Amphetamine and tranylcypromine in an animal model of depression: pharmacological specificity of the reversal effect

Behavioral Animal Models and Neural-Circuit Framework of Depressive Disorder

Depressive disorder is a chronic, recurring, and potentially life-endangering neuropsychiatric disease. According to a report by the World Health Organization, the global population suffering from depression is experiencing a significant annual increase. Despite its prevalence and considerable impact on people, little is known about its pathogenesis. One major reason is the scarcity of reliable animal models due to the absence of consensus on the pathology and etiology of depression. Furthermore, the neural circuit mechanism of depression induced by various factors is particularly complex. Considering the variability in depressive behavior patterns and neurobiological mechanisms among different animal models of depression, a comparison between the neural circuits of depression induced by various factors is essential for its treatment. In this review, we mainly summarize the most widely used behavioral animal models and neural circuits under different triggers of depression, aiming to provide a theoretical basis for depression prevention.

Social-pair judgment bias testing in slow-growing broiler chickens raised in low- or high-complexity environments

Impacts of environmental complexity on affective states in slow-growing broiler chickens (Gallus gallus domesticus) are unknown. Chickens' performance in judgment bias tests (JBT) can be limited as they are tested individually, causing fear and anxiety. The objectives were to apply a social-pair JBT to assess the effect of environmental complexity on slow-growing broiler chickens` affective states, and assess the impact of fearfulness, anxiety, and chronic stress on JBT performance. Six-hundred Hubbard Redbro broilers were housed in six low-complexity (similar to commercial) or six high-complexity (permanent and temporary enrichments) pens. Twelve chicken pairs were trained (1 pair/pen, n = 24 chickens) using a multimodal approach (visual and spatial cues), with reward and neutral cues of opposing color and location. Three ambiguous cues were tested: near-positive, middle, and near-neutral cues. Approach and pecking behavior were recorded. Eighty-three percent of chickens (20/24) were successfully trained in 13 days. Fearfulness, anxiety, and chronic stress did not impact chickens' performance. Chickens successfully discriminated between cues. Low-complexity chickens approached the middle cue faster than high-complexity chickens, indicating that they were in a more positive affective state. The environmental complexity provided in this study did not improve affective states in slow-growing broiler chickens compared to a control. A social-pair JBT resulted in excellent learning and testing outcomes in slow-growing broilers.

Psychological dominant stressor modification to an animal model of depression with chronic unpredictable mild stress

Background and Aim

Chronic unpredictable mild stress (CUMS) is a protocol widely used to create an animal model of depression with food deprivation, water deprivation, and physical-dominant stressors as routine procedures. However, human depression mainly involves psychological stressors and does not always involve a lack of food and water; thus, CUMS procedures should be modified accordingly. Therefore, this study aimed to create an animal model of depression, mainly focusing on a psychologically dominant stressor without food and water deprivation.

Materials and Methods

The CUMS and control groups, respectively, received CUMS modification (psychologically dominant stressors without food and water deprivation) for 21 days. A 24-h sucrose preference test (SPT) was used to assess the successful creation of an animal model of depression. Daily food intake measurements, weekly weight monitoring, and weight gain calculations were performed. Either an independent sample t-test or the Mann-Whitney test was used.

Results

Of the 42 rats included, 39 completed the study. Chronic unpredictable mild stress procedures for 21 days significantly reduced the SPT (p < 0.05), mean body weight (p < 0.05), and weekly weight gain (p < 0.05) in the CUMS group compared to the control group. However, the weekly average food intake did not statistically differ between the two groups.

Conclusion

Psychological dominant CUMS modification to an animal model of depression resulted in lower SPT, body weight, and weekly weight gain in the CUMS group than in the control group.

Saikosaponin D exerts antidepressant effect by regulating Homer1-mGluR5 and mTOR signaling in a rat model of chronic unpredictable mild stress

BACKGROUND

Many studies about depression have focused on the dysfunctional synaptic signaling in the hippocampus that drives the pathophysiology of depression. Radix Bupleuri has been used in China for over 2000 years to regulate liver-qi. Extracted from Radix Bupleuri, Saikosaponin D (SSD) is a pharmacologically active substance that has antidepressant effects. However, its underlying mechanism remains unknown.

MATERIALS AND METHODS

A chronic unpredictable mild stress (CUMS) paradigm was used as a rat model of depression. SD rats were randomly assigned to a normal control (NC) group or one exposed to a CUMS paradigm. Of the latter group, rats were assigned to four subgroups: no treatment (CUMS), fluoxetine-treated (FLU), high-dose and low-dose SSD-treated (SSDH and SSDL). SSD was orally administrated of 1.50 mg/kg and 0.75 mg/kg/days for three weeks in the SSDH and SSDL groups, respectively. Fluoxetine was administrated at a dose of 2.0 mg/kg/days. SSD's antidepressant effects were assessed using the open field test, forced swim test, and sucrose preference test. Glutamate levels were quantified by ELISA. Western blot and immunochemical analyses were conducted to quantify proteins in the Homer protein homolog 1 (Homer1)-metabotropic glutamate receptor 5 (mGluR5) and mammalian target of rapamycin (mTOR) pathways in the hippocampal CA1 region. To measure related gene expression, RT-qPCR was employed.

