Effects of Acute and Chronic Stressors and CRF in Rat and Mouse Tests for Depression

Protective Role and Functional Engineering of Neuropeptides in Depression and Anxiety: An Overview

Behavioral disorders, such as anxiety and depression, are prevalent globally and touch children and adults on a regular basis. Therefore, it is critical to comprehend how these disorders are affected. It has been demonstrated that neuropeptides can influence behavior, emotional reactions, and behavioral disorders. This review highlights the majority of the findings demonstrating neuropeptides' behavioral role and functional engineering in depression and anxiety. Gut-brain peptides, hypothalamic releasing hormone peptides, opioid peptides, and pituitary hormone peptides are the four major groups of neuropeptides discussed. Some neuropeptides appear to promote depression and anxiety-like symptoms, whereas others seem to reduce it, all depending on the receptors they are acting on and on the brain region they are localized in. The data supplied here are an excellent starting point for future therapy interventions aimed at treating anxiety and depression.

Female-specific role of ciliary neurotrophic factor in the medial amygdala in promoting stress responses

Ciliary neurotrophic factor (CNTF) is produced by astrocytes which have been implicated in regulating stress responses. We found that CNTF in the medial amygdala (MeA) promotes despair or passive coping, i.e., immobility in an acute forced swim stress, in female mice, while having no effect in males. Neutralizing CNTF antibody injected into the MeA of wildtype females reduced activation of downstream STAT3 (Y705) 24 and 48 h later. In concert, the antibody reduced immobility in the swim test in females and only after MeA injection, but not when injected in the central or basolateral amygdala. Antibody injected into the male MeA did not affect immobility. These data reveal a unique role of CNTF in female MeA in promoting despair or passive coping behavior. Moreover, 4 weeks of chronic unpredictable stress (CUS) increased immobility in the swim test and reduced sucrose preference in wildtype CNTF+/+, but not CNTF−/− littermate, females. Following CUS, 10 min of restraint stress increased plasma corticosterone levels only in CNTF+/+ females. In males, the CUS effects were present in both genotypes. Further, CUS increased CNTF expression in the MeA of female, but not male, mice. CUS did not alter CNTF in the female hippocampus, hypothalamus and bed nucleus of stria terminalis. This suggests that MeA CNTF has a female-specific role in promoting CUS-induced despair or passive coping, behavioral anhedonia and neuroendocrine responses. Compared to CNTF+/+ mice, CNTF−/− mice did not show differences in CUS-induced anxiety-like behavior and sensorimotor gating function as measured by elevated T-Maze, open field and pre-pulse inhibition of the acoustic startle response. Together, this study reveals a novel CNTF-mediated female-specific mechanism in stress responses and points to opportunities for developing treatments for stress-related disorders in women.

•

CNTF in the MeA promotes despair or passive coping behavior in female mice only.

•

Chronic stress upregulates CNTF in female but not male MeA.

•

CNTF contributes to chronic stress-induced despair or passive coping, anhedonia and neuroendocrine responses in females only.

•

CNTF does not affect anxiety-like behavior and sensorimotor gating function.

•

These data reveal a novel CNTF-mediated female-specific mechanism in stress responses.

Chronic Sulfasalazine Treatment in Mice Induces System xc - - Independent Adverse Effects

Despite ample evidence for the therapeutic potential of inhibition of the cystine/glutamate antiporter system x_c⁻ in neurological disorders and in cancer, none of the proposed inhibitors is selective. In this context, a lot of research has been performed using the EMA- and FDA-approved drug sulfasalazine (SAS). Even though this molecule is already on the market for decades as an anti-inflammatory drug, serious side effects due to its use have been reported. Whereas for the treatment of the main indications, SAS needs to be cleaved in the intestine into the anti-inflammatory compound mesalazine, it needs to reach the systemic circulation in its intact form to allow inhibition of system x_c⁻. The higher plasma levels of intact SAS (or its metabolites) might induce adverse effects, independent of its action on system x_c⁻. Some of these effects have however been attributed to system x_c⁻ inhibition, calling into question the safety of targeting system x_c⁻. In this study we chronically treated system x_c⁻ - deficient mice and their wildtype littermates with two different doses of SAS (160 mg/kg twice daily or 320 mg/kg once daily, i.p.) and studied some of the adverse effects that were previously reported. SAS had a negative impact on the survival rate, the body weight, the thermoregulation and/or stress reaction of mice of both genotypes, and thus independent of its inhibitory action on system x_c⁻. While SAS decreased the total distance travelled in the open-field test the first time the mice encountered the test, it did not influence this parameter on the long-term and it did not induce other behavioral changes such as anxiety- or depressive-like behavior. Finally, no major histological abnormalities were observed in the spinal cord. To conclude, we were unable to identify any undesirable system x_c⁻-dependent effect of chronic administration of SAS.

