Conditioned fear stress combined with single-prolonged stress: a new PTSD mouse model

Agmatine diminishes behavioral and endocrine alterations in a rat model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD), is a severe anxiety disorder characterized by associative fear conditioning. Single prolonged stress (SPS) is a widely accepted reliable animal model to stimulate PTSD. Agmatine is an endogenous neuromodulator of stress; however, its effect on PTSD remains to be investigated. This study explored the role of agmatine in conditioned fear response (CFR) in PTSD and highlighted the role of imidazoline receptors in the effect of agmatine. Intra-cerebroventricular (icv) surgery was done in order to facilitate drug administration. Animals were subjected to SPS. Agmatine and the involvement of imidazoline receptors (I1 and I2) were assessed for their effect in fear conditioning apparatus. During weeks 1, 2, and 3, in CFR, agmatine (40 µg/rat, icv) showed significantly decreased freezing time whereas other doses of agmatine (10 and 20 µg/rat, icv). Imidazoline (I1 and I2) receptor agonists Moxonidine (25 µg/rat, icv) and 2-BFI, (10 µg/rat, icv) respectively, at their sub-effective doses, with a submaximal dose of agmatine (20 µg/rat, icv) significantly decreased the altered freezing time during weeks 1, 2 and 3 compared to SPS animals. Moreover, the effective dose of agmatine (40 µg/rat, icv) with imidazoline (I1 and I2) receptor antagonists Efaroxan (10 µg/rat, icv) and Idazoxan (4 µg/rat, icv) respectively does not reversed the effect of agmatine on freezing. Agmatine and its combination with I1 and I2 agonists, normalized the altered freezing behavior, corticosterone level, organ coefficient of adrenal gland, neuroinflammatory and neurotrophic factor due to SPS during CFR projecting its strong therapeutic effect in SPS induced PTSD.

Post-traumatic stress disorder-induced behavioral modulation by the medial septum-medial habenula neural pathway

Post-traumatic stress disorder (PTSD) is characterized by anxiety, excessive fear, distress, and weakness as symptoms of a psychiatric disorder. However, the mechanism associated with its symptoms such as anxiety-like behaviors is not well understood. It is aimed to investigate the underlying mechanisms of the medial septum (MS)-medial habenula (MHb) neural circuit modulating the anxiety-like behaviors of PTSD mice through in vivo fiber photometry recording, optogenetics, behavioral testing by open-field and elevated plus maze, fluorescent gold retrograde tracer technology, and viral tracer technology. In the mouse PTSD model induced by compound stress consisting of single-prolonged stress combined with electrical foot shock, the average peak value of the Ca2 + signals in both the MHb and MS glutamatergic neurons significantly increased. The anterograde and retrograde tracer markers were used to indicate the possible connection between MS and MHb via glutamatergic neural pathway. After the optogenetic manipulation of the MS-MHb pathway in mice with PTSD, if the MS-MHb glutamatergic pathway was inhibited, anxiety was relieved based on changes in the various indices of behavioral experiments in mice with PTSD. Moreover, the heart rate of mice decreased. In conclusion, both glutamatergic neurons located in MS and MHb can be engaged in the development of PTSD anxiety-like behavior, and the MS-MHb can be related to the regulation of PTSD anxiety-like behavior and cardiac function through the glutamatergic neural pathway.

(2R,6R)-hydroxynorketamine alleviates PTSD-like endophenotypes by regulating the PI3K/AKT signaling pathway in rats

BACKGROUND

Patients diagnosed with post-traumatic stress disorder (PTSD) mainly exhibit enduring adverse emotions, heightening susceptibility to suicidal thoughts and behaviors. Notably, metabolites of ketamine, particularly (2R,6R)-hydroxyketamine (HNK), have demonstrated favorable antidepressant properties. However, the precise mechanism through which HNK exerts its therapeutic effects on negative emotional symptoms in PTSD patients should be fully elucidated.

METHODS

In this investigation, a model involving a single prolonged stress and plantar shock (SPS&S) was utilized, followed by the administration of (2R, 6R)-HNK into the lateral ventricle subsequent to the recovery phase. The evaluation of PTSD-related behaviors was conducted through the open field test (OFT), elevated plus maze test (EMPT), and forced swim test (FST). The expression of phosphatidylinositol 3-kinase (PI3K)/phosphokinase B (AKT) signaling pathway in rat brain regions was analyzed using molecular biology experiments.

RESULTS

SPS&S rats displayed adverse emotional behaviors characterized by depression and anxiety. Treatment with (2R, 6R)-HNK enhanced exploratory behavior and reversed negative emotional behaviors. This intervention mitigated disruptions in the expression levels of PI3K/AKT signaling pathway-associated proteins in the HIP and PFC, without influencing PI3K/AKT signaling in the AMY of SPS&S rats.

CONCLUSION

Traumatic stress can trigger negative emotional reactions in rats, potentially involving the PI3K/AKT signaling pathway in the HIP, PFC, and AMY. The (2R, 6R)-HNK compounds have demonstrated the potential to mitigate adverse emotions in rats subjected to the SPS&S paradigm. This effect may be attributed to the modulation of the PI3K/AKT signaling pathway in the HIP, and PFC, with a particularly notable impact observed in the HIP region.

