Influence of chronic unpredictable stress on the allergic responses in rats

Neuroscience and treatment of asthma, new therapeutic strategies and future aspects

AIMS

Asthma is an airway inflammatory disease that is affected by neurological and psychological factors. The aim of present review is to investigating the relationship between neural functions and neurobiological changes and asthma symptoms.

MAIN METHODS

The information in this article is provided from articles published in English and reputable database using appropriate keywords from 1970 to October 2020.

KEY FINDINGS

The symptoms of asthma such as cough, difficult breathing, and mucus secretion get worse when a person is suffering from stress, anxiety, and depression. The function of the insula, anterior cingulate cortex, and hypothalamic-pituitary-adrenal axis changes in response to stress and psychological disease; then the stress hormones are produced from neuroendocrine system, which leads to asthma exacerbation. The evidence represents that psychological therapies or neurological rehabilitation reduces the inflammation through modulating the activity of neurocircuitry and the function of brain centers involved in asthma. Moreover, the neurotrophins and neuropeptides are the key mediators in the neuro-immune interactions, which secrete from the airway nerves in response to brain signals, and they could be the target of many new therapies in asthma.

SIGNIFICANCE

This review provides an insight into the vital role of the central and peripheral nervous system in development and exacerbation of asthma and provides practical approaches and strategies on neural networks to improve the airway inflammation and asthma severity.

Unpredictable Chronic Stress Alters Adenosine Metabolism in Zebrafish Brain

Stress is considered a risk factor for several human disorders. Despite the broad knowledge of stress responses in mammals, data on the relationship between unpredictable chronic stress (UCS) and its effects on purinergic signaling are limited. ATP hydrolysis by ectonucleotidases is an important source of adenosine, and adenosine deaminase (ADA) contributes to the control of the nucleoside concentrations. Considering that some stress models could affect signaling systems, the objective of this study was to investigate whether UCS alters ectonucleotidase and ADA pathway in zebrafish brain. Additionally, we analyzed ATP metabolism as well as ada1, ada2.1, ada2.2, adaL, and adaasi gene expression in zebrafish brain. Our results have demonstrated that UCS did not alter ectonucleotidase and soluble ADA activities. However, ecto-ADA activity was significantly decreased (26.8%) in brain membranes of animals exposed to UCS when compared to the control group. Quantitative reverse transcription PCR (RT-PCR) analysis did not show significant changes on ADA gene expression after the UCS exposure. The brain ATP metabolism showed a marked increase in adenosine levels (ADO) in animals exposed to UCS. These data suggest an increase on extracellular adenosine levels in zebrafish brain. Since this nucleoside has neuromodulatory and anxiolytic effects, changes in adenosine levels could play a role in counteracting the stress, which could be related to a compensatory mechanism in order to restore the homeostasis.

Cohabitation with a sick partner increases allergic lung inflammatory response in mice

The bidirectional relationship between the nervous system and the immune system is relevant for homeostatic organism maintenance. Studies from our laboratory showed that 14days of cohabitation with a sick partner (injected with Ehrlich tumor cells-TAE) produced behavioral, neurochemical, endocrinological and immunological changes. This study analyzes the effects of cohabitation with an Ehrlich tumor-bearing animal on ovalbumin (OVA)-induced lung inflammatory response in mice. Pairs of male mice were divided into three groups: naïve, control and experimental. Animals of the naïve group were kept undisturbed being used for the assessment of basal parameters. One animal of each experimental and control pair of mice was immunized with OVA. On ED(0), these OVA-immunized animals received an OVA booster. At this day (D(0)) the experimental mice that were kept undisturbed were inoculated with 5×10(6) Ehrlich tumor cells; their immunized cage-mates were then referred as to CSP ("companion of sick partner"). The undisturbed mice of each control pair were i.p. treated on D(0) with 0.9% NaCl; their sensitized cage-mates were subsequently referred as CHP ("companion of health partner"). The OVA challenge was performed on CSP and CHP mice on ED(12) and ED(13); blood and tissue collection were performed on ED(14). Fourteen days after cohabitation, in comparison to the CHP mice, the CSP mice displayed the following: (1) an increased number of eosinophils and neutrophils in the BAL, (2) a decreased bone marrow cell count, (3) increased levels of IL-4 and IL-5 and decreased levels of IL-10 and IFN-γ in the BAL supernatant, (5) increased levels of IgG1-OVA, decreased levels of IgG2a-OVA and no changes in OVA-specific IgE in the peripheral blood, (6) increased expression of L-selectin in the BAL granulocytes, (7) decreased tracheal reactivity to methacholine measured in vitro, (8) no changes in plasma corticosterone levels and (9) increased levels of plasmatic noradrenaline. These results suggest that allergic lung inflammatory response exacerbation in CSP mice is a consequence of the psychological stress induced by forced cohabitation with the sick partner. Strong involvement of the sympathetic nervous system (SNS) through adrenaline and noradrenaline release and a shift of the Th1/Th2 cytokine profile toward a Th2 response were considered to be the mechanisms underlying the cell recruitment to the animal's airways.

