Stress models of depression

Repetitive transcranial magnetic stimulation (rTMS) for depressive-like symptoms in rodent animal models

Repetitive transcranial magnetic stimulation (rTMS) emerged as a non-invasive brain stimulation technique in the treatment of psychiatric disorders. Both preclinical and clinical studies as well as systematic reviews provide a heterogeneous picture, particularly concerning the stimulation protocols used in rTMS. Here, we present a review of rTMS effects in rodent models of depressive-like symptoms with the aim to identify the most relevant factors that lead to an increased therapeutic success. The influence of different factors, such as the stimulation parameters (stimulus frequency and intensity, duration of stimulation, shape and positioning of the coil), symptom severity and individual characteristics (age, species and genetic background of the rodents), on the therapeutic success are discussed. Accumulating evidence indicates that rTMS ameliorates a multitude of depressive-like symptoms in rodent models, most effectively at high stimulation frequencies (≥5 Hz) especially in adult rodents with a pronounced pathological phenotype. The therapeutic success of rTMS might be increased in the future by considering these factors and using more standardized stimulation protocols.

Chronic Stress-Induced Neuroinflammation: Relevance of Rodent Models to Human Disease

The brain is the central organ of adaptation to stress because it perceives and determines threats that induce behavioral, physiological, and molecular responses. In humans, chronic stress manifests as an enduring consistent feeling of pressure and being overwhelmed for an extended duration. This can result in a persistent proinflammatory response in the peripheral and central nervous system (CNS), resulting in cellular, physiological, and behavioral effects. Compounding stressors may increase the risk of chronic-stress-induced inflammation, which can yield serious health consequences, including mental health disorders. This review summarizes the current knowledge surrounding the neuroinflammatory response in rodent models of chronic stress-a relationship that is continually being defined. Many studies investigating the effects of chronic stress on neuroinflammation in rodent models have identified significant changes in inflammatory modulators, including nuclear factor-κB (NF-κB) and toll-like receptors (TLRs), and cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, and IL-6. This suggests that these are key inflammatory factors in the chronic stress response, which may contribute to the establishment of anxiety and depression-like symptoms. The behavioral and neurological effects of modulating inflammatory factors through gene knockdown (KD) and knockout (KO), and conventional and alternative medicine approaches, are discussed.

Transient Elevation of Plasma Glucocorticoids Supports Psilocybin-Induced Anxiolysis in Mice

While correlations between drug-induced cortisol elevation, self-reported anxiety, and treatment outcomes have been reported for human studies during psilocybin-assisted psychotherapy, the mechanistic relationship between psychedelic-associated alterations in plasma glucocorticoid responses and the time course of anxious responsiveness remains unclear. Using rodents, both time-bound manipulation of glucocorticoid concentrations and assessment of anxiety-like behaviors can be achieved. Here, 3 mg/kg IP psilocybin was found to have anxiolytic-like effects in C57BL/6 male mice at 4 h after treatment. These effects were not altered by pretreatment with a 5-HT2A antagonist but were blunted by pretreatment with a glucocorticoid receptor antagonist or suppression of psilocybin-induced corticosterone elevations. Anxiolytic-like effects were also observed at 4 h following treatment with the nonpsychedelic 5-HT2A agonist lisuride at a dose causing a similar increase in plasma glucocorticoids as that seen with psilocybin, as well as following stress-induced (via repeated injection) glucocorticoid release alone. Psilocybin's anxiolytic-like effects persisted at 7 days following administration. The long-term anxiolytic effects of psilocybin were lost when psilocybin was administered to animals with ongoing chronic elevations in plasma corticosterone concentrations. Overall, these experiments indicate that acute, resolvable psilocybin-induced glucocorticoid release drives the postacute anxiolytic-like effects of psilocybin in mice and that its long-term anxiolytic-like effects can be abolished in the presence of chronically elevated plasma glucocorticoid elevations.

COVID-19-related stressors and depression in Chinese adolescents: The effects of life history strategies and gender

PURPOSE

The COVID-19 pandemic has changed the way people live, affecting both their physical and mental health. Adolescents are vulnerable to the stress of the pandemic, and may experience indicators of psychological distress, such as depression. This study aimed to examine the impact of COVID-19-related stressors on depression and the mediating role of life history strategies.

METHODS

A two-wave longitudinal study was conducted with 1123 adolescents (51.20% girls, M_age = 14.30) recruited from three junior high schools in the Northeastern province of China. Adolescents' life history strategies, depressive symptoms, and demographic variables were assessed at Time 1 (November 2019) and Time 2 (August 2020), and adolescents' experience of COVID-19-related stressors was assessed at Time 2. None of participants was infected by COVID-19 virus.

RESULTS

COVID-19-related stressors were positively associated with depressive symptoms at Time 2 (β = 0.08, p < 0.01), after controlling for gender, age, SES and depressive symptoms at Time 1. And life history strategies partially mediated the relation of pandemic stress to depression (indirect effect = 0.02, p < 0.05, 95% CI [0.004, 0.034]). There were no gender differences in the relations between stress on depression.

LIMITATIONS

The sample was from a district where the pandemic was not very severe, which may limit generalizability of the results.

CONCLUSIONS

This study revealed that COVID-19-related stressors may have a long-term impact on adolescents, increasing depression through speeding up their life history strategies. Interventions should focus on life history strategies, particularly cognitive style, among adolescents during and after the pandemic.

