Long-lasting hippocampal synaptic protein loss in a mouse model of posttraumatic stress disorder

Maladaptation of dentate gyrus mossy cells mediates contextual discrimination deficit after traumatic stress

Fear overgeneralization is a maladaptive response to traumatic stress that is associated with the inability to discriminate between threat and safety contexts, a hallmark feature of post-traumatic stress disorder (PTSD). However, the neural mechanisms underlying this deficit remain unclear. Here, we show that traumatic stress exposure impairs contextual discrimination between threat and safety contexts in the learned helplessness (LH) model. Mossy cells (MCs) in the dorsal hippocampus are suppressed in response to traumatic stress. Bidirectional manipulation of MC activity in the LH model reveals that MC inhibition is causally linked to impaired contextual discrimination. Mechanistically, MC inhibition increases the number of active granule cells in a given context, significantly overlapping context-specific ensembles. Our study demonstrates that maladaptive inhibition of MCs after traumatic stress is a substantial mechanism underlying fear overgeneralization with contextual discrimination deficit, suggesting a potential therapeutic target for cognitive symptoms of PTSD.

Heterogenous effect of early adulthood stress on cognitive aging and synaptic function in the dentate gyrus

Cognitive aging widely varies among individuals due to different stress experiences throughout the lifespan and vulnerability of neurocognitive mechanisms. To understand the heterogeneity of cognitive aging, we investigated the effect of early adulthood stress (EAS) on three different hippocampus-dependent memory tasks: the novel object recognition test (assessing recognition memory: RM), the paired association test (assessing episodic-like memory: EM), and trace fear conditioning (assessing trace memory: TM). Two-month-old rats were exposed to chronic mild stress for 6 weeks and underwent behavioral testing either 2 weeks or 20 months later. The results show that stress and aging impaired different types of memory tasks to varying degrees. RM is affected by combined effect of stress and aging. EM became less precise in EAS animals. TM, especially the contextual memory, showed impairment in aging although EAS attenuated the aging effect, perhaps due to its engagement in emotional memory systems. To further explore the neural underpinnings of these multi-faceted effects, we measured long-term potentiation (LTP), neural density, and synaptic density in the dentate gyrus (DG). Both stress and aging reduced LTP. Additionally, the synaptic density per neuron showed a further reduction in the stress aged group. In summary, EAS modulates different forms of memory functions perhaps due to their substantial or partial dependence on the functional integrity of the hippocampus. The current results suggest that lasting alterations in hippocampal circuits following EAS could potentially generate remote effects on individual variability in cognitive aging, as demonstrated by performance in multiple types of memory.

The effect of SSRIs on fear learning: a systematic review and meta-analysis

RATIONALE

Selective serotonin reuptake inhibitors (SSRIs) are considered first-line medication for anxiety-like disorders such as panic disorder, generalized anxiety disorder, and post-traumatic stress disorder. Fear learning plays an important role in the development and treatment of these disorders. Yet, the effect of SSRIs on fear learning are not well known.

OBJECTIVE

We aimed to systematically review the effect of six clinically effective SSRIs on acquisition, expression, and extinction of cued and contextual conditioned fear.

METHODS

We searched the Medline and Embase databases, which yielded 128 articles that met the inclusion criteria and reported on 9 human and 275 animal experiments.

RESULTS

Meta-analysis showed that SSRIs significantly reduced contextual fear expression and facilitated extinction learning to cue. Bayesian-regularized meta-regression further suggested that chronic treatment exerts a stronger anxiolytic effect on cued fear expression than acute treatment. Type of SSRI, species, disease-induction model, and type of anxiety test used did not seem to moderate the effect of SSRIs. The number of studies was relatively small, the level of heterogeneity was high, and publication bias has likely occurred which may have resulted in an overestimation of the overall effect sizes.

CONCLUSIONS

This review suggests that the efficacy of SSRIs may be related to their effects on contextual fear expression and extinction to cue, rather than fear acquisition. However, these effects of SSRIs may be due to a more general inhibition of fear-related emotions. Therefore, additional meta-analyses on the effects of SSRIs on unconditioned fear responses may provide further insight into the actions of SSRIs.

Chemokine receptor 5 signaling in PFC mediates stress susceptibility in female mice

Chronic stress induces changes in the periphery and the central nervous system (CNS) that contribute to neuropathology and behavioral abnormalities associated with psychiatric disorders. In this study, we examined the impact of peripheral and central inflammation during chronic social defeat stress (CSDS) in female mice. Compared to male mice, we found that female mice exhibited heightened peripheral inflammatory response and identified C-C motif chemokine ligand 5 (CCL5), as a stress-susceptibility marker in females. Blocking CCL5 signaling in the periphery promoted resilience to CSDS. In the brain, stress-susceptible mice displayed increased expression of C-C chemokine receptor 5 (CCR5), a receptor for CCL5, in microglia in the prefrontal cortex (PFC). This upregulation was associated with microglia morphological changes, their increased migration to the blood vessels, and enhanced phagocytosis of synaptic components and vascular material. These changes coincided with neurophysiological alterations and impaired blood-brain barrier (BBB) integrity. By blocking CCR5 signaling specifically in the PFC were able to prevent stress-induced physiological changes and rescue social avoidance behavior. Our findings are the first to demonstrate that stress-mediated dysregulation of the CCL5-CCR5 axis triggers excessive phagocytosis of synaptic materials and neurovascular components by microglia, resulting in disruptions in neurotransmission, reduced BBB integrity, and increased stress susceptibility. Our study provides new insights into the role of cortical microglia in female stress susceptibility and suggests that the CCL5-CCR5 axis may serve as a novel sex-specific therapeutic target for treating psychiatric disorders in females.