Stress-induced mast cell activation in glabrous and hairy skin

Mast cells play a key role in modulation of stress-induced cutaneous inflammation. In this study we investigate the impact of repeated exposure to stress on mast cell degranulation, in both hairy and glabrous skin. Adult male Wistar rats were randomly divided into four groups: Stress 1 day (n = 8), Stress 10 days (n = 7), Stress 21 days (n = 6), and Control (n = 8). Rats in the stress groups were subjected to 2 h/day restraint stress. Subsequently, glabrous and hairy skin samples from animals of all groups were collected to assess mast cell degranulation by histochemistry and transmission electron microscopy. The impact of stress on mast cell degranulation was different depending on the type of skin and duration of stress exposure. Short-term stress exposure induced an amplification of mast cell degranulation in hairy skin that was maintained after prolonged exposure to stress. In glabrous skin, even though acute stress exposure had a profound stimulating effect on mast cell degranulation, it diminished progressively with long-term exposure to stress. The results of our study reinforce the view that mast cells are active players in modulating skin responses to stress and contribute to further understanding of pathophysiological mechanisms involved in stress-induced initiation or exacerbation of cutaneous inflammatory processes.

Icariin attenuates glucocorticoid insensitivity mediated by repeated psychosocial stress on an ovalbumin-induced murine model of asthma

Evidence shows that psychosocial stress exacerbates asthma, but there is little intervention to alleviate negative effects of psychosocial stress on asthma. We investigated the role of icariin in anti-inflammation and anti-anxiety potential in a murine model combined psychosocial stress with allergic exposure. The results indicated that icariin administered remarkable increased activity in the center of the open field, reversed airway hyperresponsivenesss, reduced inflammatory cytokine infiltration to the lung and whole body and also in part recovered glucocorticoid responsiveness. Furthermore, our data also showed that icariin significantly inhibited increases of corticosterone and markedly increased glucocorticoid receptor mRNA and protein expression in the lungs of mice exposed to both stress and allergen. Collectively, we speculate that inducing glucocorticoid receptor modulation might be the potential mechanisms of icariin to facilitate corticosteroid responsiveness of cytokine production.

Essential roles of endogenous glucocorticoids and TNF/TNFR1 in promoting bone-marrow eosinopoiesis in ovalbumin-sensitized, airway-challenged mice

AIMS

Stress mechanisms paradoxically contribute to allergic episodes in humans and mice. Glucocorticoids (GC) and interleukin (IL)-5 synergically upregulate murine bone-marrow eosinophil production. Here we explored the role of endogenous GC in allergen-stimulated bone-marrow eosinophil production in ovalbumin-sensitized/challenged mice.

MAIN METHODS

In BALB/c or C57BL/6 mice, sensitized and intranasally challenged with ovalbumin, we monitored eosinophil numbers in freshly harvested or cultured bone-marrow, and plasma corticosterone levels. Metyrapone (MET) was used to inhibit GC synthesis, and RU486 to block GC actions. In sensitized mice challenged intraperitoneally, we examined the relationship between eosinophilia of bone-marrow and peritoneal cavity, in the absence or presence of RU486. In experiments involving in vivo neutralization of tumor necrosis factor-α (TNF) by specific antibodies, or using mice which lack functional type I TNF receptors (TNFRI), we evaluated the relationship between TNF blockade, corticosterone levels, RU486 or MET treatment and challenge-induced bone-marrow eosinophilia.