Antidepressant-like Effect of 3-n-Butylphthalide in Rats Exposed to Chronic Unpredictable Mild Stress: Modulation of Brain-Derived Neurotrophic Factor Level and mTOR Activation in Cortex

3-n-Butylphthalide (NBP), an extract from seeds of Apium graveolens Linn. (Chinese celery), has been demonstrated to have antidepressant effects in suspension chronic-stressed rats by our group. The purpose of this study was to investigate the possible involvement of brain-derived neurotrophic factor (BDNF) and mammalian target of rapamycin (mTOR) in the antidepressant mechanism of NBP. Chronic unpredictable mild stress (CUMS) was applied for 6 weeks to induced a depressive-like behavior, characterized by decreased locomotor activity, sucrose preference and the NE, DA and 5-HT levels in cortex. Oral treatment with NBP (30 or 100 mg/kg, p.o.), similarly to fluoxetine (2 mg/kg, p.o.), can prevention of these alterations. The NBP (30 or 100 mg/kg, p.o.) reversed the decrease in the BDNF, p-ERK, mTOR and synapsin-1 protein levels in rat cortex caused by CUMS. And rapamycin, an mTOR inhibitor, completely inhibited the antidepressant-like activity of NBP in vivo. In conclusion, these findings indicate that NBP treatment attenuated the depression-like behaviors through the modulation of serotonergic system and BDNF-ERK-mTOR signaling in rat.

Escitalopram Targets Oxidative Stress, Caspase-3, BDNF and MeCP2 in the Hippocampus and Frontal Cortex of a Rat Model of Depression Induced by Chronic Unpredictable Mild Stress

In recent years, escitalopram (ESC) has been suggested to have different mechanisms of action beyond its well known selective serotonin reuptake inhibition. The aim of this study is to investigate the effects of escitalopram on oxidative stress, apoptosis, brain-derived neurotrophic factor (BDNF), Methyl-CpG-binding protein 2 (MeCP2), and oligodendrocytes number in the brain of chronic unpredictable mild stress-induced depressed rats. The animals were randomised in four groups (8 in each group): control, stress, stress + ESC 5 and stress + ESC 5/10. ESC was administered for 42 days in a fixed dose (5 mg/kg b.w.) or in an up-titration regimen (21 days ESC 5 mg/kg b.w. then 21 days ESC 10 mg/kg b.w.). Sucrose preference test (SPT) and elevated plus maze (EPM) were also performed. ESC improved the percentage of sucrose preference, locomotion and anxiety. ESC5/10 reduced the oxidative damage in the hippocampus and improved the antioxidant defence in the hippocampus and frontal lobe. ESC5/10 lowered caspase 3 activity in the hippocampus. Escitalopram had a modulatory effect on BDNF and the number of oligodendrocytes in the hippocampus and frontal lobe and also improved the MeCP2 expressions. The results confirm the multiple pathways implicated in the pathogenesis of depression and suggest that escitalopram exerts an antidepressant effect via different intricate mechanisms.

Melatonin attenuated the behavioral despair induced by acute neurogenic stress through blockade of N-methyl D-aspartate receptors in mice

It has been well documented that administration of melatonin could reveal antidepressant-like effect in rodents. However, the protective effect of melatonin on stress-induced depression/anxiety and its underlying mechanism is yet to be understood. In this regard, in the current study, acute foot-shock stress (FSS) was used to evaluate the antidepressant-like effect of melatonin on neurogenic stress-induced depression in mice. Behavioral evaluation was done by using the forced swimming test (FST) and Open-field test (OFT). Melatonin, MK-801, and ketamine (NMDA receptor antagonists), and NMDA (NMDA receptor agonist) were used to elucidate any association between melatonin and NMDA pathway in behavioral despair induced by acute-FSS. Applying acute-FSS to mice significantly induced depressant-like behavior in FST without any significant impact on locomotor activity in the OFT. We observed that melatonin (dose-dependently) significantly improved the depressant-like effect of FSS, but it did not impact the locomotion in animals. Acute injection of MK-801 at sub-effective doses (0.01 mg/kg) or ketamine (0.1 mg/kg) potentiated the antidepressant-like effect of a sub-effective dose of melatonin. However, the sub-effective dose of NMDA (30 mg/kg) abolished the protective effect of melatonin on the behavioral profile of stressed animals. Our results could reflect the antidepressant-like effect of melatonin on neurogenic stress-induced depressive behaviors in mice. Also, our results showed that NMDA receptors could be involved in the antidepressant-like effect of melatonin.

Therapeutic potential of mangiferin in the treatment of various neuropsychiatric and neurodegenerative disorders

Xanthones are important chemical class of bioactive products that confers therapeutic benefits. Of several xanthones, mangiferin is known to be distributed widely across several fruits, vegetables and medicinal plants. Mangiferin has been shown to exert neuroprotective effects in both in-vitro and in-vivo models. Mangiferin attenuates cerebral infarction, cerebral edema, lipid peroxidation (MDA), neuronal damage, etc. Mangiferin further potentiate levels of endogenous antioxidants to confer protection against the oxidative stress inside the neurons. Mangiferin is involved in the regulation of various signaling pathways that influences the production and levels of proinflammatory cytokines in brain. Mangiferin cosunteracted the neurotoxic effect of amyloid-beta, MPTP, rotenone, 6-OHDA etc and confer protection to neurons. These evidence suggested that the mangiferin may be a potential therapeutic strategy for the treatment of various neurological disorders. The present review demonstrated the pharmacodynamics-pharmacokinetics of mangiferin and neurotherapeutic potential in several neurological disorders with underlying mechanisms.

Welfare Assessment and Identification of the Associated Risk Factors Compromising the Welfare of Working Donkeys (Equus asinus) in Egyptian Brick Kilns

Simple Summary

Working donkeys suffer from many welfare challenges associated with, for example, physical health, poor living conditions, and unfair treatment. The aim of this study is to assess the welfare of working donkeys in the El-Saf brick kilns, identifying the health risk factors, establishing welfare regulations, enacting legislation, and implementing welfare strategies aimed at improving the quality of life of donkeys and owners within communities. The study found that working donkeys in Egypt suffer from many types of wounds associated with parts of the harness, such as the saddle, breeching, and neck collar, and with excessive force/beating, the shaft of the cart, and improper tethering. They often live in unhealthy housing situations, and a high percentage suffer from aggressive behavior. The study found an association between these health risks, behavioral parameters, and body condition in Egyptian working donkeys. Body condition was affected by multiple factors, including the number of hours worked/day, the number of donkeys/kilns, the distance from loading to unloading bricks in an oven, and the amount of concentrated food/donkey.