Aberrant ventral dentate gyrus structure and function in trauma susceptible mice

Post-traumatic stress disorder (PTSD) is a psychiatric disorder vulnerable individuals can develop following a traumatic event, whereas others are resilient. Enhanced insight into the mechanistic underpinnings contributing to these inter-individual differences in trauma susceptibility is key to improved treatment and prevention. Aberrant function of the hippocampal dentate gyrus (DG) may contribute to its psychopathology, with the dorsal DG potentially encoding trauma memory generalization and the ventral DG anxiety. Using a mouse model, we hypothesized that susceptibility to develop PTSD-like symptoms following trauma will be underpinned by aberrant DG structure and function. Mice were exposed to a traumatic event (unpredictable, inescapable foot shocks) and tested for PTSD-like symptomatology following recovery. In four independent experiments, DG neuronal morphology, synaptic protein gene and protein expression, and neuronal activity during trauma encoding and recall were assessed. Behaviorally, trauma-susceptible animals displayed increased anxiety-like behavior already prior to trauma, increased novelty-induced freezing, but no clear differences in remote trauma memory recall. Comparison of the ventral DG of trauma susceptible vs resilient mice revealed lower spine density, reduced expression of the postsynaptic protein homer1b/c gene and protein, a larger population of neurons active during trauma encoding, and a greater presence of somatostatin neurons. In contrast, the dorsal DG of trauma-susceptible animals did not differ in terms of spine density or gene expression but displayed more active neurons during trauma encoding and a lower amount of somatostatin neurons. Collectively, we here report on specific structural and functional changes in the ventral DG in trauma susceptible male mice.

Post-traumatic stress disorder: clinical and translational neuroscience from cells to circuits

Post-traumatic stress disorder (PTSD) is a maladaptive and debilitating psychiatric disorder, characterized by re-experiencing, avoidance, negative emotions and thoughts, and hyperarousal in the months and years following exposure to severe trauma. PTSD has a prevalence of approximately 6-8% in the general population, although this can increase to 25% among groups who have experienced severe psychological trauma, such as combat veterans, refugees and victims of assault. The risk of developing PTSD in the aftermath of severe trauma is determined by multiple factors, including genetics - at least 30-40% of the risk of PTSD is heritable - and past history, for example, prior adult and childhood trauma. Many of the primary symptoms of PTSD, including hyperarousal and sleep dysregulation, are increasingly understood through translational neuroscience. In addition, a large amount of evidence suggests that PTSD can be viewed, at least in part, as a disorder that involves dysregulation of normal fear processes. The neural circuitry underlying fear and threat-related behaviour and learning in mammals, including the amygdala-hippocampus-medial prefrontal cortex circuit, is among the most well-understood in behavioural neuroscience. Furthermore, the study of threat-responding and its underlying circuitry has led to rapid progress in understanding learning and memory processes. By combining molecular-genetic approaches with a translational, mechanistic knowledge of fear circuitry, transformational advances in the conceptual framework, diagnosis and treatment of PTSD are possible. In this Review, we describe the clinical features and current treatments for PTSD, examine the neurobiology of symptom domains, highlight genomic advances and discuss translational approaches to understanding mechanisms and identifying new treatments and interventions for this devastating syndrome.

Comparison between cannabidiol and sertraline for the modulation of post-traumatic stress disorder-like behaviors and fear memory in mice

RATIONALE AND OBJECTIVES

Post-traumatic stress disorder (PTSD) is characterized by poor adaptation to a traumatic experience and disturbances in fear memory regulation, and currently lacks effective medication. Cannabidiol is a main constituent of Cannabis sativa; it has no psychotomimetic effects and has been implicated in modulating fear learning in mammals. Using a mouse PTSD model, we investigated the effects of CBD on PTSD-like behaviors and the modulation of trauma-related fear memory, a crucial process leading to core symptoms of PTSD.

METHODS

We applied the modified pre-shock model to evaluated PTSD-like behaviors from days 3 to 26. The measures included the freezing time to the conditioned context, open field test, elevated plus maze test, and social interaction test. CBD and sertraline were administered at different stages of fear memory.

RESULTS

CBD (10 mg/kg, i.p.) administration alleviated main PTSD-like symptoms in the mouse pre-shock model by attenuating trauma-related fear memory and anxiety-like behavior, and increasing social interaction behavior. The effects of CBD were apparent irrespective of whether it was administered before, during, or after re-exposure to the aversive context. However, sertraline (15 mg/kg, p.o.) was only effective when administered before the behavioral test. CBD also reduced the consolidation, retrieval, and reconsolidation of trauma-related fear memory, whereas sertraline only reduced fear-memory retrieval.

CONCLUSION

CBD produced anti-PTSD-like actions in mice and disrupted trauma-related fear memory by interfering with multiple aspects of fear memory processing. These findings indicate that CBD may be a promising candidate for treating PTSD.

Structural correlates of trauma-induced hyperarousal in mice

Post-traumatic stress disorder (PTSD) is a chronic disease caused by traumatic incidents. Numerous studies have revealed grey matter volume differences in affected individuals. The nature of the disease renders it difficult to distinguish between a priori versus a posteriori changes. To overcome this difficulty, we studied the consequences of a traumatic event on brain morphology in mice before and 4 weeks after exposure to brief foot shocks (or sham treatment), and correlated morphology with symptoms of hyperarousal. In the latter context, we assessed hyperarousal upon confrontation with acoustic, visual, or composite (acoustic/visual/tactile) threats and integrated the individual readouts into a single Hyperarousal Score using logistic regression analysis. MRI scans with subsequent whole-brain deformation-based morphometry (DBM) analysis revealed a volume decrease of the dorsal hippocampus and an increase of the reticular nucleus in shocked mice when compared to non-shocked controls. Using the Hyperarousal Score as regressor for the post-exposure MRI measurement, we observed negative correlations with several brain structures including the dorsal hippocampus. If the development of changes with respect to the basal MRI was considered, reduction in globus pallidus volume reflected hyperarousal severity. Our findings demonstrate that a brief traumatic incident can cause volume changes in defined brain structures and suggest the globus pallidus as an important hub for the control of fear responses to threatening stimuli of different sensory modalities.

