Effects of chronic mild stress on sexual behavior, locomotor activity and consumption of sucrose and saccharine solutions

CTN-986, a compound extracted from cottonseeds, increases cell proliferation in hippocampus in vivo and in cultured neural progenitor cells in vitro

We have previously reported that Quercetin 3-O-b-D-apiofuranosyl-(1-->2)-[a-L-rhamnopyranosyl-(1-->6)]-b-D-glucopyranoside (CTN-986), a potential antidepressant extracted from glandless cottonseeds, exerted a notable antidepressant-like effect in experimental animal models. Recent evidence suggested, at least in some animal models, that the behavioral effects of chronic antidepressant treatment were mediated by the stimulation of hippocampal neurogenesis. To explore possible mechanisms of CTN-986's antidepressant-like effect, CTN-986 (10 mg/kg, i.g) or imipramine (IMI, 10 mg/kg, i.g) was administered once per day to the chronically stressed mice over 21 days. Immunohistochemical analysis revealed that chronic CTN-986 treatment increased bromodeoxyuridine (BrdU; thymidine analog as a marker for dividing cells)-positive cells in the hippocampal dentate gyrus in stressed mice, as was the case with chronic IMI treatment. Moreover, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay and [3H] thymidine incorporation assay, it was found that exposure to CTN-986 for 4 days dose-dependently increased the proliferation of the cultured hippocampal neural progenitor cells (NPCs). This effect was significantly reversed by co-incubation with serotonin 1A (5-HT1A) receptor antagonist WAY100635. These results indicate that CTN-986 increase hippocampal NPCs proliferation which might be closely related to the activation of the 5-HT1A receptor. This finding can shed light on the mechanisms for its antidepressant-like effects.

Sex differences in psychopathology: of gonads, adrenals and mental illness

Stress-related disorders such as anxiety and depression are disproportionately prevalent in women. Women are more likely to experience depression and anxiety disorders during periods of marked hormonal fluctuations, suggesting that gonadal hormones are involved in stress pathology. Depression and anxiety are both associated with aberrant secretion of glucocorticoids, which also show marked fluctuations across the reproductive cycle and in response to gonadal steroids. Thus, interactions between gonadal and stress hormones may play a major role in predisposing females to stress-related disease. The purpose of this brief review is to highlight preclinical data regarding the role of estrogens in depression and anxiety-like behaviors. While it is evident the exogenous estrogens modulate affective behavior in rodents, there is some disagreement in the literature, perhaps related to experimental designs that vary with respect to administration parameters and stress. Beneficial effects of estrogens on mood are most likely due to estrogen receptor (ER)beta signaling. The antidepressant and anxiolytic effects of ERbeta are consistent with its role in attenuating glucocorticoid responses to stress, suggesting that estrogens, acting at ERbeta, may improve mood by suppressing glucocorticoid hyperactivity. However, additional studies demonstrate that ERbeta signaling in the hippocampus is sufficient to induce antidepressant and anxiolytic behaviors. Thus, ERbeta may improve mood via primary actions on hypothalamic (i.e., paraventricular nucleus) and/or extra-hypothalamic sites. Overall, the preclinical research suggests that selective ER modulators targeting ERbeta may be an attractive alternative or adjunct treatment to currently prescribed antidepressants or anxiolytics.

Prenatal alcohol exposure increases vulnerability to stress and anxiety-like disorders in adulthood

Children and adults with fetal alcohol spectrum disorder (FASD) have elevated rates of depression and anxiety disorders compared to control populations. The effects of prenatal alcohol exposure (PAE) on anxiety, locomotor activity, and hormonal reactivity in male and female rats tested on the elevated plus maze (EPM), a task commonly used to assess anxiety-like behaviors in rodents, were examined. Pregnant dams were assigned to PAE, pair-fed (PF), or ad libitum-fed control (C) groups. At adulthood, half of all male (N= 60) and female (N= 60) PAE, PF, and C offspring were exposed to 10 days of chronic mild stress (CMS); the other half remained undisturbed. Animals were then tested on the EPM, and blood collected 30 min posttest for analysis of corticosterone (CORT), testosterone, estradiol, and progesterone. Overall, CMS exposure produced a significant anxiogenic profile. Moreover, CMS increased anxiety-like behavior in PAE males and females compared to controls and eliminated the locomotor hyperactivity observed in nonstressed PAE females. CMS also increased post-EPM CORT, testosterone, and progesterone levels in all groups, with CORT and progesterone levels significantly higher in PAE than in C females. By contrast, CMS selectively lowered estradiol levels in PAE and PF, but not C, females. CMS exposure reveals sexually dimorphic behavioral and endocrine alterations in PAE compared to C animals. Together, these data suggest the possibility that fetal reprogramming of hypothalamic-pituitary-adrenal (HPA) and -gonadal (HPG) systems by alcohol may underlie, at least partly, an enhanced susceptibility of fetal alcohol-exposed offspring to depression/anxiety-like disorders in adulthood.

