The role of the medial prefrontal cortex-amygdala circuit in stress effects on the extinction of fear

Social hierarchy differentially influences the anxiety-like behaviors and dendritic spine density in prefrontal cortex and limbic areas in male rats

Social hierarchy is a fundamental feature of social organization that can influence brain and emotional processing regarding social ranks. Several areas, including the medial prefrontal cortex (mPFC), the hippocampus, and the basolateral nucleus of the amygdala (BLA), are recognized to be involved in the regulation of emotional processing. However, its delicate structural correlates in brain regions are poorly understood. To address this issue, social hierarchy in home-caged sibling Wistar rats (three male rats/cage) was determined by employing a social confrontation tube test (postnatal weeks 9-12). Then, locomotor activity and anxiety-like behaviors were evaluated using an open-field test (OFT) and elevated plus-maze (EPM) at 13 weeks of age. The rapid Golgi impregnation method was conducted to quantify the spine density of the first secondary branch of the primary dendrite in 20 µm length. The results indicated that dominant rats had significantly higher anxiety-like behaviors compared to subordinates, as was evident by lower open-arm entries and time spent in the EPM and lower entries and time spent in the center of OFT. The spine density analysis revealed a significantly higher number of spines in subordinates compared to the dominant rats in dmPFC pyramidal neurons and the apical and basal dendrites of hippocampal CA1 pyramidal neurons. However, the spine density of pyramidal-like neurons in the BLA was higher in dominant rats. Our findings suggest that dominant social rank is associated with higher anxiety and differential density of the dendritic spine in the prefrontal cortex and limbic regions of the brain in male rats.

Minimizing Variability in Developmental Fear Studies in Mice: Toward Improved Replicability in the Field

In rodents, the first weeks of postnatal life feature remarkable changes in fear memory acquisition, retention, extinction, and discrimination. Early development is also marked by profound changes in brain circuits underlying fear memory processing, with heightened sensitivity to environmental influences and stress, providing a powerful model to study the intersection between brain structure, function, and the impacts of stress. Nevertheless, difficulties related to breeding and housing young rodents, preweaning manipulations, and potential increased variability within that population pose considerable challenges to developmental fear research. Here we discuss several factors that may promote variability in studies examining fear conditioning in young rodents and provide recommendations to increase replicability. We focus primarily on experimental conditions, design, and analysis of rodent fear data, with an emphasis on mouse studies. The convergence of anatomical, synaptic, physiological, and behavioral changes during early life may increase variability, but careful practice and transparency in reporting may improve rigor and consensus in the field. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC.

Pathophysiological and therapeutic implications of neuropeptide S system in neurological disorders

Neuropeptide S (NPS) is a 20 amino acids-containing neuroactive molecule discovered by the reverse pharmacology method. NPS is detected in specific brain regions like the brainstem, amygdala, and hypothalamus, while its receptor (NPSR) is ubiquitously expressed in the central nervous system (CNS). Besides CNS, NPS and NPSR are also expressed in the peripheral nervous system. NPSR is a G-protein coupled receptor that primarily uses Gq and Gs signaling pathways to mediate the actions of NPS. In animal models of Parkinsonism and Alzheimer's disease, NPS exerts neuroprotective effects. NPS suppresses oxidative stress, anxiety, food intake, and pain, and promotes arousal. NPSR facilitates reward, reinforcement, and addiction-related behaviors. Genetic variation and single nucleotide polymorphism in NPSR are associated with depression, schizophrenia, rheumatoid arthritis, and asthma. NPS interacts with several neurotransmitters including glutamate, noradrenaline, serotonin, corticotropin-releasing factor, and gamma-aminobutyric acid. It also modulates the immune system via augmenting pro-inflammatory cytokines and plays an important role in the pathogenesis of rheumatoid arthritis and asthma. In the present review, we discussed the distribution profile of NPS and NPSR, signaling pathways, and their importance in the pathophysiology of various neurological disorders. We have also proposed the areas where further investigations on the NPS system are warranted.

Chronic pain as an emergent property of a complex system and the potential roles of psychedelic therapies

Despite research advances and urgent calls by national and global health organizations, clinical outcomes for millions of people suffering with chronic pain remain poor. We suggest bringing the lens of complexity science to this problem, conceptualizing chronic pain as an emergent property of a complex biopsychosocial system. We frame pain-related physiology, neuroscience, developmental psychology, learning, and epigenetics as components and mini-systems that interact together and with changing socioenvironmental conditions, as an overarching complex system that gives rise to the emergent phenomenon of chronic pain. We postulate that the behavior of complex systems may help to explain persistence of chronic pain despite current treatments. From this perspective, chronic pain may benefit from therapies that can be both disruptive and adaptive at higher orders within the complex system. We explore psychedelic-assisted therapies and how these may overlap with and complement mindfulness-based approaches to this end. Both mindfulness and psychedelic therapies have been shown to have transdiagnostic value, due in part to disruptive effects on rigid cognitive, emotional, and behavioral patterns as well their ability to promote neuroplasticity. Psychedelic therapies may hold unique promise for the management of chronic pain.

Pathophysiology in cortico-amygdala circuits and excessive aversion processing: the role of oligodendrocytes and myelination

Stress-related psychiatric illnesses, such as major depressive disorder, anxiety and post-traumatic stress disorder, present with alterations in emotional processing, including excessive processing of negative/aversive stimuli and events. The bidirectional human/primate brain circuit comprising anterior cingulate cortex and amygdala is of fundamental importance in processing emotional stimuli, and in rodents the medial prefrontal cortex-amygdala circuit is to some extent analogous in structure and function. Here, we assess the comparative evidence for: (i) Anterior cingulate/medial prefrontal cortex<->amygdala bidirectional neural circuits as major contributors to aversive stimulus processing; (ii) Structural and functional changes in anterior cingulate cortex<->amygdala circuit associated with excessive aversion processing in stress-related neuropsychiatric disorders, and in medial prefrontal cortex<->amygdala circuit in rodent models of chronic stress-induced increased aversion reactivity; and (iii) Altered status of oligodendrocytes and their oligodendrocyte lineage cells and myelination in anterior cingulate/medial prefrontal cortex<->amygdala circuits in stress-related neuropsychiatric disorders and stress models. The comparative evidence from humans and rodents is that their respective anterior cingulate/medial prefrontal cortex<->amygdala circuits are integral to adaptive aversion processing. However, at the sub-regional level, the anterior cingulate/medial prefrontal cortex structure-function analogy is incomplete, and differences as well as similarities need to be taken into account. Structure-function imaging studies demonstrate that these neural circuits are altered in both human stress-related neuropsychiatric disorders and rodent models of stress-induced increased aversion processing. In both cases, the changes include altered white matter integrity, albeit the current evidence indicates that this is decreased in humans and increased in rodent models. At the cellular-molecular level, in both humans and rodents, the current evidence is that stress disorders do present with changes in oligodendrocyte lineage, oligodendrocytes and/or myelin in these neural circuits, but these changes are often discordant between and even within species. Nonetheless, by integrating the current comparative evidence, this review provides a timely insight into this field and should function to inform future studies-human, monkey and rodent-to ascertain whether or not the oligodendrocyte lineage and myelination are causally involved in the pathophysiology of stress-related neuropsychiatric disorders.