Analysis of the cerebellar molecular stress response led to first evidence of a role for FKBP51 in brain FKBP52 expression in mice and humans

As the cerebellar molecular stress response is understudied, we assessed protein expression levels of hypothalamic-pituitary-adrenal (HPA) axis regulators and neurostructural markers in the cerebellum of a male PTSD mouse model and of unstressed vs. stressed male FK506 binding protein 51 (Fkbp5) knockout (KO) vs. wildtype mice. We explored the translatability of our findings in the Fkbp5 KO model to the situation in humans by correlating mRNA levels of candidates with those of FKBP5 in two whole transcriptome datasets of post-mortem human cerebellum and in blood of unstressed and stressed humans. Fkbp5 deletion rescued the stress-induced loss in hippocampal, prefrontal cortical, and, possibly, also cerebellar FKBP52 expression and modulated post-stress cerebellar expression levels of the glucocorticoid receptor (GR) and possibly (trend) also of glial fibrillary acidic protein (GFAP). Accordingly, expression levels of genes encoding for these three genes correlated with those of FKBP5 in human post-mortem cerebellum, while other neurostructural markers were not related to Fkbp5 either in mouse or human cerebellum. Also, gene expression levels of the two immunophilins correlated inversely in the blood of unstressed and stressed humans. We found transient changes in FKBP52 and persistent changes in GR and GFAP in the cerebellum of PTSD-like mice. Altogether, upon elucidating the cerebellar stress response we found first evidence for a novel facet of HPA axis regulation, i.e., the ability of FKBP51 to modulate the expression of its antagonist FKBP52 in the mouse and, speculatively, also in the human brain and blood and, moreover, detected long-term single stress-induced changes in expression of cerebellar HPA axis regulators and neurostructural markers of which some might contribute to the role of the cerebellum in fear extinction.

MMP9 mRNA is a potential diagnostic and treatment monitoring marker for PTSD: Evidence from mice and humans

Although matrix metalloproteinase 9 (MMP9) has been found associated with various psychiatric disorders and with threat memories in humans, its role in post-traumatic stress disorder (PTSD) and related animal models is understudied. Thus, we analyzed MMP9 mRNA expression kinetics during two different stress experiments, i.e., the Trier Social Stress Test and the dexamethasone suppression test (DST), in whole blood of two independent cohorts of PTSD patients vs. non-traumatized healthy controls (HC) and, moreover, in a mouse model of PTSD and in dexamethasone-treated mice. Besides MMP9, we quantified mRNA levels of four of its regulators, i.e., interleukin (IL)-1 receptor 1 and 2 (IL1R1, IL1R2), IL-6 receptor and tumor necrosis factor receptor 1 (TNFR1) in 10 patients exposed to the DST before vs. after successful PTSD psychotherapy vs. 13 HC and, except from Il6r, also in different brain regions of the PTSD mouse model. We are the first to show that blood MMP9 mRNA concentrations were elevated after acute dexamethasone in PTSD patients, improved upon partial remission of PTSD and were, furthermore, also elevated, together with its regulator Tnfr1, in the prefrontal cortex of PTSD-like mice. In contrast, blood TNFR1 and IL1R2 were markedly underexpressed in PTSD patients. In conclusion, we found translational evidence supporting that, I, TNFR1 and MMP9 mRNA expression might be involved in PTSD pathobiology, II, might constitute potential diagnostic blood biomarkers for PTSD and, importantly, III, post-dexamethasone blood MMP9 hyperexpression, which speculatively results from post-dexamethasone underexpression of IL1R2, might serve also as potential treatment monitoring biomarker for PTSD.

Oxytocin receptor is a potential biomarker of the hyporesponsive HPA axis subtype of PTSD and might be modulated by HPA axis reactivity traits in humans and mice

This study aimed to identify yet unavailable blood biomarkers for the responsive and the hyporesponsive hypothalamic-pituitary-adrenal (HPA) axis subtypes of posttraumatic stress disorder (PTSD). As, I, we recently discovered the intranasal neuropeptide oxytocin to reduce experimentally provoked PTSD symptoms, II, expression of its receptor (OXTR) has hitherto not been assessed in PTSD patients, and III, oxytocin and OXTR have previously been related to the HPA axis, we considered both as suitable candidates. During a Trier Social Stress Test (TSST), we compared serum oxytocin and blood OXTR mRNA concentrations between female PTSD patients, their HPA axis reactivity subtypes and sex and age-matched healthy controls (HC). At baseline, both candidates differentiated the hyporesponsive HPA axis subtype from HC, however, only baseline OXTR mRNA discriminated also between subtypes. Furthermore, in the hyporesponsive HPA axis subgroup, OXTR mRNA levels correlated with PTSD symptoms and changed markedly during the TSST. To assess the influence of (traumatic) stress on the cerebral expression of oxytocin and its receptor and to test their suitability as biomarkers for the mouse PTSD-like syndrome, we then analyzed oxytocin, its mRNA (Oxt) and Oxtr mRNA in three relevant brain regions and Oxt in blood of a PTSD mouse model. To further explore the HPA axis reactivity subtype dependency of OXTR, we compared cerebral OXTR protein expression between mice exhibiting two different HPA axis reactivity traits, i.e., FK506 binding protein 51 knockout vs. wildtype mice. In summary, blood OXTR mRNA emerged as a potential biomarker of the hyporesponsive HPA axis PTSD subtype and prefrontal cortical Oxtr and Oxt of the mouse PTSD-like syndrome. Moreover, we found first translational evidence for a HPA axis responsivity trait-dependent regulation of OXTR expression. The lack of a cohort of the (relatively rare) hyporesponsive HPA axis subtype of HC is a limitation of our study.

A multispecies probiotic accelerates fear extinction and inhibits relapse in mice: Role of microglia

The relapse of fear memory remains a clinical challenge in treatment of fear-related disorders. Here we tested the effects and underlying mechanisms of probiotics treatment after fear conditioning on fear extinction. We found that fear conditioning induced synapse loss, microglial activation, and synaptic phagocytosis of activated microglial cells in hippocampal dentate gyrus of mice. And probiotics treatment (1 capsule/day/mice) after fear conditioning for 27 days inhibited these changes, promoted fear extinction, and inhibited the recovery of fear memory even 7 days after extinction. 16S rRNA gene sequencing demonstrated that probiotics supplement after fear conditioning partially normalized fear conditioning-induced dysbiosis of gut microbiota. In addition, we also found that repopulation of microglial cells in fear conditioning mice via PLX3397 treatment promoted long-term extinction of fear memory. Probiotics treatment after fear conditioning inhibited microglial activation and had similar therapeutic effects as the microglial cell repopulation induced by PLX3397 treatment. These data showed that (1) probiotics treatment after fear conditioning might promote long-term fear extinction which could be associated with the mitigation of synaptic pruning of activated microglial cells; (2) probiotics may be applicable as therapeutic strategy to inhibit microglial activation and treat fear-related disorders.

