Depression: The predisposing influence of stress

Engineered bacterial extracellular vesicles for central nervous system diseases

The prevalence of central nervous system (CNS) diseases is on the rise as the population ages. The presence of various obstacles, particularly the blood-brain barrier (BBB), poses a challenge for drug delivery to the CNS. An expanding body of study suggests that gut microbiota (GM) plays an important role in CNS diseases. The communication between GM and CNS diseases has received increasing attention. Accumulating evidence indicates that the GM can modulate host signaling pathways to regulate distant organ functions by delivering bioactive substances to host cells via bacterial extracellular vesicles (BEVs). BEVs have emerged as a promising platform for the treatment of CNS diseases due to their nanostructure, ability to penetrate the BBB, as well as their low toxicity, high biocompatibility, ease of modification and large-scale culture. Here, we discuss the biogenesis, internalization mechanism and engineering modification methods of BEVs. We then focus on the use and potential role of BEVs in the treatment of CNS diseases. Finally, we outline the main challenges and future prospects for the application of BEVs in CNS diseases. We hope that the comprehensive understanding of the BEVs-based gut-brain axis will provide new insights into the treatment of CNS diseases.

Mental health progress requires causal diagnostic nosology and scalable causal discovery

Nine hundred and seventy million individuals across the globe are estimated to carry the burden of a mental disorder. Limited progress has been achieved in alleviating this burden over decades of effort, compared to progress achieved for many other medical disorders. Progress on outcome improvement for all medical disorders, including mental disorders, requires research capable of discovering causality at sufficient scale and speed, and a diagnostic nosology capable of encoding the causal knowledge that is discovered. Accordingly, the field's guiding paradigm limits progress by maintaining: (a) a diagnostic nosology (DSM-5) with a profound lack of causality; (b) a misalignment between mental health etiologic research and nosology; (c) an over-reliance on clinical trials beyond their capabilities; and (d) a limited adoption of newer methods capable of discovering the complex etiology of mental disorders. We detail feasible directions forward, to achieve greater levels of progress on improving outcomes for mental disorders, by: (a) the discovery of knowledge on the complex etiology of mental disorders with application of Causal Data Science methods; and (b) the encoding of the etiological knowledge that is discovered within a causal diagnostic system for mental disorders.

Antidepressant modulation of isolation and restraint stress effects on brain chemistry and morphology

Stress elicits adaptive responses from the brain, but it can also lead to maladaptive consequences. For example, stress can precipitate mental illness, including depression. Prolonged stress also causes damage to neurons in the hippocampus. Antidepressant drugs must be evaluated, not only for their ability to potentiate adaptive responses, but also to inhibit maladaptive consequences of stress. Ongoing research in our laboratory has compared the atypical tricyclic antidepressant, tianeptine, with the typical tricyclics, desipramine and imipramine, with respect to the effects of isolation and repeated restraint stress. Tianeptine and desipramine similarly attenuated isolation stress-induced increases in locus coeruleus and midbrain tyrosine hydroxylase mRNA levels and isolation-stress induced decreases in preproenkephalin mRNA levels in striatum and nucleus accumbens. However, tianeptine and imipramine differed in their effects in the cerebral cortex and hippocampus on 5HT2, and 5HT1A receptor levels but, surprisingly, produced similar effects on levels of the serotonin transporter labelled with [3H] paroxetine. Tianeptine also prevented stress-induced reductions in the length and number of branchpoints of dendrites of CA3 pyramidal neurons in hippocampus; comparison with effects of typical tricyclics are ongoing. Tianeptine also blocked effects of corticosterone treatment to reduce branching and length of CA3 dendrites. These actions of tianeptine may be due to interactions between 5HT and excitatory amino acids in the mossy fiber terminals on CA3 pyramidal neurons. Taken together, these results indicate that tianeptine has unique properties compared to some other antidepressant drugs, but shares in common with those drugs the ability to attenuate stress effects on tyrosine hydroxylase gene expression and on the serotonin transporter. It remains to be seen whether these actions are the basis of a common antidepressant action.