Retrograde amnesia for the stress-induced impairment of extinction: time-dependent and not so forgotten

We investigated whether retrograde amnesia for the stress-induced impairment of extinction retrieval shares similar characteristics with original acquisition memories. The first experiment demonstrated that cycloheximide administered shortly after a single restraint stress session alleviated the impairment of extinction retrieval but not when administered following a longer delay (i.e., the amnesia for stress is time-dependent). A second experiment showed that the retrograde amnesia for stress could be alleviated by a second brief exposure to the stressor. These results demonstrating that amnesia for stress shares characteristics similar to original memories are explained using a retrieval-based memory integration model of retrograde amnesia.

A 4-session written emotional disclosure intervention lowers 6-month sympathoadrenal urinary output in persons living with HIV

OBJECTIVE

We previously reported that a brief guided written emotional disclosure (WED) intervention resulted in significant reductions in post-traumatic stress disorder (PTSD) symptomology in women, but not men, living with HIV. Levels of 24-hour urinary output of epinephrine (E) and norepinephrine (NE) are shown to be elevated in persons diagnosed with PTSD. The current study tested whether there was an effect for the 4-week WED intervention on 6-month change in urinary E and NE output amongst persons living with HIV.

METHOD

Fourteen women and 11 men living with HIV randomized to four 30-min expressive writing sessions of either trauma writing or daily events writing in the parent trial were included based upon collection of urine specimens at baseline, 1-, and 6-months after the intervention. Total volume (µg) and concentration (µg/ml) of urinary E and NE were derived from the specimens as study outcomes.

RESULTS

Four repeated measures analyses of covariance (ANCOVA) were performed to evaluate study outcomes using trauma- versus daily-writing as the between-subject factors and collection time point as the within-subject factor, controlling for age and sex. A group x time interaction was observed wherein the trauma writing treatment group showed a significantly greater decrease in total urinary output, F(2, 46) = 4.03, p = .03, and concentration, F(2, 46) = 4.74, p = .01 of epinepherine. Post-hoc analyses revealed the interaction effect for the total, F(2, 22) = 4.82, p = .03, and concentration, F(2, 22) = 7.57, p = .005, of urinary E output over 6-months was significant for women. Interactions were not observed in urinary NE output.

CONCLUSIONS

Significant reductions in the total output and concentration of urinary E were found up to 6-months following initiation of a 4-session guided written emotional disclosure intervention. Profiles of sympathoadrenal activity and response to expressive writing differ between men and women living with HIV. Futher research is need to characterize the putative pathways linking sympathoadrenal response to upstream neurobiological function and downstream inflammatory-immune status in women living with HIV and PTSD.

Long-term effects of chronic stress models in adult mice

Neuropsychiatric disorders, such as major depression, anxiety disorders, and post-traumatic stress disorder, tend to be long-term conditions in whose development and maintenance stress are central pathogenic factors. Translational mouse models are widely used in neuropsychiatric research, exploiting social and non-social stressors to investigate the mechanisms underlying their detrimental effects. However, most studies focus on the short-term consequences of chronic stress, whereas only a few are interested in the long-term course. This is counterintuitive given the human conditions that preclinical models are designed to mimic. In this review, we have summarized the limited work to date on long-term effects of chronic stress in mice models. First, the different models are presented and a definition of short- vs. long-term sequelae is proposed. On this basis, behavioral, endocrine, and vegetative effects are addressed before examining data on cellular and molecular alterations in the brain. Finally, future directions for research on the long-term effects of stress are discussed.

Stress circuitry: mechanisms behind nervous and immune system communication that influence behavior

Inflammatory processes are increased by stress and contribute to the pathology of mood disorders. Stress is thought to primarily induce inflammation through peripheral and central noradrenergic neurotransmission. In healthy individuals, these pro-inflammatory effects are countered by glucocorticoid signaling, which is also activated by stress. In chronically stressed individuals, the anti-inflammatory effects of glucocorticoids are impaired, allowing pro-inflammatory effects to go unchecked. Mechanisms underlying this glucocorticoid resistance are well understood, but the precise circuits and molecular mechanisms by which stress increases inflammation are not as well known. In this narrative review, we summarize the mechanisms by which chronic stress increases inflammation and contributes to the onset and development of stress-related mood disorders. We focus on the neural substrates and molecular mechanisms, especially those regulated by noradrenergic signaling, that increase inflammatory processes in stressed individuals. We also discuss key knowledge gaps in our understanding of the communication between nervous and immune systems during stress and considerations for future therapeutic strategies. Here we highlight the mechanisms by which noradrenergic signaling contributes to inflammatory processes during stress and how this inflammation can contribute to the pathology of stress-related mood disorders. Understanding the mechanisms underlying crosstalk between the nervous and immune systems may lead to novel therapeutic strategies for mood disorders and/or provide important considerations for treating immune-related diseases in individuals suffering from stress-related disorders.

Effects of long-term individual housing of middle-aged female Octodon degus on spatial learning and memory in the Barnes maze task

Introduction

Prolonged social isolation is a form of passive chronic stress that has consequences on human and animal behavior. The present study was undertaken to elucidate whether the long-term isolation would precipitate age-related changes in anxiety and spatial learning and memory in degus.

Methods

We investigated the effects of long-term social isolation on anxiety levels in the light-dark test, and spatial orientation abilities in the Barnes maze. Middle-aged female Octodon degus were allocated to either group-housed (3 animals per cage) or individually-housed for 5 months.

Results

Under this experimental condition, there were no significant group differences in the anxiety level tested in the light-dark test and in the motivation to escape from the Barnes maze. There were no significant differences in cortisol levels between individually- and group-housed animals. On the last acquisition training day of spatial learning, individually- housed animals had a significantly higher number of correct responses and a smaller number of reference and working memory errors than the group-housed animals. In addition, isolated animals showed a tendency for reference and working memory impairment on the retention trial, while group-housed degus showed improvement in these parameters.

Discussion and conclusion

The present study indicates that prolonged social isolation during adulthood in female degus has a dual effect on spatial orientation. Specifically, it results in a significant improvement in acquisition skills but a slight impairment in memory retention. The obtained cognitive changes were not accompanied by modification in anxiety and cortisol levels.

Systemic corticosterone administration impairs the late fear memory reconsolidation via basolateral amygdala glucocorticoid receptors: dependence on the time window and memory age

Glucocorticoid receptors (GRs) of the basolateral amygdala (BLA) play an important role in memory reconsolidation. The present study investigated the role of the BLA GRs in the late reconsolidation of fear memory using an inhibitory avoidance (IA) task in male Wistar rats. Stainless steel cannulae were implanted bilaterally into the BLA of the rats. After 7 days of recovery, the animals were trained in a one-trial IA task (1mA, 3s). In Experiment one, 48h after the training session, the animals received 3 systemic doses of corticosterone (CORT; 1, 3, or 10 mg/kg, i.p.) followed by an intra-BLA microinjection of the vehicle (0.3µl/side) at different time points (immediately, 12, or 24h) after memory reactivation. Memory reactivation was performed by returning the animals to the light compartment while the sliding door was open. No shock was delivered during memory reactivation. CORT (10 mg/kg) injection 12h after memory reactivation most effectively impaired the late memory reconsolidation (LMR). In the second part of Experiment one, immediately, 12, or 24h after memory reactivation, GR antagonist RU38486 (RU; 1ng/0.3µl/side) was injected into BLA following a systemic injection of CORT (10 mg/kg) to examine whether it would block the CORT effect. RU inhibited the impairing effects of CORT on LMR. In Experiment two, the animals received CORT (10 mg/kg) with time windows immediately, 3, 6, 12, and 24h after memory reactivation. Again, CORT (10 mg/kg) injection 12h after MR impaired LMR. Memory reactivation was performed in the third Experiment, 7, 14, 28, or 56 days after the training session. Injection of CORT (10 mg/kg) 12h later had no significant effect on the LMR. The impairing effect of CORT was seen only in 2-day-old but not 7, 14, 28, and 56-day-old memories. GRs located in BLA seem to play an important role in the LMR of young memory, as with increasing the age of memories, they become less sensitive to manipulation.