RESULTS

CUMS-exposed rats treated with SSD exhibited increases in food intake, body weight, and improvements in the time spent in the central are and total distance traveled in the OFT, and less pronounced pleasure-deprivation behaviors. SSD also decreased glutamate levels in CA1. In CA1 region of CUMS-exposed rats, SSD treatment increased mGluR5 expression while decreasing Homer1 expression. SSD also increased expressions of postsynaptic density protein 95 (PSD95) and synapsin I (SYP), and the ratios of p-mTOR/mTOR, p-p70S6k/p70S6k, and p-4E-BP1/4E-BP1 in the CA1 region in CUMS-exposed rats.

CONCLUSIONS

SSD treatment reduces glutamate levels in the CA1 region and promotes the expression of the synaptic proteins PSD-95 and SYP via the regulation of the Homer1-mGluR5 and downstream mTOR signaling pathways. These findings suggest that SSD could act as a natural neuroprotective agent in the prevention of depression.

Specific and cumulative lifetime stressors in the aetiology of major depression: A longitudinal community-based population study

AIMS

Early-life stressful circumstances (i.e. childhood maltreatment) coupled with stressful events later in life increase the likelihood of subsequent depression. However, very few studies have been conducted to examine the specific and cumulative effects of these stressors in the development of depression. There is also a paucity of research that simultaneously considers the role of biological factors combined with psychosocial stressors in the aetiology of depression. Guided by the biopsychosocial model proposed by Engel, the present study aims to examine to what extent the experience of stressors across the lifespan is associated with depression while taking into account the role of genetic predispositions.

METHODS

Data analysed were from the Social and Psychiatric Epidemiology Catchment Area of the Southwest of Montreal (ZEPSOM), a large-scale, longitudinal community-based cohort study. A total of 1351 participants with complete information on the lifetime diagnoses of depression over a 10-year follow-up period were included in the study. Stressful events across the lifespan were operationalised as specific, cumulative and latent profiles of stressful experiences. Latent profile analysis (LPA) was used to explore the clustering of studied stressors including childhood maltreatment, poor parent-child relationship, and stressful life events. A polygenetic risk score was calculated for each participant to provide information on genetic liability. Multivariate logistic regression was used to examine the association between specific, cumulative and latent profiles of stressors and subsequent depression.

RESULTS

We found that different subtypes of childhood maltreatment, child-parent bonding and stressful life events predicted subsequent depression. Furthermore, a significant association between combined effects of cumulative stressful experiences and depression was found [odds ratio (OR) = 1.20, 95% confidence interval (CI): 1.12-1.28]. Three latent profiles of lifetime stressors were identified in the present study and named as 'low-level of stress' (75.1%), 'moderate-level of stress' (6.8%) and 'high-level of stress' (18.1%). Individuals with a 'high-level of stress' had a substantially higher risk of depression (OR = 1.80, 95% CI: 1.08-3.00) than the other two profiles after adjusting for genetic predispositions, socio-demographic characteristics, and health-related factors.

CONCLUSIONS

While controlling for genetic predispositions, the present study provides robust evidence to support the independent and cumulative as well as compositional effects of early- and later-on lifetime psychosocial stressors in the subsequent development of depression. Consequently, mental illness prevention and mental health promotion should target the occurrence of stressful events as well as build resilience in people so they can better cope with stress when it inevitably occurs.

Xiaoyaosan Alleviates Hippocampal Glutamate-Induced Toxicity in the CUMS Rats via NR2B and PI3K/Akt Signaling Pathway

