Behavioural and biochemical studies of citalopram and WAY 100635 in rat chronic mild stress model

Elevated Expression of HSP72 in the Prefrontal Cortex and Hippocampus of Rats Subjected to Chronic Mild Stress and Treated with Imipramine

The HSP70 and HSP90 family members belong to molecular chaperones that exhibit protective functions during the cellular response to stressful agents. We investigated whether the exposure of rats to chronic mild stress (CMS), a validated model of depression, affects the expression of HSP70 and HSP90 in the prefrontal cortex (PFC), hippocampus (HIP) and thalamus (Thal). Male Wistar rats were exposed to CMS for 3 or 8 weeks. The antidepressant imipramine (IMI, 10 mg/kg, i.p., daily) was introduced in the last five weeks of the long-term CMS procedure. Depressive-like behavior was verified by the sucrose consumption test. The expression of mRNA and protein was quantified by real-time PCR and Western blot, respectively. In the 8-week CMS model, stress alone elevated HSP72 and HSP90B mRNA expression in the HIP. HSP72 mRNA was increased in the PFC and HIP of rats not responding to IMI treatment vs. IMI responders. The CMS exposure increased HSP72 protein expression in the cytosolic fraction of the PFC and HIP, and this effect was diminished by IMI treatment. Our results suggest that elevated levels of HSP72 may serve as an important indicator of neuronal stress reactions accompanying depression pathology and could be a potential target for antidepressant strategy.

Sestrin modulator NV-5138 produces rapid antidepressant effects via direct mTORC1 activation

Preclinical studies demonstrate that rapid acting antidepressants, including ketamine require stimulation of mTORC1 signaling. This pathway is regulated by neuronal activity, endocrine and metabolic signals, notably the amino acid leucine, which activates mTORC1 signaling via binding to the upstream regulator sestrin. Here, we examined the antidepressant actions of NV-5138, a novel highly selective small molecule modulator of sestrin that penetrates the blood brain barrier. The results demonstrate that a single dose of NV-5138 produced rapid and long-lasting antidepressant effects, and rapidly reversed anhedonia caused by chronic stress exposure. The antidepressant actions of NV-5138 required BDNF release as the behavioral responses are blocked by infusion of a BDNF neutralizing antibody into the medial prefrontal cortex (mPFC) or in mice with a knock-in of a BDNF polymorphism that blocks activity dependent BDNF release. NV-5138 administration also rapidly increased synapse number and function in the mPFC, and reversed the synaptic deficits caused by chronic stress. Together, the results demonstrate that NV-5138 produced rapid synaptic and antidepressant behavioral responses via activation of the mTORC1 pathway and BDNF signaling, indicating that pharmacological modulation of sestrin is a novel approach for development of rapid acting antidepressants.

The Effect of Traditional Chinese Medicine Zhike-Houpu Herbal Pair on Depressive Behaviors and Hippocampal Serotonin 1A Receptors in Rats After Chronic Unpredictable Mild Stress

OBJECTIVE

Zhike-Houpu herbal pair (ZKHPHP) is a well-known Chinese medicine to treat gastrointestinal motility dysfunction. Recently, many researchers have found that some of the compounds of ZKHPHP such as meranzin hydrate and magnolol have antidepressant effects. However, little is known about the antidepressant mechanism of ZKHPHP. Therefore, the main aim of the study is to evaluate the antidepressant-like effects of ZKHPHP and its possible mechanism of action on 5-hydroxytryptamine receptor 1A (HTR1A) in the hippocampus CA1 region in rats exposed to chronic unpredictable mild stress.

METHODS

Male Sprague Dawley rats were randomly divided into the following six groups: normal, model, ZKHPHP (3 g/kg), ZKHPHP (10 g/kg), ZKHPHP (20 g/kg), and ZKHPHP (30 g/kg); n = 8 per group. We exposed the rats to chronic unpredictable mild stress and then assessed antidepressant-like effects of ZKHPHP by measuring weight change, observing the open-field test, and measuring sucrose water consumption. The antidepressant mechanism was examined by measuring the effect of ZKHPHP on HTR1A protein expression and HTR1A mRNA expression in the hippocampus CA1 region by using immunohistochemistry analysis, Western blotting, and real-time reverse transcription-polymerase chain reaction.

RESULTS

ZKHPHP (10 or 20 g/kg) reduced the incidence of depressive-like behaviors and increased HTR1A protein and HTR1A mRNA expression in the hippocampus CA1 in rats displaying depressive behavior, whereas ZKHPHP (3 or 30 g/kg) had no obvious effect on the measured depression indicators.

CONCLUSIONS

These data show that ZKHPHP has antidepressant-like effects based on a chronic unpredictable mild stress-induced depression model in rats. ZKHPHP may be attractive as an antidepressant because of its beneficial effects on depression and the absence of gastrointestinal dysregulation, which is a frequently observed unintended effect of many commonly used antidepressive medications.

Long-lasting monoaminergic and behavioral dysfunctions in a mice model of socio-environmental stress during adolescence

Adolescence is one of the critical periods of development and has great importance to health for an individual as an adult. Stressors or traumatic events during this period are associated with several psychiatric disorders as related to anxiety or depression and cognitive impairments, but whether negative experiences continue to hinder individuals as they age is not as well understood. We determined how stress during adolescence affects behavior and neurochemistry in adulthood. Using an unpredictable paradigm (2 stressors per day for 10days) in Balb/c mice, behavioral, hormonal, and neurochemical changes were identified 20days after the cessation of treatment. Adolescent stress increased motor activity, emotional arousal and vigilance, together with a reduction in anxiety, and also affected recognition memory. Furthermore, decreased serotonergic activity on hippocampus, hypothalamus and cortex, decreased noradrenergic activity on hippocampus and hypothalamus, and increased the turnover of dopamine in cortex. These data suggest behavioral phenotypes associated with emotional arousal, but not depression, emerge after cessation of stress and remain in adulthood. Social-environmental stress can induce marked and long-lasting changes in HPA resulting from monoaminergic neurotransmission, mainly 5-HT activity.

Stress: perspectives on its impact on cognition and pharmacological treatment

Stress in life is unavoidable, affecting everyone on a daily basis. Psychological stress in mammals triggers a rapidly organized response for survival, but it may also cause a variety of behavioral disorders and damage cognitive function. Stress is associated with biases in cognitive processing; some of the most enduring memories are formed by traumatic events. Our understanding of how cognition is shaped by stress is still relatively primitive; however, evidence is rapidly accumulating that the 'mature' brain has a great capacity for plasticity and that there are numerous ways through which pharmacological therapeutics could rescue cognitive function and regain cognitive balance. In this review, we discuss recent advances in our understanding of the interplay between stress and cognitive processes and potential therapeutic approaches to stress-related behavioral and cognitive disorders.