KEY FINDINGS

RU486 or MET pretreatments abolished challenge-induced increases in eosinophil numbers in bone-marrow (in vivo and ex vivo), and in the peritoneal cavity. MET, but not RU486, prevented the challenge-induced increase in corticosterone levels. Challenge-induced bone-marrow eosinophilia and corticosterone surge were abolished in TNFRI-deficient mice. Anti-TNF-treatment very effectively prevented challenge-induced bone-marrow eosinophilia, in the absence of RU486 or MET, but had no independent effect in the presence of either drug.

SIGNIFICANCE

Endogenous GC was essential for allergen challenge-induced increases in eosinophil numbers inside bone-marrow. This effect required TNF and TNFRI, which suggests an immunoendocrine mechanism.

Epidemiology of stress and asthma: from constricting communities and fragile families to epigenetics

Several epidemiologic frameworks, exemplified through extant research examples, provide insight into the role of stress in the expression of asthma and other allergic disorders. Biologic, psychological, and social processes interact throughout the life course to influence disease expression. Studies exploiting a child development framework focus on critical periods of exposure, including the in utero environment, to examine the influence of stress on disease onset. Early stress effects that alter the normal course of morphogenesis and maturation that affect both structure and function of key organ systems (eg, immune, respiratory) may persist into adult life underscoring the importance of a life course perspective. Other evidence suggests that maternal stress influences programming of integrated physiologic systems in their offspring (eg, neuroendocrine, autonomic, immune function) starting in pregnancy; consequently stress effects may be transgenerational. A multilevel approach that includes an ecological perspective may help to explain heterogeneities in asthma expression across socioeconomic and geographic boundaries that to date remain largely unexplained. Evolving studies incorporating psychological, behavioral, and physiologic correlates of stress more specifically inform underlying mechanisms operating in these critical periods of development. The role of genetics, gene by environment interactions, and epigenetic mechanisms of gene expression have been sparsely examined in epidemiologic studies on stress and asthma although overlapping evidence provides proof of concept for such studies in the future.

Perinatal stress and early life programming of lung structure and function

Exposure to environmental toxins during critical periods of prenatal and/or postnatal development may alter the normal course of lung morphogenesis and maturation, potentially resulting in changes that affect both structure and function of the respiratory system. Moreover, these early effects may persist into adult life magnifying the potential public health impact. Aberrant or excessive pro-inflammatory immune responses, occurring both locally and systemically, that result in inflammatory damage to the airway are a central determinant of lung structure-function changes throughout life. Disruption of neuroendocrine function in early development, specifically the hypothalamic-pituitary-adrenal (HPA) axis, may alter functional status of the immune system. Autonomic nervous system (ANS) function (sympathovagal imbalance) is another integral component of airway function and immunity in childhood. This overview discusses the evidence linking psychological factors to alterations in these interrelated physiological processes that may, in turn, influence childhood lung function and identifies gaps in our understanding.

Social stress and asthma: the role of corticosteroid insensitivity

Psychosocial stress alters susceptibility to infectious and systemic illnesses and may enhance airway inflammation in asthma by modulating immune cell function through neural and hormonal pathways. Stress activates the hypothalamic-pituitary-adrenal axis. Release of endogenous glucocorticoids, as a consequence, may play a prominent role in altering the airway immune homeostasis. Despite substantial corticosteroid and catecholamine plasma levels, chronic psychosocial stress evokes asthma exacerbations. Animal studies suggest that social stress induces corticosteroid insensitivity that in part may be a result of impaired glucocorticoid receptor expression and/or function. Such mechanisms likely promote and amplify airway inflammation in response to infections, allergen, or irritant exposure. This review discusses evidence of an altered corticosteroid responsive state as a consequence of chronic psychosocial stress. Elucidation of the mechanisms of stress-induced impairment of glucocorticoid responsiveness and immune homeostasis may identify novel therapeutic targets that could improve asthma management.

Airway cytokine responses to acute and repeated stress in a murine model of allergic asthma

Although stress is known to exacerbate asthma, the underlying mechanisms are unclear. Using a murine model of allergic asthma, Th1 (interleukin [IL]-2 and gamma-interferon [IFN-γ]) and Th2 (IL-4 and IL-5) airway cytokine responses and Th1:Th2 cytokine ratios to acute and repeated stress were examined in bronchoalveolar lavage fluid (BALF). Asthmatic mice showed significantly higher IL-4 level and Th2 predominance, compared with healthy mice. To acute stress, asthmatic mice significantly increased IL-4 but decreased IFN-γ levels favoring Th2 predominance, whereas healthy mice significantly decreased IL-4 level favoring Th1 predominance in BALF. To repeated stress, asthmatic mice significantly decreased IFN-γ, IL-4 and IL-5 levels overall favoring Th1 predominance, whereas healthy mice basically maintained the same response profile shown to acute stress. These findings suggest that a significant shift toward Th2 predominance in asthmatic mice under acute stress may be a mechanism underlying exacerbation of asthma.