Purpose: It is revealed that Xiaoyaosan could reduce glutamate level in the hippocampus of depressed rats, whose metabolism leads to the pathophysiology of depression. However, the underlying mechanism remains unclear. This study aims to explore the effect of Xiaoyaosan on glutamate metabolism, and how to regulate the excitatory injury caused by glutamate. Methods: Rats were induced by chronic unpredictable mild stress, then divided into control, vehicle (distilled water), Xiaoyaosan, fluoxetine, vehicle (DMSO), Xiaoyaosan + Ly294002 and Ly294002 groups. Ly294002 was microinjected into the lateral ventricular catheterization at 5 mM. Xiaoyaosan (2.224 g/kg) and fluoxetine (2.0 mg/kg) were orally administered for three weeks. The open field test (OFT), forced swimming test (FST), and sucrose preference test (SPT) were used to assess depressive behavior. The glutamate and corticosterone (CORT) levels were detected by ELISA. Western blot, immunochemistry or immunofluorescence were used to detect the expressions of NR2B, MAP2, PI3K and P-AKT/Akt in the hippocampal CA1 region. The mRNA level of MAP2, NR2B and PI3K were detected by RT-qPCR. Results: Compared to the rats in control group, body weight and food intake of CUMS rats was decreased. CUMS rats also showed depression-like behavior as well as down regulate the NR2B and PI3K/Akt signaling pathway. Xiaoyaosan treatments could increase food intake and body weight as well as improved time spent in the central area, total distance traveled in the OFT. Xiaoyaosan could also decrease the immobility time as well as increase the sucrose preference in SPT. Moreover, xiaoyaosan decreased the level of glutamate in the hippocampal CA1 region and serum CORT in CUMS rats. Furthermore, xiaoyaosan improved the expression of MAP2 as well as increased the expression of NR2B, PI3K and the P-AKT/AKT ratio in the hippocampal CA1 region in the CUMS rats. Conclusion: Xiaoyaosan treatment can exert the antidepressant effect by rescuing hippocampal neurons loss induced by the glutamate-mediated excitotoxicity in CUMS rats. The underlying pathway maybe through NR2B and PI3K/Akt signaling pathways. These results may suggest the potential of Xiaoyaosan in preventing the development of depression.

Neuropharmacological and antidepressant-like effects of ZY-1408: A novel serotonin/norepinephrine reuptake inhibitor and serotonin receptor 2C antagonist

Depression is a common mental illness and leading cause of disability. Most current antidepressants are associated with significant limitations, and in particular, a delayed onset and low rate of efficacy. Consequently, there remains an ongoing need for antidepressants that are either more effective or better tolerated than existing standards. We previously identified ZY-1408 as a drug with a novel chemical structure and potential anti-depressant-like activity. Specifically, ZY-1408 is a novel serotonin 2C (5-HT_2C) receptor antagonist and serotonin/norepinephrine (5-HT/NE) reuptake inhibitor. In this study, we further investigated the antidepressant-like efficacy of ZY-1408 using in vitro and in vivo behavioral tests. ZY-1408 showed 5-HT_2C receptor antagonist and 5-HT/NE reuptake inhibitor properties in vitro. Meanwhile, ZY-1408 decreased immobility in vivo in a dose-dependent manner in rats (via the forced-swim test) and mice (via the tail-suspension test). The behavioral test results do not appear to result from stimulation of locomotor activity. In chronically stressed rats, repeated ZY-1408 treatment significantly reversed depressive-like behavior, including reduced sucrose preference, decreased locomotor activity, and prolonged time to begin eating. Furthermore, in vivo microdialysis showed that administration of ZY-1408 significantly increased extracellular concentrations of 5-HT and NE in the hippocampus of freely moving rats. Thus, ZY-1408 is a potent and orally active 5-HT_2C receptor antagonist and 5-HT/NE reuptake inhibitor with antidepressant-like activity in rodents.

Anti-stress effects of the hydroalcoholic extract of Rosa gallica officinalis in mice

Rosa gallica, a plant of the Rosa genus, has been used widely since the 13^th century and is cultivated in many areas as a medicinal plant for the preparation of herbal medicines. However, details of the neuropsychological effects of R. gallica remain unclear; therefore we aimed to investigate the neuropsychological effects of a water-soluble extract of R. gallica in male C57BL/6N mice under normal conditions and under chronic stress. We administered a water-soluble extract of R. gallica to mice and performed a series of behavioral experiments to compare the treated animals with the untreated controls. No significant differences in activity level, anxiety-like behavior, depression-like behavior, body weight, and body temperature were observed between R. gallica-treated mice and control mice. However, in mice subjected to chronic stress, the observed decrease in activity was smaller in the R. gallica-treated mice than in the control mice. The oral administration of R. gallica did not affect the normal behavior of mice. However, when the mice were subjected to stress, R. gallica exerted an anti-stress effect. Therefore, R. gallica has potential as a medicinal plant for the purpose of stress prevention.

Profiling Proteins in the Hypothalamus and Hippocampus of a Rat Model of Premenstrual Syndrome Irritability

Premenstrual syndrome (PMS) refers to several physical and mental symptoms (such as irritability) commonly encountered in clinical gynaecology. The incidence of PMS has been increasing, attracting greater attention from medical fields. However, PMS pathogenesis remains unclear. This study employed two-dimensional gel electrophoresis (2DE) for proteomic map analysis of the hypothalamus and hippocampus of rat models of premenstrual syndrome (PMS) irritability. Matrix-assisted laser desorption/ionisation time of flight mass spectroscopy (MALDI-TOF-MS) was used to identify proteins possibly related with PMS irritability. Baixiangdan, a traditional Chinese medicine effective against PMS irritability, was used in the rat model to study putative target proteins of this medicine. The hypothalamus and hippocampus of each group modelling PMS displayed the following features: decreased expression of Ulip2, tubulin beta chain 15, α actin, and interleukin 1 receptor accessory protein; increased expression of kappa-B motif-binding phosphoprotein; decreased expression of hydrolase at the end of ubiquitin carboxy, albumin, and aldolase protein; and increased expression of M2 pyruvate kinase, panthenol-cytochrome C reductase core protein I, and calcium-binding protein. Contrasting with previous studies, the current study identified new proteins related to PMS irritability. Our findings contribute to understanding the pathogenesis of PMS irritability and could provide a reference point for further studies.

