Predictability of chronic intermittent stress: effects on sympathetic-adrenal medullary responses of laboratory rats

Chronic Unpredictable Mild Stress Model of Depression: Possible Sources of Poor Reproducibility and Latent Variables

Major depressive disorder (MDD) is one of the most common mood disorders worldwide. A lack of understanding of the exact neurobiological mechanisms of depression complicates the search for new effective drugs. Animal models are an important tool in the search for new approaches to the treatment of this disorder. All animal models of depression have certain advantages and disadvantages. We often hear that the main drawback of the chronic unpredictable mild stress (CUMS) model of depression is its poor reproducibility, but rarely does anyone try to find the real causes and sources of such poor reproducibility. Analyzing the articles available in the PubMed database, we tried to identify the factors that may be the sources of the poor reproducibility of CUMS. Among such factors, there may be chronic sleep deprivation, painful stressors, social stress, the difference in sex and age of animals, different stress susceptibility of different animal strains, handling quality, habituation to stressful factors, various combinations of physical and psychological stressors in the CUMS protocol, the influence of olfactory and auditory stimuli on animals, as well as the possible influence of various other factors that are rarely taken into account by researchers. We assume that careful inspection of these factors will increase the reproducibility of the CUMS model between laboratories and allow to make the interpretation of the obtained results and their comparison between laboratories to be more adequate.

Plasma Epinephrine Contributes to the Development of Experimental Hypoglycemia-Associated Autonomic Failure

BACKGROUND

Recurrent hypoglycemia blunts counter-regulatory responses to subsequent hypoglycemic episodes, a syndrome known as hypoglycemia-associated autonomic failure (HAAF). Since adrenergic receptor blockade has been reported to prevent HAAF, we investigated whether the hypoglycemia-associated rise in plasma epinephrine contributes to pathophysiology and reported interindividual differences in susceptibility to HAAF.

METHODS

To assess the role of hypoglycemia-associated epinephrine responses in the susceptibility to HAAF, 24 adult nondiabetic subjects underwent two 2-hour hyperinsulinemic hypoglycemic clamp studies (nadir 54 mg/dL; 0-2 hours and 4-6 hours) on Day 1, followed by a third identical clamp on Day 2. We challenged an additional 7 subjects with two 2-hour infusions of epinephrine (0.03 μg/kg/min; 0-2 hours and 4-6 hours) vs saline on Day 1 followed by a 200-minute stepped hypoglycemic clamp (90, 80, 70, and 60 mg/dL) on Day 2.

RESULTS

Thirteen out of 24 subjects developed HAAF, defined by ≥20% reduction in average epinephrine levels during the final 30 minutes of the third compared with the first hypoglycemic episode (P < 0.001). Average epinephrine levels during the final 30 minutes of the first hypoglycemic episode were 2.3 times higher in subjects who developed HAAF compared with those who did not (P = 0.006).Compared to saline, epinephrine infusion on Day 1 reduced the epinephrine responses by 27% at the 70 and 60 mg/dL glucose steps combined (P = 0.04), with a parallel reduction in hypoglycemic symptoms (P = 0.03) on Day 2.

CONCLUSIONS

Increases in plasma epinephrine reproduce key features of HAAF in nondiabetic subjects. Marked interindividual variability in epinephrine responses to hypoglycemia may explain an individual's susceptibility to developing HAAF.

Apelin attenuates depressive-like behavior and neuroinflammation in rats co-treated with chronic stress and lipopolysaccharide

Several experimental studies have proved that activation of neuroinflammation pathways may contribute to the development of depression, a neuropsychiatric disorder disease. Our previous studies have shown the antidepressant properties of apelin, but the mechanism was unkown. This study was performed to verify whether the antidepressant effect of apelin was related to its anti-inflammation effect in the central nervous system. To achieve our aim, we selected the co-treatment of chronic stress and LPS to induced an inflammatory process in rats. The effect of this co-treatment was evaluated through the expression of inflammatory markers and glial cell activation. LPS injection co-treated with unpredictable chronic mild stress resulted in the activation of microglial cell and astrocyte, expression of inflammatory markers and depressive behaviors. Treatment with apelin significantly attenuates the deleterious effects in these rats. Our results showed that apelin improved depressive phenotype and decreased the activation of glial cells in stress co-treatment group. The down-regulations of p-NF-κB and p-IKKβ suggested that the effects are possibly mediated by inhibition of the NF-κB-mediated inflammatory response. These findings speculated that intracerebroventricular injection of apelin could be a therapeutic approach for the treatment of depression, and the antidepressant function of apelin may closely associated with its alleviation in neuroinflammation.

