Optimization of chronic stress paradigms using anxiety- and depression-like behavioral parameters

Methylene blue modulates β-secretase, reverses cerebral amyloidosis, and improves cognition in transgenic mice

Amyloid precursor protein (APP) proteolysis is required for production of amyloid-β (Aβ) peptides that comprise β-amyloid plaques in the brains of patients with Alzheimer disease (AD). Here, we tested whether the experimental agent methylene blue (MB), used for treatment of methemoglobinemia, might improve AD-like pathology and behavioral deficits. We orally administered MB to the aged transgenic PSAPP mouse model of cerebral amyloidosis and evaluated cognitive function and cerebral amyloid pathology. Beginning at 15 months of age, animals were gavaged with MB (3 mg/kg) or vehicle once daily for 3 months. MB treatment significantly prevented transgene-associated behavioral impairment, including hyperactivity, decreased object recognition, and defective spatial working and reference memory, but it did not alter nontransgenic mouse behavior. Moreover, brain parenchymal and cerebral vascular β-amyloid deposits as well as levels of various Aβ species, including oligomers, were mitigated in MB-treated PSAPP mice. These effects occurred with inhibition of amyloidogenic APP proteolysis. Specifically, β-carboxyl-terminal APP fragment and β-site APP cleaving enzyme 1 protein expression and activity were attenuated. Additionally, treatment of Chinese hamster ovary cells overexpressing human wild-type APP with MB significantly decreased Aβ production and amyloidogenic APP proteolysis. These results underscore the potential for oral MB treatment against AD-related cerebral amyloidosis by modulating the amyloidogenic pathway.

A robust and reliable non-invasive test for stress responsivity in mice

Stress and an altered stress response have been associated with many multifactorial diseases, such as psychiatric disorders or neurodegenerative diseases. As currently mouse mutants for each single gene are generated and phenotyped in a large-scale manner, it seems advisable also to test these mutants for alterations in their stress responses. Here we present the determinants of a robust and reliable non-invasive test for stress-responsivity in mice. Stress is applied through restraining the mice in tubes and recording behavior in the Open Field 20 min after cessation of the stress. Two hours, but not 15 or 50 min of restraint lead to a robust and reproducible increase in distance traveled and number of rearings during the first 5 min in the Open Field in C57BL/6 mice. This behavioral response is blocked by the corticosterone synthesis inhibitor metyrapone, but not by RU486 treatment, indicating that it depends on corticosteroid secretion, but is not mediated via the glucocorticoid receptor type II. We assumed that with a stress duration of 15 min one could detect hyper-responsivity, and with a stress duration of 2 h hypo-responsivity in mutant mouse lines. This was validated with two mutant lines known to show opposing effects on corticosterone secretion after stress exposure, corticotropin-releasing hormone (CRH) over-expressing mice and CRH receptor 1 knockout (KO) mice. Both lines showed the expected phenotype, i.e., increased stress responsivity in the CRH over-expressing mouse line (after 15 min restraint stress) and decreased stress responsivity in the CRHR1-KO mouse line (after 2 h of restraint stress). It is possible to repeat the acute stress test several times without the stressed animal adapting to it, and the behavioral response can be robustly evoked at different ages, in both sexes and in different mouse strains. Thus, locomotor and rearing behavior in the Open Field after an acute stress challenge can be used as reliable, non-invasive indicators of stress responsivity and corticosterone secretion in mice.

Possible additional antidepressant-like mechanism of sodium butyrate: targeting the hippocampus

Chromatin remodeling mediated by histone acetylation might be involved in the pathophysiology and the treatment of depression. Recently, it has been reported that the histone deacetylase (HDAC) inhibitors, such as sodium butyrate (SB), could be a potential therapeutic agent for depression treatment. In the present study, we aimed to clarify the antidepressant mechanism of SB in the hippocampus. The mice were exposed to chronic restraint stress (CRS) for 14 consecutive days (2 h/day) to induce depression-like behaviors. To assess depression-like behaviors, sucrose preference test, light dark test (LD), tail suspension test (TST), and forced swim test (FST) were performed after CRS. We observed that CRS decreased HDAC2 and 5 mRNA and protein levels in the hippocampus. In addition, SB co-treatment decreased the depression-like behaviors that are induced by CRS. SB prevented and normalized the phosphorylation of cAMP response element binding protein (pCREB), acetylation of histone H3 (AceH3), HDAC2, and brain-derived neurotrophic factor (BDNF) expression level that were decreased by CRS in the hippocampus. These results suggest that the decreased HDAC2 and 5 expressions in the hippocampus of CRS may be a type of spontaneous coping response against CRS. However, it seems to be unsuccessful to prevent depression induction since reduction of pCREB, AceH3 and BDNF were accompanied by CRS in the hippocampus. Moreover, the reduced AceH3 level may be associated with the decreased pCREB, which appears to lead to the decreased BDNF.

Effects of acute and chronic psychological stress on platelet aggregation in mice

Although psychological stress has long been known to alter cardiovascular function, there have been few studies on the effect of psychological stress on platelets, which play a pivotal role in cardiovascular disease. In the present study, we investigated the effects of acute and chronic psychological stress on the aggregation of platelets and platelet cytosolic free calcium concentration ([Ca(2+)]i). Mice were subjected to both transportation stress (exposure to novel environment, psychological stress) and restraint stress (psychological stress) for 2 h (acute stress) or 3 weeks (2 h/day) (chronic stress). In addition, adrenalectomized mice were subjected to similar chronic stress (both transportation and restraint stress for 3 weeks). The aggregation of platelets from mice and [Ca(2+)]i was determined by light transmission assay and fura-2 fluorescence assay, respectively. Although acute stress had no effect on agonist-induced platelet aggregation, chronic stress enhanced the ability of the platelet agonists thrombin and ADP to stimulate platelet aggregation. However, chronic stress failed to enhance agonist-induced increase in [Ca(2+)]i. Adrenalectomy blocked chronic stress-induced enhancement of platelet aggregation. These results suggest that chronic, but not acute, psychological stress enhances agonist-stimulated platelet aggregation independently of [Ca(2+)]i increase, and the enhancement may be mediated by stress hormones secreted from the adrenal glands.

Comparison of the effects of single and daily repeated immobilization stress on resting activity and heterotypic sensitization of the hypothalamic-pituitary-adrenal axis

Acute exposure to severe stressors causes marked activation of the hypothalamic-pituitary-adrenal (HPA) axis that is reflected on the day after higher resting levels of HPA hormones and sensitization of the HPA response to novel (heterotypic) stressors. However, whether a single exposure to a severe stressor or daily repeated exposure to the same (homotypic) stressor modifies these responses to the same extent has not been studied. In this experiment, we studied this issue in adult male Sprague-Dawley rats daily exposed for seven days to a severe stressor such as immobilization on boards (IMO). A first exposure to 1 h IMO resulted in a marked activation of the HPA axis as reflected in plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone, and such activation was significantly reduced after the seventh IMO. On the day after the first IMO, higher resting levels of ACTH and corticosterone and sensitization of their responses to a short exposure to an open-field (OF) were observed, together with a marked hypoactivity in this environment. Repeated exposure to IMO partially reduced hypoactivity, the increase in resting levels of HPA hormones and the ACTH responsiveness to the OF on the day after the last exposure to IMO. In contrast, corticosterone response was gradually increased, suggesting partial dissociation from ACTH. These results indicate that daily repeated exposure to the same stressor partially reduced the HPA response to the homotypic stressor as well as the sensitization of HPA axis activity observed the day after chronic stress cessation.