Central innate immunization induces tolerance against post-traumatic stress disorder-like behavior and neuroinflammatory responses in male mice

Post-traumatic stress disorder (PTSD) is a severe psychiatric disorder associated with abnormally elevated neuroinflammatory responses. Suppression of neuroinflammation is considered to be effective in ameliorating PTSD-like behaviors in rodents. Since pre-stimulation of microglia prior to stress exposure can prevent neuroinflammation, we hypothesized that pre-stimulation of microglia may prevent PTSD in animals. The results show that a single injection of a classical immune stimulant, lipopolysaccharide (LPS), at 50, 100 or 500, but not 10 μg/kg, one day before stress exposure, prevented the anxiety- and fear-like behaviors induced by modified single prolonged stress (mSPS). The time-dependent analysis shows that a single injection of LPS (100 μg/kg) either one or five, but not ten, days before stress prevented mSPS-induced anxiety- and fear-like behaviors. A second low-dose LPS injection 10 days after the first injection or a repeated LPS injection (4 × ) 10 days before stress induced tolerance to mSPS. Mechanistic studies show that a single injection of LPS one day before stress stimulation prevented mSPS-induced increases in levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and IL-6 mRNA in the hippocampus and medial prefrontal cortex. Inhibition of microglia by pretreatment with minocycline or depletion of microglia by PLX3397 abolished the preventive effect of low-dose LPS pre-injection on mSPS-induced anxiety- and fear-like behavior and neuroinflammatory responses. These results suggest that pre-stimulation of microglia may prevent the development of PTSD-like behaviors by attenuating the development of neuroinflammatory responses. This could help to develop new strategies to prevent the damaging effects of harmful stress on the brain.

Electroacupuncture modulates glutamate neurotransmission to alleviate PTSD-like behaviors in a PTSD animal model

Post-traumatic stress disorder (PTSD) is a mental disorder that develops after exposure to a traumatic event. Owing to the relatively low rates of response and remission with selective serotonin reuptake inhibitors as the primary treatment for PTSD, there is a recognized need for alternative strategies to effectively address the symptoms of PTSD. Dysregulation of glutamatergic neurotransmission plays a critical role in various disorders, including anxiety, depression, PTSD, and Alzheimer's disease. Therefore, the regulation of glutamate levels holds great promise as a therapeutic target for the treatment of mental disorders. Electroacupuncture (EA) has become increasingly popular as a complementary and alternative medicine approach. It maintains the homeostasis of central nervous system (CNS) function and alleviates symptoms associated with anxiety, depression, and insomnia. This study investigated the effects of EA at the GV29 (Yintang) acupoint three times per week for 2 weeks in an animal model of PTSD. PTSD was induced using single prolonged stress/shock (SPSS) in mice, that is, SPS with additional foot shock stimulation. EA treatment significantly reduced PTSD-like behavior and effectively regulated serum corticosterone and serotonin levels in the PTSD model. Additionally, EA treatment decreased glutamate levels and glutamate neurotransmission-related proteins (pNR1 and NR2B) in the hippocampus of a PTSD model. In addition, neuronal activity and the number of Golgi-impregnated dendritic spines were significantly lower in the EA treatment group than in the SPSS group. Notably, EA treatment effectively reduced glutamate-induced excitotoxicity (caspase-3, Bax, and pJNK). These findings suggest that EA treatment at the GV29 acupoint holds promise as a potential therapeutic approach for PTSD, possibly through the regulation of NR2B receptor-mediated glutamate neurotransmission to reduce PTSD-like behaviors.

A glutamatergic pathway between the medial habenula and the rostral ventrolateral medulla may regulate cardiovascular function in a rat model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a serious psychiatric disorder, and there is an association between it and the development of cardiovascular disease. The aim of this study was to explore whether there is a glutamatergic pathway connecting the medial habenula (MHb) with the rostral ventrolateral medulla (RVLM) that is involved in the regulation of cardiovascular function in a rat model of PTSD. Vesicular glutamate transporter 2 (VGLUT2)-positive neurons in the MHb region were retrogradely labeled with FluoroGold (FG) by the double-labeling technique of VGLUT2 immunofluorescence and FG retrograde tracing. Rats belonging to the PTSD model group were microinjected with artificial cerebrospinal fluid (ACSF) or kynurenic acid (KYN; a nonselective glutamate receptor blocker) into their RVLM. Subsequently, with electrical stimulation of MHb, the discharge frequency of the RVLM neurons, heart rate, and blood pressure were found to be significantly increased after microinjection of ACSF using an in vivo multichannel synchronous recording technology; however, this effect was inhibited by injection of KYN. The expression of N-methyl-D-aspartic acid (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits was significantly increased in RVLM of PTSD model rats analyzed by the Western blotting technique. These findings suggest that there may be a glutamatergic pathway connection between MHb and RVLM and that this pathway may be involved in the regulation of cardiovascular function in the PTSD model rats, by acting on NMDA and AMPA receptors in the RVLM.

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.

Tanshinone IIA improves contextual fear- and anxiety-like behaviors in mice via the CREB/BDNF/TrkB signaling pathway

Posttraumatic stress disorder (PTSD) is one of the most common psychiatric diseases, which is characterized by the typical symptoms such as re-experience, avoidance, and hyperarousal. However, there are few drugs for PTSD treatment. In this study, conditioned fear and single-prolonged stress were employed to establish PTSD mouse model, and we investigated the effects of Tanshinone IIA (TanIIA), a natural product isolated from traditional Chinese herbal Salvia miltiorrhiza, as well as the underlying mechanisms in mice. The results showed that the double stress exposure induced obvious PTSD-like symptoms, and TanIIA administration significantly decreased freezing time in contextual fear test and relieved anxiety-like behavior in open field and elevated plus maze tests. Moreover, TanIIA increased the spine density and upregulated synaptic plasticity-related proteins as well as activated CREB/BDNF/TrkB signaling pathway in the hippocampus. Blockage of CREB remarkably abolished the effects of TanIIA in PTSD model mice and reversed the upregulations of p-CREB, BDNF, TrkB, and synaptic plasticity-related protein induced by TanIIA. The molecular docking simulation indicated that TanIIA could interact with the CREB-binding protein. These findings indicate that TanIIA ameliorates PTSD-like behaviors in mice by activating the CREB/BDNF/TrkB pathway, which provides a basis for PTSD treatment.