Robustly High Hippocampal BDNF levels under Acute Stress in Mice Lacking the Full-length p75 Neurotrophin Receptor

BACKGROUND

Brain-derived neurotrophic factor (BDNF) exerts its effects on neural plasticity via 2 distinct receptor types, the tyrosine kinase TrkB and the p75 neurotrophin receptor (p75NTR). The latter can promote inflammation and cell death while TrkB is critically involved in plasticity and memory, particularly in the hippocampus. Acute and chronic stress have been associated with suppression of hippocampal BDNF expression and impaired hippocampal plasticity. We hypothesized that p75NTR might be involved in the hippocampal stress response, in particular in stress-induced BDNF suppression, which might be accompanied by increased neuroinflammation.

METHOD

We assessed hippocampal BDNF protein concentrations in wild-type mice compared that in mice lacking the long form of the p75NTR (p75NTR^ExIII-/-) with or without prior exposure to a 1-hour restraint stress challenge. Hippocampal BDNF concentrations were measured using an optimized ELISA. Furthermore, whole-brain mRNA expression of pro-inflammatory interleukin-6 (Il6) was assessed with RT-PCR.

RESULTS

Deletion of full-length p75NTR was associated with higher hippocampal BDNF protein concentration in the stress condition, suggesting persistently high hippocampal BDNF levels in p75NTR-deficient mice, even under stress. Stress elicited increased whole-brain Il6 mRNA expression irrespective of genotype; however, p75NTR^ExIII-/- mice showed elevated baseline Il6 expression and thus a lower relative increase.

CONCLUSIONS

Our results provide evidence for a role of p75NTR signaling in the regulation of hippocampal BDNF levels, particularly under stress. Furthermore, p75NTR signaling modulates baseline but not stress-related Il6 gene expression in mice. Our findings implicate p75NTR signaling as a potential pathomechanism in BDNF-dependent modulation of risk for neuropsychiatric disorders.

Basolateral Amygdala but Not Medial Prefrontal Cortex Contributes to Chronic Fluoxetine Treatments for PTSD Symptoms in Mice

Do chronic fluoxetine treatments reduced footshock-induced posttraumatic stress disorder (PTSD) symptoms, including fear and comorbid depression, in the situational reminder phase? Moreover, are the subareas of the medial prefrontal cortex (mPFC), including the cingulate cortex 1 (Cg1), prelimbic cortex (PrL), infralimbic cortex (IL), and basolateral amygdala (BLA), involved in the fluoxetine amelioration of PTSD symptoms? These two crucial issues were addressed in the present study. All mice were injected with chronic fluoxetine or normal saline treatments for the adaptation (14 days), footshock fear conditioning (1 day), and situational reminder (3 days) phases. After adaptation, the mice were subjected to footshock (2 mA, 10 seconds) or nonfootshock and stayed 2 min in a footshock box for 2 min for fear conditioning. Later, they were placed in the footshock box for 2 min in the situational reminder phase. In the final session of the situational reminder phase, a forced swimming test (FST) and immunohistochemical staining were conducted. The results indicated that footshock induced fear and comorbid depression. Meanwhile, chronic fluoxetine treatments reduced fear and depression behaviors. The Cg1, PrL, IL, and BLA were seemingly to increase c-Fos expression after footshock-induced PTSD symptoms in the situational reminder phase. The fluoxetine treatments reduced only the BLA's c-Fos expression. The findings suggest that BLA contributes to the fluoxetine amelioration of PTSD symptoms; however, the mPFC, including the Cg1, PrL, and IL, did not mediate PTSD symptoms' amelioration stemming from fluoxetine. The present data might help us to further understand the neural mechanism of fluoxetine treatments in PTSD symptoms.

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.

Restoring tripartite glutamatergic synapses: A potential therapy for mood and cognitive deficits in Gulf War illness

Gulf War illness is associated with a combination of exposure to war-related chemical agents and traumatic stress. Currently, there are no effective treatments, and the pathophysiology remains elusive. Neurological problems are among the most commonly reported symptoms. In this study, we investigated the glutamatergic system in the hippocampi of mice exposed to war-related chemical agents and stress. Mice developed Gulf War illness-like symptoms, including mood deficits, cognitive impairments, and fatigue. They exhibited the following pathological changes in hippocampi: elevated extracellular glutamate levels, impaired glutamatergic synapses, astrocyte atrophy, loss of interneurons, and decreased neurogenesis. LDN/OSU-215111 is a small-molecule that can strengthen the structure and function of both the astrocytic processes and the glutamatergic synapses that together form the tripartite synapses. We found that LDN/OSU-215111 effectively prevented the development of mood and cognitive deficits in mice when treatment was implemented immediately following the exposure. Moreover, when symptoms were already present, LDN/OSU-215111 still significantly ameliorated these deficits; impressively, benefits were sustained one month after treatment cessation, indicating disease modification. LDN/OSU-215111 effectively normalized hippocampal pathological changes. Overall, this study provides strong evidence that restoration of tripartite glutamatergic synapses by LDN/OSU-215111 is a potential therapy for Gulf War illness.

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Exposure to Gulf War-related agents and stress causes long-term hippocampal glutamatergic synapses impairment.

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LDN/OSU-215111, a small-molecule that enhances tripartite synapses, normalizes hippocampal deficits in a mouse model of GWI.

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LDN/OSU-215111 effectively ameliorates mood deficits, cognitive impairments, and fatigue in a mouse model of GWI.

H3K4 dimethylation at FosB promoter in the striatum of chronic stressed rats promotes morphine-induced conditioned place preference

Expression of FosB gene in striatum is essential in addiction establishment. Activated glucocorticoid receptors (GRs) induce FosB gene expression in response to stressor. Therefore, elevation of FosB expression in striatum serves as one mechanism by which stress increases risk for addiction. In this study, adult male Sprague-Dawley rats were used to investigate whether chronic stress result in histone modifications at FosB gene promoter in striatum and how these histone modifications affect FosB expression and the establishment of addiction behavior after administration of drugs of abuse. Animals were randomly assigned to three groups: Electric foot shock (EFS) group received 7-day EFS to induce chronic stress; electric foot shock plus mifepristone (EFS + Mif) group were injected with mifepristone, a nonspecific GRs antagonist, before EFS; control group did not receive any EFS. All groups then received 2-day conditioned place preference (CPP) training with morphine (5 mg/kg body weight) to test vulnerability to drug addiction. Before and after morphine administration, FosB mRNA in striatum was quantified by real-time RT-PCR. Levels of histone H3/H4 acetylation and histone H3K4 dimethylation at FosB promoter in striatum after morphine administration were measured by using chromatin immunoprecipitation (ChIP) plus real-time PCR. EFS group had stronger place preference to morphine and had significantly higher level of FosB mRNA in striatum than the other two groups. H3K4 dimethylation was 2.6-fold higher in EFS group than control group, while no statistical difference in H3/H4 acetylation. Mifepristone administration before EFS decreased histone H3K4 dimethylation and FosB mRNA in striatum, and also diminished morphine-induced conditioned place preference. Altogether, increased level of H3K4 dimethylation at FosB promoter in striatum is partially dependent on the activation of GR and responsible for the elevated level of morphine-induced FosB mRNA in chronic stressed animals.

