Microbiota-immune-brain interactions: A new vision in the understanding of periodontal health and disease.

This review highlights the significance of interactions between the microbiota, immune system, nervous and hormonal systems, and the brain on periodontal health and disease. Microorganisms in the microbiota, immune cells, and neurons communicate via homeostatic nervous and hormonal systems, regulating vital body functions. By modulating pro-inflammatory and anti-inflammatory adaptive immune responses, these systems control the composition and number of microorganisms in the microbiota. The strength of these brain-controlled responses is genetically determined but is sensitive to early childhood stressors, which can permanently alter their responsiveness via epigenetic mechanisms, and to adult stressors, causing temporary changes. Clinical evidence and research with humans and animal models indicate that factors linked to severe periodontitis enhance the responsiveness of these homeostatic systems, leading to persistent hyperactivation. This weakens the immune defense against invasive symbiotic microorganisms (pathobionts) while strengthening the defense against non-invasive symbionts at the gingival margin. The result is an increased gingival tissue load of pathobionts, including Gram-negative bacteria, followed by an excessive innate immune response, which prevents infection but simultaneously destroys gingival and periodontal tissues. Thus, the balance between pro-inflammatory and anti-inflammatory adaptive immunity is crucial in controlling the microbiota, and the responsiveness of brain-controlled homeostatic systems determines periodontal health.

Cognitive functioning and cortisol profiles in first episode major depression.

Major Depressive Disorder (MDD) is often associated with high levels of stress and disturbances in the Hypothalamic Pituitary Adrenal (HPA) system, yielding high levels of cortisol, in addition to cognitive dysfunction. Previous studies have shown a relationship between cortisol profile and cognitive functioning in recurrent MDD in general. More specifically, the association between hypercortisolism and cognitive functioning, such as memory and Executive Functioning (EF), and also more recently cortisol suppression has been explored. However, no studies have investigated these relationships in patients diagnosed with first episode MDD. The aim of the present study was to examine the relationship between cortisol levels before and after the Dexamethasone suppression test (DST) and cognitive function in first episode MDD patients. Twenty-one patients meeting the DSM-IV criteria for a first episode of MDD diagnosis were included in the study. The control group was matched for age, gender and education level. Cortisol was measured in saliva collected with Salivette sampling devices. Saliva samples were collected 4 times during a 24 hours period over two consecutive days: at awakening, after 45 minutes, after 7 hours and at 11 pm. Dexamethasone (1.0 mg) was given orally on Day 1 at 11 pm. The neuropsychological test battery consisted of standardized tests measuring executive functioning (EF) and memory functioning. Cortisol levels did not differ significantly between patients and controls on Day 1, except for the last sample before Dexamethasone administration, where the control group showed higher levels. Both groups showed suppression after Dexamethasone. On Day 2 there was a significant difference between groups at the third sample, showing a significantly lower level in the control group, suggesting that the controls have a more effective suppression profile than the patients. There were no significant correlations between cortisol levels before or after Dexamethasone and cognitive measures. The results indicate impairment on HPA-axis functioning in first episode MDD patients, with less suppression functioning compared to healthy controls, but no relationship between cortisol profile and cognitive functioning in EF or Memory.

Maternal depression and infant daytime cortisol.

The effect of maternal depressive disorder on infant daytime cortisol production was studied in three groups of infants; one group with mothers with comorbid depression and anxiety (n = 19), a second group with mothers with depression only (n = 7), and a third group with non-depressed mothers (n = 24). The infants' cortisol production pattern was measured when they were 6, 12, and 18 months old in combination with repeated measures of parenting stress and depression symptoms. Multilevel modeling analyses showed that infants of mothers with comorbid depression and anxiety had relatively higher cortisol production from morning to bedtime and higher bedtime values as compared to infants of non-depressed mothers and infants of depressed only mothers when they were 6 and 12 months old, but not when 18 months old. The results were interpreted in light of possible changes in the infants' stress regulatory capacities or changes in maternal coping strategies at infant age 18 months.

Does a single exposure to social defeat render rats more vulnerable to chemically induced colitis than brief inescapable foot-shocks?