Stressor control and regional inflammatory responses in the brain: regulation by the basolateral amygdala

Increasing evidence has connected the development of certain neuropsychiatric disorders, as well as neurodegenerative diseases, to stress-induced dysregulation of the immune system. We have shown that escapable (ES) and inescapable (IS) footshock stress, and memories associated with ES or IS, can differentially alter inflammatory-related gene expression in brain in a region dependent manner. We have also demonstrated that the basolateral amygdala (BLA) regulates stress- and fear memory-induced alterations in sleep, and that differential sleep and immune responses in the brain to ES and IS appear to be integrated during fear conditioning and then reproduced by fear memory recall. In this study, we investigated the role of BLA in influencing regional inflammatory responses within the hippocampus (HPC) and medial prefrontal cortex (mPFC) by optogenetically stimulating or inhibiting BLA in male C57BL/6 mice during footshock stress in our yoked shuttlebox paradigm based on ES and IS. Then, mice were immediately euthanized and RNA extracted from brain regions of interest and loaded into NanoString® Mouse Neuroinflammation Panels for compilation of gene expression profiles. Results showed differential regional effects in gene expression and activated pathways involved in inflammatory-related signaling following ES and IS, and these differences were altered depending on amygdalar excitation or inhibition. These findings demonstrate that the stress-induced immune response, or "parainflammation", is affected by stressor controllability and that BLA influences regional parainflammation to ES or IS in HPC and mPFC. The study illustrates how stress-induced parainflammation can be regulated at the neurocircuit level and suggests that this approach can be useful for uncovering circuit and immune interactions in mediating differential stress outcomes.

Modeling integrated stress, sleep, fear and neuroimmune responses: Relevance for understanding trauma and stress-related disorders

Sleep and stress have complex interactions that are implicated in both physical diseases and psychiatric disorders. These interactions can be modulated by learning and memory, and involve additional interactions with the neuroimmune system. In this paper, we propose that stressful challenges induce integrated responses across multiple systems that can vary depending on situational variables in which the initial stress was experienced, and with the ability of the individual to cope with stress- and fear-inducing challenges. Differences in coping may involve differences in resilience and vulnerability and/or whether the stressful context allows adaptive learning and responses. We provide data demonstrating both common (corticosterone, SIH and fear behaviors) and distinguishing (sleep and neuroimmune) responses that are associated with an individual's ability to respond and relative resilience and vulnerability. We discuss neurocircuitry regulating integrated stress, sleep, neuroimmune and fear responses, and show that responses can be modulated at the neural level. Finally, we discuss factors that need to be considered in models of integrated stress responses and their relevance for understanding stress-related disorders in humans.

The Impact of Sleep on Fear Extinction

Sleep plays a crucial role in the consolidation of memories, including those for fear acquisition and extinction training. This chapter reviews findings from studies testing this relationship in laboratory, naturalistic, and clinical settings. While evidence is mixed, several studies in humans have linked fear and extinction recall/retention to both rapid eye-movement and slow wave sleep. Sleep appears to further aid in the processing of both simulated and actual trauma and improves psychotherapeutic treatment outcomes in those with anxiety and trauma- and stressor-related disorders. This chapter concludes with a discussion of the current challenges facing sleep and emotional memory research in addition to suggestions for improving future research.

Diagnostic delay of oral squamous cell carcinoma and the fear of diagnosis: A scoping review

The mortality rate of patients affected with oral squamous cell carcinoma (OSCC) has been stable in recent decades due to several factors, especially diagnostic delay, which is often associated with a late stage diagnosis and poor prognosis. The aims of this paper were to: analyze diagnostic delay in OSCC and to discuss the various psychological factors of patients with OSCC, with particular attention to the patient's fear of receiving news regarding their health; and the professional dynamics related to the decision-making processes in cases of suspected OSCC. A preliminary review of literature focusing on OSCC diagnostic delay was performed. Seven articles were included with the diagnostic delay ranging from 45  days to approximately 6  months. Patients' fears and, to a lesser degree, the concerns of dentists, were found to be still poorly investigated. On the basis of the authors' professional experience, the development of oral lesions of unknown origin may generate different behaviors in the decision-making processes by patients and clinicians, and fear may play a key role in the distinct steps of this process. It is crucial to increase awareness and inform patients about the onset of OSCC, and contemporaneously encourage experimental studies on patients' fear and professional behaviors with respect to communication regarding OSCC.

Therapeutic potential of brain stimulation techniques in the treatment of mental, psychiatric, and cognitive disorders

Treatment for brain diseases has been disappointing because available medications have failed to produce clinical response across all the patients. Many patients either do not respond or show partial and inconsistent effect, and even in patients who respond to the medications have high relapse rates. Brain stimulation has been seen as an alternative and effective remedy. As a result, brain stimulation has become one of the most valuable therapeutic tools for combating against brain diseases. In last decade, studies with the application of brain stimulation techniques not only have grown exponentially but also have expanded to wide range of brain disorders. Brain stimulation involves passing electric currents into the cortical and subcortical area brain cells with the use of noninvasive as well as invasive methods to amend brain functions. Over time, technological advancements have evolved into the development of precise devices; however, at present, most used noninvasive techniques are repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), whereas the most common invasive technique is deep brain stimulation (DBS). In the current review, we will provide an overview of the potential of noninvasive (rTMS and tDCS) and invasive (DBS) brain stimulation techniques focusing on the treatment of mental, psychiatric, and cognitive disorders.

Intra-mPFC injection of sodium butyrate promotes BDNF expression and ameliorates extinction recall impairment in an experimental paradigm of post-traumatic stress disorder

Objectives

Therapeutic strategies that facilitate extinction are promising in the treatment of post-traumatic stress disorder (PTSD). Brain-derived neurotrophic factor (BDNF) has a crucial role in neural plasticity, a process needed for the retention of fear extinction. In this study, we investigated the effects of local administration of a histone deacetylase (HDAC) inhibitor, sodium butyrate (NaBu), on BDNF transcription and behavioral markers of extinction in the single prolonged stress (SPS) model of PTSD.

Materials and Methods

NaBu was infused into the infralimbic (IL) subregion of the medial prefrontal cortex (mPFC) of male rats. The freezing response was recorded as the criterion to assess fear strength on the day of extinction as well as 24 hr later in the retention test. Other behavioral tests were also measured to evaluate the anxiety level, locomotor activity, and working memory on the retention day. HDAC activity and BDNF mRNA expression were evaluated after the behavioral experiments.

Results

NaBu facilitated the recall of fear extinction in SPS rats (P<0.0001). SPS rats had higher HDAC activity (P<0.0001) and lower BDNF expression (P<0.05) than non-SPS animals. Also, anxiety was higher in the SPS group (P<0.0001), but locomotor activity (P=0.61) and working memory (P=0.36) were not different between SPS and Non-SPS groups.