Social stress enhances allergen-induced airway inflammation in mice and inhibits corticosteroid responsiveness of cytokine production

Chronic psychosocial stress exacerbates asthma, but the underlying mechanisms remain poorly understood. We hypothesized that psychosocial stress aggravates allergic airway inflammation by altering innate immune cell function. The effects of stress on airway inflammation, lung function, and glucocorticoid responsiveness were studied in a novel in vivo murine model of combined social disruption stress and allergic sensitization. The effects of corticosterone were assessed on cytokine profile and glucocorticoid receptor activation in LPS-stimulated spleen cell cultures in vitro. Airway inflammation resolved 48 h after a single allergen provocation in sensitized control mice, but not in animals that were repeatedly exposed to stress before allergen challenge. The enhanced eosinophilic airway inflammation 48 h after allergen challenge in these mice was associated with increased levels of IL-5, GM-CSF, IgG1, thymus-activated and regulatory chemokine, TNF-alpha, and IL-6 in the airways and a diminished inhibition of these mediators by corticosterone in LPS-stimulated splenocyte cultures in vitro. Stress-induced reduction of the corticosteroid effects paralleled increased p65 expression and a decreased DNA-binding capability of the glucocorticoid receptor in vitro. Furthermore, glucocorticoid receptor mRNA and protein expression in the lungs of mice exposed to both stress and allergen was markedly reduced in comparison with that in either condition alone or in naive mice. Thus, exposure to repeated social stress before allergen inhalation enhances and prolongs airway inflammation and alters corticosterone responsiveness. We speculate that these effects were mediated at least in part by impaired glucocorticoid receptor expression and function.

Anti-inflammatory effects of hydroalcoholic extract and two biflavonoids from Garcinia gardneriana leaves in mouse paw oedema

Garcinia gardneriana (Planch. & Triana) Zappi (Clusiaceae) is widely distributed in Brazil and used in folk medicine to treat inflammation, pain, and urinary tract and other infections. However, very few studies have analyzed these therapeutic effects. In this study, the anti-inflammatory effects of the hydroalcoholic extracts from Garcinia gardneriana (HEGG) and some of its isolated biflavonoids were evaluated. The results showed that HEGG from the leaves, bark and seeds reduced carrageenan-induced mouse paw inflammation, in addition to diminishing the myeloperoxidase activity in the stimulated tissues. The reduction of neutrophil infiltration by treatment with the HEGG from leaves was confirmed by histology. The leaf extract also reduced the paw oedema evoked by bradykinin, histamine, prostaglandin E2 and 12-O-tetradecanoylphorbol acetate. However, it partially decreased substance P and compound 48/80-caused paw oedema, without any influence on the arachidonic acid-induced oedema. Both of the isolated compounds, fukugetin and GB-2a, prevented the carrageenan-induced paw oedema. In conclusion, this study showed important anti-inflammatory effects of HEGG through its interaction with different intracellular signaling pathways, without interfering with the formation of arachidonic acid (AA) metabolites. These characteristics, in addition to the wide distribution and culturing ease of the plant, confirm its popular use and highlight its promise in the development of new anti-inflammatory drugs.

Stress-induced differences in primary and secondary resistance against bacterial sepsis corresponds with diverse corticotropin releasing hormone receptor expression by pulmonary CD11c+ MHC II+ and CD11c- MHC II+ APCs