Differential proteomic analysis of the anti-depressive effects of oleamide in a rat chronic mild stress model of depression

Depression is a complex psychiatric disorder, and its etiology and pathophysiology are not completely understood. Depression involves changes in many biogenic amine, neuropeptide, and oxidative systems, as well as alterations in neuroendocrine function and immune-inflammatory pathways. Oleamide is a fatty amide which exhibits pharmacological effects leading to hypnosis, sedation, and anti-anxiety effects. In the present study, the chronic mild stress (CMS) model was used to investigate the antidepressant-like activity of oleamide. Rats were exposed to 10weeks of CMS or control conditions and were then subsequently treated with 2weeks of daily oleamide (5mg/kg, i.p.), fluoxetine (10mg/kg, i.p.), or vehicle. Protein extracts from the hippocampus were then collected, and hippocampal maps were generated by way of two-dimensional gel electrophoresis (2-DE). Altered proteins induced by CMS and oleamide were identified through mass spectrometry and database searches. Compared to the control group, the CMS rats exhibited significantly less body weight gain and decreased sucrose consumption. Treatment with oleamide caused a reversal of the CMS-induced deficit in sucrose consumption. In the proteomic analysis, 12 protein spots were selected and identified. CMS increased the levels of adenylate kinase isoenzyme 1 (AK1), nucleoside diphosphate kinase B (NDKB), histidine triad nucleotide-binding protein 1 (HINT1), acyl-protein thioesterase 2 (APT-2), and glutathione S-transferase A4 (GSTA4). Compared to the CMS samples, seven spots changed significantly following treatment with oleamide, including GSTA4, glutathione S-transferase A6 (GSTA6), GTP-binding nuclear protein Ran (Ran-GTP), ATP synthase subunit d, transgelin-3, small ubiquitin-related modifier 2 (SUMO2), and eukaryotic translation initiation factor 5A-1 (eIF5A1). Of these seven proteins, the level of eIF5A1 was up-regulated, whereas the remaining proteins were down-regulated. In conclusion, oleamide has antidepressant-like properties in the CMS rat model. The identification of proteins altered by CMS and oleamide treatment provides support for targeting these proteins in the development of novel therapies for depression.

The effect of Chaihu-Shugan-San and its components on the expression of ERK5 in the hippocampus of depressed rats

ETHNOPHARMACOLOGICAL RELEVANCE

Chaihu-Shugan-San (CSS) is a well-known, Chinese traditional medicine used to treat depression. Little is known about the antidepressant mechanism of CSS. The main aims of the this study were to evaluate the antidepressant-like effects of CSS and its components and further explore the CSS׳s effect upon signal transduction of extracellular signal-regulated kinase 5 (ERK5) expressions in the hippocampus of rats with depression induced by chronic unpredicted mild stress.

MATERIALS AND METHODS

SD rats were randomly divided into six groups: Normal; Model; CSS; Component I; Component II; and Fluoxetine. Antidepressant-like effects of CSS and two of its constituents, Components I and II in aqueous extract, were assessed using rats exposed to chronic unpredictable mild stress (CUMS) by measuring weight change, observing the open-field test and measuring sucrose water consumption. Antidepressant mechanism were examined by measuring the effect of CSS, and two of its constituents, on extracellular signal-regulated kinase 5 (ERK5) expression, phosphorylation-ERK5 (p-ERK5), and ERK5 mRNA in the hippocampus by using western blotting and Real-time Polymerase Chain Reaction (PCR). Three preparations were prepared: (1) an aqueous extract of CSS (5.9 g/kg·d); (2) Component I (3.3 g/kg·d); and (3) Component II (2.6 g/kg·d). During the 28-day CUMS, the three preparations were intragastrically administered all three preparations. Simultaneously a parallel positive fluoxetine control group was given fluoxetine hydrochloride (1.8mg/kg·d). Normal and Model groups were intragastrically administered with a isovolumic distilled water (4.5 ml/kg·d).

RESULTS

Depressed rats had decreased weight gain; decreased locomotor activity as measured by the open field test; and reduced sucrose consumption. The rats׳ hippocampus ERK5 activation was significantly suppressed. CSS reduced the incidence of depressive-like behaviors and increased ERK5 activation in depressed rats at the same rate as fluoxetine. Component I, and II, each had only a partial effect on the depression indicators measured.

CONCLUSIONS

CSS aqueous extract has antidepressant-like effects on CUMS-induced depression model rats. The antidepressant effect of CSS is greater than that of either the two separate components measured. CSS׳s antidepressant mechanism may be mediated by reversing the stress-induced disruption of ERK5 activity.

Sex differences in stress-induced social withdrawal: role of brain derived neurotrophic factor in the bed nucleus of the stria terminalis

Depression and anxiety disorders are more common in women than men, and little is known about the neurobiological mechanisms that contribute to this disparity. Recent data suggest that stress-induced changes in neurotrophins have opposing effects on behavior by acting in different brain networks. Social defeat has been an important approach for understanding neurotrophin action, but low female aggression levels in rats and mice have limited the application of these methods primarily to males. We examined the effects of social defeat in monogamous California mice (Peromyscus californicus), a species in which both males and females defend territories. We demonstrate that defeat stress increases mature brain-derived neurotrophic factor (BDNF) protein but not mRNA in the bed nucleus of the stria terminalis (BNST) in females but not males. Changes in BDNF protein were limited to anterior subregions of the BNST, and there were no changes in the adjacent nucleus accumbens (NAc). The effects of defeat on social withdrawal behavior and BDNF were reversed by chronic, low doses of the antidepressant sertraline. However, higher doses of sertraline restored social withdrawal and elevated BDNF levels. Acute treatment with a low dose of sertraline failed to reverse the effects of defeat. Infusions of the selective tyrosine-related kinase B receptor (TrkB) antagonist ANA-12 into the anterior BNST specifically increased social interaction in stressed females but had no effect on behavior in females naïve to defeat. These results suggest that stress-induced increases in BDNF in the anterior BNST contribute to the exaggerated social withdrawal phenotype observed in females.

Antidepressant-like activity of Chaihu-Shugan-San aqueous extract in rats and its possible mechanism

BACKGROUND

Chaihu-Shugan-San (CHSGS), a traditional Chinese medicinal formula, is commonly used for the treatment of depression in China. However, the molecular mechanism underlying its antidepressant action is unknown.

OBJECTIVE

The objective of this study is to evaluate the antidepressant-like effects of CHSGS and further explore the possible molecular mechanism implicated in its actions.