The role of the brain-gut-microbiota axis in psychology: The importance of considering gut microbiota in the development, perpetuation, and treatment of psychological disorders

INTRODUCTION

The prevalence of psychological disorders remains stable despite steady increases in pharmacological treatments suggesting the need for auxiliary treatment options. Consideration of the brain-gut-microbiota axis (BGMA) has made inroads into reconceptualizing psychological illness from a more holistic perspective. While our understanding of the precise role of gut microbiota (GM) in psychological illness is in its infancy, it represents an attractive target for novel interventions.

METHOD

An extensive review of relevant literature was undertaken.

RESULTS

Gut microbiota are proposed to directly and indirectly influence mood, cognition, and behavior which are key components of mental health. This paper outlines how GM may be implicated in psychological disorders from etiology through to treatment and prevention using the Four P model of case formulation.

CONCLUSION

Moving forward, integration of GM into the conceptualization and treatment of psychological illness will require the discipline of psychology to undergo a significant paradigm shift. While the importance of the GM in psychological well-being must be respected, it is not proposed to be a panacea, but instead, an additional arm to a multidisciplinary approach to treatment and prevention.

Search Activity Concept: Relationship between Behavior, Health and Brain Functions

Search activity concept provides a new classification of the behavior which distinguishes search activity (activity in the uncertain situation with the constant feedback between behavior and its outcome), stereotyped behavior with a definite probability forecast, panic (activity without feedback between activity and its outcome) and renunciation of search. Only search activity which includes fight, flight, orienting behavior and creativity raises the body’s resistance to stress, to natural and experimentally induced pathology whereas renunciation of search which display itself in freezing, helplessness and depression forms a nonspecific predisposition to somatic disturbances (e.g. psychosomatic diseases). Dreams in REM sleep are regarded as a specific form of search activity aimed at compensating for the lack of search in waking. REM sleep deprivation on a small as well as on rotating platform raises the requirement in REM sleep by frustrating search activity. It is suggested that in wakefulness characterized by the prominent search activity the inhibitory alpha-2- adrenoreceptors became less sensitive to stimulation and consequently in this state the activity of the brain monoamine neurons is less limited by the level of brain monoamines. During renunciation of search brain monoamine synthesis is not stimulated by monoamine exhaustion. In REM sleep the critical level of brain monoamines for search activity to start is lower than in wakefulness and alpha-2-adrenoreceptors are less sensitive than in the state of renunciation of search although more sensitive than during search behavior in waking. REM sleep indirectly contributes to memory consolidation by carrying out its main function — restoration of search activity. A functionally sufficient REM sleep contains search activity in dreams (subject is active in his/her own dream scenario) while in functionally insufficient REM sleep dreams are characterized by subject’s passive position and feeling of helplessness. REM sleep insufficiency is an obligate condition for mental and somatic disorders to appear. The difference between normal (adaptive) and pathological (maladaptive) emotional tension is determined by the presence or absence of search activity in the structure of emotional tension. Repression of the unacceptable motive causing neurotic anxiety is a human variant of renunciation of search. Hypochondriac symptoms are in negative relationships with psychosomatic disorders and they, as well as positive symptoms in schizophrenia and anorectic behavior in anorexia nervosa, represent a pathological misdirected search activity.

Stress and Depression among Veterinary Medical Students

While existing literature suggests that professional students (e.g., medical, dental, law, nursing, etc.) experience high levels of stress and depression, the experiences of veterinary medical students have been less well examined. The purpose of this study was to explore the levels of stress and depression among veterinary medical students and to examine the relationship between these variables. Study participants were 1,245 veterinary medical students from North America. The findings provide support for the assertion that veterinary medical students experience high levels of stress and depression. Results also indicated that there is a correlation between stress and depression for veterinary medical students and that female students experience higher levels of stress and depression than their male counterparts.

