Influence of a psychogenic and a neurogenic stressor on several indices of immune functioning in different strains of mice

Differential susceptibility of BALB/c, C57BL/6N, and CF1 mice to photoperiod changes

OBJECTIVE

Circadian disturbances common to modern lifestyles have been associated with mood disorders. Animal models that mimic such rhythm disturbances are useful in translational research to explore factors contributing to depressive disorders. This study aimed to verify the susceptibility of BALB/c, C57BL/6N, and CF1 mice to photoperiod changes.

METHODS

Thermochron iButtons implanted in the mouse abdomen were used to characterize temperature rhythms. Mice were maintained under a 12:12 h light-dark (LD) cycle for 15 days, followed by a 10:10 h LD cycle for 10 days. Cosinor analysis, Rayleigh z test, periodograms, and Fourier analysis were used to analyze rhythm parameters. Paired Student's t test was used to compare temperature amplitude, period, and power of the first harmonic between normal and shortened cycles.

RESULTS

The shortened LD cycle significantly changed temperature acrophases and rhythm amplitude in all mouse strains, but only BALB/c showed altered period.

CONCLUSION

These findings suggest that BALB/c, the preferred strain for stress-induced models of depression, should also be favored for exploring the relationship between circadian rhythms and mood. Temperature rhythm proved to be a useful parameter for characterizing rhythm disruption in mice. Although disruption of temperature rhythm has been successfully documented in untethered mice, an evaluation of desynchronization of other rhythms is warranted.

Stress conditioning in mice: alterations in immunity and tumor growth

The neuroendocrine and autonomic nervous systems are known regulators of brain-immune interaction. However, the functional significance of this interaction under stress is not fully understood. We investigated the effect of a stress paradigm by applying electric foot shock followed by three reminders, on behavior, immune parameters, and lymphoma tumor growth. Male C3H mice were divided into two groups: Group 1-exposed to electric foot shock followed by three reminders, and Group 2-untreated (controls). Sets of mice underwent the elevated plus maze, staircase, and hot plate tests. After foot shock, natural killer (NK) cell activity, and lymphocyte proliferation were measured. In addition, sets of mice were either vaccinated twice with B-cell lymphoma 38C-13 immunoglobulin for determination of anti-idiotype (Id) antibodies in sera, or inoculated with tumor cells and monitored for tumor development and survival time. Mice exposed to electric foot shock followed by the three reminders had higher NK cell activity, levels of anti-Id antibodies, and a higher proliferation rate of splenocytes in response to mitogens, than the control mice. The exposed mice also showed attenuated tumor growth. Thus, the stress paradigm inhibited tumor development and lead to some immune changes that were not accompanied by behavioral changes.

Strain-specific outcomes of repeated social defeat and chronic fluoxetine treatment in the mouse

Social stress is a risk factor for affective disorders in vulnerable individuals. Although the biological nature of stress susceptibility/resilience remains to be elucidated, genetic variation is considered amongst the principal contributors to brain disorders. Furthermore, genetic predisposition may be determinant for the therapeutic outcome, as proposed for antidepressant treatments. In the present studies we compared the inherently diverse genetic backgrounds of 2 mouse strains by assessing the efficacy of a chronic antidepressant treatment in a repeated social stress procedure. C57BL/6J and BalbC mice underwent 10-day social defeats followed by 28-day fluoxetine treatment (10 mg/kg/mL, p.o.). In C57BL/6J, most of the social defeat-induced changes were of metabolic nature including persistently altered feed efficiency and decreased abdominal fat stores that were ameliorated by fluoxetine. BalbC mouse behavior was persistently affected by social defeat both in the social avoidance and the forced swim tests, and in either procedure it was restored by chronic fluoxetine, whereas their endocrine parameters were mostly unaffected. The highlighted strain-specific responsivity to the metabolic and behavioral consequences of social defeat and to the chronic antidepressant treatment offers a promising research tool to further explore the underlying neural mechanisms and genetic basis of stress susceptibility and treatment response.