Stress responses have been associated with altered immunity and depending upon the type of stressor, can have diverse effects on disease outcomes. As the first line of defense against potential pathogens, alterations in cellular immune responses along the respiratory tract can have a significant impact on the manifestation of local and systemic disease. Utilizing a murine model of respiratory pneumonia, the current study investigated the effects of restraint stress on the induction of primary and secondary immunity along the respiratory tract, influencing host susceptibility. Female CD-1 mice were subjected to three hours of restraint stress over a period of four days followed by primary and secondary Streptococcus pneumoniae infection via intranasal route. Stress exposure led to increased retention of bacterial carriage in the lungs, enhanced polymorphonuclear cells and a preferential decrease in pulmonary CD11c(+) MHC II(+) cells resulting in delayed lethality during primary infection but significant impairment of acquired immune protection after secondary infection. We also provide evidence to support a role for lung-associated corticotropin releasing hormone regulation through peripheral CRH and diverse CRH receptor expression by MHC II(+) antigen presenting cells (APCs). We conclude that repeated restraint stress has distinct influences on immune cell populations that appear to be important in the generation of innate and adaptive immune responses along the respiratory tract with the potential to influence local and systemic protection against disease pathogenesis.

Stress effects on lung function in asthma are mediated by changes in airway inflammation

OBJECTIVE

To examine the association of changes in current negative mood and long-term daily hassles with changes in lung function and airway inflammation in patients suffering from asthma and in healthy controls. Associations between psychological factors and asthma symptoms have been documented, but the relationship between airway inflammation and psychological factors has been largely unexplored.

METHOD

Data were analyzed from 46 asthma patients and 25 controls who completed questionnaires on current mood and daily hassles at two assessments 3 months apart. Lung function was measured by spirometry (forced expiratory volume in the first second (FEV(1))) and airway inflammation by the fraction of nitric oxide in exhaled air (FeNO). Regression analyses controlling for allergen load and air pollution (ozone) were calculated to study the association between changes in psychological factors and changes in lung function and airway inflammation, and to examine the mediational role of airway inflammation in the stress-lung function association.

RESULTS

In patients with asthma, increases in negative affect were associated with decreases in FEV(1) and increases in FeNO. For daily hassles, a reverse pattern of associations was found, with decreases in daily hassles linked to decreases in FEV(1) and increases in FeNO. Mediation analyses showed that FeNO was a significant mediator of the association of both negative affect and daily hassles with lung function changes. No significant associations were found for healthy controls.

CONCLUSION

Psychological variables are consistently associated with spirometric lung function and airway inflammation in asthma patients. For asthma patients, effects of acute negative affect must be distinguished from more chronic distress due to daily hassles.

The role of stress in asthma: insight from studies on the effect of acute and chronic stressors in models of airway inflammation

Asthma, a chronic inflammatory disease of the airways, is greatly influenced by psychosocial factors and stress. This review looks at clinical studies that have shown strong associations between psychological stress and asthma to identify potential mechanisms for these interactions. Furthermore, we review animal studies involving stress and airway inflammation or airway hyperresponsiveness, and discuss possible mechanisms of stress action in asthma. In conclusion, further research, both in humans and in animal models, into the mechanisms of stress-induced changes in asthma exacerbation are required to help better understand the complex makeup of asthma and assist in the development of therapies directed at the interplay between the nervous system and airway inflammation.

Effects of stress and neuropeptides on airway responses in ovalbumin-sensitized rats

OBJECTIVE

The aim of this study was to investigate the influence of stress and neuropeptides on airway responses in ovalbumin (OVA)-sensitized rats.

METHODS

Three experimental conditions were employed: neonatal capsaicin treatment, foot shock stress and OVA sensitization. For neuropeptide depletion, male Wistar rats were neonatally treated with capsaicin (50 mg/kg) or with control solution 2 days after birth. Ninety days later, they were injected with OVA and aluminum hydroxide (ED0) or no injection. Thereafter, rats of the stressed groups were individually placed in a shuttle box where they received 50 mild escapable foot shocks/day; the stressful stimuli were repeated until ED14, when the animals received OVA aerosol. Pulmonary mechanic function was measured before and after OVA challenge in anesthetized and mechanically ventilated rats.

RESULTS

Data on ultrasonic vocalizations and corticosterone showed high levels of anxiety in stressed animals. As expected, a significant increment in airway elastance and resistance after the OVA challenge was found in sensitized rats compared to non-sensitized ones. Capsaicin treatment decreased the values of elastance in sensitized and non-stressed rats; however, after the OVA challenge, elastance was increased in stressed animals. No differences were found in the levels of resistance among sensitized and non-stressed rats; however, a reduced increment in resistance was verified in capsaicin-treated, stressed animals.

CONCLUSIONS

Our results suggest that neurokinin depletion and stress may affect smooth muscle tonus around the airways during an anaphylactic reaction. These data suggest that stress and neuropeptides play a significant role in pulmonary function in OVA-sensitized rats.

