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

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.

Estradiol valerate elicits antidepressant-like effects in middle-aged female rats under chronic mild stress

The purpose of this study was to analyze the antidepressant-like actions of estradiol valerate (1 or 2 mg/rat, single injection) or citalopram (5 or 10 mg/kg, chronically administered for 21 days) given independently or combined at low doses, to middle-aged ovariectomized female rats, as a model of human menopause. Animals were exposed to chronic mild stress, a model of depression that mimics anhedonia as revealed by diminished sucrose solution intake. Stressed rats decreased their sucrose preference 1 week after chronic stress and treatment with vehicle did not reverse this reduction. A single injection of estradiol valerate (2 mg/rat) produced an antidepressant-like action, evidenced as an increase in sucrose preference specific to stressed rats. Chronic citalopram (10 mg/kg) produced an antidepressant-like effect after 1 week. A single low-dose of estradiol valerate (1 mg/rat) did not potentiate or shorten the latency of action of chronic citalopram (5 mg/kg). These results reveal the antidepressant-like action of estrogens in middle-aged rats exposed to chronic stress. These data may be of importance for clinical depression in menopausal women.

cDNA microarray analysis of gene expression in the cerebral cortex and hippocampus of BALB/c mice subjected to chronic mild stress

Depressive disorders are devastating metal illness that can lead to deterioration in the social and occupational functioning of affected individuals. The etiology and pathophysiology of depression remain unknown. Present study was performed to better understand the underlying causes of depression. An experimental animal depression was induced in male BALB/c mice subjected to a chronic mild stress (CMS) procedure involving different stressor for consecutive 4 weeks. A cDNA microarray was employed to study the effects of CMS on the gene expression in cerebral cortex and hippocampus. 4-week CMS caused a significant reduction of 2% sucrose consumption. Morris water maze procedure showed impairment in cognitive function in stressed mice. Results of microarray showed that there were 102 and 60 genes were markedly affected by CMS treatment in cerebral cortex and hippocampus regions, respectively, including DNA damage/repair-related enzymes, anti-oxidant enzyme, and cyclin and cyclin-dependent kinase (CDK). These findings suggest that multiple biochemical effects play an important role the etiology of depression.

High susceptibility to chronic social stress is associated with a depression-like phenotype

Chronic stress is a key risk factor for a variety of diseases, including depression. There is a large degree of individual variation in the ability to recover successfully from a chronic stress exposure, but the determinants of this individual stress susceptibility are still poorly understood. We recently developed a novel mouse paradigm for chronic social stress during adolescence, which closely mimics the human condition of chronic social stress in respect to construct, face and predictive validity. By applying this chronic stress model to a large number of animals we aimed at identifying individuals that are either resilient or vulnerable to the persistent effects of chronic social stress exposure. Animals showing markedly elevated basal corticosterone levels 5 weeks following the end of the stress paradigm were considered "vulnerable", whereas individuals recovering quickly and being indistinguishable from controls were classified as "resilient". Stress vulnerability was associated with an increased level of corticotropin-releasing hormone in the paraventricular nucleus, decreased hippocampal mineralocorticoid receptor expression as well as increased anxiety- and depression-like behavior compared to resilient and control animals. In summary, we show that by using a large cohort of animals it is possible to select individuals that are vulnerable or resilient to the lasting effects of chronic social stress. The vulnerable phenotype mimics many aspects of stress-related human affective disorders and this may be used as a novel approach to study depression in an animal model, ultimately contributing to a better understanding and treatment of stress-related disorders.

Sustained stress-induced changes in mice as a model for chronic depression

RATIONALE

Major depression is a chronic disabling disorder, often preceded by stress. Despite emerging clinical interest in mechanisms perpetuating episodes of depression and/or establishing increased vulnerability for relapse, little attention has been paid to address these aspects in experimental models. Here, we studied the long-term neuroadaptive effects of chronic mild stress (CMS) as well as the effectiveness of a course of an antidepressant treatment.

METHODS

CMS was applied for 6 weeks, and paroxetine was administered from the third week and continued for 2 weeks thereafter. In order to validate our CMS procedure, we first studied short-term (24 h after CMS) hippocampal cell proliferation and neurogenesis, along with anhedonic-like behaviour. Subsequently, we examined the long-term (one month after CMS) anhedonia, hippocampal neurogenesis, the regulation of c-Fos immunoreactivity and neurotransmitter levels in different areas as well as cortical spine density and hippocampal expression of synaptic proteins.

RESULTS

CMS induced a decrease in short-term neurogenesis that was fully recovered in the long term. In addition, CMS-induced lasting anhedonia and region-specific changes in neuronal activity (c-Fos immunoreactivity) and neurotransmitter (glutamate and GABA) levels. Repeated paroxetine reverted these effects with the exception of decreased neuronal activity in the dentate gyrus (DG) and GABA levels in the ventral hippocampus. Moreover, CMS downregulated the GAD65 and VGLUT1 expressions.

CONCLUSION

This study shows region-specific long-term neurobiological adaptations induced by CMS and residual hippocampal signs after paroxetine treatment. We propose the use of this model to study molecular mechanisms involved in chronic depression and vulnerability for relapse.

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 electroconvulsive therapy and propofol on spatial memory and glutamatergic system in hippocampus of depressed rats

OBJECTIVES

This animal study tested the spatial learning memory of "depressed" rats undergoing electroconvulsive therapy (ECT) or ECT combined with propofol and aimed to reveal the glutamatergic mechanisms in the hippocampus.

METHODS

Sixty Sprague-Dawley rats were randomly divided into 5 groups (n = 12 rats per group): control group, depression group, propofol group, ECT group, and propofol + ECT group. Rats were stressed repeatedly for 21 days to establish depression model. After the model was set up, rats of the propofol group were administrated with propofol (100 mg/kg). Rats of ECT group were administered ECT once on alternate days for 2 weeks. ECT + propofol group rats were given ECT after anesthesia with propofol (100 mg/kg). Spatial memory was assessed by Morris water maze. Glutamate content in hippocampus was measured by chromatometry. N-methyl d-aspartate (NMDA)-NR2B expression was detected by immunohistochemistry.

RESULTS

After treatment, the behavior level of rats in ECT group and ECT + propofol group was higher than that in depression group, and there was no significance between ECT group and ECT + propofol group. The evasive latency of rats detected by Morris water maze got shorter and shorter from the first day to fourth day. The evasive latency in ECT group was longer than that in ECT + propofol group and depression group, and the evasive latency in ECT + propofol group was shorter than that in depression group. Glutamate contents in hippocampus of rats in depression group and propofol group were higher than those in other groups, and glutamate content in ECT group was lower than that in other groups. The content in ECT + propofol group was lower than that in depression group, but higher than that in ECT group. N-methyl d-aspartate-NR2B expression in hippocampus of rats in depression group was lower than that in control group, but the expressions in ECT group and ECT + propofol group were higher than that in control group, and the expression in ECT + propofol group was lower than that in ECT group.