Patterns of immunotoxicity associated with chronic as compared with acute exposure to chemical or physical stressors and their relevance with regard to the role of stress and with regard to immunotoxicity testing

Previous studies have demonstrated that the stress response induced by some drugs and chemicals contributes in a predictable way to alteration of particular immunological parameters in mice. It has not been determined if mice can become tolerant or habituated with regard to the stress response and consequent immunological effects. Addressing this issue was the purpose of the present study. Mice were dosed daily for 28 days with atrazine, ethanol, propanil, or subjected to restraint, which are known to induce neuroendocrine stress responses and thereby to alter several immunological parameters. On day 29, a blood sample was taken and the spleen was removed for analysis of cellular phenotypes, differential cell counts (for blood), and natural killer (NK) cell activity. Corticosterone concentration at various times after dosing (or restraint) was also measured. Comparison of these results with results from previous studies with a single acute exposure revealed that the corticosterone response was almost completely absent in mice treated with ethanol, reduced in mice treated with restraint and propanil, and for atrazine the response was the same as noted for acute exposure. In most cases, the changes in immunological parameters were consistent with expectations based on these corticosterone responses. However, in a few cases (e.g., NK cell activity), it was clear that there were effects not mediated by stress. These results indicate that the nature of the stressor determines whether mice become tolerant with regard to the stress response and consequent immunological effects. This finding has practical implications for safety testing in mice.

Effects of repetitive stress during the acute phase of Trypanosoma cruzi infection on chronic Chagas' disease in rats

The effect of repetitive stress during acute infection with Trypanosoma cruzi (T. cruzi) on the chronic phase of ensuing Chagas' disease was the focus of this investigation. The aim of this study was to evaluate in Wistar rats the influence of repetitive stress during the acute phase of infection (7 days) with the Y strain of T. cruzi on the chronic phase of the infection (at 180 days). Exposure to ether vapor for 1 min twice a day was used as a stressor. Repetitive stress enhanced the number of circulating parasites and cardiac tissue disorganization, from a moderate to a severe diffuse mononuclear inflammatory process and the presence of amastigote burden in the cardiac fibers. Immunological parameters revealed that repetitive stress triggered a reduced concanavalin A induced splenocyte proliferation in vitro with major effects on the late chronic phase. Serum interleukin-12 concentration decreased in both stressed and infected rats in the early phase of infection although it was higher on 180 days post-infection. These results suggest that repetitive stress can markedly impair the host's immune system and enhance the pathological process during the chronic phase of Chagas' disease.

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.

Central mechanisms of HPA axis regulation by voluntary exercise

Stress exerts complex effects on the brain and periphery, dependent on the temporal profile and intensity of the stressor. The consequences of a stressful event can also be determined by other characteristics of the stressor, such as whether it is predictable and controllable. While the traditional view has focused primarily on the negative effects of stress on a variety of somatic systems, emerging data support the idea that certain forms of stress can enhance cellular function. Here we review the current literature on the hypothalamic-pituitary-adrenal (HPA) axis regulation by wheel running, a voluntary and controllable stressor with a distinct temporal profile. While running indeed activates a number of systems related to the stress response, other mechanisms exist to reduce the reactivity to this stressor, with possible crosstalk between running and other forms of stress.