Effects of stress and MDMA on hippocampal gene expression

MDMA (3,4-methylenedioxymethamphetamine) is a substituted amphetamine and popular drug of abuse. Its mood-enhancing short-term effects may prompt its consumption under stress. Clinical studies indicate that MDMA treatment may mitigate the symptoms of stress disorders such as posttraumatic stress syndrome (PTSD). On the other hand, repeated administration of MDMA results in persistent deficits in markers of serotonergic (5-HT) nerve terminals that have been viewed as indicative of 5-HT neurotoxicity. Exposure to chronic stress has been shown to augment MDMA-induced 5-HT neurotoxicity. Here, we examine the transcriptional responses in the hippocampus to MDMA treatment of control rats and rats exposed to chronic stress. MDMA altered the expression of genes that regulate unfolded protein binding, protein folding, calmodulin-dependent protein kinase activity, and neuropeptide signaling. In stressed rats, the gene expression profile in response to MDMA was altered to affect sensory processing and responses to tissue damage in nerve sheaths. Subsequent treatment with MDMA also markedly altered the genetic responses to stress such that the stress-induced downregulation of genes related to the circadian rhythm was reversed. The data support the view that MDMA-induced transcriptional responses accompany the persistent effects of this drug on neuronal structure/function. In addition, MDMA treatment alters the stress-induced transcriptional signature.

Anti-Depressant Like Effect of Methyl Gallate Isolated from Acer barbinerve in Mice

In the present study, the anti-depressant like effect of methyl gallate (MG) isolated from the stem bark of Acer barbinerve was examined in ICR mice. Body weight (BDW) and blood glucose (BDG) levels significantly decreased in the repeated restraint stress (RRS) group (2 h/day for 14 days) compared to the no stress (NS) group. To examine the effect of MG on RS-induced BDW loss and hypoglycemia, MG (10 mg/kg) and the anti-depressant fluoxetine (10 mg/kg) were administered daily for 14 days. Orally administered MG and fluoxetine significantly attenuated the RS-induced BDW loss and hypoglycemia. Interestingly, MG administered mice showed increased BDG levels in the normal and glucose feeding condition. Chronic RS-subjected mice showed immobilized and depressed behaviors. The effect of MG on the depressed behaviors was evaluated using the tail-suspension test (TST) and the forced swimming test (FST). In both tests, RS-induced immobilized behaviors were significantly reversed in MG and fluoxetine administered groups. Taken together, MG significantly attenuated the RS-induced BDW loss, hypoglycemia, and depressed behaviors. Considering that decreased BDG levels (hypoglycemia) can cause depression, MG may exert its anti-depressant like effect by preventing hypoglycemia. Our results suggest that MG isolated from A. barbinerve can exert anti-depressant like effect, and could be used as a new and natural anti-depressant therapy.

1-Methyl-1,2,3,4-tetrahydroisoquinoline, an endogenous Neuroprotectant and MAO inhibitor with antidepressant-like properties in the rat

Oxidative stress is a major contributing factor in a range of brain pathologies and in the etiology of depression. 1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) is an endogenous substance which is present in the mammalian brain and exhibits neuroprotective, and monoamine oxidase (MAO)-inhibiting properties. In the present study, in order to investigate the potential role of 1MeTIQ as an antidepressant, we tested antidepressant-like effects of 1MeTIQ in comparison with desipramine (a classic antidepressant) in the forced swimming test (FST), and using HPLC methodology, we measured the concentrations of monoamines (dopamine, noradrenaline, serotonin) and the rate of their metabolism. 1MeTIQ given alone as well as in combination with desipramine produced an antidepressant-like effect and decreased the immobility time in the FST. Neurochemical data have shown that 1MeTIQ like desipramine, activated the noradrenergic system. However, the mechanism of action of 1MeTIQ is broader than the actions of desipramine, and 1MeTIQ inhibits the MAO-dependent oxidation of dopamine and serotonin in all investigated structures. We can conclude that 1MeTIQ exhibits antidepressant-like activity in the FST in the rat. The mechanism of its antidepressant action differs from desipramine and seems to be mostly associated with the inhibition of the catabolism of monoamines and their increased concentrations in the brain. 1MeTIQ seems to be very beneficial from the clinical point of view as a reversible MAO inhibitor with a significant antidepressant effects.

The effects of a standardized Acanthopanax koreanum extract on stress-induced behavioral alterations in mice

ETHNOPHARMACOLOGICAL RELEVANCE

The roots and stem bark of Acanthopanax koreanum Nakai (Araliaceae), a well-known herbal medicine in Jeju Island, Korea, has been used as a tonic agent in treating stress-related states. Despite its popular application, the anti-anxiety or anti-depressive action of Acanthopanax koreanum is not yet known.

AIM OF THE STUDY

This study aimed to determine the effects of Acanthopanax koreanum on stress-induced behavioral alterations such as anxiety and depression.

MATERIALS AND METHODS

Mice in the acute stress group were exposed to immobilization stress for 2h followed by electric foot shocks (0.5 mA in 1 s duration with a 10 s inter-shock interval) for 2 min, while sub-chronically stressed mice were exposed to these stresses for 2 weeks, once per day. 70% ethanolic extract of Acanthopanax koreanum (EEAK) (25, 50, 100, or 200 mg/kg) was administered once or sub-chronically (for 2 weeks) 1h prior to stress induction. Anxiety- or depression-like behavioral changes were evaluated using the elevated plus-maze (EPM) test and the forced swimming test (FST) a day after the final stress induction. Corticosterone levels and spleen weight were measured after conducting all the behavioral assays. The numbers of BrdU- or DCX-immunopositive cells in the hippocampal region of sub-chronically stressed mice were measured 2 days after EEAK treatment.

RESULTS

The percentage of time spent in the open arms was decreased in both the acutely and chronically stressed mice. In the FST, the immobility time was increased by only chronic stress, but not by acute stress. Acute or sub-chronic administration of EEAK significantly prevented the anxiety- or depression-like behavioral changes caused by stress. EEAK also attenuated stress-induced decrease and increase of spleen weight and corticosterone levels, respectively. Furthermore, the sub-chronic administration of EEAK (100 or 200 mg/kg, for 2 weeks) increased the number of BrdU-, doublecortin-, and neuropeptide Y-positive cells in the hippocampal region of the sub-chronically stressed mice.

CONCLUSION

EEAK attenuated the behavioral and biochemical changes in acute or sub-chronic stressed mice. These results suggest the therapeutic potential of Acanthopanax koreanum for the treatment of stress-related neuropsychiatric disorders including anxiety disorders or major depressive disorder.

Urine scent marking (USM): a novel test for depressive-like behavior and a predictor of stress resiliency in mice

Decreased interest in pleasurable stimuli including social withdrawal and reduced libido are some of the key symptomatic criteria for major depression, and thus assays that measure social and sexual behavior in rodents may be highly appropriate for modeling depressive states. Here we present a novel approach for validating rodent models of depression by assessing male urine scent marking (USM) made in consequence to a spot of urine from a proestrous female. USM is an ethologically important form of sexual communication expressed by males to attract females. The expression of this behavior is highly sensitive and adaptive to environmental cues and social status. We hypothesized that male USM behavior offers a naturalistic measure of social motivation that can be used to evaluate hedonic behaviors relevant to the study of mood disorders. We demonstrated that 1) adult male mice displayed a strong preference for marking proestrous female urine with a high degree of specificity, 2) exposure to chronic social defeat profoundly decreased USM whereas exposure to environmental enrichment increased USM, 3) the standard antidepressant fluoxetine reversed declines in USM induced by social defeat, 4) USM behavior closely correlated with other hedonic measures, and 5) USM scores in non-stressed mice predicted behavioral outcomes after defeat exposure such that mice displaying high preference for marking female urine prior to social defeat showed behavioral resiliency after social defeat. The findings indicate that the USM test is a sensitive, validated measure of psychosocial stress effects that has high predictive value for examination of stress resiliency and vulnerability and their neurobiological substrates.