CONCLUSIONS

The glutamate content in hippocampus of depressed rats heightens, and the NMDA-NR2B expression down-regulated, which may cause "depression" symptoms and learning memory impairment. After ECT, the glutamate contents decreased, and NMDA-NR2B expression up-regulated, the depression symptoms improved, and the spatial memory worsened simultaneously. However, propofol inhibited the excessive decrease of glutamate and excessive up-regulation of NMDA-NR2B caused by ECT, and both the depression symptoms and the spatial memory of depressed rats improved.

Strain differences in the chronic mild stress animal model of depression

Hypothalamic-pituitary-adrenal (HPA) axis dysfunction has been implicated in depression pathology. In the present study, we used a chronic mild stress (CMS) animal model of depression to examine the responses of three strains of rats that have different HPA axis responsiveness; and whether the behavioral changes observed are correlated with changes in hippocampal cell proliferation and survival. In addition, in most of the CMS experiments the rats are kept in singly housed condition. Since rats are social animals we also examined whether prolonged single housing condition affects the behavior of the rats. The results showed that rats with a hyperactive HPA axis, the inbred Fischer (F344) rat, were the most responsive to CMS. The inbred Lewis (LEW) rat, which has a hypoactive HPA axis, did not show anhedonia after CMS treatment but showed other signs of distress. The responses of the outbred Sprague-Dawley (SD) rats were variable; this strain was very sensitive to the single housing condition. Prolonged single housing condition itself could induce helplessness behavior in the rats. The results from hippocampal cell proliferation of the three strains indicated that cell proliferation was not related to anhedonia induced by CMS. We conclude that F344 rat is the strain most sensitive to CMS treatment and is probably the stain of choice for CMS experiments.

Glial pathology in an animal model of depression: reversal of stress-induced cellular, metabolic and behavioral deficits by the glutamate-modulating drug riluzole

Growing evidence indicates that glia pathology and amino-acid neurotransmitter system abnormalities contribute to the pathophysiology and possibly the pathogenesis of major depressive disorder. This study investigates changes in glial function occurring in the rat prefrontal cortex (PFC) after chronic unpredictable stress (CUS), a rodent model of depression. Furthermore, we analyzed the effects of riluzole, a Food and Drug Administration-approved drug for the treatment of amyotrophic laterosclerosis, known to modulate glutamate release and facilate glutamate uptake, on CUS-induced glial dysfunction and depressive-like behaviors. We provide the first experimental evidence that chronic stress impairs cortical glial function. Animals exposed to CUS and showing behavioral deficits in sucrose preference and active avoidance exhibited significant decreases in 13C-acetate metabolism reflecting glial cell metabolism, and glial fibrillary associated protein (GFAP) mRNA expression in the PFC. The cellular, metabolic and behavioral alterations induced by CUS were reversed and/or blocked by chronic treatment with the glutamate-modulating drug riluzole. The beneficial effects of riluzole on CUS-induced anhedonia and helplessness demonstrate the antidepressant action of riluzole in rodents. Riluzole treatment also reversed CUS-induced reductions in glial metabolism and GFAP mRNA expression. Our results are consistent with recent open-label clinical trials showing the drug's effect in mood and anxiety disorders. This study provides further validation of hypothesis that glial dysfunction and disrupted amino-acid neurotransmission contribute to the pathophysiology of depression and that modulation of glutamate metabolism, uptake and/or release represent viable targets for antidepressant drug development.

The female urine sniffing test: a novel approach for assessing reward-seeking behavior in rodents

BACKGROUND

Abnormal hedonic behavior is a key feature of many psychiatric disorders. Several paradigms measure reward-seeking behavior in rodents, but each has limitations. We describe a novel approach for monitoring reward-seeking behavior in rodents: sniffing of estrus female urine by male mice, along with number of ultrasonic vocalizations (USVs) emitted during the test.

METHODS

The female urine sniffing test (FUST) was designed to monitor reward-seeking activity in rodents together with tests of helplessness and sweet solution preference. USVs and dopamine release from the nucleus accumbens (NAc) were recorded. Sniffing activity was measured in 1) manipulation-naive C57BL/6J and 129S1/SVImJ mice and Wistar-Kyoto rats; 2) stressed mice; 3) two groups of mice that underwent the learned helplessness paradigm-one untreated, and one treated with the SSRI citalopram; and 4) GluR6 knockout mice, known to display lithium-responsive, mania-related behaviors.

RESULTS

Males from all three strains spent significantly longer sniffing female urine than sniffing water. Males emitted USVs and showed significantly elevated NAc dopamine levels while sniffing urine. Foot-shock stress significantly reduced female urine sniffing time. Compared with mice that did not undergo the LH paradigm, LH males spent less time sniffing female urine, and citalopram treatment alleviated this reduction. Compared with their wildtype littermates, GluR6KO males sniffed female urine longer and showed enhanced saccharin preference.

CONCLUSIONS

In rodents, sniffing female urine is a preferred activity accompanied by biological changes previously linked to reward-seeking activities. The FUST is sensitive to behavioral and genetic manipulation and to relevant drug treatment.

Prenatal alcohol exposure: fetal programming and later life vulnerability to stress, depression and anxiety disorders

Children with fetal alcohol spectrum disorder (FASD) exhibit cognitive, neuropsychological and behavioral problems, and numerous secondary disabilities including depression and anxiety disorders. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is common in depression/anxiety, reflected primarily in increased HPA tone or activity. Prenatal alcohol exposure (PAE) increases HPA tone and results in HPA dysregulation throughout life, paralleling many of the HPA changes in depression/anxiety. We review data demonstrating altered HPA function and increased depression/anxiety in FASD. In the context of the stress-diathesis model, we discuss the hypothesis that fetal programming of the HPA axis by PAE alters neuroadaptive mechanisms that mediate the stress response, thus sensitizing the organism to stressors encountered later in life, and mediating, at least partly, the increased vulnerability to depression/anxiety disorders. Furthermore, we present evidence demonstrating sex-specific alterations in both hormonal and behavioral responsiveness to tasks measuring depressive- and anxiety-like behaviors in PAE offspring. Overall, the research suggests that the stress-diathesis model provides a powerful approach for elucidating mechanisms underlying the increased vulnerability to mental illness among individuals with FASD, and developing appropriate treatments for these individuals. Dr. Seymour Levine's seminal work on the long-term consequences of early life experiences formed a framework for the development of the research described in this review.