Chronic mild stress (CMS) in mice: of anhedonia, 'anomalous anxiolysis' and activity

Background

In a substantial proportion of depressed patients, stressful life events play a role in triggering the evolution of the illness. Exposure to stress has effects on different levels in laboratory animals as well and for the rat it has been shown that chronic mild stress (CMS) can cause antidepressant-reversible depressive-like effects. The adoption of the model to the mouse seems to be problematic, depending on the strain used and behavioural endpoint defined. Our aim was to evaluate the applicability of CMS to mice in order to induce behavioural alterations suggested to reflect depression-like symptoms.

Methodology/Principal Findings

A weekly CMS protocol was applied to male mice of different mouse strains (D2Ola, BL/6J and BL/6N) and its impact on stress-sensitive behavioural measures (anhedonia-, anxiety- and depression-related parameters) and body weight was assessed. Overnight illumination as commonly used stressor in CMS protocols was particularly investigated in terms of its effect on general activity and subsequently derived saccharin intake. CMS application yielded strain-dependent behavioural and physiological responses including ‘paradox’ anxiolytic-like effects. Overnight illumination was found to be sufficient to mimic anhedonic-like behaviour in BL/6J mice when being applied as sole stressor.

Conclusions/Significance

The CMS procedure induced some behavioural changes that are compatible with the common expectations, i.e. ‘anhedonic’ behaviour, but in parallel behavioural alterations were observed which would be described as ‘anomalous’ (e.g. decreased anxiety). The results suggest that a shift in the pattern of circadian activity has a particular high impact on the anhedonic profile. Changes in activity in response to novelty seem to drive the ‘anomalous’ behavioural alterations as well.

Memory-enhancing treatments reverse the impairment of inhibitory avoidance retention in sepsis-surviving rats

Introduction

Survivors from sepsis have presented with long-term cognitive impairment, including alterations in memory, attention, concentration, and global loss of cognitive function. Thus, we evaluated the effects of memory enhancers in sepsis-surviving rats.

Methods

The rats underwent cecal ligation and perforation (CLP) (sepsis group) with 'basic support' (saline at 50 mL/kg immediately and 12 hours after CLP plus ceftriaxone at 30 mg/kg and clindamycin at 25 mg/kg 6, 12, and 18 hours after CLP) or sham-operated (control group). After 10 or 30 days, rats were submitted to an inhibitory avoidance task. After task training, animals received injections of saline, epinephrine, naloxone, dexamethasone, or glucose. Twenty-four hours afterwards, animals were submitted to the inhibitory avoidance test.

Results

We demonstrated that memory enhancers reversed impairment in the sepsis group 10 and 30 days after sepsis induction. This effect was of lower magnitude when compared with sham animals 10 days, but not 30 days, after sepsis.

Conclusions

Using different pharmacologic approaches, we conclude that the adrenergic memory formation pathways are responsive in sepsis-surviving animals.

Distinct neural circuits reflect sex, sexual maturity, and reproductive status in response to stress in Drosophila melanogaster

Studies in mammalian systems have shown an array of changes in transmitter signaling in diverse brain regions in response to stress, which differ depending on the age and genetic makeup of the animal, as well as the type of stress. Here, we exploit the genetic tractability of the fruit fly, Drosophila melanogaster, a comparatively simple but useful model in which to elucidate conserved components of stress response pathways. We show that structures within the mushroom bodies and central complex, two distinct anatomical regions within the Drosophila brain, modulate behavioral responses to two different environmental stressors. Modification of behavioral output after exposure to these stressors was dependent on the sex, sexual maturity, and reproductive status of the animal. These parameters also affected whether a mutant Drosophila strain carrying specific defects within the mushroom bodies and/or central complex modified its response to stress relative to wild-type flies. Our results suggest that for each population, unique subsets of neurons are recruited into the stress response circuitry and differentially affect locomotor behavior and cardiac function. These data also provide evidence for neural plasticity in the adult insect brain.