Methods for Evaluating the Combined Effects of Chemical and Nonchemical Exposures for Cumulative Environmental Health Risk Assessment

Cumulative risk assessment (CRA) has been proposed as a means of evaluating possible additive and synergistic effects of multiple chemical, physical and social stressors on human health, with the goal of informing policy and decision-making, and protecting public health. Routine application of CRA to environmental regulatory and policy decision making, however, has been limited due to a perceived lack of appropriate quantitative approaches for assessing combined effects of chemical and nonchemical exposures. Seven research projects, which represented a variety of disciplines, including population health science, laboratory science, social sciences, geography, statistics and mathematics, were funded by the US Environmental Protection Agency (EPA) to help address this knowledge gap. We synthesize key insights from these unique studies to determine the implications for CRA practice and priorities for further research. Our analyses of these seven projects demonstrate that the necessary analytical methods to support CRA are available but are ultimately context-dependent. These projects collectively provided advancements for CRA in the areas of community engagement, characterization of exposures to nonchemical stressors, and assessment of health effects associated with joint exposures to chemical and psychosocial stressors.

Antidepressant like effects of hydrolysable tannins of Terminalia catappa leaf extract via modulation of hippocampal plasticity and regulation of monoamine neurotransmitters subjected to chronic mild stress (CMS)

Terminalia catappa L. belonging to Combretaceae family is a folk medicine, known for its multiple pharmacological properties, but the neuro-modulatory effect of TC against chronic mild stress was seldom explored. The present study was designed to elucidate potential antidepressant-like effect of Terminalia cattapa (leaf) hydro-alcoholic extract (TC) by using CMS model for a period of 7 weeks. Identification of hydrolysable tannins was done by using LC-MS. After the CMS exposure, mice groups were administered with imipramine (IMP, 10mg/kg, i.p.) and TC (25, 50 and 100mg/kg of TC, p.o.). Behavioural paradigms used for the study included forced swimming test (FST), tail suspension test (TST) and sucrose preference test (SPT). After behavioural tests, monoamine neurotransmitter, cortisol, AchE, oxidative stress levels and mRNA expression studies relevant to depression were assessed. TC supplementation significantly reversed CMS induced immobility time in FST and other behavioural paradigms. Moreover, TC administration significantly restored CMS induced changes in concentrations of hippocampal neurotransmitters (5-HT, DA and NE) as well as levels of acetyl cholinesterase, cortisol, monoamine oxidases (MAO-A, MAO-B), BDNF, CREB, and p-CREB. It suggests that TC supplementation could supress stress induced depression by regulating monoamine neurotransmitters, CREB, BDNF, cortisol, AchE level as well as by amelioration of oxidative stress. Hence TC can be used as a complementary medicine against depression-like disorder.

Learning about stress: neural, endocrine and behavioral adaptations

In this review, nonassociative learning is advanced as an organizing principle to draw together findings from both sympathetic-adrenal medullary and hypothalamic-pituitary-adrenocortical (HPA) axis responses to chronic intermittent exposure to a variety of stressors. Studies of habituation, facilitation and sensitization of stress effector systems are reviewed and linked to an animal's prior experience with a given stressor, the intensity of the stressor and the appraisal by the animal of its ability to mobilize physiological systems to adapt to the stressor. Brain pathways that regulate physiological and behavioral responses to stress are discussed, especially in light of their regulation of nonassociative processes in chronic intermittent stress. These findings may have special relevance to various psychiatric diseases, including depression and post-traumatic stress disorder (PTSD).

Chronic stress alters the expression levels of longevity-related genes in the rat hippocampus

The molecular mechanisms underlying the negative effects of psychological stress on cellular stress during aging and neurodegenerative diseases are poorly understood. The main objective of this study was to test the effect of chronic psychological stress, and the consequent increase of circulating glucocorticoids, on several hippocampal genes involved in longevity. Sirtuin-1, p53, thioredoxin-interacting protein, and heat shock protein 70 were studied at the mRNA and protein levels in stressed and non-stressed animals. Stress treatment for 10 days decreased sirtuin-1 and heat shock protein 70 levels, but increased levels of p53, thioredoxin-interacting protein and the NADPH oxidase enzyme. Examination of protein expression following two months of stress treatment indicated that sirtuin-1 remained depressed. In contrast, an increase was observed for thioredoxin-interacting protein, heat shock protein 70, p53 and the NADPH oxidase enzyme. The effect of stress was reversed by mifepristone, a glucocorticoid receptor antagonist. These data suggest that chronic stress could contribute to aging in the hippocampus.

Gender-dependent effect on nociceptive response induced by chronic variable stress

It has previously been reported that exposure to repeated restraint stress induces hyperalgesia in male rats, an effect that was not observed in females. The aim of the present study was to investigate the effects of chronic variable stress over 40days on nociception threshold indexed by tail-flick latency in male and female adult rats. The results showed different behavior in chronically stressed animals when compared to the control group: male rats showed a decrease in tail-flick latency while females presented an increase in this parameter. For female rats this effect was independent of the phase of the estrous cycle. Several sources of data indicate that behavioral and physiological responses to stress are sexually dimorphic, including in nociception, and the estrous cycle appears to be a factor that influences opioid analgesia in female. These effects are modulated by the strain and conditions of nociception assay. Additional studies concerning the mechanisms involved in the hyperalgesic response in males and the differences on nociceptive response in females chronically exposed to stress are needed.

