Acute episodes of predator exposure in conjunction with chronic social instability as an animal model of post-traumatic stress disorder

Social-Single Prolonged Stress affects contextual fear conditioning in male and female Wistar rats: Molecular insights in the amygdala

Stress exposure can lead to post-traumatic stress disorder (PTSD) in male and female rats. Social-Single Prolonged Stress (SPS) protocol has been considered a potential PTSD model. This study aimed to pharmacologically validate the Social-SPS as a PTSD model in male and female rats. Male and female Wistar rats (60-day-old) were exposed to Social-SPS protocol and treated with fluoxetine (10 mg/Kg) or saline solution intraperitoneally 24 h before euthanasia. Two cohorts of animals were used; for cohort 1, male and female rats were still undisturbed until day 7 post-Social-SPS exposure, underwent locomotor and conditioned fear behaviors, and were euthanized on day 9. Animals of cohort 2 were subjected to the same protocol but were re-exposed to contextual fear behavior on day 14. Results showed that fluoxetine-treated rats gained less body weight than control and Social-SPS in both sexes. Social-SPS effectively increased the freezing time in male and female rats on day eight but not on day fourteen. Fluoxetine blocked the increase of freezing in male and female rats on day 8. Different mechanisms for fear behavior were observed in males, such as Social-SPS increased levels of glucocorticoid receptors and Beclin-1 in the amygdala. Social-SPS was shown to increase the levels of NMDA2A, GluR-1, PSD-95, and CAMKII in the amygdala of female rats. No alterations were observed in the amygdala of rats on day fourteen. The study revealed that Social-SPS is a potential PTSD protocol applicable to both male and female rats.

The Search for Diagnostic Criteria to Divide the Wistar Rat Population into Phenotypes during Modeling of Post-Traumatic Stress Disorder

The levels of circulating hormones (corticosterone, testosterone, and leptin) and interleukins were studied in sexually mature male Wistar rats against the background of post-traumatic stress disorder (predator threat stress). It was found that in addition to the previously used anxiety index determined by animal behavior, the population of stressed individuals can be divided into stress-resistant and stress-sensitive phenotypes by the level of leptin and the index of anabolism (testosterone/corticosterone ratio). For the first time, it was determined that in stress-resistant rats, the levels of leptin and the testosterone/corticosterone index exceeds the control values, while in stress-sensitive individuals, these indicators are much lower.

Effect of Papaver rhoeas hydroalcoholic extract on blood corticosterone and psychosocial behaviors in the mice model of predator exposure-induced post-traumatic stress disorder

The function of hypothalamic-pituitary-adrenal (HPA) axis and psychosocial behaviors are affected in post-traumatic stress disorder (PTSD). Based on presence of several beneficial alkaloids in Papaver rhoeas (PR) plant, we assessed the effects of PR hydroalcoholic extract on blood corticosterone and psychosocial behaviors in the mice model of predator exposure-induced PTSD. Male NMARI mice were assigned into two main groups (control or PTSD) according to stress exposure (presence or absent of the predator). Each main group was divided into four subgroups according to treatment with the different doses of PR extract. Mice were treated intraperitoneally by PR extract at three different doses (1,5&10 mg/kg) 30 min before the beginning of test on days 1, 2&3. Corticosterone concentration determined in the blood samples on days 1, 3&21, and mice examined for the psychosocial behaviors on the third day. PTSD induction in mice by exposing to hungry predator increased blood corticosterone and changed the psychosocial and physiological behaviors. PR extract decreased blood corticosterone in PTSD mice on the third day as well as 21st day. Also, PR extract improved the psychosocial and physiological behaviors in PTSD mice. Moreover, PR extract increased blood corticosterone in control mice at a dose-response manner. PR extract is able to decrease blood corticosterone in PTSD condition and probably prevent the HPA hyperactivity in PTSD mice when exposed to the stress stimuli. Accordingly, decreased blood corticosterone by PR extract might be involved in improvement of the physiological and psychosocial behaviors in PTSD mice.

Development of an Animal Model of Military-Relevant Traumatic Stress

INTRODUCTION

Acute Stress Reactions (ASRs) affect a subgroup of individuals who experience traumatic stress. In the context of military operations, such reactions are often termed Combat and Operational Stress Reactions (COSRs). COSRs not only encompass all symptoms of ASRs but also include additional symptoms related to military combat and may develop at a rate higher than the general public experiences ASRs. Despite an obvious need, there are currently no approved pharmacologic treatments or guidelines for ASR and/or COSR. Preclinical rodent stress models and behavioral assessments are used to evaluate pharmacotherapies and elucidate underlying mechanisms. Here, we combined established traumatic stress models to develop a model of traumatic stress relevant to military trauma exposure and measured behavioral outcomes that reflect outcomes observed in ASRs and COSRs.

MATERIALS AND METHODS

Adult male rats underwent exposure to either a combination of two or three traumatic stress exposures (e.g., predator exposure, underwater trauma (UWT), and/or inescapable shock) or control procedures. Behavioral performance on the open field, elevated plus maze, and acoustic startle response (SR) was then assessed 24- and 48-hours following stress/control procedures.

RESULTS

In Experiment 1, rats were exposed to a two-stressor model, where predator exposure was coupled with UWT. Minor behavioral deficits were observed in SR for stress-exposed rats as compared to controls. In Experiment 2, inescapable shock was added to predator exposure and UWT. Behavioral performance deficits were observed across all behavioral tests. In Experiment 3, procedures from Experiment 2 were repeated with the only major modification being a shortened predator exposure duration, which resulted in performance deficits in SR only.

CONCLUSIONS

We found that the three-stressor model of Experiment 2 resulted in the greatest overall behavioral disturbance (both in the number of variables and magnitude of stress effects). Interestingly, behavioral deficits elicited from the shorter predator exposure were distinct from those observed with longer predator exposure times. Together, these results generally suggest that combined preclinical stressors with military-relevant elements result in behavioral performance deficits reflective of post-trauma phenotypes in Soldiers. The present findings support the use of both physical and psychological stressors to model operationally relevant traumatic stress exposure.

To Predict, Prevent, and Manage Post-Traumatic Stress Disorder (PTSD): A Review of Pathophysiology, Treatment, and Biomarkers

Post-traumatic stress disorder (PTSD) can become a chronic and severely disabling condition resulting in a reduced quality of life and increased economic burden. The disorder is directly related to exposure to a traumatic event, e.g., a real or threatened injury, death, or sexual assault. Extensive research has been done on the neurobiological alterations underlying the disorder and its related phenotypes, revealing brain circuit disruption, neurotransmitter dysregulation, and hypothalamic–pituitary–adrenal (HPA) axis dysfunction. Psychotherapy remains the first-line treatment option for PTSD given its good efficacy, although pharmacotherapy can also be used as a stand-alone or in combination with psychotherapy. In order to reduce the prevalence and burden of the disorder, multilevel models of prevention have been developed to detect the disorder as early as possible and to reduce morbidity in those with established diseases. Despite the clinical grounds of diagnosis, attention is increasing to the discovery of reliable biomarkers that can predict susceptibility, aid diagnosis, or monitor treatment. Several potential biomarkers have been linked with pathophysiological changes related to PTSD, encouraging further research to identify actionable targets. This review highlights the current literature regarding the pathophysiology, disease development models, treatment modalities, and preventive models from a public health perspective, and discusses the current state of biomarker research.