Association between repeated unpredictable chronic mild stress (UCMS) procedures with a high fat diet: a model of fluoxetine resistance in mice

Major depressive disorder is a debilitating disease. Unfortunately, treatment with antidepressants (ADs) has limited therapeutic efficacy since resistance to AD is common. Research in this field is hampered by the lack of a reliable natural animal model of AD resistance. Depression resistance is related to various factors, including the attendance of cardiovascular risk factors and past depressive episodes. We aimed to design a rodent model of depression resistance to ADs, associating cardiovascular risk factors with repeated unpredicted chronic mild stress (UCMS). Male BALB/c mice were given either a regular (4% fat) or a high fat diet (45% fat) and subjected to two 7-week periods of UCMS separated by 6 weeks. From the second week of each UCMS procedure, vehicle or fluoxetine (10 mg/kg, i.p.) was administrated daily. The effects of the UCMS and fluoxetine in both diet conditions were assessed using physical (coat state and body weight) and behavioural tests (the reward maze test and the splash test). The results demonstrate that during the second procedure, UCMS induced behavioural changes, including coat state degradation, disturbances in self-care behaviour (splash test) and anhedonia (reward maze test) and these were reversed by fluoxetine in the regular diet condition. In contrast, the high-fat diet regimen prevented the AD fluoxetine from abolishing the UCMS-induced changes. In conclusion, by associating UCMS-an already validated animal model of depression-with high-fat diet regimen, we designed a naturalistic animal model of AD resistance related to a sub-nosographic clinical entity of depression.

A novel chronic social stress paradigm in female mice

Major depression is one of the most prevalent stress-related psychiatric diseases. Next to environmental influences such as chronic social stress, gender is among the strongest risk factors for major depression, with women having a twice as high risk to develop the disease compared to men. While there is abundant literature on the effects of chronic social stress in male rodents, there is a serious lack of information on gender-specific effects. Especially in mice, which due to the wide availability of transgenic lines offer a unique opportunity to study gene x environment interactions, there is no existing model of chronic social stress that is applicable to both sexes. We here describe the effects of chronic social stress based on the disruption of the social network in a group-housed situation in female mice, a model that was recently described and validated for male mice. In this model, the group composition of the mice is changed twice per week for a period of 7 weeks, covering the adolescent and early adulthood period. We observed that housing in an unpredictable social environment resulted in chronic stress in female mice. The observed effects, which included increased adrenal weight, decreased thymus weight, increased corticosterone levels, and increased anxiety-like behavior, were very similar to the described effects of this paradigm in male mice. In addition, we observed a distinct expression of stress system-related genes in female mice following chronic stress exposure. Our results validate this model as a suitable approach to study chronic social stress in female mice and open up the opportunity to use this model with transgenic or knockout mouse lines.

Effects of SYJN, a Chinese herbal formula, on chronic unpredictable stress-induced changes in behavior and brain BDNF in rats

AIM OF THE STUDY

Suyu-Jiaonang (SYJN) is a Chinese herbal formula that contains four herbs: Bupleurum chinense DC, Curcuma aromatica Salisb., Perilla frutescens (Linn.) Britt., and Acorus tatarinowii Schott. Previous studies conducted in our laboratory have revealed an antidepressant-like effect of the formula in various mouse models of behavioral despair. The present study aimed to investigate whether SYJN could produce antidepressant-like effects in chronic unpredictable stress (CUS)-induced depression model in rats and its possible mechanism(s).

MATERIALS AND METHODS

Rats were subjected to an experimental setting of CUS. The effect of SYJN treatment on CUS-induced depression was examined using behavioral tests including the sucrose consumption and open field tests. The mechanism underlying the antidepressant-like action of SYJN was examined by measuring brain-derived neurotrophic factor (BDNF) protein and mRNA expression in brain tissues of CUS-exposed rats.

RESULTS

Exposure to CUS for 4 weeks caused depression-like behavior in rats, as indicated by significant decreases in sucrose consumption and locomotor activity (assessed in the open field test). In addition, it was found that BDNF protein and mRNA levels in the hippocampus and frontal cortex were lower in CUS-treated rats, as compared to controls. Daily intragastric administration of SYJN (1300 or 2600 mg/kg) during the 4-week period of CUS significantly suppressed behavioral changes and attenuated the CUS-induced decrease in BDNF protein and mRNA levels in the hippocampus and frontal cortex.

CONCLUSION

The results suggest that SYJN alleviates depression induced by CUS. The antidepressant-like activity of SYJN is likely mediated by the increase in BDNF expression in brain tissues.

Sini tang prevents depression-like behavior in rats exposed to chronic unpredictable stress

Sini Tang, a Chinese traditional prescription containing three herbs, has been widely used for Yang-deficiency. Recent clinical studies have shown that Sini Tang could treat and improve depression symptoms, but the mechanisms underlying the antidepressant effect of Sini Tang remains unknown. In rats with chronic unpredictable stress (CUS), we examined the effects of Sini Tang on sucrose preference and open field exploratory behavior. The levels of corticosterone level in plasma and corticotropin-releasing hormone (CRH) mRNA expression in hypothalamus were also measured by enzyme-linked immunosorbent assays (ELISA) and real-time reverse transcription PCR (RT-PCR), respectively. Rats subjected to CUS exhibited decreases in sucrose preference and ambulation in the open field test. These were all attenuated by Sini Tang in a dose-dependent manner. Biochemically, Sini Tang also reversed CUS-induced increases in corticosterone in plasma and CRH mRNA in the hypothalamus. The behavioral effects of the Sini Tang were correlated to the biochemical actions. These results suggest that Sini Tang produces an antidepressant-like effect, which appears to involve CRH in the brain.

Anhedonia in postpartum rats

Postpartum depression (PPD) is a debilitating illness, yet little is known about its causes. The purpose of this study was to examine a major symptom of depression during the postpartum period, anhedonia, by comparing sucrose preference in female rats that had undergone actual pregnancy or hormone-simulated pregnancy (HSP) to their respective controls. Whereas HSP rats showed significantly less preference than vehicle control rats for 1% sucrose solution during the first three weeks of the "postpartum" period, previously pregnant females showed only slightly depressed sucrose preference for the first 1-2 days postpartum, compared to non-pregnant controls. Habituation to 1% sucrose during the pregnancy period, which increased preference upon later testing in previously pregnant rats tested on postpartum day 2, did not significantly increase preference in HSP rats, suggesting that depressed preference in the latter group was not due to neophobia. Pre-treatment with desipramine did not prevent suppressed sucrose preference in HSP rats, and preference was even further suppressed following chronic sertraline treatment. These results suggest that estradiol withdrawal following HSP may cause anhedonia during the early "postpartum" period. In contrast, females that have undergone actual pregnancy are less likely to show this effect, suggesting that postpartum hormonal changes other than the dramatic decline in estradiol may buffer its negative mood effects.

Stress-related endocrinological and psychopathological effects of short- and long-term 50Hz electromagnetic field exposure in rats

It is believed that different electromagnetic fields do have beneficial and harmful biological effects. The aim of the present work was to study the long-term consequences of 50 Hz electromagnetic field (ELF-EMF) exposure with special focus on the development of chronic stress and stress-induced psychopathology. Adult male Sprague-Dawley rats were exposed to ELF-EMF (50 Hz, 0.5 mT) for 5 days, 8h daily (short) or for 4-6 weeks, 24h daily (long). Anxiety was studied in elevated plus maze test, whereas depression-like behavior of the long-treated group was examined in the forced swim test. Some days after behavioral examination, the animals were decapitated among resting conditions and organ weights, blood hormone levels as well as proopiomelanocortin mRNA level from the anterior lobe of the pituitary gland were measured. Both treatments were ineffective on somatic parameters, namely none of the changes characteristic to chronic stress (body weight reduction, thymus involution and adrenal gland hypertrophy) were present. An enhanced blood glucose level was found after prolonged ELF-EMF exposure (p=0.013). The hormonal stress reaction was similar in control and short-term exposed rats, but significant proopiomelanocortin elevation (p<0.000) and depressive-like behavior (enhanced floating time; p=0.006) were found following long-term ELF-EMF exposure. Taken together, long and continuous exposure to relatively high intensity electromagnetic field may count as a mild stress situation and could be a factor in the development of depressive state or metabolic disturbances. Although we should stress that the average intensity of the human exposure is normally much smaller than in the present experiment.