Age-dependent effects of chronic stress on brain plasticity and depressive behavior

Exposure to chronic mild stress (CMS) is known to induce anhedonia in adult animals, and is associated with induction of depression in humans. However, the behavioral effects of CMS in young animals have not yet been characterized, and little is known about the long-term neurochemical effects of CMS in either young or adult animals. Here, we found that CMS induces anhedonia in adult but not in young animals, as measured by a set of behavioral paradigms. Furthermore, while CMS decreased neurogenesis and levels of brain-derived neurotrophic factor (BDNF) in the hippocampus of adult animals, it increased these parameters in young animals. We also found that CMS altered alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor GluR1 subunit levels in the hippocampus and the nucleus accumbens of adult, but not young animals. Finally, no significant differences were observed between the effects of CMS on circadian corticosterone levels in the different age groups. The substantially different neurochemical effects chronic stress exerts in young and adult animals may explain the behavioral resilience to such stress young animals possess.

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

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

The total flavonoids extracted from Xiaobuxin-Tang up-regulate the decreased hippocampal neurogenesis and neurotrophic molecules expression in chronically stressed rats

Xiaobuxin-Tang (XBXT), a traditional Chinese herbal decoction, has been used for the treatment of depressive disorders for centuries in China. Our previous studies have demonstrated that the total flavonoids (XBXT-2) isolated from the extract of XBXT reversed behavioral alterations and serotonergic dysfunctions in chronically stressed rats. Recently, accumulating studies have suggested the behavioral effects of chronic antidepressants treatment might be mediated by the stimulation of hippocampal neurogenesis. In present study, we explored the effect of XBXT-2 on hippocampal neurogenesis and neurotrophic signal pathway in chronically stressed rats. Our immunohistochemistry results showed that concomitant administration of XBXT-2 (25, 50 mg/kg, p.o., 28 days, the effective doses for behavioral responses) significantly increased hippocampal neurogenesis in chronically stressed rats. Four weeks after BrdU injection, result in double immunofluorescence labeling showed that some of the newly generated cells in hippocampus co-expressed with NSE or GFAP, markers for neurons or astrocytes, respectively. Furthermore, XBXT-2 treatment reserved stress-induced decrease of hippocampal BDNF and pCREB (Ser133) expression, two important factors which were closely related to hippocampal neurogenesis. As a positive control drug, imipramine (10 mg/kg, p.o.) exerted same effects. In conclusion, the increase of neurogenesis, as well as expression of BDNF and pCREB in hippocampus may be one of the molecular and cellular mechanisms underlying the antidepressant action of XBXT-2.

Role for serotonin in the antidepressant-like effect of a flavonoid extract of Xiaobuxin-Tang

Xiaobuxin-Tang (XBXT), a traditional Chinese herbal decoction, has been used for the treatment of depressive disorders for centuries in China. Herein, we explored the antidepressant-like effect and its monoaminergic mechanism of the total flavonoids (XBXT-2) isolated from the extract of XBXT. In present study, single XBXT-2 (25, 50, 100 mg/kg, p.o.) administration significantly potentiated the mouse head-twitch response induced by 5-hydroxytryptophan (5-HTP, a metabolic precursor to serotonin), and also, decreased the immobility time in mouse tail suspension test, which was completely prevented by p-chlorophenylalanine (PCPA, an inhibitor of serotonin synthesis) pretreatment. However, single treatment with XBXT-2 had no effect on yohimbine toxicity and high dose of apomorphine-induced hypothermia in mice. These results indicated that acute treatment with XBXT-2 produced serotonergic, but not noradrenergic activation. In addition, chronic XBXT-2 (25, 50 mg/kg, p.o., 28 days) treatments significantly reversed the depressive-like behaviors in chronically mildly stressed (CMS) rats, including the reduced sucrose preference, deficient locomotor activity and prolonged latency to novelty-suppressed feeding. Furthermore, XBXT-2 normalized the neurotransmitter changes, including the decreased serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) levels in hippocampus and prefrontal cortex in CMS rats. These findings confirm the antidepressant-like effect of XBXT-2 in CMS model of rats, which may be primarily based on its serotonergic activation.