Abstract

Donkeys are a cornerstone in human existence, having played an important role throughout history in different economic activities, such as working in brick kilns in Egypt. This study was conducted from January 2017 to the end of April 2017 in the El-Saf brick kilns, which are located to the south of the Giza Governorate and 57 Km away from Cairo. Physical clinical health and behavior data were collected from 179 donkeys spanning over a random sample of 20 brick kilns selected from the El-Saf brick kilns. Behavioral, physical health, harness, and environmental parameters were assessed and recorded. The study found that 80 ± 3% (n = 179) of kiln donkeys have some type of wound, and the most serious wound is a beating wound (49 ± 3.7%), which is caused by drivers hitting the donkeys. The drivers are mostly children, who have insufficient knowledge, skills, and attitudes to effectively communicate with their donkeys and no motivation to enhance the welfare of these equids. Other wounds are related to the harness, such as the breeching (10 ± 2.2%), saddle (43 ± 3.7%), neck collar (40 ± 3.6%), and shaft of the cart (12 ± 2.4%). A poor body condition was seen in 56 ± 3.7% of kiln donkeys. A correlation in terms of the prevalence of wounds was found between the body condition (p-value < 0.01) and/or cleanliness of the harness. There was a negative association between the body condition and wound prevalence in brick kilns (Pearson coefficient of correlation −0.71). The physical enviromental factors that affect the body condition of working donkeys are the working hours of donkeys/day, the number of donkeys in a kiln, the distance from loading to the oven, and the concentrated food/donkey (p-value < 0.01). These three variables can explain 78.85% of the variability in body conditions based on a 1–5 scale. In addition to health parameters, behavior parameters, such as the donkeys’ general attitude, reaction to observers, and chin contact are associated with the body condition (p-value < 0.01). As a consequence, it is important for the owners of working donkeys to pay attention to their body condition in order to avoid compromising their body condition and welfare.

The Wistar-Kyoto rat model of endogenous depression: A tool for exploring treatment resistance with an urgent need to focus on sex differences

Major depressive disorder (MDD) is one of the leading causes of years lived with disability and contributor to the burden of disease worldwide. The incidence of MDD has increased by ~20% in the last decade. Currently antidepressant drugs such as the popular selective serotonin reuptake inhibitors (SSRIs) are the leading form of pharmaceutical intervention for the treatment of MDD. SSRIs however, are inefficient in ameliorating depressive symptoms in ~50% of patients and exhibit a prolonged latency of efficacy. Due to the burden of disease, there is an increasing need to understand the neurobiology underpinning MDD and to discover effective treatment strategies. Endogenous models of MDD, such as the Wistar-Kyoto (WKY) rat provide a valuable tool for investigating the pathophysiology of MDD. The WKY rat displays behavioural and neurobiological phenotypes similar to that observed in clinical cases of MDD, as well as resistance to common antidepressants. Specifically, the WKY strain exhibits increased anxiety- and depressive-like behaviours, as well as alterations in Hypothalamic Pituitary Adrenal (HPA) axis, serotonergic, dopaminergic and neurotrophic systems with emerging studies suggesting an involvement of neuroinflammation. More recent investigations have shown evidence for reduced cortical and hippocampal volumes and altered glutamatergic signalling in the WKY strain. Given the growing interest in therapeutics targeting the glutamatergic system, the WKY strain presents itself as a potentially useful tool for screening novel antidepressant drugs and their efficacy against treatment resistant depression. However, despite the sexual dimorphism present in the pathophysiology and aetiology of MDD, sex differences in the WKY model are rarely investigated, with most studies focusing on males. Accordingly, this review highlights what is known regarding sex differences and where further research is needed. Whilst acknowledging that investigation into a range of depression models is required to fully elucidate the underlying mechanisms of MDD, here we review the WKY strain, and its relevance to the clinic.

Animal models of major depression: drawbacks and challenges

Major depression is a leading contributor to the global burden of disease. This situation is mainly related to the chronicity and/or recurrence of the disorder, and to poor response to antidepressant therapy. Progress in this area requires valid animal models. Current models are based either on manipulating the environment to which rodents are exposed (during the developmental period or adulthood) or biological underpinnings (i.e. gene deletion or overexpression of candidate genes, targeted lesions of brain areas, optogenetic control of specific neuronal populations, etc.). These manipulations can alter specific behavioural and biological outcomes that can be related to different symptomatic and pathophysiological dimensions of major depression. However, animal models of major depression display substantial shortcomings that contribute to the lack of innovative pharmacological approaches in recent decades and which hamper our capabilities to investigate treatment-resistant depression. Here, we discuss the validity of these models, review putative models of treatment-resistant depression, major depression subtypes and recurrent depression. Furthermore, we identify future challenges regarding new paradigms such as those proposing dimensional rather than categorical approaches to depression.