The Evolving Role of Animal Models in the Discovery and Development of Novel Treatments for Psychiatric Disorders

Historically, animal models have been routinely used in the characterization of novel chemical entities (NCEs) for various psychiatric disorders. Animal models have been essential in the in vivo validation of novel drug targets, establishment of lead compound pharmacokinetic to pharmacodynamic relationships, optimization of lead compounds through preclinical candidate selection, and development of translational measures of target occupancy and functional target engagement. Yet, with decades of multiple NCE failures in Phase II and III efficacy trials for different psychiatric disorders, the utility and value of animal models in the drug discovery process have come under intense scrutiny along with the widespread withdrawal of the pharmaceutical industry from psychiatric drug discovery. More recently, the development and utilization of animal models for the discovery of psychiatric NCEs has undergone a dynamic evolution with the application of the Research Domain Criteria (RDoC) framework for better design of preclinical to clinical translational studies combined with innovative genetic, neural circuitry-based, and automated testing technologies. In this chapter, the authors will discuss this evolving role of animal models for improving the different stages of the discovery and development in the identification of next generation treatments for psychiatric disorders.

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

Exploring the effect of loneliness on fear: Implications for the effect of COVID-19-induced social disconnection on anxiety

The consequences of the COVID-19 pandemic have resulted in many disruptions to daily life, including an abrupt increase in social disconnection. As measures were put in place to combat the spread of COVID-19, people across the globe began living in states of limited social contact, fostering feelings of social isolation and loneliness. Previous literature suggests that these increases in social disconnection can have profound effects on both physical and mental health, perhaps especially in the case of fear disorders. The combination of feeling disconnected from others and the high level of daily threat experienced due to COVID-19 created conditions under which dysfunctional and persistent fears were especially likely to develop. Building on current understanding of the harmful effects of social disconnection on well-being in general as well as specific implications for fear, here we present findings from three preliminary investigations that are the first to directly examine the effects of loneliness on how fears are learned and maintained. The Results of this work show that loneliness impairs the process by which fears are extinguished, which is central to both the regulation of fear and treatment of fear disorders, and provide insight into potential avenues to mitigate such effects.

Neuroinflammation in Post-Traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a well-known mental illness, which is caused by various stressors, including memories of past physical assaults and psychological pressure. It is diagnosed as a mental and behavioral disorder, but increasing evidence is linking it to the immune system and inflammatory response. Studies on the relationship between inflammation and PTSD revealed that patients with PTSD had increased levels of inflammatory cytokine biomarkers, such as interleukin-1, interleukin-6, tumor necrosis factor-α, nuclear factor-κB, and C-reactive protein, compared with healthy controls. In addition, animal model experiments imitating PTSD patients suggested the role of inflammation in the pathogenesis and pathophysiology of PTSD. In this review, we summarize the definition of PTSD and its association with increased inflammation, its mechanisms, and future predictable diseases and treatment possibilities. We also discuss anti-inflammatory treatments to address inflammation in PTSD.

Pharmahuasca and DMT Rescue ROS Production and Differentially Expressed Genes Observed after Predator and Psychosocial Stress: Relevance to Human PTSD

Post-traumatic stress disorder (PTSD) is associated with cognitive deficits, oxidative stress, and inflammation. Animal models have recapitulated features of PTSD, but no comparative RNA sequencing analysis of differentially expressed genes (DEGs) in the brain between PTSD and animal models of traumatic stress has been carried out. We compared DEGs from the prefrontal cortex (PFC) of an established stress model to DEGs from the dorsolateral PFC (dlPFC) of humans. We observed a significant enrichment of rat DEGs in human PTSD and identified 20 overlapping DEGs, of which 17 (85%) are directionally concordant. N,N-dimethyltryptamine (DMT) is a known indirect antioxidant, anti-inflammatory, and neuroprotective compound with antidepressant and plasticity-facilitating effects. We tested the capacity of DMT, the monoamine oxidase inhibitor (MAOI) harmaline, and "pharmahuasca" (DMT + harmaline) to reduce reactive oxygen species (ROS) production and inflammatory gene expression and to modulate neuroplasticity-related gene expression in the model. We administered DMT (2 mg/kg IP), harmaline (1.5 mg/kg IP), pharmahuasca, or vehicle every other day for 5 days, following a 30 day stress regiment. We measured ROS production in the PFC and hippocampus (HC) by electron paramagnetic resonance spectroscopy and sequenced total mRNA in the PFC. We also performed in vitro assays to measure the affinity and efficacy of DMT and harmaline at 5HT_2AR compared to 5-HT. DMT and pharmahuasca reduced ROS production in the PFC and HC, while harmaline had mixed effects. Treatments normalized 9, 12, and 14 overlapping DEGs, and pathway analysis implicated that genes were involved in ROS production, inflammation, growth factor signaling, neurotransmission, and neuroplasticity.

The effect of traumatic exposure on thymus weight level after dexamethasone application in rats

Introduction: Thymus is the central lymphoid organ responsible for proper immune cell maturation, hence ensuring functional T cell repertoire. Stress induces elevated levels of hormones that profoundly alter immune response. Susceptibility to physiologically synthesised and exogenously applied glucocorticoids make thymus an ideal substrate for anatomical and morphological analysis. Aim: Our research aimed to investigate the impact of endogenous and exogenous glucocorticoids on thymus weight level. Material and methods: Experimental procedure was conducted on male Wistar rats, 12 in total, divided into 2 groups - control and experimental. Latter was exposed to two kinds of stressors. Acute stress included immobilization with exposure to the predator's odor. Chronic social stress included rotation of the animals held in pairs. On the 11th day of the experimental procedure, half of the experimental group received dexamethasone treatment (impact of endogenous + exogenous glucocorticoids) while the other half did not (impact of endogenous glucocorticoids). After the experiment, animals were sacrificed and their thymuses were obtained and measured. For statistical analysis, ANOVA was used to test differences between groups and LSD test for each group testing. Results: Results showed statistically significant differences between the thymus mass of different groups (F=4.336, p=0.048). The part of the experimental group that received dexamethasone had a smaller thymus weight level compared to the part of the experimental group that received no treatment (p=0.024). No statistically relevant results were obtained after comparing thymus masses from impact of endogenous glucocorticoids and control group (p>0.05). Conclusion: Exogenous glucocorticoids induce morphological changes in thymus which are observed in decreased weight level. Stress induced thymus apoptosis, but it was not sufficient to lead to decrease in thymic mass. Our further experiments will put emphasis on understanding of morphological and anatomical changes caused by stress.

Volumetric analysis of hippocampus and amygdala in animal model of PTSD

Introduction: Posttraumatic stress disorder (PTSD) represents a mental disorder that occurs after life threatening situations. Animal models in psychiatry studies represent a base from which results and conclusions can be translated to human population. Amygdala and hippocampus are important neuroanatomical substrates possibly relevant to PTSD pathogenesis. Aim: The aim of study was to investigate volumetric changes that occur in hippocampus and amygdala related to PTSD animal model. Material and methods: Experiment was conducted on adult male Wistar rats. They were two groups, experimental and control. Experimental paradigm lasted for 31 days during which animals were exposed to acute and chronic stress. Acute stress was performed on the first day and ten days later. In between, animals were exposed to chronic social stress by pair rotations. Before second acute stress exposure, experimental group was divided in two subgroups from which one received dexamethasone dose. After the experiment ended, animals were sacrificed and the brain was extracted. Following the freezing process, brain tissue samples were cut and prepared for microscopy using. This was followed by volumetric analysis of hippocampus and amygdala. Measurements were performed bilaterally using Image Tool 3.0 Software. Results: Results showed volumetric changes in these structures. Hippocampus had smaller volume in the experimental subgroup without dexamethasone (x̄ = 0.6144) compared to the control group (x̄ = 0.9688). Amygdala, as well, had smaller volumes in same subgroup compared to the control (x̄ = 10.0156 compared to x̄ = 11.5041). Conclusion: Our study provided results in agreement with several previous studies on rodents and contributes to the assumption that hippocampus and amygdala have significance in PTSD etiology. Further goal is to expand our study which will help us to better understand the disorder itself.

