Amaia Arregi

Time-dependent behavioral, neurochemical, and immune consequences of repeated experiences of social defeat stress in male mice and the ameliorative effects of fluoxetine.

This study attempted to determine whether differing numbers of days of repeated defeat experience altered behavior, immune measures, and neuroendocrine mediators in mice. OF1 male mice were socially stressed by repeated experiences of defeat in a sensorial contact model. Subjects exposed to nine defeats showed more stretch-attend postures and fewer active defense elements than counterparts exposed to 23 defeats. Submissive subjects with nine experiences of defeat also had a lower splenocyte proliferative response than unmanipulated controls. The proliferation index progressively increased but at a higher rate in manipulated controls than in socially stressed subjects, resulting in a significant immunosuppressive effect after 23 days of exposure to social stressors. Nine days of such exposure resulted in higher hypothalamic ratios of serotonin and dopamine to their major metabolites than in unmanipulated or manipulated controls and subjects socially stressed for 23 days. The data generally indicate that the acute social stressors (such as nine defeats) produce a profile of behavioral and physiological variables characteristic of a state of anxiety. The proliferation index was also lower after 52 days of social stress than in manipulated controls. Fluoxetine treatment appeared to have an anxiolytic effect, reducing immobility, and even seemed to protect subjects from the immune impairment and endocrine alteration caused by social stressors. The results generally provide clues that improve our knowledge of the consequences of social stressors and their possible treatment.

Social stress paradigms in male mice: Variations in behavior, stress and immunology

Male OF1 strain mice were allocated, after 2 weeks of individual housing, to cohabitating (6 or 16 days), fixed dyadic interaction pairs (6 or 16 daily encounters) or control groups (6 or 16 days). These different social stress situations were assessed for their effects on splenic contents of NE, IL-1 and IL-2 and serum levels of corticosterone. Spleen NE contents showed no significant variations, but serum corticosterone titers were generally higher in interacting pairs and subordinates. Splenic IL-2 did not respond in the same way to the treatments as IL-1. The differences in splenic interleukin contents could not be simply related to observed changes in serum corticosterone levels. Different mechanisms appear to regulate changes in glucocorticoids and the measured cytokines. These physiological phenomena do not simply reflect in the animals social status (dominant or submissive). The intensity and duration of the agonistic behavior displayed as well as the interaction experience accumulated may account for the observed differences between the paradigms.

Individual differences in chronically defeated male mice: Behavioral, endocrine, immune, and neurotrophic changes as markers of vulnerability to the effects of stress

This study aimed to analyze different behavioral profiles in response to chronic social defeat using the sensorial contact model. We hypothesized that a passive profile, unlike an active one, would be associated with behavioral and physiological characteristics related to depression. Six-week-old OF1 male mice were subjected to defeat for 21 consecutive days. A combination of cluster and discriminant analyses of the behavior exhibited during confrontation on Day 21 established two behavioral profiles: active (n = 22) and passive (n = 34). Passive mice, with a high level of immobility and low non-social exploration, had higher plasma corticosterone concentrations than active mice after 21 days of defeat. Three days after the last defeat, passive mice had lower corticosterone levels than manipulated-control mice (n = 11). Higher levels of interleukin-6 and tumor necrosis factor-α (TNF-α) in the spleen and lower hippocampal brain-derived neurotrophic factor levels were observed in passive mice in comparison with those in active mice and the manipulated controls. The only differences observed in active mice in relation to the manipulated control were higher plasma corticosterone (Day 21) and TNF-α levels. The results show that different behavioral profiles in response to chronic defeat are associated with different physiological profiles, and that the passive profile presents physiological characteristics previously associated with depression.

Behavioral coping strategies in response to social stress are associated with distinct neuroendocrine, monoaminergic and immune response profiles in mice.

Individual variation in behavioral coping strategies to stress implies that animals may have a distinct physiological adaptation to stress; these differences may underlie differences in vulnerability to stress-related diseases. This study was designed to test the hypothesis that different behavioral coping strategies (active vs. passive) are stable over time and that they would be associated with differences in hypothalamic-pituitary-adrenal (HPA) and sympathetic-adreno-medular (SAM) axes, and monoaminergic and immune activity. Male mice were subjected to social stress. Twelve days after the first social interaction, mice were subjected to a second identical social stress interaction. Behavior was videotaped and assessed during both sessions. One hour after the final social interaction, serum was collected for corticosterone and adrenaline concentrations and brains were collected for hypothalamic corticotrophin-releasing hormone (CRH) mRNA expression. Monoaminergic system activity was determined by mRNA expression of serotonin, dopamine and noradrenaline synthetic enzymes in the brain stem. Immune system activity was determined by mRNA expression of hypothalamic interleukin-1β (IL-1β) and splenic IL-1β and interleukin-2 (IL-2). Mice engaging in a passive strategy had higher serum corticosterone and lower serum adrenaline concentrations than the active group. The passive group showed lower hypothalamic mRNA expression of IL-1β and CRH and lower splenic mRNA expression of IL-2 and IL-1β relative to mice in the active group. An active strategy was associated with higher expression of the dopaminergic synthetic enzyme, while a passive strategy was associated with decreased expression of the serotonergic synthetic enzyme. These findings indicate that individual coping strategies are stable over time and are related to differences in the physiological stress response and immune activity.