Circadian dependence of corticosterone release to light exposure in the rat

Previous studies have demonstrated a positive correlation between glucocorticoid levels and circadian reentrainment time following a shift in the light:dark (LD) cycle. We conducted a series of experiments to examine the circadian dependence of the corticosterone (CORT) response to light. Exp. 1 measured CORT release in rats exposed to light at six timepoints. Light presented during the subjective night increased CORT (p<0.05), while light presented during the subjective day did not. In Exp. 2, we documented the time course of the CORT response to light in entrained animals. Rats exposed to light at zeitgeber time (ZT) 18 had a maximal increase in CORT levels following 60 min of stimulus presentation (p<0.05). There was also an increase in adrenocorticotropic hormone following 15 min of light at ZT18 (p<0.05). In an effort to elucidate the effect of changes in the LD cycle on the circadian profile of CORT, Exp. 3 followed the CORT rhythm (in cerebrospinal fluid) of rats prior to and following a shift in the LD cycle. The CORT nadir was elevated following a 6 h photic advance (p<0.05), as was the mean CORT concentration during the peak phase (p<0.05). Most components of the circadian CORT rhythm, however, failed to show an immediate shift towards the change in the light cycle. Together, these data support the hypothesis that a photic phase-shift results in elevated CORT levels, while the rhythm of CORT secretion is robust against changes in the photic environment.

Stress and prolactin effects on bone marrow myeloid cells, serum chemokine and serum glucocorticoid levels in mice

OBJECTIVE

Current evidence supports the conclusion that prolactin (PRL) is not an obligate immunoregulatory hormone and influences the immune system predominantly during stress conditions. In this study, we examined the impact of PRL on the psychogenic stress-induced responses of myeloid cells.

METHODS

Seven-week-old PRL+/- (normal) and PRL-/- (deficient) mice were exposed to a predator for 1 h/day on 3 consecutive days. Another group of PRL-deficient mice received either 1 pituitary graft (hyperprolactinemic) or sham surgery at 5 weeks of age, while PRL-normal mice only received sham surgery. Two weeks later, these mice were also subjected to predator exposure. One day after the last predator exposure session, all mice were killed and the bone marrow and blood harvested.

RESULTS

Significant differences in the myeloid cells between PRL-normal and PRL-deficient mice only occurred in stressed conditions. The median serum corticosterone levels were consistently higher in PRL-deficient mice. The implantation of a pituitary graft lowered the corticosterone levels to those observed in PRL-normal mice. The absolute number of immature neutrophils as well as the numbers of granulocyte macrophage, monocyte/macrophage and granulocyte colonies were significantly higher in the stressed PRL-deficient mice; however, only the increased number of immature neutrophils was reversed by pituitary grafting.

CONCLUSIONS

Our findings support previous observations that PRL influences myeloid cells of the bone marrow most profoundly in stressed conditions. However, the mechanism by which PRL influences bone marrow myeloid cells during stress cannot be explained solely by its effect on serum corticosterone.

Recent progress in animal modeling of immune inflammatory processes in schizophrenia: implication of specific cytokines

Epidemiologic studies demonstrate significant environmental impact of maternal viral infection and obstetric complications on the risk of schizophrenia and indicate their detrimental influences on brain development in this disorder. Based on these findings, animal models for schizophrenia have been established using double stranded RNA, bacterial lipopolysaccharides, hippocampal lesion, or prenatal/perinatal ischemia. Key molecules regulating such immune/inflammatory reactions are cytokines, which are also involved in brain development, regulating dopaminergic and GABAergic differentiation, and synaptic maturation. Specific members of the cytokine family, such as interleukin-1, epidermal growth factor, and neuregulin-1, are induced after infection and brain injury; therefore, certain cytokines are postulated to have a central role in the neurodevelopmental defects of schizophrenia. Recently, to test this hypothesis, a variety of cytokines were administered to rodent pups. Cytokines administered in the periphery penetrated the immature blood-brain barrier and perturbed phenotypic neural development. Among the many cytokines examined, epidermal growth factor (or potentially other ErbB1 ligands) and interleukin-1 specifically induced the most severe and persistent behavioral and cognitive abnormalities, most of which were ameliorated by antipsychotics. These animal experiments illustrate that, during early development, these cytokine activities in the periphery perturbs normal brain development and impairs later psychobehavioral and/or cognitive traits. The neurodevelopmental and behavioral consequences of prenatal/perinatal cytokine activity are compared with those of other schizophrenia models and cytokine interactions with genes are also discussed in this review.