The chronic mild stress (CMS) model of depression: History, evaluation and usage

Now 30 years old, the chronic mild stress (CMS) model of depression has been used in >1300 published studies, with a year-on-year increase rising to >200 papers in 2015. Data from a survey of users show that while a variety of names are in use (chronic mild/unpredictable/varied stress), these describe essentially the same procedure. This paper provides an update on the validity and reliability of the CMS model, and reviews recent data on the neurobiological basis of CMS effects and the mechanisms of antidepressant action: the volume of this research may be unique in providing a comprehensive account of antidepressant action within a single model. Also discussed is the use of CMS in drug discovery, with particular reference to hippocampal and extra-hippocampal targets. The high translational potential of the CMS model means that the neurobiological mechanisms described may be of particular relevance to human depression and mechanisms of clinical antidepressant action.

Oxidative stress: a potential link between emotional wellbeing and immune response

Emotional wellbeing is central to normal health and good living. Persistent psychological stress often disrupts emotional wellbeing and triggers onset of neuropsychiatric ailments. An integrated, multisystemic stress response involving neuroinflammatory, neuroendocrine and metabolic cascades seem to have some causative links. Of particular interest are the neuroinflammatory processes. Psychological stress has been suggested to negatively affect normal functioning of the immune system contributing to the pathophysiology of some neuropsychiatric conditions. Thus examination of the interaction between the immune system and the central nervous system is likely to reveal molecular targets critical for development of potential therapeutic and preventive measures. This review is a summarized discussion of evidence linking impact of psychological stress on the immune system, with a particular emphasis on oxidative stress mechanisms by which mental stress potentially impacts immune function leading to activation of multiple cascades resulting in subsequent manifestation of psychiatric symptomologies.

Chronic administration of bacopa monniera increases BDNF protein and mRNA expressions: a study in chronic unpredictable stress induced animal model of depression

OBJECTIVE

The present study aimed to investigate whether graded doses of Bacopa Monniera (BM) extract could produce antidepressant-like effects in chronic unpredictable stress (CUS) induced depression in rats and its possible mechanism(s).

METHODS

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

RESULTS

Exposure to CUS for 4 weeks caused depression-like behavior in rats, as indicated by significant decreases in sucrose consumption, locomotor activity and escape latency. In addition, it was found that BDNF protein and mRNA levels in the hippocampus and frontal cortex were lower in CUS-treated rats, as compared to controls. Daily administration of the graded doses of BM extract during the 4-week period of CUS significantly suppressed behavioral changes and attenuated the CUS-induced decrease in BDNF protein and mRNA levels in the hippocampus and frontal cortex.

CONCLUSION

The results suggest that BM extract alleviates depression induced by CUS. Present study also confirms that 80-120 mg/kg doses of BM extract have significantly higher antidepressant-like activity.

Mechanistic study on the antidepressant-like effect of danggui-shaoyao-san, a chinese herbal formula

Danggui-Shaoyao-San (DSS), a famous Chinese herbal formula, has been widely used in the treatment of various diseases. Previous studies have shown that DSS produces antidepressant-like effect in rodents. This study aims to investigate the mechanism(s) underlying the antidepressant-like action of DDS. The results showed that DSS treatment significantly antagonized reserpine-induced ptosis in mice. In addition, DSS treatment significantly increased sucrose consumption in chronic unpredictable stress- (CUS-) treated mice. DSS treatment also markedly attenuated CUS-induced decreases in noradrenaline and dopamine concentrations in mouse brain. Furthermore, DSS treatment significantly reversed CUS-induced increase in serum malondialdehyde (MDA) content and decrease in serum superoxide dismutase (SOD) activity in mice. The results suggest that the antidepressant-like activity of DSS is probably mediated by the modulation of central monoamine neurotransmitter systems and the reduction of oxidative stress.

Activating effects of chronic variable stress in rats with different exploratory activity: association with dopamine d(1) receptor function in nucleus accumbens

BACKGROUND/AIMS

Rats display persistent behavioural phenotypes of low (LE) versus high (HE) exploratory activity in the exploration box paradigm. LE rats that prefer passive coping strategies show differential dopaminergic activity in the striatum. The main hypothesis of this study was that chronic variable stress (CVS) would have a higher impact on LE rats.