Chronic stress enhances microglia activation and exacerbates death of nigral dopaminergic neurons under conditions of inflammation

Background

Parkinson’s disease is an irreversible neurodegenerative disease linked to progressive movement disorders and is accompanied by an inflammatory reaction that is believed to contribute to its pathogenesis. Since sensitivity to inflammation is not the same in all brain structures, the aim of this work was to test whether physiological conditions as stress could enhance susceptibility to inflammation in the substantia nigra, where death of dopaminergic neurons takes place in Parkinson’s disease.

Methods

To achieve our aim, we induced an inflammatory process in nonstressed and stressed rats (subject to a chronic variate stress) by a single intranigral injection of lipopolysaccharide, a potent proinflammogen. The effect of this treatment was evaluated on inflammatory markers as well as on neuronal and glial populations.

Results

Data showed a synergistic effect between inflammation and stress, thus resulting in higher microglial activation and expression of proinflammatory markers. More important, the higher inflammatory response seen in stressed animals was associated with a higher rate of death of dopaminergic neurons in the substantia nigra, the most characteristic feature seen in Parkinson’s disease. This effect was dependent on glucocorticoids.

Conclusions

Our data demonstrate that stress sensitises midbrain microglia to further inflammatory stimulus. This suggests that stress may be an important risk factor in the degenerative processes and symptoms of Parkinson’s disease.

Memantine treatment reverses anhedonia, normalizes corticosterone levels and increases BDNF levels in the prefrontal cortex induced by chronic mild stress in rats

Memantine is a N-methyl-D-aspartate (NMDA) receptor antagonist and several studies have pointed to the NMDA receptor antagonists as a potential therapeutic target for the treatment of depression. The present study was aimed to evaluate the behavioral and physiological effects of administration of memantine in rats exposed to the chronic mild stress (CMS) model. To this aim, after 40 days of exposure to CMS procedure, rats were treated with memantine (20 mg/kg) for 7 days. In this study, sweet food consumption, adrenal gland weight, corticosterone levels, and brain-derived-neurotrophic factor (BDNF) protein levels in the prefrontal cortex, hippocampus and amygdala were assessed. Our results demonstrated that chronic stressful situations induced anhedonia, hypertrophy of adrenal gland weight, and an increase of corticosterone levels in rats, but did not alter BDNF protein levels in the rat brain. Memantine treatment reversed anhedonia and the increase of adrenal gland weight, normalized corticosterone levels and increased BDNF protein levels in the prefrontal cortex in stressed rats. Finally, these findings further support the hypothesis that NMDA receptor antagonists such as memantine could be helpful in the pharmacological treatment of depression.

Evaluation of brain and kidney energy metabolism in an animal model of contrast-induced nephropathy

Contrast-induced nephropathy is a common cause of acute renal failure in hospitalized patients, occurring from 24 to 48 h and up to 5 days after the administration of iodinated contrast media. Encephalopathy may accompany acute renal failure and presents with a complex of symptoms progressing from mild sensorial clouding to delirium and coma. The mechanisms responsible for neurological complications in patients with acute renal failure are still poorly known, but several studies suggest that mitochondrial dysfunction plays a crucial role in the pathogenesis of uremic encephalopathy. Thus, we measured mitochondrial respiratory chain complexes and creatine kinase activities in rat brain and kidney after administration of contrast media. Wistar rats were submitted to 6.0 ml/kg meglumine/sodium diatrizoate administration via the tail vein (acute renal failure induced by contrast media) and saline in an equal volume with the radiocontrast material (control group); 6 days after, the animals were killed and kidney and brain were obtained. The results showed that contrast media administration decreased complexes I and IV activities in cerebral cortex; in prefrontal cortex, complex I activity was inhibited. On the other hand, contrast media administration increased complexes I and II-III activities in hippocampus and striatum and complex IV activity in hippocampus. Moreover, that administration of contrast media also decreased creatine kinase activity in the cerebral cortex. The present findings suggest that the inhibition of mitochondrial respiratory chain complexes and creatine kinase caused by the acute renal failure induced by contrast media administration may be involved in the neurological complications reported in patients and might play a role in the pathogenesis of the encephalopathy caused by acute renal failure.

