rats, vulnerable rats exhibiting more proliferation than resilient rats, but both were greater than both control groups. Stress animals were hypothermic throughout the swim stress procedures but exhibited a stress-induced fever following the initial swim trials. The observed differences may have important predictive and theoretical utility for vulnerable and resilient profiles.

Stress and adult neurogenesis

Stress hormones have potent growth-inhibiting effects on a variety of peripheral tissues. Consistent with this general function, stress has been shown to inhibit cell proliferation and, ultimately, neurogenesis in the hippocampus. This effect appears to be common across mammalian species, life stages, and most types of stressors. Although some evidence points to a role for glucocorticoids in mediating this effect, contradictory data exist. This review considers the growing literature on this subject with specific emphasis on paradoxical findings and the role of glucocorticoids in modulating adult neurogenesis.

Impact of water temperature and stressor controllability on swim stress-induced changes in body temperature, serum corticosterone, and immobility in rats

The present study compared the effects of three different water temperatures (20, 25, and 30 degrees C) and stressor controllability on several physiological and behavioral endpoints in an intermittent swim stress paradigm. The escape latency of rats in the 20 and 25 degrees C water was less than that observed for the 30 degrees C group. Both escape and yoked groups at 20 and 25 degrees C exhibited moderate to severe hypothermia following the swim stress session that returned to prestress levels 30-40 min post-stress. At 30 degrees C core body temperature (Tb) only decreased by 1 degree C for either swim group. Following swim, serum corticosterone (CORT) levels were significantly elevated in both escape and yoked groups in comparison to confined and home cage controls. The confined control group showed a significant elevation that was approximately halfway between the home cage control and the swim stress groups. At 30 degrees C, there was still a significant elevation of serum CORT in both swim groups in comparison to confined and home cage controls. Therefore, 30 degrees C appears to be the optimal water temperature to evaluate stress controllability effects in the current paradigm. In a final experiment, swim stressor controllability effects were examined in a 5 min forced swim test (FST) 24 h following the initial stress exposure. Rats exposed to yoked-inescapable swim stress at 30 degrees C exhibited more immobility than their escapable swim stress and confined counterparts, while the escape and confined controls did not differ. These results demonstrate that the behavioral deficits observed in the FST are attributable to the stress of inescapable swim and not swim stress per se.

Activity and plasticity in the CA1, the dentate gyrus, and the amygdala following controllable vs. uncontrollable water stress

The level of controllability has been shown to modulate the effects of stress on physiology and behavior. In the present study, we investigated the effects of controllable vs. uncontrollable stressors on plasticity in hippocampal CA1, the dentate gyrus (DG), and basal amygdala nucleus (B) in the rat, using the electrophysiological procedure of long-term potentiation (LTP). A naive group was left undisturbed until the electrophysiological recording commenced. Rats of the two controllable stress groups were trained in the Morris water maze to locate an invisible underwater platform (the first group), or visible platform (the second group), thus escaping from the water, before the recording. The uncontrollable stress group underwent the same procedure (exposure time to water was adjusted to the averaged exposure time of the first controllable group) without the escape platform. We first assessed the effects of stress and controllability on LTP in CA1. Both controllable stressors and the uncontrollable stress impaired CA1 LTP, with a more robust effect induced by the uncontrollable stress. We further assessed the effects of the same procedures on LTP in DG and B. The uncontrollable stress enhanced LTP in DG and increased baseline responses (suggesting uncontrollable stress-induced plasticity) in the amygdala. All the stressors decreased amygdalar LTP. An assessment of plasma levels of corticosterone (CORT), following the behavioral procedures, revealed an enhancement in CORT release following the uncontrollable, but not controllable stress, indicating the uncontrollable condition as the most stressful. These findings provide insight into the differential effects of stress and stress controllability on different hippocampal subregions and the amygdala.