METHODS

Animals were submitted to a CVS regimen lasting 32 days that was followed by a behavioural test battery. The functional states of their dopamine D(1) and D(2) receptors were measured in the striatum and nucleus accumbens (NAcc). Cerebral oxidative metabolism was assessed via cytochrome c oxidase histochemistry in 65 brain regions.

RESULTS

CVS decreased weight gain, to a higher extent in LE rats, and lowered the sucrose preference after the first week, but habituation to the anhedonic effect had developed by the end of the experiment. CVS did not change the behavioural phenotypes initially assigned. No effect of stress on D(2) receptor function was found. Chronically stressed animals exhibited higher levels of social interaction and D(1) receptor-mediated cAMP accumulation in the NAcc, but not in the striatum. CVS was associated with higher oxidative metabolism levels in the anteroventral thalamus, median raphe nuclei and central periaqueductal grey matter. These changes after stress did not depend upon the exploratory phenotype.

CONCLUSION

This study revealed changes in brain biochemistry after habituation to CVS that might be implicated in successful adaptation to chronic stress.

Behavioral animal models of depression

Depression is a chronic, recurring and potentially life-threatening illness that affects up to 20% of the population across the world. Despite its prevalence and considerable impact on human, little is known about its pathogenesis. One of the major reasons is the restricted availability of validated animal models due to the absence of consensus on the pathology and etiology of depression. Besides, some core symptoms such as depressed mood, feeling of worthlessness, and recurring thoughts of death or suicide, are impossible to be modeled on laboratory animals. Currently, the criteria for identifying animal models of depression rely on either of the 2 principles: actions of known antidepressants and responses to stress. This review mainly focuses on the most widely used animal models of depression, including learned helplessness, chronic mild stress, and social defeat paradigms. Also, the behavioral tests for screening antidepressants, such as forced swimming test and tail suspension test, are also discussed. The advantages and major drawbacks of each model are evaluated. In prospective, new techniques that will be beneficial for developing novel animal models or detecting depression are discussed.

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

AIM OF THE STUDY

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Models of depression

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

Effects of peony glycosides on mice exposed to chronic unpredictable stress: further evidence for antidepressant-like activity

ETHNOPHARMACOLOGY RELEVANCE

Peony, the processed root of Paeonia lactiflora Pall. (Ranunculaceae), is a component herb of many traditional formulae for the treatment of depression-like disorders.

AIM OF THE STUDY

The present study aimed to investigate whether the total glycosides of peony (TGP) could prevent depression induced by chronic stress.

MATERIALS AND METHODS

Mice were subjected to an experimental setting of chronic unpredictable stress (CUS). The effect of TGP treatment on CUS-induced depression was examined by measuring behavioral and neurochemical parameters of depression and the antioxidant status of brain tissue.

RESULTS

CUS-induced depression, as indicated by a significant increase in immobility time in the tail suspension test, was associated with increases in the activities of monoamine oxidases, depletion of reduced glutathione, and an increase in malondialdehyde level, in mice brains. TGP treatment alleviated the extent of CUS-induced depression and the associated impairment of antioxidant status in the mouse brain.

CONCLUSION

The results suggest that TGP alleviates depression induced by chronic unpredictable stress. The antidepressant-like activity of TGP is probably mediated by inhibition of monoamine oxidases and the attenuation of oxidative stress in mouse brain.

Chronic stress impairs spatial memory and motivation for reward without disrupting motor ability and motivation to explore

This study uses an operant, behavioral model to assess the daily changes in the decay rate of short-term memory, motivation, and motor ability in rats exposed to chronic restraint. Restraint decreased reward-related motivation by 50% without altering memory decay rate or motor ability. Moreover, chronic restraint impaired hippocampal-dependent spatial memory on the Y maze (4-hr delay) and produced CA3 dendritic retraction without altering hippocampal-independent maze navigation (1-min delay) or locomotion. Thus, mechanisms underlying motivation for food reward differ from those underlying Y maze exploration, and neurobiological substrates of spatial memory, such as the hippocampus, differ from those that underlie short-term memory. Chronic restraint produces functional, neuromorphological, and physiological alterations that parallel symptoms of depression in humans.

Stress models of depression: Forming genetically vulnerable strains

Among the most useful models for depressive disorders are those, which involve a stress induced change in behaviour. Learned helplessness is one such model and is induced through exposure to uncontrollable and unpredictable aversive events. Learned helplessness as induced in rats using foot shock is well characterized and has good face validity and predictive validity as a model of depression, including alterations in HPA axis activity and REM sleep characteristic of depression. The data concerning the validity will be briefly reviewed. The model can also be used to look at the role of genetics through selective breeding. These studies will be reviewed and the utility of the genetic strains for understanding the interaction of stress and affect will be examined. A second model of depression using exposure to chronic stress also has high face and predictive validity. A new form of this approach, recently described, also is suitable for the examination of genetic factors leading to depressive like behaviour and this will be presented.