Chronic stress and lithium treatments alter hippocampal glutamate uptake and release in the rat and potentiate necrotic cellular death after oxygen and glucose deprivation

This study was undertaken to evaluate the effects of chronic variate stress and lithium treatment on glutamatergic activity and neuronal vulnerability of rat hippocampus. Male Wistar rats were simultaneously treated with lithium and submitted to a chronic variate stress protocol during 40 days, and afterwards the hippocampal glutamatergic uptake and release, measured in slices and synaptosomes, were evaluated. We observed an increased synaptosomal [(3)H]glutamate uptake and an increase in [(3)H]glutamate stimulated release in hippocampus of lithium-treated rats. Chronic stress increased basal [(3)H]glutamate release by synaptosomes, and decreased [(3)H]glutamate uptake in hippocampal slices. When evaluating cellular vulnerability, both stress and lithium increased cellular death after oxygen and glucose deprivation (OGD). We suggest that the manipulation of glutamatergic activity induced by stress may be in part responsible for the neuroendangerment observed after stress exposure, and that, in spite of the described neuroprotective effects of lithium, it increased the neuronal vulnerability after OGD.

Inhibition of mitochondrial respiratory chain in the brain of rats after hepatic failure induced by acetaminophen

Hepatic encephalopathy is an important cause of morbidity and mortality in patients with severe hepatic failure. This disease is clinically characterized by a large variety of symptoms including motor symptoms, cognitive deficits, as well as changes in the level of alertness up to hepatic coma. Acetaminophen is frequently used in animals to produce an experimental model to study the mechanisms involved in the progression of hepatic disease. The brain is highly dependent on ATP and most cell energy is obtained through oxidative phosphorylation, a process requiring the action of various respiratory enzyme complexes located in a special structure of the inner mitochondrial membrane. In this context, the authors evaluated the activities of mitochondrial respiratory chain complexes in the brain of rats submitted to acute administration of acetaminophen and treated with the combination of N-acetylcysteine (NAC) plus deferoxamine (DFX) or taurine. These results showed that acetaminophen administration inhibited the activities of complexes I and IV in cerebral cortex and that the treatment with NAC plus DFX or taurine was not able to reverse this inhibition. The authors did not observe any effect of acetaminophen administration on complexes II and III activities in any of the structures studied. The participation of oxidative stress has been postulated in the hepatic encephalopathy and it is well known that the electron transport chain itself is vulnerable to damage by reactive oxygen species. Since there was no effect of NAC + DFX, the effect of acetaminophen was likely to be due to something else than oxidative stress.

Chronic variable stress alters inflammatory and cholinergic parameters in hippocampus of rats

In the present study we investigated the effect of chronic variable stress (CVS) on some parameters of the immune system, including levels of cytokines [interleukin 1β (IL-1 β), interleukin 6 (IL-6), tumor necrosis factor α (TNF- α)] and chemokine CCL2 (MCP-1) in the hippocampus of rats. Acetylcholinesterase activity was also evaluated. Sixty-day old Wistar rats were submitted to different mild stressors for 40 days. After the last stress section, the cytokines and MCP-1 were determined by immunoassay and acetylcholinesterase activity by colorimetric method. Results showed that chronic stress significantly increased the levels of IL-1β, IL-6 and TNF-α, but did not alter the levels of MCP-1. In addition, acetylcholinesterase activity was increased in the hippocampus of rats subjected to CVS. These findings suggest that inflammation and cholinergic dysfunction may be, at least in part, important contributors to the neurological dysfunction observed in some depressed patients.

Effect of chronic administration of ketamine on the mitochondrial respiratory chain activity caused by chronic mild stress

Rezin GT, Gonçalves CL, Daufenbach JF, Carvalho-Silva M, Borges LS, Vieira JS, Hermani FV, Comim CM, Quevedo J, Streck EL. Effect of chronic administration of ketamine on the mitochondrial respiratory chain activity caused by chronic mild stress.

OBJECTIVE

Recently, we reported that mitochondrial respiratory chain complexes I, III and IV were inhibited in the cerebral cortex and cerebellum of rats submitted to chronic mild stress (CMS) and that acute ketamine administration reversed this effect. Therefore, we investigated whether the inhibition of these enzymes may be reversed by chronic administration of ketamine.

METHODS

Adult male Wistar rats were submitted to CMS and chronically treated with ketamine. After 40 days of CMS, consumption of sweet food, adrenal gland weight, body weight and enzymatic activity of the complexes were measured.

RESULTS

We verified that CMS decreased the intake of sweet food, increased the adrenal gland weight and the control group gained weight after 40 days but the stressed group did not; ketamine administration reversed these effects. We also verified that chronic administration of ketamine reversed the inhibition of complexes I, III and IV in cerebral cortex. However, in cerebellum, only complex IV inhibition was reversed. The chronic ketamine administration partially reverses the inhibition caused by CMS.

CONCLUSION

We hypothesise that CMS inhibits complexes I, III and IV activities and that chronic administration of ketamine administration partially reverses such an effect. Therefore, it seems reasonable to propose that ketamine administration might be a useful therapy for patients affected by major depression.