The α1-adrenergic receptors in the amygdala regulate the induction of learned despair through protein kinase C-beta signaling

Hyperactivity of amygdala is observed in patients with major depressive disorder. Although the role of α1-adrenoceptor in amygdala on fear memory has been well studied, the role of α1-adrenoceptor in amygdala on depression-like behaviors remains unclear. Therefore, we investigated the effect of α1A-adrenoreceptor in amygdala on despair behavior, evaluated by the immobility time during tail suspension test (TST), pharmacological intervention, and immunohistological methods. C57BL6/J mice given a bilateral intra-amygdala injection of artificial cerebrospinal fluid exhibited an increased duration of immobility in the latter half of both trials of TST with a 24-h interval, a phenomenon known as learned despair. Intra-amygdala injection of WB4101 (1.7 nmol/0.1 µl), an α1 adrenoreceptor antagonist, but not propranolol (250 pmol/0.1 µl), a β-adrenoreceptor antagonist, blocked the induction of learned despair during TST. Immunostaining experiments revealed that ~61-75% of α1A-adrenoreceptor-positive neurons were colocalized with GAD65/67 in amygdala, implying that the α1-adrenoceptors in amygdala may enormously regulate the GABA release. Protein kinase C-beta (PKCβ) was predominantly expressed in the α1A-adrenoreceptor-positive neurons in the BLA, whereas protein kinase C-epsilon (PKCε) was highly expressed with the α1A-adrenoreceptor in the Central nucleus of amygdala. Intra-amygdala injection of ruboxistaurin (10 pmol/0.1 µl), a PKCβ inhibitor, blocked the induction of learned despair during TST, whereas neither TAT-εV1-2 (500 ng/0.1 μl), a cell-permeant PKCε inhibitory peptide, nor HBDDE (50 pmol/0.1 µl), an inhibitor of PKCα and -γ, affected the duration of immobility during TST. These data suggest that the α1-adrenoreceptor in amygdala regulates the induction of learned despair via PKCβ.

Familiarization effects on the behavioral disinhibition of the cerebellar Lurcher mutant mice: use of the innovative Dual Maze

Anxiety-related behaviors in mice are often assessed over short periods starting immediately after introducing the animals in a dedicated apparatus. In these usual conditions (5-10 min periods), the cerebellar Lurcher mutants showed disinhibited behaviors characterized by abnormally high exploration of the aversive areas in the elevated plus-maze test. We nevertheless observed that this disinhibition sharply weakened after 10 min. We therefore decided to further investigate the influence of the disinhibition on the intrinsic and anxiety-related exploratory behaviors in Lurcher mice, with a special focus on familiarization effects. To this end, we used an innovative apparatus, the Dual Maze, permitting to tune the familiarization level of animals to the experimental context before they are faced with more (open configuration of the device) or less (closed configuration of the device) aversive areas. Chlordiazepoxide administration in BALB/c mice in a preliminary experiment confirmed both the face and the predictive validity of our device as anxiety test and its ability to measure exploratory motivation. The results obtained with the Lurcher mice in the open configuration revealed that 20 min of familiarization to the experimental context abolished the behavioral abnormalities they exhibited when not familiarized with it. In addition, their exploratory motivation, as measured in the closed configuration, was comparable to that of their non-mutant littermates, whatever the level of familiarization applied. Exemplifying the interest of this innovative device, the results we obtained in the Lurcher mutants permitted to differentiate between the roles played by the cerebellum in exploratory motivation and stress-related behaviors.

Cardiac Protective Role of Heat Shock Protein 27 in the Stress Induced by Drugs of Abuse

Heat shock proteins (HSP) are induced after different stress situations. Some of these proteins, particularly HSP-27, function as markers to indicate cellular stress or damage and protect the heart during addictive processes. Morphine withdrawal induces an enhancement of sympathetic activity in parallel with an increased HSP-27 expression and phosphorylation, indicating a severe situation of stress. HSP-27 can interact with different intracellular signaling pathways. Propranolol and SL-327 were able to antagonize the activation of hypothalamic-pituitary adrenal (HPA) axis and the phosphorylation of HSP-27 observed during morphine withdrawal. Therefore, β-adrenergic receptors and the extracellular signal-regulated kinase (ERK) pathway would be involved in HPA axis activity, and consequently, in HSP-27 activation. Finally, selective blockade of corticotrophin releasing factor (CRF)-1 receptor and the genetic deletion of CRF1 receptors antagonize cardiac adaptive changes. These changes are increased noradrenaline (NA) turnover, HPA axis activation and decreased HSP-27 expression and phosphorylation. This suggests a link between the HPA axis and HSP-27. On the other hand, morphine withdrawal increases µ-calpain expression, which in turn degrades cardiac troponin T (cTnT). This fact, together with a co-localization between cTnT and HSP-27, suggests that this chaperone avoids the degradation of cTnT by µ-calpain, correcting the cardiac contractility abnormalities observed during addictive processes. The aim of our research is to review the possible role of HSP-27 in the cardiac changes observed during morphine withdrawal and to understand the mechanisms implicated in its cardiac protective functions.