Tranylcypromine, but not moclobemide, prolongs the inhibitory action of dopamine on midbrain dopaminergic neurons: an in vitro electrophysiological study

The degradation of dopamine by monoamine oxidase (MAO) enzymes plays an important role in the function of dopamine receptors in the central nervous system. Accordingly, it has already been reported that the blockade of MAO by specific inhibitors prolongs the effects of dopamine on its receptors. By using intracellular electrophysiological recordings, here we report that the irreversible MAO A and B inhibitor tranylcypromine, but not the reversible MAO A inhibitor moclobemide, potentiates DA responses in rat midbrain dopaminergic neurones maintained in vitro. Moclobemide was not effective even when the MAO B enzymes were additionally blocked by the MAOI deprenyl. Thus, our electrophysiological findings confirm that the degradation DA is very important to control the effects of this catecholamine at a cellular level. Furthermore, they demonstrate that tranylcypromine potentiates DA neurotransmission while moclobemide is devoid of dopaminergic action in an in vitro condition. The phenomena reported above support the hypothesis that part of the antidepressant and antiparkinsonian effects of tranylcypromine depend on an action on DA transmission.

Sucrose and quinine intake by maternally-deprived and control rhesus monkeys

Clinical depression is often characterized by a loss of interest or pleasure in formerly enjoyable activities. Analogs of anhedonia are established in rats, but the generality of this phenomenon to other species is unknown. Maternally-deprived rhesus macaques show a wide range of behavioral abnormalities that are reversed by chronic antidepressant treatment. We tested consumption by maternally deprived versus control macaques of sweetened (seven sucrose concentrations) or bitter water (four quinine concentrations) versus plain water to evaluate a non-human primate model of depression for signs of anhedonia. All monkeys consumed more sweetened than tap water, but maternally-deprived monkeys had a diminished preference for sweetened water than did controls. However, maternally deprived animals consumed more bitter water than did controls. Baseline fluid consumption did not differ. The data suggest that 'anhedonia' in animal models may be secondary to a generally attenuated responsiveness to stimuli, rather than a unitary reduction in responsiveness to the appetitive properties of stimuli. We conclude that maternally-deprived rhesus monkeys do not display gustatory signs of anhedonia, but rather of insensitivity to gustatory stimuli.

Chronic social stress conditions differentially modify vulnerability to amphetamine self-administration

Using social instability and cohabitation with females as chronic stress, we observed that neuroendocrine systems were differentially activated according to the experimental design. We show here that amphetamine self-administration, a paradigm to study the reinforcing effects of psychostimulants, is also differentially affected by these conditions. Coexistence with females increases amphetamine self-administration and this effect is reduced when social instability is superimposed. On the other hand, locomotor response to amphetamine is not modified by either social factor, suggesting a specific involvement of a subset of dopaminergic neurons.

Suppression of sucrose drinking by chronic mild unpredictable stress: a methodological analysis

Previous studies have demonstrated that chronic exposure of rats to a melange of ultra-mild stressors causes an antidepressant-reversible decrease in the intake of palatable weak sucrose solutions, as well as other evidence of insensitivity to rewards. In the present study, we analyzed some of the behavioral requirements for the suppression of consummatory behaviour by chronic mild stress. Rats exposed to our standard chronic mild stress protocol and tested following 20 h food and water deprivation showed a decrease in intake of 1% sucrose, but not of water or chow. The effect on sucrose intake was also present, but smaller, in non-deprived animals, and wa seen in both singly- and pair-housed animals. Experiments designed to identify the crucial elements of the stress procedure showed that one element, paired housing (in animals normally housed singly) was particularly potent. However, no one element was either necessary to cause the decrease in sucrose intake, or sufficient to maintain the impairment for longer than 4 weeks: Variety and frequency of microstressors appeared to be the essential features of procedures causing a prolonged anhedonia.

Critique: Research strategies for decoding the neurochemical basis of resistance to stress

Because stress is implicated in serious psychiatric and physical illnesses, it is important to investigate the central neurochemical mechanisms which determine resistance to stress. Two features of much existing animal work limit its relevance to man. First, it has disregarded differences between individuals, focussing instead on group means. Secondly, it has concentrated on noxious forms of stress. Preliminary studies suggest that inferences from this work may not apply to individual differences, or to non-noxious stress. Therefore, a strategy is proposed for addressing the neurochemical basis of individual differences in resistance to non-noxious stress.

