An Overview of Translationally Informed Treatments for Posttraumatic Stress Disorder: Animal Models of Pavlovian Fear Conditioning to Human Clinical Trials

Adrenalectomy exacerbates stress-induced impairment in fear discrimination: A causal role for kynurenic acid?

Impaired activity of the hypothalamic-pituitary axis and reduced blood levels of glucocorticoids (GCs) are signature features of stress-related maladies. Recent evidence suggests a possible role of the tryptophan metabolite kynurenic acid (KYNA) in this context. Here we investigated possible causal relationships in adult male rats, using stress-induced fear discrimination as a translationally relevant behavioral outcome measure. One week following adrenalectomy (ADX) or sham surgery, animals were for 2 h either physically restrained or exposed to a predator odor, which caused a much milder stress response. Extracellular KYNA levels were determined before, during and after stress by in vivo microdialysis in the prefrontal cortex. Separate cohorts underwent a fear discrimination procedure starting immediately after stress termination. Different auditory conditioned stimuli (CS) were either paired with a foot shock (CS+) or non-reinforced (CS-). One week later, fear was assessed by re-exposing the animals to each CS. Separate groups of rats were treated with the KYNA synthesis inhibitor BFF-816 prior to stress initiation to test a causal role of KYNA in fear discrimination. Restraint stress raised extracellular KYNA levels by ∼85 % in ADX rats for several hours, and these animals were unable to discriminate between CS+ and CS-. Both effects were prevented by BFF-816 and were not observed after exposure to predator odor or in sham-operated rats. These findings suggest that a causal connection exists between adrenal function, stress-induced KYNA increases, and behavioral deficits. Pharmacological inhibition of KYNA synthesis may therefore be an attractive, novel option for the treatment of stress-related disorders.

Basal forebrain cholinergic systems as circuits through which traumatic stress disrupts emotional memory regulation

Contextual and spatial systems facilitate changes in emotional memory regulation brought on by traumatic stress. Cholinergic basal forebrain (chBF) neurons provide input to contextual/spatial systems and although chBF neurons are important for emotional memory, it is unknown how they contribute to the traumatic stress effects on emotional memory. Clusters of chBF neurons that project to the prefrontal cortex (PFC) modulate fear conditioned suppression and passive avoidance, while clusters of chBF neurons that project to the hippocampus (Hipp) and PFC (i.e. cholinergic medial septum and diagonal bands of Broca (chMS/DBB neurons) are critical for fear extinction. Interestingly, neither Hipp nor PFC projecting chMS/DBB neurons are critical for fear extinction. The retrosplenial cortex (RSC) is a contextual/spatial memory system that receives input from chMS/DBB neurons, but whether this chMS/DBB-RSC circuit facilitates traumatic stress effects on emotional memory remain unexplored. Traumatic stress leads to neuroinflammation and the buildup of reactive oxygen species. These two molecular processes may converge to disrupt chBF circuits enhancing the impact of traumatic stress on emotional memory.

A network approach to posttraumatic stress disorder: Comparing interview and self-report networks

OBJECTIVE

Trauma-related fear (e.g., reexperiencing), impaired reward (e.g., anhedonia), and interpersonal (e.g., detachment) processes may be functionally intertwined, giving rise to chronic psychopathology after a trauma. Network analyses can help pinpoint symptom drivers and treatment targets, but studies examining posttraumatic stress disorder (PTSD) treatment-seeking individuals are lacking.

METHOD

Treatment-seeking adults with primary PTSD (N = 350) completed interview and self-report measures of PTSD severity (PSS-I; PSS-SR). Self-report and interview-based networks were estimated and compared.

RESULTS

Both networks suggested distinct but interconnected communities of reexperiencing and dysphoric symptoms (e.g., interpersonal detachment, numbing). Centrality profiles were strongly associated across networks (rs = .71), with cued reexperiencing and interpersonal detachment showing strong centrality. Self-reported symptoms were more interconnected, suggesting lower specificity.

CONCLUSIONS

For those seeking treatment, interrelated fear and interpersonal processes may drive functional impairment in PTSD, and interview-based networks may help better delineate influential symptoms. Therapeutically, targeting cued reexperiencing and interpersonal detachment may facilitate broader symptom decreases. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Molecular pathways underlying sympathetic autonomic overshooting leading to fear and traumatic memories: looking for alternative therapeutic options for post-traumatic stress disorder

The sympathoadrenal medullary system and the hypothalamic-pituitary-adrenal axis are both activated upon stressful events. The release of catecholamines, such as dopamine, norepinephrine (NE), and epinephrine (EPI), from sympathetic autonomic nerves participate in the adaptive responses to acute stress. Most theories suggest that activation of peripheral β-adrenoceptors (β-ARs) mediates catecholamines-induced memory enhancement. These include direct activation of β-ARs in the vagus nerve, as well as indirect responses to catecholamine-induced glucose changes in the brain. Excessive sympathetic activity is deeply associated with memories experienced during strong emotional stressful conditions, with catecholamines playing relevant roles in fear and traumatic memories consolidation. Recent findings suggest that EPI is implicated in fear and traumatic contextual memories associated with post-traumatic stress disorder (PTSD) by increasing hippocampal gene transcription (e.g., Nr4a) downstream to cAMP response-element protein activation (CREB). Herein, we reviewed the literature focusing on the molecular mechanisms underlying the pathophysiology of memories associated with fear and traumatic experiences to pave new avenues for the treatment of stress and anxiety conditions, such as PTSD.

Extinction in multiple contexts reduces the return of extinguished responses: A multilevel meta-analysis

Extinguished responses have been shown to reappear under several circumstances, and this reappearance is considered to model behaviors such as relapse after exposure therapy. Conducting extinction in multiple contexts has been explored as a technique to decrease the recovery of extinguished responses. The present meta-analysis aimed to examine whether extinction in multiple contexts can consistently reduce the recovery of extinguished responses. After searching in several databases, experiments were included in the analysis if they presented extinction in multiple contexts, an experimental design, and an adequate statistical report. Cohen's d was obtained for each critical comparison and weighted to obtain the sample's average weighted effect size. Analyses were then performed using a multilevel meta-analytic approach. Twenty-five studies were included, with a total sample of 37 experiments or critical comparisons. The analyses showed a large effect size for the sample, moderated by the length of conditioned stimulus exposure, type of experimental subject, and type of recovery. The robust effect of extinction in multiple contexts on relapse should encourage clinicians to consider extinction in multiple contexts as a useful technique in therapy and research.

The role of avoidance in modulating single prolonged stress effects on emotional memory in male and female rats

The incidence of post traumatic stress disorder (PTSD) is greater in women than men, but mechanisms via which this difference manifests remain under explored. The single prolonged stress (SPS) rodent model of traumatic stress has been used to identify mechanisms through which traumatic stress leads to deficits in retaining extinction (a core PTSD symptom), but has been mostly utilized in male model systems. Recent studies have observed that SPS leads to changes in persistent fear memory in female rats, though these results are variable. This variability could be driven by changes in behavioral strategy in females during extinction, but this possibility has not been sufficiently explored. To address this, we examined the impact of SPS on freezing and avoidance (a core PTSD symptom) during extinction in male and female rats. In male rats, SPS enhanced acquisition of conditioned freezing, but did not enhance freezing during extinction training or testing. SPS also decreased avoidance during extinction training, but not extinction testing. In female rats, SPS had no impact on conditioned freezing. Avoidance was not observed in control rats, but emerged in SPS/female rats during extinction testing. Furthermore, avoidance was negatively correlated with freezing in female rats (high avoidance associated with lower freezing), but this relationship was disrupted with SPS. The results suggest that introducing avoidance during extinction negates SPS effects on extinction retention in male and female rats, control/female rats engage in avoidance to regulate fear expression, and this relationship is disrupted with SPS.