Epigenetic Approach to PTSD: In the Aspects of Rat Models

Posttraumatic stress disorder (PTSD) is a stress-related mental disorder and develops after exposure to life-threatening traumatic experiences. The risk factors of PTSD included genetic factors; alterations in hypothalamic–pituitary–adrenal (HPA) axis; neurotrophic, serotonergic, dopaminergic, and catecholaminergic systems; and a variety of environmental factors, such as war, accident, natural disaster, pandemic, physical, or sexual abuse, that cause stress or trauma in individuals. To be able to understand the molecular background of PTSD, rodent animal models are widely used by researchers. When looking for a solution for PTSD, it is important to consider preexisting genetic risk factors and physiological, molecular, and biochemical processes caused by trauma that may cause susceptibility to this disorder. In studies, it is reported that epigenetic mechanisms play important roles in the biological response affected by environmental factors, as well as the task of programming cell identity. In this article, we provided an overview of the role of epigenetic modifications in understanding the biology of PTSD. We also summarized the data from animal studies and their importance during the investigation of PTSD. This study shed light on the epigenetic background of stress and PTSD.

Cardiovascular Neuroendocrinology: Emerging Role for Neurohypophyseal Hormones in Pathophysiology

Arginine vasopressin (AVP) and oxytocin (OXY) are released by magnocellular neurosecretory cells that project to the posterior pituitary. While AVP and OXY currently receive more attention for their contributions to affiliative behavior, this mini-review discusses their roles in cardiovascular function broadly defined to include indirect effects that influence cardiovascular function. The traditional view is that neither AVP nor OXY contributes to basal cardiovascular function, although some recent studies suggest that this position might be re-evaluated. More evidence indicates that adaptations and neuroplasticity of AVP and OXY neurons contribute to cardiovascular pathophysiology.

Glucocorticoid Abnormalities in Female Rats Exposed to a Predator-Based Psychosocial Stress Model of PTSD

People with post-traumatic stress disorder (PTSD) exhibit heightened anxiety and enhanced negative feedback of the hypothalamus-pituitary-adrenal (HPA) axis. We previously reported that male rats exposed to a predator-based psychosocial stress model of PTSD exhibited comparable changes in anxiety-like behavior and HPA axis activity, including lower baseline levels of corticosterone and a greater suppression of corticosterone after dexamethasone administration. Here, we assessed whether we would observe similar effects in female rats exposed to this model. Adult female Sprague-Dawley rats were exposed to a cat on two occasions (separated by 10 days), in combination with chronic social instability. Three weeks after the second cat exposure, we assessed anxiety-like behavior on an elevated plus maze (EPM) and collected blood samples from rats in the absence or presence of dexamethasone to quantify serum corticosterone levels. Although stressed females did not display heightened anxiety on the EPM, they exhibited significantly lower overall corticosterone levels and a greater suppression of corticosterone after dexamethasone administration. The observation of significantly lower overall corticosterone levels in stressed females was replicated in a separate, independent experiment. These findings suggest that the predator-based psychosocial stress model of PTSD may be useful for studying mechanisms that underlie changes in HPA axis function in females exposed to trauma.

In the great pond snail (Lymnaea stagnalis), two stressors that individually enhance memory in combination block memory formation

Stress plays an important role in memory formation in the great pond snail (Lymnaea stagnalis (Linnaeus, 1758)). Individual stressors have been shown to enhance or to perturb long-term memory (LTM) formation. However, when snails perceive a combination of two stressors, it is unclear the outcome with regards to LTM formation. Here we first show that when L. stagnalis are exposed individually to either a predator stressor (crayfish effluent (CE), which is a kairomone) or a thermal stressor (30 °C), LTM formation is enhanced. In their natural environment, L. stagnalis may experience temperatures approaching 30 °C and they may encounter crayfish at the same time. How such a combination of stressors alters adaptive behaviour is unknown. Here we show that when these two stressors are combined, LTM formation is blocked. Since boiling CE inactivates the kairomone, we used previously boiled CE that we combined with the thermal stressor and found that LTM formation is again enhanced. These data show that (i) it cannot accurately be predicted how a combination of stressors when combined interact to alter LTM formation and (ii) there is a difference between hot CE and room temperature CE.

Live predator stress in adolescence results in distinct adult behavioral consequences and dorsal diencephalic brain activation patterns

Exposure to traumatic events during childhood increases the risk of adult psychopathology, including anxiety, depression, alcohol use disorders and their co-morbidity. Early life trauma also results in increased symptom complexity, treatment resistance and poor treatment outcomes. The purpose of this study was to establish a novel rodent model of adolescent stress, based on an ethologically relevant life-threatening event, live predator exposure. Rats were exposed to a live predator for 10 min. at three different time points (postnatal day (PND)31, 46 and 61). Adult depression-, anxiety-like behaviors and ethanol consumption were characterized well past the last acute stress event (two weeks). Behavioral profiles across assessments were developed to characterize individual response to adolescent stress. CNS activation patterns in separate groups of subjects were characterized after the early (PND31) and last predator exposure (PND61). Subjects exposed to live-predator adolescent stress generally exhibited less exploratory behavior, less propensity to venture into open spaces, a decreased preference for sweet solutions and decreased ethanol consumption in a two-bottle preference test. Additional studies demonstrated blunted cortisol response and CNS activation patterns suggestive of habenula, rostromedial tegmental (RMTg), dorsal raphe and central amygdala involvement in mediating the adult consequences of adolescent stress. Thus, adolescent stress in the form of live-predator exposure results in significant adult behavioral and neurobiological disturbances. Childhood trauma, its impact on neurodevelopment and the subsequent development of mood disorders is a pervasive theme in mental illness. Improving animal models and our neurobiological understanding of the symptom domains impacted by trauma could significantly improve treatment strategies.

Every-other day fasting prevents memory impairment induced by high fat-diet: Role of oxidative stress

Imbalance of diet consumption results in memory and learning deterioration. High-fat diet (HFD) causes neuronal damage and eventually cognitive impairment, which can be related to increasing oxidative stress in the brain. Using the every other day fasting (EODF) paradigm, as a method of dietary restriction is thought to provide protection of learning and memory in several experimental studies. In the current work, the preventive effect of EODF paradigm on memory impairment-induced by HFD was investigated. Adult male Wistar rats were fed with HFD using the EODF paradigm for six weeks. At the end of these six weeks, and while the previous treatment were continued, rats were examined for learning and memory (both the short-term and the long-term memory) using the radial arm water maze (RAWM). Oxidative stress in the brain, namely in the hippocampus was also assessed. Chronic administration of HFD induced impairment in both, short- and long- term memory that was prevented using EODF paradigm. Furthermore, EODF prevented HFD-induced decrease in the activities of the antioxidant enzymes, SOD and catalase along with reduction of glutathione (GSH) level and the ratio of reduced glutathione/oxidized glutathione (GSH/GSSG ratio). The EODF also inhibited rise in oxidized glutathione (GSSG) and thiobarbituric acid reactive substances (TBARS) seen with HFD. In conclusion, EODF ameliorated oxidative stress and memory impairment induced by chronic HFD. This probably, can be explained by the ability of EODF to normalize mechanisms involved in oxidative stress in the hippocampus.