Modelling posttraumatic stress disorders in animals

Animal models of posttraumatic stress disorder are useful tools to reveal the neurobiological basis of the vulnerability to traumatic events, and to develop new treatment strategies, as well as predicting treatment response contributing to personalized medicine approach. Different models have different construct, face and predictive validity and they model different symptoms of the disease. The most prevalent models are the single prolonged stress, electric foot-shock and predator odor. Freezing as 're-experiencing' in cluster B and startle as 'arousal' in cluster E according to DSM-5 are the most frequently studied parameters; however, several other symptoms related to mood, cognitive and social skills are part of the examinations. Beside behavioral characteristics, symptoms of exaggerated sympathetic activity and hypothalamic-pituitary-adrenocortical axis as well as signs of sleep disturbances are also warranted. Test battery rather than a single test is required to describe a model properly and the results should be interpreted in a comprehensive way, e.g. creating a z-score. Research is shifting to study larger populations and identifying the features of the resilient and vulnerable individuals, which cannot be easily done in humans. Incorporation of the "three hit theory" in animal models may lead to a better animal model of vulnerability and resilience. As women are twice as vulnerable as men, more emphasize should be taken to include female animals. Moreover, hypothesis free testing and big data analysis may help to identify an array of biomarkers instead of a single variable for identification of vulnerability and for the purpose of personalized medicine.

Intranasal Cotinine Plus Krill Oil Facilitates Fear Extinction, Decreases Depressive-Like Behavior, and Increases Hippocampal Calcineurin A Levels in Mice

Failure in fear extinction is one of the more troublesome characteristics of posttraumatic stress disorder (PTSD). Cotinine facilitates fear memory extinction and reduces depressive-like behavior when administered 24 h after fear conditioning in mice. In this study, it was investigated the behavioral and molecular effects of cotinine, and other antidepressant preparations infused intranasally. Intranasal (IN) cotinine, IN krill oil, IN cotinine plus krill oil, and oral sertraline were evaluated on depressive-like behavior and fear retention and extinction after fear conditioning in C57BL/6 mice. Since calcineurin A has been involved in facilitating fear extinction in rodents, we also investigated changes of calcineurin in the hippocampus, a region key on contextual fear extinction. Short-term treatment with cotinine formulations was superior to krill oil and oral sertraline in reducing depressive-like behavior and fear consolidation and enhancing contextual fear memory extinction in mice. IN krill oil slowed the extinction of fear. IN cotinine preparations increased the levels of calcineurin A in the hippocampus of conditioned mice. In the light of the results, the future investigation of the use of IN cotinine preparations for the extinction of contextual fear memory and treatment of treatment-resistant depression (TRD) in PTSD is discussed.

Chronic Intermittent Ethanol Exposure Alters Stress Effects on (3α,5α)-3-hydroxy-pregnan-20-one (3α,5α-THP) Immunolabeling of Amygdala Neurons in C57BL/6J Mice

The GABAergic neuroactive steroid (3α,5α)-3-hydroxy-pregnan-20-one (3α,5α-THP, allopregnanolone) is decreased in various brain regions of C57BL/6J mice following exposure to an acute stressor or chronic intermittent ethanol (CIE) exposure and withdrawal. It is well established that there are complex interactions between stress and ethanol drinking, with mixed literature regarding the effects of stress on ethanol intake. However, there is little research examining how chronic ethanol exposure alters stress responses. The present work examined the impact of CIE exposure and withdrawal on changes in brain levels of 3α,5α-THP, as well as hormonal and behavioral responses to forced swim stress (FSS). Adult male C57BL/6J mice were exposed to four cycles of CIE to induce ethanol dependence. Following 8 h or 72 h withdrawal, mice were subjected to FSS for 10 min, and 50 min later brains were collected for immunohistochemical analysis of cellular 3α,5α-THP. Behavioral and circulating corticosterone responses to FSS were quantified. Following 8 h withdrawal, ethanol exposure potentiated the corticosterone response to FSS. Following 72 h withdrawal, this difference was no longer observed. Following 8 h withdrawal, stress-exposed mice showed no differences in immobility, swimming or struggling behavior. However, following 72 h withdrawal, ethanol-exposed mice showed less immobility and greater swimming behavior compared to air-exposed mice. Interestingly, cellular 3α,5α-THP levels were increased in the lateral amygdala 8 h and 72 h post-withdrawal in stressed ethanol-exposed mice compared to ethanol-exposed/non-stressed mice. In the paraventricular nucleus of the hypothalamus, stress exposure decreased 3α,5α-THP levels compared to controls following 72 h withdrawal, but no differences were observed 8 h post-withdrawal. There were no differences in cellular 3α,5α-THP levels in the nucleus accumbens shell at either withdrawal time point. These data suggest that there are different mechanisms mediating hormonal, behavioral, and brain responses to stress following CIE exposure. The lateral amygdala appears to be an extremely sensitive brain region exhibiting changes in cellular 3α,5α-THP levels following CIE and exposure to swim stress. It is likely that these changes in cellular 3α,5α-THP levels in the lateral amygdala contribute to the behavioral effects observed following 72 h withdrawal.