A Ventromedial Prefrontal-to-Lateral Entorhinal Cortex Pathway Modulates the Gain of Behavioral Responding During Threat

BACKGROUND

The ability to correctly associate cues and contexts with threat is critical for survival, and the inability to do so can result in threat-related disorders such as posttraumatic stress disorder. The prefrontal cortex (PFC) and hippocampus are well known to play critical roles in cued and contextual threat memory processing. However, the circuits that mediate prefrontal-hippocampal modulation of context discrimination during cued threat processing are less understood. Here, we demonstrate the role of a previously unexplored projection from the ventromedial region of PFC (vmPFC) to the lateral entorhinal cortex (LEC) in modulating the gain of behavior in response to contextual information during threat retrieval and encoding.

METHODS

We used optogenetics followed by in vivo calcium imaging in male C57/B6J mice to manipulate and monitor vmPFC-LEC activity in response to threat-associated cues in different contexts. We then investigated the inputs to, and outputs from, vmPFC-LEC cells using Rabies tracing and channelrhodopsin-assisted electrophysiology.

RESULTS

vmPFC-LEC cells flexibly and bidirectionally shaped behavior during threat expression, shaping sensitivity to contextual information to increase or decrease the gain of behavioral output in response to a threatening or neutral context, respectively.

CONCLUSIONS

Glutamatergic vmPFC-LEC cells are key players in behavioral gain control in response to contextual information during threat processing and may provide a future target for intervention in threat-based disorders.

Disturbances in fear extinction learning after mild traumatic brain injury in mice are accompanied by alterations in dendritic plasticity in the medial prefrontal cortex and basolateral nucleus of the amygdala

Mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD) have emerged as the signature injuries of the U.S. veterans who served in Iraq and Afghanistan, and frequently co-occur in both military and civilian and populations. To better understand how fear learning and underlying neural systems might be altered after mTBI we examined the acquisition of cued fear conditioning and its extinction along with brain morphology and dendritic plasticity in a mouse model of mTBI. To induce mTBI in adult male C57BL/6J mice, a lateral fluid percussive injury (LFP 1.7) was produced using a fluid pulse of 1.7 atmosphere force to the right parietal lobe. Behavior in LFP 1.7 mice was compared to behavior in mice from two separate control groups: mice subjected to craniotomy without LFP injury (Sham) and mice that did not undergo surgery (Unoperated). Following behavioral testing, neural endpoints (dendritic structural plasticity and neuronal volume) were assessed in the basolateral nucleus of the amygdala (BLA), which plays a critical sensory role in fear learning, and medial prefrontal cortex (mPFC), responsible for executive functions and inhibition of fear behaviors. No gross motor abnormalities or increased anxiety-like behaviors were observed in LFP or Sham mice after surgery compared to Unoperated mice. We found that all mice acquired fear behavior, assessed as conditioned freezing to auditory cue in a single session of 6 trials, and acquisition was similar across treatment groups. Using a linear mixed effects analysis, we showed that fear behavior decreased overall over 6 days of extinction training with no effect of treatment group across extinction days. However, a significant interaction was demonstrated between the treatment groups during within-session freezing behavior (5 trials per day) during extinction training. Specifically, freezing behavior increased across within-session extinction trials in LFP 1.7 mice, whereas freezing behavior in control groups did not change on extinction test days, reflecting a dissociation between within-trial and between-trial fear extinction. Additionally, LFP mice demonstrated bilateral increases in dendritic spine density in the BLA and decreases in dendritic complexity in the PFC. The translational implications are that individuals with TBI undergoing fear extinction therapy may demonstrate within-session aberrant learning that could be targeted for more effective treatment interventions.

The role of estrogen receptor manipulation during traumatic stress on changes in emotional memory induced by traumatic stress

RATIONALE

Traumatic stress leads to persistent fear, which is a core feature of post-traumatic stress disorder (PTSD). Women are more likely than men to develop PTSD after trauma exposure, which suggests women are differentially sensitive to traumatic stress. However, it is unclear how this differential sensitivity manifests. Cyclical changes in vascular estrogen release could be a contributing factor where levels of vascular estrogens (and activation of estrogen receptors) at the time of traumatic stress alter the impact of traumatic stress.

METHODS

To examine this, we manipulated estrogen receptors at the time of stress and observed the effect this had on fear and extinction memory (within the single prolonged stress (SPS) paradigm) in female rats. In all experiments, freezing and darting were used to measure fear and extinction memory.

RESULTS

In Experiment 1, SPS enhanced freezing during extinction testing, and this effect was blocked by nuclear estrogen receptor antagonism prior to SPS. In Experiment 2, SPS decreased conditioned freezing during the acquisition and testing of extinction. Administration of 17β-estradiol altered freezing in control and SPS animals during the acquisition of extinction, but this treatment had no effect on freezing during the testing of extinction memory. In all experiments, darting was only observed to footshock onset during fear conditioning.

CONCLUSION

The results suggest multiple behaviors (or different behavioral paradigms) are needed to characterize the nature of traumatic stress effects on emotional memory in female rats and that nuclear estrogen receptor antagonism prior to SPS blocks SPS effects on emotional memory in female rats.

TRPV1 modulation of contextual fear memory depends on stimulus intensity and endocannabinoid signalling in the dorsal hippocampus

The transient receptor potential vanilloid type-1 (TRPV1) channels have been implicated in the modulation of aversive responses. The endocannabinoid anandamide acts as an endogenous TRPV1 agonist, exerting opposite functions at TRPV1 and type-1 cannabinoid receptors (CB₁R). Here we tested the hypothesis that hippocampal TRPV1 modulates contextual fear memory retrieval and investigated the influence of the aversive stimulus intensity as well as the role of endocannabinoid signaling. Male C57BL/6J mice were tested for contextual fear memory after low-, moderate-, or high-intensity shock protocols. The selective TRPV1 blockers SB366791 (1-10 nmol) and 6-I-NC (2 nmol) were infused via intra-dorsal hippocampus before the retrieval test session. The local levels of endocannabinoids and Arc and Zif268 mRNAs, involved in synaptic plasticity and memory, were quantified. First, both TRPV1 blockers reduced memory retrieval in animals exposed to moderate or high (but not low) intensity training protocols. In the second series of results, the magnitude of the freezing responses positively correlated with the hippocampal anandamide levels; TRPV1 and CB₁R were found co-localized in this brain region; and the CB₁R antagonist, AM251, prevented the effects of SB366791. Thus, endocannabinoid signaling possibly mediates the effects of TRPV1 blockers. Finally, inhibition of memory retrieval by TRPV1 blockers increased Arc and Zif268 mRNAs and impaired fear memory reinstatement. In conclusion, the modulation of fear memories by dorsal hippocampal TRPV1 channels may depend on the aversive stimulus intensity and occur via anandamide/CB₁ signaling. Moreover, TRPV1 blockers promote Arc and Zif268 transcription, with subsequent attenuation of aversive memory reinstatement.

Blockade of D-serine signaling and adult hippocampal neurogenesis attenuates remote contextual fear memory following multiple memory retrievals in male mice

The retrieval of fear memories induces two opposing processes, reconsolidation, and extinction. The memory reconsolidation is an active process that involves gene expression and updates an existing memory. It is hypothesized that blockade of reconsolidation by manipulating the neurobiological factors, which are mechanistically involved in the process, could weaken or disrupt the original fear memory. The N-methyl-D-aspartate (NMDA) receptor and hippocampal neurogenesis play crucial roles in hippocampus-dependent memory processes, including reconsolidation. Using contextual fear conditioning paradigm with multiple retrievals, we attempted to weaken the original contextual fear memory by repeatedly disrupting retrieval-induced reconsolidation via downregulation of NMDA receptor signaling and inhibition of neurogenesis. In the first experiment, prior to fear conditioning, NMDA receptor signaling was downregulated by the genetic reduction of its co-agonist, D-serine, and the neurogenesis was dampened by focal X-ray irradiation on the hippocampus. We found that simultaneous D-serine reduction and neurogenesis dampening resulted in a progressive decrease in freezing following each retrieval, leading to an attenuation of remote contextual fear memory on day 28. In the second experiment using the same behavioral protocols, after conditioning, pharmacological approaches were conducted to simultaneously block D-serine signaling and neurogenesis, resulting in a similar suppressive effect on the remote fear memory. The present findings provide insights for understanding the role of D-serine-mediated NMDA receptor signaling and neurogenesis in memory retrieval and the maintenance of remote fear memory, and improving the efficacy of exposure-based therapy for the treatment of post-traumatic stress disorder (PTSD).