Chronic variable stress induces oxidative stress and decreases butyrylcholinesterase activity in blood of rats

Depressive disorders, including major depression, are serious and disabling, whose mechanisms are not clearly understood. Since life stressors contribute in some fashion to depression, chronic variable stress (CVS) has been used as an animal model of depression. In the present study we evaluated some parameters of oxidative stress [thiobarbituric acid reactive substances (TBARS), catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx)], and inflammatory markers (interleukin 6, C reactive protein, tumor necrosis factor-alpha and nitrites), as well as the activity of butyrylcholinesterase in blood of rats subjected to chronic stress. Homocysteine and folate levels also were measured. Stressed animals were submitted to different mild stressors for 40 days. After CVS, a reduction in weight gain was observed in the stressed group, as well as an increase in immobility time in the forced swimming test as compared with controls. Stressed animals presented a significant increase on TBARS and SOD/CAT ratio, but stress did not alter GPx activity and any inflammatory parameters studied. CVS caused a significant inhibition on serum butyrylcholinesterase activity. Stressed rats had higher plasmatic levels of homocysteine without differences in folate levels. Although it is difficult to extrapolate our findings to the human condition, the alterations observed in this work may be useful to help to understand, at least in part, the pathophysiology of depressive disorders.

Chronic variable stress impairs energy metabolism in prefrontal cortex and hippocampus of rats: prevention by chronic antioxidant treatment

Since chronic stress has been used widely for studying clinical depression and that brain energy metabolism and oxidative stress might be involved in the pathophysiology of this illness, the objective of this study was investigate the activities of pyruvate kinase, complex II and IV (cytocrome c oxidase) in hippocampus and prefrontal cortex of rats submitted to chronic variable stress. We also evaluated if vitamins E and C administration could prevent such effects. During 40 days adult rats from the stressed group were subjected to one stressor per day, at a different time each day, in order to minimize predictability. The stressed group had gained less weight while its immobilization time in the forced swimming test was greater than that of the control group. Results showed that stressed group presented an inhibition in the activities of complex II and cytochrome c oxidase in prefrontal cortex, while in hippocampus just complex IV was inhibited. Pyruvate kinase activity was not altered in stressed group when compared to control. Vitamins E and C administration prevented the alterations on respiratory chain caused by stress. These data suggest that the impairment of energy metabolism and oxidative stress could be related with the pathogenic pathways in stress related disorders.

Effects of beta-carboline harmine on behavioral and physiological parameters observed in the chronic mild stress model: further evidence of antidepressant properties

The chronic mild stress (CMS) model has been used as an animal model of depression which induces anhedonic behavior in rodents. The present study was aimed to evaluate the behavioral and physiological effects of administration of beta-carboline harmine in rats exposed to CMS procedure. To this aim, after 40 days of exposure to CMS procedure, rats were treated with harmine (15 mg/kg/day) for 7 days. In this study, sweet food consumption, adrenal gland weight, adrenocorticotrophin hormone (ACTH) levels, and hippocampal brain-derived-neurotrophic factor (BDNF) protein levels were assessed. Our findings demonstrated that chronic stressful situations induced anhedonia, hypertrophy of adrenal gland weight, increase ACTH circulating levels in rats and increase BDNF protein levels. Interestingly, treatment with harmine reversed anhedonia, the increase of adrenal gland weight, normalized ACTH circulating levels and BDNF protein levels. Finally, these findings further support the hypothesis that harmine could be a new pharmacological tool for the treatment of depression.

Ketamine treatment reverses behavioral and physiological alterations induced by chronic mild stress in rats

Several studies have supported the idea that ionotropic glutamate N-methyl-d-aspartate receptor (NMDA) is an important player in the etiology of psychopathologies, such as anxiety disorders and major depression. Additionally, studies have shown that ketamine induces antidepressant effects in humans as well as in rodents subjected to animal models of depression. In this context, the present study was aimed to evaluate behavioral and physiological effects of acute and chronic administration of ketamine, a NMDA receptor antagonist, in rats exposed to chronic mild stress (CMS). After 40 days of CMS, rats were treated with ketamine (15 mg/kg) and sweet food consumption, body and adrenal gland weight, corticosterone and adrenocorticotropic (ACTH) hormone levels, and hippocampal BDNF protein levels were assessed. Our findings demonstrated that CMS evoked anhedonia, induced hypertrophy of adrenal gland, impaired gain of body weight and increased corticosterone and ACTH circulating levels in rats. Acute and chronic treatment with ketamine reversed the increase in adrenal gland weight, promoted regain of body weight, and normalized corticosterone and ACTH circulating levels. Repeated, but not acute, administration of ketamine reversed anhedonia-like behavior, although the treatment with ketamine per se increased sweet food consumption in non-stressed rats. Finally, acute and chronic ketamine treatment did not alter hippocampal BDNF protein levels in stressed rats. In conclusion, these findings support the idea of a putative role of NMDA receptors in mood-related symptoms, and rapid and robust effects of ketamine in reverting mainly physiological alterations induced by chronic mild stressful situations in rats.