BDNF prevents central oxidative damage in a chronic unpredictable mild stress model: The possible role of PRDX-1 in anhedonic behavior

Prolonged activation of the hypothalamic-pituitary-adrenal (HPA) axis and sustained increase of glucocorticoids have been evidenced in major depression and are related to changes involving neurotrophins and markers of oxidative stress in response to inflammation. This study aimed to evaluate central measures of brain-derived neurotrophic factor (BDNF), oxidative damage and total antioxidant capacity in rats submitted to chronic unpredictable mild stress (CUMS), as well as to investigate the relationship between BDNF levels and differentially processes. For this purpose, male Wistar rats were submitted to CUMS for six weeks. Based on a sucrose preference test (SPT), the animals were divided into anhedonic or non-anhedonic clusters. Afterwards, forced swim test (FST) and open field test (OFT) were performed, and the animals were euthanized. Brain tissue was collected, followed by quantification of oxidative damage, total antioxidant capacity and BDNF levels. Anhedonic behavior was evidenced in stress-susceptible animals through decreased sucrose preference. No differences were found in FST or OFT results. We observed increased BDNF levels in the hippocampus (HPC) of animals exposed to the CUMS protocol, accompanied by decreased total antioxidant capacity, despite the absence of oxidative damage to lipids and proteins. Moreover, we used a bioinformatics approach to identify proteins involved in oxidative stress and inflammation pathways, which were differentially expressed in anhedonic animals from other studies with similar experimental protocol. expressed proteins (DEP) involved in oxidative stress and inflammatory biological Anhedonic behavior was associated with peroxiredoxin-1 (PRDX-1) up-regulation and down-regulation of proteins involved with apoptotic and inflammation signaling (RELA, ASK-1 and TAK-1) in the HPC. Taken together, these data suggest that BDNF and PRDX-1 might be involved in initial stress response, playing a compensatory role by preventing oxidative damage to lipids and proteins through the modulation of antioxidant defense after CUMS in anhedonic animals.

A study of limbic brain derived neurotrophic factor gene expression in male Sprague-Dawley rats trained on a learned helplessness task

BACKGROUND

Brain derived neurotrophic factor (BDNF) has been linked to the etiology and pathology of Major Depressive Disorder (MDD). Here, the relationship between learned helplessness (LH), a cognitive/motivational state relevant to MDD, and BDNF mRNA in various limbic regions, was investigated.

METHODS

In Sprague-Dawley male rats, LH was induced by escape training, using a triadic design of stressor controllability involving exposure to no shocks (NS), escapable shocks (ES) or yoked inescapable shocks (IES). LH was subsequently assessed in an active avoidance task, and levels of BDNF mRNA in limbic brain regions were compared across the triad following testing.

RESULTS

Although the IES group displayed greater LH, BDNF mRNA levels were lower in the hippocampus and higher in the nucleus accumbens of both IES and ES groups. In contrast, BDNF mRNA in the basolateral amygdala was elevated only in rats exposed to IES.

CONCLUSION

These results suggest that the inability to control an aversive stimulus can lead to a LH behavioural phenotype that is associated with region-specific alterations of BDNF gene expression in limbic nuclei.

Role of Chronic Stress and Exercise on Microvascular Function in Metabolic Syndrome

PURPOSE

The present study examined the effect of unpredictable chronic mild stress (UCMS) on peripheral microvessel function in healthy and metabolic syndrome (MetS) rodents and whether exercise training could prevent the vascular dysfunction associated with UCMS.

METHODS

Lean and obese (model of MetS) Zucker rats (LZR and OZR) were exposed to 8 wk of UCMS, exercise (Ex), UCMS + Ex, or control conditions. At the end of the intervention, gracilis arterioles (GA) were isolated and hung in a pressurized myobath to assess endothelium-dependent (EDD) and endothelium-independent (EID) dilation. Levels of nitric oxide (NO) and reactive oxygen species (ROS) were measured through 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate and dihydroethidium staining, respectively.

RESULTS

Compared with LZR controls, EDD and EID were lower (P = 0.0001) in LZR-UCMS. The OZR-Ex group had a higher EDD (P = 0.0001) and EID (P = 0.003) compared with OZR controls, whereas only a difference in EDD (P = 0.01) was noted between the LZR-control and LZR-Ex groups. Importantly, EDD and EID were higher in the LZR (P = 0.0001; P = 0.02) and OZR (P = 0.0001; P = 0.02) UCMS + Ex groups compared with UCMS alone. Lower NO bioavailability and higher ROS were noted in the LZR-UCMS group (P = 0.0001), but not OZR-UCMS, compared with controls. The Ex and UCMS-Ex groups had higher NO bioavailability (P = 0.0001) compared with the control and UCMS groups, but ROS levels remained high.

CONCLUSIONS

The comorbidity between UCMS and MetS does not exacerbate the effects of one another on GA EDD responses, but does lead to the development of other vasculopathy adaptations, which can be partially explained by alterations in NO and ROS production. Importantly, exercise training alleviates most of the negative effects of UCMS on GA function.

Effects of chronic unpredictable mild stress induced prenatal stress on neurodevelopment of neonates: Role of GSK-3β

Prenatal stress (PNS) has gained attention with regard to its impact on hippocampal neurogenesis in neonates which serves as a risk factor for postnatal neurodevelopmental deficits. Evidences from animal models have suggested that depression responsive hypothalamic-pituitary-adrenal (HPA) axis and its hormonal response via cortisol, is responsible for critical neurodevelopmental deficits in the offspring which is transduced due to gestational stress. But knowledge in the area of assessing the effects of maternal chronic unpredictable mild stress (CUMS) on neurogenesis and expression of some key signaling molecules in the offsprings are limited. We have used Wistar rats to induce PNS in offsprings by maternal CUMS during pregnancy. Prefrontal cortex (PFC) and hippocampus were assessed for biomarkers of oxidative stress, neurogenesis, neurodevelopmental signaling molecules and DNA damage in the male Wister offsprings. Our investigations resulted in sufficient evidences which prove how maternal psychological stress has widespread effect on the fetal outcomes via major physiological alteration in the antioxidant levels, neurogenesis, signaling molecules and DNA damage. PNS leads to the upregulation of GSK-3β which in turn inhibited mRNA and protein expressions of sonic hedgehog (SHH), β-catenin, Notch and brain derived neurotrophic factor (BDNF). The study explored multifaceted signaling molecules especially, GSK-3β responsible for crosstalks between different neurodevelopmental molecules like SHH, Notch, BDNF and β-catenin affecting neurodevelopment of the offsprings due to PNS.