Evidence for the role of corticotropin-releasing factor in major depressive disorder

Major depressive disorder (MDD) is a devastating disease affecting over 300 million people worldwide, and costing an estimated 380 billion Euros in lost productivity and health care in the European Union alone. Although a wealth of research has been directed toward understanding and treating MDD, still no therapy has proved to be consistently and reliably effective in interrupting the symptoms of this disease. Recent clinical and preclinical studies, using genetic screening and transgenic rodents, respectively, suggest a major role of the CRF1 gene, and the central expression of CRF1 receptor protein in determining an individual's risk of developing MDD. This gene is widely expressed in brain tissue, and regulates an organism's immediate and long-term responses to social and environmental stressors, which are primary contributors to MDD. This review presents the current state of knowledge on CRF physiology, and how it may influence the occurrence of symptoms associated with MDD. Additionally, this review presents findings from multiple laboratories that were presented as part of a symposium on this topic at the annual 2014 meeting of the International Behavioral Neuroscience Society (IBNS). The ideas and data presented in this review demonstrate the great progress that has been made over the past few decades in our understanding of MDD, and provide a pathway forward toward developing novel treatments and detection methods for this disorder.

Postnatal loss of hap1 reduces hippocampal neurogenesis and causes adult depressive-like behavior in mice

Depression is a serious mental disorder that affects a person’s mood, thoughts, behavior, physical health, and life in general. Despite our continuous efforts to understand the disease, the etiology of depressive behavior remains perplexing. Recently, aberrant early life or postnatal neurogenesis has been linked to adult depressive behavior; however, genetic evidence for this is still lacking. Here we genetically depleted the expression of huntingtin-associated protein 1 (Hap1) in mice at various ages or in selective brain regions. Depletion of Hap1 in the early postnatal period, but not later life, led to a depressive-like phenotype when the mice reached adulthood. Deletion of Hap1 in adult mice rendered the mice more susceptible to stress-induced depressive-like behavior. Furthermore, early Hap1 depletion impaired postnatal neurogenesis in the dentate gyrus (DG) of the hippocampus and reduced the level of c-kit, a protein expressed in neuroproliferative zones of the rodent brain and that is stabilized by Hap1. Importantly, stereotaxically injected adeno-associated virus (AAV) that directs the expression of c-kit in the hippocampus promoted postnatal hippocampal neurogenesis and ameliorated the depressive-like phenotype in conditional Hap1 KO mice, indicating a link between postnatal-born hippocampal neurons and adult depression. Our results demonstrate critical roles for Hap1 and c-kit in postnatal neurogenesis and adult depressive behavior, and also suggest that genetic variations affecting postnatal neurogenesis may lead to adult depression.

Although the majority of the neurons in the brain are generated during embryonic stage, new neurons are continuously being produced postnatally, and at a much lower rate in adulthood. As postnatal neurogenesis is a key component of the brain maturation process that creates dynamic ‘wirings’ in the brain necessary for an individual to grow, learn, and cope with the external world, attenuated postnatal neurogenesis may affect an individual’s mental stability, rendering a higher susceptibility to depression later in life. In the current study, we genetically ablated the expression of huntingtin-associated protein 1 (Hap1) in mice at various ages or in selective brain regions, and found that early loss of Hap1 significantly reduces postnatal hippocampal neurogenesis, and leads to adult depressive-like behavior. We also found c-kit as an effector to mediate the neurogenesis defect and adult depressive-like phenotype in mice lacking Hap1. The results provide the first genetic evidence to demonstrate the importance of postnatal neurogenesis in adult depression, and may offer new avenues in the prevention and treatment of depression. Our study also has potential implications to other adult-onset mental disorders.

Resilience to the effects of social stress: evidence from clinical and preclinical studies on the role of coping strategies

The most common form of stress encountered by people stems from one's social environment and is perceived as more intense than other types of stressors. One feature that may be related to differential resilience or vulnerability to stress is the type of strategy used to cope with the stressor, either active or passive coping. This review focuses on models of social stress in which individual differences in coping strategies produce resilience or vulnerability to the effects of stress. Neurobiological mechanisms underlying these individual differences are discussed. Overall, the literature suggests that there are multiple neural mechanisms that underlie individual differences in stress-induced resilience and vulnerability. How these mechanisms interact with one another to produce a resilient or vulnerable phenotype is not understood and such mechanisms have been poorly studied in females and in early developmental periods. Finally, we propose that resilience may be stress context specific and resilience phenotypes may need to be fine-tuned to suit a shifting environment.

•

Resilience is considered positive adaptation in the face of adversity.

•

Coping strategy impacts one's susceptibility to social stress-induced psychopathology.

•

Neurobiological substrates such as CRF, NPY and DA may impact stress susceptibility.

•

Individual differences within females and during adolescence are poorly understood.

Developing zebrafish models relevant to PTSD and other trauma- and stressor-related disorders

While post-traumatic stress disorder (PTSD) and other trauma- and stress-related disorders (TSRDs) represent a serious societal and public health concern, their pathogenesis is largely unknown. Given the clinical complexity of TSRD development and susceptibility, greater investigation into candidate biomarkers and specific genetic pathways implicated in both risk and resilience to trauma becomes critical. In line with this, numerous animal models have been extensively used to better understand the pathogenic mechanisms of PTSD and related TSRD. Here, we discuss the rapidly increasing potential of zebrafish as models of these disorders, and how their use may aid researchers in uncovering novel treatments and therapies in this field.