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

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

Body weight gain and diurnal differences of corticosterone changes in response to acute and chronic stress in rats

Plasmatic levels of corticosterone display a circadian rhythm, with the higher values occurring during the dark phase in nocturnally feeding animals. Stressful situations induce a rise of corticosterone levels and this endocrine response to stress also presents circadian variations. The higher increase of corticosterone in response to stress occurs when the hormone is in its lower circadian level, and the minimum responses occurring at the peak. Since it has been shown that plasma hormones respond differently to different stressors, in the present study, we compared the acute and chronic effects of four different stressors: electric foot shocks (3 mA, 1/s, 5 min), immobilization during two hours or six hours, and immersion in cold water (15 degrees C) for 15 min. Stressors were applied, both acutely and chronically (during 4, 12 and 20 days) at the onset of the light phase as well as at the onset of the dark phase of the light/dark cycle. Body weight was assessed every day, and at the end of the manipulations plasmatic corticosterone levels were determined from the trunk blood. Adrenal and testicular weights were also assessed. Acute exposure to stressors increased plasmatic corticosterone levels significantly when the stressors were applied at the beginning of the light phase of the cycle. In the dark phase, only two hours of immobilization and immersion in cold water caused an increase in plasmatic corticosterone. With repeated exposure, electric foot shocks failed to induce significant changes in corticosterone levels in any phase of the light-dark cycle. Immobilization stress induced a significant rise in corticosterone levels only when the stressor was applied during the light phase. Immersion in cold water elicited a clear increase in plasmatic corticosterone levels in all the periods tested, regardless of the time of the cycle in which the stressor was applied. We did not observe a loss in body weight, but rather a smaller weight gain in stressed rats. Body weight gain was minimum in rats exposed to immersion and 6 hours of immobilization. Adrenal hypertrophy was observed in rats exposed to these same stressors. We conclude that: 1) the activation of the hypothalamus-pituitary-adrenal axis by stress depends mainly on the characteristics of the stressor; 2) the response of this axis to stress also depends on the time of day in which the stressor is applied.

The stressed hippocampus, synaptic plasticity and lost memories

Stress is a biologically significant factor that, by altering brain cell properties, can disturb cognitive processes such as learning and memory, and consequently limit the quality of human life. Extensive rodent and human research has shown that the hippocampus is not only crucially involved in memory formation, but is also highly sensitive to stress. So, the study of stress-induced cognitive and neurobiological sequelae in animal models might provide valuable insight into the mnemonic mechanisms that are vulnerable to stress. Here, we provide an overview of the neurobiology of stress memory interactions, and present a neural endocrine model to explain how stress modifies hippocampal functioning.

Predictable stress promotes place preference and low mesoaccumbens dopamine response

Aversive stimuli that are signaled, and therefore predictable, are preferred to unsignaled ones and promote less severe stress-related disturbances. Since stressful events are known to activate mesoaccumbens dopamine (DA) transmission, in the present experiments, we evaluated possible differences in mesoaccumbens DA response to predictable and unpredictable footshocks. Mice of the inbred strain DBA/2 were trained for conditioned place preference (CPP) in shuttle boxes. The procedure promoted significant preference for the compartment previously paired with predictable shocks (PR) to that paired with unpredictable shocks (NP). Mesoaccumbens levels of DA and its metabolites were therefore evaluated either after the first or the last (third) training session. A significant increase of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels were observed in animals exposed for the first time to the apparatus without shock delivery (SHAM) or to the PR and NP conditions compared with unhandled mice. There was no difference between PR and NP values, and DOPAC and HVA levels in both groups differed from those observable in the SHAM-exposed group. However, trained mice exposed to NP showed a significant elevation of DOPAC and HVA levels in comparison with those exposed to PR. These results show that information about predictability of aversive stimuli reduces central stress responses and suggest a possible relationship between reduced stressfulness and preference for predictable aversive experiences.

Behavioral analysis of stress controllability effects in a new swim stress paradigm

Previous animal stress studies have illustrated the marked impact of coping on subsequent behavior and physiology by using shock as the stressor. The current study evaluates the generality of shock stress controllability effects in a new swim stress paradigm on several dependent measures: behavioral despair, analgesia, shuttlebox escape, and alcohol reactivity. In this new paradigm, rats in the escape group are able to learn the behavioral response as evidenced by significant reduction in the acquisition of a lever press response. Both escape and yoked subjects showed "behavioral despair" in comparison to both restrained and home cage controls when tested 24 h later. In the standard shuttlebox escape task 24-h post-stress, no group differences emerged, although a trend for poorer performance in the yoked subjects was evident. No group differences were observed in pain sensitivity after the first or second forced swim exposure. Finally, stress controllability effects were observed in behavioral reactivity to alcohol 2-h post-stress as measured by rotarod performance. This effect is opposite to the previous observations with the tailshock stress controllability paradigm. These results suggest that (1) there are certain similarities, but some fundamental differences between the behavioral endpoints measured following intermittent swim stress in comparison to the well-established effects of the intermittent tailshock stress model and (2) the qualitative nature of a stressor may markedly influence the behavioral and physiological consequences of stress and coping.