Fluoxetine protects against inflammation and promotes autophagy in mice model of post-traumatic stress disorder

Post-traumatic stress disorder is a major public health problem due to its frequency, chronicity, and disability that impact daily life. Studies have evidenced that the activation/inhibition of autophagy and excessive activation of microglia have a relationship with PTSD. For this purpose, C57BL/6 mice were employed to establish the post-traumatic stress disorder pathology mice model by conditioned fear and single prolonged stress (CF + SPS). Fluoxetine and PLX3397 were administered. PTSD-like behaviors were alleviated following fluoxetine treatment, evidenced via open field and conditioned fear test. Autophagy-associated proteins were upregulated, and inflammation factors were reduced after fluoxetine treatment. Microglia depletion mice showed a lower inflammatory level. In conclusion, fluoxetine can promote autophagy and inhibit neuroinflammation in mice model of PTSD, providing a theoretical basis for fluoxetine in treating PTSD.

Fabp7 Is Required for Normal Sleep Suppression and Anxiety-Associated Phenotype following Single-Prolonged Stress in Mice

Humans with post-traumatic stress disorder (PTSD) exhibit sleep disturbances that include insomnia, nightmares, and enhanced daytime sleepiness. Sleep disturbances are considered a hallmark feature of PTSD; however, little is known about the cellular and molecular mechanisms regulating trauma-induced sleep disorders. Using a rodent model of PTSD called "Single Prolonged Stress" (SPS) we examined the requirement of the brain-type fatty acid binding protein Fabp7, an astrocyte expressed lipid-signaling molecule, in mediating trauma-induced sleep disturbances. We measured baseline sleep/wake parameters and then exposed Fabp7 knock-out (KO) and wild-type (WT) C57BL/6N genetic background control animals to SPS. Sleep and wake measurements were obtained immediately following the initial trauma exposure of SPS, and again 7 days later. We found that active-phase (dark period) wakefulness was similar in KO and WT at baseline and immediately following SPS; however, it was significantly increased after 7 days. These effects were opposite in the inactive-phase (light period), where KOs exhibited increased wake in baseline and following SPS, but returned to WT levels after 7 days. To examine the effects of Fabp7 on unconditioned anxiety following trauma, we exposed KO and WT mice to the light-dark box test before and after SPS. Prior to SPS, KO and WT mice spent similar amounts of time in the lit compartment. Following SPS, KO mice spent significantly more time in the lit compartment compared to WT mice. These results demonstrate that mutations in an astrocyte-expressed gene (Fabp7) influence changes in stress-dependent sleep disturbances and associated anxiety behavior.

A single brief stressful event time-dependently affects object recognition memory and promotes familiarity preference in marmoset monkeys

A stressful experience can enhance information storage and impair memory retrieval in the rodent novel object recognition (NOR) task. However, recent conflicting results underscore the need for further investigation. Nonhuman primates may provide a unique, underexplored and more translational means to investigate stress-mediated changes in memory. Therefore, we assessed whether a single brief extrinsic stress event affects information encoding, storage and/or retrieval in adult marmoset monkeys submitted to the NOR task. This consisted of an initial 10 min familiarization period with two identical neutral objects. After a 6 h delay, a 10 min test trial was held where a new and familiar object could be explored. Stress was induced by a 15 min restraint event held before or after the encoding phase, or prior to retrieval. Pre-encoding stress had no effect on task performance, as this group displayed above-chance novelty preference similar to non-stressed controls. Post-encoding stress induced memory deficits, with both objects being explored equally. Interestingly, pre-retrieval stress induced an above-chance familiarity preference. A single brief stressful event thus affects recognition memory in a time-dependent manner. Also, negative discrimination ratios can be used as a measure of memory in the NOR task and a change in strategy may not mean memory failure in spontaneous learning paradigms.

BHLHE40 modulates post-traumatic stress disorder behaviors with the involvement of the PI3K/AKT signaling pathway

Post-traumatic stress disorder (PTSD) is closely related to the exposure to traumatic events and results in the structural and functional changes of hippocampus. Human basic helix-loop-helix family member e40 (BHLHE40) was reported to be implicated with neuron maturity and neuronal differentiation. The present study aimed to reveal the role of BHLHE40 on single-prolonged stress (SPS) model of PTSD in mice. The morris water maze test, open field test and contextual fear test were conducted to assess memory deficits, anxiety-like behaviors, and freezing of mice. Western blot was performed to identify proteins and reveal their levels in hippocampal tissues. We found that mice receiving SPS exhibited increased anxiety-like behaviors, memory deficits, and prolonged freezing time. The protein levels of BHLHE40 were downregulated in the hippocampal tissues of SPS mice. SPS reduced the protein levels of glutamate receptors, while overexpression of BHLHE40 promoted glutamate receptor protein levels in SPS mice. Moreover, BHLHE40 overexpression activated the PI3K/AKT pathway. BHLHE40 overexpression ameliorated the SPS-induced PTSD-like behavioral deficits. Overall, BHLHE40 promotes glutamate receptor protein levels to ameliorate PTSD-like behaviors with the involvement of the PI3K/AKT pathway. This novel discovery may provide a potential target for the improvement of PTSD.