Chronic imipramine treatment normalizes levels of tyrosine hydroxylase in the locus coeruleus of chronically stressed rats

Previous studies have demonstrated that chronic stress increases and antidepressant treatments decrease levels of tyrosine hydroxylase (TH) in locus coeruleus (LC). In the present study, the influence of chronic antidepressant treatment on the induction of TH immunoreactivity in response to cold stress is examined. It was found that chronic imipramine pretreatment (18 days) attenuated the induction of TH in response to cold stress, resulting in levels of TH immunoreactivity not different from control. In contrast, imipramine pretreatment for 1 or 7 days was not sufficient to normalize the stress-induced elevation of TH immunoreactivity. These findings raise the possibility that the therapeutic action of antidepressants may be derived, in part, from the ability of these treatments to normalize levels of TH and thereby the function of the NE neurotransmitter system under conditions of stress.

Chronic mild stress-induced anhedonia: a realistic animal model of depression

Chronic sequential administration of a variety of mild stressors causes a decrease in responsiveness to rewards in rats, which is reversed by chronic administration of antidepressant drugs. This paper reviews the validity of chronic mild stress-induced anhedonia as an animal model of depression, and the evidence that changes in hedonic responsiveness in this model are mediated by changes in the sensitivity of dopamine D2 receptors in the nucleus accumbens. The review opens with an analysis of the design features of animal models of depression, and ends with a brief account of other animal models of anhedonia.

Neonatal chronic stress induces subsensitivity to chronic stress in adult rats. I. Effects on forced swim behavior and endocrine responses

An influence of early stimulation on sensitivity to acute stress in adulthood has been reported. The purpose of the present work was to determine the effect of exposure of male and female rats to three models of chronic stress (unpredictable stress, cold stress and handling) from day 2 to day 15 of life on behavioral and endocrine sensitivity to chronic stresses in adulthood. The chronic stresses applied in adulthood were a model of intermittent cold stress (daily 30-min sessions at -20 degrees C for 15 days) and the Katz's model of unpredictable chronic stress (15 days). Forced swim behavior and serum concentration of the stress-sensitive hormones, corticosterone and prolactin, were chosen to investigate stress sensitivity. It was found that all neonatal treatments stimulated body weight gain, did not cause infant mortality and did not affect forced swim behavior as adult. The repetitive exposure to cold stress in adulthood did not cause major impairment of forced swim behavior and did not affect basal levels of serum corticosterone and prolactin in either control or experimental rats. These findings support the view that repeated stressors can induce behavioral and endocrine adaptation in rats. The neonatal treatments did not affect this characteristic. The exposure of control rats to the unpredictable stress model severely impaired forced swim behavior and increased basal levels of serum corticosterone and prolactin. This observation conforms to the view that standard laboratory rats cannot adapt to unpredictable chronic stress. This has been reported to cause a behavioral depression syndrome comprising forced swim deficit and endocrine alterations.(ABSTRACT TRUNCATED AT 250 WORDS)

MIF-1 is active in a chronic stress animal model of depression

MIF-1 was tested in an animal model of depression that used unpredictable chronic stress. In this paradigm, rats received either no stressors or a daily protocol of a variety of stressors for 20 days, during which time daily, intraperitoneal injections of various compounds were given. The tricyclic antidepressant imipramine (5 mg/kg) and low doses (0.1 and 1.0 mg/kg) of MIF-1 significantly increased activity and decreased defecation in an open field on day 21. No dose of naloxone (0.01-10.0 mg/kg) acted as an antidepressant. A high dose (10.0 mg/kg) of MIF-1 significantly increased the effects of chronic stress and produced hyperalgesia. Chronically-stressed rats were significantly more analgesic than controls. The results indicate that MIF-1 can act as an antidepressant in this model.

A further analysis of behavioral and endocrine effects of unpredictable chronic stress

Tolerance can develop when rats are repeatedly exposed to some predictable stressors. This does not occur, however, when rats are exposed to unpredictable chronic stress. In this study we have analyzed some behavioral and endocrine effects in male and female rats treated daily with unpredictable emotional stressor (ES-groups) or unpredictable physical stressors (PS-groups) over a 14-day period. Animals were then submitted to three behavioral tests at 24 hr intervals. Experiment 1 shows that when rats were tested in an enriched environment both total motor activity and exploration of the novel object were impaired by the PS treatment. This suggests the occurrence of motivational deficit. The fact that the PS-groups also showed increased intratest defecation suggests increased emotionality. When animals were submitted to an emergence test the PS-groups showed longer emergence latency, lower frequency of emergencies and lower time spent exploring the emergence compartment than the ES- and the C-group. This strongly supports that the PS treatment increased emotionality in rats. When ES- and PS-groups were exposed to a forced swim test they showed longer immobility duration (despair reaction) but only the PS-group displayed lower frequency of jumps (escape reaction). Results of all tests performed revealed that females were more resistant than males to the behavioral effects of the PS treatment. The day after the behavioral testing was completed, basal levels of corticosterone and prolactin were investigated in male subjects. The PS-group showed higher baseline levels of these "stress labile" hormones than the ES and the C-group.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of sucrose preference by chronic unpredictable mild stress, and its restoration by a tricyclic antidepressant

Rats exposed chronically (5-9 weeks) to a variety of mild unpredictable stressors showed a reduced consumption of and preference for saccharin or sucrose solutions. Preference deficits took at least 2 weeks to develop and were maintained for more than 2 weeks after termination of the stress regime. Sucrose preference was unaffected by 1 week of treatment with the tricyclic antidepressant DMI but returned to normal after 2-4 weeks of DMI treatment. DMI did not alter sucrose preference in unstressed animals. No significant changes were seen in saline preference either during stress or following drug treatment. DMI reduced blood corticosterone and glucose levels, but stress did not significantly alter either measure. The results are discussed in terms of an animal model of endogenous depression.