Enzymatic Depletion of the Polysialic Acid Moiety Associated with the Neural Cell Adhesion Molecule Inhibits Antidepressant Efficacy

Antidepressant drugs are too often ineffective, the exact mechanism of efficacy is still ambiguous, and there has been a paucity of novel targets for pharmacotherapy. In an attempt to understand the pathogenesis of depression and subsequently develop more efficacious antidepressant drugs, multiple theories have been proposed, including the modulation of neurotransmission, the upregulation of neurogenesis and neurotrophic factors, normalizing hypothalamic-pituitary-adrenal reactivity, and the reduction of neuroinflammation; all of which have supporting lines of evidence. Therefore, an ideal molecular target for novel pharmaceutical intervention would function at the confluence of these theories. The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) functions broadly, serving to mediate synaptic plasticity, neurogenesis, neurotrophic factor signaling, and inflammatory signaling throughout the brain; all of which are associated with the pathophysiology and treatment of depression. Moreover, the expression of PSA-NCAM is reduced by depression, and conversely enhanced by antidepressant treatment, particularly within the hippocampus. Here we demonstrate that selectively cleaving the polysialic acid moiety, using the bacteriophage-derived enzyme endoneuraminidase N, completely inhibits the antidepressant efficacy of the selective-serotonin reuptake inhibitor fluoxetine (FLX) in a chronic unpredictable stress model of depression. We also observe a corresponding attenuation of FLX-induced hippocampal neuroplasticity, including decreased hippocampal neurogenesis, synaptic density, and neural activation. These data indicate that PSA-NCAM-mediated neuroplasticity is necessary for antidepressant action; therefore PSA-NCAM represents an interesting, and novel, target for pharmacotherapy.

Influences of Chronic Mild Stress Exposure on Motor, Non-Motor Impairments and Neurochemical Variables in Specific Brain Areas of MPTP/Probenecid Induced Neurotoxicity in Mice

Parkinson's disease (PD) is regarded as a movement disorder mainly affecting the elderly population and occurs due to progressive loss of dopaminergic (DAergic) neurons in nigrostriatal pathway. Patients suffer from non-motor symptoms (NMS) such as depression, anxiety, fatigue and sleep disorders, which are not well focussed in PD research. Depression in PD is a predominant /complex symptom and its pathology lies exterior to the nigrostriatal system. The main aim of this study is to explore the causative or progressive effect of chronic mild stress (CMS), a paradigm developed as an animal model of depression in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (25 mg/kg. body wt.) with probenecid (250 mg/kg, s.c.) (MPTP/p) induced mice model of PD. After ten i.p. injections (once in 3.5 days for 5 weeks) of MPTP/p or exposure to CMS for 4 weeks, the behavioural (motor and non-motor) impairments, levels and expressions of dopamine (DA), serotonin (5-HT), DAergic markers such as tyrosine hydroxylase (TH), dopamine transporter (DAT), vesicular monoamine transporters-2 (VMAT 2) and α-synuclein in nigrostriatal (striatum (ST) and substantia nigra (SN)) and extra-nigrostriatal (hippocampus, cortex and cerebellum) tissues were analysed. Significantly decreased DA and 5-HT levels, TH, DAT and VMAT 2 expressions and increased motor deficits, anhedonia-like behaviour and α-synuclein expression were found in MPTP/p treated mice. Pre and/or post exposure of CMS to MPTP/p mice further enhanced the MPTP/p induced DA and 5-HT depletion, behaviour abnormalities and protein expressions. Our results could strongly confirm that the exposure of stress after MPTP/p injections worsens the symptoms and neurochemicals status of PD.

Adult neurogenesis and mental illness

Several lines of evidence suggest that adult neurogenesis, the production of new neurons in adulthood, may play a role in psychiatric disorders, including depression, anxiety, and schizophrenia. Medications and other treatments for mental disorders often promote the proliferation of new neurons; the time course for maturation and integration of new neurons in circuitry parallels the delayed efficacy of psychiatric therapies; adverse and beneficial experiences similarly affect development of mental illness and neurogenesis; and ablation of new neurons in adulthood alters the behavioral impact of drugs in animal models. At present, the links between adult neurogenesis and depression seem stronger than those suggesting a relationship between new neurons and anxiety or schizophrenia. Yet, even in the case of depression there is currently no direct evidence for a causative role. This article reviews the data relating adult neurogenesis to mental illness and discusses where research needs to head in the future.