Cardiac autonomic imbalance by social stress in rodents: understanding putative biomarkers

Exposure to stress or traumatic events can lead to the development of depression and anxiety disorders. In addition to the debilitating consequences on mental health, patients with psychiatric disorders also suffer from autonomic imbalance, making them susceptible to a variety of medical disorders. Emerging evidence utilizing spectral analysis of heart rate variability (HRV), a reliable non-invasive measure of cardiovascular autonomic regulation, indicates that patients with depression and various anxiety disorders (i.e., panic, social, generalized anxiety disorders, and post traumatic stress disorder) are characterized by decreased HRV. Social stressors in rodents are ethologically relevant experimental stressors that recapitulate many of the dysfunctional behavioral and physiological changes that occur in psychological disorders. In this review, evidence from clinical studies and preclinical stress models identify putative biomarkers capable of precipitating the comorbidity between disorders of the mind and autonomic dysfunction. Specifically, the role of corticotropin releasing factor, neuropeptide Y and inflammation are investigated. The impetus for this review is to highlight stress-related biomarkers that may prove critical in the development of autonomic imbalance in stress -related psychiatric disorders.

Individual differences in the neurobiology of social stress: implications for depression-cardiovascular disease comorbidity

Stress initiates a cascade of complex neural and peripheral changes that promote healthy adaption to stress, but when unabated, leads to pathology. Fascinating individual differences arise in the ability to cope with a stressor, rendering an individual more or less likely to develop stress-induced pathologies such as depression, anxiety, and cardiovascular disease. In this review we evaluate recent findings that investigate the neural underpinnings of adopting a passive or active coping response during social defeat stress. Because passive coping is associated with vulnerability to stress-related pathologies and active coping confers resiliency, understanding neurobiological adaptations associated with these diverse coping strategies may reveal biomarkers or targets impacting stress susceptibility. The co-occurrence of stress-induced depression and cardiovascular disease is becoming increasingly clear. Therefore this review focuses on the central mechanisms capable of contributing to psychopathology and cardiovascular disease such as corticotropin releasing factor, neuropeptide Y, monoamines, cytokines and oxidative stress. The impetus for this review is to highlight neurobiological systems that warrant further evaluation for their contribution to the pathophysiology of depression-cardiovascular disease comorbidity.

The role of guanfacine as a therapeutic agent to address stress-related pathophysiology in cocaine-dependent individuals

The pathophysiology of cocaine addiction is linked to changes within neural systems and brain regions that are critical mediators of stress system sensitivity and behavioral processes associated with the regulation of adaptive goal-directed behavior. This is characterized by the upregulation of core adrenergic and corticotropin-releasing factor mechanisms that subserve negative affect and anxiety and impinge upon intracellular pathways in the prefrontal cortex underlying cognitive regulation of stress and negative emotional state. Not only are these mechanisms essential to the severity of cocaine withdrawal symptoms, and hence the trajectory of clinical outcome, but also they may be particularly pertinent to the demography of cocaine dependence. The ability of guanfacine to target overlapping stress, reward, and anxiety pathophysiology suggests that it may be a useful agent for attenuating the stress- and cue-induced craving state not only in women but also in men. This is supported by recent research findings from our own laboratory. Additionally, the ability of guanfacine to improve regulatory mechanisms that are key to exerting cognitive and emotional control over drug-seeking behavior also suggests that guanfacine may be an effective medication for reducing craving and relapse vulnerability in many drugs of abuse. As cocaine-dependent individuals are typically polydrug abusers and women may be at a greater disadvantage for compulsive drug use than men, it is plausible that medications that target catecholaminergic frontostriatal inhibitory circuits and simultaneously reduce stress system arousal may provide added benefits for attenuating cocaine dependence.

Cellular adaptations of dorsal raphe serotonin neurons associated with the development of active coping in response to social stress

BACKGROUND

Social stress is a risk factor for affective disorders for certain vulnerable individuals. Stress and depression are linked in part through regulation of the dorsal raphe (DR)-serotonin (5-HT) system by the stress-related neuropeptide, corticotropin-releasing factor (CRF). We used a rat social stress model that shows individual differences in coping strategies to determine whether differences in CRF-5-HT interactions underlie individual differences in the vulnerability to social stress.

METHODS

Rats were exposed to the resident-intruder model of social stress for 5 days. In vivo single-unit recordings assessed DR-5-HT neuronal responses to CRF and immunoelectron microscopy assessed CRF1 and CRF2 cellular localization 24 hours after the last stress.

RESULTS

Rats responded to social stress passively, assuming defeat with short latencies (48%), or actively, with proactive behaviors and longer defeat latencies (LL, 52%). Whereas CRF (30 ng, intra-DR) inhibited 5-HT neuronal activity of control and SL rats, it activated 5-HT neurons of LL rats, an effect that was CRF2-mediated. Consistent with this, social stress promoted CRF1 internalization together with CRF2 recruitment to the plasma membrane of DR neurons selectively in LL rats.