Schisandrin rescues depressive-like behaviors induced by chronic unpredictable mild stress via GDNF/ERK1/2/ROS and PI3K/AKT/NOX signaling pathways in mice

The current study aimed to prove the antidepressant-like effects and the probable mechanisms of Schisandrin on depression, which induced by chronic unpredictable mild stress (CUMS) in mice. Four weeks of CUMS exposure resulted in depressive-like behavior, as indicated by the significant decrease in sucrose consumption and increase the immobility time in the forced swim test, but without any influence on the locomotor activity. Further, there were significant downregulations of GDNF/ERK1/2/ROS and PI3K/AKT/NOX signaling pathways in the hippocampus and prefrontal cortex in depressed mice. Treatment of mice with Schisandrin (30mg/kg) and Fluoxetine (10mg/kg) significantly ameliorated all the behavioral and biochemical changes induced by CUMS. These results suggest that Schisandrin produces an antidepressant-like effect in CUMS-induced mice, which possibly mediated, at least in part, by rectifying the signaling pathways of GDNF/ERK1/2/ROS and PI3K/AKT/NOX.

Neuroplasticity-related mechanisms underlying the antidepressant-like effects of traditional herbal medicines

Traditional herbal medicine can offer efficacious and safe alternative pharmacotherapies for depression. The ability of an herbal medicine to produce neuroadaptive processes, that enhance neuroplasticity and cellular resilience in response to chronic stress, may point to its antidepressant potential. We suggest that among many investigated herbal medicines, those that can enhance neuroplasticity may have stronger therapeutic potential. The current article presents a summary of traditional herbal medicines, which are thought to exert antidepressant-like effects in chronic stress models via neuroplasticity enhancement. Brain-derived neurotrophic factor (BDNF) is a biomarker for neuroplasticity-related mechanisms compromised in depression and recovered by conventional antidepressants, including synaptic plasticity, cell survival, neurogenesis and spine formation. We therefore presumed that if an herbal medicine up-regulates BDNF in the hippocampus and/or prefrontal cortex (PFC), its antidepressant-like effect is mediated, at least partially, via neuroplasticity-related mechanisms. Literature search was performed using the general terms depression, stress, neuroplasticity and herbal medicines. Screening of retrieved preclinical studies revealed 30 traditional herbal medicines: 8 single herbs, 15 bioactive constituents, and 7 herbal formulas. The antidepressant-like effects of these medicines were associated with reversal of chronic stress-induced impairment in neuroplasticity, most notably by BDNF up-regulation, activation of BDNF downstream signaling pathways and increase in neurogenesis in the hippocampus and/or PFC/frontal cortex. In light of the ability of these medicines to enhance neuroplasticity, we suggest that they may be suitable candidates for clinical investigation in depressed individuals. Once their efficacy, tolerability and safety will be substantiated, they may serve as natural alternatives to conventional antidepressants.

Baicalin ameliorates chronic unpredictable mild stress-induced depressive behavior: Involving the inhibition of NLRP3 inflammasome activation in rat prefrontal cortex

Abnormal activation of nucleotide-binding domain, leucine-rich repeat, pyrin domain containing protein 3 (NLRP3) inflammasome could induce inflammation in the central nervous system and result in the hyperactivity of HPA axis, which were involved in the pathophysiology of depression. Baicalin, a major polyphenol compound extracts from Scutellaria radix roots, has been previously confirmed to normalize the hyperactivity of HPA axis in rats received chronic mild stress. However, its antidepressant effects and mechanisms are remains unclear in chronic unpredictable mild stress (CUMS) model of depression. In this study, CUMS treated rats showed a notable depressive-like behavior (decreased sucrose intake and locomotor activity, and increased immobility time), and significant increase in the activation of NLRP3 inflammasome and the levels of pro-inflammatory cytokines (IL-1β and IL-6) in rat prefrontal cortex. Treatment with baicalin (20, 40mg/kg) significantly reversed these changes. The present study confirmed that baicalin has antidepressant effect and its mechanisms likely related to the inhibition of NLRP3 inflammasome activation in rat prefrontal cortex.

Neurosteroids and potential therapeutics: Focus on pregnenolone

Considerable evidence from preclinical and clinical studies shows that steroids and in particular neurosteroids are important endogenous modulators of several brain-related functions. In this context, it remains to be elucidated whether neurosteroids may serve as biomarkers in the diagnosis of disorders and might have therapeutic potential for the treatment of these disorders. Pregnenolone (PREG) is the main steroid synthesized from cholesterol in mammals and invertebrates. PREG has three main sources of synthesis, the gonads, adrenal glands and brain and is submitted to various metabolizing pathways which are modulated depending on various factors including species, steroidogenic tissues and steroidogenic enzymes. Looking at the whole picture of steroids, PREG is often known as the precursor to other steroids and not as an active steroid per se. Actually, physiological and brain functions have been studied mainly for steroids that are very active either binding to specific intracellular receptors, or modulating with high affinity the abundant membrane receptors, GABAA or NMDA receptors. However, when high sensitive and specific methodological approaches were available to analyze low concentrations of steroids and then match endogenous levels of different steroid metabolomes, several studies have reported more significant alterations in PREG than in other steroids in extraphysiological or pathological conditions, suggesting that PREG could play a functional role as well. Additionally, several molecular targets of PREG were revealed in the mammalian brain and beneficial effects of PREG have been demonstrated in preclinical and clinical studies. On this basis, this review will be divided into three parts. The first provides a brief overview of the molecular targets of PREG and the pharmacological effects observed in animal and human studies. The second will focus on the possible functional role of PREG with an outline of the modulation of PREG levels in animal and in human research. Finally, the review will highlight the possible therapeutic uses of PREG that point towards the development of pregnenolone-like molecules.