The effect of stressor controllability on stress-induced neuropeptide mRNA expression within the paraventricular nucleus of the hypothalamus

Many stressors elicit changes in corticotrophin (CRH), enkephalin (ENK), and neurotensin (NT) mRNA levels within the medial parvocellular region of the paraventricular nucleus of the hypothalamus (mpPVN), and the pattern of changes in mRNA levels appears to depend on the physical characteristics of the stressor. We questioned whether psychologically distinct stressors would cause different patterns of neuropeptide mRNA expression within the PVN. Psychologically distinct stressors were created by employing a paradigm of escapable (controllable) vs. non-escapable (yoked) tail shock. An adult male rats could terminate the stress stimulus by performing wheel-turning behaviour; his behaviour also terminated the stress for his yoked partner, who had no control over the termination of the shock. Four h post-stress, brains were collected and processed for in-situ hybridization histochemistry. Tail-shock stress stimulated a significant increase in CRH, ENK, and NT mRNA levels within the mpPVN. The number of CRH identified neurones coexpressing AVP mRNA was also significantly elevated in both stress groups. Moreover, the pattern and magnitude of the stress-induced increases in mRNA was similar in both stress groups. Additionally, no stress-induced changes in CRH mRNA levels were observed in the central nucleus of the amygdala. In sum, two psychologically distinct stressors, escapable vs. yoked tail shock stress, stimulated similar increases in CRH, NT, ENK, and AVP mRNA levels within the mpPVN. These results suggest that physical attributes of a stress, rather than psychological, may be the more important factors in determining the PVN mRNA response.

Increased anxiety of mice lacking the serotonin1A receptor

Brain serotonin (5-HT) has been implicated in a number of physiological processes and pathological conditions. These effects are mediated by at least 14 different 5-HT receptors. We have inactivated the gene encoding the 5-HT1A receptor in mice and found that receptor-deficient animals have an increased tendency to avoid a novel and fearful environment and to escape a stressful situation, behaviors consistent with an increased anxiety and stress response. Based on the role of the 5-HT1A receptor in the feedback regulation of the 5-HT system, we hypothesize that an increased serotonergic neurotransmission is responsible for the anxiety-like behavior of receptor-deficient animals. This view is consistent with earlier studies showing that pharmacological activation of the 5-HT system is anxiogenic in animal models and also in humans.

Analysis of the importance of controllable versus uncontrollable stress on subsequent behavioral and physiological functioning

Original observations of the effects of stress exposure on behavioral, physiological and pathological indices were documented in the mid 1960s [J.B. Overmier, Interference with avoidance behavior: failure to avoid traumatic shock, J. Exp. Psychol. 78 (1968) 340-343 [12]; J.B. Overmier, M.E.P. Seligman, Effects of inescapable shock upon subsequent escape and avoidance learning, J. Comp. Physiol. Psychol. 63 (1967) 28-33 [13]; M.E.P. Seligman, S.F. Maier, Failure to escape traumatic shock, J. Exp. Psychol. 74 (1967) 1-9 [15]; J.M. Weiss, Effects of coping responses on stress, J. Comp. Physiol. Psychol. 65 (1968) 251-260 [18]]. Studies employing the triadic design (e.g. escapable stress, yoked-inescapable stress and no stress) indicated that the deficits following stress exposure were not caused by stress per se, rather the uncontrollability of the stress was the critical determinant. In this paradigm, the first group (escape) receives exposure to an environmental event that it can "control" by performing a behavioral response. Stress control or coping behavior includes the ability to alter the onset, duration, intensity or pattern of an aversive experience [S.F. Maier, M.E.P. Seligman, Learned helplessness: theory and evidence, J. Exp. Psychol.: Gen. 105 (1976) 3-46 [10]]. The second group is "yoked" to its escape partner and receives the identical physical stressor as its escape counterpart, but there is no behavioral response that the yoked subject can make to alter the outcome. The third group (naive) receives no stress exposure and is either restrained in the experimental apparatus or remains in the home cage until subsequent testing. Researchers using this triadic design should be aware of the concerns of certain investigators [R.M. Church, Systematic effect of random error in the yoked control design, Psychol. Bull. 62 (1964) 122-131 [3]; E.A. Wasserman, Response bias in the yoked control procedure, Behav. Brain Sci. 11 (1988) 477-478 [17]] who have raised important issues about the validity of the yoked control design because of the possibility of systematic biases. For example, individual differences in stress reactivity may result in random error in the yoked control group. This point will be addressed further in Section 5. This procedure allows the investigator to analyze the contributions of the importance of psychological dynamics of stress on a variety of dependent measures including: behavioral, pharmacological, neurochemical and immunological indices.