Behavioral and neurochemical responses in mice bearing tumors submitted to social stress

Through the proinflammatory cytokines secreted in response to inflammation or injury, the immune system produces physiological and behavioral alterations. This study analyzes the effects on behavior, mononuclear proliferative response and central monoamine activity in response to the inoculation of tumor cells in mice submitted to social stress. Two groups of male OF1 mice were used, one of which was inoculated with B16 melanoma cells. Both groups were subdivided into two new groups, with one being submitted to social stress through sensory contact model with a selected aggressive subject, and the other being handled without social interaction. Subjects were exposed to social stress for a 24-h period, with three 5 min intervals of direct physical interaction, where the behavior was recorded and assessed. One hour after the stress and/or handling, they were put down and samples taken for physiological assessment. Significant behavioral changes were found in subjects with implanted tumors, mainly characterized by an increase in avoidance behavior and a decrease in immobility, defense-submission and non-social exploration behavior, coupled with an increase in the spleen mononuclear cell proliferative response. Similarly, an increase was observed in the density of dopamine(2) (D(2))-receptors in the striatum (SRT) and an increase in dopaminergic (DOPAC/DA) and serotonergic (5HIAA/5HT) turnover in the hypothalamus. The increase in the density of D(2)-receptors in the SRT coincides with the decrease in some behaviors with a predominant motor component. The results indicate significant changes in the defensive strategy used to cope with situations of intense social stress in mice bearing tumors.

Coping with Chronic Social Stress in Mice: Hypothalamic-Pituitary-Adrenal/ Sympathetic-Adrenal-Medullary Axis Activity, Behavioral Changes and Effects of Antalarmin Treatment: Implications for the Study of Stress-Related Psychopathologies

The aim of this study was to analyze the individual differences that lead to the development of psychopathological changes in response to chronic social stress. We also assessed the ability of an antagonist of the corticotrophin-releasing hormone (CRH) receptors to reverse the effects of stress. Male adult mice were exposed to repeated defeat experiences for 21 days using a sensorial contact model. After 18 days of defeat, two groups of subjects were established (active and passive), according to their behaviors during social confrontation. Antalarmin treatment was given for 4 and 6 days. The results corroborated previous data indicating that subjects who adopted a passive coping strategy had higher corticosterone levels after 21 days of defeat and decreased resting levels 3 days later. Moreover, they showed higher resting expression levels of hypothalamic CRH than their active counterparts. On day 24, the experimental animals were subjected to another social defeat to determine whether the stress response remained. The increase in corticosterone and hypothalamic CRH levels was similar for all of the stressed subjects, but the passive subjects also had a greater CRH response in the amygdala. Passive subjects had decreased levels of adrenal dopamine β-hydroxylase, tyrosine hydroxylase and plasma adrenaline compared to the active subjects, and lower plasma noradrenaline levels than manipulated controls. The passive profile of physiological changes in both the hypothalamic-pituitary-adrenal and sympathetic-adrenal-medullary (SAM) axes has been associated with changes related to mood disorders, such as posttraumatic stress disorder and depression. The active coping profile is characterized by similar corticosterone resting levels to controls and increased SAM activity. Both profiles showed alterations in the novel palatable and forced swimming tests, with the passive profile being the most vulnerable to the effects of stress in this last test. Pharmacological treatment with antalarmin failed to reverse the effects of stress.

Effects of a putative antidepressant with a rapid onset of action in defeated mice with different coping strategies

There is evidence suggesting that stressful social events may result in depressive-like disorders, but the development of these disorders depend on the way in which people cope with stress. Although antidepressants are useful their drawback is a delay in the therapeutic effects, moreover not all the patients show an adequate response to this treatment. The aim of this study was to analyse the effect of RS 67333, which is a 5-HT(4) receptor partial agonist and a putative antidepressant which exhibits a rapid onset of action and to determine whether this drug reverses the behavioural and physiological effects that are generated by chronic defeat in subjects who manifest a more vulnerable profile in their response to stress. Male mice were exposed to defeat for 21 consecutive days using a sensorial contact model. After 18 days of defeat, 2 groups of subjects were established, active and passive, in accordance with the behaviour that was manifested during social confrontation, and drug treatment was initiated for 5 days. Finally, the animals were subjected to a forced swimming test (FST). The results revealed higher corticosterone levels in passive mice after the last defeat. Additionally, 3 days after the last defeat, they showed lower corticosterone levels and higher splenic IL-6 and TNF-α levels and hypothalamic GR mRNA levels when compared to their active and manipulated control counterparts. Passive mice had higher 5-HT(1A) receptor mRNA levels than the manipulated controls and a lower MR/GR ratio than active mice. Similar to stress, the drug increased hypothalamic GR mRNA levels, but it did not affect other measured physiological variables or social behaviour, which suggested that the mechanism of this drug is not the most adequate for reversing stress-induced effects in this model. Nevertheless, the treatment increased swimming and decreased immobility in the FST, suggesting an antidepressant potential for this drug.