Beyond Fear, Extinction, and Freezing: Strategies for Improving the Translational Value of Animal Conditioning Research

Translational neuroscience for anxiety has had limited success despite great progress in understanding the neurobiology of Pavlovian fear conditioning and extinction. This chapter explores the idea that conditioning paradigms have had a modest impact on translation because studies in animals and humans are misaligned in important ways. For instance, animal conditioning studies typically use imminent threats to assess short-duration fear states with single behavioral measures (e.g., freezing), whereas human studies typically assess weaker or more prolonged anxiety states with physiological (e.g., skin conductance) and self-report measures. A path forward may be more animal research on conditioned anxiety phenomena measuring dynamic behavioral and physiological responses in more complex environments. Exploring transitions between defensive brain states during extinction, looming threats, and post-threat recovery may be particularly informative. If care is taken to align paradigms, threat levels, and measures, this strategy may reveal stable patterns of non-conscious defense in animals and humans that correlate better with conscious anxiety. This shift in focus is also warranted because anxiety is a bigger problem than fear, even in disorders defined by dysfunctional fear or panic reactions.

Enhancing Fear Extinction: Pharmacological Approaches

Extinction is the process by which the memory of a learned conditioned association decreases over time and with introduction of new associations. It is a vital part of fear learning, and it is critical to recovery in multiple fear-related disorders, including Specific and Social Phobias, Panic Disorder, Obsessive Compulsive Disorder (OCD), and Posttraumatic Stress Disorder (PTSD). The process of extinction is also the underlying mechanism for recovery in gold-standard therapies for PTSD, including prolonged exposure, cognitive processing therapy, eye movement desensitization and procession, as well as other empirically-based paradigms. Pharmacological modulators of extinction are thus promising targets for treatment of fear-related disorders. We focus here on emerging psychopharmacological treatments to facilitate extinction: D-cycloserine, scopolamine, losartan, ketamine, and 3,4-methylenedioxymethamphetamine. We also provide an overview of recent advances in molecular pathways that show promise as targets for extincion and inhibitory learning, including pathways related to cannabinoid, brain-derived neurotrophic factor, hypothalamic-pituitary-adrenal signaling, and promising work in neurosteroid compounds.

Using expectation violation models to improve the outcome of psychological treatments

Expectations are a central maintaining mechanism in mental disorders and most psychological treatments aim to directly or indirectly modify clinically relevant expectations. Therefore, it is crucial to examine why patients with mental disorders maintain dysfunctional expectations, even in light of disconfirming evidence, and how expectation-violating situations should be created in treatment settings to optimize treatment outcome and reduce the risk of treatment failures. The different psychological subdisciplines offer various approaches for understanding the underlying mechanisms of expectation development, persistence, and change. Here, we convey recommendations on how to improve psychological treatments by considering these different perspectives. Based on our expectation violation model, we argue that the outcome of expectation violation depends on several characteristics: features of the expectation-violating situation; the dynamics between the magnitude of expectation violation and cognitive immunization processes; dealing with uncertainties during and after expectation change; controlled and automatic attention processes; and the costs of expectation changes. Personality factors further add to predict outcomes and may offer a basis for personalized treatment planning. We conclude with a list of recommendations derived from basic psychology that could contribute to improved treatment outcome and to reduced risks of treatment failures.

Treatment efficacy of tDCS and predictors of treatment response in patients with post-traumatic stress disorder

BACKGROUND

Although transcranial direct stimulation (tDCS) has been proposed as an alternative treatment option for various psychiatric disorders, there is inconsistent information regarding the treatment effects of tDCS for patients with post-traumatic stress disorder (PTSD). This study aimed to investigate the tDCS efficacy and identify predictors of treatment response to tDCS in patients with PTSD.

METHOD

Fifty-one patients received 10 sessions of tDCS involving the position of the anode over the F3 area and cathode over the F4 as a condition of 2.0 mA and 20 min duration. Digit span test and 10 questionnaires (Clinician-Administered PTSD Scale (CAPS), Cognitive Emotion Regulation Questionnaire (CERQ), Multidimensional Experiential Avoidance Questionnaire (MEAQ), etc.) were used to measure tDCS effects on PTSD symptoms and identify predictors of response to tDCS.

RESULTS

1) 50.9 % of patients had a significant reduction in the frequency and severity of PTSD symptoms, 2) PTSD-related symptoms such as depression, anxiety, rumination, and quality of life were significantly improved, 3) baseline scores on rumination and digit span test significantly predicted treatment response to tDCS.

LIMITATIONS

This study was open design without a sham control group. Also, the patients' medications were not controlled.

CONCLUSION

This study highlighted the efficacy of frontal tDCS for the treatment of patients with PTSD and identified rumination and digit span as favorable predictive factors for the outcomes of tDCS.

Refinement of the stress-enhanced fear learning model of post-traumatic stress disorder: a behavioral and molecular analysis

Post-traumatic stress disorder (PTSD) is a debilitating mental health condition for which current treatments have long-term efficacy in 50% of patients. There is a clear need for better understanding of the mechanisms underlying PTSD and the development of new treatment approaches. Analog trauma procedures in animals, such as the stress-enhanced fear learning (SEFL) procedure, can be used to produce behavioral and neurobiological changes that have validity in modeling PTSD. However, by necessity, the modeling of PTSD in animals requires them to potentially experience pain and suffering. Consistent with the '3Rs' (reduction, refinement and replacement) of animal research, this study aimed to determine whether the SEFL procedure can be refined to reduce potential animal pain and suffering while retaining the same behavioral and neurobiological changes. Here we showed that PTSD-relevant changes could be produced in both behavior and the brain of rats that were group- rather than single-housed and that received lower-magnitude electric shocks in the 'trauma analog' session. We also varied the number of shock exposures in the trauma analog session, finding SEFL-susceptible and SEFL-resilient populations at all levels of shock exposure, but with greater levels of shock increasing the proportion of rats showing the SEFL-susceptible phenotype. These data demonstrate that the SEFL procedure can be used as an animal analog of PTSD with reduced potential pain and suffering to the animals and that variations in the procedure could be used to generate specific proportions of SEFL-susceptible and SEFL-resilient animals in future studies.

Alpha-2 Adrenoreceptor Antagonist Yohimbine Potentiates Consolidation of Conditioned Fear

BACKGROUND

Hyperconsolidation of aversive associations and poor extinction learning have been hypothesized to be crucial in the acquisition of pathological fear. Previous animal and human research points to the potential role of the catecholaminergic system, particularly noradrenaline and dopamine, in acquiring emotional memories. Here, we investigated in a between-participants design with 3 groups whether the noradrenergic alpha-2 adrenoreceptor antagonist yohimbine and the dopaminergic D2-receptor antagonist sulpiride modulate long-term fear conditioning and extinction in humans.

METHODS

Fifty-five healthy male students were recruited. The final sample consisted of n = 51 participants who were explicitly aware of the contingencies between conditioned stimuli (CS) and unconditioned stimuli after fear acquisition. The participants were then randomly assigned to 1 of the 3 groups and received either yohimbine (10 mg, n = 17), sulpiride (200 mg, n = 16), or placebo (n = 18) between fear acquisition and extinction. Recall of conditioned (non-extinguished CS+ vs CS-) and extinguished fear (extinguished CS+ vs CS-) was assessed 1 day later, and a 64-channel electroencephalogram was recorded.