Conclusion

Our findings provide evidence that the mechanism of action of NaBu in the improvement of extinction recall is mediated, in part, by enhancing histone acetylation and reviving BDNF expression in IL.

The infralimbic mineralocorticoid blockage prevents the stress-induced impairment of aversive memory extinction in rats

Individuals deal with adversity and return to a normal lifestyle when adversity ends. Nevertheless, in specific cases, traumas may be preceded by memory distortions in stress-related malaises, and memory extinction impairment is strictly associated with the symptoms of post-traumatic stress disorder. Glucocorticoids (GCs), the central stress mediator, target mineralocorticoid (MR) and glucocorticoid (GR) receptors and coordinate stress responses. Despite MRs being present in brain regions essential to cognition, emotions, and initial stress processing, such as the medial prefrontal cortex (mPFC), most studies attempt to elucidate the stress-induced deleterious actions of GCs via GR. Therefore, it is necessary to understand the relationship between stress, infralimbic mPFC (IL), and memory and how MR-mediated intracellular signaling influences this relationship and modulates memory extinction. We observed that acutely restraint-stressed male Wistar rats showed high corticosterone (CORT) levels, and previous intra-IL-spironolactone administration (a selective MR antagonist) decreased it 60 min after the stress started. Intra-IL-CORT118335, a novel mixed MR/GR selective modulator, increased CORT throughout stress exposure. Ten days after stress, all rats increased freezing in the memory retrieval test and acquired the aversive contextual memory. During the extinction test, intra-IL injection of spironolactone, but not CORT118335, prevented the stress-impaired memory extinction, suggesting that the IL-MR activity controls CORT concentration, and it is crucial to the establishment of late extinction impairment. Also, the concomitant GR full activation overrode MR blockage. It increased CORT levels leading to the stress-induced extinction memory impairment, reinforcing that the MR/GR balance is crucial to predicting stress-induced behavioral outcomes.

Exposure to acute stress affects the retrieval of out-group related bias in healthy men

Individuals have a tendency to show enhanced vigilance to groups of which they themselves are not a member. Stress can up-regulate hypervigilance towards threatening stimuli and was shown to promote the reinstatement of out-group related biases in a previous study conducted in women only. The current study examines how exposure to acute stress affects the retrieval of out-group related extinction biases in male participants. Results showed that men exerted a specific out-group related bias at the beginning of extinction training indexed by higher skin conductance responses (SCRs) towards out-group faces, while stress led to a return of this extinguished out-group bias. Specifically, the stress group showed higher SCRs towards out-group faces during retrieval compared to the control group and the bias index was negatively related to post-stress cardiovascular recovery. These results indicate the important interaction between stress and intergroup bias in fear conditioning, along with a potential modulation of sex.

Single Prolonged Stress Reduces Intrinsic Excitability and Excitatory Synaptic Drive Onto Pyramidal Neurons in the Infralimbic Prefrontal Cortex of Adult Male Rats

Post-traumatic stress disorder (PTSD) is a chronic, debilitating mental illness marked by abnormal fear responses and deficits in extinction of fear memories. The pathophysiology of PTSD is linked to decreased activation of the ventromedial prefrontal cortex (vmPFC). This study aims to investigate underlying functional changes in synaptic drive and intrinsic excitability of pyramidal neurons in the rodent homolog of the vmPFC, the infralimbic cortex (IL), following exposure to single prolonged stress (SPS), a paradigm that mimics core symptoms of PTSD in rats. Rats were exposed to SPS and allowed 1 week of recovery, following which brain slices containing the PFC were prepared for whole-cell patch clamp recordings from layer V pyramidal neurons in the IL. Our results indicate that SPS reduces spontaneous excitatory synaptic drive to pyramidal neurons. In addition, SPS decreases the intrinsic membrane excitability of IL PFC pyramidal cells, as indicated by an increase in rheobase, decrease in input resistance, hyperpolarization of resting membrane potential, and a reduction in repetitive firing rate. Our results suggest that SPS causes a lasting reduction in PFC activity, supporting a body of evidence linking traumatic stress with prefrontal hypoactivity.

Cannabis use and posttraumatic stress disorder comorbidity: Epidemiology, biology and the potential for novel treatment approaches

Cannabis use is increasing among some demographics in the United States and is tightly linked to anxiety, trauma, and stress reactivity at the epidemiological and biological level. Stress-coping motives are highly cited reasons for cannabis use. However, with increased cannabis use comes the increased susceptibility for cannabis use disorder (CUD). Indeed, CUD is highly comorbid with posttraumatic stress disorder (PTSD). Importantly, endogenous cannabinoid signaling systems play a key role in the regulation of stress reactivity and anxiety regulation, and preclinical data suggest deficiencies in this signaling system could contribute to the development of stress-related psychopathology. Furthermore, endocannabinoid deficiency states, either pre-existing or induced by trauma exposure, could provide explanatory insights into the high rates of comorbid cannabis use in patients with PTSD. Here we review clinical and preclinical literature related to the cannabis use-PTSD comorbidity, the role of endocannabinoids in the regulation of stress reactivity, and potential therapeutic implications of recent work in this area.

Environmental enrichment prevents the late effect of acute stress-induced fear extinction deficit: the role of hippocampal AMPA-GluA1 phosphorylation

The persistence of anxiety and the deficit of fear memory extinction are both phenomena related to the symptoms of a trauma-related disorder, such as post-traumatic stress disorder (PTSD). Recently we have shown that single acute restraint stress (2 h) in rats induces a late anxiety-related behavior (observed ten days after stress), whereas, in the present work, we found that the same stress impaired fear extinction in animals conditioned ten days after stress. Fourteen days of environmental enrichment (EE) prevented the deleterious effect of stress on fear memory extinction. Additionally, we observed that EE prevented the stress-induced increase in AMPA receptor GluA1 subunit phosphorylation in the hippocampus, but not in the basolateral amygdala complex and the frontal cortex, indicating a potential mechanism by which it exerts its protective effect against the stress-induced behavioral outcome.

Intra-amygdala metaplasticity modulation of fear extinction learning

The amygdala is a key brain region involved in emotional memory formation. It is also responsible for memory modulation in other brain areas. Under extreme conditions, amygdala modulation may lead to the generation of abnormal plasticity and trauma-related psychopathologies. However, the amygdala itself is a dynamic brain region, which is amenable to long-term plasticity and is affected by emotional experiences. These alterations may modify the way the amygdala modulates activity and plasticity in other related brain regions, which in turn may alter the animal's response to subsequent challenges in what could be termed as "Behavioral metaplasticity."Because of the reciprocal interactions between the amygdala and other emotion processing regions, such as the medial prefrontal cortex (mPFC) or the hippocampus, experience-induced intra-amygdala metaplasticity could lead to alterations in mPFC-dependent or hippocampus-dependent behaviors. While initiated by alterations within the basolateral amygdala (BLA), such alterations in other brain regions may come to be independent of BLA modulation, thus establishing what may be termed "Trans-regional metaplasticity." In this article, we review evidence supporting the notions of intra-BLA metaplasticity and how this may develop into "Trans-regional metaplasticity." Future research is needed to understand how such dynamic metaplastic alterations contribute to developing psychopathologies, and how this knowledge may be translated into promoting novel interventions in psychopathologies associated with fear, stress, and trauma.