Early-life psychological stress exacerbates adult mouse asthma via the hypothalamus-pituitary-adrenal axis

RATIONALE

Despite accumulating evidence that psychological stress has a short-lasting detrimental effect on asthma, little is known about the way stress in childhood predisposes to adult asthma.

OBJECTIVES

Using a communication box, we investigated the long-lasting effect of early psychological and physical stress on adult asthma in mice.

METHODS

Male BALB/c mice were exposed to either psychological stress or physical stress three times (every other day) during their fourth week of life. The mice were sensitized to ovalbumin at 8 and 10 weeks, and an ovalbumin airway challenge was conducted at the age of 11 weeks.

RESULTS

Twenty-four hours after ovalbumin challenge, both psychological and physical stress-exposed mice exhibited a significant acceleration in the number of total mononuclear cells and eosinophils and airway hyperresponsiveness compared with control mice. No differences in serum anti-OVA-specific immunoglobulin E levels were found between stress-exposed and control animals after antigen sensitization. In the psychological stress group, but not in the physical stress group, an elevation of the serum corticosterone levels during ovalbumin challenge was significantly attenuated in comparison with the control group. Moreover, pretreatment with RU-486, a glucocorticoid receptor antagonist, before ovalbumin challenge completely inhibited a psychological stress-induced exacerbation of asthma. However, pretreatment with GR-82334, a neurokinin-1 receptor antagonist, failed to affect physical stress-induced augmentation of airway inflammation.

CONCLUSION

Early psychological and physical stresses aggravated adult asthma via hyporesponsiveness of the hypothalamic-pituitary-adrenal axis during antigen challenge and via a pathway(s) distinct from the hypothalamic-pituitary-adrenal axis or neurokinin-1 receptors.

Stress induces substance P in vagal sensory neurons innervating the mouse airways

BACKGROUND

Tachykinins-like substance P (SP) have been shown to play an important role in initiating and perpetuating airway inflammation. Furthermore, they are supposed to be released into tissues in response to stress.

OBJECTIVE

The aim of this study was to investigate the effects of stress alone or in combination with allergic airway inflammation on SP expression in sensory neurons innervating the mouse airways.

METHODS

Balb/c mice were systemically sensitized to ovalbumin (OVA), followed by allergen aerosol exposure, and compared with non-sensitized controls. Additionally, OVA-sensitized and -challenged and non-sensitized mice were exposed to sound stress. SP expression in airway-specific and overall vagal sensory neurons of the jugular and nodose ganglion complex was analysed using retrograde neuronal tracing in combination with immunohistochemistry. Preprotachykinin A (PPT-A) mRNA, the precursor for SP, was quantified in lung tissue by real-time PCR. Bronchoalveolar lavage (BAL) fluid was obtained, and cell numbers and differentiation were determined.

RESULTS

Stress and/or allergic airway inflammation significantly increased SP expression in retrograde-labelled vagal sensory neurons from the mouse lower airways compared with controls [stress: 15.7+/-0.8% (% of retrograde-labelled neurons, mean+/-SEM); allergen: 17.9+/-0.4%; allergen/stress: 13.1+/-0.7% vs. controls: 6.3+/-0.3%]. Similarly, SP expression increased in overall vagal sensory neurons identified by the neuronal marker protein gene product (PGP) 9.5 [stress: 9.3+/-0.6% (% of PGP 9.5-positive neurons, means+/-SEM); allergen: 12.5+/-0.4%; allergen/stress: 10.2+/-0.4% vs. controls: 5.1+/-0.3%]. Furthermore, stress significantly increased PPT-A mRNA expression in lung tissue from OVA-sensitized and -challenged animals, and immune cells were identified as an additional source of SP in the lung by immunohistochemistry. Associated with enhanced neuronal SP expression, a significantly higher number of leucocytes were found in the BAL following allergen exposure. Further, stress significantly increased allergen-induced airway inflammation identified by increased leucocyte numbers in BAL fluids.

CONCLUSION

The central event of sound stress leads to the stimulation of SP expression in airway-specific neurons. However, in sensitized stressed mice an additional local source of SP (probably inflammatory cells) might enhance allergic airway inflammation.