All mammals are to different degrees exposed to stressors being physical or social, which may affect health and well-being. Stressful and traumatic situations have direct effects on immune responses that may alter susceptibility to developing somatic illnesses. In animal research, different types of stressors have been investigated in studying the effect on bowel disorders, some stressors being more or less of environmental origin. We aimed, therefore, to explore whether a more natural stressor would differ from a stressor of more unnatural characteristics on dextran sulphate sodium (DSS) induced colitis in adult rats. Specifically, whether social stress within a single social defeat (SD) paradigm would be a more potent stressor than brief inescapable foot-shocks (IFS) in causing elevated faecal granulocyte marker protein (GMP), and crypt- and inflammation scores in colonic tissue. Three groups of male Wistar rats were used; socially defeated rats; inescapable foot-shock rats; and comparison rats. Main findings showed no difference between the groups on GMP levels. However, there was a significant difference on inflammation and crypt scores for the distal part of colon, detected through histology, where socially defeated rats were more susceptible. A single SD seems to be more adverse than inescapable foot-shock on DSS induced colitis, but further studies are recommended to validate a broader range of different outcomes comparing two such different rodent stress models.

Emotional stress and orthodontic tooth movement: effects on apical root resorption, tooth movement, and dental tissue expression of interleukin-1 alpha and calcitonin gene-related peptide immunoreactive nerve fibres in rats.

The aim of the study was to investigate the effect of emotional stress on apical root resorption (ARR) and tooth displacement during orthodontic tooth movement in rats. A further area of interest was to evaluate if the expression of interleukin-1 alpha (IL-1alpha) as well as the density and distribution of peptidergic nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP) in the periodontal ligament (PDL) are associated with possible stress-induced changes in root resorption and tooth movement. A total of 52 male Wistar rats, aged 6 weeks, were divided in three experimental and one control group (n = 4). Group 1 had orthodontic tooth movement and received foot shocks (OTMS; n = 16), group 2 had orthodontic tooth movement but received no foot shocks (OTMNS; n = 16), and group 3 had no orthodontic tooth movement and received foot shocks (NOTMS; n = 16). Each group was further divided into four subgroups (n = 4), corresponding to the period of the experiment, i.e. 3, 7, 13, and 21 days. At the end of each experimental period, the blood samples were taken, the animals were sacrificed, and the jaws excised, deminerialized, and processed for immunocytochemistry. One-way analysis of variance was used to detect inter-group differences for all investigated variables. CGRP immunopositive nerve fibres were evaluated qualitatively. All the experimental groups demonstrated higher corticosterone levels than the control group, suggesting a stress-induced experience by orthodontic treatment per se. The OTMS group had the least amount of cellular cementum throughout the experimental periods and showed significant reduction in tooth displacement, especially at 3 and 7 days. No obvious changes were observed in the dental tissue expression of IL-1alpha and CGRP immunoreactive nerve fibres between the stressed and non-stressed orthodontically treated groups.

Vitamin D Supplementation during Winter: Effects on Stress Resilience in a Randomized Control Trial.

Vitamin D status may be important for stress resilience. This study investigated the effects of vitamin D supplements during winter on biological markers of stress resilience such as psychophysiological activity, serotonin, and cortisol in a placebo-controlled, randomized clinical trial. Eighty-six participants were randomly assigned to the Intervention (vitamin D) or Control (placebo) groups. Before and after the intervention participants were exposed to an experimental stress procedure. Psychophysiological activity was measured during three main conditions: baseline, stress, and recovery. Fasting blood samples were taken in the morning and saliva samples were collected at seven different time points across 24 h. Prior to intervention both groups had normal/sufficient vitamin D levels. Both groups showed a normal pattern of psychophysiological responses to the experimental stress procedure (i.e., increased psychophysiological responses from resting baseline to stress-condition, and decreased psychophysiological responses from stress-condition to recovery; all p < 0.009). Post-intervention, the Intervention group showed increased vitamin D levels (p < 0.001) and normal psychophysiological responses to the experimental stress procedure (p < 0.001). Importantly, the Control group demonstrated a classic nadir in vitamin D status post-intervention (spring) (p < 0.001) and did not show normal psychophysiological responses. Thus, physiologically the Control group showed a sustained stress response. No significant effects of vitamin D were found on serotonin and cortisol.