Brain region-specific reduction in c-Fos expression associated with an anxiolytic effect of yokukansan in rats

ETHNOPHARMACOLOGICAL RELEVANCE

A traditional Japanese (Kampo) medicine, yokukansan, has long been used to treat neurosis, insomnia, and night crying and irritability in children. Recently, this medicine has reported to improve the behavioral and psychological symptoms of dementia that often become problematic in patients with Alzheimer's disease and other forms of dementia.

AIM OF THE STUDY

Several animal studies have reported that yokukansan has an anxiolytic effect. However, the underlying mechanisms are not yet understood. In the present study, we investigated the effects in rats of single and repeated administrations of yokukansan on anxiety-like behaviors, stress responses, and the brain regions involved.

MATERIALS AND METHODS

Yokukansan dissolved in water (100 or 300 mg/kg) was administered orally to F344/N male rats 1h before each test or for two weeks before the tests began. Locomotor activity and anxiety-related behavior in the open-field test and the elevated plus-maze test, serum corticosterone levels, and restraint stress-induced c-Fos expression in various brain regions as a marker of neuronal activation were evaluated in both the vehicle-treated and yokukansan-treated rats.

RESULTS

A single administration of yokukansan had no effect on locomotor activity or anxiety-like behavior; however, repeated administration decreased anxiety-like behavior in a dose-dependent manner. Neither single nor repeated administration of yokukansan had an effect on the basal or stress-induced levels of serum corticosterone. For c-Fos expression, restraint stress increased the number of c-Fos-positive cells in the subdivisions of the prefrontal cortex, amygdala, and hypothalamus. Repeated administration of yokukansan decreased the stress-induced c-Fos expression in the prelimbic cortex and the basolateral and medial amygdaloid nuclei.

CONCLUSIONS

The present study indicates that repeated oral administration of yokukansan has an anxiolytic effect and that this effect may be associated with attenuated neuronal activity in the medial prefrontal cortex and amygdala.

Etazolate rescues behavioral deficits in chronic unpredictable mild stress model: modulation of hypothalamic-pituitary-adrenal axis activity and brain-derived neurotrophic factor level

Preliminary study in our laboratory showed that etazolate produced antidepressant- and anxiolytic-like effects in rodent models, however, the ability of etazolate to produce antidepressant- and anxiolytic-like effects and underlying mechanism(s) in chronic unpredictable mild stress (CUMS) model have not been adequately addressed. This study was aimed to investigate the beneficial effects of etazolate on CUMS-induced behavioral deficits (depression- and anxiety-like behaviors). In addition, the possible underlying mechanism(s) of etazolate in CUMS model was also investigated by measuring serum corticosterone (CORT) and brain-derived neurotrophic factor (BDNF) levels. Mice were subjected to a battery of stressors for 28 days. Etazolate (0.5 and 1 mg/kg, p.o.) and fluoxetine (20mg/kg, p.o.) were administered during the last 21 days (8-28th) of the CUMS paradigm. The results showed that 4-weeks CUMS produces significant depression-like behavior in tail suspension test (TST) and partial anxiety-like behavior in elevated plus maze (EPM) and open field test (OFT). Stressed mice have also shown a significant high serum CORT and low BDNF level. Chronic treatment with etazolate (0.5 and 1mg/kg., p.o.) and fluoxetine (20mg/kg., p.o.) produced significant antidepressant-like behavior in TST (decreased duration of immobility), whereas, partial anxiolytic-like behavior in EPM (increased percentage of open arm entries) and OFT (increased % central ambulation score, total ambulation score and time spent in center zone). In addition, etazolate and fluoxetine treatment significantly (p<0.05) increased the BDNF level and inhibited the hypothalamic-pituitary-adrenocortical (HPA) axis hyperactivity, as evidenced by low serum CORT level in stressed mice. In addition, etazolate and fluoxetine also showed significant antidepressant- and anxiolytic-like effects in normal control mice. In this study no significant changes were observed in locomotor activity in actophotometer test. Moreover, we did not find any effect of etazolate and fluoxetine on CORT and BDNF levels in normal control mice. In conclusion, the results of the present study suggested compelling evidences that etazolate has more marked effect on depression-like behavior in mice, which is atleast in part may be related to their modulating effects on the HPA axis and BDNF level.