CONCLUSIONS

These data suggest that a proactive coping strategy toward social stress is associated with a redistribution of CRF1 and CRF2 in DR-5-HT neurons that primes the system to be activated by subsequent stress. The lack of this adaptation in passive coping rats may contribute to their depressive-like phenotype. These studies provide a cellular mechanism for individual differences in stress responses and consequences.

Acute illness-induced behavioral alterations are similar to those observed during withdrawal from acute alcohol exposure

Exposure to an immunogen results in a constellation of behavioral changes collectively referred to as "sickness behaviors," with alterations in cytokine expression previously shown to contribute to this sickness response. Since behaviors observed during ethanol withdrawal are strikingly similar to sickness behaviors, we hypothesized that behavioral manifestations of ethanol withdrawal might be an expression of sickness behaviors induced by ethanol-related changes in peripheral and/or central cytokine expression. Accordingly, behaviors exhibited during a modified social investigation test were first characterized in male rats following an acute injection of lipopolysaccharide (LPS; 100μg/kg). Subsequently, behavioral changes after either a high (4-g/kg; Experiment 2) or low dose (0.5g/kg; Experiment 3) of ethanol were also examined in the same social investigation test, as well as in the forced-swim test (FST; Experiment 4). Results from these experiments demonstrated similar reductions in both exploration and social investigatory behavior during acute illness and ethanol withdrawal, while a seemingly paradoxical decrease in immobility was observed in the FST during acute ethanol withdrawal. In follow-up studies, neither indomethacin (Experiment 5) nor interleukin-1 receptor antagonist (Experiment 6) pre-exposure reversed the ethanol withdrawal-induced behavioral changes observed in this social investigation test. Taken together, these studies demonstrate that the behavioral sequelae of acute illness and ethanol withdrawal are similar in nature, while antagonist studies suggest that these behavioral alterations are not reversed by blockade of IL-1 receptors or inhibition of prostaglandin synthesis. Though a direct mechanistic link between cytokines and the expression of acute ethanol withdrawal-related behaviors has yet to be found, future studies examining the involvement of brain cytokines as potential mediators of ethanol effects are greatly needed.

Depressive and cardiovascular disease comorbidity in a rat model of social stress: a putative role for corticotropin-releasing factor

RATIONALE

Depression is associated with medical comorbidities, particularly cardiovascular disease. However, mechanisms linking depression and cardiovascular disease remain unclear.

OBJECTIVES

This study investigated whether the rat resident-intruder model of social stress would elicit behavioral dysfunctions and autonomic changes characteristic of psychiatric/cardiovascular comorbidity. Furthermore, the efficacy of the corticotropin-releasing factor-1 (CRF(1)) receptor antagonist, NBI-30775 (NBI), or the tricyclic antidepressant, desipramine (DMI), to prevent social stress-induced behavioral, neuroendocrine, and cardiovascular changes were evaluated.

METHODS

Adult male rats were exposed to resident-intruder stress (seven consecutive days) and systemically administered NBI (10 mg/kg/7 days), DMI (10 mg/kg/14 days), or vehicle. The efficacy of NBI and DMI to alter the behavioral and neuroendocrine responses to social stress was assessed. Furthermore, their effects on stress-induced forced swim behavior (FST), bladder and adrenal weight, and heart rate variability (HRV) were examined.

RESULTS

NBI, but not DMI, increased time spent in an upright, defensive posture and the latency to submit to the resident. Additionally, only NBI reduced social stress-induced adrenocorticotropic hormone and corticosterone release. Social stress increased FST immobility, caused bladder and adrenal hypertrophy, and decreased HRV. Both NBI and DMI blocked stress-induced increases in immobility during the FST. However, only NBI inhibited social stress-induced adrenal and bladder hypertrophy and decreases in heart rate variability.

CONCLUSIONS

Rat resident-intruder stress paradigm models aspects of psychiatric/medical comorbidity. Furthermore, the CRF system may contribute to both the behavioral response during social stress and its behavioral and autonomic consequences, offering insight into potential therapy to treat these comorbid conditions.

MRI in animal models of psychiatric disorders

Here we describe MRI and (1)H MRS protocols for the investigation of animal models (mainly mice and rats) of psychiatric disorders. The introduction provides general findings from brain imaging studies in patients with psychiatric diseases and refers to general rules regarding the use of animal models in research. The methods section includes a selection of basic 9.4 T MRI and MRS protocols applicable for the investigation of animal models of psychiatric disorders (T1W, T2W, FLAIR, (1)H MRS). The notes section discusses in detail a series of factors that can influence the outcome of the experiment: from animal handling, stress-triggering aspects, and experimental design-related factors to technical aspects that affect T (1) and T (2) measurements.