RESULTS

The yohimbine group showed increased salivary alpha-amylase activity, confirming a successful manipulation of central noradrenergic release. Elevated fear-conditioned bradycardia and larger differential amplitudes of the N170 and late positive potential components in the event-related brain potential indicated that yohimbine treatment (compared with a placebo and sulpiride) enhanced fear recall during day 2.

CONCLUSIONS

These results suggest that yohimbine potentiates cardiac and central electrophysiological signatures of fear memory consolidation. They thereby elucidate the key role of noradrenaline in strengthening the consolidation of conditioned fear associations, which may be a key mechanism in the etiology of fear-related disorders.

Neuronal activity in sensory cortex predicts the specificity of learning in mice

Learning to avoid dangerous signals while preserving normal responses to safe stimuli is essential for everyday behavior and survival. Following identical experiences, subjects exhibit fear specificity ranging from high (specializing fear to only the dangerous stimulus) to low (generalizing fear to safe stimuli), yet the neuronal basis of fear specificity remains unknown. Here, we identified the neuronal code that underlies inter-subject variability in fear specificity using longitudinal imaging of neuronal activity before and after differential fear conditioning in the auditory cortex of mice. Neuronal activity prior to, but not after learning predicted the level of specificity following fear conditioning across subjects. Stimulus representation in auditory cortex was reorganized following conditioning. However, the reorganized neuronal activity did not relate to the specificity of learning. These results present a novel neuronal code that determines individual patterns in learning.

The neural mechanisms underpinning the specificity of fear memories remains poorly understood. Here, the authors highlight how neural activity prior to fear learning impacts fear memory specificity.

Effects of Sevoflurane and Propofol on Posttraumatic Stress Disorder After Emergency Trauma: A Double-Blind Randomized Controlled Trial

OBJECTIVE

Posttraumatic stress disorder (PTSD) is a frequent and disabling consequence of traumatic events. A previous study found that early use of propofol was a potential risk factor for PTSD. This prospective study aimed to investigate the effect of propofol and sevoflurane on PTSD after emergency surgery in trauma patients.

METHODS

A total of 300 trauma patients undergoing emergency surgery were randomly divided into two groups and anesthetized with propofol and/or sevoflurane. Perioperative clinical data were collected. The incidence of PTSD was evaluated with the Clinician-Administered PTSD Scale for DSM-5 (CAPS-5) in the two groups 1 month after the operation. The relevance of the injury time and CAPS-5 scores was assessed by Spearman correlation analysis. Logistic regression analysis was used to analyze the risk factors for PTSD.

RESULTS

The incidence of PTSD in the propofol group was higher than that in the sevoflurane group 1 month postoperatively (23.2 vs. 12.2%, P = 0.014). The injury time was negatively correlated with the CAPS-5 score in the propofol group (r = -0.226, P < 0.001). In the logistic regression analysis, the utilization of propofol was an independent risk factor for PTSD (P = 0.017).

CONCLUSION

Early use of propofol general anesthesia in emergency surgery for trauma patients may increase the risk of PTSD.

CLINICAL TRIAL REGISTRATION

www.chictr.org.cn, identifier: ChiCTR2100050202.

Maternal Separation Induces Sex-Specific Differences in Sensitivity to Traumatic Stress

Post-traumatic stress disorder (PTSD) is a debilitating psychiatric disorder with a high economic burden. Two risk factors for increasing the chances of developing PTSD are sex (being female) and early life stress. These risk factors suggest that early life stress-induced changes and sex differences in emotional circuits and neuroendocrinological systems lead to susceptibility to traumatic stress. Exploring mechanisms via which stress leads to specific effects can be accomplished in animal models, but reliable animal models that allow for an examination of how early life stress interacts with sex to increase susceptibility to traumatic stress is lacking. To address this, we examined the effects of early life stress [using the maternal separation (MS) model] and late adolescence/early adult traumatic stress [using the single prolonged stress (SPS) model] on startle reactivity, anxiety-like behavior in the open field (OF), and basal corticosterone levels in male and female rats. Female rats exposed to MS and SPS (MS/SPS) showed enhanced startle reactivity relative to MS/control female rats. Enhanced startle reactivity was not observed in MS/SPS male rats. Instead, non-maternally separated male rats that were exposed to SPS showed enhanced startle reactivity relative to controls. Female rats had enhanced locomotor activity in the OF and higher basal corticosterone levels in comparison to males, but measures in the OF and basal corticosterone were not affected by MS or SPS. Overall the results suggest that the combined MS and SPS models can be used to explore how changes in maternal care during infancy lead to sex differences in sensitivity to the effects of traumatic stress as adolescents and adults.

Deficiency of the CYLD Impairs Fear Memory of Mice and Disrupts Neuronal Activity and Synaptic Transmission in the Basolateral Amygdala

Fear learning and memory are crucial for animal survival. Abnormal fear memory is a hallmark of many neuropsychiatric disorders. Appropriate neuronal activation and excitability in the basolateral amygdala (BLA) are necessary for the formation of fear memory. The gene cylindromatosis (Cyld), which encodes a lysine-63 deubiquitinase, is expressed in several brain regions including the amygdala. The functions of the cylindromatosis protein (CYLD) in the regulation of the neuronal activity, neural circuits and fear memory, remain largely unknown, however. Here, we report that Cyld knockout impairs amygdala-dependent tone-cued fear memory. The number of c-Fos⁺ neurons responding to the tone-cued fear test was reduced in the BLA of Cyld^–/– mice, suggesting that the absence of CYLD causes aberrant neuronal activation. We found that this aberrant neuronal activation in the BLA of Cyld^–/– mice may relate to the decreased excitability of principal neurons. Another possibility of aberrant neuronal activation could be the impaired excitatory synaptic transmission in the BLA of Cyld^–/– mice. Specifically, both the frequency of spontaneous excitatory postsynaptic currents and the amplitude of miniature excitatory postsynaptic currents in BLA principal neurons were decreased. In addition, Cyld mutation caused an increase in both the frequency of miniature inhibitory postsynaptic currents in principal neurons and the number of parvalbumin⁺ interneurons, consistent with excessive local circuit inhibition in the BLA of Cyld^–/– mice. Taken together, these results suggest that CYLD deficiency disrupts the neuronal activity and synaptic transmission in the BLA of mice which may contribute to the impaired fear memory observed in Cyld^–/– mice.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

Many physiologic effects of l-glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, are mediated via signaling by ionotropic glutamate receptors (iGluRs). These ligand-gated ion channels are critical to brain function and are centrally implicated in numerous psychiatric and neurologic disorders. There are different classes of iGluRs with a variety of receptor subtypes in each class that play distinct roles in neuronal functions. The diversity in iGluR subtypes, with their unique functional properties and physiologic roles, has motivated a large number of studies. Our understanding of receptor subtypes has advanced considerably since the first iGluR subunit gene was cloned in 1989, and the research focus has expanded to encompass facets of biology that have been recently discovered and to exploit experimental paradigms made possible by technological advances. Here, we review insights from more than 3 decades of iGluR studies with an emphasis on the progress that has occurred in the past decade. We cover structure, function, pharmacology, roles in neurophysiology, and therapeutic implications for all classes of receptors assembled from the subunits encoded by the 18 ionotropic glutamate receptor genes. SIGNIFICANCE STATEMENT: Glutamate receptors play important roles in virtually all aspects of brain function and are either involved in mediating some clinical features of neurological disease or represent a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of this class of receptors will advance our understanding of many aspects of brain function at molecular, cellular, and system levels and provide new opportunities to treat patients.