The psychology of tooth wear

AIM

To review the main psychological and mental conditions that are manifested dentally in the form of tooth wear. These conditions include depression, eating disorders, and alcohol and drug use disorders. The paper will also review the comorbidity of these conditions and the relevance of other medical conditions and lifestyle factors, such as gastroesophageal reflux disorder, smoking and diet, in the expression of tooth wear.

CONCLUSION

A holistic, multidisciplinary, healthcare approach is required in management of tooth wear patients with underlying mental health disorders. Dentists and Dental Care Professionals can have an important role in identifying these mental disorders through the observed tooth wear. They can also play a key role in monitoring patients' response and compliance to medical treatment through the monitoring of tooth wear progression and expression.

5-HT2A receptors in the orbitofrontal cortex facilitate reversal learning and contribute to the beneficial cognitive effects of chronic citalopram treatment in rats

Chronic stress is a risk factor for depression, and chronic stress can induce cognitive impairments associated with prefrontal cortical dysfunction, which are also major components of depression. We have previously shown that 5 wk chronic intermittent cold (CIC) stress induced a reversal-learning deficit in rats, associated with reduced serotonergic transmission in the orbitofrontal cortex (OFC) that was restored by chronic treatment with a selective serotonin reuptake inhibitor (SSRI). However, the mechanisms underlying the beneficial cognitive effects of chronic SSRI treatment are currently unknown. Thus, the purpose of this study was to investigate the potential modulatory influence specifically of 5-HT2A receptors (5-HT2ARs) in the OFC on reversal learning, and their potential contribution to the beneficial cognitive effects of chronic SSRI treatment. Bilateral microinjections of the selective 5-HT2AR antagonist, MDL 100,907 into OFC (0.02-2.0 nmol) had a dose-dependent detrimental effect on a reversal-learning task, suggesting a facilitatory influence of 5-HT2ARs in the OFC. In the next experiment, rats were exposed to 5 wk CIC stress, which compromised reversal learning, and treated chronically with the SSRI, citalopram (20 mg/kg.d) during the final 3 wk of chronic stress. Chronic citalopram treatment improved reversal learning in the CIC-stressed rats, and bilateral microinjection of MDL 100,907 (0.20 nmol, the optimal dose from the preceding experiment) into OFC once again had a detrimental effect on reversal learning, opposing the beneficial effect of citalopram. We conclude that 5-HT2ARs in the OFC facilitate reversal learning, and potentially contribute to the beneficial cognitive effects of chronic SSRI treatment.

From the stressed adolescent to the anxious and depressed adult: investigations in rodent models

Anxiety and depression are the most prevalent of the psychiatric disorders. The average age of onset of these disorders is in adolescence, and stressful experiences are recognized as an important pathway to such dysfunction. Until recently, however, most animal models of these disorders involved adult males. We provide a brief overview of anxiety and depression and the extent to which adolescent rodents are a valid model for their investigation, and briefly review the main measures of anxiety-like and depressive behaviour in rodents. The focus of the review is investigations in which adolescent rodents were exposed to chronic stressors, describing our research using social instability stress and that of other researchers using various social and non-social stressors. The evidence to date suggests stress in adolescence alters the trajectory of brain development, and particularly that of the hippocampus, increasing anxiety and depressive behaviour in adulthood.

Effects of brief stress exposure during early postnatal development in balb/CByJ mice: I. Behavioral characterization

Early life stress has been linked to the etiology of mental health disorders. Rodent models of neonatal maternal separation stress frequently have been used to explore the long-term effects of early stress on changes in affective and cognitive behaviors. However, most current paradigms risk metabolic deprivation, due to prolonged periods of pup removal from the dam. We have developed a new paradigm in Balb/CByJ mice, that combines very brief periods of maternal separation with temperature stress to avoid the confound of nutritional deficiencies. We have also included a within-litter control group of pups that are not removed from the dam. The present experiments provide an initial behavioral characterization of this new model. We show that neonatally stressed mice display increased anxiety and aggression along with increased locomotion but decreased exploratory behavior. In contrast, littermate controls show increased exploration of novelty, compared to age-matched, colony-reared controls. Behavioral changes in our briefly stressed mice substantially concur with the existing literature, except that we were unable to observe any cognitive deficits in our paradigm. However, we show that within litter control pups also sustain behavioral changes suggesting complex and long-lasting interactions between different environmental factors in early postnatal life.