Cannabinoids ameliorate impairments induced by chronic stress to synaptic plasticity and short-term memory

Repeated stress is one of the environmental factors that precipitates and exacerbates mental illnesses like depression and anxiety as well as cognitive impairments. We have previously shown that cannabinoids can prevent the effects of acute stress on learning and memory. Here we aimed to find whether chronic cannabinoid treatment would alleviate the long-term effects of exposure to chronic restraint stress on memory and plasticity as well as on behavioral and neuroendocrine measures of anxiety and depression. Late adolescent rats were exposed to chronic restraint stress for 2 weeks followed each day by systemic treatment with vehicle or with the CB1/2 receptor agonist WIN55,212-2 (1.2 mg/kg). Thirty days after the last exposure to stress, rats demonstrated impaired long-term potentiation (LTP) in the ventral subiculum-nucleus accumbens (NAc) pathway, impaired performance in the prefrontal cortex (PFC)-dependent object-recognition task and the hippocampal-dependent spatial version of this task, increased anxiety levels, and significantly reduced expression of glucocorticoid receptors (GRs) in the amygdala, hippocampus, PFC, and NAc. Chronic WIN55,212-2 administration prevented the stress-induced impairment in LTP levels and in the spatial task, with no effect on stress-induced alterations in unconditioned anxiety levels or GR levels. The CB1 antagonist AM251 (0.3 mg/kg) prevented the ameliorating effects of WIN55,212-2 on LTP and short-term memory. Hence, the beneficial effects of WIN55,212-2 on memory and plasticity are mediated by CB1 receptors and are not mediated by alterations in GR levels in the brain areas tested. Our findings suggest that cannabinoid receptor activation could represent a novel approach to the treatment of cognitive deficits that accompany a variety of stress-related neuropsychiatric disorders.

Gene expression in amygdala as a function of differential trait anxiety levels in genetically heterogeneous NIH-HS rats

To identify genes involved in anxiety/fear traits, we analyzed the gene expression profile in the amygdala of genetically heterogeneous NIH-HS rats. The NIH-HS rat stock has revealed to be a unique genetic resource for the fine mapping of Quantitative Trait Loci (QTLs) to very small genomic regions, due to the high amount of genetic recombinants accumulated along more than 50 breeding generations, and for the same reason it can be expected that those genetically heterogeneous rats should be especially useful for studying differential gene expression as a function of anxiety-(or other)-related traits. We selected high- and low-anxious NIH-HS rats differing in their number of avoidances in a single 50-trial session of the two-way active avoidance task. Rats were also tested in unconditioned anxiety tests (e.g., elevated zero-maze). Three weeks after behavioural testing, the amygdala was dissected and prepared for the microarray study. There appeared 6 significantly down-regulated and 28 up-regulated genes (fold-change >|2|, FDR<0.05) between the low- and high-anxious groups, with central nervous system-related functions. Regression analyses (stepwise) revealed that differential expression of some genes could be predictive of anxiety/fear responses. Among those genes for which the present results suggest a link with individual differences in trait anxiety, six relevant genes were examined with qRT-PCR, four of which (Ucn3, Tacr3, H2-M9 and Arr3) were validated. Remarkably, some of them are characterized by sharing known functions related with hormonal HPA-axis responses to (and/or modulation of) stress, anxiety or fear, and putative involvement in related neurobehavioural functions. The results confirm the usefulness of NIH-HS rats as a good animal model for research on the neurogenetic basis of anxiety and fear, while suggesting the involvement of some neuropeptide/neuroendocrine pathways on the development of differential anxiety profiles.

Mood and memory function in ovariectomised rats exposed to social instability stress

This study aims to compare the effects of social instability stress on memory and anxiety- and depressive-like behaviour between sham-operated controls and ovariectomised (OVX) rats. Forty adult female Sprague-Dawley rats (8 weeks old) were randomly divided into four groups, (n = 10 per group). These were non-stressed sham-operated control rats, stressed sham-operated control rats, non-stressed OVX rats, and stressed OVX rats. The rats were subjected to social instability stress procedure for 15 days. Novel object recognition, open field, and forced swim tests were conducted after the stress procedure. Serum estradiol, ACTH and corticosterone levels were measured using commercially available ELISA kits. Lower serum estradiol level and uterine weight with higher weight gain were observed in OVX rats compared to sham-operated controls. Serum ACTH, and corticosterone levels were higher in stressed compared to non-stressed groups. Memory deficit and anxiety- and depressive-like behaviour were significantly increased in stressed compared to non-stressed OVX rats but these changes were not seen in sham-operated controls. These results suggest that the high circulating corticosterone acts synergistically with low circulating estradiol to exert negative effects on mood and memory function.

Sex differences in anxiety and emotional behavior

Research has elucidated causal links between stress exposure and the development of anxiety disorders, but due to the limited use of female or sex-comparative animal models, little is known about the mechanisms underlying sex differences in those disorders. This is despite an overwhelming wealth of evidence from the clinical literature that the prevalence of anxiety disorders is about twice as high in women compared to men, in addition to gender differences in severity and treatment efficacy. We here review human gender differences in generalized anxiety disorder, panic disorder, posttraumatic stress disorder and anxiety-relevant biological functions, discuss the limitations of classic conflict anxiety tests to measure naturally occurring sex differences in anxiety-like behaviors, describe sex-dependent manifestation of anxiety states after gestational, neonatal, or adolescent stressors, and present animal models of chronic anxiety states induced by acute or chronic stressors during adulthood. Potential mechanisms underlying sex differences in stress-related anxiety states include emerging evidence supporting the existence of two anatomically and functionally distinct serotonergic circuits that are related to the modulation of conflict anxiety and panic-like anxiety, respectively. We discuss how these serotonergic circuits may be controlled by reproductive steroid hormone-dependent modulation of crfr1 and crfr2 expression in the midbrain dorsal raphe nucleus and by estrous stage-dependent alterations of γ-aminobutyric acid (GABAergic) neurotransmission in the periaqueductal gray, ultimately leading to sex differences in emotional behavior.

Anxiolytic effects of herbal ethanol extract from Gynostemma pentaphyllum in mice after exposure to chronic stress

In this study, the effects of herbal ethanol extracts of Gynostemma pentaphyllum (GP-EX), on chronic electric footshock (EF) stress-induced anxiety disorders were investigated in mice, which were orally treated with GP-EX (30 mg/kg and 50 mg/kg) once a day for 14 days, followed by exposure to EF stress (2 mA, with an interval and duration of 10 s for 3 min). After the final exposure to EF stress, the elevated plus-maze and marble burying tests were performed, and the levels of dopamine and serotonin in the brain, the serum levels of corticosterone, and the expression of c-Fos in the paraventricular nuclei (PVN) were determined. Treatment with GP-EX (30 mg/kg and 50 mg/kg) significantly recovered the number of entries into open arms and time spent on open arms, which was reduced by chronic EF stress. GP-EX (30 mg/kg and 50 mg/kg) also reduced the number of marbles buried, which was increased by chronic EF stress. In addition, electric EF stress significantly decreased the levels of dopamine and serotonin in the brain, which was recovered by treatment with GP-EX (30 mg/kg and 50 mg/kg). The serum levels of corticosterone, which were markedly increased by chronic EF stress, were reduced by treatment with GP-EX (30 mg/kg and 50 mg/kg). Chronic EF stress-induced increases in c-Fos expression were also markedly reduced by GP-EX (30 mg/kg and 50 mg/kg) in the PVN. These results suggest that GP-EX shows anxiolytic functions, determined by the elevated plus-maze and marble burying tests, which are mediated by modulating the activity of dopamine and serotonin neurons as well as the expression of c-Fos in the brain, and the serum levels of corticosterone. Clinical trials of herbal GP-EX and its bioactive components need further investigation.

Ferulic acid is a nutraceutical β-secretase modulator that improves behavioral impairment and alzheimer-like pathology in transgenic mice

Amyloid precursor protein (APP) proteolysis is required for production of amyloid-β (Aβ) peptides that comprise β-amyloid plaques in brains of Alzheimer's disease (AD) patients. Recent AD therapeutic interest has been directed toward a group of anti-amyloidogenic compounds extracted from plants. We orally administered the brain penetrant, small molecule phenolic compound ferulic acid (FA) to the transgenic PSAPP mouse model of cerebral amyloidosis (bearing mutant human APP and presenilin-1 transgenes) and evaluated behavioral impairment and AD-like pathology. Oral FA treatment for 6 months reversed transgene-associated behavioral deficits including defective: hyperactivity, object recognition, and spatial working and reference memory, but did not alter wild-type mouse behavior. Furthermore, brain parenchymal and cerebral vascular β-amyloid deposits as well as abundance of various Aβ species including oligomers were decreased in FA-treated PSAPP mice. These effects occurred with decreased cleavage of the β-carboxyl-terminal APP fragment, reduced β-site APP cleaving enzyme 1 protein stability and activity, attenuated neuroinflammation, and stabilized oxidative stress. As in vitro validation, we treated well-characterized mutant human APP-overexpressing murine neuron-like cells with FA and found significantly decreased Aβ production and reduced amyloidogenic APP proteolysis. Collectively, these results highlight that FA is a β-secretase modulator with therapeutic potential against AD.