Fear conditioning and extinction in obsessive-compulsive disorder: A systematic review

Laboratory experiments using fear conditioning and extinction protocols help lay the groundwork for designing, testing, and optimizing innovative treatments for anxiety-related disorders. Yet, there is limited basic research on fear conditioning and extinction in obsessive-compulsive disorder (OCD). This is surprising because exposure-based treatments based on associative learning principles are among the most popular and effective treatment options for OCD. Here, we systematically review and critically assess existing aversive conditioning and extinction studies of OCD. Across 12 studies, there was moderate evidence that OCD is associated with abnormal acquisition of conditioned responses that differ from comparison groups. There was relatively stronger evidence of OCD's association with impaired extinction processes. This included multiple studies finding elevated conditioned responses during extinction learning and poorer threat/safety discrimination during recall, although a minority of studies yielded results inconsistent with this conclusion. Overall, the conditioning model holds value for OCD research, but more work is necessary to clarify emerging patterns of results and increase clinical translational utility to the level seen in other anxiety-related disorders. We detail limitations in the literature and suggest next steps, including modeling OCD with more complex conditioning methodology (e.g., semantic/conceptual generalization, avoidance) and improving individual-differences assessment with dimensional techniques.

Posttraumatic Stress Disorder and Cardiovascular Disease: State of the Science, Knowledge Gaps, and Research Opportunities

Posttraumatic stress disorder (PTSD) is characterized by a persistent maladaptive reaction after exposure to severe psychological trauma. Traumatic events that may precipitate PTSD include violent personal assaults, natural and human-made disasters, and exposure to military combat or warfare. There is a growing body of evidence for associations of PTSD with major risk factors for cardiovascular disease (CVD), such as hypertension and diabetes, as well as with major CVD outcomes, such as myocardial infarction and heart failure. However, it is unclear whether these associations are causal or confounded. Furthermore, the biological and behavioral mechanisms underlying these associations are poorly understood. Here, the available evidence on the association of PTSD with CVD from population, basic, and genomic research as well as from clinical and translational research are reviewed, seeking to identify major research gaps, barriers, and opportunities in knowledge acquisition and technology as well as research tools to support and accelerate critical research for near-term and longer-term translational research directions. Large-scale, well-designed prospective studies, capturing diverse and high-risk populations, are warranted that include uniform phenotyping of PTSD as well as broad assessment of biological and behavioral risk factors and CVD outcomes. Available evidence from functional brain imaging studies demonstrates that PTSD pathophysiology includes changes in specific anatomical brain regions and circuits, and studies of immune system function in individuals with PTSD suggest its association with enhanced immune inflammatory activity. However, establishment of animal models and human tissue biobanks is also warranted to elucidate the potential causal connection of PTSD-induced brain changes and/or inflammation with CVD pathophysiology. Emerging large-scale genome-wide association studies of PTSD will provide an opportunity to conduct mendelian randomization studies that test hypotheses regarding the presence, magnitude, and direction of causal associations between PTSD and CVD outcomes. By identifying research gaps in epidemiology and genomics, animal, and human translational research, opportunities to better justify and design future interventional trials are highlighted that may test whether treatment of PTSD or underlying neurobiological or immune dysregulation may improve or prevent CVD risk or outcomes.

Translating Across Circuits and Genetics Toward Progress in Fear- and Anxiety-Related Disorders

(Reprinted with permission from Am J Psychiatry 2020; 177:214-222).

NPY Released From GABA Neurons of the Dentate Gyrus Specially Reduces Contextual Fear Without Affecting Cued or Trace Fear

Disproportionate, maladapted, and generalized fear are essential hallmarks of posttraumatic stress disorder (PTSD), which develops upon severe trauma in a subset of exposed individuals. Among the brain areas that are processing fear memories, the hippocampal formation exerts a central role linking emotional-affective with cognitive aspects. In the hippocampus, neuronal excitability is constrained by multiple GABAergic interneurons with highly specialized functions and an extensive repertoire of co-released neuromodulators. Neuropeptide Y (NPY) is one of these co-transmitters that significantly affects hippocampal signaling, with ample evidence supporting its fundamental role in emotional, cognitive, and metabolic circuitries. Here we investigated the role of NPY in relation to GABA, both released from the same interneurons of the dorsal dentate gyrus (DG), in different aspects of fear conditioning. We demonstrated that activation of dentate GABA neurons specifically during fear recall reduced cue-related as well as trace-related freezing behavior, whereas inhibition of the same neurons had no significant effects. Interestingly, concomitant overexpression of NPY in these neurons did not further modify fear recall, neither under baseline conditions nor upon chemogenetic stimulation. However, potentially increased co-release of NPY substantially reduced contextual fear, promoted extinction learning, and long-term suppression of fear in a foreground context–conditioning paradigm. Importantly, NPY in the dorsal DG was not only expressed in somatostatin neurons, but also in parvalbumin-positive basket cells and axoaxonic cells, indicating intense feedback and feedforward modulation of hippocampal signaling and precise curtailing of neuronal engrams. Thus, these findings suggest that co-release of NPY from specific interneuron populations of the dorsal DG modifies dedicated aspects of hippocampal processing by sharpening the activation of neural engrams and the consecutive fear response. Since inappropriate and generalized fear is the major impediment in the treatment of PTSD patients, the dentate NPY system may be a suitable access point to ameliorate PTSD symptoms and improve the inherent disease course.

GluN2D NMDA Receptors Gate Fear Extinction Learning and Interneuron Plasticity

The cerebellum is critically involved in the formation of associative fear memory and in subsequent extinction learning. Fear conditioning is associated with a long-term potentiation at both excitatory and inhibitory synapses onto Purkinje cells. We therefore tested whether fear conditioning unmasks novel forms of synaptic plasticity, which enable subsequent extinction learning to reset cerebellar circuitry. We found that fear learning enhanced GABA release from molecular layer interneurons and this was reversed after fear extinction learning. Importantly an extinction-like stimulation of parallel fibers after fear learning is sufficient to induce a lasting decrease in inhibitory transmission (I-LTD_stim) in the cerebellar cortex, a form of plasticity that is absent in naïve animals. While NMDA (N-methyl-D-aspartate) receptors are required for the formation and extinction of associative memory, the role of GluN2D, one of the four major NMDA receptor subunits, in learning and memory has not been determined. We found that fear conditioning elevates spontaneous GABA release in GluN2D KO as shown in WT mice. Deletion of GluN2D, however, abolished the I-LTD_stim induced by parallel fiber stimulation after learning. At the behavioral level, genetic deletion of GluN2D subunits did not affect associative learning and memory retention, but impaired subsequent fear extinction learning. D-cycloserine, a partial NMDA receptor (NMDAR) agonist, failed to rescue extinction learning in mutant mice. Our results identify GluN2D as a critical NMDAR subunit for extinction learning and reveal a form of GluN2D-dependent metaplasticity that is associated with extinction in the cerebellum.

Transcranial photobiomodulation prevents PTSD-like comorbidities in rats experiencing underwater trauma

Maladaptive fear memory processing after a traumatic event is a major contributor to the development of the comorbidities related to posttraumatic stress disorder (PTSD). An intervention to normalize this process could be a first-line treatment to prevent PTSD development. However, little progress has been made in identifying interventions that can prevent trauma survivors from developing PTSD. A treatment that could help trauma survivors cope with traumatic memories and decrease the prevalence of PTSD is thus in high demand. This study was designed to investigate the potential beneficial effects of early photobiomodulation (PBM) interventions to prevent PTSD-like comorbidities in animals. PTSD-like comorbidities in rats were induced by an underwater trauma (UWT) procedure, followed by multiple swimming sessions on later days for memory recall. Immediately after UWT and swimming, rats were restrained with or without PBM treatment (808 nm, 25 mW/cm2, 3 J/day). PTSD-like commodities, such as anxiety-like behavior, depression-like behavior, and cognitive dysfunction, were reproduced in UWT-rats. These comorbidities, however, could be prevented by early PBM interventions. By measuring the expression of immediate early genes (IEGs) as neuronal activity markers, we found that PBM treatment differentially regulated Arc and c-fos expression in the hippocampus and amygdala, two PTSD-related brain regions. Additionally, PBM boosted ATP production and regulated protein expression in the hippocampus following stress. Our results demonstrate that PBM can modulate brain activity in response to traumatic and stressful events and that early PBM intervention can prevent the occurrence of PTSD-like comorbidities in rats.