Systematic Review and Methodological Considerations for the Use of Single Prolonged Stress and Fear Extinction Retention in Rodents

Posttraumatic stress disorder (PTSD) is a mental health condition triggered by experiencing or witnessing a terrifying event that can lead to lifelong burden that increases mortality and adverse health outcomes. Yet, no new treatments have reached the market in two decades. Thus, screening potential interventions for PTSD is of high priority. Animal models often serve as a critical translational tool to bring new therapeutics from bench to bedside. However, the lack of concordance of some human clinical trial outcomes with preclinical animal efficacy findings has led to a questioning of the methods of how animal studies are conducted and translational validity established. Thus, we conducted a systematic review to determine methodological variability in studies that applied a prominent animal model of trauma-like stress, single prolonged stress (SPS). The SPS model has been utilized to evaluate a myriad of PTSD-relevant outcomes including extinction retention. Rodents exposed to SPS express an extinction retention deficit, a phenotype identified in humans with PTSD, in which fear memory is aberrantly retained after fear memory extinction. The current systematic review examines methodological variation across all phases of the SPS paradigm, as well as strategies for behavioral coding, data processing, statistical approach, and the depiction of data. Solutions for key challenges and sources of variation within these domains are discussed. In response to methodological variation in SPS studies, an expert panel was convened to generate methodological considerations to guide researchers in the application of SPS and the evaluation of extinction retention as a test for a PTSD-like phenotype. Many of these guidelines are applicable to all rodent paradigms developed to model trauma effects or learned fear processes relevant to PTSD, and not limited to SPS. Efforts toward optimizing preclinical model application are essential for enhancing the reproducibility and translational validity of preclinical findings, and should be conducted for all preclinical psychiatric research models.

Increased persistence of avoidance behaviour and social deficits with L.rhamnosus JB-1 or selective serotonin reuptake inhibitor treatment following social defeat

Chronic social defeat (CSD) in mice has been suggested as a model for studying post-traumatic stress disorder (PTSD). Our previous work indicated that exposure to Lactobacillus rhamnosus JB-1 (JB-1) during CSD can attenuate subsequent behavioural and immune disruption, suggesting a potential for microbe based therapeutic approaches in PTSD. In the current study, we assessed the ability of JB-1 to mitigate the behavioral consequences of CSD when treatment is instigated in the early post-stress period and compared the probiotic effects with those of the selective serotonin reuptake inhibitor (SSRI), sertraline. JB-1 or sertraline were administered orally 48 h following 10-days of CSD in male C57BL/6 mice. Contrary to our hypothesis of a beneficial effect, 30 days of treatment with either JB-1 or sertraline increased the persistence of both aggressor avoidance and reduced sociability in defeated mice. This was accompanied by lower hippocampal mRNA expression for genes related to fear memory. Defeated mice treated with either JB-1 or sertraline also exhibited systemic immune changes, with a decrease in Th1 cells, activated monocytes, and the monocyte chemoattractant CCL2. This study identifies potentially detrimental effects of both JB-1 and sertraline if administered in the early post-trauma period and suggests caution should be applied when considering psychobiotic or SSRI based approaches for early intervention in trauma related psychiatric disorders.

New neurons restore structural and behavioral abnormalities in a rat model of PTSD

Post-traumatic stress disorder (PTSD) has been associated with anxiety, memory impairments, enhanced fear, and hippocampal volume loss, although the relationship between these changes remain unknown. Single-prolonged stress (SPS) is a model for PTSD combining three forms of stress (restraint, swim, and anesthesia) in a single session that results in prolonged behavioral effects. Using pharmacogenetic ablation of adult neurogenesis in rats, we investigated the role of new neurons in the hippocampus in the long-lasting structural and behavioral effects of SPS. Two weeks after SPS, stressed rats displayed increased anxiety-like behavior and decreased preference for objects in novel locations regardless of the presence or absence of new neurons. Chronic stress produced by daily restraint for 2 or 6 hr produced similar behavioral effects that were also independent of ongoing neurogenesis. At a longer recovery time point, 1 month after SPS, rats with intact neurogenesis had normalized, showing control levels of anxiety-like behavior. However, GFAP-TK rats, which lacked new neurons, continued to show elevated anxiety-like behavior and enhanced serum corticosterone response to anxiogenic experience. Volume loss in ventral CA1 region of the hippocampus paralleled increases in anxiety-like behavior, occurring in all rats exposed to SPS at the early time point and only rats lacking adult neurogenesis at the later time point. In chronic stress experiments, volume loss occurred broadly throughout the dentate gyrus and CA1 after 6-hr daily stress but was not apparent in any hippocampal subregion after 2-hr daily stress. No effect of SPS was seen on cell proliferation in the dentate gyrus, but the survival of young neurons born a week after stress was decreased. Together, these data suggest that new neurons are important for recovery of normal behavior and hippocampal structure following a strong acute stress and point to the ventral CA1 region as a potential key mediator of stress-induced anxiety-like behavior.

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.