Effect of electric foot shock and psychological stress on activities of murine splenic natural killer and lymphokine-activated killer cells, cytotoxic T lymphocytes, natural killer receptors and mRNA transcripts for granzymes and perforin

To explore the mechanism of stress-induced inhibition of natural killer (NK) activity, female C57BL/6 mice were stimulated by electric foot shock and psychological stress for 7 days consecutively. The shocked mice received scrambled, uncontrollable, inescapable 0.6 mA electric shocks in a communication box 120 times during 60 min. The mice in the psychological stress group were put into the communication box without electric foot shock. The plasma corticosterone level in both stressed groups was significantly higher than that in controls on days 1, 3, 5 and 7 and showed the highest level on day 3 in the foot shock stress. According to these results, therefore, we investigated the effect of stress on immunological function on day 3, and measured body weight, weight of the spleen, number of splenocytes, splenic NK, lymphokine-activated killer (LAK) and cytotoxic T lymphocyte (CTL) activities, NK receptors, and mRNA transcripts for granzymes A and B and perforin in splenocytes. The NK, LAK and CTL activities, and NK receptors in mice with both types of stress were significantly decreased compared to those of the control mice, but the decreases were greater in the foot-shocked mice than in the psychological-stress mice. The mRNA transcripts for granzyme A and perforin were significantly decreased only in the foot-shocked mice. On the other hand, the foot-shock stress increased granzyme B. The above findings suggest that stress induced inhibition of NK, LAK and CTL activities partially via affecting NK receptors, granzymes and perforin.

Environmental enrichment in mice decreases anxiety, attenuates stress responses and enhances natural killer cell activity

The importance of environment in the regulation of brain, behaviour and physiology has long been recognized in biological, social and medical sciences. Animals maintained under enriched conditions have clearly been shown to have better learning abilities than those maintained under standard conditions. However, the effects of environmental enrichment (EE) on immunity and emotionality have been less documented and remain questionable. Therefore, we investigated the effect of EE on natural killer (NK) cell activity, psychological stress responses and behavioural parameters. Male C3H mice were housed either in enriched or standard conditions for 6 weeks. Behaviour was then examined by the grip-strength test, staircase and elevated plus maze, and corticosterone levels and NK cell activity were measured. Furthermore, animals exposed to the stress paradigm, achieved by electric shock with reminders, were tested for freezing time in each reminder. Corticosterone levels were also measured. The EE mice showed decreased anxiety-like behaviour and higher activity compared to standard mice, as revealed by a greater percentage of time spent in the open arms of the elevated plus maze, and a higher rate of climbing the staircase. A shorter freezing time in the stress paradigm and no corticosterone level reactivity were measured in EE mice. In addition, NK cell activity in spleens of EE mice was higher than that demonstrated in those of standard mice. Thus, EE has a beneficial effect on anxiety-like behaviour, stress response and NK cell activity. The effect on NK cell activity is promising, due to the role of NK cells in host resistance.

Stress-induced suppression of in vivo splenic cytokine production in the rat by neural and hormonal mechanisms

The mechanisms mediating the effects of stress on immune function have yet to be fully described. In vitro studies have demonstrated a role for both the sympathetic nervous system (SNS) and the hypothalamic pituitary adrenal axis (HPAA) in regulating immune responses following exposure to various stressors. The purpose of the present set of experiments was to determine the in vivo contribution of the HPAA and SNS in regulating the effects of stress on lipopolysaccharide (LPS) induced splenic cytokine production. For this, rats with combinations of sham surgeries, splenic nerve cuts (SNC), and adrenalectomies (ADX) were exposed to 15 min of 1.6 mA intermittent footshock immediately following the intravenous (i.v.) injection of 0.1 microg of LPS. Although footshock was immunosuppressive to most indices of cytokine production, neither SNC nor ADX alone blocked the effects of stress on splenic immune function. However the combination of these two manipulations significantly abrogated the immunosuppressive effects of stress on cytokine production. Adrenal demedullation of animals with a SNC demonstrated that the SNS, not the HPAA, was primarily responsible for the immunosuppressive effects of stress.