Rat behavior after chronic variable stress and partial lesioning of 5-HT-ergic neurotransmission: effects of citalopram

Deficits in serotonergic (5-HT-ergic) neurotransmission and stressful life events have been implicated in affective disorders, and chronic variable stress (CVS) can elicit behavioral changes reminiscent of increased emotionality, anxiety and atypical depression after partial 5-HT depletion. This study examined the effect of chronic citalopram treatment (10 mg/kg daily) on these changes. Parachloroamphetamine (PCA) (2 mg/kg) reduced the levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the frontal cortex, increased anxiety in the social interaction test, and increased activity in the open field. CVS reduced social activity in the social interaction test and immobility time in the forced swimming test. Reduction of excrements left during immobilization indicated partial adaptation with the CVS. Specific stressors had different effects on body weight gain, shorter lasting stressors having a smaller effect in general than those that lasted longer. Combination of CVS and PCA increased sucrose intake after two weeks of stress. In addition, combination of the two treatments reduced diving in the forced swimming test. Citalopram prevented the increase in sucrose consumption in the PCA+CVS rats, and in 5-HT-depleted animals blocked the increase in struggling and reduced the number of defecations in the forced swim test. In conclusion, citalopram treatment prevented several effects of either 5-HT depletion or combined PCA+CVS treatment, suggesting that these behavioral changes could be used in studies on the neural mechanisms underlying emotional behavior that may have relevance to the neurobiology of depression.

Relationship between stress, eating behavior, and obesity

Stress is thought to influence human eating behavior and has been examined in animal and human studies. Our understanding of the stress-eating relation is confounded by limitations inherent in the study designs; however, we can make some tentative conclusions that support the notion that stress can influence eating patterns in humans. Stress appears to alter overall food intake in two ways, resulting in under- or overeating, which may be influenced by stressor severity. Chronic life stress seems to be associated with a greater preference for energy- and nutrient-dense foods, namely those that are high in sugar and fat. Evidence from longitudinal studies suggests that chronic life stress may be causally linked to weight gain, with a greater effect seen in men. Stress-induced eating may be one factor contributing to the development of obesity. Future studies that measure biological markers of stress will assist our understanding of the physiologic mechanism underlying the stress-eating relation and how stress might be linked to neurotransmitters and hormones that control appetite.

Sex and diet affect the behavioral response of rats to chronic mild stressors

To investigate the interaction between sex, stressors, and dietary choice in rats, a preferred diet under the influence of chronic mild stressors was empirically determined to consist of soybeans and cookies in addition to lab chow. This preferred mixed diet was then tested for its influence on several behavioral tests at the end of prolonged exposure to the potential stressors. Rats of both sexes decreased their frequency of rearing but increased their attention to novelty in response to stressors. In the elevated plus maze, diet interacted with exposure to stressors to influence time spent in the open arm in females but not males. In the forced swim test, females but not males fed the mixed diet showed increased immobility, whether exposed to stressors or not. Finally, females but not males showed a differential effect of diet under stressors on the sucrose preference test, but this result was confounded by estrus cycling, demonstrating the importance of this factor in analyzing behavior in females. These results suggest that male and female rats differ in their susceptibility to the behavioral-modifying influences of stressors. And to the extent that diet serves as a coping mechanism, it does so differently in males and females.

Chronic low dose ovine corticotropin releasing factor or urocortin II into the rostral dorsal raphe alters exploratory behavior and serotonergic gene expression in specific subregions of the dorsal raphe

Corticotropin releasing factor (CRF) family peptides play key roles in integrating neural responses to stress. Both major CRF receptors have been pharmacologically identified in the dorsal raphe nucleus (DRN), a stress sensitive and internally heterogeneous nucleus supplying many forebrain regions with serotonergic input. Despite the involvement of chronic stress and serotonergic dysfunction in human mood and anxiety disorders, little is known about the effects of chronic CRF receptor activation on the DRN. We infused ovine CRF (1 ng/h), urocortin II (UCNII, 1 ng/h), or vehicle alone into rat DRN over 6 days. During infusion, animals were allowed to freely explore an open field for 15 min on each of 2 days, with the addition of a novel object on the second day. Following behavioral testing, 5-HT1A, 5-HT1B, 5-HT transporter (SERT), and tryptophan hydroxylase-2 (Tph2) expression was examined through the DRN by in situ hybridization. Ovine CRF infusion resulted in significantly decreased novel object touches, climbs, as well as increased latency to first novel object contact. UCNII had a similar but less dramatic effect, decreasing only climbing behavior. Both ovine CRF and UCNII blunted the decrease in corner time expected on re-exposure to the open field. Both peptides also produced regionally specific changes in gene expression: 5-HT1A expression was increased 30% in the mid-rostral ventromedial DRN, while SERT was decreased by 30% in the mid-caudal shell dorsomedial DRN. There also appeared to be a shift in the relative level of Tph2 expression between the ventromedial and core dorsomedial DRN at the mid-rostral level. Changes in 5-HT1A, SERT, and relative Tph2 mRNA abundance were correlated with novel object exploration. These findings suggest chronic intra-DRN administration of CRF agonists decreases exploratory behavior, while producing subregionally limited changes in serotonergic gene expression. These studies may be relevant to mechanisms underlying behavioral changes after chronic stress.