Intranasal oxytocin decreases fear generalization in males, but does not modulate discrimination threshold

BACKGROUND

A previously acquired fear response often spreads to perceptually or conceptually close stimuli or contexts. This process, known as fear generalization, facilitates the avoidance of danger, and dysregulations in this process play an important role in anxiety disorders. Oxytocin (OT) has been shown to modulate fear learning, yet effects on fear generalization remain unknown.

METHODS

We employed a randomized, placebo-controlled, double-blind, between-subject design during which healthy male participants received either intranasal OT or placebo (PLC) following fear acquisition and before fear generalization with concomitant acquisition of skin conductance responses (SCRs). Twenty-four to 72 h before the fear learning and immediately after the fear generalization task, participants additionally complete a discrimination threshold task.

RESULTS

Relative to PLC, OT significantly reduced perceived risk and SCRs towards the CS+ and GS1 (the generalization stimulus that is most similar to CS+) during fear generalization, whereas the discrimination threshold was not affected.

CONCLUSIONS

Together, the results suggest that OT can attenuate fear generalization in the absence of effects on discrimination threshold. This study provides the first evidence for effects of OT on fear generalization in humans and suggests that OT may have therapeutic potential in anxiety disorders characterized by dysregulated fear generalization.

Cannabis Use in People With Obsessive-Compulsive Symptomatology: Results From a Mexican Epidemiological Sample

Recent studies suggest that the endocannabinoid system could play an important role in the physiopathology of obsessive-compulsive disorder (OCD). There are reports of effective treatment with derivatives of tetrahydrocannabinol (THC). The study of the genetic factor associated with psychiatric disorders has made possible an exploration of its contribution to the pharmacological response. However, very little is known about the genetic factor or the prevalence of cannabis use in the Mexican population with OCD. The objective of this study is to compare the prevalence of use and dependence on cannabis in individuals with obsessive-compulsive symptomatology (OCS) with that of individuals with other psychiatric symptoms (psychosis, depression, and anxiety), and to explore the association between genetic risk and use. The study includes a total of 13,130 individuals evaluated in the second stage of the 2016 National Survey of Drug, Alcohol, and Tobacco Use (Encodat 2016), with genetic analysis (polygenic risk scoring) of a subsample of 3,521 individuals. Obsessive symptomatology had a prevalence of 7.2% and compulsive symptomatology a prevalence of 8.6%. The proportion of individuals with OCS who had ever used cannabis was 23.4%, and of those with cannabis dependency was 2.7%, the latter figure higher than that in individuals with other psychiatric symptoms (hypomania, 2.6%; anxiety, 2.8%; depression, 2.3%), except psychosis (5.9%). Individuals with OCS who reported using cannabis had an increased genetic risk for cannabis dependence but not for OCD. We thus cannot know how the increased genetic risk of cannabis dependence in people with OCD is influenced by their pharmacological response to derivatives of THC. The results, however, suggest paths for future studies.

Pharmacotherapy of 1,044 inpatients with posttraumatic stress disorder: current status and trends in German-speaking countries

Posttraumatic stress disorder (PTSD) is a debilitating psychiatric disorder with limited approved pharmacological treatment options and high symptom burden. Therefore, real-life prescription patterns may differ from guideline recommendations, especially in psychiatric inpatient settings. The European Drug Safety Program in Psychiatry ("Arzneimittelsicherheit in der Psychiatrie", AMSP) collects inpatients' prescription rates cross-sectionally twice a year in German-speaking psychiatric hospitals. For this study, the AMSP database was screened for psychiatric inpatients with a primary diagnosis of PTSD between 2001 and 2017. N = 1,044 patients with a primary diagnosis of PTSD were identified with 89.9% taking psychotropics. The average prescription rate was 2.4 (standard deviation: 1.5) psychotropics per patient with high rates of antidepressant drugs (72.0%), antipsychotics drugs (58.4%) and tranquilizing drugs (29.3%). The presence of psychiatric comorbidities was associated with higher rates of psychotropic drug use. The most often prescribed substances were quetiapine (24.1% of all patients), lorazepam (18.1%) and mirtazapine (15.0%). The use of drugs approved for PTSD was low (sertraline 11.1%; paroxetine 3.7%). Prescription rates of second-generation antipsychotic drugs increased, while the use of tranquilizing drugs declined over the years. High prescription rates and extensive use of sedative medication suggest a symptom-driven prescription (e.g., hyperarousal, insomnia) that can only be explained to a minor extent by existing comorbidities. The observed discrepancy with existing guidelines underlines the need for effective pharmacological and psychological treatment options in psychiatric inpatient settings.

Habenula kisspeptin retrieves morphine impaired fear memory in zebrafish

The habenula is an evolutionarily conserved brain structure, which has recently been implicated in fear memory. In the zebrafish, kisspeptin (Kiss1) is predominantly expressed in the habenula, which has been implicated as a modulator of fear response. Hence, in the present study, we questioned whether Kiss1 has a role in fear memory and morphine-induced fear memory impairment using an odorant cue (alarm substances, AS)-induced fear avoidance paradigm in adult zebrafish, whereby the fear-conditioned memory can be assessed by a change of basal place preference (= avoidance) of fish due to AS-induced fear experience. Subsequently, to examine the possible role of Kiss1 neurons-serotonergic pathway, kiss1 mRNA and serotonin levels were measured. AS exposure triggered fear episodes and fear-conditioned place avoidance. Morphine treatment followed by AS exposure, significantly impaired fear memory with increased time-spent in AS-paired compartment. However, fish administered with Kiss1 (10^–21 mol/fish) after morphine treatment had significantly lower kiss1 mRNA levels but retained fear memory. In addition, the total brain serotonin levels were significantly increased in AS- and Kiss1-treated groups as compared to control and morphine treated group. These results suggest that habenular Kiss1 might be involved in consolidation or retrieval of fear memory through the serotonin system.

PI3K-Akt Signaling in the Basolateral Amygdala Facilitates Traumatic Stress Enhancements in Fear Memory

BACKGROUND

A core symptom of posttraumatic stress disorder is persistent fear memory, which can be defined as fear memory that is resistant to updating, inhibition, or extinction. posttraumatic stress disorder emerges after traumatic stress exposure, but neurobiological mechanisms via which traumatic stress leads to persistent fear memory are not well defined. Akt signaling within the amygdala (Amy) is enhanced with traumatic stress, and phosphatidylinositol kinase 3 (PI3K) activation of Akt within the basolateral Amy (BLA) has been implicated as critical to fear memory formation. These findings raise the possibility that traumatic stress enhances PI3K→Akt signaling in the BLA, which leads to persistent fear memory.

METHODS

To test this hypothesis, rats were exposed to traumatic stress using the single prolonged stress model, and changes in Akt phosphorylation were assayed in the Amy at 0 and 30 minutes after fear conditioning (FC). In a separate experiment, we inhibited PI3K→Akt signaling in the BLA prior to FC and observed the effect this had on acquisition, expression, and extinction of FC in stressed and control rats.

RESULTS

Enhanced Akt phosphorylation in the Amy at both time points was observed in stressed rats, but not in control rats. PI3K→Akt inhibition in the BLA had no effect on freezing in control rats but decreased freezing during extinction training and testing in stressed rats.

CONCLUSION

These findings suggest that PI3K→Akt signaling in the BLA could be a mechanism via which traumatic stress leads to fear memory that is resistant to extinction.