Effects of adipokinetic hormone/red pigment-concentrating hormone family of peptides in olfactory bulbectomy model and posttraumatic stress disorder model of rats

One of the major neuropeptide groups in insects is adipokinetic hormone/red pigment-concentrating hormone (AKH/RPCH) family of peptides. AKH had improving effects on depression and anxiety in animal models and it may be a new treatment choice in these disorders. Aim of this study was to investigate effects of Anax imperator AKH (Ani-AKH), Libellula auripennis AKH (Lia-AKH) and Phormia-Terra hypertrehalosemic hormone (Pht-HrTH) on animal behavior in olfactory bulbectomy (OBX) model and in posttraumatic stress disorder (PTSD) model of Wistar-albino rats. Lia-AKH and Pht-HrTH significantly increased time spent in escape platform's quadrant compared to sham control while Lia-AKH significantly increased time spent in escape platform's quadrant compared to OBX controls in probe trial of Morris water maze (MWM). Ani-AKH, Lia-AKH and Pht-HrTH significantly decreased immobility time compared to OBX controls in forced swimming test (FST). Pht-HrTH significantly increased %open arm time compared to OBX controls in elevated plus maze (EPM) test. Ani-AKH significantly increased %open arm entry compared to sham control while Ani-AKH and Pht-HrTH significantly increased %open arm entry compared to OBX controls in EPM. In PTSD study Ani-AKH and Lia-AKH significantly decreased immobility time compared to traumatized controls in FST. In acoustic startle reflex test, Ani-AKH, Lia-AKH and Pht-HrTH significantly decreased average startle amplitude compared to non-traumatized controls in PTSD study. Metabolomic studies showed that AKH may affect glutamatergic and dopaminergic system and neurochemistry. In conclusion, AKH peptides had wide ranging effects on behavior and improved performance in OBX and PTSD models in rats.

Animal models for the discovery of novel drugs for post-traumatic stress disorder

INTRODUCTION

Existing pharmacological treatments for PTSD are limited and have been used primarily because of their effectiveness in other psychiatric conditions. To generate novel, PTSD specific pharmacotherapy, researchers must utilize animal models to assess the efficacy of experimental drugs.

AREAS COVERED

This review includes a discussion of factors that should be considered when developing an animal model of PTSD, as well as descriptions of the most commonly used models. Researchers have utilized physical stressors, psychological stressors, or a combination of the two to induce PTSD-like physiological and behavioral sequelae in animals. Such models have provided researchers with a valuable tool to examine the neurobiological mechanisms underlying the condition.

EXPERT OPINION

PTSD is a heterogeneous disorder that manifests as different symptom clusters in different individuals. Thus, there cannot be a one-size-fits-all approach to modeling the disorder in animals. Preclinical investigators must adopt a concentrated effort aimed at modeling specific PTSD subtypes and the distinct symptom profiles that result from specific types of human trauma. Moreover, researchers have focused so much on modeling a single PTSD syndrome in animals that studies examining only specific facets of the disorder are largely ignored. Future research employing animal models of PTSD requires greater focus on the nuances of PTSD.

Hexobarbital Sleep Test for Predicting the Susceptibility or Resistance to Experimental Posttraumatic Stress Disorder

Hexobarbital sleep test (HST) was performed in male Wistar rats (hexobarbital 60 mg/kg, i.p.) 30 days prior to stress exposure. Based on the duration of hexobarbital-induced sleep, rats were divided into two groups, animals with high intensity (fast metabolizers (FM), sleep duration <15 min) or low intensity of hexobarbital metabolism (slow metabolizers (SM), sleep duration ≥15 min). The SM and FM groups were then divided into two subgroups: unstressed and stressed groups. The stressed subgroups were exposed to predator scent stress for 10 days followed by 15 days of rest. SM and FM rats from the unstressed group exhibited different behavioral and endocrinological patterns. SM showed greater anxiety and higher corticosterone levels. In stressed animals, anxiety-like posttraumatic stress disorder (PTSD) behavior was aggravated only in SM. Corticosterone levels in the stressed FM, PTSD-resistant rats, were lower than in unstressed SM. Thus, HST was able to predict the susceptibility or resistance to experimental PTSD, which was consistent with the changes in glucocorticoid metabolism.

Chronic stress and endothelial dysfunction: mechanisms, experimental challenges, and the way ahead

Although chronic stress is an important risk factor for cardiovascular diseases (CVD) onset, the underlying mechanisms driving such pathophysiological complications remain relatively unknown. Here, dysregulation of innate stress response systems and the effects of downstream mediators are strongly implicated, with the vascular endothelium emerging as a primary target of excessive glucocorticoid and catecholamine action. Therefore, this review article explores the development of stress-related endothelial dysfunction by focusing on the following: 1) assessing the phenomenon of stress and complexities surrounding this notion, 2) discussing mechanistic links between chronic stress and endothelial dysfunction, and 3) evaluating the utility of various preclinical models currently employed to study mechanisms underlying the onset of stress-mediated complications such as endothelial dysfunction. The data reveal that preclinical models play an important role in our efforts to gain an increased understanding of mechanisms underlying stress-mediated endothelial dysfunction. It is our understanding that this provides a good foundation going forward, and we propose that further efforts should be made to 1) more clearly define the concept of stress and 2) standardize protocols of animal models with specific guidelines to better indicate the mental complications that are simulated.

Why behavioral neuroscience still needs diversity?: A curious case of a persistent need

In the past few decades, a substantial portion of neuroscience research has moved from studies conducted across a spectrum of animals to reliance on a few species. While this undoubtedly promotes consistency, in-depth analysis, and a better claim to unraveling molecular mechanisms, investing heavily in a subset of species also restricts the type of questions that can be asked, and impacts the generalizability of findings. A conspicuous body of literature has long advocated the need to expand the diversity of animal systems used in neuroscience research. Part of this need is utilitarian with respect to translation, but the remaining is the knowledge that historically, a diverse set of species were instrumental in obtaining transformative understanding. We argue that diversifying matters also because the current approach limits the scope of what can be discovered. Technological advancements are already bridging several practical gaps separating these two worlds. What remains is a wholehearted embrace by the community that has benefitted from past history. We suggest the time for it is now.

Rodent models of post-traumatic stress disorder: behavioral assessment

Although the etiology and expression of psychiatric disorders are complex, mammals show biologically preserved behavioral and neurobiological responses to valent stimuli which underlie the use of rodent models of post-traumatic stress disorder (PTSD). PTSD is a complex phenotype that is difficult to model in rodents because it is diagnosed by patient interview and influenced by both environmental and genetic factors. However, given that PTSD results from traumatic experiences, rodent models can simulate stress induction and disorder development. By manipulating stress type, intensity, duration, and frequency, preclinical models reflect core PTSD phenotypes, measured through various behavioral assays. Paradigms precipitate the disorder by applying physical, social, and psychological stressors individually or in combination. This review discusses the methods used to trigger and evaluate PTSD-like phenotypes. It highlights studies employing each stress model and evaluates their translational efficacies against DSM-5, validity criteria, and criteria proposed by Yehuda and Antelman's commentary in 1993. This is intended to aid in paradigm selection by informing readers about rodent models, their benefits to the clinical community, challenges associated with the translational models, and opportunities for future work. To inform PTSD model validity and relevance to human psychopathology, we propose that models incorporate behavioral test batteries, individual differences, sex differences, strain and stock differences, early life stress effects, biomarkers, stringent success criteria for drug development, Research Domain Criteria, technological advances, and cross-species comparisons. We conclude that, despite the challenges, animal studies will be pivotal to advances in understanding PTSD and the neurobiology of stress.