Deletion of Long Isoform of Eukaryotic Elongation Factor 1Bδ Leads to Audiogenic Seizures and Aversive Stimulus-Induced Long-Lasting Activity Suppression in Mice

Alternative splicing enables a gene to give rise to diverse protein products. The Eef1d gene produces two isoforms: a short isoform that encodes translation elongation factor 1Bδ (eEF1Bδ1), and a long isoform that encodes the heat shock-responsive transcription factor eEF1BδL. Previously, we found that eEF1BδL was a splice variant that was specific to the brain and testis, and the protein encoded is thought to have a function in the central nervous system. In this study, we generated knockout (KO) mice of C57BL/6J background that selectively lacked a specific exon in Eef1d for the long isoform. These KO mice lacked eEF1BδL, but not eEF1Bδ1, in the brain. Although the KO mice showed normal anxiety-related and learning behavior in behavioral tests, some showed severe seizures in response to loud sounds (90 dBA), an audiogenic seizures (AGS) response. Furthermore, after the KO mice had been subjected to the fear conditioning test, they showed remarkably decreased locomotor activity in their home cage and in the open-field and elevated plus-maze tests. After the fear conditioning test, a significant decrease in brain weight, atrophy of the hippocampus and midbrain, and reduced cortical layer thickness were observed in the KO mice. We also found a compensatory increase in the eEF1Bδ1 level and elevated protein synthesis with the induction of endoplasmic reticulum stress markers in these mice. Our results suggest that eEF1BδL has an important role in normal brain function especially when exposed to external stimuli.

Radix Polygalae Extract Attenuates PTSD-like Symptoms in a Mouse Model of Single Prolonged Stress and Conditioned Fear Possibly by Reversing BAG1

Radix Polygalae (RP) has been used to relieve psychological stress in traditional oriental medicine. Recently, cell protective, antiamnestic and antidepressant-like effects were disclosed but the possible application of RP to post-traumatic stress disorder, in which exaggerated fear memory persists, has not yet been explored. For this purpose, the effects of RP on fear behavior was examined in a mouse model of single prolonged stress and conditioned fear (SPS-CF), previously shown to mimic key symptoms of post-traumatic stress disorder. Male mice received daily oral dose of RP extract or vehicle during the SPS-CF procedure. Then fear-related memory (cohort 1, n=25), non-fear-related memory (cohort 2, n=38) and concentration-dependent effects of RP on fear memory (cohort 3, n=41) were measured in 3 separate cohort of animals. Also working memory and anxiety-like behaviors were measured in cohort 1. RP-treated SPS-CF mice exhibited attenuated contextual but not cued freezing and no impairments in the working memory and spatial reference memory performances relative to vehicle-treated SPS-CF controls. RP-treated SPS-CF and naive mice also demonstrated no difference in anxiety-like behavior levels relative to vehicle-treated SPS-CF and naive controls, respectively. In the hippocampus of SPS-CF mice, expression of BAG1, which regulates the activity of GR, was decreased, whereas RP increased expression of BAG1 in naïve and SPS-CF mice. These results suggest that RP exerts some symptomatic relief in a mouse with exaggerated fear response. RP and its molecular components may thus constitute valuable research targets in the development of novel therapeutics for stress-related psychological disorders.

Current Status of Animal Models of Posttraumatic Stress Disorder: Behavioral and Biological Phenotypes, and Future Challenges in Improving Translation

Increasing predictability of animal models of posttraumatic stress disorder (PTSD) has required active collaboration between clinical and preclinical scientists. Modeling PTSD is challenging, as it is a heterogeneous disorder with ≥20 symptoms. Clinical research increasingly utilizes objective biological measures (e.g., imaging, peripheral biomarkers) or nonverbal behaviors and/or physiological responses to complement verbally reported symptoms. This shift toward more-objectively measurable phenotypes enables refinement of current animal models of PTSD, and it supports the incorporation of homologous measures across species. We reviewed >600 articles to examine the ability of current rodent models to probe biological phenotypes of PTSD (e.g., sleep disturbances, hippocampal and fear-circuit dysfunction, inflammation, glucocorticoid receptor hypersensitivity) in addition to behavioral phenotypes. Most models reliably produced enduring generalized anxiety-like or depression-like behaviors, as well as hyperactive fear circuits, glucocorticoid receptor hypersensitivity, and response to long-term selective serotonin reuptake inhibitors. Although a few paradigms probed fear conditioning/extinction or utilized peripheral immune, sleep, and noninvasive imaging measures, we argue that these should be incorporated more to enhance translation. Data on female subjects, on subjects at different ages across the life span, or on temporal trajectories of phenotypes after stress that can inform model validity and treatment study design are needed. Overall, preclinical (and clinical) PTSD researchers are increasingly incorporating homologous biological measures to assess markers of risk, response, and treatment outcome. This shift is exciting, as we and many others hope it not only will support translation of drug efficacy from animal models to clinical trials but also will potentially improve predictability of stage II for stage III clinical trials.