Levels of circulating interleukin-1 receptor antagonist and C-reactive protein in long-term survivors of testicular cancer with chronic cancer-related fatigue.

Low-grade inflammatory responses may be related to the pathogenesis of cancer-related fatigue (CRF). We investigated circulating levels of various inflammatory markers in relation to chronic CRF (6 month duration) in Norwegian long-term survivors of testicular cancer (TCSs). We compared 92 TCSs with chronic CRF (cases) to 191 TCS without (controls) at median age 45 years (range 23-73), and median 11 years post-treatment (range 5-20). Chronic CRF was defined using the Fatigue Questionnaire, while plasma concentrations of cytokines and serum CRP were determined by various immunoassays. Higher levels of interleukin-1 receptor antagonist (IL-1ra) (p=.002) and C-Reactive protein (CRP) (p=.036) were found in cases compared to controls. No differences were observed for interleukin-6 (IL-6), soluble Tumor Necrosis Factor Receptor type 1 (sTNF-R1) or neopterin. Both IL-1ra and CRP were correlated with physical but not with mental fatigue. In logistic regression analyses IL-1ra and CRP explained 3.5% and 2.8%, respectively, of the variance in chronic CRF. Single adjustments for depression, anxiety and neuroticism each raised the models' explained variance to approximately 35%. Those factors did not significantly alter the relationship between chronic CRF and IL-1ra/CRP. BMI and smoking emerged as possible confounding factors. These results indicate that chronic CRF in TCSs is associated with higher levels of circulating IL-1ra and CRP, possibly mediated by physiological morbidity. Hence, the findings lend some support to the hypothesis that low-grade inflammatory processes are involved in the pathogenesis of chronic CRF in cancer survivors.

A systematic review of studies utilizing hair glucocorticoids as a measure of stress suggests the marker is more appropriate for quantifying short-term stressors.

Quantitating glucocorticoids (GCs) in hairs is a popular method for assessing chronic stress in studies of humans and animals alike. The cause-and-effect relationship between stress and elevated GC levels in hairs, sampled weeks later, is however hard to prove. This systematic review evaluated the evidence supporting hair glucocorticoids (hGCs) as a biomarker of stress. Only a relatively small number of controlled studies employing hGC analyses have been published, and the quality of the evidence is compromised by unchecked sources of bias. Subjects exposed to stress mostly demonstrate elevated levels of hGCs, and these concentrations correlate significantly with GC concentrations in serum, saliva and feces. This supports hGCs as a biomarker of stress, but the dataset provided no evidence that hGCs are a marker of stress outside of the immediate past. Only in cases where the stressor persisted at the time of hair sampling could a clear link between stress and hGCs be established.

A double exposure to social defeat induces sub-chronic effects on sleep and open field behaviour in rats.

Social defeat, resulting from the fight for a territory is based on the resident-intruder paradigm. A male rat intruder is placed in the territory of an older, bigger and more aggressive male resident and is defeated. In the present study, a double exposure to social defeat increased sleep fragmentation due to an increased amount of waking and slow-wave-sleep-1 (SWS-1) episodes. Also, social defeat increased the amount of slow-wave-sleep-2 (SWS-2). In repeated exposures to an open field, socially defeated rats showed low central activity and persistent defecation indicating high emotionality. The strongest effects of social defeat on sleep and open field behaviour were seen sub-chronically after stress. Social defeat did not induce changes in rapid eye movement (REM) sleep (e.g. total amount, latency), sleep latency, sexual activity, body weight or adrenal weight. A negative correlation between habituation in open field central activity and total sleep fragmentation indicates a commonality of effects of social defeat on both behaviour and sleep.

Chronic cancer-related fatigue in long-term survivors of testicular cancer.