Chronic administration of fluoxetine alters locomotor behavior, but does not potentiate the locomotor stimulating effects of CRH in juvenile Chinook salmon (Oncorhynchus tshawytscha)

The present study investigated: 1) the behavioral effects of chronic administration of a serotonin uptake inhibitor (fluoxetine) in juvenile Chinook salmon, Oncorhynchus tshawytscha and, 2) whether chronic administration of fluoxetine alters the behavioral effects of corticotropin-releasing hormone (CRH). Chronic (20 day) treatment with fluoxetine decreased locomotor activity when compared to fish given long-term injections of saline. An intracerebroventricular (i.c.v.) injection of CRH had no effect on locomotor activity following a 20 day intraperitoneal treatment with either saline or fluoxetine. Chronic treatment with fluoxetine also increased the amount of time fish spent near the center of the tank. A similar increase was seen in fish given a chronic intraperitoneal (i.p.) series of saline followed by an acute i.c.v. injection of CRH. However, the effect was not additive when fish were given chronic i.p. injections of fluoxetine followed by an acute i.c.v. injection of CRH. These results provide evidence to support the hypothesis that the serotonergic system is involved in mediating locomotor activity and habitat choice in teleosts.

Kindling epileptogenesis in immature rats leads to persistent depressive behavior

Depression is a frequent comorbidity in epilepsy patients. A variety of biological factors may underlie epilepsy-associated depression. We examined whether kindling-induced chronic increase in seizure susceptibility is accompanied by behavioral symptoms of depression. Three-week-old Wistar rats underwent rapid kindling: 84 initially subconvulsant electrical stimulations of ventral hippocampus delivered every 5 minutes, followed by depression-specific behavioral tests performed 2 and 4 weeks later. Kindled animals exhibited a sustained increase in immobility time in the forced swim test and the loss of taste preference toward calorie-free saccharin, as compared with controls. Initial loss of preference toward the intake of calorie-containing sucrose was followed by the increased consumption at 4 weeks. At both time points, animals exhibited enhanced seizure susceptibility on test stimulations of the hippocampus. We conclude that neuronal plastic changes associated with the kindling state are accompanied by the development of depressive behavior.

Icariin from Epimedium brevicornum attenuates chronic mild stress-induced behavioral and neuroendocrinological alterations in male Wistar rats

Chronic mild stress (CMS) is suggested to produce abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis and hypothalamus-pituitary-thyroid (HPT) axis. Therefore, compound that attenuates the neuroendocrinological alterations may have potential as antidepressant. The behavioral and neuroendocrinological effects of icariin, a major constituent of flavonoids isolated from Epimedium brevicornum, were investigated in the CMS model of depression in male Wistar rats. CMS procedure caused an anhedonic state in rats resulted in increased corticotropin-releasing factor (CRF) concentrations in dissected brain regions and serum, decreased total triiodothyronine (tT3) in serum with no significant changes in serum adrenocorticotrophic hormone (ACTH) and thyroxine (tT4). Administration of icariin reversed CMS-induced sucrose intake reduction and CRF elevation. These results suggested that icariin possessed potent antidepressant-like activities which were at least in part mediated by improving the abnormalities in the HPA axis functions. However, we did not find a clear correlation between the HPT axis and icariin treatment in the CMS-treated rats.