Effects of brief stress exposure during early postnatal development in Balb/CByJ mice: II. Altered cortical morphology

Early life experience can significantly determine later mental health status and cognitive function. Neonatal stress, in particular, has been linked to the etiology of mental health disorders as divergent as mood disorder, schizophrenia, and autism. Our study uses a Balb/CByJ mouse model to test the hypothesis, that neonatal stress will alter development and subsequent environmental modulation of neocortex. Using a split litter design, we generated stressed mice (STR) and within litter controls (LMC) along with age-matched, untreated animals (AMC), to serve as across litter controls. Short, daily exposure to a psychosocial/physical stressor, during the first week of life, resulted by adulthood in significant changes in neocortical thickness and architecture, which were further modulated by exposure to behavioral testing. Surprisingly, cortical size in LMC mice was also affected. These observations were compared to the effects of environmental enrichment in the same mouse strain. Our data indicate that LMC and STR males share with environmentally enriched males, an increase in thickness in infra-granular cortical layers, while STR also display a stress selective decrease in supragranular layers, in response to behavioral training as adults.

Peripheral oxytocin administration buffers autonomic but not behavioral responses to environmental stressors in isolated prairie voles

Negative social experiences such as social stressors and isolation influence mental and physical illnesses, including affective disorders and heart disease. Studies focused on socially monogamous prairie voles can provide insight into neurobiological systems that underlie the consequences of negative social interactions. Female prairie voles were exposed to 28 days of social isolation or pairing with a female sibling (control). Voles were administered daily oxytocin [20 μg/50 μl, subcutaneous (sc)] or saline vehicle (50 μl, sc) for 14 days and exposed to two behavioral stressors [elevated plus maze (EPM) and resident-intruder test]. Brain tissue was collected for analysis of central peptide levels in the hypothalamic paraventricular nucleus (PVN). Isolation produced autonomic changes [increased heart rate (HR) and decreased HR variability) during both acute stressors and increased anxiety behaviors in the EPM. Oxytocin injection prevented the autonomic consequences of the acute stressors in isolated prairie voles, but did not affect the behaviors tested under the present conditions. Oxytocin had no effect on the behavioral or autonomic responsiveness in paired prairie voles. Oxytocin injection may exert a beneficial effect on autonomic responses to stressors in isolated animals through increasing the number of oxytocin-containing neurons and decreasing the number of corticotropin-releasing hormone-containing neurons in the PVN. Oxytocinergic mechanisms may serve to compensate for autonomic responses associated with chronic isolation and exposure to both social and non-social acute stressors.

Activating effects of chronic variable stress in rats with different exploratory activity: association with dopamine d(1) receptor function in nucleus accumbens

BACKGROUND/AIMS

Rats display persistent behavioural phenotypes of low (LE) versus high (HE) exploratory activity in the exploration box paradigm. LE rats that prefer passive coping strategies show differential dopaminergic activity in the striatum. The main hypothesis of this study was that chronic variable stress (CVS) would have a higher impact on LE rats.

METHODS

Animals were submitted to a CVS regimen lasting 32 days that was followed by a behavioural test battery. The functional states of their dopamine D(1) and D(2) receptors were measured in the striatum and nucleus accumbens (NAcc). Cerebral oxidative metabolism was assessed via cytochrome c oxidase histochemistry in 65 brain regions.

RESULTS

CVS decreased weight gain, to a higher extent in LE rats, and lowered the sucrose preference after the first week, but habituation to the anhedonic effect had developed by the end of the experiment. CVS did not change the behavioural phenotypes initially assigned. No effect of stress on D(2) receptor function was found. Chronically stressed animals exhibited higher levels of social interaction and D(1) receptor-mediated cAMP accumulation in the NAcc, but not in the striatum. CVS was associated with higher oxidative metabolism levels in the anteroventral thalamus, median raphe nuclei and central periaqueductal grey matter. These changes after stress did not depend upon the exploratory phenotype.