A reduced number of hippocampal granule cells does not associate with an anhedonia-like phenotype in a rat chronic mild stress model of depression

Several clinical and preclinical studies have indicated that hippocampal shrinkage and decreased neurogenesis are implicated in the pathology of depression. Recent animal studies have shown, however, that the development of depression-related symptoms may take place through neurogenesis-independent pathways. To evaluate whether the stress-induced morphological changes in the hippocampal formation are causally related to the development of anhedonia-like symptoms, we combined the chronic mild stress (CMS) rat model of depression with stereological estimations of the number of proliferating progenitors, the total number of granule cells, and the volume of the ventral hippocampal formation (VHF). First, we found that stress-susceptible and stress-resilient animals, as categorized according to the behavioral read-out, both have a decrease in hippocampal cell proliferation. Our results also indicated that the anhedonia-like state in CMS rats develops prior to maximal suppression of cell proliferation, but correlates with a reduction in the total number of granule cells in the VHF. Furthermore, recovery from depression-related symptoms correlated with re-establishment of proliferation rates, but not with the total number of granule cells. Notably, decreases in the number of granule cells occurred independently of the induction of an anhedonia-like phenotype. There were no stress-induced changes in the volume of the VHF. We conclude that cell proliferation and a reduction in the total number of granule cells in the VHF are triggered by chronic stress, but do not associate with development of an anhedonia-like state in rats.

Long-term treatment with peony glycosides reverses chronic unpredictable mild stress-induced depressive-like behavior via increasing expression of neurotrophins in rat brain

The root part of Paeonia lactiflora Pall., commonly known as peony, is a commonly used Chinese herb for the treatment of depression-like disorders. Previous studies in our laboratory have showed that total glycosides of peony (TGP) produced antidepressant-like action in various mouse models of behavioral despair. The present study aimed to investigate the mechanism(s) underlying the antidepressant-like action of TGP by measuring neurotrophins including brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in non-stressed and chronic unpredictable mild stress (CUMS)-treated rats. TGP (80 or 160 mg/kg/day) was administered by oral gavage to the animals for 5 weeks. The results showed that CUMS caused depression-like behavior in rats, as indicated by the significant decreases in sucrose consumption and locomotor activity (assessed by open-field test). In addition, it was found that BDNF contents in the hippocampus and frontal cortex were significantly decreased in CUMS-treated rats. CUMS treatment also significantly decreased the level of NGF in the frontal cortex of the animals. Daily intragastric administration of TGP (80 or 160 mg/kg/day) during the five weeks of CUMS significantly suppressed behavioral and biochemical changes induced by CUMS. Treating non-stressed animals with TGP (160 mg/kg) for 5 weeks also significantly increased BDNF contents in the hippocampus and frontal cortex, and NGF contents in the frontal cortex. The results suggest that the antidepressant-like action of TGP is mediated, at least in part, by increasing the expression of BDNF and NGF in selective brain tissues.

Peripheral and cerebral metabolic abnormalities of the tryptophan-kynurenine pathway in a murine model of major depression

Occurring both peripherally and centrally, the kynurenine pathway (KP) - an alternative pathway to 5-HT synthesis from tryptophan (TRP) - could be of particular value to better understand the link between peripheral changes of circulating levels of glucocorticoids (GC)/proinflammatory cytokines and altered neurotransmission observed in depressed patients. Indeed, it is activated by these mediators of stress and can produce several neuroactive compounds like quinolinic acid (QUIN) and kynurenic acid (KYNA) that can respectively increase and decrease glutamate concentration in brain. In order to characterize the role of both the peripheral and cerebral KP in the pathophysiology of depressive disorders, we used the Unpredictable Chronic Mild Stress (UCMS) to induce a depressive-like syndrome and we then measured the level of relevant TRP-KYN pathway metabolites: KYN, 3-hydroxykynurenine (3HK; precursor of QUIN) and KYNA. We also measured TRP-5HT pathway metabolites: TRP, 5-HT, 5-HIAA. We showed that UCMS increased TRP catabolism along the KP in the periphery. 5-HT and KYN were found to be strongly negatively correlated in all brain structures of control mice and of UCMS mice except in the hippocampus. More importantly we found that KYN was preferentially metabolized along the QUIN pathway at the subcortical level (amygdala/striatum) whereas, at the cortical level (cingulate cortex), the QUIN pathway was reduced. Considering the role of these metabolites on the glutamatergic neurotransmission, we propose that such KP alterations could participate to the cortical/subcortical glutamatergic alterations reported in depressed patients.

Susceptibility of a potential animal model for pathological anxiety to chronic mild stress

When anxiety-related behaviour in animals appears to lack adaptive value, it might be defined as pathological. Adaptive behaviour can be assessed for example by changes in behavioural responses over time, i.e. habituation. Thus, non-adaptive anxiety would be reflected by a lack of habituation. Recently, we found that 129P3/J mice are characterised by non-adaptive avoidance behaviour after repeated test exposure. The present study was aimed at investigating the sensitivity of the behavioural profile of these animals to exposure to a chronic mild stress (CMS) paradigm followed by repeated exposure to the modified hole board test. If the behavioural profile of 129P3/J mice mirrors pathological anxiety, their behavioural habituation under repeated test exposure conditions should be affected by CMS treatment. The results confirm the profound lack of habituation with respect to anxiety-related behaviour in both control and CMS treated mice. Additionally, CMS treated animals revealed a lower exploratory behaviour, reduced locomotor activity and increased arousal-related behaviour over time when compared to control individuals, proving an extension of their impaired habituation behaviour. Although no effects of CMS treatment on plasma corticosterone levels were found, higher immediate early gene expression in the bed nucleus of the stria terminalis and the ventrolateral periaqueductal grey in CMS treated mice indicated that 129P3/J mice are susceptible to the negative effects of CMS treatment at both the behavioural and the functional level. These results support the hypothesis that 129P3/J mice might be an interesting model for pathological anxiety.