Searching for the biological pathways between stress and health

Population-based, person-specific health surveys, with concomitant biological measures, should provide important information about the processes by which socioeconomic and psychosocial factors embed themselves in human health. Questionnaire responses allow for assessment of the perceived psychosocial environment, but biological measurements will measure the status of the psychoneuroimmunology/ psychoneuroendocrinology (PNI/PNE) pathways and may allow us to identify people who have "adapted" to their stress because of experience, expectations, stoicism, etc. This review sets criteria to evaluate potential physiological markers of chronic stress. Because population health surveys involve a massive number of samples, special consideration must be given to the laboratory analysis method and transportation time of the markers chosen. We reviewed five areas: glycosylated proteins, the immune system, hemostasis peripheral benzodiazepine receptors, and the waist-hip ratio.

Hypothalamic-pituitary-adrenal function in chronic intermittently cold-stressed neonatally handled and non handled rats

Neonatally handled (H) animals, as adults, exhibit lower ACTH and corticosterone (B) responses to a number of acute stressors compared to their non-handled (NH) counterparts. However, little is known about activity within the hypothalamic-pituitary-adrenal (HPA) axis of H and NH animals under conditions of chronic stress. We, therefore, examined HPA function in adult H and NH rats exposed to chronic intermittent cold stress (4 h of 4 degrees C cold a day for 21 days; H CHR and NH CHR) and in control H and NH (H CTL and NH CTL) rats. H CTL and NH CTL animals displayed comparable ACTH and B responses to a single, acute exposure to cold. We found that H CHR animals exhibited lower levels of ACTH, but not B, during the 21st exposure to cold (the homotypic stressor) compared to the first exposure to cold in H CTL; however, ACTH and B levels in NH CHR were not different from those in NH CTL. In contrast, NH CHR animals hypersecreted ACTH and B in response to restraint (the novel, heterotypic stressor) compared to NH CTL and both H groups, whereas H CHR and H CTL animals did not differ in their responses to restraint. These endocrine responses were associated with increased basal median eminence levels of both CRH and AVP in H CHR and NH CHR relative to their control groups (with NH CHR exhibiting the highest absolute levels of each secretagogue), and with decreased glucocorticoid receptor densities in septum of both H CHR and NH CHR. In addition, the expected lower glucocorticoid receptor density in hippocampus and frontal cortex of NH rats compared to H rats was observed. We believe that the difference in glucocorticoid receptor density between H and NH animals in the hippocampus and frontal cortex and the associated differences in secretagogue content in the median eminence are related to the hypersecretion of ACTH and B in the NH CHR relative to the other groups. Furthermore, we hypothesize that an active inhibitory process is involved in the adaptation of HPA responses of H CHR animals to the homotypic stressor, and present a working model of regulation of activity within the CRH/AVP neurons in the PVN.

Opioid footshock-induced analgesia in mice acutely falls by stress prolongation

The application of 80 footshocks (S-80) to mice induces a decrease in nociceptive responses as measured by the tail-flick test, which is opioid mediated as well as prevented by naloxone (10 mg/kg, SC). When the stress is prolonged up to 240 shocks (S-240) (i.e., from 6 min 40 s to 20 min), no analgesia can be seen immediately after the stress. We have examined the two most obvious possibilities, but they do not seem to be responsible for this fact. When morphine (1-5 mg/kg IP) is injected in the S-240 situation, a potentiation of its analgesic effects is seen, so that a desensitization of mu opioid receptors is unlikely. On the other hand, although cortisol (3-30 mg/kg IP) inhibits the analgesic response to S-80, metyrapone (40 and 80 mg/kg IP) and cortexolone (3-18 mg/kg IP) do not cause S-240 to be analgesic. Thus, an increase of endogenous glucocorticoids released during the long-duration stress does not seem responsible for the lack of analgesia after S-240.