Chronic Lithium Treatment has Antioxidant Properties but does not Prevent Oxidative Damage Induced by Chronic Variate Stress

This study evaluated the effects of chronic stress and lithium treatments on oxidative stress parameters in hippocampus, hypothalamus, and frontal cortex. Adult male Wistar rats were divided into two groups: control and submitted to chronic variate stress, and subdivided into treated or not with LiCl. After 40 days, rats were killed, and lipoperoxidation, production free radicals, total antioxidant reactivity (TAR) levels, and superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were evaluated. The results showed that stress increased lipoperoxidation and that lithium decreased free radicals production in hippocampus; both treatments increased TAR. In hypothalamus, lithium increased TAR and no effect was observed in the frontal cortex. Stress increased SOD activity in hippocampus; while lithium increased GPx in hippocampus and SOD in hypothalamus. We concluded that lithium presented antioxidant properties, but is not able to prevent oxidative damage induced by chronic variate stress.

Stress increases vulnerability to inflammation in the rat prefrontal cortex

Inflammation could be involved in some neurodegenerative disorders that accompany signs of inflammation. However, because sensitivity to inflammation is not equal in all brain structures, a direct relationship is not clear. Our aim was to test whether some physiological circumstances, such as stress, could enhance susceptibility to inflammation in the prefrontal cortex (PFC), which shows a relative resistance to inflammation. PFC is important in many brain functions and is a target for some neurodegenerative diseases. We induced an inflammatory process by a single intracortical injection of 2 microg of lipopolysaccharide (LPS), a potent proinflammogen, in nonstressed and stressed rats. We evaluated the effect of our treatment on inflammatory markers, neuronal populations, BDNF expression, and behavior of several mitogen-activated protein (MAP) kinases and the transcription factor cAMP response element-binding protein. Stress strengthens the changes induced by LPS injection: microglial activation and proliferation with an increase in the levels of the proinflammatory cytokine tumor necrosis factor-alpha; loss of cells such as astroglia, seen as loss of glial fibrillary acidic protein immunoreactivity, and neurons, studied by neuronal-specific nuclear protein immunohistochemistry and GAD67 and NMDA receptor 1A mRNAs expression by in situ hybridization. A significant increase in the BDNF mRNA expression and modifications in the levels of MAP kinase phosphorylation were also found. In addition, we observed a protective effect from RU486 [mifepristone (11beta-[p-(dimethylamino)phenyl]-17beta-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one)], a potent inhibitor of the glucocorticoid receptor activation. All of these data show a synergistic effect between inflammation and stress, which could explain the relationship described between stress and some neurodegenerative pathologies.

Na+,K(+)-ATPase activity is reduced in hippocampus of rats submitted to an experimental model of depression: effect of chronic lithium treatment and possible involvement in learning deficits

This study was undertaken to verify the effects of chronic stress and lithium treatments on the hippocampal Na+,K(+)-ATPase activity of rats, as well as to investigate the effects of stress interruption and post-stress lithium treatment on this enzyme activity and on spatial memory. Two experiments were carried out; in the first experiment, adult male Wistar rats were divided into two groups: control and submitted to a chronic variate stress paradigm, and subdivided into treated or not with LiCl. After 40 days of treatment, rats were killed, and Na+,K(+)-ATPase activity was determined. In the second experiment, rats were stressed during 40 days, and their performance was evaluated in the Water Maze task. The stressed group was then subdivided into four groups, with continued or interrupted stress treatment and treated or not with lithium for 30 additional days. After a second evaluation of performance in the Water Maze, rats were killed and Na+,K(+)-ATPase activity was also measured. Results showed an impairment in Na+,K(+)-ATPase activity and in Water Maze performance of chronically stressed rats, which were prevented by lithium treatment and reversed by lithium treatment and by stress interruption. These results suggest that the modulation of Na+,K(+)-ATPase activity may be one of the mechanisms of action of lithium in the treatment of mood disorders.

Interaction between estradiol replacement and chronic stress on feeding behavior and on serum leptin

Exposure to stress may cause either an increase or a decrease in food intake. Behavioral and physiological responses to stress, including alterations in feeding behavior, are sexually dimorphic. This study aimed to evaluate the interaction between estradiol levels and chronic variate stress on the intake of sweet food and on serum levels of leptin, a hormone secreted by the adipose cells with a role in the regulation of body weight. Adult female Wistar rats were used. After ovariectomy, the animals received estradiol replacement (or oil) subcutaneously. Rats were then divided in controls and stressed (submitted to 30 days of variate stress). Consumption of sweet food and of serum leptin was measured. Although animals receiving estradiol replacement presented smaller weight gain, they showed an increased consumption of sweet food. Chronic variate stress decreased sweet food intake at 30, but not at 20, days of treatment. Estradiol replacement in the stressed group prevented both the reduction observed in sweet food intake and the increase in leptin levels. These results suggest that there is an interaction between chronic stress and estradiol replacement in feeding behavior concerning sweet food consumption, and this interaction may be related to altered leptin levels.