Dose-dependent effects of caffeine on behavior and thermoregulation in a chronic unpredictable stress model of depression in rats

The effects of the non-selective adenosine A(1)/A(2) receptor antagonist caffeine on behavior and thermoregulation in chronic unpredictable stress (CUS) model of depression was studied in Wistar rats. In the open field (OF) test, caffeine dose-dependently increased motor activity while decreased grooming and time spent in the corner. Five-week exposure to CUS procedure had the opposite effect in rats. Caffeine reversed CUS-induced effects on the above mentioned parameters. Caffeine (40 mg/kg) increased the motor activity in plus maze (PM) test while at doses of 20 and 40 mg/kg it decreased the number of entries in the open arms. Whereas CUS did not change the level of anxiety, caffeine (2, 20 and 40 mg/kg) administered after CUS diminished it by increasing the time in open arms. Caffeine dose-dependently decreased the immobility time while CUS had the opposite increasing effect in forced swimming test (FST). Caffeine at doses of 20 and 40 mg/kg reversed the effect of CUS on immobility in FST. Caffeine produced dose-dependent rice of body temperature in both non-treated and CUS-treated rats. The hyperthermic effect in normal rats pretreated with caffeine lasted about 90 min while in caffeine-pretreated rats exposed to CUS it lasted about 150 min. High dose of caffeine (100mg/kg) induced significant hypothermia between 90th and 150th minute in control rats and hyperthermia between 30th and 60th minute in CUS-treated rats. These results suggest a putative role of this methylxanthine in the adaptive responses to chronic unpredictable stress stimuli.

Nuclear factor-kappaB is a critical mediator of stress-impaired neurogenesis and depressive behavior

Proinflammatory cytokines, such as IL-1beta, have been implicated in the cellular and behavioral effects of stress and in mood disorders, although the downstream signaling pathways underlying these effects have not been determined. In the present study, we demonstrate a critical role for NF-kappaB signaling in the actions of IL-1beta and stress. Stress inhibition of neurogenesis in the adult hippocampus, which has been implicated in the prodepressive effects of stress, is blocked by administration of an inhibitor of NF-kappaB. Further analysis reveals that stress activates NF-kappaB signaling and decreases proliferation of neural stem-like cells but not early neural progenitor cells in the adult hippocampus. We also find that depressive-like behaviors caused by exposure to chronic stress are mediated by NF-kappaB signaling. Together, these data identify NF-kappaB signaling as a critical mediator of the antineurogenic and behavioral actions of stress and suggest previously undescribed therapeutical targets for depression.

Prenatal alcohol exposure and chronic mild stress differentially alter depressive- and anxiety-like behaviors in male and female offspring

BACKGROUND

Fetal Alcohol Spectrum Disorder (FASD) is associated with numerous neurobehavioral alterations, as well as disabilities in a number of domains, including a high incidence of depression and anxiety disorders. Prenatal alcohol exposure (PAE) also alters hypothalamic-pituitary-adrenal (HPA) function, resulting in increased responsiveness to stressors and HPA dysregulation in adulthood. Interestingly, data suggest that pre-existing HPA abnormalities may be a major contributory factor to some forms of depression, particularly when an individual is exposed to stressors later in life. We tested the hypothesis that exposure to stressors in adulthood may unmask an increased vulnerability to depressive- and anxiety-like behaviors in PAE animals.

METHODS

Male and female offspring from prenatal alcohol (PAE), pair-fed (PF), and ad libitum-fed control (C) treatment groups were tested in adulthood. Animals were exposed to 10 consecutive days of chronic mild stress (CMS), and assessed in a battery of well-validated tasks sensitive to differences in depressive- and/or anxiety-like behaviors.

RESULTS

We report here that the combination of PAE and CMS in adulthood increases depressive- and anxiety-like behaviors in a sexually dimorphic manner. PAE males showed impaired hedonic responsivity (sucrose contrast test), locomotor hyperactivity (open field), and alterations in affiliative and nonaffiliative social behaviors (social interaction test) compared to control males. By contrast, PAE and, to a lesser extent, PF, females showed greater levels of "behavioral despair" in the forced swim test, and PAE females showed altered behavior in the final 5 minutes of the social interaction test compared to control females.

CONCLUSIONS

These data support the possibility that stress may be a mediating or contributing factor in the psychopathologies reported in FASD populations.

Recapitulation and reversal of a persistent depression-like syndrome in rodents

Alterations in multiple biological functions, such as transcription factor activity, are implicated in the neurobiology of depression, based primarily on the characterization of antidepressant efficacy in naïve rodents rather than on models that capture the protracted feelings of anhedonia and helplessness that typify depression. This unit presents rat and mouse models of depression that involve chronic oral exposure to the stress-associated adrenal hormone, corticosterone (CORT), resulting in anhedonic- and helplessness-like behaviors that are persistent yet reversible by chronic antidepressant treatment. Prior CORT exposure also chronically influences molecular targets hypothesized to contribute to negative mood. One example is phosphorylation of cAMP response element binding protein in the hippocampus and nucleus accumbens. Prior chronic CORT exposure provides an alternative method to chronic mild stress models of depression that is easily replicable and persists well beyond the CORT exposure period, thereby modeling the persistent depressive-like state in humans.

Models of depression

The incidence of depressive illness is high in the United States and worldwide, and the inadequacy of currently available drug treatments contributes to the significant health burden associated with depression. A basic understanding of the underlying disease processes in depression is lacking, and therefore, recreating the disease in animal models is not possible. Currently used models of depression attempt to produce quantifiable correlates of human symptoms in experimental animals. The models differ in the degree to which they produce features that resemble a depressive-like state, and models that include stress exposure are widely used. Paradigms that employ acute or subchronic stress exposure include learned helplessness, forced swim test, and tail suspension test, which employ relatively short-term exposure to inescapable or uncontrollable stress and can reliably detect antidepressant drug response. Longer-term models include chronic mild stress models, early-life stress models, and social conflict models, which may more accurately simulate processes that lead to depression. These models each have varying degrees of face, construct, and predictive validity for depression and contribute differently to our understanding of antidepressant processes.

Decreased expression of serotonin 1A receptor in the dentate gyrus in association with chronic mild stress: a rat model of post-stroke depression

Alterations of serotonin (5-HT) neurotransmission are implicated in post-stroke depression (PSD). Serotonin 1A (5-HT(1A)) receptor-based abnormalities have been the focus of intensive study in depression. Here we investigated the expression of the 5-HT(1A) receptor and gene in the hippocampal dentate gyrus (DG) by chronic mild stress (CMS) after stroke and the effect of citalopram. Male Sprague-Dawley rats were separated into control, stress only, ischemic stroke, PSD and citalopram-treated groups. The putative PSD animal model involved cerebral ischemia induced by left middle cerebral artery occlusion (MCAO) followed by exposure to CMS combined with single housing. All animals were assessed for depression-like behavior. The 5-HT(1A) receptor and mRNA level in DG were quantified by Western immunoblotting and Real-time RT-PCR, respectively, on the 19th and 28th days after initiating CMS. PSD animals displaying a behavioral index of depression (anhedonia) have significantly decreased protein expression of 5-HT(1A) receptors and mRNA level relative to ischemic stroke animals at each timepoint, respectively, and all these were reversed by citalopram. The dysfunction of the of 5-HT(1A) receptor in DG may play an important role in the pathogenesis of PSD and become a potential target for therapeutic intervention in the rat. The results provide partial support for the psychosocial and biological etiology of PSD and further predict the etiologic validity of the PSD model.