Continuous exposure to a novel stressor based on water aversion induces abnormal circadian locomotor rhythms and sleep-wake cycles in mice

Psychological stressors prominently affect diurnal rhythms, including locomotor activity, sleep, blood pressure, and body temperature, in humans. Here, we found that a novel continuous stress imposed by the perpetual avoidance of water on a wheel (PAWW) affected several physiological diurnal rhythms in mice. One week of PAWW stress decayed robust circadian locomotor rhythmicity, while locomotor activity was evident even during the light period when the mice are normally asleep. Daytime activity was significantly upregulated, whereas nighttime activity was downregulated, resulting in a low amplitude of activity. Total daily activity gradually decreased with increasing exposure to PAWW stress. The mice could be exposed to PAWW stress for over 3 weeks without adaptation. Furthermore, continuous PAWW stress enhanced food intake, but decreased body weight and plasma leptin levels, indicating that sleep loss and PAWW stress altered the energy balance in these mice. The diurnal rhythm of corticosterone levels was not severely affected. The body temperature rhythm was diurnal in the stressed mice, but significantly dysregulated during the dark period. Plasma catecholamines were elevated in the stressed mice. Continuous PAWW stress reduced the duration of daytime sleep, especially during the first half of the light period, and increased nighttime sleepiness. Continuous PAWW stress also simultaneously obscured sleep/wake and locomotor activity rhythms compared with control mice. These sleep architecture phenotypes under stress are similar to those of patients with insomnia. The stressed mice could be entrained to the light/dark cycle, and when they were transferred to constant darkness, they exhibited a free-running circadian rhythm with a timing of activity onset predicted by the phase of their entrained rhythms. Circadian gene expression in the liver and muscle was unaltered, indicating that the peripheral clocks in these tissues remained intact.

Task-specific compensation and recovery following focal motor cortex lesion in stressed rats

One reason for the difficulty to develop effective therapies for stroke is that intrinsic factors, such as stress, may critically influence pathological mechanisms and recovery. In cognitive tasks, stress can both exaggerate and alleviate functional loss after focal ischemia in rodents. Using a comprehensive motor assessment in rats, this study examined if chronic stress and corticosterone treatment affect skill recovery and compensation in a task-specific manner. Groups of rats received daily restraint stress or oral corticosterone supplementation for two weeks prior to a focal motor cortex lesion. After lesion, stress and corticosterone treatments continued for three weeks. Motor performance was assessed in two skilled reaching tasks, skilled walking, forelimb inhibition, forelimb asymmetry and open field behavior. The results revealed that persistent stress and elevated corticosterone levels mainly limit motor recovery. Treated animals dropped larger amounts of food in successful reaches and showed exaggerated loss of forelimb inhibition early after lesion. Stress also caused a moderate, but non-significant increase in infarct size. By contrast, stress and corticosterone treatments promoted reaching success and other quantitative measures in the tray reaching task. Comparative analysis revealed that improvements are due to task-specific development of compensatory strategies. These findings suggest that stress and stress hormones may partially facilitate task-specific and adaptive compensatory movement strategies. The observations support the notion that hypothalamic-pituitary-adrenal axis activation may be a key determinant of recovery and motor system plasticity after ischemic stroke.

Fluoxetine prevents development of an early stress-related molecular signature in the rat infralimbic medial prefrontal cortex. Implications for depression?

Background

Psychological stress, particularly in chronic form, can lead to mood and cognitive dysfunction and is a major risk factor in the development of depressive states. How stress affects the brain to cause psychopathologies is incompletely understood. We sought to characterise potential depression related mechanisms by analysing gene expression and molecular pathways in the infralimbic medial prefrontal cortex (ILmPFC), following a repeated psychological stress paradigm. The ILmPFC is thought to be involved in the processing of emotionally contextual information and in orchestrating the related autonomic responses, and it is one of the brain regions implicated in both stress responses and depression.

Results

Genome-wide microarray analysis of gene expression showed sub-chronic restraint stress resulted predominantly in a reduction in transcripts 24 hours after the last stress episode, with 239 genes significantly decreased, while just 24 genes had increased transcript abundance. Molecular pathway analysis using DAVID identified 8 pathways that were significantly enriched in the differentially expressed gene list, with genes belonging to the brain-derived neurotrophic factor – neurotrophin receptor tyrosine kinase 2 (BDNF-Ntrk2) pathway most enriched. Of the three intracellular signalling pathways that are downstream of Ntrk2, real-time quantitative PCR confirmed that only the PI3K-AKT-GSK3B and MAPK/ERK pathways were affected by sub-chronic stress, with the PLCγ pathway unaffected. Interestingly, chronic antidepressant treatment with the selective serotonin reuptake inhibitor, fluoxetine, prevented the stress-induced Ntrk2 and PI3K pathway changes, but it had no effect on the MAPK/ERK pathway.

Conclusions

These findings indicate that abnormal BDNF-Ntrk2 signalling may manifest at a relatively early time point, and is consistent with a molecular signature of depression developing well before depression-like behaviours occur. Targeting this pathway prophylactically, particularly in depression-susceptible individuals, may be of therapeutic benefit.

NADPH oxidase mediates depressive behavior induced by chronic stress in mice

Stress is a potent risk factor for depression, yet the underlying mechanism is not clearly understood. In the present study, we explored the mechanism of development and maintenance of depression in a stress-induced animal model. Mice restrained for 2 h daily for 14 d showed distinct depressive behavior, and the altered behavior persisted for >3 months in the absence of intervention. Acute restraint induced a surge of oxidative stress in the brain, and stress-induced oxidative stress progressively increased with repetition of stress. In vitro, the stress hormone glucocorticoid generated superoxide via upregulation of NADPH oxidase. Consistently, repeated restraints increased the expression of the key subunits of NADPH oxidase, p47phox and p67phox, in the brain. Moreover, stressed brains markedly upregulated the expression of p47phox to weak restress evoked in the poststress period, and this molecular response was reminiscent of amplified ROS surge to restress. Pharmacological inhibition of NADPH oxidase by the NADPH oxidase inhibitor apocynin during the stress or poststress period completely blocked depressive behavior. Consistently, heterozygous p47phox knock-out mice (p47phox(+/-)) or molecular inhibition of p47phox with Lenti shRNA-p47phox in the hippocampus suppressed depressive behavior. These results suggest that repeated stress promotes depressive behavior through the upregulation of NADPH oxidase and the resultant metabolic oxidative stress, and that the inhibition of NADPH oxidase provides beneficial antidepression effects.

Chemotherapy drug thioTEPA exacerbates stress-induced anhedonia and corticosteroid responses but not impairment of hippocampal cell proliferation in adult mice

Cancer patients often suffer long-lasting affective and cognitive impairments as a result of chemotherapy treatment. Previous work in our lab has shown deficits in learning and memory and hippocampal cell proliferation in mice lasting up to 20 weeks following acute administration of thioTEPA. In this study, the effects of thioTEPA in conjunction with effects of chronic stress on depression-related behavior were examined in C57BL/6J mice, 12 weeks following thioTEPA administration. Chemotherapy-treated mice showed a diminished sucralose preference compared to controls that was further exacerbated after 2 weeks of daily restraint stress. This intensifying effect was not observed in the Porsolt forced swim test. Moreover, stress-induced corticosteroid responses were exaggerated in thioTEPA-treated mice. Cell proliferation in the dentate gyrus of the hippocampus was also impaired similarly by prior thioTEPA treatment and by daily restraint stress, with no additive effect. Results suggest that some depression-related impairments may be exacerbated by chemotherapy treatment through altered corticosteroid regulation.