MATERIALS AND METHODS

THE RATS WERE RANDOMLY DIVIDED INTO FOUR GROUPS: The normal control group, the model control group, the CHSGS group and the fluoxetine control group. The antidepressant-like effects of CHSGS aqueous extract were assessed in rats exposed to chronic mild stress (CMS) using the open-field test and sucrose water consumption test, its underlying mechanism of anti-depression was explored by determining the effect of CHSGS on the extracellular signal-regulated kinase (ERK) and phospho-ERK (P-ERK) in the hippocampus using western blot. The aqueous extract of CHSGS at a dose of standard (5.9 g/kg·d) was administered intragastrically for 14 days during the CMS model while the fluoxetine control group was given at the same time using fluoxetine hydrochloride (1.8 mg/kg·d).

RESULTS

The stressed rats demonstrated decreased locomotor activity in open field test and reduction in sucrose consumption and decreased levels of P-ERK1/2 and the ratio of P-ERK1/2 to total ERK1/2 in the hippocampus. CHSGS alleviated the depressive-like behaviors and increased levels of P-ERK1/2 and the ratio of P-ERK1/2 to total ERK1/2 in stressed rats as well as fluoxetine.

CONCLUSION

In summary, these results suggest that CHSGS aqueous extract possesses an antidepressant-like activity in CMS induced depression model rats, which might be mediated, at least in part, by reversing the stress-induced disruption of ERK activity.

A new stress model, a scream sound, alters learning and monoamine levels in rat brain

Most existing animal models for stress involve the simultaneous application of physical and psychological stress factors. In the current study, we described and used a novel psychological stress model (scream sound stress). To study the validity of it, we carried out acute and chronic scream sound stress. First, adult Sprague-Dawley (SD) rats were randomly divided into white noise, stress and background groups. The white noise group and stress group were treated with white noise and scream sound for 4h in the morning respectively. Compared with white noise and background groups, exposure to acute scream sound increased corticosterone (CORT) level and decreased latency in Morris water maze (MWM) test. The levels of noradrenaline (NE), dopamine (DA), 5-hydroxytryptamine (5-HT), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were altered in the striatum, hypothalamus and hippocampus of stress rats. Second, adult SD rats were randomly divided into background and stress groups, which were treated with scream sound for three weeks. Exposure to chronic scream sound suppressed body weight gain, increased corticosterone (CORT) level, influenced the morphology of adrenal gland, improved spleen and thymus indices, and decreased latency in MWM test. NE, DA, DOPAC, HVA and 5-HIAA levels were also altered in the brain of stress rats. Our results suggested that scream sound, as a novel stressor, facilitated learning ability, as well as altered monoamine levels in the rat brain. Moreover, scream sound is easy to apply and can be applied in more animals at the same time.

Neurobiology of chronic mild stress: parallels to major depression

The chronic mild (or unpredictable/variable) stress (CMS) model was developed as an animal model of depression more than 20 years ago. The foundation of this model was that following long-term exposure to a series of mild, but unpredictable stressors, animals would develop a state of impaired reward salience that was akin to the anhedonia observed in major depressive disorder. In the time since its inception, this model has also been used for a variety of studies examining neurobiological variables that are associated with depression, despite the fact that this model has never been critically examined to validate that the neurobiological changes induced by CMS are parallel to those documented in depressive disorder. The aim of the current review is to summarize the current state of knowledge regarding the effects of chronic mild stress on neurobiological variables, such as neurochemistry, neurochemical receptor expression and functionality, neurotrophin expression and cellular plasticity. These findings are then compared to those of clinical research examining common variables in populations with depressive disorders to determine if the changes observed following chronic mild stress are in fact consistent with those observed in major depression. We conclude that the chronic mild stress paradigm: (1) evokes an array of neurobiological changes that mirror those seen in depressive disorders and (2) may be a suitable tool to investigate novel systems that could be disturbed in depression, and thus aid in the development of novel targets for the treatment of depression.

5-HT(3) receptor mediates the dose-dependent effects of citalopram on pentylenetetrazole-induced clonic seizure in mice: involvement of nitric oxide

Citalopram is a selective serotonin reuptake inhibitor (SSRI), widely used in the treatment of depressive disorders. It has been shown that citalopram affects seizure susceptibility. Although the exact mechanism of these effects are not yet fully understood, recent data suggest that 5HT(3) receptors and nitric oxide (NO) might participate in the central effects of SSRIs. In this study in a mouse model of clonic seizure induced by pentylenetetrazole we investigated whether 5-HT(3) receptors are involved in the effects of citalopram on seizure threshold. In our experiments, citalopram at lower doses (0.5 and 1mg/kg, i.p) significantly increased the seizure threshold and at higher doses (≥25mg/kg) showed proconvulsive effects. Moreover, mCPBG (a 5-HT(3) receptor agonist) at low and non-effective doses augmented while non-effective doses of tropisetron prevented the anticonvulsive properties of citalopram. On the other hand, Low doses of nitric oxide synthase inhibitors l-NAME and 7-NI alone or in combination with lower doses of 5-HT(3) receptor agonist enhanced the anticonvulsive property of citalopram, while l-arginine (NO precursor) alone or in combination with tropisetron blocked the protective effect of citalopram. In summary, our findings demonstrate that 5-HT(3) receptor mediates the anticonvulsant properties of low doses of citalopram, whereas it seems that the proconvulsive effect is mostly mediated through the NO pathway and can be totally blocked by NOS inhibitors. This could propose a new approach toward finding the mechanism of citalopram activity, curtailing the adverse effects of citalopram and perhaps managing the convulsions as a vicious consequence of citalopram overdose.

Stress induces glucocorticoid-mediated apoptosis of rat Leydig cells in vivo

Stress can disrupt endocrine signalling in the male reproductive axis through high concentrations of glucocorticoids, the hallmark of stress. Our previous work revealed that a stress level of exogenous glucocorticoids could induce apoptosis of rat Leydig cells, which are the primary source of testosterone. The aim of this study was to investigate whether stress can induce apoptosis in rat Leydig cells in vivo and, if so, whether the process is the result of a direct effect of glucocorticoids. In a chronically stressed rat model, serum corticosterone concentration was increased significantly whereas serum testosterone was decreased. The frequency of apoptotic Leydig cells in stressed rats was also increased. Adrenalectomised rats subjected to chronic stress showed an elevated serum testosterone, while the apoptotic frequency of Leydig cells was not increased. It was established that glucocorticoid-induced Leydig cell apoptosis is mediated by glucocorticoid receptors (GRs), which translocate from cytoplasm to nucleus. Adenovirus microRNA-induced downregulation of GR expression in vitro alleviated the corticosterone-induced increase in apoptosis of Leydig cells. These results indicate that the stress-induced increase in corticosterone secretion resulted in apoptosis in rat Leydig cells in vivo, and thereby decreased testosterone synthesis.