Effects of activation and blockade of dopamine receptors on the extinction of a passive avoidance reaction in mice with a depressive-like state

Learning and extinction of a conditioned passive avoidance reaction resulting from neuropharmacological actions on dopamine D(1) and D(2) receptors were demonstrated to be specific in intact mice and in mice with a depressive-like state. Learning was degraded only after administration of the D(2) receptor antagonist sulpiride and was independent of the initial functional state of the mice. In intact mice, activation of D(2) receptors with quinpirole led to a deficit of extinction, consisting of a reduction in the ability to acquire new inhibitory learning in conditions associated with the disappearance of the expected punishment. In mice with the "behavioral despair" reaction, characterized by delayed extinction, activation of D(1) receptors with SKF38393 normalized this process, while the D(2) agonist was ineffective. A positive effect consisting of accelerated extinction of the memory of fear of the dark ("dangerous") sector of the experimental chamber was also seen on blockade of both types of dopamine receptor.

Environmental enrichment reduces cocaine seeking and reinstatement induced by cues and stress but not by cocaine

Whereas earlier studies have focused on the preventive effects of enriched environments (EE) in drug addiction, in a recent study we suggested that EE can also have 'curative' effects. In fact, we found that cocaine addiction-related behaviors can be eliminated by housing cocaine-treated mice in EE during periods of forced abstinence. However, those results were obtained with two simple models of addiction, conditioned place preference (CPP), and behavioral sensitization. In this study, we used intravenous drug self-administration procedures in rats to further investigate the beneficial effects of EE on cocaine addiction in a reinstatement model of relapse. Singly housed rats learned to self-administer cocaine during 10 consecutive daily sessions (0.6 mg/injection, 6 h/day). They were then housed three per cage in either standard environments (SE) or EE and were kept abstinent in the animal facility until testing for extinction and reinstatement. We found that 30 days of EE significantly and consistently reduced cocaine seeking during a 6-h extinction session. In addition, EE significantly reduced cue- and stress-induced reinstatement. Surprisingly, given our earlier results in mice with CPP, EE did not reduce cocaine-induced reinstatement regardless of the level of exposure to cocaine and the duration of the period of abstinence and exposure to EE. Altogether, these results support the hypothesis that EE can reduce cocaine-induced craving and highlight the importance of positive life conditions in facilitating abstinence and preventing relapse to cocaine addiction.

Chronic treatment with the selective NOP receptor antagonist [Nphe 1, Arg 14, Lys 15]N/OFQ-NH 2 (UFP-101) reverses the behavioural and biochemical effects of unpredictable chronic mild stress in rats

INTRODUCTION

The present study was designed to assess the antidepressant effects of UFP-101, a selective nociceptin/orphanin FQ peptide (NOP) receptor antagonist, in a validated animal model of depression: the chronic mild stress (CMS).

MATERIALS AND METHODS AND RESULTS

UFP-101 (5, 10 and 20 nmol/rat; i.c.v., once a day for 21 days) dose- and time-dependently reinstated sucrose consumption in stressed animals without affecting the same parameter in non-stressed ones. In the forced swimming test, UFP-101 reduced immobility of stressed rats from day 8 of treatment. After a 3-week treatment, rats were killed for biochemical evaluations. UFP-101 abolished increase in serum corticosterone induced by CMS and reverted changes in central 5-HT/5-HIAA ratio. The behavioural and biochemical effects of UFP-101 mimicked those of imipramine, the reference antidepressant drug, administered at the dose of 15 mg/kg (i.p.). Co-administration of nociceptin/orphanin FQ (5 nmol/rat, from day 12 to 21) prevented the effects of UFP-101. Brain-derived neurotrophic factor mRNA and protein in hippocampus were not reduced by CMS nor did UFP-101 modify these parameters.

DISCUSSION AND CONCLUSION

This study demonstrated that chronic treatment with UFP-101 produces antidepressant-like effects in rats subjected to CMS supporting the proposal that NOP receptors represent a candidate target for the development of innovative antidepressant drugs.

Oxytocin protects against negative behavioral and autonomic consequences of long-term social isolation

Positive social interactions and social support may protect against various forms of mental and physical illness, although the mechanisms for these effects are not well identified. The socially monogamous prairie vole, which--like humans--forms social bonds and displays high levels of parasympathetic activity, has provided a useful model for investigating neurobiological systems that mediate the consequences of sociality. In the present study, adult female prairie voles were exposed to social isolation or continued pairing with a female sibling (control conditions) for 4 weeks. During weeks 3 and 4 of this period, animals were administered oxytocin (20 microg/50 microl, s.c.) or saline vehicle (50 microl, s.c.) daily for a total of 14 days. In Experiment 1, autonomic parameters were recorded during and following isolation or pairing. Isolation (vs. pairing) significantly increased basal heart rate (HR) and reduced HR variability and vagal regulation of the heart; these changes in isolated animals were prevented with oxytocin administration. In Experiment 2, behaviors relevant to depression [sucrose intake and swimming in the forced swim test (FST)] were measured as a function of isolation. Isolation reduced sucrose intake and increased immobility in the FST; these behaviors also were prevented by oxytocin. Administration of oxytocin did not significantly alter cardiac, autonomic or behavioral responses of paired animals. These findings support the hypothesis that oxytocinergic mechanisms can protect against behavioral and cardiac dysfunction in response to chronic social stressors, and can provide insight into social influences on behavior and autonomic function in humans.

Peony glycosides produce antidepressant-like action in mice exposed to chronic unpredictable mild stress: effects on hypothalamic-pituitary-adrenal function and brain-derived neurotrophic factor

The root part of Paeonia lactiflora Pall. (Ranunculaceae), commonly known as peony, is a commonly used Chinese herb for the treatment of depression-like disorders. Previous studies in our laboratory have demonstrated that total glycosides of peony (TGP) produced antidepressant-like action in various mouse models of behavioral despair. The present study aimed to examine whether TGP could affect the chronic unpredictable mild stress (CUMS)-induced depression in mice. The mechanism(s) underlying the antidepressant-like action was investigated by measuring serum corticosterone level, glucocorticoid receptor (GR) and brain-derived neurotrophic factor (BDNF) mRNA levels in brain tissues. CUMS, being lasted for 6 weeks, caused depression-like behavior in mice, as indicated by the significant decrease in sucrose consumption and increase in immobility time in the forced swim test. Whereas serum corticosterone level was significantly increased in mice exposed to CUMS, expressions of GR mRNA in hippocampus, and BDNF mRNA in hippocampus and frontal cortex, were decreased in CUMS-treated mice. Daily intragastric administration of TGP (80 or 160 mg/kg/day) during the six weeks of CUMS significantly suppressed behavioral and biochemical changes induced by CUMS. The results suggest that the antidepressant-like action of TPG is likely mediated by modulating the function of hypothalamic-pituitary-adrenal axis and increasing the expression of BDNF in brain tissues.