Pre-clinical models of reward deficiency syndrome: A behavioral octopus

Individuals with mood disorders or with addiction, impulsivity and some personality disorders can share in common a dysfunction in how the brain perceives reward, where processing of natural endorphins or the response to exogenous dopamine stimulants is impaired. Reward Deficiency Syndrome (RDS) is a polygenic trait with implications that suggest cross-talk between different neurological systems that include the known reward pathway, neuroendocrine systems, and motivational systems. In this review we evaluate well-characterized animal models for their construct validity and as potential models for RDS. Animal models used to study substance use disorder, major depressive disorder (MDD), early life stress, immune dysregulation, attention deficit hyperactivity disorder (ADHD), post traumatic stress disorder (PTSD), compulsive gambling and compulsive eating disorders are discussed. These disorders recruit underlying reward deficiency mechanisms in multiple brain centers. Because of the widespread and remarkable array of associated/overlapping behavioral manifestations with a common root of hypodopaminergia, the basic endophenotype recognized as RDS is indeed likened to a behavioral octopus. We conclude this review with a look ahead on how these models can be used to investigate potential therapeutics that target the underlying common deficiency.

Myocardial fibrosis, inflammation, and altered cardiac gene expression profiles in rats exposed to a predator-based model of posttraumatic stress disorder

People who are exposed to life-threatening trauma are at risk of developing posttraumatic stress disorder (PTSD). In addition to psychological manifestations, PTSD is associated with an increased risk of myocardial infarction, arrhythmias, hypertension, and other cardiovascular problems. We previously reported that rats exposed to a predator-based model of PTSD develop myocardial hypersensitivity to ischemic injury. This study characterized cardiac changes in histology and gene expression in rats exposed this model. Male rats were subjected to two cat exposures (separated by a period of 10 d) and daily cage-mate changes for 31 d. Control rats were not exposed to the cat or cage-mate changes. Ventricular tissue was analyzed by RNA sequencing, western blotting, histology, and immunohistochemistry. Multifocal lesions characterized by necrosis, mononuclear cell infiltration, and collagen deposition were observed in hearts from all stressed rats but none of the control rats. Gene expression analysis identified clusters of upregulated genes associated with endothelial to mesenchymal transition, endothelial migration, mesenchyme differentiation, and extracellular matrix remodeling in hearts from stressed rats. Consistent with endothelial to mesenchymal transition, rats from stressed hearts exhibited increased expression of α-smooth muscle actin (a myofibroblast marker) and a decrease in the number of CD31 positive endothelial cells. These data provide evidence that predator-based stress induces myocardial lesions and reprograming of cardiac gene expression. These changes may underlie the myocardial hypersensitivity to ischemia observed in these animals. This rat model may provide a useful tool for investigating the cardiac impact of PTSD and other forms of chronic psychological stress.Lay summaryChronic predator stress induces the formation of myocardial lesions characterized by necrosis, collagen deposition, and mononuclear cell infiltration. This is accompanied by changes in gene expression and histology that are indicative of cardiac remodeling. These changes may underlie the increased risk of arrhythmias, myocardial infarction, and other cardiac pathologies in people who have PTSD or other forms of chronic stress.

Investigating Individual Pre-trauma Susceptibility to a PTSD-Like Phenotype in Animals

Post-Traumatic Stress Disorder (PTSD) is a complex condition that develops after experiencing a severe emotional trauma, with or without physical trauma. There is no known cure and evidence-based treatments, which are effective in reducing symptoms, have low retention rates. It is therefore important, in addition to seeking new therapeutics, to identify ways to reduce the likelihood of developing PTSD. The fact that some, but not all, individuals exposed to the same traumatic event develop PTSD suggests that there is individual susceptibility. Investigating susceptibility and underlying factors will be better guided if there is a coherent framework for such investigations. In this review, we propose that susceptibility is a dynamic state that is comprised of susceptibility factors (before trauma) and sequalae factors (during or after trauma, but before PTSD diagnosis). We define key features of susceptibility and sequalae factors as: (1) they are detectable before trauma (susceptibility factors) or during/shortly after trauma (sequalae factors), (2) they can be manipulated, and (3) manipulation of these factors alters the likelihood of developing PTSD, thus affecting resilience. In this review we stress the importance of investigating susceptibility to PTSD with appropriate animal models, because prospective human studies are expensive and manipulation of susceptibility and sequalae factors for study purposes may not always be feasible. This review also provides a brief overview of a subset of animal models that study PTSD-related behaviors and related alterations in endocrine and brain systems that focus on individual differences, peri- and post-trauma. Attention is drawn to the RISP model (Revealing Individual Susceptibility to a PTSD-like Phenotype) which assesses susceptibility before trauma. Using the RISP model and expression of plasticity-associated immediate early genes, Arc and Homer1a, we have identified impaired hippocampal function as a potential susceptibility factor. We further discuss other putative susceptibility factors and approaches to mitigate them. We assert that this knowledge will guide successful strategies for interventions before, during or shortly after trauma that can decrease the probability of developing PTSD.

The predator odor avoidance model of post-traumatic stress disorder in rats

Individuals with post-traumatic stress disorder avoid trauma-related stimuli and exhibit blunted hypothalamic-pituitary-adrenal axis response at the time of trauma. Our laboratory uses predator odor (i.e. bobcat urine) stress to divide adult Wistar rats into groups that exhibit high (avoiders) or low (nonavoiders) avoidance of a predator odor-paired context, modeling the fact that not all humans exposed to traumatic events develop psychiatric conditions. Male avoiders exhibit lower body weight gain after stress, as well as extinction-resistant avoidance that persists after a second stress exposure. These animals also show attenuated hypothalamic-pituitary-adrenal axis response to predator odor that predicts subsequent avoidance of the odor-paired context. Avoiders exhibit unique brain activation profiles relative to nonavoiders and controls (as measured by Fos immunoreactivity), and higher corticotropin-releasing factor levels in multiple brain regions. Furthermore, avoider rats exhibit escalated and compulsive-like alcohol self-administration after traumatic stress. Here, we review the predator odor avoidance model of post-traumatic stress disorder and its utility for tracking behavior and measuring biological outcomes predicted by avoidance. The major strengths of this model are (i) etiological validity with exposure to a single intense stressor, (ii) established approach distinguishing individual differences in stress reactivity, and (iii) robust behavioral and biological phenotypes during and after trauma.

A predator-based psychosocial stress animal model of PTSD in females: Influence of estrous phase and ovarian hormones

Traumatized women are more likely than traumatized men to develop post-traumatic stress disorder (PTSD). Still, the inclusion of females in animal models of PTSD has largely been avoided, likely due to the variable hormone profile of female rodents. Because a valid animal model of PTSD that incorporates females is still needed, we examined the influence of estrous stage and ovarian hormones on the female rat response to a predator-based psychosocial stress model of PTSD. Female Sprague-Dawley rats were exposed to psychosocial stress or control conditions for 31 days. Stressed rats were given two cat exposures and daily social instability; control rats were handled daily. Beginning on Day 32, rats underwent physiological or behavioral testing. In Experiment 1, vaginal smears were collected on days of the first and second cat exposures and each day of behavioral testing to determine estrous stage. In Experiments 2 and 3, ovariectomized or sham control rats were exposed to stress or control conditions. Then, they were given behavioral testing (Exp 2), or their hearts were isolated and subjected to ischemia/reperfusion on a Langendorff isolated heart system (Exp 3). Chronic stress increased anxiety-like behavior, irrespective of estrous stage or ovariectomy condition. Ovariectomized females displayed greater startle responses and anxiety-like behavior than sham rats. Stress had no impact on myocardial sensitivity to ischemic injury; however, ovariectomized females exhibited greater ischemia-induced infarction than sham rats. These findings suggest that ovarian hormones may prevent anxiety-like behavior and be cardioprotective in non-stressed controls, but they do not interact with chronic stress to influence the development of PTSD-like sequelae in female rats.