Brain Marker Links Stress and Nicotine Abstinence

BACKGROUND

Subjective stress is a well-documented predictor of early smoking relapse, yet our understanding of stress and tobacco use is limited by reliance on self-reported measures of stress. We utilized a validated functional neuroimaging paradigm to examine whether stress exposure during early abstinence alters objective measures of brain function.

METHODS

Seventy-five participants underwent blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) during the Montreal Imaging Stress Task (MIST) on two occasions: once during smoking satiety and once following biochemically confirmed 24-hour abstinence (order counterbalanced). The primary outcome measure was brain response during stress (vs. control) blocks of the MIST, assessed using whole-brain analysis corrected for multiple comparisons using clusters determined by Z ≥ 3.1.

RESULTS

Abstinence (vs. satiety) was associated with significantly increased activation in the left inferior frontal gyrus, a brain region associated with inhibitory control. Abstinence-induced change in brain response to stress was positively associated with change in self-reported stress.

CONCLUSIONS

This study provides objective evidence that the brain response to stress is altered during the first 24 hours of a quit attempt compared to smoking satiety.

IMPLICATIONS

These results point to the potential value of inoculating smokers with stress management training prior to a quit attempt.

Modulatory effects of dynamic fMRI-based neurofeedback on emotion regulation networks in adolescent females

Research has shown that difficulties with emotion regulation abilities in childhood and adolescence increase the risk for developing symptoms of mental disorders, e.g anxiety. We investigated whether functional magnetic resonance imaging (fMRI)-based neurofeedback (NF) can modulate brain networks supporting emotion regulation abilities in adolescent females.

We performed three experiments (Experiment 1: N ​= ​18; Experiment 2: N ​= ​30; Experiment 3: N ​= ​20). We first compared different NF implementations regarding their effectiveness of modulating prefrontal cortex (PFC)-amygdala functional connectivity (fc). Further we assessed the effects of fc-NF on neural measures, emotional/metacognitive measures and their associations. Finally, we probed the mechanism underlying fc-NF by examining concentrations of inhibitory and excitatory neurotransmitters.

Results showed that NF implementations differentially modulate PFC-amygdala fc. Using the most effective NF implementation we observed important relationships between neural and emotional/metacognitive measures, such as practice-related change in fc was related with change in thought control ability. Further, we found that the relationship between state anxiety prior to the MRI session and the effect of fc-NF was moderated by GABA concentrations in the PFC and anterior cingulate cortex.

To conclude, we were able to show that fc-NF can be used in adolescent females to shape neural and emotional/metacognitive measures underlying emotion regulation. We further show that neurotransmitter concentrations moderate fc–NF–effects.

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Neurofeedback implementations differentially modulate PFC-amygdala connectivity.

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Functional connectivity neurofeedback affect measures of emotion regulation.

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Neurotransmitter concentrations moderate neurofeedback effects.

Mathematics anxiety and cognition: an integrated neural network model

Many students suffer from anxiety when performing numerical calculations. Mathematics anxiety is a condition that has a negative effect on educational outcomes and future employment prospects. While there are a multitude of behavioral studies on mathematics anxiety, its underlying cognitive and neural mechanism remain unclear. This article provides a systematic review of cognitive studies that investigated mathematics anxiety. As there are no prior neural network models of mathematics anxiety, this article discusses how previous neural network models of mathematical cognition could be adapted to simulate the neural and behavioral studies of mathematics anxiety. In other words, here we provide a novel integrative network theory on the links between mathematics anxiety, cognition, and brain substrates. This theoretical framework may explain the impact of mathematics anxiety on a range of cognitive and neuropsychological tests. Therefore, it could improve our understanding of the cognitive and neurological mechanisms underlying mathematics anxiety and also has important applications. Indeed, a better understanding of mathematics anxiety could inform more effective therapeutic techniques that in turn could lead to significant improvements in educational outcomes.

Forget the stress: retrograde amnesia for the stress-induced impairment of extinction retrieval

We investigated whether cycloheximide (CHX) would induce amnesia for the stress-induced impairment of extinction retrieval. First, a single restraint stress session was demonstrated to impair extinction retrieval, but not fear conditioning. A second experiment showed that when CHX was administered immediately after restraint, rats exhibited significant extinction retrieval at test (i.e., retrograde amnesia for the stress). In a third experiment, the stress session impaired various amounts of extinction durations, suggesting that the stress inhibited extinction retrieval rather than enhancing the original fear learning. These results suggest memories for acute stress are susceptible to disruption, which could have clinical implications.

Retrieval-Extinction and Relapse Prevention: Rewriting Maladaptive Drug Memories?

Addicted individuals are highly susceptible to relapse when exposed to drug-associated conditioned stimuli (CSs; "drug cues") even after extensive periods of abstinence. Until recently, these maladaptive emotional drug memories were believed to be permanent and resistant to change. The rediscovery of the phenomenon of memory reconsolidation-by which retrieval of the memory can, under certain conditions, destabilize the previously stable memory before it restabilizes in its new, updated form-has led to the hypothesis that it may be possible to disrupt the strong maladaptive drug-memories that trigger a relapse. Furthermore, recent work has suggested that extinction training "within the reconsolidation window" may lead to a long-term reduction in relapse without the requirement for pharmacological amnestic agents. However, this so-called "retrieval-extinction" effect has been inconsistently observed in the literature, leading some to speculate that rather than reflecting memory updating, it may be the product of facilitation of extinction. In this mini review article, we will focus on factors that might be responsible for the retrieval-extinction effects on preventing drug-seeking relapse and how inter-individual differences may influence this therapeutically promising effect. A better understanding of the psychological and neurobiological mechanisms underpinning the "retrieval-extinction" paradigm, and individual differences in boundary conditions, should provide insights with the potential to optimize the translation of "retrieval-extinction" to clinical populations.

Social buffering enhances extinction of conditioned fear responses by reducing corticosterone levels in male rats

The presence of an affiliative conspecific reduces stress responses to a wide variety of stimuli, which is termed "social buffering." We previously reported that social buffering in male rats ameliorated behavioral responses, as well as hypothalamic-pituitary-adrenal axis activation, elicited by an auditory conditioned stimulus (CS). In addition, subjects that experienced social buffering did not show stress responses when re-exposed to the CS the next day in the absence of an accompanying rat. However, the mechanisms underlying this enhancement of between-session extinction are poorly understood. In Experiment 1, we compared corticosterone levels at 0, 10, and 15 min after extinction training. Subjects that experienced social buffering had lower corticosterone levels than subjects that trained alone at the end of extinction training. However, corticosterone levels at 10 and 15 min after training were not affected by the experience of social buffering. These results suggest that a lower level of corticosterone during extinction training had an important role in the enhancement of extinction. To directly assess this, in Experiment 2, we manipulated the corticosterone level during extinction training. We found that a subcutaneous injection of corticosterone before extinction training blocked the enhancement of extinction by social buffering. These results demonstrate that the enhancement is caused by a low level of corticosterone during the training. Taken together, we suggest that social buffering enhances extinction of conditioned fear responses by reducing corticosterone levels in male rats.