Immune changes during acute cold/restraint stress-induced inhibition of host resistance to Listeria

Experiments were conducted to delineate the cellular changes modulated by acute cold/restraint stress (ACRS), a physical and psychological stressor, in response to a Listeria monocytogenes(LM) infection. In addition to wild type (WT) BALB/c mice, CD4-deficient (CD4-/-) BALB/c mice, which have no effective adaptive immunity, were used to determine the involvement of adaptive versus innate immunity. ACRS-induced suppression of host resistance to LM was not observed in CD4-/- mice, suggesting the involvement of CD4+T cells in the acute cold/restraint stress (ACRS)-induced inhibition. The in vivo splenic leukocyte phenotypes and activities of WT BALB/c mice after infection and in vitro lymphocyte responses to heat-killed LM (HKLM) also were examined. There were no significant differences in the numbers of splenic T and B lymphocytes, natural killer cells, macrophages, or neutrophils between nonstressed and ACRS-treated WT mice. However, higher levels of activated T cells and non-T lymphocytes were observed in the ACRS-treated mice; beta-adrenergic receptor (beta-ADR) antagonists (propranolol and atenolol) eliminated these elevated levels of activation, as well as the ACRS-induced suppression of host resistance. ACRS and control mice also had equivalent activation of macrophages. With in vitro HKLM stimulation, splenocytes from ACRS-treated mice produced significantly higher levels of IFNgamma and slightly higher levels of IL-6 in comparison with the nonstressed mice, although equivalent levels of lymphocyte proliferation were obtained. Additionally, ACRS-treated mice showed comparable elevation of serum nitric oxide after infection, indicating macrophage bactericidal activity similar to nonstressed mice. Thus, it appears that ACRS inhibits host resistance through regulatory CD4+ T cells and/or effector cell functions downstream of CD4+ T cell activation, as well as through beta-ADR signaling, in that blockage of these receptors appears to aid host defenses by means other than elevation of helper T cell activity. Because CD4 T cell deficiency and beta-ADR blockage produced equivalent effects, beta-ADR+ CD4+ T cells may have a negative role on host defenses after ACRS.

The effect of emotional stress on the primary humoral immunity of rats

The effect of exposure to emotional stress on humoral immune function after injection with ovalbumin, a novel antigen, was studied in adult male Wistar rats. Emotional stress was induced by randomly giving empty water bottles to rats trained to drink water at set times. The results showed that emotional stress induced the decrease in spleen weight and specific immunoglobulin G antibody level to ovalbumin, and increased levels of epinephrine, norepinephrine and corticosterone. A decrease of antibody levels correlated negatively with an increase in plasma norepinephrine levels. These findings suggest that emotional stress can modulate immune function, and that sympathetic nervous system may be involved in this immunomodulation.

Stress and the immune system

Stressors can positively or adversely affect immune and inflammatory responses. However, the current understanding of these effects at the cellular and molecular levels is not sufficient to allow prediction of the effects of a particular stressor on a particular immune or inflammatory function. Three complementary conceptual frameworks are presented that may prove useful in developing such an understanding. In addition, specific examples of the action of particular stress mediators on particular immune or inflammatory end points are discussed, and the relationship of these observations to the conceptual frameworks is indicated. Several of the effects discussed are relevant clinically, and the prospects for pharmacological intervention to prevent adverse effects of stressors on the immune system are discussed. Finally, some of the factors that can (sometimes unexpectedly) influence the outcome of stress-immunology studies and some of the pitfalls that continue to make this area of research controversial in some circles are discussed.