Clinical Therapeutic Strategy and Neuronal Mechanism Underlying Post-Traumatic Stress Disorder (PTSD)

Post-traumatic stress disorder (PTSD) is characterized by an exaggerated response to contextual memory and impaired fear extinction, with or without mild cognitive impairment, learning deficits, and nightmares. PTSD is often developed by traumatic events, such as war, terrorist attack, natural calamities, etc. Clinical and animal studies suggest that aberrant susceptibility of emotion- and fear-related neurocircuits, including the amygdala, prefrontal cortex (PFC), and hippocampus may contribute to the development and retention of PTSD symptoms. Psychological and pharmacological therapy, such as cognitive behavioral therapy (CBT), and treatment with anti-depressive agents and/or antipsychotics significantly attenuate PTSD symptoms. However, more effective therapeutics are required for improvement of quality of life in PTSD patients. Previous studies have reported that ω3 long-chain polyunsaturated fatty acid (LCPUFA) supplements can suppress the development of PTSD symptoms. Fatty acid binding proteins (FABPs) are essential for LCPUFA intracellular trafficking. In this review, we have introduced Fabp3 null mice as an animal model of PTSD with impaired fear extinction. Moreover, we have addressed the neuronal circuits and novel therapeutic strategies for PTSD symptoms.

Stress Across Generations: DNA Methylation as a Potential Mechanism Underlying Intergenerational Effects of Stress in Both Post-traumatic Stress Disorder and Pre-clinical Predator Stress Rodent Models

Although most humans will experience some type of traumatic event in their lifetime only a small set of individuals will go on to develop post-traumatic stress disorder (PTSD). Differences in sex, age, trauma type, and comorbidity, along with many other elements, contribute to the heterogenous manifestation of this disorder. Nonetheless, aberrant hypothalamus-pituitary-adrenal (HPA) axis activity, especially in terms of cortisol and glucocorticoid receptor (GR) alterations, has been postulated as a tenable factor in the etiology and pathophysiology of PTSD. Moreover, emerging data suggests that the harmful effects of traumatic stress to the HPA axis in PTSD can also propagate into future generations, making offspring more prone to psychopathologies. Predator stress models provide an ethical and ethologically relevant way to investigate tentative mechanisms that are thought to underlie this phenomenon. In this review article, we discuss findings from human and laboratory predator stress studies that suggest changes to DNA methylation germane to GRs may underlie the generational effects of trauma transmission. Understanding mechanisms that promote stress-induced psychopathology will represent a major advance in the field and may lead to novel treatments for such devastating, and often treatment-resistant trauma and stress-disorders.

Animal Models of PTSD: A Critical Review

The goals of animal research in post-traumatic stress disorder (PTSD) include better understanding the neurophysiological etiology of PTSD, identifying potential targets for novel pharmacotherapies, and screening drugs for their potential use as PTSD treatment in humans. Diagnosis of PTSD relies on a patient interview and, as evidenced by changes to the diagnostic criteria in the DSM-5, an adequate description of this disorder in humans is a moving target. Therefore, it may seem insurmountable to model the construct of PTSD in animals such as rodents. Fortunately, the neural circuitry involved in fear and anxiety, thought to be essential to the etiology of PTSD in humans, is highly conserved throughout evolution. Furthermore, many symptoms can be modeled using behavioral tests that have face, construct, and predictive validity. Because PTSD is precipitated by a definite traumatic experience, animal models can simulate the induction of PTSD, and test causal factors with longitudinal designs. Accordingly, several animal models of physical and psychological trauma have been established. This review discusses the widely used animal models of PTSD in rodents, and overviews their strengths and weaknesses in terms of face, construct, and predictive validity.

Myocardial hypersensitivity to ischemic injury is not reversed by clonidine or propranolol in a predator-based rat model of posttraumatic stress disorder

Individuals with posttraumatic stress disorder (PTSD) are at increased risk for cardiovascular disease. We previously reported that a predator-based model of PTSD increases myocardial sensitivity to ischemic injury. Heightened sympathetic signaling has a well-established role in the formation of anxiety associated with PTSD and may also contribute to worsening of myocardial injury in the ischemic heart. Thus, we examined whether suppression of sympathetic tone protects the ischemic heart in rats subjected to this model of PTSD. Rats were treated with saline or clonidine throughout the 31-day stress paradigm. Behavior on the elevated plus maze (EPM) was assessed on Day 32, and hearts were subjected to an ischemic insult on day 33. Stressed rats exhibited increased anxiety on the EPM and significantly larger myocardial infarcts following ischemia. Clonidine reversed the anxiety-like behavior but had no impact on infarct size. In a subsequent experiment, rats were treated with propranolol in their drinking water throughout the stress paradigm. Propranolol had no effect on either anxiety or myocardial sensitivity to ischemic injury. These findings suggest that the myocardial hypersensitivity to ischemic injury observed in this model is not caused by increased sympathetic tone or chronic β-adrenergic receptor signaling.

Comparing Perika St. John's Wort and Sertraline for Treatment of Posttraumatic Stress Disorder in Mice

Posttraumatic stress disorder (PTSD) is a serious mental health condition that affects some individuals who have witnessed or experienced a life-threatening or traumatic event. An enhanced or exaggerated acoustic startle response (ASR), reflecting heightened sensitivity to unexpected, loud sound, is a hallmark symptom of PTSD. Antidepressant medications, such as sertraline, are first-line pharmacotherapeutic agents in the treatment of PTSD, but concerns about potential side effects or taking synthetic drugs prompt discovery of naturalistic therapeutic agents. This study examined the relative effectiveness of a compound containing St. John's Wort (SJW), an herb widely prescribed for depression in Europe and sold as a dietary supplement in the United States, compared to sertraline (Zoloft) in a mouse model of PTSD. Thirty-six mice were tested for baseline ASR, then they were exposed to rats in a predator exposure paradigm known to induce PTSD-like symptoms. Mice were randomly divided into three groups for treatment (control, sertraline, SJW), and ASR was retested one week later. One-way ANOVAs found no significant group differences in ASR amplitude at baseline but a significant effect of Treatment Group after predator exposure, F(2, 33) = 5.645, p = .008, n² = .225, when SJW-treated mice had ASR amplitudes that were significantly lower than sertraline-treated mice (by 27%) and controls (by 26%). Fecal boli counts showed a similar pattern, with lowest counts in SJW-treated mice. These results suggest SJW could be considered for studies of PTSD treatment in humans as well.

Animal models of PTSD: a challenge to be met

Recent years have seen increased interest in psychopathologies related to trauma exposure. Specifically, there has been a growing awareness to posttraumatic stress disorder (PTSD) in part due to terrorism, climate change-associated natural disasters, the global refugee crisis, and increased violence in overpopulated urban areas. However, notwithstanding the increased awareness to the disorder, the increasing number of patients, and the devastating impact on the lives of patients and their families, the efficacy of available treatments remains limited and highly unsatisfactory. A major scientific effort is therefore devoted to unravel the neural mechanisms underlying PTSD with the aim of paving the way to developing novel or improved treatment approaches and drugs to treat PTSD. One of the major scientific tools used to gain insight into understanding physiological and neuronal mechanisms underlying diseases and for treatment development is the use of animal models of human diseases. While much progress has been made using these models in understanding mechanisms of conditioned fear and fear memory, the gained knowledge has not yet led to better treatment options for PTSD patients. This poor translational outcome has already led some scientists and pharmaceutical companies, who do not in general hold opinions against animal models, to propose that those models should be abandoned. Here, we critically examine aspects of animal models of PTSD that may have contributed to the relative lack of translatability, including the focus on the exposure to trauma, overlooking individual and sex differences, and the contribution of risk factors. Based on findings from recent years, we propose research-based modifications that we believe are required in order to overcome some of the shortcomings of previous practice. These modifications include the usage of animal models of PTSD which incorporate risk factors and of the behavioral profiling analysis of individuals in a sample. These modifications are aimed to address factors such as individual predisposition and resilience, thus taking into consideration the fact that only a fraction of individuals exposed to trauma develop PTSD. We suggest that with an appropriate shift of practice, animal models are not only a valuable tool to enhance our understanding of fear and memory processes, but could serve as effective platforms for understanding PTSD, for PTSD drug development and drug testing.