Animal models of post-traumatic stress disorder and novel treatment targets

Understanding the neurobiological basis of post-traumatic stress disorder (PTSD) is fundamental to accurately diagnose this neuropathology and offer appropriate treatment options to patients. The lack of pharmacological effects, too often observed with the most currently used drugs, the selective serotonin reuptake inhibitors (SSRIs), makes even more urgent the discovery of new pharmacological approaches. Reliable animal models of PTSD are difficult to establish because of the present limited understanding of the PTSD heterogeneity and of the influence of various environmental factors that trigger the disorder in humans. We summarize knowledge on the most frequently investigated animal models of PTSD, focusing on both their behavioral and neurobiological features. Most of them can reproduce not only behavioral endophenotypes, including anxiety-like behaviors or fear-related avoidance, but also neurobiological alterations, such as glucocorticoid receptor hypersensitivity or amygdala hyperactivity. Among the various models analyzed, we focus on the social isolation mouse model, which reproduces some deficits observed in humans with PTSD, such as abnormal neurosteroid biosynthesis, changes in GABAA receptor subunit expression and lack of pharmacological response to benzodiazepines. Neurosteroid biosynthesis and its interaction with the endocannabinoid system are altered in PTSD and are promising neuronal targets to discover novel PTSD agents. In this regard, we discuss pharmacological interventions and we highlight exciting new developments in the fields of research for novel reliable PTSD biomarkers that may enable precise diagnosis of the disorder and more successful pharmacological treatments for PTSD patients.

Possible Role of CRF-Hcrt Interaction in the Infralimbic Cortex in the Emergence and Maintenance of Compulsive Alcohol-Seeking Behavior

Alcohol use disorder (AUD) is a chronic, relapsing disorder that is characterized by the compulsive use of alcohol despite numerous health, social, and economic consequences. Initially, the use of alcohol is driven by positive reinforcement. Over time, however, alcohol use can take on a compulsive quality that is driven by the desire to avoid the negative consequences of abstinence, including negative affect and heightened stress/anxiety. This transition from positive reinforcement- to negative reinforcement-driven consumption involves the corticotropin-releasing factor (CRF) system, although mounting evidence now suggests that the CRF system interacts with other neural systems to ultimately produce behaviors that are symptomatic of compulsive alcohol use, such as the hypocretin (Hcrt) system. Hypocretins are produced exclusively in the hypothalamus, but Hcrt neurons project widely throughout the brain and reach regions that perform regulatory functions for numerous behavioral and physiological responses-including the infralimbic cortex (IL) of the medial prefrontal cortex (mPFC). Although the entire mPFC undergoes neuroadaptive changes following prolonged alcohol exposure, the IL appears to undergo more robust changes compared with other mPFC substructures. Evidence to date suggests that the IL is likely involved in EtOH-seeking behavior, but ambiguities with respect to the specific role of the IL in this regard make it difficult to draw definitive conclusions. Furthermore, the manner in which CRF interacts with Hcrt in this region as it pertains to alcohol-seeking behavior is largely unknown, although immunohistochemical and electrophysiological experiments have shown that CRF and Hcrt directly interact in the mPFC, suggesting that the interaction between CRF and Hcrt in the IL may be critically important for the development and subsequent maintenance of compulsive alcohol seeking. This review aims to consolidate recent literature regarding the role of the IL in alcohol-seeking behavior and to discuss evidence that supports a functional interaction between Hcrt and CRF in the IL.

Functional Compartmentalization of the Contribution of Hippocampal Subfields to Context-Dependent Extinction Learning

During extinction learning (EL), an individual learns that a previously learned behavior no longer fulfills its original purpose, or is no longer relevant. Recent studies have contradicted earlier theories that EL comprises forgetting, or the inhibition of the previously learned behavior, and indicate that EL comprises new associative learning. This suggests that the hippocampus is involved in this process. Empirical evidence is lacking however. Here, we used fluorescence in situ hybridization of somatic immediate early gene (IEG) expression to scrutinize if the hippocampus processes EL. Rodents engaged in context-dependent EL and were also tested for renewal of (the original behavioral response to) a spatial appetitive task in a T-maze. Whereas distal and proximal CA1 subfields processed both EL and renewal, effects in the proximal CA1 were more robust consistent with a role of this subfield in processing context. The lower blade of the dentate gyrus (DG) and the proximal CA3 subfields were particularly involved in renewal. Responses in the distal and proximal CA3 subfields suggest that this hippocampal subregion may also contribute to the evaluation of the reward outcome. Taken together, our findings provide novel and direct evidence for the involvement of distinct hippocampal subfields in context-dependent EL and renewal.

The interaction between stress and chronic pain through the lens of threat learning

Stress and pain are interleaved at multiple levels - interacting and influencing each other. Both are modulated by psychosocial factors including fears, beliefs, and goals, and are served by overlapping neural substrates. One major contributing factor in the development and maintenance of chronic pain is threat learning, with pain as an emotionally-salient threat - or stressor. Here, we argue that threat learning is a central mechanism and contributor, mediating the relationship between stress and chronic pain. We review the state of the art on (mal)adaptive learning in chronic pain, and on effects of stress and particularly cortisol on learning. We then provide a theoretical integration of how stress may affect chronic pain through its effect on threat learning. Prolonged stress, as may be experienced by patients with chronic pain, and its resulting changes in key brain networks modulating stress responses and threat learning, may further exacerbate these impairing effects on threat learning. We provide testable hypotheses and suggestions for how this integration may guide future research and clinical approaches in chronic pain.

Dopamine effects on stress-induced working memory deficits

The prefrontal cortex (PFC) plays a critical role in mediating executive functions and orchestrating the way in which we think, decide, and behave. Many studies have shown that PFC neurons not only play a major role in mediating behavioral responses to stress but are also sensitive to stress and undergo remodeling following stress exposure. Activation of the hypothalamic-pituitary-adrenal axis as a result of stress initiates a flood of alterations in prefrontal neurotransmitter release. Dopamine (DA) neurotransmission in the PFC is involved in the modulation of stress responsiveness. Compelling results show that stressful events are associated with increased DA concentrations in the medial PFC. Excessive DA-ergic activity in the medial prefrontal cortex following stress has a negative impact on working memory and executive functions in rodents, monkeys, and humans, making them unable to processing information selectively and impairing cognitive function. Therefore, an exact understanding of these mechanisms may provide important insights into the pathophysiology of executive dysfunction and novel treatment avenues. The present review provides a summary of the neuronal circuitry involved in alterations of PFC dopaminergic neurons under conditions of stress, and then addresses the interaction of PFC DA with glucocorticoids leading to impairment of working memory under conditions of stress.

Sphingosine-1-phosphate receptor 3 in the medial prefrontal cortex promotes stress resilience by reducing inflammatory processes

Stress can promote the development of psychiatric disorders, though some individuals are more vulnerable to stress compared to others who are more resilient. Here we show that the sphingosine-1-phosphate receptor 3 (S1PR3) in the medial prefrontal cortex (mPFC) of rats regulates resilience to chronic social defeat stress. S1PR3 expression is elevated in the mPFC of resilient compared to vulnerable and control rats. Virally-mediated over-expression of S1PR3 in the mPFC produces a resilient phenotype whereas its knock-down produces a vulnerable phenotype, characterized by increased anxiety- and depressive-like behaviors, and these effects are mediated by TNFα. Furthermore, we show that S1PR3 mRNA in blood is reduced in veterans with PTSD compared to combat-exposed control subjects and its expression negatively correlates with symptom severity. Together, these data identify S1PR3 as a regulator of stress resilience and reveal sphingolipid receptors as important substrates of relevance to stress-related psychiatric disorders.