Repeated Short-term (2h×14d) Emotional Stress Induces Lasting Depression-like Behavior in Mice

Chronic behavioral stress is a risk factor for depression. To understand chronic stress effects and the mechanism underlying stress-induced emotional changes, various animals model have been developed. We recently reported that mice treated with restraints for 2 h daily for 14 consecutive days (2h-14d or 2h×14d) show lasting depression-like behavior. Restraint provokes emotional stress in the body, but the nature of stress induced by restraints is presumably more complex than emotional stress. So a question remains unsolved whether a similar procedure with "emotional" stress is sufficient to cause depression-like behavior. To address this, we examined whether "emotional" constraints in mice treated for 2h×14d by enforcing them to individually stand on a small stepping platform placed in a water bucket with a quarter full of water, and the stress evoked by this procedure was termed "water-bucket stress". The water-bucket stress activated the hypothalamus-pituitary-adrenal gland (HPA) system in a manner similar to restraint as evidenced by elevation of serum glucocorticoids. After the 2h×14d water-bucket stress, mice showed behavioral changes that were attributed to depression-like behavior, which was stably detected >3 weeks after last water-bucket stress endorsement. Administration of the anti-depressant, imipramine, for 20 days from time after the last emotional constraint completely reversed the stress-induced depression-like behavior. These results suggest that emotional stress evokes for 2h×14d in mice stably induces depression-like behavior in mice, as does the 2h×14d restraint.

Epigenetic programming of neurodegenerative diseases by an adverse environment

Experience and environment can critically influence the risk and progression of neurodegenerative disorders. Epigenetic mechanisms, such as miRNA expression, DNA methylation, and histone modifications, readily respond to experience and environmental factors. Here we propose that epigenetic regulation of gene expression and environmental modulation thereof may play a key role in the onset and course of common neurological conditions, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. For example, epigenetic mechanisms may mediate long-term responses to adverse experience, such as stress, to affect disease susceptibility and the course of neurodegenerative events. This review introduces the epigenetic components and their possible role in mediating neuropathological processes in response to stress. We argue that epigenetic modifications will affect neurodegenerative events through altered gene function. The study of epigenetic states in neurodegenerative diseases presents an opportunity to gain new insights into risk factors and pathogenic mechanisms. Moreover, research into epigenetic regulation of disease may revolutionize health care by opening new avenues of personalized, preventive and curative medicine.

Regular exercise cures depression-like behavior via VEGF-Flk-1 signaling in chronically stressed mice

In animals, chronic stress leads to the development of depression-like behavior and decreases neurogenesis and blood vessel density in hippocampus, whereas antidepressants increase adult neurogenesis in hippocampus. Regular exercise training also has antidepressant action and increases hippocampal neurogenesis; however, whether exercise-induced antidepressant action is related to hippocampal microvasculature is unclear. To address this issue, we compared depression-like behavior, blood vessel density, and neurogenesis in hippocampal dentate gyrus between stressed and exercised mice with or without administration of inhibitor of vascular endothelial growth factor (VEGF) receptor. Chronic stress led to the development of depression-like behavior, decreased blood vessel density, and neurogenesis in hippocampus. Regular exercise training improved depression-like behavior, the decrease of hippocampal blood vessel density, and neurogenesis in the stress state, whereas the combination of regular exercise and administration of SU1498, VEGF receptor Flk-1 inhibitor, canceled the exercise-induced antidepressant effect. These findings suggested that the improvement of hippocampal blood vessel and adult neurogenesis via VEGF signaling pathway is necessary for exercise-induced antidepressant effect.

Tannic acid is a natural β-secretase inhibitor that prevents cognitive impairment and mitigates Alzheimer-like pathology in transgenic mice

Amyloid precursor protein (APP) proteolysis is essential for production of amyloid-β (Aβ) peptides that form β-amyloid plaques in brains of Alzheimer disease (AD) patients. Recent focus has been directed toward a group of naturally occurring anti-amyloidogenic polyphenols known as flavonoids. We orally administered the flavonoid tannic acid (TA) to the transgenic PSAPP mouse model of cerebral amyloidosis (bearing mutant human APP and presenilin-1 transgenes) and evaluated cognitive function and AD-like pathology. Consumption of TA for 6 months prevented transgene-associated behavioral impairment including hyperactivity, decreased object recognition, and defective spatial reference memory, but did not alter nontransgenic mouse behavior. Accordingly, brain parenchymal and cerebral vascular β-amyloid deposits and abundance of various Aβ species including oligomers were mitigated in TA-treated PSAPP mice. These effects occurred with decreased cleavage of the β-carboxyl-terminal APP fragment, lowered soluble APP-β production, reduced β-site APP cleaving enzyme 1 protein stability and activity, and attenuated neuroinflammation. As in vitro validation, we treated well characterized mutant human APP-overexpressing murine neuron-like cells with TA and found significantly reduced Aβ production associated with less amyloidogenic APP proteolysis. Taken together, these results raise the possibility that dietary supplementation with TA may be prophylactic for AD by inhibiting β-secretase activity and neuroinflammation and thereby mitigating AD pathology.

Gene expression patterns in the hippocampus and amygdala of endogenous depression and chronic stress models

The etiology of depression is still poorly understood, but two major causative hypotheses have been put forth: the monoamine deficiency and the stress hypotheses of depression. We evaluate these hypotheses using animal models of endogenous depression and chronic stress. The endogenously depressed rat and its control strain were developed by bidirectional selective breeding from the Wistar-Kyoto (WKY) rat, an accepted model of major depressive disorder (MDD). The WKY More Immobile (WMI) substrain shows high immobility/despair-like behavior in the forced swim test (FST), while the control substrain, WKY Less Immobile (WLI), shows no depressive behavior in the FST. Chronic stress responses were investigated by using Brown Norway, Fischer 344, Lewis and WKY, genetically and behaviorally distinct strains of rats. Animals were either not stressed (NS) or exposed to chronic restraint stress (CRS). Genome-wide microarray analyses identified differentially expressed genes in hippocampi and amygdalae of the endogenous depression and the chronic stress models. No significant difference was observed in the expression of monoaminergic transmission-related genes in either model. Furthermore, very few genes showed overlapping changes in the WMI vs WLI and CRS vs NS comparisons, strongly suggesting divergence between endogenous depressive behavior- and chronic stress-related molecular mechanisms. Taken together, these results posit that although chronic stress may induce depressive behavior, its molecular underpinnings differ from those of endogenous depression in animals and possibly in humans, suggesting the need for different treatments. The identification of novel endogenous depression-related and chronic stress response genes suggests that unexplored molecular mechanisms could be targeted for the development of novel therapeutic agents.

Cyto- and chemoarchitecture of the hypothalamic paraventricular nucleus in the C57BL/6J male mouse: a study of immunostaining and multiple fluorescent tract tracing

The paraventricular nucleus of the hypothalamus (PVH) plays a critical role in the regulation of autonomic, neuroendocrine, and behavioral activities. This understanding has come from extensive characterization of the PVH in rats, and for this mammalian species we now have a robust model of basic PVH neuroanatomy and function. However, in mice, whose use as a model research animal has burgeoned with the increasing sophistication of tools for genetic manipulation, a comparable level of PVH characterization has not been achieved. To address this, we employed a variety of fluorescent tract tracing and immunostaining techniques in several different combinations to determine the neuronal connections and cyto- and chemoarchitecture of the PVH in the commonly used C57BL/6J male mouse. Our findings reveal a distinct organization in the mouse PVH that is substantially different from the PVH of male rats. The differences are particularly evident with respect to the spatial relations of two principal neuroendocrine divisions (magnocellular and parvicellular) and three descending preautonomic populations in the PVH. We discuss these data in relation to what is known about PVH function and provide the work as a resource for further studies of the neuronal architecture and function of the mouse PVH.