Microglial cell hyper-ramification and neuronal dendritic spine loss in the hippocampus and medial prefrontal cortex in a mouse model of PTSD

Few animal models exist that successfully reproduce several core associative and non-associative behaviours relevant to post-traumatic stress disorder (PTSD), such as long-lasting fear reactions, hyperarousal, and subtle attentional and cognitive dysfunction. As such, these models may lack the face validity required to adequately model pathophysiological features of PTSD such as CNS grey matter loss and neuroinflammation. Here we aimed to investigate in a mouse model of PTSD whether contextual fear conditioning associated with a relatively high intensity footshock exposure induces loss of neuronal dendritic spines in various corticolimbic brain regions, as their regression may help explain grey matter reductions in PTSD patients. Further, we aimed to observe whether these changes were accompanied by alterations in microglial cell number and morphology, and increased expression of complement factors implicated in the mediation of microglial cell-mediated engulfment of dendritic spines. Adult male C57Bl6J mice were exposed to a single electric footshock and subsequently underwent phenotyping of various PTSD-relevant behaviours in the short (day 2-4) and longer-term (day 29-31). 32 days post-exposure the brains of these animals were subjected to Golgi staining of dendritic spines, microglial cell Iba-1 immunohistochemistry and immunofluorescent staining of the complement factors C1q and C4. Shock exposure promoted a lasting contextual fear response, decreased locomotor activity, exaggerated acoustic startle responses indicative of hyperarousal, and a short-term facilitation of sensorimotor gating function. The shock triggered loss of dendritic spines on pyramidal neurons was accompanied by increased microglial cell number and complexity in the medial prefrontal cortex and dorsal hippocampus, but not in the amygdala. Shock also increased expression of C1q in the pyramidal layer of the CA1 region of the hippocampus but not in other brain regions. The present study further elaborates on the face and construct validity of a mouse model of PTSD and provides a good foundation to explore potential molecular interactions between microglia and dendritic spines.

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.

Memory generalization after one-trial contextual fear conditioning: Effects of sex and neuropeptide S receptor deficiency

One-trial contextual fear conditioning in laboratory mice results in a fear memory which is relatively specific to the original conditioning context shortly after conditioning but becomes more unspecific after an incubation time of one month. This process is called generalization of fear memory and is used to investigate processes which might be involved in the pathogenesis of post-traumatic stress disorder. In the present study, we investigated the effects of sex and neuropeptide S receptor (NPSR) deficiency in one-trial contextual fear conditioning. In addition to contextual fear, we also measured startle reactivity, anxiety and corticosterone plasma levels of the mice. Our data show main effects of sex and NPSR-deficiency on freezing behavior, startle magnitude, and anxiety levels. However, generalization of contextual fear memory after incubation time was not affected by sex. Notably, NPSR-deficient mice had a more specific fear memory shortly after conditioning than their wildtype littermates but after incubation time, all genotypes had a generalized fear memory. The present data further show that plasma corticosterone levels are increased after incubation time. This increase was significantly more pronounced in NPSR-deficient mice. Taken together, our study confirms the suitability of one-trial contextual fear conditioning to study the effects of incubation time on fear memory generalization but also indicates the need for control groups without incubation. We further demonstrate that the increase of plasma corticosterone levels after incubation time is exaggerated in NPSR-deficient mice. The latter finding suggests an important role of the NPS system in the regulation of corticosterone release.

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.

Closed Loop Deep Brain Stimulation for PTSD, Addiction, and Disorders of Affective Facial Interpretation: Review and Discussion of Potential Biomarkers and Stimulation Paradigms

The treatment of psychiatric diseases with Deep Brain Stimulation (DBS) is becoming more of a reality as studies proliferate the indications and targets for therapies. Opinions on the initial failures of DBS trials for some psychiatric diseases point to a certain lack of finesse in using an Open Loop DBS (OLDBS) system in these dynamic, cyclical pathologies. OLDBS delivers monomorphic input into dysfunctional brain circuits with modulation of that input via human interface at discrete time points with no interim modulation or adaptation to the changing circuit dynamics. Closed Loop DBS (CLDBS) promises dynamic, intrinsic circuit modulation based on individual physiologic biomarkers of dysfunction. Discussed here are several psychiatric diseases which may be amenable to CLDBS paradigms as the neurophysiologic dysfunction is stochastic and not static. Post-Traumatic Stress Disorder (PTSD) has several peripheral and central physiologic and neurologic changes preceding stereotyped hyper-activation behavioral responses. Biomarkers for CLDBS potentially include skin conductance changes indicating changes in the sympathetic nervous system, changes in serum and central neurotransmitter concentrations, and limbic circuit activation. Chemical dependency and addiction have been demonstrated to be improved with both ablation and DBS of the Nucleus Accumbens and as a serendipitous side effect of movement disorder treatment. Potential peripheral biomarkers are similar to those proposed for PTSD with possible use of environmental and geolocation based cues, peripheral signs of physiologic arousal, and individual changes in central circuit patterns. Non-substance addiction disorders have also been serendipitously treated in patients with OLDBS for movement disorders. As more is learned about these behavioral addictions, DBS targets and effectors will be identified. Finally, discussed is the use of facial recognition software to modulate activation of inappropriate responses for psychiatric diseases in which misinterpretation of social cues feature prominently. These include Autism Spectrum Disorder, PTSD, and Schizophrenia-all of which have a common feature of dysfunctional interpretation of facial affective clues. Technological advances and improvements in circuit-based, individual-specific, real-time adaptable modulation, forecast functional neurosurgery treatments for heretofore treatment-resistant behavioral diseases.