Chronic antidepressant treatment exerts sexually dimorphic immunomodulatory effects in an experimental model of major depression: do females lack an advantage?

Major depression is a stress-related disorder that affects about 20% of the population, with women outnumbering men by 2:1. However, research focusing on stress/antidepressant-related immunomodulation overlooks sex differences, although an established sexual dimorphism also characterizes the immune system. We report for the first time that both chronic clomipramine treatment (10 mg/kg, twice daily) and chronic mild stress (CMS) application in rats, exert sexually dimorphic effects on cellular immunoreactivity (natural killer and lymphokine-activated killer cell cytotoxicity and interleukin-2-induced T-cell proliferation), with females presenting a relatively immunosuppressed phenotype compared to males. Moreover, following chronic antidepressant treatment, thymic monoamines presented sex-related alterations, as well as intriguing associations with peripheral T-cell responses. This study highlights the sex-related effects of chronic clomipramine treatment and CMS application on the cellular arm of immunity, and represents a preliminary exposé of a thymus-dependent route pertaining to the interactions between antidepressants and the immune system.

Vascular endothelial growth factor signaling is required for the behavioral actions of antidepressant treatment: pharmacological and cellular characterization

This study extends earlier work on the role of vascular endothelial growth factor (VEGF) in the actions of antidepressant treatment in two key areas. First, by determining the requirement for VEGF in the actions of a 5-HT selective reuptake inhibitor (SSRI), fluoxetine in behavioral models of depression/antidepressant response; and second, by examining the role of the 5-HT1A receptor subtype in the regulation of VEGF, and the cellular localization of antidepressant regulation of VEGF expression. The results show that pharmacological inhibition of VEGF receptor signaling blocks the behavioral actions of fluoxetine in rats subjected to chronic unpredictable stress. Infusions of SU5416 or SU1498, two structurally dissimilar inhibitors of VEGF-Flk-1 receptor signaling, block the antidepressant effects of fluoxetine on sucrose preference, immobility in the forced swim test, and latency to feed in the novelty suppressed feeding paradigm. We also show that activation of 5-HT1A receptors is sufficient to induce VEGF expression and that a 5-HT1A antagonist blocks both the increase in VEGF and behavioral effects induced by fluoxetine. Finally, double labeling studies show that chronic fluoxetine administration increases VEGF expression in both neurons and endothelial cells in the hippocampus. Taken together these studies show that VEGF is necessary for the behavioral effects of the SSRI fluoxetine, as well as norepinephrine selective reuptake inhibitor, and that these effects may be mediated by 5-HT1A receptors located on neurons and endothelial cells.

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.

Combined administration of the mixture of honokiol and magnolol and ginger oil evokes antidepressant-like synergism in rats

Magnolia bark combined with ginger rhizome is a common drug pair in traditional Chinese prescriptions for the treatment of depression. In the present study, we examined antidepressant-like effects of the mixture of honokiol and magnolol (HMM) from magnolia bark and essential oil from ginger rhizome (OGR) alone and in combination in chronic unpredictable mild stress (CUMS) of rats. Behavioral (sucrose intake, immobility time of forced swimming test) and biochemical parameters [serotonin (5-HT) in prefrontal cortex, hippocampus, and striatum, gastric mucosa cholecystokinin (CCK) and serum gastrin (GAS) levels] were simultaneously examined in the CUMS rats. 20 mg/kg HMM alone, but not OGR, significantly increased sucrose intake and reduced immobility time in the CUMS rats. Moreover, 20 mg/kg HMM and 14 mg/kg OGR in combination exhibited significant synergistic effects on sucrose intake increase and immobility time reduction in the CUMS rats. HMM elevated 5-HT levels in various brain regions, and OGR reduced gastric mucosa CCK and serum GAS levels in the CUMS rats. These results suggested that the synergistic antidepressant-like effects of compatibility of HMM with OGR might be mediated simultaneously by regulation of the serotonergic and gastroenteric system functions. These findings also provided a pharmacological basis for the clinical application of this drug pair of magnolia bark and ginger rhizome in traditional Chinese medicine.

A molecular signature of depression in the amygdala

OBJECTIVE

Major depressive disorder is a heterogeneous illness with a mostly uncharacterized pathology. Recent gene array attempts to identify the molecular underpinnings of the illness in human postmortem subjects have not yielded a consensus. The authors hypothesized that controlling several sources of clinical and technical variability and supporting their analysis with array results from a parallel study in the unpredictable chronic mild stress (UCMS) rodent model of depression would facilitate identification of the molecular pathology of major depression.

METHOD

Large-scale gene expression was monitored in postmortem tissue from the anterior cingulate cortex and amygdala in paired male subjects with familial major depression and matched control subjects without major depression (N=14-16 pairs). Area dissections and analytical approaches were optimized. Results from the major depression group were compared with those from the UCMS study and confirmed by quantitative polymerase chain reaction and Western blot. Gene coexpression network analysis was performed on transcripts with conserved major depression-UCMS effects.

RESULTS

Significant and bidirectional predictions of altered gene expression were identified in amygdala between major depression and the UCMS model of depression. These effects were detected at the group level and also identified a subgroup of depressed subjects with a more homogeneous molecular pathology. This phylogenetically conserved "molecular signature" of major depression was reversed by antidepressants in mice, identified two distinct oligodendrocyte and neuronal phenotypes, and participated in highly cohesive and interactive gene coexpression networks.

CONCLUSIONS

These studies demonstrate that the biological liability to major depression is reflected in a persistent molecular pathology that affects the amygdala, and support the hypothesis of maladaptive changes in this brain region as a putative primary pathology in major depression.

The mood-improving actions of antidepressants do not depend on neurogenesis but are associated with neuronal remodeling

The mechanisms underlying the initiation/onset of, and the recovery from, depression are still largely unknown; views that neurogenesis in the hippocampus may be important for the pathogenesis and amelioration of depressive symptoms have gained currency over the years although the original evidence has been challenged. In this study, an unpredictable chronic mild stress protocol was used to induce a depressive-like phenotype in rats. In the last 2 weeks of stress exposure, animals were treated with the antidepressants fluoxetine, imipramine, CP 156,526 or SSR 1494515, alone or combined with methylazoxymethanol, a cytostatic agent used to arrest neurogenesis. We found that antidepressants retain their therapeutic efficacy in reducing both measured indices of depression-like behavior (learned helplessness and anhedonia), even when neurogenesis is blocked. Instead, our experiments suggest re-establishment of neuronal plasticity (dendritic remodeling and synaptic contacts) in the hippocampus and prefrontal cortex, rather than neurogenesis, as the basis for the restoration of behavioral homeostasis by antidepressants.

Childhood adversity is associated with left basal ganglia dysfunction during reward anticipation in adulthood

BACKGROUND

Childhood adversity increases the risk of psychopathology, but the neurobiological mechanisms underlying this vulnerability are not well-understood. In animal models, early adversity is associated with dysfunction in basal ganglia regions involved in reward processing, but this relationship has not been established in humans.