Juvenile social subjugation induces a sex-specific pattern of anxiety and depression-like behaviors in adult rats

Child abuse is the most significant environmental risk factor for the development of mood disorders, which occur twice as frequently in women as in men. To determine whether juvenile social subjugation (JSS) of rats induces mood disorder-like symptoms, we exposed 28 day-old male and female rats to daily aggressive acts from aggressive male residents. Each rat received pins, kicks, and dominance postures from the resident for 10 min per day for 10 days. When the rats were adults, we tested their anxiety- and depression-like behaviors. In addition, we measured circulating basal and stress-evoked corticosterone (CORT) levels, and weighed the adrenal glands. Although the amount of JSS was indistinguishable between males and females, females were nonetheless more severely affected by the experience. Subjugated females became immobile more quickly during forced swim tests, and made fewer investigatory approaches during the social interaction test than control females. Juvenile social subjugation increased closed arm time in the elevated plus maze of males and females, but the effect of social subjugation was greater in females. Finally, stress-evoked CORT levels were significantly higher, and adrenal gland weights were significantly heavier, in subjugated females relative to their controls and to subjugated males. Our results demonstrate that JSS increases depression- and anxiety-like behaviors and sensitizes the stress response system in a sex-specific manner.

Corticotropin releasing factor-1 receptor antagonism alters the biochemical, but not behavioral effects of repeated interleukin-1β administration

Activation of the immune system via administration of cytokines is used for the treatment of chronic viral infections such as hepatitis C and for cancers resistant to radiotherapy. Cytokine-based treatments induce a range of "sickness" behaviors (e.g. depression, anxiety, pain, anorexia, and fatigue). Activation of the hypothalamic pituitary-adrenal axis via the induction of corticotropin releasing factor (CRF) may underlie these unwanted side effects. This study used repeated systemic injections of the pro-inflammatory cytokine interleukin-1β (IL-1β) to model the sickness behaviors and biochemical effects of immune system activation. We assessed the ability of CRF type I receptor (CRF(1)) antagonism to reduce biochemical and behavioral signs of sickness induced by IL-1β treatment. Forty Wistar rats were assigned to one of four groups: 1) saline+vehicle; 2) saline+DMP904 (CRF(1) antagonist); 3) IL-1β+vehicle; 4) IL-1β+DMP904. Rats received intraperitoneal injections of either DMP904 or vehicle and of IL-1β or saline for six days. Sickness behavior was evaluated using body weight assessments and forced swim testing (FST). Blood and brain samples were collected to measure cytokine, p38 mitogen-activated protein kinase (MAPK), and phospho-p38 MAPK levels using multiplex techniques. There were significant reductions in body weights and FST immobility times associated with IL-1β administration. Rats administered IL-1β had significantly higher serum levels of IL-10, but not interferon-γ. Within the hippocampus, IL-1β reduced levels of p38 MAPK, but had no impact on levels of phospho-p38 MAPK except in the presence of DMP904. When administered alone, DMP904 had no significant effect on p38 MAPK or phospho-p38 MAPK in the hippocampus, but when given with IL-1β led to increased phosphorylation of p38 MAPK. IL-1β and DMP904 reduced levels of p38 MAPK within the hypothalamus, while co-administration of IL-1β and DMP904 abolished the effects of either drug alone. IL-1β decreased immobility time in the FST, and led to reductions in body weight, changes in serum cytokine levels and p38 MAPK regulation within the hippocampus and hypothalamus. DMP904 blocked some of the neurochemical effects of IL-1β, but did not impact the behavioral measures, or serum cytokines. Thus, additional studies will be needed to determine whether CRF(1) antagonism is an effective treatment for cytokine-induced sickness. This article is part of a Special Issue entitled 'Anxiety and Depression'.

mRNA expression of corticotropin-releasing factor and urocortin 1 after restraint and foot shock together with alprazolam administration

Corticotropin-releasing factor (CRF) is expressed in the paraventricular nucleus of the hypothalamus (PVN), and act centrally to provoke stress-like autonomic and behavioral responses. Urocortins 1-3 are additional ligands to the CRF receptors 1 and 2. Ucn 1 neurons are primarily concentrated in the Edinger-Westphal (EW) nucleus and also have been associated with stress responses. It is also known that UCN 1 respond in different ways depending on the stressor presented. Benzodiazepines can act via the CRF peptidergic system and chronic administration of alprazolam does not interfere with CRF mRNA expression in the PVN, but significantly increase Ucn 1 mRNA expression in the EW. The aim of our study was to investigate the relationship between different stressor stimuli, foot shock (FS) and restraint (R), and the mRNA expression of CRF and Ucn 1 in the PVN and EW using alprazolam (A). We employed fos activation and in situ hybridization. Restraint group presented increased fos-ir and CRF mRNA expression in the PVN compared to FS group. The stress responses of R group were prevented by A. In the EW, fos-ir was higher in the FS group than in the R group, whereas Ucn 1 mRNA expression was higher in the R group than in the FS group. Alprazolam significantly increased fos-ir and Ucn 1 mRNA expression in both groups. Our results show that PVN and EW respond in different ways to the same stressors. Furthermore, EW of stressed animals replies in a complementary way comparing to PVN with the use of Alprazolam.