Acute inescapable stress alleviates fear extinction recall deficits caused by serotonin transporter abolishment

Life stress increases risk for developing post-traumatic stress disorder (PTSD), and more prominently so in short-allele carriers of the serotonin transporter linked polymorphic region (5-HTTLPR). Serotonin transporter knockout (5-HTT^-/-) rats show compromised extinction (recall) of conditioned fear, which might mediate the increased risk for PTSD and reduce the therapeutic efficacy of exposure therapy. Here, we assessed whether acute inescapable stress (IS) differentially affects fear extinction and extinction recall in 5-HTT^-/- rats and wildtype controls. Surprisingly, IS experience improved fear extinction recall in 5-HTT^-/- rats to the level of wildtype animals, while wildtypes were unaffected by this IS. Thus, whereas 5-HTT^-/- rats evidently were more responsive to the stressor, the behavioral consequences presented themselves as adaptive.

Anxiety like behavior due to perinatal exposure to Bisphenol-A is associated with decrease in excitatory to inhibitory synaptic density of male mouse brain

Bisphenol-A (BPA) is a synthetic endocrine disruptor which causes anxiety like behavior in rodents, though the underlying mechanism is not clearly understood. As excitatory-inhibitory synaptic proteins are the key regulators of anxiety, we have examined the effect of perinatal exposure to BPA on this behavior and the expression of excitatory (PSD95), inhibitory (gephyrin) and presynaptic density marker (synaptophysin) proteins in cerebral cortex and hippocampus of 3 and 8 weeks postnatal male mice. In open field (OF) test, BPA exposure reduced the time spent, number of entries and distance travelled in the central zone as compared to control in 8 weeks mice. On the other hand, elevated plus maze (EPM) results showed decrease in time spent and number of entries to the open arms. Immunoblotting and immunofluorescence analysis showed significant downregulation of PSD95 and synaptophysin, but upregulation of gephyrin, leading to reduction in excitatory to inhibitory protein ratio and synaptic density in postnatal 3 and 8 weeks mice. Thus, our findings show that the anxiety like behavior due to perinatal exposure to BPA is associated with decrease in excitatory to inhibitory synaptic density in postnatal male mice.

Fluoxetine treatment prevents the inflammatory response in a mouse model of posttraumatic stress disorder

Despite intense research efforts the molecular mechanisms affecting stress-vulnerable brain regions in posttraumatic stress disorder (PTSD) remain elusive. In the current study we have applied global transcriptomic profiling to a PTSD mouse model induced by foot shock fear conditioning. We compared the transcriptomes of prelimbic cortex, anterior cingulate cortex (ACC), basolateral amygdala, central nucleus of amygdala, nucleus accumbens (NAc) and CA1 of the dorsal hippocampus between shocked and non-shocked (control) mice, with and without fluoxetine treatment by RNA sequencing. Differentially expressed (DE) genes were identified and clustered for in silico pathway analysis. Findings in relevant brain regions were further validated with immunohistochemistry. DE genes belonging to 11 clusters were identified including increased inflammatory response in ACC in shocked mice. In line with this finding, we noted higher microglial activation in ACC of shocked mice. Chronic fluoxetine treatment initiated in the aftermath of the trauma prevented inflammatory gene expression alterations in ACC and ameliorated PTSD-like symptoms, implying an important role of the immune response in PTSD pathobiology. Our results provide novel insights into molecular mechanisms affected in PTSD and suggest therapeutic applications with anti-inflammatory agents.

Fluoxetine Treatment Rescues Energy Metabolism Pathway Alterations in a Posttraumatic Stress Disorder Mouse Model

Posttraumatic stress disorder (PTSD) is a prevalent psychiatric disorder. Several studies have attempted to characterize molecular alterations associated with PTSD, but most findings were limited to the investigation of specific cellular markers in the periphery or defined brain regions. In the current study, we aimed to unravel affected molecular pathways/mechanisms in the fear circuitry associated with PTSD. We interrogated a foot shock-induced PTSD mouse model by integrating proteomics and metabolomics profiling data. Alterations at the proteome level were analyzed using in vivo (15)N metabolic labeling combined with mass spectrometry in the prelimbic cortex (PrL), anterior cingulate cortex (ACC), basolateral amygdala, central nucleus of the amygdala and CA1 of the hippocampus between shocked and nonshocked (control) mice, with and without fluoxetine treatment. In silico pathway analyses revealed an upregulation of the citric acid cycle pathway in PrL, and downregulation in ACC and nucleus accumbens (NAc). Chronic fluoxetine treatment prevented decreased citric acid cycle activity in NAc and ACC and ameliorated conditioned fear response in shocked mice. Our results shed light on the role of energy metabolism in PTSD pathogenesis and suggest potential therapy through mitochondrial targeting.

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.

Identification and characterization of HPA-axis reactivity endophenotypes in a cohort of female PTSD patients

Analysis of the function of the hypothalamic-pituitary-adrenal (HPA)-axis in patients suffering from posttraumatic stress disorder (PTSD) has hitherto produced inconsistent findings, inter alia in the Trier Social Stress Test (TSST). To address these inconsistencies, we compared a sample of 23 female PTSD patients with either early life trauma (ELT) or adult trauma (AT) or combined ELT and AT to 18 age-matched non-traumatized female healthy controls in the TSST which was preceded by intensive baseline assessments. During the TSST, we determined a variety of clinical, psychological, endocrine and cardiovascular parameters as well as expression levels of four HPA-axis related genes. Using a previously reported definition of HPA-axis responsive versus non-responsive phenotypes, we identified for the first time two clinically and biologically distinct HPA-axis reactivity subgroups of PTSD. One subgroup ("non-responders") showed a blunted HPA-axis response and distinct clinical and biological characteristics such as a higher prevalence of trauma-related dissociative symptoms and of combined AT and ELT as well as alterations in the expression kinetics of the genes encoding for the mineralocorticoid receptor (MR) and for FK506 binding protein 51 (FKBP51). Interestingly, this non-responder subgroup largely drove the relatively diminished HPA axis response of the total cohort of PTSD patients. These findings are limited by the facts that the majority of patients was medicated, by the lack of traumatized controls and by the relatively small sample size. The here for the first time identified and characterized HPA-axis reactivity endophenotypes offer an explanation for the inconsistent reports on HPA-axis function in PTSD and, moreover, suggest that most likely other factors than HPA-axis reactivity play a decisive role in determination of PTSD core symptom severity.