Upregulation of tumor necrosis factor-alpha by stress and substance p in a murine model of allergic airway inflammation

OBJECTIVE

Clinical observation has suggested that stress and asthma morbidity are associated, though underlying mechanisms are not clearly understood. After having established a mouse model of stress-exacerbated allergic airway inflammation, we demonstrated a stress-mediating role for neurokinin-1 receptor, the main substance P (SP) receptor. Here, our aim was to investigate the influence of stress or exogenously applied SP on airway inflammation and on the local cytokine production of immune cells.

METHODS

BALB/c mice were systemically sensitized to ovalbumin (OVA) and repeatedly challenged with OVA aerosol. Sound stress was applied to the animals for 24 h, starting with the first airway challenge. Alternatively, one group of non-stressed mice received intranasal SP before airway challenges. Cell numbers were determined in bronchoalveolar lavage (BAL) fluid. Leukocytes from mediastinal lymph nodes were analyzed by flow cytometry to determine the percentages of T cells producing interleukin-4, interferon-gamma and tumor necrosis factor-alpha.

RESULTS

In BAL fluids of stressed or SP-treated animals, significantly higher total cell counts were found compared to non-stressed mice. In lymph nodes, the percentage of TNF-alpha-positive T cells was higher in stressed mice and mice after application of SP. In contrast, the influence of stress did not increase the percentages of interferon-gamma-positive CD3+ cells, meanwhile the application of SP increased the percentages of T cells positive for this cytokine.

CONCLUSION

Our data provide further evidence for a stress-mediating neuroimmunological pathway that, putatively via SP, is able to influence the composition of immune cells in different compartments of allergic airway inflammation.

Chronic mild stress (CMS) revisited: consistency and behavioural-neurobiological concordance in the effects of CMS

The chronic mild stress (CMS) model of depression has high validity but has in the past been criticized for being difficult to replicate. However, a large number of recent publications have confirmed that CMS causes behavioural changes in rodents that parallel symptoms of depression. This review summarizes studies from over sixty independent research groups that have reported decreases in reactivity to rewards, and a variety of other depression-like behaviours, in rats or mice, following exposure to CMS. Together, these changes are referred to as a 'depressive' behavioural profile. Almost every study that has examined the effects of chronic antidepressant treatment in these procedures has reported that antidepressants were effective in reversing or preventing these 'depressive' behavioural changes. (The single exception is a study in which the duration of treatment was too brief to constitute an adequate trial.) There are also a handful of reports of CMS causing significant effects in the opposite direction, termed here an 'anomalous' behavioural profile. There are six neurobiological parameters that have been studied in both 'anhedonic' and 'anomalous' animals: psychostimulant and place-conditioning effects of dopamine agonists; dopamine D2 receptor number and message; inhibition of dopamine turnover by quinpirole, and beta-adrenergic receptor binding. On all six measures, CMS caused opposite effects in animals displaying 'depressive' and 'anomalous' profiles. Thus, there is overwhelming evidence that under appropriate experimental conditions, CMS can cause antidepressant-reversible depressive-like effects in rodents; however, the 'anomalous' profile that is occasionally reported appears to be a genuine phenomenon, and these two sets of behavioural effects appear to be associated with opposite patterns of neurobiological changes.

Opposing effects of short- and long-term stress on airway inflammation

Between 20% and 35% of subjects with asthma experience asthma exacerbations during periods of stress. The biological mechanisms underlying these exacerbations are not clearly understood, and the role of psychologic factors in the pathophysiology of asthma remains controversial. We investigated the ability of psychologic stress to modulate airway inflammation and airway hyperresponsiveness (AHR) to methacholine in a murine model of asthma. Animals were exposed to a stressor daily for 3 (short-term stress) or 7 (long-term stress) days. After allergen challenge, AHR was assessed through plethysmography, and bronchoalveolar lavage cells were counted as a measure of inflammation. After short-term stress, inflammatory cell number was decreased compared with unstressed animals, whereas levels of interleukin (IL)-6, IL-9, and IL-13 were increased. Administration of a corticosteroid receptor antagonist, before stress, prevented the decrease in inflammatory cell numbers. In contrast, animals stressed for 7 consecutive days showed a significant increase in inflammatory cell numbers, which was independent of the glucocorticoid response, but no change in cytokine levels. AHR was not altered in stressed animals. Our results indicate that repeated exposure to stress over the long term engages different mechanisms than short-term stress and can exacerbate the chronic inflammatory responses of the airway.