Ketamine ameliorates severe traumatic event-induced antidepressant-resistant depression in a rat model through ERK activation

Treatment-resistant depression (TRD) is a major public health issue, as it is common for patients with depression to fail to respond to adequate trials of antidepressants. However, a well-established animal model of TRD is still warranted. The present study focused on selective serotonin reuptake inhibitor (SSRI) resistance, and aimed to investigate whether higher levels of traumatic stress caused by greater numbers of foot-shocks may lead to severe depression and to examine the feasibility of this as an animal model of SSRI-resistant depression. To reveal the correlation between traumatic stress and severe depression, rats received 3, 6 and 10 tone (conditioned stimulus, CS)-shock (unconditioned stimulus, US) pairings to mimic mild, moderate, and severe traumatic events, and subsequent depressive-like behaviors and protein immunocontents were analyzed. The antidepressant efficacy was assessed for ketamine and SSRI (i.e., fluoxetine) treatment. We found that only the severe stress group presented depressive-like behaviors. Phosphorylation of extracellular signal-regulated kinases (ERKs) was decreased in the amygdala and prefrontal cortex (PFC). The immunocontents of GluA1 and PSD 95 were increased in the amygdala and decreased in the PFC. Moreover, the glutamate-related abnormalities in the amygdala and PFC were normalized by single-dose (10 mg/kg, i.p.) ketamine treatment. In contrast, the depressive-like behaviors were not reversed by 28 days of fluoxetine treatment (10 mg/kg, i.p.) in the severe stress group. Our data demonstrated that high levels of traumatic stress could lead to SSRI-resistant depressive symptoms through impacts on the glutamatergic system, and that this rat model has the potential to be a feasible animal model of SSRI-resistant depression.

Animal Models of PTSD: The Socially Isolated Mouse and the Biomarker Role of Allopregnanolone

Post-traumatic stress disorder (PTSD) is a debilitating undertreated condition that affects 8%-13% of the general population and 20%-30% of military personnel. Currently, there are no specific medications that reduce PTSD symptoms or biomarkers that facilitate diagnosis, inform treatment selection or allow monitoring drug efficacy. PTSD animal models rely on stress-induced behavioral deficits that only partially reproduce PTSD neurobiology. PTSD heterogeneity, including comorbidity and symptoms overlap with other mental disorders, makes this attempt even more complicated. Allopregnanolone, a neurosteroid that positively, potently and allosterically modulates GABAA receptors and, by this mechanism, regulates emotional behaviors, is mainly synthesized in brain corticolimbic glutamatergic neurons. In PTSD patients, allopregnanolone down-regulation correlates with increased PTSD re-experiencing and comorbid depressive symptoms, CAPS-IV scores and Simms dysphoria cluster scores. In PTSD rodent models, including the socially isolated mouse, decrease in corticolimbic allopregnanolone biosynthesis is associated with enhanced contextual fear memory and impaired fear extinction. Allopregnanolone, its analogs or agents that stimulate its synthesis offer treatment approaches for facilitating fear extinction and, in general, for neuropsychopathologies characterized by a neurosteroid biosynthesis downregulation. The socially isolated mouse model reproduces several other deficits previously observed in PTSD patients, including altered GABAA receptor subunit subtypes and lack of benzodiazepines pharmacological efficacy. Transdiagnostic behavioral features, including expression of anxiety-like behavior, increased aggression, a behavioral component to reproduce behavioral traits of suicidal behavior in humans, as well as alcohol consumption are heightened in socially isolated rodents. Potentials for assessing novel biomarkers to predict, diagnose, and treat PTSD more efficiently are discussed in view of developing a precision medicine for improved PTSD pharmacological treatments.

MRI Shows that Exhaustion Syndrome Due to Chronic Occupational Stress is Associated with Partially Reversible Cerebral Changes

The present study investigates the cerebral effects of chronic occupational stress and its possible reversibility. Forty-eight patients with occupational exhaustion syndrome (29 women) and 80 controls (47 women) underwent structural magnetic resonance imaging (MRI) and neuropsychological testing. Forty-four participants (25 patients, 19 controls) also completed a second MRI scan after 1-2 years. Only patients received cognitive therapy. The stressed group at intake had reduced thickness in the right prefrontal cortex (PFC) and left superior temporal gyrus (STG), enlarged amygdala volumes, and reduced caudate volumes. Except for the caudate volume, these abnormalities were more pronounced in females. They were all related to perceived stress, which was similar for both genders. Thickness of the PFC also correlated with an impaired ability to down-modulate negative emotions. Thinning of PFC and reduction of caudate volume normalized in the follow-up. The amygdala enlargement and the left STG thinning remained. Longitudinal changes were not detected among controls. Chronic occupational stress was associated with partially reversible structural abnormalities in key regions for stress processing. These changes were dynamically correlated with the degree of perceived stress, highlighting a possible causal link. They seem more pronounced in women, and could be a substrate for an increased cerebral vulnerability to stress-related psychiatric disorders.

The Dynamic Duo: Combining noninvasive brain stimulation with cognitive interventions

Pharmacotherapy, psychotherapy, and non-invasive brain stimulation (NIBS)¹ each show efficacy in the treatment of psychiatric disorders; however, more efficacious interventions are needed as reflected by an overall unmet need in mental health care. While each modality has typically been studied and developed as a monotherapy, in practice they are typically used in combination. Research has begun to emerge studying the potential synergistic actions of multi-modal, combination therapies. For example, NIBS combined with rehabilitation strategies have demonstrated some success for speech and motor rehabilitation in stroke patients. In this review we present evidence suggesting that combining NIBS with targeted, cognitive interventions offers a potentially powerful new approach to treating neuropsychiatric disorders. Here we focus on NIBS studies using transcranial direct current stimulation (tDCS)² and transcranial magnetic stimulation (TMS)³ given that these modalities are relatively safe, noninvasive, and can be performed simultaneously with neurocognitive interventions. We review the concept of "state dependent" effects of NIBS and highlight how simultaneous or sequential cognitive interventions could help optimize NIBS therapy by providing further control of ongoing neural activity in targeted neural networks. This review spans a range of neuropsychiatric disorders including major depressive disorder, schizophrenia, generalized anxiety, and autism. For each disorder, we emphasize neuroanatomical circuitry that could be engaged with combination therapy and critically discuss the literature that has begun to emerge. Finally, we present possible underlying mechanisms and propose future research strategies that may further refine the potential of combination therapies.

Top-down and bottom-up control of stress-coping

In this 30th anniversary issue review, we focus on the glucocorticoid modulation of limbic-prefrontocortical circuitry during stress-coping. This action of the stress hormone is mediated by mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) that are co-expressed abundantly in these higher brain regions. Via both receptor types, the glucocorticoids demonstrate, in various contexts, rapid nongenomic and slower genomic actions that coordinate consecutive stages of information processing. MR-mediated action optimises stress-coping, whereas, in a complementary fashion, the memory storage of the selected coping strategy is promoted via GR. We highlight the involvement of adipose tissue in the allocation of energy resources to central regulation of stress reactions, point to still poorly understood neuronal ensembles in the prefrontal cortex that underlie cognitive flexibility critical for effective coping, and evaluate the role of cortisol as a pleiotropic regulator in vulnerability to, and treatment of, trauma-related psychiatric disorders.