CONCLUSION

This study revealed changes in brain biochemistry after habituation to CVS that might be implicated in successful adaptation to chronic stress.

A psychobiological theory of attachment

This article describes a neurobiological basis for the “first attachment” of the primate infant to its caretaker. The infant normally internalizes a neurobiological “image” of the behavioral and emotional characteristics of its caregiver that later regulates important features of its brain function. Current models of sensorimotor analysis and its relation to emotion suggest that sensorimotor systems are also habit and memory systems, their functional status and lability regulated in part by biogenic amine systems. The intertwined development of neural and social functions can sometimes go awry. If the attachment process fails or the caregiver is incompetent, the infant may become socially dysfunctional. This helps explain the developmental psychopathology and later vulnerability to adult psychopathology that result from disruptions of social attachment.

Cardiac dysfunction and hypothalamic activation during a social crowding stressor in prairie voles

Negative social interactions produce several detrimental consequences in humans and non-human animals; and conversely, positive social interactions may have stress-buffering effects on both behavior and physiology. However, the mechanisms underlying specific stressor-responsiveness in the context of the social environment are not well understood. The present study investigated the integration of behavior, cardiac function, and Fos-immunoreactivity in the hypothalamic paraventricular nucleus during an acute social stressor in female, socially monogamous prairie voles exposed to previous long-term pairing (control conditions) or isolation. Animals previously exposed to social isolation displayed increased heart rate, attenuated heart rate variability, and increased incidence of cardiac arrhythmias during an acute crowding stressor versus animals previously exposed to social pairing; these cardiac alterations were not secondary to behavioral changes during the crowding stressor. Furthermore, social isolation was associated with increased c-Fos-immunoreactivity in the hypothalamic paraventricular nucleus following the crowding stressor, versus social pairing. The prairie vole provides a useful model for understanding how the social environment contributes to changes in behavior, cardiac function, and central stress-regulatory processes in humans.

Testosterone decrease does not play a major role in the suppression of hippocampal cell proliferation following social defeat stress in rats

Stress of social defeat in rodents is known to have a strong and long-lasting effect on brain, physiology and behavior, which bears similarities with certain human stress related psychopathologies. Previous experiments in this lab showed that social defeat stress suppresses testosterone secretion and causes a lasting desensitization of the serotonergic 5-HT(1A) receptors. Testosterone supplementation in socially stressed tree shrews prevented a decrease in hippocampal 5-HT(1A) receptor binding. These receptors are hypothesized to play an important role in neurogenesis in this brain structure. We designed the present experiment to test if social defeat reduces hippocampal cell proliferation and neurogenesis in rats and if testosterone supplementation can prevent this reduction. The results indicate that repeated social defeat stress on 5 successive days induces a significant drop in plasma testosterone levels in male rats and suppresses hippocampal cell proliferation 24h and 3weeks after the end of the stress period. Testosterone supplementation prevented the social stress induced drop in plasma testosterone levels. The hormone supplementation also reduced the negative effect of stress on hippocampal BrdU labeling at 3weeks post-defeat. This effect was, however, rather weak and was caused by the tendency of the hormone in itself to suppress proliferation and the failure to fully recover the proliferation rate. Survival of dentate gyrus cells that either proliferated prior to the stress period or 24h after the last defeat was not affected by the social defeats. Thus the stress-induced lowering of hippocampal cell proliferation is not likely to be caused by transient inhibition of testosterone secretion during social stress.

Effect of tryptophan-rich egg protein hydrolysate on brain tryptophan availability, stress and performance

BACKGROUND & AIMS

Reduced brain serotonin function is involved in stress-related disturbances and may particularly occur under chronic stress. Although serotonin production directly depends on the availability of its plasma dietary amino acid precursor tryptophan (TRP), previously described effects of tryptophan-rich food sources on stress-related behavior are rather modest. Recently, an egg protein hydrolysate (EPH) was developed that showed a much greater effect on brain TRP availability than pure TRP and other TRP-food sources and therefore may be more effective for performance under stress. The aim of the present study was to investigate the effects of EPH compared to placebo protein on plasma amino acids, stress coping and performance in subjects with high and low chronic stress vulnerabilities.