Melanoma tumors alter proinflammatory cytokine production and monoamine brain function, and induce depressive-like behavior in male mice.

Depression is a commonly observed disorder among cancer patients; however, the mechanisms underlying the relationship between these disorders are not well known. We used an animal model to study the effects of tumor development on depressive-like behavior manifestation, proinflammatory cytokine expression, and central monoaminergic activity. Male OF1 mice were inoculated with B16F10 melanoma tumor cells and subjected to a 21-day behavioral evaluation comprising the novel palatable food (NPF) test and tail suspension test (TST). The mRNA expression levels of proinflammatory cytokines, interleukin (IL)-1β and IL-6, and tumor necrosis factor-alpha (TNF-α), were measured in the hypothalamus and hippocampus and the levels of IL-6 and TNF-α were measured in the blood plasma. We similarly determined the monoamine turnover in various brain areas. The tumors resulted in increasing the immobility in TST and the expression level of IL-6 in the hippocampus. These increases corresponded with a decrease in dopaminergic activity in the striatum and a decrease in serotonin turnover in the prefrontal cortex. Similarly, a high level of tumor development produced increases in the brain expression levels of IL-6 and TNF-α and plasma levels of IL-6. Our findings suggest that these alterations in inflammatory cytokines and monoaminergic system function might be responsible for the manifestation of depressive-like behaviors in tumor-bearing mice.

Effects of antalarmin and nadolol on the relationship between social stress and pulmonary metastasis development in male OF1 mice

It has been found that acute social stress in male OF1 mice produced a general immunosuppression and increased B16F10 tumor development. This study examined the effects of blocking either the hypothalamic-pituitary-adrenocortical (HPA) axis or the sympathetic adrenomedullary (SAM) system on the impact of such stress on tumor development. Naive male OF1 mice were individually housed for 12 days before being inoculated with tumor cells or vehicle. Six days later, tumor-bearing mice were inoculated with antalarmin (a corticotropin-releasing factor receptor antagonist), nadolol (a beta-adrenergic antagonist) or vehicle. All these mice were subjected to social stress by pairing them for 24h with counterparts selected for their high and homogeneous levels of aggressiveness. The pairs were only in physical contact for three 5-min periods, being in sensory contact for the rest of this period. One hour after social stress, serum corticosterone and IFN-gamma levels were analyzed in each experimental group. Fifteen days later, lungs were removed to determine the number of metastatic foci with their areas, and blood samples were taken to assess serum titers of corticosterone and IFN-gamma. Both antalarmin and nadolol-treated mice developed significantly fewer metastatic foci with smaller areas than vehicle-treated subjects although only the group treated with antalarmin had reduced corticosterone levels. This study confirms that social stress has complex effects on immune system and tumor development that are not simply linked to corticosterone titers.

Reduced hippocampal IL-10 expression, altered monoaminergic activity and anxiety and depressive-like behavior in female mice subjected to chronic social instability stress

Evidence indicates that release of pro-inflammatory cytokines induced by social stress contributes to affective disorders. Additionally, there are known sex differences in both the stress response and the stressors that can elicit this response. In this regard, the chronic social instability (CSI) rodent model of stress appears to be the best fit for the social nature of females. This study analyzed the effects of CSI on female mouse behavior, hippocampal cytokine expression, tryptophan metabolism and monoaminergic activity. The activity of hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes were also measured. Results showed a decrease in sucrose consumption in stressed subjects, indicative of anhedonic behavior and an increase in climbing activity in the forced swimming test (FST) and in whisking behavior, which have been associated with anxiety. Decreased interleukin-10 (IL-10) expression was found in the hippocampus of the stressed mice, while no differences in pro-inflammatory cytokine expression and tryptophan (TRYP), kynurenine (KYN) or 3-hydroxy kynurenine (3-HK) levels were found. Increased hippocampal serotoninergic and noradrenergic activity was observed in stressed mice. The higher plasma corticosterone and lower hypothalamic glucocorticoid receptor (GR) expression levels showed an increase in HPA activity after CSI. No differences were found in the plasma estradiol levels or the central estrogen receptors (ERα and ERβ) expression levels. These data indicate that the CSI stress-induced behavioral and physiological changes associated with anxiety and depressive disorders. Although additional studies are warranted, the results suggest an involvement of anti-inflammatory cytokines in the biobehavioral effects of social stress in female mice.