Stress, immunity, cytokines and depression

The current issue of Acta Neuropsychiatrica presents a series of papers which together provide a broad overview relating stress, immunity, cytokine activity and depressive illness, as well as the influence of cytokines on other neurological disorders. This introduction to the issue presents a broad perspective of the impact of stressors on immune functioning in animal studies and in humans, considering the potential effects of acute, subchronic and chronic stressors, as well as the contribution of previous stressor experience in promoting neurochemical and immunological alterations. Given the supposition that cytokines may act as immunotransmitters, and immune challenge may be viewed as a stressor, a brief review is provided concerning the impact of stressors and cytokine challenges on central neurochemical functioning, with particular emphasis on the commonalties between the effects of these treatments. It is suggested that by virtue of the neurochemical changes imparted by cytokines, a depressive affect may be instigated, just as it is in response to psychogenic stressors. To this end, an overview is presented concerning the relationship between cytokines and depression, as well as the influence of cytokine treatments on behavioral changes in animal studies and among patients receiving immunotherapy. Provisionally, the data support the view that activation of the inflammatory response system may contribute to affective illness, and that cytokines may act as signaling molecules to activate central nervous system processes regulating mood states.

Stressor-induced modulation of immune function: a review of acute, chronic effects in animals

The present paper reviews recent studies on the effects of stress on immune function in laboratory animals. The emphasis is on those studies where a simultaneous comparison of acute and chronic stress regimens was determined, although additional relevant studies are also reviewed. The effects of stress on basic measurements of cellular and humoral immune measures are discussed, including the growing number of studies that have reported alterations in macrophage functions. The latter are key elements in the innate immune response, and like measurements of T cell function and antibody production, are inhibited and enhanced by stressor exposure. This review does not focus on the mechanisms by which stress alters immune function, there being little to add conceptually in terms of what was reported previously (see Kusnecov AW, Rabin BS, Int Arch Allergy Immunol 1994;105:107-121.). However, a question is raised in the conclusion as to how stressor effects on immune function should be interpreted, for it is clear that immunological processes in and of themselves elicit central nervous system responses that neurochemically and endocrinologically do not differ from those produced in response to psychological stressors. Therefore, at least in the short term stressor-induced immune changes may not necessarily reflect maladaptive adjustments, although, as demonstrated by some studies reviewed in this paper, they may pose a serious risk to health should stressor exposure be persistent and uncontrolled.

Suppression of host resistance to Listeria monocytogenes by acute cold/restraint stress: lack of direct IL-6 involvement

We conducted kinetic studies to evaluate the effects of acute cold/restraint stress (ACRS) on both primary and secondary host resistance to Listeria monocytogenes (LM). The involvement of IL-6 also was investigated using IL-6 knockout (KO) mice on the BALB/c background. ACRS dramatically increased the serum corticosterone levels, indicating that ACRS activated the hypothalamic-pituitary-adrenal (HPA) axis. ACRS significantly inhibited host resistance to LM during a primary but not a secondary LM infection. During the primary infection, ACRS caused a significant delay in clearance of LM, loss of body weight, reduced food/water intake, and elevated levels of pro-inflammatory cytokines (IL-6, IL-1beta, and TNFalpha) and IFNgamma. ACRS IL-6 KO mice showed higher LM burdens than did IL-6 KO controls, suggesting that IL-6 is not required for the ACRS-impairment of host resistance. Elevated levels of IL-1beta and TNFalpha may compensate for the absence of IL-6 and maintain the ACRS-induced impairment, in that the serum and splenic IL-1beta and TNFalpha levels were significantly higher in infected ACRS IL-6 KO mice, but not in control IL-6 KO mice, as compared to respective wild type controls. ACRS appears to inhibit IL-6 independent mechanisms associated with innate immunity and/or the development of adaptive immunity, but these reactions are unable to modulate the more efficient secondary immune responses.