Biochemical and behavioral correlates of chronic stress: effects of tricyclic antidepressants

Using a chronic stress model of depression, the biochemical, hormonal, and neurochemical effects of chronic stress were determined in male CD-1 mice. The effects of chronic administration of three tricyclic antidepressants (TCA): chlorimipramine, amitriptyline and desmethylimipramine, as well as fluoxetine, a specific serotonin uptake inhibitor, were also evaluated. Exposure to acute noise/light stress dramatically increased motor activity (behavioral activation) in comparison with basal (unstressed) activity. However, animals with a history of chronic stress exhibited reduced basal activity levels as well as a decreased behavioral activation response to acute stress. There was also exaggerated corticosterone (CS) responding in both of these behavioral test situations attributable to prior chronic stress exposure. Chronic treatment with any of the TCAs significantly restored the behavioral activation response to acute stress and normalized CS responding in chronically stressed animals. Chronic fluoxetine treatment was ineffective. In chronically stressed, but behaviorally untested (quiescent) mice, there were no changes in CS levels, but norepinephrine (NE) and 5-hydroxyindoleacetic acid (5-HIAA) levels were increased. However, chronically stressed mice tested for basal motor activity showed large NE decreases, while those receiving acute stress exposure prior to testing showed large NE decreases and further 5-HIAA increases. There were no alterations on neurochemical parameters due to any drug treatment which could be correlated with a possible mechanism for their efficacy, although evidence suggested NE involvement. It was further proposed that the chronic stress paradigm induced conditioned neuroendocrine and neurochemical responses.

The validity of animal models of depression

Eighteen animal models of depression are reviewed in relation to three sets of validating criteria. Of the 18 models, five could only be assessed for predictive validity, seven could be assessed for predictive and face validity, and six could potentially have predictive, face and construct validity. Some traditional models (reserpine reversal, amphetamine potentiation) are rejected as invalid; the models with the highest overall validity are the intracranial self-stimulation, chronic stress and learned helplessness models in rats, and the primate separation model.

Animal model of depression: tests of three structurally and pharmacologically novel antidepressant compounds

Previous studies have identified behavioral and neuroendocrine abnormalities in chronically stressed rats which resemble some of the more prominent features of clinical depression. These abnormalities have proved responsive to pharmacotherapy by standard antidepressant drugs and related somatic treatments. Several structurally and pharmacologically atypical compounds, resembling neither standard agents, nor each other, have recently been identified as clinically effective antidepressants. There drugs do not show typical preclinical response profiles in other drug screening tests and, therefore, represent critical instances for evaluating the selectivity of the chronic stress model. Three drugs were tested, these being iprindole, bupropion, and mianserine; a tricyclic indole, propriophenone, and tetracyclic compound respectively. Four circulating measures, which previously proved most useful in discriminating antidepressant potential, and a measure of circulating corticosterone were obtained for subjects examined factorially in a 2x2x2 experimental design (chronic stress vs none, acute stress vs none, and drugs vs control). All compounds proved capable of reversing chronic stress induced behavioral deficits, and all but one compound reversed the attendant basal hypersecretion of corticosterone. These findings argue that the chronic stress model provides an accurate and selective assessment of the therapeutic potential of both standard and structurally novel compounds.

Amitriptyline and scopolamine in an animal model of depression

Adult male Sprague-Dawley rats were subjected to acute (95 dB white noise) or chronic stress, or their combination. In comparison with unstressed controls, stressed rats were more active upon several measures of open field activity. A history of chronic stress eliminated the acute stress induced activation. Concurrent treatment of chronically stressed rats with amitriptyline or scopolamine, or with a combination of both drugs resulted in selective behavioral improvement (i.e., in motor activity, latency, defecation) for amitriptyline and combined treatment rats, with significant restoration of the normal behavioral response. Scopolamine however was only marginally effective. A higher dose of scopolamine proved effective, but only with a marked disruption of baseline activity. Examination of plasma corticosterone titers indicated that chronic stress induced an elevation of basal levels and that this was reversed by amitriptyline, scopolamine, and combined drug treatment. Thus while behavioral depression and elevated corticosteroids may covary they are not identically mediated.