The orally active melanocortin-4 receptor antagonist BL-6020/979: a promising candidate for the treatment of cancer cachexia

BACKGROUND: Under physiological conditions, the melanocortin system is a crucial part of the complex network regulating food intake and energy expenditure. In pathological states, like cachexia, these two parameters are deregulated, i.e., food intake is decreased and energy expenditure is increased-a vicious combination leading to catabolism. Agouti-related protein (AgRP), the endogenous antagonist at the melanocortin-4 receptor (MC-4R), was found to increase food intake and to reduce energy expenditure. This qualifies MC-4R blockade as an attractive mode of action for the treatment of cachexia. Based on this rationale, a novel series of small-molecule MC-4R antagonists was designed, from which the orally active compound BL-6020/979 (formerly known as SNT207979) emerged as the first promising development candidate showing encouraging pre-clinical efficacy and safety properties which are presented here. METHODS AND RESULTS: BL-6020/979 is an orally available, selective and potent MC-4R antagonist with a drug-like profile. It increased food intake and decreased energy expenditure in healthy wild-type but not in MC-4R deficient mice. More importantly, it ameliorated cachexia-like symptoms in the murine C26 adenocarcinoma model; with an effect on body mass and body composition and on the expression of catabolic genes. Moreover, BL-6020/979 showed antidepressant-like properties in the chronic mild stress model in rats and exhibits a favorable safety profile. CONCLUSION: The properties of BL-6020/979 demonstrated in animal models and presented here make it a promising candidate suitable for further development towards a first-in-class treatment option for cachexia that potentially opens up the opportunity to treat two hallmarks of the disease, i.e., decreased food intake and increased energy expenditure, with one drug.

Nicotine reverses anhedonic-like response and cognitive impairment in the rat chronic mild stress model of depression: comparison with sertraline

Smoking rates among depressed individuals are higher than is observed in the background population, and nicotine alleviates depressive symptoms. In rodents, nicotine shows antidepressant-like effects in the forced swim and learned helplessness paradigms. Clinical depression is associated with both anhedonia and cognitive impairments. In rats, chronic mild stress (CMS) decreases voluntary sucrose intake, reflecting an anhedonic-like state, and impairs performance in the spontaneous alternation behaviour (SAB) test, suggesting impaired cognitive function. Here, we examine the effect of chronic treatment of nicotine (0.4 mg/kg/day) and sertraline (5 mg/kg/day) on CMS-induced anhedonic-like behaviour and impairment in the SAB test. Nicotine and sertraline administered individually or in combination show significant and equally efficacious reversal of the CMS-induced decrease in sucrose intake, implying there is no additive or synergistic effect of the nicotine + sertraline combination. In the SAB test, nicotine, but not sertraline or nicotine + sertraline, reversed the CMS-induced impairment. The present results show that the effect of nicotine on a CMS-induced anhedonic-like state in rats is similar to that of a standard antidepressant drug. Moreover, the data suggest that nicotine alleviates CMS-induced cognitive disturbance. A treatment strategy involving the targeting of nicotinic acetylcholine receptors may prove beneficial for emotional and cognitive disturbances associated with depression.

Antidepressant effects of the extract YZ-50 from Polygala tenuifolia in chronic mild stress treated rats and its possible mechanisms

YZ-50 is an active fraction obtained from the root of Polygala tenuifolia Willd. (Polygalaceae) extract and it has been reported previously to exert beneficial effects on mental health in depressed sufferers, however, its mechanism of action remains unresolved. This study utilized the chronic mild stress (CMS) model of depression in Sprague-Dawley rats to evaluate the effects of YZ-50 on depressive behaviors. Furthermore, we tested the hypothesis that the capacity of YZ-50 to reverse the harmful effects of CMS is relative to the hypothalamo-pituitary-adrenal (HPA) system and brain-derived neurotrophic factor (BDNF) in the hippocampus. Repeated administration of YZ-50 for 28 days at the doses of 140 and 280 mg/kg in CMS, YZ-50 reversed the CMS-induced changes in sucrose consumption, plasma corticosterone levels and open field activity. In addition, CMS significantly decreased hippocampal BDNF mRNA levels. However, YZ-50 counteracted a decrease in hippocampal BDNF mRNA caused by CMS. In conclusion, YZ-50 reversed the harmful effects of CMS on mood and behaviors in rats and it possesses an antidepressant property that is at least in part mediated by the neuroendocrine and neuropropective systems, and it is likely that the HPA system plays an important role in this process.

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.

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.

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.

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.

Chronic citalopram treatment elevates serotonin synthesis in flinders sensitive and flinders resistant lines of rats, with no significant effect on Sprague-Dawley rats

The influence of citalopram on regional 5-hydroxytryptamine (serotonin, 5-HT) synthesis, one of the most important presynaptic parameters of serotonergic neurotransmission, was studied. Sprague-Dawley (SPD) rats were used as the controls, and Flinders Resistant Line (FRL) rats were used as auxiliary controls, to hopefully obtain a better understanding of the effects of citalopramon Flinders Sensitive Line (FSL; "depressed") rats. Regional 5-HT synthesis was evaluated using a radiographic method with a labelled tryptophan analog tracer. In each strain of rats, the animals were treated with citalopram (10 mg/(kg day)) or saline for 14 days. The groups consisted of between fourteen and twenty rats. There were six groups of rats with citalopram (CIT) and saline (SAL) groups in each of the strains (SPD-AL, SPD-IT, FRL-AL, FRL-IT, FSL-AL and FSL-IT). A two-factor analysis of variance was used to evaluate the effect of the treatment c., SPD-SAL relative to SPD-CIT) followed by planned comparisons to evaluate the effect in each brain region. In addition, the planned comparison with appropriate contrast was used to evaluate a relative effects in SPD relative to FSL and FRL, and FSL relative to FRL groups. A statistical analysis was first performed in the a priori selected regions, because we had learned, from previous work, that it was possible to select the brain regions in which neurochemical variables had been altered by the disorder and subsequent antidepressant treatments. The results clearly show that citalopram treatment does not have an overall effect on synthesis in the control SPD rats; there was no significant (p > 0.05) difference between the SPD-SAL and SPD-CIT rats. In "depressed" FSL rats, citalopram produced a significant (p < 0.05) elevation of synthesis in seventeen out of thirty-four regions, with a significant (p < 0.05) reduction in the dorsal and median raphe. In the FRL rats, there was a significant (p < 0.05) elevation in the synthesis in twenty-two out of thirty-four brain regions, with a reduction in the dorsal raphe. In addition to these regions magnus raphe was different in the SPD and FSL groups, but it was on the statistical grounds identified as an outlier. There were significant changes produced in the FSL and FRL rats in thirteen out of seventeen a priori selected brain regions, while in the SPD rats, citalopram produced significant changes in only four out of seventeen a priori selected regions. The statistical evaluation also revealed that changes produced by citalopram in the FSL and FRL rats were significantly greater than those in the SPD rats and that there was no significant difference between the effect produced in the FSL and FRL rats. The presented results suggest that in "depressed" FSL rats, the antidepressant citalopram elevates 5-HT synthesis, which probably in part relates to the reported improved in behaviour with citalopram.