NK T cells contribute to expansion of CD8(+) T cells and amplification of antiviral immune responses to respiratory syncytial virus

CD1d-deficient mice have normal numbers of T lymphocytes and natural killer cells but lack Valpha14(+) natural killer T cells. Respiratory syncytial virus (RSV) immunopathogenesis was evaluated in 129xC57BL/6, C57BL/6, and BALB/c CD1d(-/-) mice. CD8(+) T lymphocytes were reduced in CD1d(-/-) mice of all strains, as shown by cell surface staining and major histocompatibility complex class I tetramer analysis, and resulted in strain-specific alterations in illness, viral clearance, and gamma interferon (IFN-gamma) production. Transient activation of NK T cells in CD1d(+/+) mice by alpha-GalCer resulted in reduced illness and delayed viral clearance. These data suggest that early IFN-gamma production and efficient induction of CD8(+)-T-cell responses during primary RSV infection require CD1d-dependent events. We also tested the ability of alpha-GalCer as an adjuvant to modulate the type 2 immune responses induced by RSV glycoprotein G or formalin-inactivated RSV immunization. However, immunized CD1-deficient or alpha-GalCer-treated wild-type mice did not exhibit diminished disease following RSV challenge. Rather, some disease parameters, including cytokine production, eosinophilia, and viral clearance, were increased. These findings indicate that CD1d-dependent NK T cells play a role in expansion of CD8(+) T cells and amplification of antiviral responses to RSV.

Stressful animal housing conditions and their potential effect on sympathetic neurotransmission in mice

Although the sympathetic nervous system (SNS) plays a major role in mediating the peripheral stress response, due consideration is not usually given to the effects of prolonged stress on the SNS. The present study examined changes in neurotransmission in the SNS after exposure of mice (BALB/c) to stressful housing conditions. Focal extracellular recording of excitatory junction currents (EJCs) was used as a relative measure of neurotransmitter release from different regions of large surface areas of the mouse vas deferens. Mice were either group housed (control), isolation housed (social deprivation), group housed in a room containing rats (rat odor stress), or isolation housed in a room containing rats (concurrent stress). Social deprivation and concurrent stressors induced an increase of 30 and 335% in EJC amplitude, respectively. The success rate of recording EJCs from sets of varicosities in the concurrent stressor group was greater compared with all other groups. The present study has shown that some common animal housing conditions act as stressors and induce significant changes in sympathetic neurotransmission.

Central monoamine activity in genetically distinct strains of mice following a psychogenic stressor: effects of predator exposure

The effects of psychogenic stressors, rat exposure and fox urine odor, on central monoamine functioning was assessed in two inbred strains of mice, BALB/cByJ and C57BL/6ByJ, thought to be differentially reactive to stressors. These stressors markedly increased NE utilization, as reflected by MHPG accumulation, in the locus coeruleus, hippocampus, prefrontal cortex and central amygdala. Likewise, the 5-HT metabolite, 5-HIAA, was elevated in hippocampus, prefrontal cortex and central amygdala, and to some extent DOPAC accumulation was increased in the prefrontal cortex. In most brain regions, the neurochemical effects of the stressors were comparable in the two mouse strains. However, central amygdala 5-HIAA elevations as well as DOPAC increases in the prefrontal cortex elicited by fox odor were greater in C57BL/6ByJ than in BALB/cByJ mice. Although BALB/cByJ mice are more behaviorally reactive than C57BL/6ByJ mice, and also show greater corticosterone elevations in response to neurogenic and systemic stressors, it was previously shown that differential corticosterone changes were not elicited by a predator exposure. Taken together with earlier findings, it appears that despite greater behavioral reactivity/anxiety, the strain-specific neurochemical changes elicited may be situation-specific such that the profile apparent in response to neurogenic and systemic stressors may not be evident in response to predator-related threats.