Reduction of hippocampal Na+, K+-ATPase activity in rats subjected to an experimental model of depression

The effect of a model of depression using female rats on Na+, K+-ATPase activity in hippocampal synaptic plasma membranes was studied. In addition, the effect of further chronic treatment with fluoxetine on this enzyme activity was verified. Sweet food consumption was measured to evaluate the efficacy of this model in inducing a state of reduced response to rewarding stimili. After 40 days of mild stress, a reduction in sweet food ingestion was observed. Reduction of hippocampal Na+, K+-ATPase activity was also observed. Treatment with fluoxetine increased this enzyme activity and reversed the effect of stress. Chronic fluoxetine decreased the ingestion of sweet food in both groups. This result is in agreement with suggestions that reduction of Na+, K+-ATPase activity is a caracteristic of depressive disorders. Fluoxetine reversed this effect. Therefore it is possible that altered Na+, K+-ATPase activity may be involved in the pathophysiology of depression in patients.

Stressor specificity of central neuroendocrine responses: implications for stress-related disorders

Despite the fact that many research articles have been written about stress and stress-related diseases, no scientifically accepted definition of stress exists. Selye introduced and popularized stress as a medical and scientific idea. He did not deny the existence of stressor-specific response patterns; however, he emphasized that such responses did not constitute stress, only the shared nonspecific component. In this review we focus mainly on the similarities and differences between the neuroendocrine responses (especially the sympathoadrenal and the sympathoneuronal systems and the hypothalamo-pituitary-adrenocortical axis) among various stressors and a strategy for testing Selye's doctrine of nonspecificity. In our experiments, we used five different stressors: immobilization, hemorrhage, cold exposure, pain, or hypoglycemia. With the exception of immobilization stress, these stressors also differed in their intensities. Our results showed marked heterogeneity of neuroendocrine responses to various stressors and that each stressor has a neurochemical "signature." By examining changes of Fos immunoreactivity in various brain regions upon exposure to different stressors, we also attempted to map central stressor-specific neuroendocrine pathways. We believe the existence of stressor-specific pathways and circuits is a clear step forward in the study of the pathogenesis of stress-related disorders and their proper treatment. Finally, we define stress as a state of threatened homeostasis (physical or perceived treat to homeostasis). During stress, an adaptive compensatory specific response of the organism is activated to sustain homeostasis. The adaptive response reflects the activation of specific central circuits and is genetically and constitutionally programmed and constantly modulated by environmental factors.

The effect of acute and chronic restraint on the central expression of prepro-neuropeptide Y mRNA in normotensive and hypertensive rats

Neuropeptide Y (NPY), one of the most abundant neuropeptides found in the central nervous system (CNS), has been implicated in the regulation of many autonomic functions, including cardiovascular control and the central stress response. The present study represents a detailed investigation of the effects of acute and chronic restraint stress on the expression of the mRNA encoding the NPY precursor, prepro-NPY, in the CNS of normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) using in situ hybridization histochemistry. Basal (unstressed) levels of prepro-NPY mRNA expression were found to be significantly increased in the hypothalamic arcuate nucleus of SHR compared to WKY rats, with similar levels of prepro-NPY mRNA expression found in the remaining central nuclei. Following exposure to both acute and chronic restraint, significant changes in prepro-NPY mRNA expression were found in a variety of central regions in both strains, including the arcuate nucleus and hippocampus (both strains), medial amygdala and cortex (WKY only), and dentate gyrus, nucleus of the solitary tract and ventrolateral medulla (SHR only). A comparison of the temporal response to restraint revealed that significant differences between strains existed in regions such as the arcuate nucleus, hippocampus and dentate gyrus, providing further evidence that hypertensive rats apparently have an impaired neural stress response. The present study demonstrates that exposure to restraint results in significant changes in prepro-NPY mRNA expression in specific nuclei of both WKY and SHR that are components of not only the central circuitry regulating the stress response, but also the neural network modulating autonomic function.