Sex differences in oxidant/antioxidant balance under a chronic mild stress regime

The deterioration of homeostasis between oxidant/antioxidant species may represent an important mechanism linking psychological stress to cardiovascular risk despite the many sex differences in stress responsiveness. The goal of the present study was to investigate the influence of chronic mild stress (CMS), a widely accepted animal model of depression, on oxidative homeostasis-allostasis markers and sICAM-1, a marker of endothelial injury, in the serum of Wistar rats, by taking into account the effect of sex. After six weeks of exposure to mild unpredictable environmental stressors, both male and female rat groups displayed typical changes in hedonic status (anhedonia), which is a core symptom of human depression. Control female rats had higher (nitrite and nitrate) NOx, lower malondealdehyde (MDA) levels with lower activity of antioxidant enzymes and sICAM-1 levels than did control males. CMS induced oxidant/antioxidant responses in both sexes. Females tended to increase their nitric oxide (NO) levels further, while MDA levels did not reach those of males, thus retaining significantly higher NO bioavailability than in males. Concerning the antioxidant enzymes, CMS-females exhibited significantly higher glutathione peroxidase (GPx) activity and lower glutathione reductase (GR) and superoxide dismutase (SOD) activity compared to CMS-males. The CMS response in females was accompanied by lower sICAM-1 levels than in males, suggesting lower endothelial injury. In conclusion, the results of the present study showed that CMS induces different oxidative stress and compensatory responses in both sexes probably due to differences in the mechanisms regulating oxidant/antioxidant pathways.

Anhedonia and activity deficits in rats: impact of post-stroke depression

Animal models may allow investigation into the aetiology and treatment of various human disorders. In the present study, a rat model for post-stroke depression (PSD) has been developed using middle cerebral artery occlusion (MCAO), followed by an 18-day chronic mild stress (CMS) paradigm in conjuncture with isolation rearing. The open-field test (OFT) and the sucrose consumption test were used to assess depression-like behaviour and the effects of the antidepressant citalopram. CMS induced behavioural changes in the ischemic animals, including decreased locomotor and rearing activity and reduced sucrose preference (compared with baseline, control and stroke groups respectively), all these behaviours were reversed by chronic administration of citalopram. During the recovery period for the PSD models, the open-field activity and preference for sweet sucrose solution decreased continually, opposed to rats subjected to stress only. Decreased locomotor and rearing represents activity deficits, whereas reduced sucrose preference may indicate desensitisation of the brain reward mechanism (anhedonia). Our findings suggest that anhedonia, one of the core symptoms in patients with PSD, and activity deficits can be found in the MCAO+CMS group of animals. Furthermore, citalopram can ameliorate the behavioural abnormalities observed in these animals. With high validity, good operability and repeatability, our findings suggest that the ischemic rat CMS model is an appropriate model for further PSD research.

Antidepressant-like effects of curcumin on serotonergic receptor-coupled AC-cAMP pathway in chronic unpredictable mild stress of rats

Serotonergic receptors take their physiologic effects by affecting adenylyl cyclase (AC) catalytic activity and cyclic adenosine monophosphate (cAMP) concentration. AC-cAMP second messenger pathway has been recently suggested to play an important role in depression. Therefore, the compound that regulates the signal pathway may have potential as antidepressant. Curcumin is the main component of Curcuma longa L, a well-known indigenous herb with comprehensive bioactivities. In the present study, we investigated the effects of chronic unpredictable mild stress (CUMS) and curcumin on behaviours and serotonergic receptor-coupled AC-cAMP signal pathway in rats. Curcumin produced beneficial effects on the stressed rats by effectively improving CUMS-induced low sucrose consumption and reducing serum corticosterone levels in rats. Moreover, curcumin enhanced AC activity and cAMP levels in platelet and various brain regions, and up-regulated mRNA expressions of AC subtypes AC 2, AC 8 and cAMP response element binding protein (CREB) in the hippocampus, cortex and hypothalamus of the CUMS rats. Curcumin also attenuated CUMS-induced reductions of 5-hydroxytryptamine (5-HT) levels and high expressions of central 5-HT(1A/1B/7) receptors in rats. These results suggested that the potent antidepressant property of curcumin might be attributed to its improvement of AC-cAMP pathway as well as CREB via suppressing central 5-HT(1A/1B/7) receptors in the CUMS rats. Our findings provided a basis for examining the interaction of serotonergic receptors and AC-cAMP pathway in depression and curcumin treatment.

Acute and chronic effects of citalopram on 5-HT1A receptor-labeling by [18F]MPPF and -coupling to receptors-G proteins

Selective serotonin reuptake inhibitors take several weeks to produce their maximal therapeutic antidepressant effect. This delay has been attributed to the gradual desensitization of somatodendritic serotonin 5-HT(1A) autoreceptors. We evaluated adaptive changes of 5-HT(1A) receptors after acute and chronic citalopram challenges in rat. Small animal positron emission tomography trial and quantitative ex vivo autoradiography studies using [(18)F]MPPF were employed, as well as in vitro 8-OH-DPAT-stimulated [(35)S]-GTPgammaS binding assay. Additionally, 5-HT(1A) receptor knock-out mice were used to assess the specificity of [(18)F]MPPF. Acute treatment with citalopram did not alter [(18)F]MPPF binding in dorsal raphe nucleus (DR), frontal cortex, or hippocampus. The absence of [(18)F]MPPF binding in the brain of 5-HT(1A) knock-out mice demonstrates the specificity of MPPF for 5-HT(1A) receptor brain imaging, but the high affinity of [(18)F]MPPF compared to 5-HT suggests that it would only be displaced by dramatic increases in extracellular 5-HT. Chronic citalopram did not modify 5-HT(1A) receptor density in any of the brain regions studied. In addition, this treatment did not modify 8-OH-DPAT-stimulated [(35)S]-GTPgammaS binding in DR, although a significant increase was observed in frontal cortex and hippocampus. [(18)F]MPPF appears to be an efficient radioligand to quantify specifically 5-HT(1A) receptor density in brain imaging. The delayed therapeutic efficacy of citalopram did not appear to be linked to either a downregulation of 5-HT(1A) receptors or to a 5-HT(1A) receptor-G protein decoupling process in serotonergic neurons, but to increased functional sensitivity of postsynaptic 5-HT(1A) receptors.