Norepinephrine and corticosterone in the medial prefrontal cortex and hippocampus predict PTSD-like symptoms in mice

This study measured changes in brain extracellular norepinephrine (NE) and free corticosterone (CORT) levels in a mouse model of post-traumatic stress disorder and related them to hyperarousal and fear memory retention. To this end, microdialysis in the medial prefrontal cortex (mPFC) and the hippocampus (HPC) of male C57BL/6NCrl mice was performed during an acoustic startle response (ASR) and following an electric foot shock (FS), as well as during an ASR and recall of contextual fear (CF) 1 day later. Changes in ASR-stimulated NE levels in the mPFC corresponded to ASR 34 days after FS. Changes in basal and ASR-stimulated extracellular NE levels in the HPC, in contrast, were related to expression of early (day 2) and late (day 34) CF after FS. The increase in extracellular NE levels correlated in a U-shape manner with arousal levels and CF, thus suggesting a non-direct relationship. Stress of different modalities/strength (ASR, FS and CF) caused a similar relative increase in free CORT levels both in the mPFC and the HPC. One day after FS, ASR-induced increases in the CORT content in the mPFC tended to correlate with the FS-potentiated ASR in a U-shape manner. Taken together, these data show that the intracerebral increase in free CORT was likely related to an immediate response to stress, whereas NE neurotransmission in the forebrain predicted arousal and CF 1 month after trauma.

A role for synapsin in FKBP51 modulation of stress responsiveness: Convergent evidence from animal and human studies

Both the molecular co-chaperone FKBP51 and the presynaptic vesicle protein synapsin (alternatively spliced from SYN1-3) are intensively discussed players in the still insufficiently explored pathobiology of psychiatric disorders such as major depression, schizophrenia and posttraumatic stress disorder (PTSD). To address their still unknown interaction, we compared the expression levels of synapsin and five other neurostructural and HPA axis related marker proteins in the prefrontal cortex (PFC) and the hippocampus of restrained-stressed and unstressed Fkbp5 knockout mice and corresponding wild-type littermates. In addition, we compared and correlated the gene expression levels of SYN1, SYN2 and FKBP5 in three different online datasets comprising expression data of human healthy subjects as well as of predominantly medicated patients with different psychiatric disorders. In summary, we found that Fkbp5 deletion, which we previously demonstrated to improve stress-coping behavior in mice, prevents the stress-induced decline in prefrontal cortical (pc), but not in hippocampal synapsin expression. Accordingly, pc, but not hippocampal, synapsin protein levels correlated positively with a more active mouse stress coping behavior. Searching for an underlying mechanism, we found evidence that deletion of Fkbp5 might prevent stress-induced pc synapsin loss, at least in part, through improvement of pc Akt kinase activity. These results, together with our finding that FKBP5 and SYN1 mRNA levels were regulated in opposite directions in the PFC of schizophrenic patients, who are known for exhibiting an altered stress-coping behavior, provide the first evidence of a role for pc synapsin in FKBP51 modulation of stress responsiveness. This role might extend to other tissues, as we found FKBP5 and SYN1 levels to correlate inversely not only in human PFC samples but also in other expression sites. The main limitation of this study is the small number of individuals included in the correlation analyses. Future studies will have to verify the here-postulated role of the FKBP51-Akt kinase-synapsin pathway in stress responsiveness.

Searching for non-genetic molecular and imaging PTSD risk and resilience markers: Systematic review of literature and design of the German Armed Forces PTSD biomarker study

Biomarkers allowing the identification of individuals with an above average vulnerability or resilience for posttraumatic stress disorder (PTSD) would especially serve populations at high risk for trauma exposure like firefighters, police officers and combat soldiers. Aiming to identify the most promising putative PTSD vulnerability markers, we conducted the first systematic review on potential imaging and non-genetic molecular markers for PTSD risk and resilience. Following the PRISMA guidelines, we systematically screened the PubMed database for prospective longitudinal clinical studies and twin studies reporting on pre-trauma and post-trauma PTSD risk and resilience biomarkers. Using 25 different combinations of search terms, we retrieved 8151 articles of which we finally included and evaluated 9 imaging and 27 molecular studies. In addition, we briefly illustrate the design of the ongoing prospective German Armed Forces (Bundeswehr) PTSD biomarker study (Bw-BioPTSD) which not only aims to validate these previous findings but also to identify novel and clinically applicable molecular, psychological and imaging risk, resilience and disease markers for deployment-related psychopathology in a cohort of German soldiers who served in Afghanistan.

GAD65 haplodeficiency conveys resilience in animal models of stress-induced psychopathology

GABAergic mechanisms are critically involved in the control of fear and anxiety, but their role in the development of stress-induced psychopathologies, including post-traumatic stress disorder (PTSD) and mood disorders is not sufficiently understood. We studied these functions in two established mouse models of risk factors for stress-induced psychopathologies employing variable juvenile stress and/or social isolation. A battery of emotional tests in adulthood revealed the induction of contextually generalized fear, anxiety, hyperarousal and depression-like symptoms in these paradigms. These reflect the multitude and complexity of stress effects in human PTSD patients. With factor analysis we were able to identify parameters that reflect these different behavioral domains in stressed animals and thus provide a basis for an integrated scoring of affectedness more closely resembling the clinical situation than isolated parameters. To test the applicability of these models to genetic approaches we further tested the role of GABA using heterozygous mice with targeted mutation of the GABA synthesizing enzyme GAD65 [GAD65(+/−) mice], which show a delayed postnatal increase in tissue GABA content in limbic and cortical brain areas. Unexpectedly, GAD65(+/−) mice did not show changes in exploratory activity regardless of the stressor type and were after the variable juvenile stress procedure protected from the development of contextual generalization in an auditory fear conditioning experiment. Our data demonstrate the complex nature of behavioral alterations in rodent models of stress-related psychopathologies and suggest that GAD65 haplodeficiency, likely through its effect on the postnatal maturation of GABAergic transmission, conveys resilience to some of these stress-induced effects.