Disease progression in a mouse model of amyotrophic lateral sclerosis: the influence of chronic stress and corticosterone

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by motor neuron cell loss, muscular atrophy, and a shortened life span. Survival is highly variable, as some patients die within months, while others live for many years. Exposure to stress or the development of a nonoptimal stress response to disease might account for some of this variability. We show in the SOD1(G93A) mouse model of ALS that recurrent exposure to restraint stress led to an earlier onset of astrogliosis and microglial activation within the spinal cord, accelerated muscular weakness, and a significant decrease in median survival (105 vs. 122 d) when compared to nonstressed animals. Moreover, during normal disease course, ALS mice display a cacostatic stress response by developing an aberrant serum corticosterone circadian rhythm. Interestingly, we also found that higher corticosterone levels were significantly correlated with both an earlier onset of paralysis (males: r(2)=0.746; females: r(2)=0.707) and shorter survival times (males: r(2)=0.680; females: r(2)=0.552) in ALS mice. These results suggest that stress is capable of accelerating disease progression and that strategies that modulate glucocorticoid metabolism might be a viable treatment approach for ALS.

Behavioral stress causes mitochondrial dysfunction via ABAD up-regulation and aggravates plaque pathology in the brain of a mouse model of Alzheimer disease

Basic and clinical studies have reported that behavioral stress worsens the pathology of Alzheimer disease (AD), but the underlying mechanism has not been clearly understood. In this study, we determined the mechanism by which behavioral stress affects the pathogenesis of AD using Tg-APPswe/PS1dE9 mice, a murine model of AD. Tg-APPswe/PS1dE9 mice that were restrained for 2h daily for 16 consecutive days (2-h/16-day stress) from 6.5months of age had significantly increased Aβ(1-42) levels and plaque deposition in the brain. The 2-h/16-day stress increased oxidative stress and induced mitochondrial dysfunction in the brain. Treatment with glucocorticoid (corticosterone) and Aβ in SH-SY5Y cells increased the expression of 17β-hydroxysteroid dehydrogenase (ABAD), mitochondrial dysfunction, and levels of ROS, whereas blockade of ABAD expression by siRNA-ABAD in SH-SY5Y cells suppressed glucocorticoid-enhanced mitochondrial dysfunction and ROS accumulation. The 2-h/16-day stress up-regulated ABAD expression in mitochondria in the brain of Tg-APPswe/PS1dE9 mice. Moreover, all visible Aβ plaques were costained with anti-ABAD in the brains of Tg-APPswe/PS1dE9 mice. Together, these results suggest that behavioral stress aggravates plaque pathology and mitochondrial dysfunction via up-regulation of ABAD in the brain of a mouse model of AD.

Convergent functional genomic studies of ω-3 fatty acids in stress reactivity, bipolar disorder and alcoholism

Omega-3 fatty acids have been proposed as an adjuvant treatment option in psychiatric disorders. Given their other health benefits and their relative lack of toxicity, teratogenicity and side effects, they may be particularly useful in children and in females of child-bearing age, especially during pregnancy and postpartum. A comprehensive mechanistic understanding of their effects is needed. Here we report translational studies demonstrating the phenotypic normalization and gene expression effects of dietary omega-3 fatty acids, specifically docosahexaenoic acid (DHA), in a stress-reactive knockout mouse model of bipolar disorder and co-morbid alcoholism, using a bioinformatic convergent functional genomics approach integrating animal model and human data to prioritize disease-relevant genes. Additionally, to validate at a behavioral level the novel observed effects on decreasing alcohol consumption, we also tested the effects of DHA in an independent animal model, alcohol-preferring (P) rats, a well-established animal model of alcoholism. Our studies uncover sex differences, brain region-specific effects and blood biomarkers that may underpin the effects of DHA. Of note, DHA modulates some of the same genes targeted by current psychotropic medications, as well as increases myelin-related gene expression. Myelin-related gene expression decrease is a common, if nonspecific, denominator of neuropsychiatric disorders. In conclusion, our work supports the potential utility of omega-3 fatty acids, specifically DHA, for a spectrum of psychiatric disorders such as stress disorders, bipolar disorder, alcoholism and beyond.

Region-specific involvement of BDNF secretion and synthesis in conditioned taste aversion memory formation

Brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin-related kinase receptor B (TrkB), play a critical role in activity-dependent plasticity processes such as long-term potentiation, learning, and memory. It has been shown that BDNF exerts different or even opposite effects on behavior depending on the neural circuit. However, the detailed role of BDNF in memory process on the basis of its location has not been fully understood. Here, we aim to investigate the regional specific involvement of BDNF/TrkB in hippocampal-independent conditioned taste aversion (CTA) memory processes. We found region-specific changes in BDNF expression during CTA learning. CTA conditioning induced increased BDNF levels in the central nuclei of amygdala (CeA) and insular cortex, but not in the basolateral amygdala (BLA) and ventromedial prefrontal cortex. Interestingly, we found that the enhanced TrkB phosphorylation occurred at the time point before the increased BDNF expression, suggesting rapid induction of activity-dependent BDNF secretion by CTA learning. Moreover, targeted infusion of BDNF antibodies or BDNF antisense oligonucleotides revealed that activity-dependent BDNF secretion and synthesis in the CeA, but not the BLA, was respectively involved in the short- and long-term memory formation of CTA. Finally, we found that infusion of exogenous BDNF into the CeA could enhance CTA learning. These data suggest that region-specific BDNF release and synthesis temporally regulate different CTA memory phases through activation of TrkB receptors.

Profiling of hypothalamic and hippocampal gene expression in chronically stressed rats treated with St. John's wort extract (STW 3-VI) and fluoxetine

RATIONALE

Hypericum perforatum L., known as St. John's wort (SJW), is used as a phytotherapeutic agent for the treatment of mild to moderate forms of depression.

OBJECTIVES

The aim of the present study was to evaluate the effect of SJW extract (STW 3-VI; 250 and 500 mg/kg; p.o.) and fluoxetine (10 mg/kg, p.o.) on genes involved in the pathogenesis of depression using a chronic restraint stress (CRS) model in rats. Of particular interest was the assessment of similarities and differences between SJW extract and fluoxetine on the gene expression level in two different brain regions.

RESULTS

Hypothalamic and hippocampal tissues were analyzed using the Affymetrix gene chip Rat Genome 230 2.0 Array, which comprises more than 30,000 rat transcripts. Limma program and PANTHER database were used to evaluate the microarray data. Genes involved in the pathways of inflammatory processes (Mapk8), oxidative stress (Gpx3, Gstm3, Sod3) or Alzheimer's disease (Sncb, Apbb1ip) were altered by both fluoxetine and SJW extract. For all groups, several signaling pathways were identified which could provide a link between the various hypotheses of depression.

CONCLUSION

In conclusion, microarray analysis proved to be a valuable tool to identify a large number of genes and resulting pathways that may serve as novel drug targets or predict drug responsiveness for SJW or fluoxetine. Based on our comprehensive analysis, it was possible to identify similarities and differences between SJW and fluoxetine which may help to better understand their molecular action and, in addition, help to find novel treatment strategies for stress-related depression.

Shared changes in gene expression in frontal cortex of four genetically modified mouse models of depression

This study aimed to identify whether genetic manipulation of four systems implicated in the pathogenesis of depression converge on shared molecular processes underpinning depression-like behaviour in mice. Altered 5HT function was modelled using the 5-HT transporter knock out mouse, impaired glucocorticoid receptor (GR) function using an antisense-induced knock down mouse, disrupted glutamate function using a heterozygous KO of the vesicular glutamate transporter 1 gene, and impaired cannabinoid signalling using the cannabinoid 1 receptor KO mouse. All 4 four genetically modified mice were previously shown to show exaggerated helpless behaviour compared to wild-type controls and variable degrees of anxiety and anhedonic behaviour. mRNA was extracted from frontal cortex and hybridised to Illumina microarrays. Combined contrast analysis was used to identify genes showing different patterns of up- and down-regulation across the 4 models. 1823 genes were differentially regulated. They were over-represented in gene ontology categories of metabolism, protein handling and synapse. In each model compared to wild-type mice of the same genetic background, a number of genes showed increased expression changes of >10%, other genes showed decreases in each model. Most of the genes showed mixed effects. Several previous array findings were replicated. The results point to cellular stress and changes in post-synaptic remodelling as final common mechanisms of depression and resilience.