Effects of Rhodiola rosea L. extract on behavioural and physiological alterations induced by chronic mild stress in female rats

Rhodiola rosea L. is one of the most popular adaptogen and an antistress plant in European and Asiatic traditional medicine. Our previous studies have confirmed the adaptogenic and antistress properties of a single administration of R. rosea L. extract in rats exposed to acute stress. There is increasing evidence that prolonged exposure to stressful life events and depression are both related to significant behavioural, endocrinological and neurobiological changes in human and animal subjects. The aim of this study was to determine whether chronic treatment with a hydroalcoholic R. rosea extract (RHO) standardized in 3% rosavin and 1% salidroside can prevent alterations induced in female rats following 6 weeks of a chronic mild stress (CMS) procedure. This was analysed through the behavioural and physiological parameters of consumption of 1% sucrose solution, locomotor and exploratory activities, body weight gain and oestrous cycle length. After the first 3 weeks of stress, RHO was administered daily by gavage at doses of 10, 15 and 20 mg/kg for the remaining 3 weeks. In addition, the antidepressant drug fluoxetine (10 mg/kg os), which has been shown to reverse CMS-induced disruptions, was used as the reference treatment. Rats subjected to the CMS procedure demonstrated decreased sucrose intake, reduced moving behaviour, minimized weight gain and dysregulation of their oestrous cycle. Treatment with RHO completely reverted all of these changes. The effects of RHO were comparable to those of fluoxetine. Interestingly, neither RHO nor fluoxetine influence the behavioural and physiological parameters tested in non-stressed animals. These findings strongly showed that chronic administration of RHO results in potent inhibition of the behavioural and physiological changes induced by chronic exposure to mild stressors.

Differential effects of chronic antidepressant treatment on shuttle box escape deficits induced by uncontrollable stress

RATIONALE

The transient behavioral deficit produced in rodents by typical learned helplessness (LH) procedures limits the utility of LH in identifying the therapeutic mechanisms associated with chronic antidepressant administration. In addition, LH procedures do not differentiate between different antidepressant classes as observed in the forced swim test.

OBJECTIVES

To produce both a long lasting and antidepressant reversible behavioral deficit in a modified LH procedure that administers inescapable shock (IS) in the same operant chamber used for shuttle box escape testing.

RESULTS

A single IS session produced a robust increase in the number of escape failures (FR-2 escape contingency) that endured for at least 21 days. This escape deficit was reversed by desipramine (24 mg/kg/day, 6 days) at the first shuttle box session. Fluoxetine (5 mg/kg/day, 6 and 21 days) improved escape performance only after repeated test sessions. In contrast, fluoxetine (5 mg/kg/day, 21 days) completely reversed the first shuttle box test escape deficit induced by exposure to a chronic unpredictable stress procedure devoid of shocks or exposure to operant chambers. These differential drug effects may be due to the presence or absence of contextual cues during escape testing. Repeated re-exposure to the IS context enhanced the FR-2 escape deficit.

CONCLUSIONS

These data suggest that performing escape testing and IS in the same environment improves the preclinical modeling of the time-dependency and behavioral pattern of antidepressant response observed clinically. Additionally, contextual information associated with the IS environment modulates escape performance and may interact differentially with discrete antidepressant classes.

Effects of repeated citalopram treatments on chronic mild stress-induced growth associated protein-43 mRNA expression in rat hippocampus

Although growth associated protein-43 (GAP-43) is known to play a significant role in the regulation of axonal growth and the formation of new neuronal connections in the hippocampus, there is only a few studies on the effects of acute stress on GAP-43 mRNA expression in the hippocampus. Moreover, the effects of repeated citalopram treatment on chronic mild stress (CMS)-induced changes in GAP-43 mRNA expression in the hippocampus have not been explored before. To explore this question, male rats were exposed to acute immobilization stress or CMS. Also, citalopram was given prior to stress everyday during CMS procedures. Acute immobilization stress significantly increased GAP-43 mRNA expression in all subfields of the hippocampus, while CMS significantly decreased GAP-43 mRNA expression in the dentate granule cell layer (GCL). Repeated citalopram treatment decreased GAP-43 mRNA expression in the GCL compared with unstressed controls, but this decrease was not further potentiated by CMS exposure. Similar decreases in GAP-43 mRNA expression were observed in CA1, CA3 and CA4 areas of the hippocampus only after repeated citalopram treatment in CMS-exposed rats. This result indicates that GAP-43 mRNA expression in the hippocampus may differently respond to acute and chronic stress, and that repeated citalopram treatment does not change CMS-induced decreases in GAP-43 mRNA expression in the GCL.

The selective 5-HT(6) receptor antagonist SB-399885 enhances anti-immobility action of antidepressants in rats

The aim of the present study was to investigate the effect of antidepressant drugs (characterized by a different mechanism of action), administered jointly with the selective 5-HT(6) receptor antagonist N-[3,5-dichloro-2-(methoxy)phenyl]-4-(methoxy)-3-(1-piperazinyl)benzenesulfonamide (SB-399885), in the forced swim test in rats. All the compounds under study were given intraperitoneally in doses which did not shorten the immobility time of rats. Co-administration of SB-399885 (3 mg/kg) and imipramine (20 mg/kg), desipramine (20 mg/kg), bupropion (5 mg/kg) or moclobemide (20 mg/kg), produced significant anti-immobility action, whereas SB-399885 (3 mg/kg) given jointly with citalopram (20 mg/kg) did not affect immobility time. None of the compounds studied, given alone or jointly, increased the general activity of rats measured in the open field test. The obtained results indicate that the blockade of 5-HT(6) receptors may facilitate the anti-immobility effect of imipramine, desipramine, bupropion or moclobemide in the forced swim test.