Chronic stress alters adrenal clock function in a sexually dimorphic manner

Glucocorticoid production is gated at the molecular level by the circadian clock in the adrenal gland. Stress influences daily rhythms in behavior and physiology, but it remains unclear how stress affects the function of the adrenal clock itself. Here, we examine the influence of stress on adrenal clock function by tracking PERIOD2::LUCIFERASE (PER2::LUC) rhythms in vitro Relative to non-stressed controls, adrenals from stressed mice displayed marked changes in PER2::LUC rhythms. Interestingly, the effect of stress on adrenal rhythms varied by sex and the type of stress experienced in vivo To investigate the basis of sex differences in the adrenal response to stress, we next stimulated male and female adrenals in vitro with adrenocorticotropic hormone (ACTH). ACTH shifted phase and increased amplitude of adrenal PER2::LUC rhythms. Both phase and amplitude responses were larger in female adrenals than in male adrenals, an observation consistent with previously described sex differences in the physiological response to stress. Lastly, we reversed the sex difference in adrenal clock function using stress and sex hormone manipulations to test its role in driving adrenal responses to ACTH. We find that adrenal responsiveness to ACTH is inversely proportional to the amplitude of adrenal PER2::LUC rhythms. This suggests that larger ACTH responses from female adrenals may be driven by their lower amplitude molecular rhythms. Collectively, these results indicate a reciprocal relationship between stress and the adrenal clock, with stress influencing adrenal clock function and the state of the adrenal clock gating the response to stress in a sexually dimorphic manner.

Single-Prolonged Stress: A Review of Two Decades of Progress in a Rodent Model of Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a common, costly, and often debilitating psychiatric condition. However, the biological mechanisms underlying this disease are still largely unknown or poorly understood. Considerable evidence indicates that PTSD results from dysfunction in highly-conserved brain systems involved in stress, anxiety, fear, and reward. Pre-clinical models of traumatic stress exposure are critical in defining the neurobiological mechanisms of PTSD, which will ultimately aid in the development of new treatments for PTSD. Single prolonged stress (SPS) is a pre-clinical model that displays behavioral, molecular, and physiological alterations that recapitulate many of the same alterations observed in PTSD, illustrating its validity and giving it utility as a model for investigating post-traumatic adaptations and pre-trauma risk and protective factors. In this manuscript, we review the present state of research using the SPS model, with the goals of (1) describing the utility of the SPS model as a tool for investigating post-trauma adaptations, (2) relating findings using the SPS model to findings in patients with PTSD, and (3) indicating research gaps and strategies to address them in order to improve our understanding of the pathophysiology of PTSD.

Using the Single Prolonged Stress Model to Examine the Pathophysiology of PTSD

The endurance of memories of emotionally arousing events serves the adaptive role of minimizing future exposure to danger and reinforcing rewarding behaviors. However, following a traumatic event, a subset of individuals suffers from persistent pathological symptoms such as those seen in posttraumatic stress disorder (PTSD). Despite the availability of pharmacological treatments and evidence-based cognitive behavioral therapy, a considerable number of PTSD patients do not respond to the treatment, or show partial remission and relapse of the symptoms. In controlled laboratory studies, PTSD patients show deficient ability to extinguish conditioned fear. Failure to extinguish learned fear could be responsible for the persistence of PTSD symptoms such as elevated anxiety, arousal, and avoidance. It may also explain the high non-response and dropout rates seen during treatment. Animal models are useful for understanding the pathophysiology of the disorder and the development of new treatments. This review examines studies in a rodent model of PTSD with the goal of identifying behavioral and physiological factors that predispose individuals to PTSD symptoms. Single prolonged stress (SPS) is a frequently used rat model of PTSD that involves exposure to several successive stressors. SPS rats show PTSD-like symptoms, including impaired extinction of conditioned fear. Since its development by the Liberzon lab in 1997, the SPS model has been referred to by more than 200 published papers. Here we consider the findings of these studies and unresolved questions that may be investigated using the model.

A perspective on the contribution of animal models to the pharmacological treatment of posttraumatic stress disorder

OBJECTIVES

Posttraumatic stress disorder (PTSD) is a prevalent, chronic, disabling disorder that may develop following exposure to a traumatic event. This review summarizes currently used animal models of PTSD and their potential role in the development of better therapeutics. Heterogeneity is one of the main characteristics of PTSD with the consequence that many pharmacological approaches are used to relieve symptoms of PTSD. To address the translational properties of the animal models, we discuss the types of stressors used, the rodent correlates of human PTSD (DSM-5) symptoms, and the efficacy of approved, recommended and off-label drugs used to treat PTSD in 'PTSD-animals'.

CONCLUSIONS

Currently available animal models reproduce most PTSD symptoms and are validated by existing therapeutics. However, novel therapeutics are needed for this disorder as not one drug alleviates all symptoms and many have side effects that lead to non-compliance among PTSD patients. The true translational power of animal models of PTSD will only be demonstrated when new therapeutics acting through novel mechanisms become available for clinical practice.

Severe, multimodal stress exposure induces PTSD-like characteristics in a mouse model of single prolonged stress

Appropriate animal models of posttraumatic stress disorder (PTSD) are needed because human studies remain limited in their ability to probe the underlying neurobiology of PTSD. Although the single prolonged stress (SPS) model is an established rat model of PTSD, the development of a similarly-validated mouse model emphasizes the benefits and cross-species utility of rodent PTSD models and offers unique methodological advantages to that of the rat. Therefore, the aims of this study were to develop and describe a SPS model for mice and to provide data that support current mechanisms relevant to PTSD. The mouse single prolonged stress (mSPS) paradigm, involves exposing C57Bl/6 mice to a series of severe, multimodal stressors, including 2h restraint, 10 min group forced swim, exposure to soiled rat bedding scent, and exposure to ether until unconsciousness. Following a 7-day undisturbed period, mice were tested for cue-induced fear behavior, effects of paroxetine on cue-induced fear behavior, extinction retention of a previously extinguished fear memory, dexamethasone suppression of corticosterone (CORT) response, dorsal hippocampal glucocorticoid receptor protein and mRNA expression, and prefrontal cortex glutamate levels. Exposure to mSPS enhanced cue-induced fear, which was attenuated by oral paroxetine treatment. mSPS also disrupted extinction retention, enhanced suppression of stress-induced CORT response, increased mRNA expression of dorsal hippocampal glucocorticoid receptors and decreased prefrontal cortex glutamate levels. These data suggest that the mSPS model is a translationally-relevant model for future PTSD research with strong face, construct, and predictive validity. In summary, mSPS models characteristics relevant to PTSD and this severe, multimodal stress modifies fear learning in mice that coincides with changes in the hypothalamo-pituitary-adrenal (HPA) axis, brain glucocorticoid systems, and glutamatergic signaling in the prefrontal cortex.