Expression of preprogalanin mRNA following acute and chronic restraint stress in brains of normotensive and hypertensive rats

Exposure to stress is known to induce widespread changes in the central nervous system (CNS) involving multiple neuropeptides. The neuropeptide galanin has been implicated in the central response to different stressors; however, the role of galanin in the response to restraint stress has not been reported. Therefore, this study utilised in situ hybridisation histochemistry to observe the effects of acute and chronic restraint stress on preprogalanin (preproGAL) mRNA expression in the CNS of normotensive (Wistar Kyoto; WKY) and Spontaneously Hypertensive (SHR) rats. Rats were exposed to 1 h of restraint for 0 (control), 1, 3, 5, or 10 consecutive days, and central preproGAL mRNA expression following these restraint periods was compared between strains. Significant differences in the basal expression of preproGAL mRNA were detected, with expression decreased by approximately 50% in the supraoptic nucleus (SON; P<0. 01) and increased by approximately 100% in the rostral ventrolateral medulla (RVLM; P<0.05) of SHR when compared to WKY. Following acute restraint (1 session), preproGAL mRNA expression was significantly increased by approximately 135% in the central nucleus of the amygdala (CeA; P<0.05) in WKY. In SHR, significant increases of up to 300% were observed in the CeA (P<0.01) and SON (P<0.05) following chronic restraint (up to 10 days). In addition, expression of preproGAL mRNA was significantly decreased in the locus coeruleus (LC) of SHR following acute restraint (1 session) (P<0.05). These results provide the first evidence that both acute (LC) and chronic (CeA, SON) restraint stress is associated with alterations in preproGAL mRNA expression. As such, the present study provides further evidence linking neurons containing galanin with the central response to restraint stress.

Fecal glucocorticoids document stress in female Barbary macaques (Macaca sylvanus)

Patterns of received aggression and the endocrine response were related to an increase in fecal glucocorticoid metabolites in an intact semifree-ranging group of Barbary macaque females in order to quantify the social stress incurred over a 20-week observation period. The novel result showed that immunoreactive cortisol and 11-oxoetiocholanolone found in the feces can indeed determine the endocrine response of the adrenal gland after a social stressor. After HPLC separation of pooled fecal samples, EIA analyses using three different assays (corticosterone, cortisol, and 11-oxoetiocholanolone) to quantify immunoreactive steroids showed that the corticosterone EIA had no distinctive immunoreactive peaks. Cortisol and 11-oxoetiocholanolone immunoassays showed respectively four and two immunoreactive substances. Time series analyses revealed a behaviorally initiated increase in concentrations of cortisol and 11-oxoetiocholanolone equivalents. Furthermore, both hormone curves exhibit comparable time functions. Either antibody is very suitable for determining glucocorticoid secretion after periods of stress.

The effects of acute and repeated restraint stress on the nociceptive response in rats

The effects of acute and repeated restraint stress on nociception, as measured by the tail-flick latency, were studied in adult male and female rats. After the exposure to a single restraint session, both male and female rats presented an increased latency in the tail-flick test. On the other hand, chronically stressed females presented a performance similar to the control group, whereas chronically stressed male rats responded to restraint with a decrease in the tail-flick latency. This response could be determined by the chronic treatment itself or by the restraint done just before the measurement. Thus, the effect of chronic stress upon basal tail-flick latency was evaluated. In male rats, this latency was significantly decreased in the stressed animals compared with the control group. In female rats, no difference between those groups was observed. Therefore, the results suggest that: (a) acute restraint stress induces an analgesic response in both male and female rats, and (b) there is a gender-specific nociceptive response induced by repeated restraint stress with a hyperalgesic effect in response to stress only in males.

Habituation and sensitization of plasma catecholamine responses to chronic intermittent stress: effects of stressor intensity

Adult male Sprague-Dawley rats were exposed acutely (1 time for 30 minutes) or chronically (30 minutes per day for 27 days) to swim stress in water maintained at either 18 degrees C, 24 degrees C or 34 degrees C. Each rat was prepared with an indwelling tail artery catheter to allow for direct measures of mean arterial pressure (MAP, mmHg) and heart rate (HR, beats per minute) and for remote collection of blood samples before, during and after the 1st or 27th swim stress session. Blood samples were later analyzed for plasma levels of norepinephrine and epinephrine to serve as an assessment of sympathetic-adrenal medullary activity. Compared to handled controls, body weight gain was reduced significantly in rats exposed chronically to swim stress at any of the 3 temperatures. However, baseline values of MAP and HR and plasma levels of norepinephrine and epinephrine were similar in chronically stressed rats compared to their handled controls. The plasma norepinephrine response of rats exposed chronically to either 18 degrees C or 24 degrees C swim stress was significantly greater than that of matched controls stressed for the first time. In contrast, the plasma epinephrine response of chronically stressed rats from these two groups was slightly but not significantly reduced compared to matched controls. For swim stress at 34 degrees C, the plasma norepinephrine and epinephrine responses of chronically stressed rats were reduced significantly compared to controls stressed for the first time. These findings demonstrate that stressor intensity affects sensitization and habituation of plasma catecholamine responses in laboratory rats exposed to chronic intermittent stress.(ABSTRACT TRUNCATED AT 250 WORDS)