Hippocampal neurogenesis and behavioural studies on adult ischemic rat response to chronic mild stress

Stress and antidepressants have been shown to influence hippocampal neurogenesis, which is hypothesized to be an etiological factor of depression. Robust ischemia-stimulated neurogenesis implies the existence of an innate response and rehabilitation mechanism to injury repair, i.e. cognitive recovery. We investigated whether unpredictable chronic mild stress (CMS) influences ischemia-stimulated compensatory neurogenesis in the hippocampus and also studied the therapeutic effect of citalopram. Adult rats were exposed to the CMS paradigm after left middle cerebral artery occlusion (MCAO). The open-field test (OFT) and the sucrose consumption test were employed to assess depression-like behaviour. The survival and fate of proliferating cells was monitored by labelling with bromodeoxyuridine (BrdU) and other cell markers. Cell proliferation was examined 1 day after the last BrdU injection, and survival and differentiation were determined up to 45 days after ischemia. The number of BrdU-positive cells that were labelled using the 2 protocols and the proportion of newborn neurons in the dentate gyrus (DG) ipsilateral to ischemia were higher than in the control. CMS induced depressive behaviours in ischemic rats, and this was accompanied by reduced proliferation and survival/neurogenic fate. All these effects were reversed by citalopram administration. These results support a putative role for ischemia-induced neurogenesis in what may be an adaptive or compensatory process, which is influenced by post-stroke stressors. This may contribute to the onset of Post-stroke depression (PSD) and thus represents a potential target for therapy.

Sex differences in the effects of two stress paradigms on dopaminergic neurotransmission

Sex differences in behavioral and neurobiological responses to stress are considered to modulate the prevalence of some psychiatric disorders, including major depression. In the present study, we compared dopaminergic neurotransmission and behavior in response to two different stress paradigms, the Forced Swim Test (FST) and the Chronic Mild Stress (CMS). Male and female rats were subjected to one session of swim stress for two consecutive days (FST) or to a variety of mild stressors alternating for six weeks (CMS). Subsequently, the tissue levels of dopamine (DA) and its metabolites (HVA and DOPAC) in the hippocampus, the hypothalamus, the prefrontal cortex and the striatum were measured using high-performance liquid chromatography (HPLC). The ratios HVA/DA and DOPAC/DA were also calculated as indices of the dopaminergic activity. Results from the FST determined that males exhibited lower immobility, higher climbing duration and increased dopaminergic activity in the prefrontal cortex and the hippocampus compared to females. CMS induced alterations in sucrose intake in both sexes, while it only decreased dopaminergic activity in the prefrontal cortex of females. These findings show that FST and CMS have different effects on the dopaminergic activity of discrete brain regions depending on the sex of the animal. These data support the growing evidence that females display a differential response and adaptation to stress than males.

Assessing activity onset time and efficacy for clinically effective antidepressant and antimanic drugs in animal models based on dominant-submissive relationships

There is confusion in the literature on the measurement of the drug activity onset time (AOT) for both clinical and non-clinical studies of antidepressant and antimanic drugs. The questions asked are: How often and at which time points should drug effects be measured? At what level of a drug effect should AOT be determined? Is the placebo (control) effect important for consideration of drug AOT? This paper reviews approaches taken to answer these questions and to assess drug therapeutic AOT. The first part of the paper is devoted to a review of methods used in clinical trials with depression as an indication. The second part is focused on approaches taken in animal models of depression and how they could help in assessing drug AOT. Finally, a summary of pharmacological values on which the AOT depends is presented and a new statistical approach to data analysis method proposed. The allied experimental design for pre-clinical and clinical studies may help to characterize and differentiate AOT for available and new generation of antidepressants and antimanic drugs.

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.

Enhancement of the anti-immobility action of antidepressants by a selective 5-HT7 receptor antagonist in the forced swimming test in mice

Using the forced swimming test in mice, we examined the effect of the following antidepressants: citalopram, imipramine, desipramine and moclobemide (which are characterized by different mechanisms of action), administered in combination with the selective 5-HT7 receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]-pyrrolidine (SB 269970). All those drugs were given in doses which did not shorten the immobility time of mice. Citalopram (1.25 mg/kg), imipramine (10 mg/kg), desipramine (5 mg/kg) or moclobemide (10 mg/kg) administered jointly with SB 269970 (5 mg/kg), produced a significant antidepressant-like effect. None of the compounds studied, given alone or in combination, increased the spontaneous locomotor activity of mice. The obtained results indicate that blockade of 5-HT7 receptors may facilitate the anti-immobility effect of antidepressants in mice.

Beneficial effects of exercise and its molecular mechanisms on depression in rats

Exercise showed the beneficial effects on mental health in depressed sufferers, whereas, its underlying mechanisms remained unresolved. This study utilized the chronic unpredictable stress (CNS) animal model of depression to evaluate the effects of exercise on depressive behaviors and spatial performance in rats. Furthermore, we tested the hypothesis that the capacity of exercise to reverse the harmful effects of CNS was relative to the hypothalamo-pituitary-adrenal (HPA) system and brain-derived neurotrophic factor (BDNF) in the hippocampus. Animal groups were exposed to CNS for 4 weeks with and without access to voluntary wheel running. Stressed rats consumed significantly less of a 1% sucrose solution during CNS and exhibited a significant decrease in open field behavior. On the other hand, they showed impaired spatial performance in Morris water maze test 2 weeks after the end of CNS. Further, CNS significantly decreased hippocampal BDNF mRNA levels. However, voluntary exercise improved or even reversed these harmful behavioral effects in stressed rats. Furthermore, exercise counteracted a decrease in hippocampal BDNF mRNA caused by CNS. In addition, we also found that CMS alone increased circulating corticosterone (CORT) significantly and decreased hippocampal glucocorticoid receptor (GR) mRNA. At the same time, exercise alone increased CORT moderately and did not affect hippocampal GR mRNA levels. While, when both CNS and exercise were combined, exercise reduced the increase of CORT and the decrease of GR caused by CMS. The results demonstrated that: (1) exercise reversed the harmful effects of CNS on mood and spatial performance in rats and (2) the behavioral changes induced by exercise and/or CNS might be associated with hippocampal BDNF levels, and in addition, the HPA system might play different roles in the two different processes.

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.

Chronic mild stress impact: are females more vulnerable?

Despite the knowledge that women are more susceptible than men to stress-related mental illness, such as major depression, there is no comprehensive estimation of the role of gender in the detrimental effects of chronic stress that might cause depression. Sex differences regarding the association of behavioral parameters with serotonergic and hypothalamic-pituitary-adrenal axis activities were investigated in the chronic mild stress model of depression. Additionally, the impact of chronic mild stress exposure on an additional/novel short-term stressful procedure, such as the forced swim test was examined in male and female rats. Female rats were found to be more vulnerable to chronic mild stress and that was depicted with disruption of sucrose intake, decreases in open field activity, increased corticosterone levels, alteration in estrous cycle and decreased serotonergic activity in hippocampus and hypothalamus. On the contrary, in males the current chronic mild stress protocol elicited only behavioral changes, such as disruption in sucrose intake and decreased open field activity. Interestingly, in response to forced swim test, females previously subjected to chronic mild stress, were found to cope better by exhibiting increased active behavior in the second forced swim test session and higher hypothalamic serotonergic activity in comparison with corresponding males. On the other hand, males were more affected by previous chronic mild stress exposure and that was manifested by decreased active behavior in the first forced swim test session and increased corticosterone levels following second forced swim test session. These data indicate that although females are more vulnerable in the application of chronic mild stress than males, in response to an additional-novel stressor (forced swim test) they show better response. Therefore, both sex/gender and combination of stressful procedures should be carefully considered in the study of the pathophysiology of stress-related mental illnesses.