Fluoxetine reverses the behavioral despair induced by neurogenic stress in mice: role of N-methyl-d-aspartate and opioid receptors

Opioid and N-methyl-d-aspartate (NMDA) receptors mediate different effects of fluoxetine. We investigated whether opioid and NMDA receptors are involved in the protective effect of fluoxetine against the behavioral despair induced by acute physical stress in male mice. We used the forced swimming test (FST), tail suspension test (TST), and open-field test (OFT) for behavioral evaluation. We used fluoxetine, naltrexone (opioid receptor antagonist), MK-801 (NMDA receptor antagonist), morphine (opioid receptor agonist), and NMDA (NMDA receptor agonist). Acute foot-shock stress (FSS) significantly induced behavioral despair (depressive-like) and anxiety-like behaviors in tests. Fluoxetine (5 mg/kg) reversed the depressant-like effect of FSS, but it did not alter the locomotion and anxiety-like behavior in animals. Acute administration of subeffective doses of naltrexone (0.3 mg/kg) or MK-801 (0.01 mg/kg) potentiated the antidepressant-like effect of fluoxetine, while subeffective doses of morphine (1 mg/kg) and NMDA (75 mg/kg) abolished this effect of fluoxetine. Also, co-administration of subeffective doses of naltrexone (0.05 mg/kg) and MK-801 (0.003 mg/kg) with fluoxetine (1 mg/kg) induced a significant decrease in the immobility time in FST and TST. Our results showed that opioid and NMDA receptors (alone or in combination) are involved in the antidepressant-like effect of fluoxetine against physical stress.

Antidepressant-like effects of albiflorin extracted from Radix paeoniae Alba

ETHNOPHARMACOLOGY RELEVANCE

Albiflorin, a monoterpene glycoside, is a main component of Radix paeoniae Alba, which could be a Chinese herbal medicine used in the treatment of psychiatric disorders. However, the exact role of albiflorin in depression is poorly understood.

AIM OF THE STUDY

The current study aimed to evaluate the antidepressant effect of albiflorin in mice and rats, and the possible mechanism was also determined.

MATERIALS AND METHODS

The antidepressant-like effects of albiflorin was determined by using animal models of depression including forced swim and tail suspension tests in mice and chronic unpredictable stress (CUS) in rats. The acting mechanism was explored by determining the effect of albiflorin on the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus by western blot and the levels of monoamine in the hippocampus by HPLC.

RESULTS

Our results showed that 7 days treatment with albiflorin significantly decreased immobility time in the forced swimming test (FST) and the tail suspension test (TST) at doses of 3.5, 7.0 and 14.0mg/kg without alter the locomotor activity in mice. Moreover, western blot analysis showed that albiflorin could increase the expression of BDNF in the hippocampus. We further exposed rats to a chronic unpredictable stress (CUS) protocol for a period of 35d to induce depressive-like behaviors. We found that chronic treatment with albiflorin, at doses of 7.0 and 14.0mg (i.g., once daily for 35d), restored the sucrose preference in CUS rats. In the open-field test, albiflorin significantly increased the number of crossings and rearings in the CUS rats at three doses. Moreover, chronic treatment with albiflorin up-regulated the hippocampal BDNF expression levels and the hippocampal 5-HT, 5-HIAA, and NA levels.

CONCLUSION

Albiflorin produced significant antidepressant-like effects, which were closely related to the hippocampal 5-HT/NE increase and BDNF expression. Our data indicated that albiflorin could be a potential anti-depressant drug.

Whole-Brain Mapping of Neuronal Activity in the Learned Helplessness Model of Depression

Some individuals are resilient, whereas others succumb to despair in repeated stressful situations. The neurobiological mechanisms underlying such divergent behavioral responses remain unclear. Here, we employed an automated method for mapping neuronal activity in search of signatures of stress responses in the entire mouse brain. We used serial two-photon tomography to detect expression of c-FosGFP - a marker of neuronal activation - in c-fosGFP transgenic mice subjected to the learned helplessness (LH) procedure, a widely used model of stress-induced depression-like phenotype in laboratory animals. We found that mice showing "helpless" behavior had an overall brain-wide reduction in the level of neuronal activation compared with mice showing "resilient" behavior, with the exception of a few brain areas, including the locus coeruleus, that were more activated in the helpless mice. In addition, the helpless mice showed a strong trend of having higher similarity in whole-brain activity profile among individuals, suggesting that helplessness is represented by a more stereotypic brain-wide activation pattern. This latter effect was confirmed in rats subjected to the LH procedure, using 2-deoxy-2[18F]fluoro-D-glucose positron emission tomography to assess neural activity. Our findings reveal distinct brain activity markings that correlate with adaptive and maladaptive behavioral responses to stress, and provide a framework for further studies investigating the contribution of specific brain regions to maladaptive stress responses.

Progesterone After Estradiol Modulates Shuttle-Cage Escape by Facilitating Volition

In animal models of depression, depression is defined as performance on a learning task. That task is typically escaping a mild electric shock in a shuttle cage by moving from one side of the cage to the other. Ovarian hormones influence learning in other kinds of tasks, and these hormones are associated with depressive symptoms in humans. The role of these hormones in shuttle-cage escape learning, however, is less clear. This study manipulated estradiol and progesterone in ovariectomized female rats to examine their performance in shuttle-cage escape learning without intentionally inducing a depressive-like state. Progesterone, not estradiol, within four hours of testing affected latencies to escape. The improvement produced by progesterone was in the decision to act, not in the speed of learning or speed of escaping. This parallels depression in humans in that depressed people are slower in volition, in their decisions to take action.