Vitamin E enhances the immune functions of young but not old mice under restraint stress

Young and old C57BL/6 male mice were given a diet containing a high dose of vitamin E (VE treatment) and its effect on the immune system was examined before and after the exposure to restraint stress. The VE treatment per se gave rise to a slight increase of splenic T cells in percentage and a significant enhancement of Con A response of spleen cells in young, but not in old mice. The VE treatment also resulted in the enhancement of production of IL-2 and IFNgamma in young, but not in old mice. Restraint stress led to thymic involution in both young and old mice. This thymic involution was not ameliorated by the VE treatment. Percentage of splenic T cells and their mitogenic response decreased just after the stress, but soon rebounded over the control level. The VE treatment further enhanced the recovery after the stress in young mice, but on the contrary suppressed the recovery in old mice. The results in the present study suggested that the VE treatment was effective in the prevention of immunological decline of young mice before and after the exposure to the stress. On the other hand, such a preventive effect was not observed in old mice that were already in the depressed state of immunological functions.

Influence of psychogenic and neurogenic stressors on neuroendocrine and central monoamine activity in fast and slow kindling rats

The central neurochemical and neuroendocrine effects of a psychogenic (ferret exposure) and a neurogenic (restraint) stressor were assessed in rats that had been selectively bred for differences in amygdala excitability manifested by either Fast or Slow amygdala kindling epileptogenesis. While these rat lines differ in their emotionality, their behavioral styles were dependent on the nature of the stressor to which they were exposed. During restraint, the Slow rats were mostly immobile, while Fast rats persistently struggled. In contrast, Fast rats were more immobile in response to the ferret. Yet, the more emotional Slow rats exhibited a greater corticosterone response to the ferret, while comparable corticosterone responses between lines were evident following restraint. Although both stressors influenced norepinephrine (NE), dopamine (DA) and/or serotonin (5-HT) activity in brain regions typically associated with stressors (e.g., locus coeruleus, paraventricular nucleus of the hypothalamus, nucleus accumbens, prefrontal cortex), considerable amine alterations were evident in the medial and basolateral amygdala nuclei, but not in the central nucleus. Moreover, greater NE changes were apparent in the medial amygdala of the left hemisphere. Similarly, DA alterations also were greater in the left medial amygdala in response to stressors. Despite very different behavioral styles, however, the two lines often exhibited similar amine alterations in response to both stressors.

Influence of psychosocial, psychogenic and neurogenic stressors on several aspects of immune functioning in mice

Analysis of stressor effects on immune functioning is complicated by the fact that the nature of the changes observed may be influenced by organismic factors (e.g., species, strain, age), the nature, severity and chronicity of the stressor, as well as the specific immune parameters being examined. It is demonstrated in the present investigation that in the highly reactive inbred BALB/cByJ mouse, the relatively hardy C57BL/6ByJ strain, as well as in the noninbred CD-1 strain, acute psychogenic (predator exposure) and neurogenic (footshock) stressors reduced splenic macrophage activity, and this effect was less marked after a chronic stressor. With protracted, but not transient, psychosocial disturbances (isolated housing) similar effects were seen, suggesting that the effect was not simply due to a change of the social mileau. The psychogenic and neurogenic stressors also enhanced LPS-stimulated lymphocyte proliferation in CD-1, but not in the inbred strains. However, isolated housing reduced both B and T cell proliferation, indicating that social isolation likely affects processes distinct from those of other stressors. Interestingly, when the aversiveness of the psychogenic stressor was increased (by decreasing the distance between the rat and the mouse) LPS-stimulated lymphocyte proliferation was reduced in the reactive BALB/cByJ strain, but increased in the hardy C57BL/6ByJ mice. This stressor, however, enhanced T cell proliferation in both strains of mice. It is suggested that analysis of stressor effects need to consider in greater detail the characteristics of the organism being stressed, as well as the characteristics of the stressor itself.