Behavioural and neurochemical effects induced by chronic mild stress applied to two different rat strains

Chronic mild stress (CMS) has been reported to induce an anhedonic-like state in rats that resembles some of the symptoms of endogenous depression in humans. In the present study, CMS-induced behavioural responses along with neurochemical alterations in dopaminergic and serotonergic function in prefrontal cortex, striatum, hypothalamus and hippocampus were examined following treatment with imipramine in Wistar and Sprague-Dawley rats. The CMS procedure lasted 7 weeks in total. Once per week, a 1-h preference test for 1% sucrose solution was conducted. Treatment with imipramine (10mg/kg i.p., once daily) commenced after experimental week 3. CMS induced significant reductions in absolute and relative sucrose intake and sucrose preference in both rat strains but their temporal pattern was different especially during the weeks 0-3. These effects were reversed by IMI. An increase in the dopaminergic and a decrease in the serotonergic activity were observed in the prefrontal cortex in both rat strains following CMS. A decrease in the striatal dopaminergic activity and an increased hippocampal serotonergic activity were also seen in both rat strains following CMS. In Wistar rats, dopaminergic and serotonergic activities were enhanced in the hypothalamus whereas in Sprague-Dawley rats no such stress-induced changes were observed. Notably, the clear decrease in sucrose consumption observed in stressed Wistar rats could be directly associated with a respective increase in the dopaminergic hypothalamic activity. Chronic treatment with imipramine normalized all neurochemical alterations induced by CMS. Our results suggest that a specific and regionally differentiated serotonin-dopamine interaction is directly related to the observed stress-induced anhedonia.

Antidepressant effects of citalopram and CRF receptor antagonist CP-154,526 in a rat model of depression

Due to the interest in the antidepressant potential of nonpeptide corticotropin-releasing factor (CRF)(1) receptor antagonists, the present investigation examined the antidepressant-like effects of the CRF(1) receptor antagonist CP-154,526 on the exaggerated swim test immobility in the Flinders Sensitive Line (FSL) rat, a genetic animal model of depression. Chronic treatment with CP-154,526 (10 mg/kg; 2x day) for 14 days increased swimming in the Flinders Sensitive Line rats. Citalopram (5 and 10 mg/kg; 2x day) and desipramine (5 mg/kg; 1x day) also significantly increased swimming in the Flinders Sensitive Line rats, as expected. However, neither CP-154,526 nor citalopram (10 mg/kg) altered swimming times in the control Flinders Resistant Line (FRL) rats. Citalopram (10 mg/kg) and CP-154,526 also increased the abnormally low level of social interaction behavior in the Flinders Sensitive Line rats. These findings indicate that citalopram and CP154,526, a CRF(1) receptor antagonist, have both antidepressant and anxiolytic effects that can be detected in an experimental model of depression only and not in "normal" control animals.

Effect of combined administration of 5-HT1A or 5-HT1B/1D receptor antagonists and antidepressants in the forced swimming test

In the present study, we examined effects of the selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor citalopram, the 5-HT/noradrenaline reuptake inhibitor imipramine, the selective noradrenaline reuptake inhibitor desipramine or the monoamine oxidase-A inhibitor moclobemide, administered in combination with the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridynyl)cyclohexanecarboxamide (WAY 100635) or the 5-HT(1B/1D) receptor antagonist N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-[1,2,4]oxadiazol-3-yl)1,1'-biphenyl-4-carboxamide (GR 127935) and the 5-HT(1B) receptor antagonist N-[3-(2-dimethylamino) ethoxy-4-methoxyphenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1'-biphenyl)-4-carboxamide (SB 216641) in the forced swimming test in rats. When given alone, citalopram (20 and 30 mg/kg), imipramine (20 mg/kg), desipramine (20 mg/kg), moclobemide (20 mg/kg), WAY 100635 (0.1 and 1 mg/kg), GR 127935 (10 and 20 mg/kg) or SB 216641 (2 mg/kg) did not shorten the immobility time of rats. Co-administration of WAY 100635 (0.1 and 1 mg/kg) and citalopram (20 mg/kg), or imipramine (20 mg/kg), or moclobemide (20 mg/kg) did not affect the immobility time of rats, whereas WAY 100635 given jointly with desipramine (20 mg/kg) induced a weak anti-immobility effect. GR 127935 (10 and 20 mg/kg) or SB 216641 (2 mg/kg) co-administered with imipramine, desipramine or moclobemide, but not citalopram, produced a significant anti-immobility action in the forced swimming test in rats. These results indicate that the blockade of 5-HT(1B) rather than 5-HT(1A) receptors may facilitate the anti-immobility effect of imipramine, desipramine or moclobemide in the forced swimming test. No interaction was observed between 5-HT(1A) or 5-HT(1B/1D) receptor antagonists and citalopram.

Evaluation of the effects of chronic mild stressors on hedonic and physiological responses: sex and strain compared

The chronic mild stress (CMS) paradigm was developed in order to simulate in animals the symptom of anhedonia, a major feature of depression. Typically, changes in hedonic status are interpreted from a decrease in either intake or preference for a mild sucrose solution. Although the incidence of clinical depression is significantly higher in women than in men, the study of this disorder in most animal models of depression has been based on the responses of male rodents. The purpose of this study was to compare the effects of 6 weeks of CMS administration among male and female rats of two rat strains, Sprague-Dawley (SD) and Long Evans (LE), with respect to physiological (body, adrenal gland, and spleen weight) and biochemical (plasma corticosterone levels) indices of stress as well as evaluations of 1 and 24 h sucrose intake and preference. Estrous cycle was tracked throughout the study. Overall, our results indicate a slower rate of weight gain in animals, greater in males, exposed to the chronic stressor regime. Furthermore, CMS is shown to disrupt estrous cycling, predominantly in the Long Evans strain of rats. The main behavioral finding was a significant reduction in 24 h sucrose intake in female treated groups, which was not accompanied by alterations in preference. Corticosterone levels were elevated in CMS-treated animals relative to the singly housed control groups, but exposure to a subsequent stressor was not influenced by the stress history. Taken together, the effects of chronic stressor exposure are evident, based on physiological and biochemical indices, although none of the measures distinguished any striking gender specific reactions. The usefulness of sucrose intake or preference as behavioral indices of CMS-induced anhedonia in males and females is modest at best.