OBJECTIVE: High prevalence of cancer-related fatigue (CRF) has been reported among many groups of cancer survivors when compared to the general population. However, this topic has rarely been studied in long-term survivors of testicular cancer (TCSs). The present multi-centre study examines the prevalence of chronic CRF in Norwegian TCSs compared to chronic general fatigue (GF) in the Norwegian general population, and associations between a variety of relevant variables and CRF in TCSs. METHODS: Participants were 1431 TCSs, aged 18-75, at an average of 11 years posttreatment (range 4.5-21 years), and a sample of 1080 age-matched men from the general Norwegian population (GenPop). The participants responded to a mailed questionnaire that included the Fatigue Questionnaire for the assessment of chronic CRF and chronic GF. RESULTS: The prevalence of chronic CRF was 17.1% (95% CI 15.2-19.1%) among TCSs compared to 9.7% of chronic GF in GenPop (95% CI 8.0-11.5%). Regression analyses showed that poor quality of life (QOL), various psychosocial and somatic problems, and neuroticism were highly associated with presence of chronic CRF in TCSs. CONCLUSION: Chronic CRF is far more common among TCSs than chronic GF in the general population and is associated with poor QOL and multiple psychological and somatic health problems. As a consequence, fatigue should be in focus during routine follow-ups as well as later in the general medical care of TCSs.

Coffee, stress and cortisol in nursing staff.

According to cognitive activation theory, long-lasting work demands without rest or lack of coping may lead to sustained activation and pathology. Cortisol is one of the most important stress hormones in humans and increased basal levels of cortisol are considered a valid marker for sustained activation. In order to investigate this association further, we investigate the relationships between salivary cortisol profiles, job stress, work load (effort/reward, demand/control) and health (subjective health complaints and health-related quality of life) in a population of health care workers. Forty-four women filled in a questionnaire and collected five saliva samples on two consecutive working days (1: wake-up time, 2: wake-up time+30 min, 3: wake-up time+45 min, 4: 1500 h and 5: 2200 h). There was no relationship between psychosocial factors at work and cortisol levels in the morning (cortisol level at wake-up time and awakening cortisol response (ACR)). Only the confounding variable tobacco reached a significant level in the hierarchical regressions analyses. Our significant findings are limited to the afternoon decline and the evening values. The decrease during the day relates to decision authority, physical functioning, general health, and vitality in the single, unadjusted regression analyses. The decrease also relates to coffee intake, which we included originally as a confounding variable. In the final hierarchical regression of the evening values, only decision authority and coffee were significantly related to cortisol levels in the evening.

Extracellular levels of serotonin and GABA in the hippocampus after chronic mild stress in rats. A microdialysis study in an animal model of depression.

One of the most established hypotheses of depression focuses on alteration of the serotonergic (5-HT) function. Recent evidence suggests that serotonergic involvement in depression may be modulated by the action of gamma-hydroxybutyric acid (GABA). Furthermore, altered GABAergic function is also evident in depressed patients and in animal models of depression. Disturbed sleep is characteristic of patients with mood disorders. The most pronounced changes of the 5-HT firing activity occur during sleep. Hence, the present paper reports a study on simultaneously measurement of hippocampal levels of serotonin and GABA during waking and sleep in the chronic mild stress (CMS) animal model of depression. The neurotransmitter findings are accompanied by depression-like symptoms (e.g. sleep alterations and reduced sucrose intake, a putative indicator of anhedonia in rodents). Our results show that animals exposed to CMS had lower hippocampal GABA levels compared to controls. In addition, after CMS there was a lack of 5-HT stage-dependency. A subgroup (five out of eight animals) showed a consistent increase in 5-HT levels in slow wave sleep and REM sleep. We also observed that this increase occurred in those animals regarded as most anhedonic (lowest intake of sucrose solution). Moreover, REM sleep was positively correlated with anhedonia. No interaction between 5-HT and GABA was found in the hippocampus. The data suggest that both GABAergic and serotonergic systems may be simultaneously but independently involved in depression. The alteration in 5-HT function may represent a link between depression-like behaviour and sleep abnormalities found in depressed patients.

Comparison of commercial ELISA assays for quantification of corticosterone in serum.