Tempering aversive/traumatic memories with cannabinoids: a review of evidence from animal and human studies

RATIONALE

Aversive learning and memory are essential to cope with dangerous and stressful stimuli present in an ever-changing environment. When this process is dysfunctional, however, it is associated with posttraumatic stress disorder (PTSD). The endocannabinoid (eCB) system has been implicated in synaptic plasticity associated with physiological and pathological aversive learning and memory.

OBJECTIVE AND METHODS

The objective of this study was to review and discuss evidence on how and where in the brain genetic or pharmacological interventions targeting the eCB system would attenuate aversive/traumatic memories through extinction facilitation in laboratory animals and humans. The effect size of the experimental intervention under investigation was also calculated.

RESULTS

Currently available data indicate that direct or indirect activation of cannabinoid type-1 (CB1) receptor facilitates the extinction of aversive/traumatic memories. Activating CB1 receptors around the formation of aversive/traumatic memories or their reminders can potentiate their subsequent extinction. In most cases, the effect size has been large (Cohen's d ≥ 1.0). The brain areas responsible for the abovementioned effects include the medial prefrontal cortex, amygdala, and/or hippocampus. The potential role of cannabinoid type-2 (CB2) receptors in extinction learning is now under investigation.

CONCLUSION

Drugs augmenting the brain eCB activity can temper the impact of aversive/traumatic experiences by diverse mechanisms depending on the moment of their administration. Considering the pivotal role the extinction process plays in PTSD, the therapeutic potential of these drugs is evident. The sparse number of clinical trials testing these compounds in stress-related disorders is a gap in the literature that needs to be addressed.

How stress and glucocorticoids timing-dependently affect extinction and relapse

In recent years, various research groups aimed to augment extinction learning (the most important underlying mechanism of exposure therapy) using glucocorticoids (GCs), in particular the stress hormone cortisol. In this review, we introduce the STaR (Stress Timing affects Relapse) model, a theoretical model of the timing-dependent effects of stress/GCs treatment on extinction and relapse. In particular, we show that (1) pre-extinction stress/GCs promote memory consolidation in a context-independent manner, making extinction memory more resistant to relapse following context change. (2) Post-extinction stress also enhances extinction consolidation, but in a context-bound manner. These differences may result from the timing-dependent effects of cortisol on emotional memory contextualization. At the neural level, extinction facilitation is reflected in alterations in the amygdala-hippocampal-prefrontal cortex network. (3) Stress/GCs before a retrieval test impair extinction retrieval and promote relapse. This may result from strengthening amygdala signaling or disruption of the inhibitory functioning of the prefrontal cortex. The STaR model can contribute to the understanding and prevention of relapse processes.

Effects of stress on the corticolimbic system: implications for chronic pain

Stress has multifaceted effects on pain. On the one hand, it is a powerful inhibitor of nociception and inflammation; on the other hand, it contributes to enhanced pathological states including the establishment and continuation of chronic pain. These seemingly paradoxical effects can be better understood by investigating how stress-induced plasticity in particular brain circuitry contributes to the chronic pain state. This review presents the rationale and evidence for the interactions between stress and pain, emphasizing underlying mechanisms and putting forth the hypothesis that stress partly mediates the deleterious effects of pain on the corticolimbic system. First, a general description of the corticolimbic circuitry predisposing and amplifying chronic pain will be discussed, followed by an overview of the neurotoxic effects of stress hormones on this circuitry. Recent studies show that the resulting perturbations to these brain circuits have significant consequences both for chronic pain and for general regulation of the stress response, primarily through feedback mechanisms controlling the hypothalamic-pituitary-adrenal axis. This overlap in effected circuitry provides a key point of comparison between stress and pain, and the similarities between the plasticity induced by chronic pain and chronic stress will be examined here. Chronic pain patients have been shown to exhibit maladaptive stress responses in general and in response to pain; the cause of this response and its consequence on pain severity will then be reviewed. Finally, factors that have been shown to lead to resilience or vulnerability for chronic pain and maladaptive stress responses will be summarized.

Preextinction Stress Prevents Context-Related Renewal of Fear

Extinction learning, which creates new safety associations, is thought to be the mechanism underlying exposure therapy, commonly used for the treatment of anxiety disorders and posttraumatic stress disorder. The relative strength and availability for retrieval of both the fear and safety memories determine the response in a given situation. While the fear memory is often context-independent and may easily generalize, extinction memory is highly context-specific. "Renewal" of the extinguished fear memory might thus occur following a shift in context. The aim of the current work was to create an enhanced and generalized extinction memory to a discrete stimulus using stress exposure before extinction learning, thereby preventing renewal. In our contextual fear conditioning paradigm, 40 healthy men acquired (Day 1), retrieved and extinguished (Day 2) the fear memories, with no differences between the stress and the control group. A significant difference between the groups emerged in the renewal test (Day 3). A renewal effect was seen in the control group (N = 20), confirming the context-dependency of the extinction memory. In contrast, the stress group (N = 20) showed no renewal effect. Fear reduction was generalized to the acquisition context as well, suggesting that stress rendered the extinction memory more context-independent. These results are in line with previous studies that showed contextualization disruption as a result of pre-learning stress, mediated by the rapid effects of glucocorticoids on the hippocampus. Our findings support research investigating the use of glucocorticoids or stress induction in exposure therapy and suggest the right timing of administration in order to optimize their effects.

Downregulation of thioredoxin-1 in the ventral tegmental area delays extinction of methamphetamine-induced conditioned place preference

BACKGROUND

Drug addiction is characterized by compulsive drug use and relapse. Thioredoxin-1 is emerging as an important modulator involved in the cellular protective response against a variety of toxic stressors. Previous study has reported that thioredoxin-1 overexpression prevents the acquisition of methamphetamine-conditioned place preference. Here, we aimed to investigate the effect of thioredoxin-1 on methamphetamine-conditioned place preference extinction and the possible mechanism.

METHODS

(a) An extinction procedure in mice was employed to investigate the effect of thioredoxin-1 on the extinction of methamphetamine-conditioned place preference. After the acquisition of methamphetamine-conditioned place preference, mice underwent the following procedures: the injection of thioredoxin-1 small interfering RNA in the ventral tegmental area followed by the post-conditioned place preference test, four days of extinction training followed by four days of recovery after surgery. (b) The levels of thioredoxin-1, dopamine D1 receptor, tyrosine hydroxylase, phosphorylated extracellular regulated kinase, and phosphorylated cyclic adenosine monophosphate response element binding protein were examined by using Western blot analysis.

RESULTS

Thioredoxin-1 downregulation in the ventral tegmental area delayed methamphetamine-conditioned place preference extinction. The expression of thioredoxin-1 was decreased in the ventral tegmental area of mice in control and negative groups after methamphetamine-conditioned place preference extinction, but not in the thioredoxin-1 siRNA group. The levels of dopamine D1 receptor, tyrosine hydroxylase, phosphorylated extracellular regulated kinase, and phosphorylated cyclic adenosine monophosphate response element binding protein were decreased in the ventral tegmental area, nucleus accumbens, and prefrontal cortex of mice in the control and negative groups after methamphetamine-conditioned place preference extinction, but were inversely increased in thioredoxin-1 siRNA group.

CONCLUSIONS

The results suggest that downregulation of thioredoxin-1 in the ventral tegmental area may delay methamphetamine-conditioned place preference extinction by regulating the mesocorticolimbic dopaminergic signaling pathway.