METHODS

Functional magnetic resonance imaging was used to examine basal ganglia responses to: 1) cues signaling possible monetary rewards and losses; and 2) delivery of monetary gains and penalties, in 13 young adults who experienced maltreatment before age 14 years and 31 nonmaltreated control subjects.

RESULTS

Relative to control subjects, individuals exposed to childhood adversity reported elevated symptoms of anhedonia and depression, rated reward cues less positively, and displayed a weaker response to reward cues in the left globus pallidus. There were no group differences in right hemisphere basal ganglia response to reward cues or in basal ganglia response to loss cues, no-incentive cues, gains, or penalties.

CONCLUSIONS

Results indicate that childhood adversity in humans is associated with blunted subjective responses to reward-predicting cues as well as dysfunction in left basal ganglia regions implicated in reward-related learning and motivation. This dysfunction might serve as a diathesis that contributes to the multiple negative outcomes and psychopathologies associated with childhood adversity. The findings suggest that interventions that target motivation and goal-directed action might be useful for reducing the negative consequences of childhood adversity.

Induction of neuronal vascular endothelial growth factor expression by cAMP in the dentate gyrus of the hippocampus is required for antidepressant-like behaviors

The cAMP cascade and vascular endothelial growth factor (VEGF) are critical modulators of depression. Here we have tested whether the antidepressive effect of the cAMP cascade is mediated by VEGF in the adult hippocampus. We used a conditional genetic system in which the Aplysia octopamine receptor (Ap oa(1)), a G(s)-coupled receptor, is transgenically expressed in the forebrain neurons of mice. Chronic activation of the heterologous Ap oa(1) by its natural ligand evoked antidepressant-like behaviors, accompanied by enhanced phosphorylation of cAMP response element-binding protein and transcription of VEGF in hippocampal dentate gyrus (DG) neurons. Selective knockdown of VEGF in these cells during the period of cAMP elevation inhibited the antidepressant-like behaviors. These findings reveal a molecular interaction between the cAMP cascade and VEGF expression, and the pronounced behavioral consequences of this interaction shed light on the mechanism underlying neuronal VEGF functions in antidepression.

Signatures of depression in non-stationary biometric time series

This paper is based on a discussion that was held during a special session on models of mental disorders, at the NeuroMath meeting in Stockholm, Sweden, in September 2008. At this occasion, scientists from different countries and different fields of research presented their research and discussed open questions with regard to analyses and models of mental disorders, in particular depression. The content of this paper emerged from these discussions and in the presentation we briefly link biomarkers (hormones), bio-signals (EEG) and biomaps (brain-maps via EEG) to depression and its treatments, via linear statistical models as well as nonlinear dynamic models. Some examples involving EEG-data are presented.

The roles of sex and serotonin transporter levels in age- and stress-related emotionality in mice

Mood disorders are influenced by genetic make-up and differentially affect men and women. The s/l promoter polymorphism in the serotonin transporter (SERT) gene moderates both trait emotion and the vulnerability to develop depressive states in humans. Similarly, male mice lacking SERT (Knockout/KO) display an elevated emotionality phenotype. We now report that the SERT-KO phenotype is maintained throughout late-adulthood, and that female KO mice develop a larger emotionality phenotype with increasing age. Thus, to test the hypothesis that these findings reflected a putative sexual dimorphism in SERT-mediated modulation of emotionality, we submitted adult male and female wild-type, heterozygous (HZ) and KO mice to unpredictable chronic mild stress (UCMS) and assessed behavioral changes. In males, the elevated SERT-KO emotion-related behavior converged with other groups after UCMS. Conversely, female SERT-KO displayed a normal non-stressed baseline, but highest UCMS-induced emotionality. SERT-HZ displayed variable and intermediate phenotypes in both experiments. Thus, consistent results across different biological modalities (age, stress) revealed a high contribution of SERT genotype for baseline "trait" emotionality in males, and low contribution for females. In contrast, age-correlated and stress-induced behavioral changes resulted in a high SERT genotype-mediated behavioral variance in females, but low in males. This suggests that high emotionality states associated with low SERT were differentially achieved in males (high baseline/trait) compared to females (increased vulnerability to develop high emotionality). This sex-by-SERT double dissociation provides a framework to investigate molecular substrates of emotionality regulation in concert with serotonin function and may contribute to the sexually dimorphic features of mood disorders.

Gender-specific impact of brain-derived neurotrophic factor signaling on stress-induced depression-like behavior

BACKGROUND

Major depressive disorder is a leading debilitating disease known to occur at a two-fold higher rate in women than in men. The neurotrophic hypothesis of depression suggests that loss of brain-derived neurotrophic factor (BDNF) may increase susceptibility for depression-like behavior, although direct evidence is lacking.

METHODS

Using the chronic unpredictable stress (CUS) paradigm, we investigated whether male and female mice with inducible BDNF deletion in the forebrain were more susceptible to depression-related behavior.

RESULTS

We demonstrate that in certain behavioral measures the loss of BDNF lowers the threshold for female mice studied at random throughout estrus to display anxiogenic and anhedonic behaviors after chronic stress compared with wild-type female mice. However, the loss of BDNF in forebrain does not increase the susceptibility to depression-like behavior in male mice.

CONCLUSIONS

These gender differences suggest a role for BDNF in mediating some aspects of depression-related behavior in females.

The effect of chronic mild stress on tumor-bearing rats' behavior and its mechanism

OBJECT

Much evidence has demonstrated that stress and tumor interact, but the mechanisms are poorly understood. The purpose of this study is to discuss the effect of unpredictable chronic mild stress (CMS) upon the behavior of Walker 256 tumor-bearing rats and its mechanism.

METHODS

Observe the effects of CMS on the sucrose consumption, activities, body weight and levels of serums TNF-alpha and IL-6 of both tumor-bearing rats and non-tumor-bearing rats, and on the levels of Bcl-2 and the phosphor-ERK1/2 in their hippocampus.

RESULTS

CMS can reduce the average sucrose consumption, behavioral scores, body weight gain, expression of Bcl-2 and p-ERK1/2 protein in hippocampus, and increase serums TNF-alpha and IL-6 of both tumor-bearing rats and non-tumor-bearing rats. The stressed tumor-bearing rats had less sucrose consumption, body weight gain and lower behavioral scores, but higher level of serum TNF-alpha than stressed non-tumor-bearing rats. A negative correlation was found between the levels of serum TNF-alpha and sucrose consumption, while a positive correlation between the expression of Bcl-2 protein in hippocampus proper and sucrose consumption.

CONCLUSION

CMS can reduce the protein levels of Bcl-2 and p-ERK1/2 in the rats' hippocampus, which contributes to the changes in the rats' behavior caused by CMS. Tumor-bearing rats are prone to behave depressively after the exposure to CMS. Our findings have suggested that the tumor, by increasing the inflammatory reaction, can be taken as a stressor, affecting the hippocampus and consequently causing depression by decreasing the expression of Bcl-2 and p-ERK1/2 in hippocampus.