Predator-based psychosocial stress model of PTSD differentially influences voluntary ethanol consumption depending on methodology

Post-traumatic stress disorder (PTSD) is a debilitating psychological disorder typified by diagnostic symptom clusters including hyperarousal, avoidance, negative cognitions and mood, and intrusive re-experiencing of the traumatic event. Patients with PTSD have been reported to self-medicate with alcohol to ameliorate hyperarousal symptoms associated with the disorder. Research utilizing rodent models of PTSD to emulate this behavioral phenomenon has thus far yielded inconsistent results. In the present study, we examined the effects of a predator-based psychosocial stress model of PTSD on voluntary ethanol consumption. In the first of two experiments, following exposure to a 31-day stress or control paradigm, rats were singly housed during the dark cycle with free access to 1% sucrose solution or 10% ethanol, which was also sweetened with 1% sucrose. Over the course of a 20-day period of ethanol access, stressed rats consumed significantly less ethanol than non-stressed rats. These counterintuitive results prompted the completion of a second experiment which was identical to the first, except rats were also exposed to the two-bottle paradigm for 20 days before the stress or control paradigm. In the second experiment, after the stress manipulation, stressed rats exhibited significantly greater ethanol preference than non-stressed rats. These findings suggest that prior exposure to ethanol influences the subsequent effect of stress on ethanol intake. They also validate the use of the present model of PTSD to examine potential mechanisms underlying stress-related changes in ethanol-seeking behavior.

Differential effects of chronic stress in young-adult and old female mice: cognitive-behavioral manifestations and neurobiological correlates

Stress-related psychopathology is highly prevalent among elderly individuals and is associated with detrimental effects on mood, appetite and cognition. Conversely, under certain circumstances repeated mild-to-moderate stressors have been shown to enhance cognitive performance in rodents and exert stress-inoculating effects in humans. As most stress-related favorable outcomes have been reported in adolescence and young-adulthood, this apparent disparity could result from fundamental differences in how aging organisms respond to stress. Furthermore, given prominent age-related alterations in sex hormones, the effect of chronic stress in aging females remains a highly relevant yet little studied issue. In the present study, female C57BL/6 mice aged 3 (young-adult) and 20-23 (old) months were subjected to 8 weeks of chronic unpredictable stress (CUS). Behavioral outcomes were measured during the last 3 weeks of the CUS protocol, followed by brain dissection for histological and molecular end points. We found that in young-adult female mice, CUS resulted in decreased anxiety-like behavior and enhanced cognitive performance, whereas in old female mice it led to weight loss, dysregulated locomotion and memory impairment. These phenotypes were paralleled by differential changes in the expression of hypothalamic insulin and melanocortin-4 receptors and were consistent with an age-dependent reduction in the dynamic range of stress-related changes in the hippocampal transcriptome. Supported by an integrated microRNA (miRNA)-mRNA expression analysis, the present study proposes that, when confronted with ongoing stress, neuroprotective mechanisms involving the upregulation of neurogenesis, Wnt signaling and miR-375 can be harnessed more effectively during young-adulthood. Conversely, we suggest that aging alters the pattern of immune activation elicited by stress. Ultimately, interventions that modulate these processes could reduce the burden of stress-related psychopathology in late life.

Maternal programming of sex-specific responses to predator odor stress in adult rats

Prenatal stress mediated through the mother can lead to long-term adaptations in stress-related phenotypes in offspring. This study tested the long-lasting effect of prenatal exposure to predator odor, an ethologically relevant and psychogenic stressor, in the second half of pregnancy. As adults, the offspring of predator odor-exposed mothers showed increased anxiety-like behaviors in commonly used laboratory tasks assessing novelty-induced anxiety, increased defensive behavior in males and increased ACTH stress reactivity in females in response to predator odor. Female offspring from predator odor-exposed dams showed increased transcript abundance of glucocorticoid receptor (NR3C1) on the day of birth and FK506 binding protein 5 (FKBP5) in adulthood in the amygdala. The increase in FKBP5 expression was associated with decreased DNA methylation in Fkbp5 intron V. These results indicate a sex-specific response to maternal programming by prenatal predator odor exposure and a potential epigenetic mechanism linking these responses with modifications of the stress axis in females. These results are in accordance with the mismatch hypothesis stating that an animal's response to cues within its life history reflects environmental conditions anticipated during important developmental periods and should be adaptive when these conditions are concurring.

Is spaceflight-induced immune dysfunction linked to systemic changes in metabolism?

The Space Shuttle Atlantis launched on its final mission (STS-135) on July 8, 2011. After just under 13 days, the shuttle landed safely at Kennedy Space Center (KSC) for the last time. Female C57BL/6J mice flew as part of the Commercial Biomedical Testing Module-3 (CBTM-3) payload. Ground controls were maintained at the KSC facility. Subsets of these mice were made available to investigators as part of NASA’s Bio-specimen Sharing Program (BSP). Our group characterized cell phenotype distributions and phagocytic function in the spleen, catecholamine and corticosterone levels in the adrenal glands, and transcriptomics/metabolomics in the liver. Despite decreases in most splenic leukocyte subsets, there were increases in reactive oxygen species (ROS)-related activity. Although there were increases noted in corticosterone levels in both the adrenals and liver, there were no significant changes in catecholamine levels. Furthermore, functional analysis of gene expression and metabolomic profiles suggest that the functional changes are not due to oxidative or psychological stress. Despite changes in gene expression patterns indicative of increases in phagocytic activity (e.g. endocytosis and formation of peroxisomes), there was no corresponding increase in genes related to ROS metabolism. In contrast, there were increases in expression profiles related to fatty acid oxidation with decreases in glycolysis-related profiles. Given the clear link between immune function and metabolism in many ground-based diseases, we propose a similar link may be involved in spaceflight-induced decrements in immune and metabolic function.