Fear Extinction Recall Modulates Human Frontomedial Theta and Amygdala Activity

Human functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) studies, as well as animal studies, indicate that the amygdala and frontomedial brain regions are critically involved in conditioned fear and that frontomedial oscillations in the theta range (4-8 Hz) may support communication between these brain regions. However, few studies have used a multimodal approach to probe interactions among these key regions in humans. Here, our goal was to bridge the gap between prior human fMRI, EEG, and animal findings. Using simultaneous EEG-fMRI recordings 24 h after fear conditioning and extinction, conditioned stimuli presented (CS+E, CS-E) and not presented during extinction (CS+N, CS-N) were compared to identify effects specific to extinction versus fear recall. Differential (CS+ vs. CS-) electrodermal, frontomedial theta (EEG) and amygdala responses (fMRI) were reduced for extinguished versus nonextinguished stimuli. Importantly, effects on theta power covaried with effects on amygdala activation. Fear and extinction recall as indicated by theta explained 60% of the variance for the analogous effect in the right amygdala. Our findings show for the first time the interplay of amygdala and frontomedial theta activity during fear and extinction recall in humans and provide insight into neural circuits consistently linked with top-down amygdala modulation in rodents.

Emotional Stress Induces Structural Plasticity in Bergmann Glial Cells via an AC5-CPEB3-GluA1 Pathway

Stress alters brain function by modifying the structure and function of neurons and astrocytes. The fine processes of astrocytes are critical for the clearance of neurotransmitters during synaptic transmission. Thus, experience-dependent remodeling of glial processes is anticipated to alter the output of neural circuits. However, the molecular mechanisms that underlie glial structural plasticity are not known. Here we show that a single exposure of male and female mice to an acute stress produced a long-lasting retraction of the lateral processes of cerebellar Bergmann glial cells. These cells express the GluA1 subunit of AMPA-type glutamate receptors, and GluA1 knockdown is known to shorten the length of glial processes. We found that stress reduced the level of GluA1 protein and AMPA receptor-mediated currents in Bergmann glial cells, and these effects were absent in mice devoid of CPEB3, a protein that binds to GluA1 mRNA and regulates GluA1 protein synthesis. Administration of a β-adrenergic receptor blocker attenuated the reduction in GluA1, and deletion of adenylate cyclase 5 prevented GluA1 suppression. Therefore, stress suppresses GluA1 protein synthesis via an adrenergic/adenylyl cyclase/CPEB3 pathway, and reduces the length of astrocyte lateral processes. Our results identify a novel mechanism for GluA1 subunit plasticity in non-neuronal cells and suggest a previously unappreciated role for AMPA receptors in stress-induced astrocytic remodeling.SIGNIFICANCE STATEMENT Astrocytes play important roles in synaptic transmission by extending fine processes around synapses. In this study, we showed that a single exposure to an acute stress triggered a retraction of lateral/fine processes in mouse cerebellar astrocytes. These astrocytes express GluA1, a glutamate receptor subunit known to lengthen astrocyte processes. We showed that astrocytic structural changes are associated with a reduction of GluA1 protein levels. This requires activation of β-adrenergic receptors and is triggered by noradrenaline released during stress. We identified adenylyl cyclase 5, an enzyme that elevates cAMP levels, as a downstream effector and found that lowering GluA1 levels depends on CPEB3 proteins that bind to GluA1 mRNA. Therefore, stress regulates GluA1 protein synthesis via an adrenergic/adenylyl cyclase/CPEB3 pathway in astrocytes and remodels their fine processes.

Translating Across Circuits and Genetics Toward Progress in Fear- and Anxiety-Related Disorders

Anxiety and fear-related disorders are common and disabling, and they significantly increase risk for suicide and other causes of morbidity and mortality. However, there is tremendous potential for translational neuroscience to advance our understanding of these disorders, leading to novel and powerful interventions and even to preventing their initial development. This overview examines the general circuits and processes thought to underlie fear and anxiety, along with the promise of translational research. It then examines some of the data-driven "next-generation" approaches that are needed for discovery and understanding but that do not always fit neatly into established models. From one perspective, these disorders offer among the most tractable problems in psychiatry, with a great deal of accumulated understanding, across species, of neurocircuit, behavioral, and, increasingly, genetic mechanisms, of how dysregulation of fear and threat processes contributes to anxiety-related disorders. One example is the progressively sophisticated understanding of how extinction underlies the exposure therapy component of cognitive-behavioral therapy approaches, which are ubiquitously used across anxiety and fear-related disorders. However, it is also critical to examine gaps in our understanding between reasonably well-replicated examples of successful translation, areas of significant deficits in knowledge, and the role of large-scale data-driven approaches in future progress and discovery. Although a tremendous amount of progress is still needed, translational approaches to understanding, treating, and even preventing anxiety and fear-related disorders offer great opportunities for successfully bridging neuroscience discovery to clinical practice.

Fear not: recent advances in understanding the neural basis of fear memories and implications for treatment development

Fear is a highly adaptive emotion that has evolved to promote survival and reproductive fitness. However, maladaptive expression of fear can lead to debilitating stressor-related and anxiety disorders such as post-traumatic stress disorder. Although the neural basis of fear has been extensively researched for several decades, recent technological advances in pharmacogenetics and optogenetics have allowed greater resolution in understanding the neural circuits that underlie fear. Alongside conceptual advances in the understanding of fear memory, this increased knowledge has clarified mechanisms for some currently available therapies for post-traumatic stress disorder and has identified new potential treatment targets.

Single prolonged stress alters neural activation in the periacqueductal gray and midline thalamic nuclei during emotional learning and memory

Clinical and preclinical studies that have examined the neurobiology of persistent fear memory in posttraumatic stress disorder (PTSD) have focused on the medial prefrontal cortex, hippocampus, and amygdala. Sensory systems, the periaqueductal gray (PAG), and midline thalamic nuclei have been implicated in fear and extinction memory, but whether neural activity in these substrates is sensitive to traumatic stress (at baseline or during emotional learning and memory) remains unexplored. To address this, we used the single prolonged stress (SPS) model of traumatic stress. SPS and control rats were either subjected to fear conditioning (CS-fear) or presented with CSs alone (CS-only) during fear conditioning. All rats were then subjected to extinction training and testing. A subset of rats were euthanized after each behavioral stage and c-Fos and c-Jun used to measure neural activation in all substrates. SPS lowered c-Jun levels in the dorsomedial and lateral PAG at baseline, but the elevated c-Jun expression in the PAG during emotional learning and memory. SPS also altered c-Fos expression during fear and extinction learning/memory in midline thalamic nuclei. These findings suggest changes in neural function in the PAG and midline thalamic nuclei could contribute to persistent fear memory induced by traumatic stress. Interestingly, SPS effects were also observed in animals that never learned fear or extinction (i.e., CS-only). This raises the possibility that traumatic stress could have broader effects on the psychological function that are dependent on the PAG and midline thalamic nuclei.

microRNA mir-598-3p mediates susceptibility to stress enhancement of remote fear memory

microRNAs (miRNAs) have emerged as potent regulators of learning, recent memory, and extinction. However, our understanding of miRNAs directly involved in regulating complex psychiatric conditions perpetuated by aberrant memory, such as in posttraumatic stress disorder (PTSD), remains limited. To begin to address the role of miRNAs in persistent memories, we performed small-RNA sequencing on basolateral amygdala (BLA) tissue and identified miRNAs altered by auditory fear conditioning (FC) one month after training. mir-598-3p, a highly conserved miRNA previously unstudied in the brain, was down-regulated in the BLA. Further decreasing BLA mir-598-3p levels did not increase strength of the remote fear memory. Given that stress is a critical component in PTSD, we next assessed the impact of stress and stress-enhanced fear learning (SEFL) on mir-598-3p levels, finding the miRNA is elevated in the BLA of male, but not female, mice susceptible to the effects of stress in SEFL. Accordingly, intra-BLA inhibition of mir-598-3p interfered with expression and extinction of the remote fear memory in male, but not female, mice. This effect could not be attributed to an anxiolytic effect of miRNA inhibition. Finally, bioinformatic analysis following quantitative proteomics on BLA tissue collected 30 d post-SEFL training identified putative mir-598-3p targets and related pathways mediating the differential susceptibility, with evidence for regulation of the actin cytoskeleton, the core mediator of structural plasticity. Taken together, the results suggest BLA mir-598-3p may be recruited by stress to mediate a critical switch from a salient remote fear memory to one that is enhanced and extinction-resistant.