The transcriptional response to chronic stress and glucocorticoid receptor blockade in the hippocampal dentate gyrus

The dentate gyrus (DG) of the hippocampus plays a crucial role in learning and memory. This subregion is unique in its ability to generate new neurons throughout life and integrate these new neurons into the hippocampal circuitry. Neurogenesis has further been implicated in hippocampal plasticity and depression. Exposure to chronic stress affects DG function and morphology and suppresses neurogenesis and long-term potentiation (LTP) with consequences for cognition. Previous studies demonstrated that glucocorticoid receptor (GR) blockade by a brief treatment with the GR antagonist mifepristone (RU486) rapidly reverses the stress and glucocorticoid effects on neurogenesis. The molecular pathways underlying both the stress-induced effects and the RU486 effects on the DG are, however, largely unknown. The aim of this study was therefore (1) to investigate by microarray analysis which genes and pathways in the DG are sensitive to chronic stress and (2) to investigate to what extent blockade of GR can normalize these stress-induced effects on DG gene expression. Chronic stress exposure affected the expression of 90 genes in the DG (P < 0.01), with an overrepresentation of genes involved in brain development and morphogenesis and synaptic transmission. RU486 treatment of stressed animals affected expression of 107 genes; however, mostly different genes than those responding to stress. Interestingly, we found CREBBP to be normalized by RU486 treatment to levels observed in control animals, suggesting that CREB-signaling may play a central role in mediating the chronic stress effects on neurogenesis, LTP and calcium currents. The identified genetic pathways provide insight into the stress-induced adaptive plasticity of the hippocampal DG that is so central in learning and memory and will direct future studies on the functional outcome and modulation of these stress effects.

Long-term ovariectomy enhances anxiety and depressive-like behaviors in mice submitted to chronic unpredictable stress

Ovarian hormones exert anti-depressive and anxiolytic actions. In this study we have analyzed the effects of ovariectomy on the development of anxiety and depression-like behaviors and on cell proliferation in the hippocampus of mice submitted to chronic unpredictable stress. Animals submitted to stress 4 months after ovariectomy showed a significant increase in immobility behavior in the forced swimming test compared to animals submitted to stress 2 weeks after ovariectomy. In addition, long-term ovariectomy resulted in a significant decrease on the time spent in the open arms in the elevated plus-maze test compared to control animals. Stress did not significantly affect cell proliferation in the hilus of the dentate gyrus. However, ovariectomy resulted in a significant decrease in cell proliferation. These results indicate that long-term deprivation of ovarian hormones enhances the effect of chronic unpredictable stress on depressive- and anxiety-like behaviors in mice. Therefore, a prolonged deprivation of ovarian hormones may represent a risk factor for the development of depressive and anxiety symptoms after the exposure to stressful experiences.

Restraint stress up-regulates lectin-like oxidized low-density lipoprotein receptor-1 in aorta of apolipoprotein E-deficient mice

Psychological stress is a risk factor for cardiovascular disease including atherosclerosis, but the mechanisms are unknown. The vascular lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is involved in vascular pathology and early atherogenesis. We hypothesized that LOX-1 is up-regulated by psychological stress via the formation of oxygen-derived free radicals, and that treatment with EUK-8 (a superoxide dismutase and catalase mimetic) prevents production of oxygen-derived free radicals and leads to reduced expression of LOX-1 in the vascular wall. As a model for psychological stress, we exposed male apolipoprotein E-deficient mice to repeated restraint stress by placement in a conical tube for 2 h per day for 14 consecutive days. Stressed and control mice were treated with EUK-8 (n = 4-5) or vehicle (n = 4-5). Reactive oxygen species and peroxynitrite levels, as detected by oxidative fluorescence microscopy, were increased in the aortic root of mice exposed to stress compared to those of controls by 212 +/- 22% (mean +/- SEM; p < 0.001) and 110 +/- 6% (p < 0.001), respectively. LOX-1, as detected by immunohistochemistry, was increased by 443 +/- 63% in stressed mice compared to control mice (p < 0.001). EUK-8 reduced reactive oxygen species, peroxynitrite, and LOX-1 levels in stressed mice compared to vehicle-treated stressed mice. To conclude, LOX-1 induced by reactive oxygen species and/or peroxynitrite could be one mechanism by which stress promotes cardiovascular disease.

Chronic Administration of Monosodium Glutamate under Chronic Variable Stress Impaired Hypothalamic-Pituitary-Adrenal Axis Function in Rats

The hypothalamic-pituitary-adrenal (HPA) axis is the primary endocrine system to respond to stress. The HPA axis may be affected by increased level of corticotrophin-releasing factors under chronic stress and by chronic administration of monosodium glutamate (MSG). The purpose of this study was to investigate whether chronic MSG administration aggravates chronic variable stress (CVS)-induced behavioral and hormonal changes. Twenty-four adult male Sprague-Dawley rats, weighing 200~220 g, were divided into 4 groups as follows: water administration (CON), MSG (3 g/kg) administration (MSG), CVS, and CVS with MSG (3 g/kg) administration (CVS+MSG). In addition, for the purpose of comparing the effect on plasma corticosterone levels between chronic stress and daily care or acute stress, 2 groups were added at the end of the experiment; the 2 new groups were as follows: naïve mice (n=7) and mice exposed to restraint stress for 2 h just before decapitation (A-Str, n=7). In an open field test performed after the experiment, the CVS+MSG group significant decrease in activity. The increase in relative adrenal weights in the CVS and CVS+MSG group was significantly greater than those in the CON and/or MSG groups. In spite of the increase in the relative adrenal weight, there was a significant decrease in the plasma corticosterone levels in the CVS+MSG group as compared to all other groups, except the naïve group. These results suggest that impaired HPA axis function as well as the decrease in the behavioral activity in adult rats can be induced by chronic MSG administration under CVS rather than CVS alone.

Antidepressant-like Effect of Kaempferol and Quercitirin, Isolated from Opuntia ficus-indica var. saboten

Opuntia ficus-indica var. saboten. is widely cultivated in Jeju Island (South Korea) for use in manufacture of health foods. This study described antidepressant effect of two flavonoids (kaempferol and quercitrin) isolated from the Opuntia ficus-indica var. saboten. The expression of the hypothalamic POMC mRNA or plasma β-endorphin levels were increased by extract of Opuntia ficus-indica var. saboten or its flavoniods administered orally. In addition, antidepressant activity was studied using tail suspension test (TST), forced swimming test (FST) and rota-rod test in chronically restraint immobilization stress group in mice. After restraint stress (2 hrs/day for 14 days), animals were kept in cage for 14 days without any further stress, bet with drugs. Mice were fed with a diet supplemented for 14 days and during the behavioral test period with kaempferol or quercitrin (30 mg/kg/day). POMC mRNA or plasma β-endorphin level was increased by extract of Opuntia ficus-indica var. saboten and its flavoniods. In addition, immobility time in TST and FST was significantly reduced by kaempferol or quercitrin. In rota-rod test, the time of permanence was maintained to the semblance of control group in turning at 15 rpm. Our results suggest that two flavonoids (kaempferol and quercitrin) isolated from the Opuntia ficus-indica var. saboten. show a potent antidepressant effect.