A comparative study of anhedonia components between major depression and schizophrenia in Chinese populations

BACKGROUND

Anhedonia is a prominent symptom of major depressive disorder (MDD) and schizophrenia. At present, it is believed that hedonic processing rather consists of the anticipatory and consummatory phase. The aim of this research is to explore the different anhedonia components in MDD and schizophrenia in Chinese populations.

METHODS

A Chinese version of the Temporal Experience of Pleasure Scale (TEPS) was used to evaluate 176 MDD patients, 346 schizophrenia patients, and 268 healthy controls. Additionally, the 17-item Hamilton Depression Rating Scale (HAMD-17) was used for MDD patients, while the Positive and Negative Syndrome Scale (PANSS) was applied for schizophrenia.

RESULTS

The scores of consummatory (TEPS-CON) and anticipatory pleasure (TEPS-ANT) in MDD and schizophrenia were both significantly lower than healthy controls (both P < 0.001). TEPS-CON and TEPS-ANT were negatively correlated with the score of HAMD-17, the duration of illness and admission times in MDD (P < 0.05 or 0.01). TEPS-CON was negatively related to PANSS total scores and negative symptoms (P < 0.05 or 0.01), but no significant correlation was found with duration of illness and admission times in schizophrenia (P > 0.05). There was no significant correlation between TEPS-ANT and any clinical variables (P > 0.05).

CONCLUSIONS

The consummatory and anticipatory pleasures were both impaired in MDD and schizophrenia. Consummatory and anticipatory anhedonia can be considered as a "state" in MDD, but as a "trait" in schizophrenia.

Hyperhomocysteinemia is a result, rather than a cause, of depression under chronic stress

Background

Although the accumulation of homocysteine (Hcy) has been implicated in the pathogenesis of depression, whether Hcy is directly involved and acts as the primary cause of depressive symptoms remains unclear. The present study was designed to clarify whether increased Hcy plays an important role in stress-induced depression.

Results

We employed the chronic unpredictable mild stress model (CUMS) of depression for 8 weeks to observe changes in the plasma Hcy level in the development of depression. The results showed that Wistar rats exposed to a series of mild, unpredictable stressors for 4 weeks displayed depression-like symptoms such as anhedonia (decreased sucrose preferences) and a decreased 5-Hydroxy Tryptophan (5-HT) concentration in the hippocampus. At the end of 8 weeks, the plasma Hcy level increased in the CUMS rats. The anti-depressant sertraline could decrease the plasma Hcy level and improve the depression-like symptoms in the CUMS rats. RhBHMT, an Hcy metabolic enzyme, could decrease the plasma Hcy level significantly, although it could not improve the depressive symptoms in the CUMS rats.

Conclusions

The results obtained from the experiments did not support the hypothesis that the increased Hcy concentration mediated the provocation of depression in CUMS rats, and the findings suggested that the increased Hcy concentration in the plasma might be the result of stress-induced depression.

Structure-activity relationship studies on neuroactive steroids in memory, alcohol and stress-related functions: a crucial benefit from endogenous level analysis

RATIONALE

New research findings in the field of neuroactive steroids strongly suggest that to understand their role in physiopathology, it is essential to accurately measure their tissue levels. Through his broad chemical expertise and extensive knowledge of steroids, Dr. Robert H. Purdy pioneered structure-activity relationship studies on these compounds and developed innovative detection assays that are essential to assess their function in biological tissues.

OBJECTIVE

The goal of the present paper is to point out the specific contributions of Dr. Purdy and his collaborators to the current knowledge on the role of neuroactive steroids in the modulation of memory and alcohol- and stress-related effects with particular emphasis on the detection assays he developed to assess their endogenous levels. Reviewed here are the major results as well as the original and valuable methodological strategies issued by the long-term collaboration between Dr Purdy and many scientists worldwide on the investigation of the structure-activity relationship of neuroactive steroids.

RESULTS

Altogether, the data presented herein put forward the original notion that knowledge of the chemical structure of steroids is essential for their detection and the understanding of their role in physiological and pathological conditions, including the stress response.

CONCLUSIONS

The current challenge is to identify and quantify using appropriate methods neuroactive steroids in the context of both animal and clinical studies in order to reveal how their levels change under physiological and disease states. Dr. Purdy passed away in September 2012, but scientists all over the world will always be grateful for his pioneering work on steroid chemistry and for his great enthusiasm in research.

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

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

Animal models of depression and neuroplasticity: assessing drug action in relation to behavior and neurogenesis

Depression is among the most prevalent forms of mental illness and a major cause of morbidity worldwide. Diagnosis of depression is mainly based on symptomatic criteria, and the heterogeneity of the disease suggests that multiple different biological mechanisms may underlie its etiology. Animal models have been important for recent advances in experimental neuroscience, including modeling of human mood disorders, such as depression and anxiety. Over the past few decades, a number of stress and neurobiochemical models have been developed as primary efficacy measures in depression trials, which are paving the way for the discovery of novel therapeutic targets. Recent data indicates that stress-related mood disorders have influence on neuroplasticity and adult neurogenesis. In this chapter, several currently available animal models are presented as powerful tools for both mechanistic studies into the neurobiology of the antidepressant response and for drug discovery.

Total flavonoids extracted from xiaobuxin-tang on the hyperactivity of hypothalamic-pituitary-adrenal axis in chronically stressed rats

Our previous studies have demonstrated that the total flavonoids (XBXT-2) isolated from the extract of Xiaobuxin-Tang (XBXT), a traditional Chinese herbal decoction, ameliorated behavioral alterations and hippocampal dysfunctions in chronically stressed rats. Studies over the last decades have suggested that the hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis is one of the most consistent findings in stress-related depression. Herein, we used the same chronic mild stress model of rats as before to further investigate the effect of XBXT-2 on the hyperactivity of HPA axis, including the stress hormones levels and glucocorticoid receptors (GRs) expression. Our ELISA results showed that chronic administration of XBXT-2 (25, 50 mg kg⁻¹, p.o., 28 days, the effective doses for behavioral responses) significantly decreased serum corticosterone level and its upstream stress hormone adrenocorticotropic hormone (ACTH) level in chronically stressed rats. Furthermore, western blotting result demonstrated XBXT-2 treatment ameliorated stress-induced decrease of GRs expression in hippocampus, an important target involved in the hyperactivity of HPA axis. These results were similar to that of classic antidepressant imipramine treatment (10 mg kg⁻¹, p.o.). In conclusion, the modulation of HPA axis produced by XBXT-2, including the inhibition of stress hormones levels and up-regulation of hippocampal GRs expression, may be an important mechanism underlying its antidepressant-like effect in chronically stressed rats.