Effects of paroxetine on PTSD-like symptoms in mice

RATIONALE

After exposure to a severe traumatic event, avoidance, fear sensitization, and increased anxiety are among features that can persist over time in people developing posttraumatic stress disorder (PTSD). Basic research on treatment interfering with these symptoms can provide insights to improve PTSD treatment.

OBJECTIVES

The purposes of the present study were to induce these behavioral changes in mice and examine whether paroxetine would interfere with their expression.

METHODS

Mice were submitted to avoidance training with a low (0.4 mA) or high (1.5 mA) foot-shock intensity, as mild and severe stressors, respectively, and posttraining avoidance was evaluated 1 and 12 days later. Fear sensitization, measured as increased freezing to a neutral tone, and enhanced contextual fear, measured as increased freezing to a conditioned context (wherein all mice received a 0.4-mA foot-shock), were assessed during this time window. An elevated plus maze test was also used to assess mouse anxiety-like behavior.

RESULTS

Persistent avoidance, persistent fear sensitization, and long-term enhancement of contextual fear and increased anxiety-like behavior were established only in mice that received the 1.5-mA foot-shock during avoidance training. Paroxetine (at 8 mg/kg/day), injected from day 5 to day 11 after avoidance training, suppressed all of these behavioral changes.

CONCLUSIONS

These data provide additional evidence for the role of paroxetine against expression of PTSD-like behaviors in mice.

Electroconvulsive seizures enhance autophagy signaling in rat hippocampus

The putative antidepressive mechanisms of a series of electroconvulsive seizures (ECS) are the following: 1) downregulation of monoaminergic receptor expression in several brain regions, 2) upregulation of the expression of brain-derived neurotrophic factor (BDNF), and 3) increased neurogenesis in the hippocampus. In this study, we used Western blot techniques to present another mechanism in which ECS enhances the autophagy signaling that is involved in the machinery related to synaptic and neural plasticity. Antibodies for conjugated Atg5-Atg12 (58kD) and cleaved light chain protein 3-II (LC3-II; 14 kD) were used to detect autophagy signals. An antibody for cleaved caspase-3 (17 kD) was used to detect alterations in apoptotic signals. Mature BDNF (14kD) expression in the hippocampus was evaluated in order to qualify the effectiveness of the ECS or stress-loading treatment. While significantly increased autophagy signals and no increases in apoptotic signals were detected in the ECS-treated rat hippocampus, the reverse (increased apoptotic signals and no altered autophagy signals) was observed in stressed rat hippocampus. No neuronal cell loss but new mossy fiber sprouting has been reported to accompany multiple ECS treatments, and recent studies have revealed that autophagy processes regulate the number of specific neurotransmitter receptors and the plasticity of synaptic components. The present study illustrated the neuroplastic and neurotrophic profiles of ECS and the neurotoxic impact of severe stress loading on hippocampal regions. This is the first report to demonstrate increased autophagy signals in ECS-treated rat hippocampus and no alterations in autophagy signals in stress-loaded rat hippocampus.

Glutamate and GABA imbalance promotes neuronal apoptosis in hippocampus after stress

Background

People who experience traumatic events have an increased risk of post-traumatic stress disorder (PTSD). However, PTSD-related pathological changes in the hippocampus and prefrontal cortex remain poorly understood.

Material/Methods

We investigated the effect of a PTSD-like animal model induced by severe stress. The experimental rats received 20 inescapable electric foot shocks in an enclosed box for a total of 6 times in 3 days. The physiological state (body weight and plasma corticosterone concentrations), emotion, cognitive behavior, brain morphology, apoptosis, and balance of gamma-aminobutyric acid (GABA) and glutamate in the hippocampus and prefrontal cortex were observed. Cell damages were examined with histological staining (HE, Nissl, and silver impregnation), while apoptosis was analyzed with flow cytometry using an Annexin V and propidium iodide (PI) binding and terminal deoxynucleotidyl transferase mediated-dUTP nick end labeling (TUNEL) method.

Results

In comparison with the sham litter-mates, the stressed rats showed decreased body weight, inhibition of hypothalamic-pituitary-adrenal (HPA) axis activation, increase in freezing response to trauma reminder, hypoactivity and anxiety-like behaviors in elevated plus maze and open field test, poor learning in Morris water maze, and shortened latency in hot-plate test. There were significant damages in the hippocampus but not in the prefrontal cortex. Imbalance between glutamate and GABA was more evident in the hippocampus than in the prefrontal cortex.

Conclusions

These results suggest that neuronal apoptosis in the hippocampus after severe traumatic stress is related to the imbalance between glutamate and GABA. Such modifications may resemble the profound changes observed in PTSD patients.