Behavioral and neurobiological consequences of prolonged glucocorticoid exposure in rats: relevance to depression

Stress is a critical environmental trigger for the development of clinical depression, yet little is known about the specific neurobiological mechanisms by which stress influences the development of depressive symptomatology. Animal models provide an efficient way to study the etiology of human disorders such as depression, and a number of preclinical models have been developed to assess the link between stress, glucocorticoids, and depressive behavior. These mode ls typically make use of repeated exposure to physical or psychological stressors in rodents or other small laboratory animals. This review focuses primarily on a recently developed preclinical model of depression that uses exogenous administration of the stress hormone corticosterone (CORT) in rodents instead of exposure to physical or psychological stressors. Repeated CORT administration in rats or mice produces reliable behavioral and neurobiological alterations that parallel many of the core symptoms and neurobiological changes associated with human depression. This provides an opportunity to study behavior and neurobiology in the same animal, so that the neurobiological factors that underlie specific symptoms can be identified. Taken together, these findings suggest that exogenous CORT administration is a useful method for studying the relationship between stress, glucocorticoids, and depression. Further study with this model may provide important new data regarding the neurobiological bases of depression.

Mice lacking adenylyl cyclase-5 cope badly with repeated restraint stress

Physiological responses to acute stress proceed with the activation of the hypothalamus-pituitary-adrenal gland (HPA) system. Many brain regions are known to modulate the HPA axis activation in stress responses, but the detailed neural circuits and signaling system in the upstream of the HPA axis have to be explored further. Type 5 adenylyl cyclase (AC5) is highly concentrated in the dorsal striatum and nucleus accumbens, which are implicated in reward and stress-related behavior. AC5(-/-) mice exposed to daily 2-hr restraint stress for only 3-5 days showed poor stress-coping responses, including severe body weight loss, poor coat condition, respiratory difficulties, and freezing behavior. Plasma corticosterone levels during 2-hr stress sessions increased in AC5(-/-) mice compared with those of AC5(+/+) mice. However, neither the corticosterone receptor antagonist RU486 nor the CRH receptor antagonist NBI27914 blocked their poor stress coping, whereas the administration of the GABA(A) receptor allosteric modulator diazepam or the D1 dopamine receptor antagonist SCH23390 prior to restraint stress sessions changed their stress-coping response to the stressed AC5(+/+) mouse level. Stress-triggered c-Fos expression was completely blunted in the dorsal striatum of AC5(-/-). These results suggest that the AC5-associated signal system and neural network are involved in the regulation of anxiety and stress-coping response.

Lithium modulates the chronic stress-induced effect on blood glucose level of male rats

In the present study we examined gross changes in the mass of whole adrenal glands and that of the adrenal cortex, as well as the serum corticosterone and glucose level of mature male Wistar rats subjected to three different treatments: animals subjected to chronic restraint-stress, animals injected with lithium (Li) and chronically stressed rats treated with Li. Under all three conditions we observed hypertrophy of whole adrenals, as well as the adrenal cortices. Chronic restraint stress, solely or in combination with Li treatment, significantly elevated the corticosterone level, but did not change the blood glucose level. Animals treated only with Li exhibited an elevated serum corticosterone level and blood glucose level. The aim of our study was to investigate the modulation of the chronic stress-induced effect on the blood glucose level by lithium, as a possible mechanism of avoiding the damage caused by chronic stress. Our results showed that lithium is an agent of choice which may help to reduce stress-elevated corticosterone and replenish exhausted glucose storages in an organism.

Chronic stress-mutated presenilin 1 gene interaction perturbs neurogenesis and accelerates neurodegeneration

Recent evidence suggests that supplemental factors coincident with aging and genetic determinants might be involved in the initial progression of Alzheimer's disease (AD). Early studies also indicate that chronic stress decreases hippocampal neurogenesis. Here, we investigate the effect of chronic stress on hippocampal neurogenesis using a transgenic mouse line (Tg) that overexpresses human presenilin 1 (PS1) with a familial AD (FAD)-related mutation in order to elucidate how the combination of chronic stress and mutated genes affects the cytoarchitecture in the hippocampal granule cell layer (GCL), which contributes to spatial learning and memory. Using an original chronic intermittent restraint stress (CIRS) protocol, we examined the effect of stress on hippocampal neurogenesis and neurodegeneration by immunohistochemical analysis. After short-term CIRS, neurodegeneration in Tg mice was significantly increased in the hippocampus with an earlier onset and progression than in the non-stressed Tg mice. Moreover, after long-term CIRS, transitional neurodegeneration appeared to proceed along the neuronal circuit involved in cognitive function in stressed Tg mice. Although the number of Pax6-positive (+) cells (mostly granule neuron precursors) did not significantly decrease during CIRS in both non-Tg and Tg mice, doublecortin (DCX) + neuronal progenitor cells in the GCL were markedly influenced in Tg mice; they were significantly reduced without stress compared with non-stressed non-Tg mice and significantly increased by CIRS compared with non-stressed Tg mice. We conclude from these results that diverse responses against stressful experiences among genetically predisposed individuals could lead to cognitive dysfunction through retardation of neuronal maturation and neurodegeneration.

Knockout of the norepinephrine transporter and pharmacologically diverse antidepressants prevent behavioral and brain neurotrophin alterations in two chronic stress models of depression

Diverse factors such as changes in neurotrophins and brain plasticity have been proposed to be involved in the actions of antidepressant drugs (ADs). However, in mouse models of depression based on chronic stress, it is still unclear whether simultaneous changes in behavior and neurotrophin expression occur and whether these changes can be corrected or prevented comparably by chronic administration of ADs or genetic manipulations that produce antidepressant-like effects such as the knockout of the norepinephrine transporter (NET) gene. Here we show that chronic restraint or social defeat stress induce comparable effects on behavior and changes in the expression of neurotrophins in depression-related brain regions. Chronic stress caused down-regulation of BDNF, nerve growth factor, and neurotrophin-3 in hippocampus and cerebral cortex and up-regulation of these targets in striatal regions. In wild-type mice, these effects could be prevented by concomitant chronic administration of five pharmacologically diverse ADs. In contrast, NET knock out (NETKO) mice were resistant to stress-induced depressive-like changes in behavior and brain neurotrophin expression. Thus, the resistance of the NETKO mice to the stress-induced depression-associated behaviors and biochemical changes highlight the importance of noradrenergic pathways in the maintenance of mood. In addition, these mice represent a useful model to study depression-resistant behaviors, and they might help to provide deeper insights into the identification of downstream targets involved in the mechanisms of antidepressants.

Predictable stress versus unpredictable stress: a comparison in a rodent model of stroke

Previous studies have associated stress with poor outcome in individuals affected by stroke. It was suggested that the effects of stress depend on the stressor's type and strength. Here we compare the effects of chronic predictable restraint stress and chronic unpredictable variable stress on motor recovery after focal lesion in the rat motor cortex. Adult male rats were pre-trained and tested in skilled reaching and skilled walking tasks. Animals were assigned to daily treatments of either restraint stress or variable stress starting 1 week prior to lesion up to 2 weeks post-lesion. One group served as lesion only control. The results revealed a distinct pattern of recovery and compensation of skilled movement. Animals exposed to predictable restraint stress had significantly lower reaching success at both pre- and post-lesion time points, and higher error rates in skilled walking when compared to lesion controls. Overall, restraint stress induced more pronounced motor impairments prior to and after injury than variable stress. Variable stress increased the number of attempts required to grasp food pellets and changed movement pattern performance. By contrast, variable stress improved limb placement accuracy when compared to lesion controls. The behavioural changes were not accompanied by differences in infarct size. These findings are in agreement with other studies reporting that both chronic predicable restraint stress and unpredictable variable stress influence the course of recovery following stroke, however, restraint stress might affect stroke recovery through a different route than variable stress.

Chronic immobilization stress induces anxiety- and depression-like behaviors and decreases transthyretin in the mouse cortex

In this study, we examined the changes in gene expression in the mouse cortex following chronic stress and behavioral tests. Mice were subjected to immobilization stress for 2h per day for 15 consecutive days and the behavior of the mice was examined. The mice in the experimental group were more anxious and depressive than the control mice. The expression of mRNA in the cortex was analyzed by microarray analysis and 63 genes were found to show a greater than twofold change in expression between the control and experimental groups. Transthyretin was further investigated because its expression showed the greatest fold change. Transthyretin mRNA expression decreased in a chronic stress-specific manner, and protein levels were reduced in the cortex but not in the choroid plexus.