METHODS

In a placebo-controlled, double-blind, crossover study, 17 participants with high and 18 participants with low chronic stress vulnerabilities were monitored for mood and performance under acute stress exposure either following intake of EPH or placebo.

RESULTS

EPH significantly increased plasma TRP availability for uptake into the brain, decreased depressive mood in all subjects and improved perceptual-motor and vigilance performance only in low chronic stress-vulnerable subjects.

CONCLUSIONS

The acute use of a TRP-rich egg protein hydrolysate (EPH) is an adequate method to increase plasma TRP for uptake into the brain and may be beneficial for perceptual-motor and vigilance performance in healthy volunteers.

ROLE OF SEROTONIN-1A RECEPTORS IN RESTRAINT-INDUCED BEHAVIORAL DEFICITS AND ADAPTATION TO REPEATED RESTRAINT STRESS IN RATS

8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), a selective 5-hydroxy-tryptamine (5-HT; serotonin)-1A agonist was used to evaluate the role 5-HT-1 A receptors in restraint-induced behavioral deficits and adaptation to repeated restraint stress in rats. Animals were injected with 8-OH-DPAT at a dose of 0.25 mg/kg 1 h before exposing to an episode of 2 h/day restraint stress daily for 5 days. Effects of drug administration and restraint stress on 24 h cumulative food intakes were monitored daily. Intensity of 8-OH-DPAT-induced serotonin syndrome was also monitored each day before submitting animals to the episode of stress. Exposure to the first episode of 2 h restraint stress resulted in a decrease in 24 h cumulative food intake and an attenuation of 8-OH-DPAT-induced serotonin syndrome monitored next day. The deficits attenuated following 2nd and 3rd 2 h/day restraint were not observed following the 4th and 5th 2 h/day restraint. The decreases of food intake following 1st and 2nd day restraint sessions were smaller in 8-OH-DPAT than saline-injected animals. Administration of 8-OH-DPAT on day 6 elicited comparable serotonin syndrome in unrestrained and repeatedly restrained groups. Brain 5-HT metabolism decreased in unrestrained but not repeatedly restrained animals. The results suggest that a decrease in serotonergic neurotransmission is involved in restraint-induced behavioral deficits while a normalization of serotonin neurotransmission due to desensitization of somatodendritic 5-HT-1A receptors may help cope with the stress demand to produce adaptation to stress.

Stress, depression and cardiovascular dysregulation: a review of neurobiological mechanisms and the integration of research from preclinical disease models

Bidirectional associations between mood disorders and cardiovascular diseases are extensively documented. However, the precise physiological and biochemical mechanisms that underlie such relationships are not well understood. This review focuses on the neurobiological processes and mediators that are common to both mood and cardiovascular disorders. The discussion places an emphasis on the role of exogenous stressors in addition to: (a) neuroendocrine and neurohumoral changes involving dysfunction of the hypothalamic-pituitary-adrenal axis and the activation of the renin-angiotensin-aldosterone system, (b) immune alterations including activation of pro-inflammatory cytokines, (c) autonomic and cardiovascular dysregulation including increased sympathetic drive, withdrawal of parasympathetic tone, cardiac rate and rhythm disturbances, and altered baroreceptor reflex function, (d) central neurotransmitter system dysfunction involving the dopamine, norepinephrine and serotonin systems, and (e) behavioral changes including fatigue and physical inactivity. The review also discusses experimental investigations using preclinical disease models to elucidate the neurobiological mechanisms underlying the link between mood disorders and cardiovascular disease. These include: (a) the chronic mild stress model of depression, (b) a model of congestive heart failure, (c) a model of cardiovascular deconditioning, (d) pharmacological manipulations of body fluid and sodium balance, and (e) pharmacological manipulations of the central serotonergic system. In combination with an extensive human research literature, the investigation of mechanisms underlying mood and cardiovascular regulation using animal models will enhance understanding the association between depression and cardiovascular disease. This will ultimately promote the development of better treatments and interventions for individuals with co-morbid psychological and somatic pathologies.