Stress-altered synaptic plasticity and DAMP signaling in the hippocampus-PFC axis; elucidating the significance of IGF-1/IGF-1R/CaMKIIα expression in neural changes associated with a prolonged exposure therapy

Traumatic stress patients showed significant improvement in behavior after a prolonged exposure to an unrelated stimulus. This treatment method attempts to promote extinction of the fear memory associated with the initial traumatic experience. However, the subsequent prolonged exposure to such stimulus creates an additional layer of neural stress. Although the mechanism remains unclear, prolonged exposure therapy (PET) likely involves changes in synaptic plasticity, neurotransmitter function and inflammation; especially in parts of the brain concerned with the formation and retrieval of fear memory (Hippocampus and Prefrontal Cortex: PFC). Since certain synaptic proteins are also involved in danger-associated molecular pattern signaling (DAMP), we identified the significance of IGF-1/IGF-1R/CaMKIIα expression as a potential link between the concurrent progression of synaptic and inflammatory changes in stress. Thus, a comparison between IGF-1/IGF-1R/CaMKIIα, synaptic and DAMP proteins in stress and PET may highlight the significance of PET on synaptic morphology and neuronal inflammatory response. In behaviorally characterized Sprague-Dawley rats, there was a significant decline in neural IGF-1 (p<0.001), hippocampal (p<0.001) and cortical (p<0.05) IGF-1R expression. These animals showed a significant loss of presynaptic markers (synaptophysin; p<0.001), and changes in neurotransmitters (VGLUT2, Tyrosine hydroxylase, GABA, ChAT). Furthermore, naïve stressed rats recorded a significant decrease in post-synaptic marker (PSD-95; p<0.01) and synaptic regulator (CaMKIIα; p<0.001). As part of the synaptic response to a decrease in brain CaMKIIα, small ion conductance channel (KCa2.2) was upregulated in the brain of naïve stressed rats (p<0.01). After a PET, an increase in IGF-1 (p<0.05) and IGF-1R was recorded in the Stress-PET group (p<0.001). As such, hippocampal (p<0.001), but not cortical (ns) synaptophysin expression increased in Stress-PET. Although PSD-95 was relatively unchanged in the hippocampus and PFC, CaMKIIα (p<0.001) and KCa2.2 (p<0.01) were upregulated in Stress-PET, and may be involved in extinction of fear memory-related synaptic potentials. These changes were also associated with a normalized neurotransmitter function, and a significant reduction in open space avoidance; when the animals were assessed in elevated plus maze (EPM). In addition to a decrease in IGF-1/IGF-1R, an increase in activated hippocampal and cortical microglia was seen in stress (p<0.05) and after a PET (Stress-PET; p<0.001). Furthermore, this was linked with a significant increase in HMGB1 (Hippocampus: p<0.001, PFC: p<0.05) and TLR4 expression (Hippocampus: p<0.01; PFC: ns) in the neurons. Taken together, this study showed that traumatic stress and subsequent PET involves an event-dependent alteration of IGF1/IGF-1R/CaMKIIα. Firstly, we showed a direct relationship between IGF-1/IGF-1R expression, presynaptic function (synaptophysin) and neurotransmitter activity in stress and PET. Secondly, we identified the possible role of CaMKIIα in post-synaptic function and regulation of small ion conductance channels. Lastly, we highlighted some of the possible links between IGF1/IGF-1R/CaMKIIα, the expression of DAMP proteins, Microglia activation, and its implication on synaptic plasticity during stress and PET.

Post-traumatic stress disorder and beyond: an overview of rodent stress models

Post-traumatic stress disorder (PTSD) is a psychiatric disorder of high prevalence and major socioeconomic impact. Patients suffering from PTSD typically present intrusion and avoidance symptoms and alterations in arousal, mood and cognition that last for more than 1 month. Animal models are an indispensable tool to investigate underlying pathophysiological pathways and, in particular, the complex interplay of neuroendocrine, genetic and environmental factors that may be responsible for PTSD induction. Since the 1960s, numerous stress paradigms in rodents have been developed, based largely on Seligman's seminal formulation of 'learned helplessness' in canines. Rodent stress models make use of physiological or psychological stressors such as foot shock, underwater trauma, social defeat, early life stress or predator-based stress. Apart from the brief exposure to an acute stressor, chronic stress models combining a succession of different stressors for a period of several weeks have also been developed. Chronic stress models in rats and mice may elicit characteristic PTSD-like symptoms alongside, more broadly, depressive-like behaviours. In this review, the major existing rodent models of PTSD are reviewed in terms of validity, advantages and limitations; moreover, significant results and implications for future research-such as the role of FKBP5, a mediator of the glucocorticoid stress response and promising target for therapeutic interventions-are discussed.

Chronic subordinate colony housing paradigm: A mouse model for mechanisms of PTSD vulnerability, targeted prevention, and treatment-2016 Curt Richter Award Paper

There is considerable individual variability in vulnerability for developing posttraumatic stress disorder (PTSD); evidence suggests that this variability is related in part to genetic and environmental factors, including adverse early life experience. Interestingly, recent studies indicate that induction of chronic low-grade inflammation may be a common mechanism underlying gene and environment interactions that increase the risk for development of PTSD symptoms, and, therefore, may be a target for novel interventions for prevention or treatment of PTSD. Development of murine models with face, construct, and predictive validity would provide opportunities to investigate in detail complex genetic, environmental, endocrine, and immunologic factors that determine vulnerability to PTSD-like syndromes, and furthermore may provide mechanistic insight leading to development of novel interventions for both prevention and treatment of PTSD symptoms. Here we describe the potential use of the chronic subordinate colony housing (CSC) paradigm in mice as an adequate animal model for development of a PTSD-like syndrome and describe recent studies that suggest novel interventions for the prevention and treatment of PTSD.

HPA Axis Interactions with Behavioral Systems

Perhaps the most salient behaviors that individuals engage in involve the avoidance of aversive experiences and the pursuit of pleasurable experiences. Engagement in these behaviors is regulated to a significant extent by an individual's hormonal milieu. For example, glucocorticoid hormones are produced by the hypothalamic-pituitary-adrenocortical (HPA) axis, and influence most aspects of behavior. In turn, many behaviors can influence HPA axis activity. These bidirectional interactions not only coordinate an individual's physiological and behavioral states to each other, but can also tune them to environmental conditions thereby optimizing survival. The present review details the influence of the HPA axis on many types of behavior, including appetitively-motivated behaviors (e.g., food intake and drug use), aversively-motivated behaviors (e.g., anxiety-related and depressive-like) and cognitive behaviors (e.g., learning and memory). Conversely, the manuscript also describes how engaging in various behaviors influences HPA axis activity. Our current understanding of the neuronal and/or hormonal mechanisms that underlie these interactions is also summarized. © 2016 American Physiological Society. Compr Physiol 6:1897-1934, 2016.

The ethical challenges of animal research

In 1966, Henry K. Beecher published an article entitled "Ethics and Clinical Research" in the New England Journal of Medicine, which cited examples of ethically problematic human research. His influential paper drew attention to common moral problems such as inadequate attention to informed consent, risks, and efforts to provide ethical justification. Beecher's paper provoked significant advancements in human research policies and practices. In this paper, we use an approach modeled after Beecher's 1966 paper to show that moral problems with animal research are similar to the problems Beecher described for human research. We describe cases that illustrate ethical deficiencies in the conduct of animal research, including inattention to the issue of consent or assent, incomplete surveys of the harms caused by specific protocols, inequitable burdens on research subjects in the absence of benefits to them, and insufficient efforts to provide ethical justification. We provide a set of recommendations to begin to address these deficits.

Glucocorticoid levels after exposure to predator odor and chronic psychosocial stress with dexamethasone application in rats

This study was conducted to explore the effects of specific psychosocial paradigm on predator animal posttraumatic stress model and to test the hypothesis that psychosocially stressed rats would exibit abnormal levels of cortisol and a larger suppression of cortisol levels after the application of dexamethasone. Animals were divided in two groups: experimental and control groups. The experimental group was exposed to two types of stressors: acute immobilization stress, and combined predator stress and daily social stress with application of dexamethasone. Blood sampling was performed at three different times. We found statistically significant results after analyzing the differences between cortisol levels in different times of blood sampling in the group of animals exposed to stress with dexamethasone application. Statistical significance was found when we compared the experimental group with the control group in terms of elevated cortisol levels during blood sampling after stress paradigm exposition. Many significant disruptions in the functioning of the hypothalamic-pituitary-adrenal axis were observed, such as decrease in basal cortisol levels and enhanced dexamethasone-induced inhibition of cortisol levels. These findings are important because their impact can translate to human individuals with posttraumatic stress disorder, which is the most important role of every animal model in research.