Antidepressant like effects of piperine in chronic mild stress treated mice and its possible mechanisms

In this study, we investigated the antidepressant-like effect of piperine in mice exposed to chronic mild stress (CMS) procedure. Repeated administration of piperine for 14 days at the doses of 2.5, 5 and 10 mg/kg reversed the CMS-induced changes in sucrose consumption, plasma corticosterone level and open field activity. Furthermore, the decreased proliferation of hippocampal progenitor cells was ameliorated and the level of brain-derived neurotrophic factor (BDNF) in hippocampus of CMS stressed mice was up-regulated by piperine treatment in the same time course. In addition, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactic dehydrogenase (LDH) assays showed that piperine (6.25-25 microM) or fluoxetine (FLU, 1 microM) dose-dependently protected primary cultured hippocampal neurons from the lesion induced by 10 microM corticosterone (CORT). Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the messenger ribonucleic acid (mRNA) level of BDNF in cultured neurons. Treatment with piperine (6.25-25 microM) for 72 h reversed the CORT-induced reduction of BDNF mRNA expression in cultured hippocampal neurons. In summary, up-regulation of the progenitor cell proliferation of hippocampus and cytoprotective activity might be mechanisms involved in the antidepressant-like effect of piperine, which may be closely related to the elevation of hippocampal BDNF level.

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

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

Selective effects of citalopram in a mouse model of stress-induced anhedonia with a control for chronic stress

A stress-induced decrease in sucrose preference in rodents is regarded as an analog of anhedonia, a key symptom of depression. We investigated the effects of citalopram, administrated via drinking water (15 mg/kg/day), in a mouse model of stress-induced anhedonia. In this model, chronic stress induces anhedonia in a subset of C57BL/6N mice, while the remaining animals do not show a hedonic deficit or other depressive-like behaviors, although they are exposed to the same stressors as the anhedonic mice. Pre-stress and post-stress treatment with citalopram counteracted the development and maintenance of anhedonia and rescued normal floating in the forced swim test, demonstrating an antidepressant-like action. During the post-stress treatment, citalopram selectively increased sucrose preference and intake on the fourth week of treatment in anhedonic mice without affecting non-anhedonic animals. Citalopram also decreased elevated water consumption in the anhedonic group. Citalopram, administered 1 week before and during a 4-week stress procedure, decreased the percentage of anhedonic mice and reduced the increase of water intake in stressed mice. This study suggests that our chronic stress paradigm can serve as a model of anhedonia, in which antidepressant treatment is selectively effective in animals with a hedonic deficit.

The many faces of progesterone: a role in adult and developing male brain

In addition to its well documented action in female-typical behaviors, progesterone exerts an influence on the brain and behavior of males. This review will discuss the role of progesterone and its receptor in male-typical reproductive behaviors in adulthood and the role of progesterone and its receptor in neural development, in both sexual differentiation of the brain as well as in the development of "non-reproductive" functions. The seemingly inconsistent and contradictory results on progesterone in males that exist in the literature illustrate the complexity of progesterone's actions and illuminate the need for further research in this area. As progestin-containing contraceptives in men are currently being tested and progesterone administration to pregnant women and premature newborns increases, a better understanding of the role of this hormone in behavior and brain development becomes essential.

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

The chronic mild stress (CMS) model of depression has high validity but has in the past been criticized for being difficult to replicate. However, a large number of recent publications have confirmed that CMS causes behavioural changes in rodents that parallel symptoms of depression. This review summarizes studies from over sixty independent research groups that have reported decreases in reactivity to rewards, and a variety of other depression-like behaviours, in rats or mice, following exposure to CMS. Together, these changes are referred to as a 'depressive' behavioural profile. Almost every study that has examined the effects of chronic antidepressant treatment in these procedures has reported that antidepressants were effective in reversing or preventing these 'depressive' behavioural changes. (The single exception is a study in which the duration of treatment was too brief to constitute an adequate trial.) There are also a handful of reports of CMS causing significant effects in the opposite direction, termed here an 'anomalous' behavioural profile. There are six neurobiological parameters that have been studied in both 'anhedonic' and 'anomalous' animals: psychostimulant and place-conditioning effects of dopamine agonists; dopamine D2 receptor number and message; inhibition of dopamine turnover by quinpirole, and beta-adrenergic receptor binding. On all six measures, CMS caused opposite effects in animals displaying 'depressive' and 'anomalous' profiles. Thus, there is overwhelming evidence that under appropriate experimental conditions, CMS can cause antidepressant-reversible depressive-like effects in rodents; however, the 'anomalous' profile that is occasionally reported appears to be a genuine phenomenon, and these two sets of behavioural effects appear to be associated with opposite patterns of neurobiological changes.