Protective effects of the novel adenosine derivative WS0701 in a mouse model of posttraumatic stress disorder

AIM

To investigate the effects of the novel N6-substituted adenosine derivative {(2R,3S,4R,5R)-3,4-dihydroxy-5-[6-[(4-hydroxy-3-methoxybenzyl)amino]-9H-purin-9-yl]tetrahydrofuran-2-yl} methyl decanoate (WS0701) on stress-induced excessive fear, anxiety, and cognitive deficits in a mouse model of posttraumatic stress disorder (PTSD).

METHODS

Male mice underwent a conditioned foot shock and single prolonged stress procedure to induce PTSD. Contextual/cued fear, elevated plus-maze, open field and novel object recognition tests were conduced to assess PTSD-like behaviors. From d 1, the mice were orally administered WS0701 (7.5, 15, or 30 mg·kg(-1)·d(-1)) or paroxetine (10 mg·kg(-1)·d(-1)) for two weeks. Apoptosis of hippocampal neurons was detected using flow cytometry and TUNEL staining, and expression of Bcl-2 and Bax in the hippocampus was measured with Western boltting and qPCR assays.

RESULTS

WS0701 administration significantly alleviated fear, anxious behaviors and memory deficits in the mouse model of PTSD. Furthermore, WS0701 administration significantly reduced the stress-induced apoptosis of hippocampal neurons, and increased the Bcl-2/Bax ratio in the hippocampus. The positive control drug paroxetine exerted similar effects on PTSD-like behaviors and hippocampal neuron apoptosis in the mouse model of PTSD, which were comparable to those caused by the high dose of WS0701.

CONCLUSION

WS0701 effectively mitigates stress-induced PTSD-like behaviors in mice, partly via inhibition of neuronal apoptosis in the hippocampus.

Single prolonged stress impairs social and object novelty recognition in rats

Posttraumatic stress disorder (PTSD) results from exposure to a traumatic event and manifests as re-experiencing, arousal, avoidance, and negative cognition/mood symptoms. Avoidant symptoms, as well as the newly defined negative cognitions/mood, are a serious complication leading to diminished interest in once important or positive activities, such as social interaction; however, the basis of these symptoms remains poorly understood. PTSD patients also exhibit impaired object and social recognition, which may underlie the avoidance and symptoms of negative cognition, such as social estrangement or diminished interest in activities. Previous studies have demonstrated that single prolonged stress (SPS), models PTSD phenotypes, including impairments in learning and memory. Therefore, it was hypothesized that SPS would impair social and object recognition memory. Male Sprague Dawley rats were exposed to SPS then tested in the social choice test (SCT) or novel object recognition test (NOR). These tests measure recognition of novelty over familiarity, a natural preference of rodents. Results show that SPS impaired preference for both social and object novelty. In addition, SPS impairment in social recognition may be caused by impaired behavioral flexibility, or an inability to shift behavior during the SCT. These results demonstrate that traumatic stress can impair social and object recognition memory, which may underlie certain avoidant symptoms or negative cognition in PTSD and be related to impaired behavioral flexibility.

The CRF₁ receptor antagonist SSR125543 prevents stress-induced cognitive deficit associated with hippocampal dysfunction: comparison with paroxetine and D-cycloserine

RATIONALE

The selective CRF1 (corticotropin releasing factor type 1) receptor antagonist SSR125543 has been previously shown to attenuate the long-term cognitive deficit produced by traumatic stress exposure. Memory disturbances described in post-traumatic stress disorder (PTSD) patients are believed to be associated with changes in neuronal activity, in particular at the level of the hippocampus.

OBJECTIVES

The present study aims at investigating whether the effects of SSR125543 (10 mg/kg/day for 2 weeks) on cognitive impairment induced by traumatic stress exposure are associated with changes in hippocampal excitability. Effects of SSR125543 were compared to those of the 5-HT reuptake inhibitor, paroxetine (10 mg/kg/day), and the partial N-methyl-D-aspartate (NMDA) receptor agonist, D-cycloserine (10 mg/kg/day), two compounds which have demonstrated clinical efficacy against PTSD.

METHODS

Mice received two unavoidable electric foot-shocks. Then, 1 or 16 days after stress, they were tested for their memory performance using the object recognition test. Neuronal excitability was recorded during the third week post-stress in the CA1 area of the hippocampus. Drugs were administered from day 1 post-stress to the day preceding the electrophysiological study.

RESULTS

Application of electric shocks produced cognitive impairment 16, but not 1 day after stress, an effect which was associated with a decrease in hippocampal neuronal excitability. Both stress-induced effects were prevented by repeated administration of SSR125543, paroxetine and D-cycloserine.

CONCLUSIONS

These findings confirm that the CRF1 receptor antagonist SSR125543 is able to attenuate the behavioral effects of traumatic stress exposure and indicate that these effects are associated with a normalization of hippocampal neuronal excitability impaired by stress.

Animal models of post-traumatic stress disorder: face validity

Post-traumatic stress disorder (PTSD) is a debilitating condition that develops in a proportion of individuals following a traumatic event. Despite recent advances, ethical limitations associated with human research impede progress in understanding PTSD. Fortunately, much effort has focused on developing animal models to help study the pathophysiology of PTSD. Here, we provide an overview of animal PTSD models where a variety of stressors (physical, psychosocial, or psychogenic) are used to examine the long-term effects of severe trauma. We emphasize models involving predator threat because they reproduce human individual differences in susceptibility to, and in the long-term consequences of, psychological trauma.