Combination of fluoxetine and extinction treatments forms a unique synaptic protein profile that correlates with long-term fear reduction in adult mice

The antidepressant fluoxetine induces synaptic plasticity in the visual and fear networks and promotes the structural remodeling of neuronal circuits, which is critical for experience-dependent plasticity in response to an environmental stimulus. We recently demonstrated that chronic fluoxetine administration together with extinction training in adult mice reduced fear in a context-independent manner. Fear conditioning and extinction alter excitatory and inhibitory transmissions within the fear circuitry. In this study, we investigated whether fluoxetine, extinction or their combination produced distinct long-lasting changes in the synaptic protein profile in the amygdala, hippocampus and prefrontal cortex of conditioned mice. We determined that extinction induced synaptophysin expression and down-regulated the GluA1:GluA2 ratio throughout the fear network in water- and fluoxetine-treated mice, suggesting a common fluoxetine-independent mechanism for increased synaptic transmission and re-arrangement of AMPA-receptors by extinction training. In contrast to common changes, the presynaptic vesicular neurotransmitter transporters VGAT and Vglut1 were upregulated after extinction in water- and fluoxetine-treated mice, respectively. The cortical levels of the GABA transporter Gat1 were reduced in high-freezing water-drinking mice, suggesting a maladaptive increase of GABA spillover at cortical inhibitory synapses. Fear conditioning decreased, and extinction induced the expression of GABA-receptor alpha1 and alpha2 subunits in water- and fluoxetine-treated mice, respectively. Only a combination of fluoxetine with extinction enhanced GluN2A expression in the amygdala and hippocampus, emphasizing the role of this NMDA-receptor subunit in the successful erasure of fear memories. Our finding provides novel data that may become helpful in developing beneficial pharmacological fear-reducing treatment strategies.

Animal models of anxiety disorders and stress

Anxiety and stress-related disorders are severe psychiatric conditions that affect performance in daily tasks and represent a high cost to public health. The initial observation of Charles Darwin that animals and human beings share similar characteristics in the expression of emotion raise the possibility of studying the mechanisms of psychiatric disorders in other mammals (mainly rodents). The development of animal models of anxiety and stress has helped to identify the pharmacological mechanisms and potential clinical effects of several drugs. Animal models of anxiety are based on conflict situations that can generate opposite motivational states induced by approach-avoidance situations. The present review revisited the main rodent models of anxiety and stress responses used worldwide. Here we defined as "ethological" the tests that assess unlearned/unpunished responses (such as the elevated plus maze, light-dark box, and open field), whereas models that involve learned/punished responses are referred to as "conditioned operant conflict tests" (such as the Vogel conflict test). We also discussed models that involve mainly classical conditioning tests (fear conditioning). Finally, we addressed the main protocols used to induce stress responses in rodents, including psychosocial (social defeat and neonatal isolation stress), physical (restraint stress), and chronic unpredictable stress.

Biomarkers in posttraumatic stress disorder: overview and implications for future research

PTSD can develop in the aftermath of traumatic incidents like combat, sexual abuse, or life threatening accidents. Unfortunately, there are still no biomarkers for this debilitating anxiety disorder in clinical use. Anyhow, there are numerous studies describing potential PTSD biomarkers, some of which might progress to the point of practical use in the future. Here, we outline and comment on some of the most prominent findings on potential imaging, psychological, endocrine, and molecular PTSD biomarkers and classify them into risk, disease, and therapy markers. Since for most of these potential PTSD markers a causal role in PTSD has been demonstrated or at least postulated, this review also gives an overview on the current state of research on PTSD pathobiology.

Regulating critical period plasticity: insight from the visual system to fear circuitry for therapeutic interventions

Early temporary windows of heightened brain plasticity called critical periods developmentally sculpt neural circuits and contribute to adult behavior. Regulatory mechanisms of visual cortex development - the preeminent model of experience-dependent critical period plasticity-actively limit adult plasticity and have proved fruitful therapeutic targets to reopen plasticity and rewire faulty visual system connections later in life. Interestingly, these molecular mechanisms have been implicated in the regulation of plasticity in other functions beyond vision. Applying mechanistic understandings of critical period plasticity in the visual cortex to fear circuitry may provide a conceptual framework for developing novel therapeutic tools to mitigate aberrant fear responses in post traumatic stress disorder. In this review, we turn to the model of experience-dependent visual plasticity to provide novel insights for the mechanisms regulating plasticity in the fear system. Fear circuitry, particularly fear memory erasure, also undergoes age-related changes in experience-dependent plasticity. We consider the contributions of molecular brakes that halt visual critical period plasticity to circuitry underlying fear memory erasure. A major molecular brake in the visual cortex, perineuronal net formation, recently has been identified in the development of fear systems that are resilient to fear memory erasure. The roles of other molecular brakes, myelin-related Nogo receptor signaling and Lynx family proteins - endogenous inhibitors for nicotinic acetylcholine receptor, are explored in the context of fear memory plasticity. Such fear plasticity regulators, including epigenetic effects, provide promising targets for therapeutic interventions.

Therapeutic Action of Fluoxetine is Associated with a Reduction in Prefrontal Cortical miR-1971 Expression Levels in a Mouse Model of Posttraumatic Stress Disorder

MicroRNAs (miRNA) are a class of small non-coding RNAs that have recently emerged as epigenetic modulators of gene expression in psychiatric diseases like schizophrenia and major depression. So far, miRNAs have neither been studied in patients suffering from posttraumatic stress disorder (PTSD) nor in PTSD animal models. Here, we present the first study exploring the connection between miRNAs and PTSD. Employing our previously established PTSD mouse model, we assessed miRNA profiles in prefrontal cortices (PFCs) dissected from either fluoxetine or control-treated wildtype C57BL/6N mice 74 days after their subjection to either a single traumatic electric footshock or mock-treatment. Fluoxetine is an antidepressant known to be effective both in PTSD patients and in mice suffering from a PTSD-like syndrome. Screening for differences in the relative expression levels of all potential miRNA target sequences of miRBase 18.0 by pairwise comparison of the PFC miRNA profiles of the four mouse groups mentioned resulted in identification of five miRNA candidate molecules. Validation of these miRNA candidates by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) revealed that the therapeutic action of fluoxetine in shocked mice is associated with a significant reduction in mmu-miR-1971 expression. Furthermore, our findings suggest that traumatic stress and fluoxetine interact to cause distinct alterations in the mouse PFC miRNA signature in the long-term.