Enzyme-linked immunosorbent assay (ELISA) kits are widely used to quantify corticosterone levels for the assessment of stress in laboratory animals. The aim of this experiment was simply to evaluate if four different and widely used commercial ELISA assays would yield the same or similar values of corticosterone in serum samples taken from laboratory rats after the mild stress of being held for sampling blood from the saphenous vein. Trunk blood was sampled from 32 male Wistar rats 30 minutes after this mild stress exposure and analysed with each of four commercial ELISA kits. Both the Arbor Assays and the DRG-4164 kits were significantly higher than the DRG-5186 and the Enzo kits. There were no significant differences between the DRG-5186 and Enzo kits. Overall the correlations between kits were high. In conclusion, the commercial ELISA kits tested in the present experiment yielded different values of total corticosterone in the same serum samples. The precision in determining true values of the corticosterone level is low for these commercial ELISA kits, although they may be used to determine relative differences within studies.

A Rodent Model of Night-Shift Work Induces Short-Term and Enduring Sleep and Electroencephalographic Disturbances.

Millions of people worldwide are working at times that overlap with the normal time for sleep. Sleep problems related to the work schedule may mediate the well-established relationship between shift work and increased risk for disease, occupational errors and accidents. Yet, our understanding of causality and the underlying mechanisms that explain this relationship is limited. We aimed to assess the consequences of night-shift work for sleep and to examine whether night-shift work-induced sleep disturbances may yield electrophysiological markers of impaired maintenance of the waking brain state. An experimental model developed in rats simulated a 4-day protocol of night-work in humans. Two groups of rats underwent 8-h sessions of enforced ambulation, either at the circadian time when the animal was physiologically primed for wakefulness (active-workers, mimicking day-shift) or for sleep (rest-workers, mimicking night-shift). The 4-day rest-work schedule induced a pronounced redistribution of sleep to the endogenous active phase. Rest-work also led to higher electroencephalogram (EEG) slow-wave (1-4 Hz) energy in quiet wakefulness during work-sessions, suggesting a degraded waking state. After the daily work-sessions, being in their endogenous active phase, rest-workers slept less and had higher gamma (80-90 Hz) activity during wake than active-workers. Finally, rest-work induced an enduring shift in the main sleep period and attenuated the accumulation of slow-wave energy during NREM sleep. A comparison of recovery data from 12:12 LD and constant dark conditions suggests that reduced time in NREM sleep throughout the recorded 7-day recovery phase induced by rest-work may be modulated by circadian factors. Our data in rats show that enforced night-work-like activity during the normal resting phase has pronounced acute and persistent effects on sleep and waking behavior. The study also underscores the potential importance of animal models for future studies on the health consequences of night-shift work and the mechanisms underlying increased risk for diseases.

Chronic mild stress inhibits BDNF protein expression and CREB activation in the dentate gyrus but not in the hippocampus proper.

Chronic stress is linked to development of depression and may trigger neurobiological changes underlying the disease. Downregulation of the secretory peptide brain-derived neurotrophic factor (BDNF) and the transcriptional regulator calcium/cyclic-AMP responsive binding protein (CREB) have been implicated in stress and depression-related pathology in animal studies. When animals are exposed to the chronic mild stress (CMS) protocol, multiple depression-like symptoms are observed. Here we investigated the effect of CMS on BDNF protein expression and CREB activation in the dentate gyrus and hippocampus proper. Rats exposed for 5 weeks to repeated, unpredictable, mild stressors showed reduced BDNF expression and inhibited phosphorylation of CREB (Ser-133) in the dentate gyrus (-25.0%+/-3.5% and -29.7+/-7.3%, respectively), whereas no significant effects were observed in the hippocampus proper. CMS-treated rats consumed less sucrose compared to control rats, indicating a state of anhedonia. Moreover, phospho-CREB levels in the dentate gyrus were positively correlated with the animals' sucrose intake at the end of the CMS protocol. These results couple chronic mild stress to a downregulation of CREB activity and BDNF protein expression specifically within the dentate gyrus and support the possibility that the BDNF-CREB system plays an important role in the response to environmental challenges.

Sensitization and conditioning as contributors to gastrointestinal vulnerability.