In animal models, psychosocial stress-induced (neuro)inflammation, apoptosis and reduced neurogenesis are associated to the onset of depression

Recently, the inflammatory and neurodegenerative (I&ND) hypothesis of depression was formulated (Maes et al., 2009), i.e. the neurodegeneration and reduced neurogenesis that characterize depression are caused by inflammation, cell-mediated immune activation and their long-term sequels. The aim of this paper is to review the body of evidence that external stressors may induce (neuro)inflammation, neurodegeneration and reduced neurogenesis; and that antidepressive treatments may impact on these pathways. The chronic mild stress (CMS) and learned helplessness (LH) models show that depression-like behaviors are accompanied by peripheral and central inflammation, neuronal cell damage, decreased neurogenesis and apoptosis in the hippocampus. External stress-induced depression-like behaviors are associated with a) increased interleukin-(IL)1β, tumor necrosis factor-α, IL-6, nuclear factor κB, cyclooxygenase-2, expression of Toll-like receptors and lipid peroxidation; b) antineurogenic effects and reduced brain-derived neurotrophic factor (BDNF) levels; and c) apoptosis with reduced levels of Bcl-2 and BAG1 (Bcl-2 associated athanogene 1), and increased levels of caspase-3. Stress-induced inflammation, e.g. increased IL-1β, but not reduced neurogenesis, is sufficient to cause depression. Antidepressants a) reduce peripheral and central inflammatory pathways by decreasing IL-1β, TNFα and IL-6 levels; b) stimulate neuronal differentiation, synaptic plasticity, axonal growth and regeneration through stimulatory effects on the expression of different neurotrophic factors, e.g. trkB, the receptor for brain-derived neurotrophic factor; and c) attenuate apoptotic pathways by activating Bcl-2 and Bcl-xl proteins, and suppressing caspase-3. It is concluded that external stressors may provoke depression-like behaviors through activation of inflammatory, oxidative, apoptotic and antineurogenic mechanisms. The clinical efficacity of antidepressants may be ascribed to their ability to reverse these different pathways.

Aging of the hypothalamic-pituitary-adrenal axis in nonhuman primates with depression-like and aggressive behavior

We have investigated aging of the hypothalamic-pituitary-adrenal (HPA) axis in female rhesus monkeys that differ in adaptive behavior. Plasma cortisol (F) and dehydroepiandrosterone sulfate (DHEA-S) concentrations under basal conditions and under acute psycho-emotional stress were evaluated in blood plasma of young (6-8 years) and old (20-27 years) female rhesus monkeys with various types of adaptive behavior (aggressive, depression-like, and average). We have found that the age-related changes in the HPA axis of monkeys with depression-like behavior were accompanied by the maximal absolute and relative hypercortisolemia under both basal conditions and stress. Moreover, young aggressive monkeys, in comparison with young monkeys of other behavior groups, demonstrated the highest plasma levels of DHEA-S and the lowest molar ratios between F and DHEA-S. Thus, age-related dysfunctions of the HPA axis are associated with adaptive behavior of animals.

The MRL/lpr mouse strain as a model for neuropsychiatric systemic lupus erythematosus

To date, CNS disease and neuropsychiatric symptoms of systemic lupus erythematosus (NP-SLE) have been understudied compared to end-organ failure and peripheral pathology. In this review, we focus on a specific mouse model of lupus and the ways in which this model reflects some of the most common manifestations and potential mechanisms of human NP-SLE. The mouse MRL lymphoproliferation strain (a.k.a. MRL/lpr) spontaneously develops the hallmark serological markers and peripheral pathologies typifying lupus in addition to displaying the cognitive and affective dysfunction characteristic of NP-SLE, which may be among the earliest symptoms of lupus. We suggest that although NP-SLE may share common mechanisms with peripheral organ pathology in lupus, especially in the latter stages of the disease, the immunologically privileged nature of the CNS indicates that early manifestations of particularly mood disorders maybe derived from some unique mechanisms. These include altered cytokine profiles that can activate astrocytes, microglia, and alter neuronal function before dysregulation of the blood-brain barrier and development of clinical autoantibody titres.

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.

Increased expression level of corticotropin-releasing hormone in the amygdala and in the hypothalamus in rats exposed to chronic unpredictable mild stress

OBJECTIVE

Corticotropin-releasing hormone (CRH) plays an important role in neuroendocrine, autonomic and behavioral responses to stressors. In the present study, the effect of chronic unpredictable mild stress (CUMS) on CRH neurons was investigated in rat brain.

METHODS

The rats were exposed to one of the stressors each day for 21 d. Immunostaining was performed to detect the CRH-positive neurons in the paraventricular nucleus (PVN) of the hypothalamus and in amygdala.

RESULTS

After the stress protocol, the animals showed a reduction in body weight gain as well as reduced sucrose preference and locomotor activity. Interestingly, the CRH neurons in both PVN and central nucleus of the amygdala (CeA) were stimulated by CUMS. The densities of CRH-containing neurons in both PVN and CeA were significantly higher than those in control group.

CONCLUSION

The CRH systems in PVN and CeA may both contribute to depression-like behaviors during CUMS.