Behavioral and neurobiological consequences of prolonged glucocorticoid exposure in rats: relevance to depression

Stress is a critical environmental trigger for the development of clinical depression, yet little is known about the specific neurobiological mechanisms by which stress influences the development of depressive symptomatology. Animal models provide an efficient way to study the etiology of human disorders such as depression, and a number of preclinical models have been developed to assess the link between stress, glucocorticoids, and depressive behavior. These mode ls typically make use of repeated exposure to physical or psychological stressors in rodents or other small laboratory animals. This review focuses primarily on a recently developed preclinical model of depression that uses exogenous administration of the stress hormone corticosterone (CORT) in rodents instead of exposure to physical or psychological stressors. Repeated CORT administration in rats or mice produces reliable behavioral and neurobiological alterations that parallel many of the core symptoms and neurobiological changes associated with human depression. This provides an opportunity to study behavior and neurobiology in the same animal, so that the neurobiological factors that underlie specific symptoms can be identified. Taken together, these findings suggest that exogenous CORT administration is a useful method for studying the relationship between stress, glucocorticoids, and depression. Further study with this model may provide important new data regarding the neurobiological bases of depression.

Individual differences in reactivity to social stress predict susceptibility and resilience to a depressive phenotype: role of corticotropin-releasing factor

Previous social stress exposure is a common risk factor for affective disorders. However, factors that determine vulnerability or resiliency to social stress-induced psychopathologies remain unclear. Using a rodent model of social stress, the present study was designed to identify putative neurobiological substrates that contribute to social stress-induced psychopathology and factors that influence or predict vulnerability. The resident-intruder model of defeat was used as a social stressor in adult male Sprague Dawley rats. The average latency to assume a subordinate posture (signaling defeat) over seven daily defeat exposures was calculated and examined with respect to endpoints of hypothalamic-pituitary-adrenal activity, components of the corticotropin-releasing factor (CRF) system, and behaviors that are relevant to human depression. In the present studies, a bimodal distribution emerged in an otherwise homogeneous population of Sprague Dawley rats such that 42% of rats exhibited short defeat latencies (<300 sec), whereas 58% of rats resisted defeat and exhibited longer latencies (>300 sec). These two phenotypes were associated with distinct endocrine and behavioral profiles as well as differences in components of the CRF system. Notably, the short-latency subpopulation exhibited hypothalamic-pituitary-adrenal dysregulation and behavior similar to that observed in melancholic depression. Examination of components of the CRF system suggested that proactive behavior in resisting defeat exhibited by long-latency rats was associated with decreased efficacy of CRF. Together, these data suggest that inherent differences in stress reactivity, perhaps as a result of differences in CRF regulation, may predict long-term consequences of social stress and vulnerability to depressive-like symptoms.

Icariin attenuates chronic mild stress-induced dysregulation of the LHPA stress circuit in rats

Chronic mild stress (CMS) is suggested to develop dysregulation of the limbic-hypothalamic-pituitary-adrenal (LHPA) stress circuit. Icariin, a major constituent of flavonoids isolated from Epimedium brevicornum, has been previously confirmed to rescue the HPA axis abnormalities in animal models of depression. However, antidepressant treatment of icariin on corticotropin-releasing factor (CRF) system within the LHPA stress circuit and its interaction with serotonergic receptor are still seldom studied in CMS model of animals. The present study further investigated the effects of CMS procedure and subsequent icariin treatment on mRNA and protein levels of CRF, CRF receptor 1 (CRFR1) and CRF binding protein (CRFBP), as well as sucrose intake in rats. Moreover, the levels of cyclic adenosine 3',5'-monophosphate (cAMP) response element binding protein (CREB), glucocorticoid receptor (GR) and 5-hydroxytryptamine 1A receptor (5-HTR1A) in hypothalamus, hippocampus and frontal cortex were simultaneously evaluated for their participations in CRF system in this model. We found that CMS procedure significantly increased CRF expression levels in the brain regions, and decreased GR and 5-HTR1A in hippocampus and frontal cortex, with sucrose intake reduction representing the hedonic deficit in rats. Icariin restored these alterations in CMS rats. These results confirmed the hypothesis that icariin exerted antidepressant-like effect via its regulation of central CRF system. And hippocampus was suggested as an important neural area controlling the LHPA stress circuit in icariin-treated CMS rats. These findings for the first time proved that the potential molecular mechanism of antidepressant action of icariin was targeted on the interaction of the LHPA stress circuit and serotonergic function in CMS rats.

The role of corticotropin-releasing factor and noradrenaline in stress-related responses, and the inter-relationships between the two systems

Substantial evidence indicates that brain neurons containing and secreting noradrenaline and corticotropin-releasing factor (CRF) are activated during stress, and that physiological and behavioural responses observed during stress can be induced by exogenous administration of CRF and adrenoceptor agonists. This review focusses on the evidence for the involvement of these two factors in stress-related responses, and the inter-relationships between them. The possible abnormalities of these two systems in depressive illness are also discussed.