Electric shocks are stressful and if signalled can result in Pavlovian conditioning of the stress response. Stress arising from such shocks or conditioned psychological "threat" influences vulnerability to gastrointestinal disorders. Reviewed are our studies with rats showing that unconditioned stress experiences sensitize the glandular portion of the stomach to later restraint-in-water induced erosions, as an animal model of ulcer disease. These stress effects are not attributable to corticoids but may be opioid/endorphin dependent. The unconditioned stress-induced sensitization is reduced by allowing the rat either control over or prediction of the shocks even though the direct experience with shocks is identical. Elicitation of the conditioned stress response by a signal during the ulcer induction or even shortly afterwards increases gastric vulnerability to erosions. We are now finding parallel unconditioned stress effects on colonic erosions and increases in intestinal permeability induced by dextran sulphate sodium, as an animal model of inflammatory bowel disease. We conclude that psychological context of past trauma and/or current threat increases vulnerability to gastrointestinal disorders.

Mild daily stressors in adulthood may counteract behavioural effects after constant presence of mother during early life.

This study investigated adult rat behaviour in three early life conditions, and how behaviour was affected after exposure to chronic mild stressors in later life. During postnatal days 2-14, male Wistar rats were exposed daily to either long or brief maternal separation, or were left undisturbed with their mothers (non-handled). As adults, non-handled and long maternally separated offspring demonstrated less object exploration than brief maternally separated offspring. Non-handled offspring also showed lower pre-pulse inhibition compared to both long and brief maternally separated offspring. Sucrose preference and open field behaviour as adults did not differ between the early life conditions. Exposure to four weeks of chronic mild stress in adulthood (mimicking daily hassles in humans) increased object exploration, increased pre-pulse inhibition and induced habituation of acoustic startle in non-handled offspring, similar to brief maternally separated offspring. Long maternally separated offspring exposed to chronic mild stress failed to show an increase in object exploration and enhanced pre-pulse inhibition, and did not show habituation of acoustic startle. In conclusion, different early life conditions have a different long-term impact on behaviour. Offspring from all three conditions differed from each other in terms of adult behaviour. Mild daily stressors in the adulthood counteracted the effects observed in the non-handled condition.

Selective hippocampal lesions do not increase adrenocortical activity.

It has been proposed that the hippocampus exerts a tonic inhibitory influence on the hypothalamic-pituitary-adrenal (HPA) stress axis. This claim rests, in particular, on the upregulation of corticosterone secretion and other measures of HPA activity after nonselective lesions of the hippocampal formation. We measured plasma corticosterone concentrations after selective neurotoxic damage to the hippocampus and the subiculum in rats. Concentrations were estimated during rest in the rat's home cage and at several time points after varying degrees of stress. Lesions of the hippocampus did not increase the concentration of corticosterone relative to control rats in any condition. Temporary inactivation of the hippocampus or the ventral subiculum by infusion of the GABAA receptor agonist muscimol also failed to induce hypersecretion, although hippocampal infusions did impair spatial memory. These results suggest that the hippocampus is not necessary for tonic inhibition of adrenocortical activity and imply that the HPA axis receives efficient negative feedback inhibition from other brain systems too.

Trauma and resulting sensitization effects are modulated by psychological factors.

Traumas have both immediate consequences and proactive consequences. Examples include learned helplessness, HPA-axis responsivity, gastrointestinal vulnerability to ulcer, and other correlates of anxiety disorders. Both immediate and proactive consequences may be modulated by behavioral and cognitive evolutionary evolved adaption processes, among which are forms of learning that enable 'coping'. Examples of associative and non-associative forms of coping and effects on learned helplessness, HPA-axis responsivity, and gastrointestinal vulnerability are presented. The importance of attention to behavioral contingencies in situations in which potentially traumatic events occur is emphasized as critical to understanding that it is not the physical event(s) per se that determine the immediate and long term consequences.

Cognitive activation theory of stress (CATS): from fish brains to the Olympics.

The Cognitive Activation Theory of Stress (CATS) offers formal and systematic definitions of the terms and concepts used in stress research. The stress response depends on acquired expectancies to the outcome of the stimulus and the available responses. The stress response itself is an alarm, an increase in arousal necessary for performance and adequate reactions to challenges. The response is healthy and necessary for survival. Only when sustained over time may potential health risks occur. The basic rules for when stress occurs are the same across cultures and species, from fish to Olympic performance in humans. The important dimensions for health are positive expectancies of outcome (coping), control, and safety, for all individuals in all species.