Fanon's Police Inspector

Frantz Fanon practiced psychiatry in a colonized Algeria during its struggle for independence. In his 1961 work The Wretched of the Earth, Fanon described cases from his treatment of Algerian nationalists and French colonists. I present one of Fanon's cases as an ethical inquiry into posttraumatic stress disorder (PTSD). A French police inspector, who is employed in torture, visits Fanon with symptoms of PTSD after escalating domestic violence. The patient asks Fanon "to help him torture … with a total peace of mind." Is it possible to treat the inspector in a meaningful way? More broadly, how might researchers and clinicians balance collective responsibilities to individual symptoms and social conditions? The answer depends on how trauma is framed: as disorder of meaning-making or circuit dysfunction, as individual illness or social rupture, as potentially gendered and racialized. These framings can reveal different views on the allocation of responsibility for the causation, expression and management of PTSD. I do not propose that it is inherently immoral to modify traumatic memories; nor do I question the efficacy of individual interventions. Rather, I ask whether PTSD has a social meaning that transcends individual comfort in decision making about erasure. What do individual interventions accomplish in the absence of concurrent political and social transformations? I argue that a holistic understanding of PTSD entails a set of social obligations: to address at its root political, gendered, and racialized violence, to repudiate occupations centered on exploitative manipulation of individuals and cultures, and to social change that prioritizes these commitments.

Fear memory-induced alterations in the mRNA expression of G proteins in the mouse brain and the impact of immediate posttraining treatment with morphine

Disturbances in fear-evoked signal transduction in the hippocampus (HP), the nuclei of the amygdala (AMY), and the prefrontal cortex (PFC) underlie anxiety-related disorders. However, the molecular mechanisms underlying these effects remain elusive. Heterotrimeric G proteins (GPs) are divided into the following four families based on the intracellular activity of their alpha subunit (Gα): Gα(s) proteins stimulate cyclic AMP (cAMP) generation, Gα(i/o) proteins inhibit the cAMP pathway, Gα(q/11) proteins increase the intracellular Ca⁺⁺ concentration and the inositol trisphosphate level, and Gα(12/13) proteins activate monomeric GP-Rho. In the present study, we assessed the effects of a fear memory procedure on the mRNA expression of the Gα subunits of all four GP families in the HP, AMY and PFC. C57BL/6 J mice were subjected to a fear conditioning (FC) procedure followed by a contextual or cued fear memory test (CTX-R and CS-R, respectively). Morphine (MOR, 1 mg/kg/ip) was injected immediately after FC to prevent the fear consolidation process. Real-time quantitative PCR was used to measure the mRNA expression levels of Gα subunits at 1 h after FC, 24 h after FC, and 1 h after the CTX-R or CS-R. In the HP, the mRNA levels of Gα(s), Gα(12) and Gα(11) were higher at 1 h after training. Gα(s) levels were slightly lower when consolidation was stabilized and after the CS-R. The mRNA levels of Gα(12) were increased at 1 h after FC, returned to control levels at 24 h after FC and increased again with the CTX-R. The increase in the Gα(11) level persisted at 24 h after FC and after CTX-R. In the AMY, no specific changes were induced by FC. In the PFC, CTX-R was accompanied by a decrease in Gα(i/o) mRNA levels; however, only Gα(i2) downregulation was prevented by MOR treatment. Hence, the FC-evoked changes in Gα mRNA expression were observed mainly in the HP and connected primarily to contextual learning. These results suggest that the activation of signaling pathways by Gα(s) and Gα(12) is required to begin the fear memory consolidation process in the HP, while signal transduction via Gα(11) is implicated in the maintenance of fear consolidation. In the PFC, the downregulation of Gα(i2) appears to be related to the contextual learning of fear.

The Endocannabinoid System: A New Treatment Target for Obsessive Compulsive Disorder?

Introduction: Obsessive-compulsive disorder (OCD) is a disabling illness that is associated with significant functional impairment. Although evidence-based pharmacotherapies exist, currently available medications are ineffective in some patients and may cause intolerable side effects in others. There is an urgent need for new treatments. Discussion: A growing body of basic and clinical research has showed that the endocannabinoid system (ECS) plays a role in anxiety, fear, and repetitive behaviors. At the same time, some patients with OCD who smoke cannabis anecdotally report that it relieves their symptoms and mitigates anxiety, and several case reports describe patients whose OCD symptoms improved after they were treated with cannabinoids. Taken together, these findings suggest that the ECS could be a potential target for novel medications for OCD. In this study, we review evidence from both animal and human studies that suggests that the ECS may play a role in OCD and related disorders. We also describe findings from studies in which cannabinoid drugs were shown to impact symptoms of these conditions. Conclusions: An emerging body of evidence suggests that the ECS plays a role in OCD symptoms and may be a target for the development of novel medications. Further exploration of this topic through well-designed human trials is warranted.

Animal Models of PTSD: A Critical Review

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

Targeting opioid dysregulation in depression for the development of novel therapeutics

Since the serendipitous discovery of the first class of modern antidepressants in the 1950's, all pharmacotherapies approved by the Food and Drug Administration for major depressive disorder (MDD) have shared a common mechanism of action, increased monoaminergic neurotransmission. Despite the widespread availability of antidepressants, as many as 50% of depressed patients are resistant to these conventional therapies. The significant length of time required to produce meaningful symptom relief with these medications, 4-6 weeks, indicates that other mechanisms are likely involved in the pathophysiology of depression which may yield more viable targets for drug development. For decades, no viable candidate target with a different mechanism of action to that of conventional therapies proved successful in clinical studies. Now several exciting avenues for drug development are under intense investigation. One of these emerging targets is modulation of endogenous opioid tone. This review will evaluate preclinical and clinical evidence pertaining to opioid dysregulation in depression, focusing on the role of the endogenous ligands endorphin, enkephalin, dynorphin, and nociceptin/orphanin FQ (N/OFQ) and their respective receptors, mu (MOR), delta (DOR), kappa (KOR), and the N/OFQ receptor (NOP) in mediating behaviors relevant to depression and anxiety. Finally, putative opioid based antidepressants that are under investigation in clinical trials, ALKS5461, JNJ-67953964 (formerly LY2456302 and CERC-501) and BTRX-246040 (formerly LY-2940094) will be discussed. This review will illustrate the potential therapeutic value of targeting opioid dysregulation in developing novel therapies for MDD.

Tinbergen's challenge for the neuroscience of behavior

Nobel laureate Nikolaas Tinbergen provided clear criteria for declaring a neuroscience problem solved, criteria which despite the passage of more than 50 years and vastly expanded neuroscience tool kits remain applicable today. Tinbergen said for neuroscientists to claim that a behavior is understood, they must correspondingly understand its (i) development and its (ii) mechanisms and its (iii) function and its (iv) evolution. Now, all four of these domains represent hotbeds of current experimental work, each using arrays of new techniques which overlap only partly. Thus, as new methodologies come online, from single-nerve-cell RNA sequencing, for example, to smart FISH, large-scale calcium imaging from cortex and deep brain structures, computational ethology, and so on, one person, however smart, cannot master everything. Our response to the likely “fracturing” of neuroscience recognizes the value of ever larger consortia. This response suggests new kinds of problems for (i) funding and (ii) the fair distribution of credit, especially for younger scientists.