Altered metabotropic glutamate receptor 5 markers in PTSD: In vivo and postmortem evidence

Deficits in prefrontal metabotropic glutamate receptor 5 are associated with functional alterations during emotional processing in bipolar disorder

BACKGROUND

Elucidating biological mechanisms contributing to bipolar disorder (BD) is key to improved diagnosis and treatment development. With converging evidence implicating the metabotropic glutamate receptor 5 (mGlu5) in the pathology of BD, here, we therefore test the hypothesis that recently identified deficits in mGlu5 are associated with functional brain differences during emotion processing in BD.

METHODS

Positron emission tomography (PET) with [18F]FPEB was used to measure mGlu5 receptor availability and functional imaging (fMRI) was performed while participants completed an emotion processing task. Data were analyzed from 62 individuals (33 ± 12 years, 45 % female) who completed both PET and fMRI, including individuals with BD (n = 18), major depressive disorder (MDD: n = 20), and psychiatrically healthy comparisons (HC: n = 25).

RESULTS

Consistent with some prior reports, the BD group displayed greater activation during fear processing relative to MDD and HC, notably in right lateralized frontal and parietal brain regions. In BD, (but not MDD or HC) lower prefrontal mGlu5 availability was associated with greater activation in bilateral pre/postcentral gyri and cuneus during fear processing. Furthermore, greater prefrontal mGlu5-related brain activity in BD was associated with difficulties in psychomotor function (r≥0.904, p≤0.005) and attention (r≥0.809, p≤0.028).

LIMITATIONS

The modest sample size is the primary limitation.

CONCLUSIONS

Deficits in prefrontal mGlu5 in BD were linked to increased cortical activation during fear processing, which in turn was associated with impulsivity and attentional difficulties. These data further implicate an mGlu5-related mechanism unique to BD. More generally these data suggest integrating PET and fMRI can provide novel mechanistic insights.

Automated radiosynthesis of mGluR5 PET tracer [18F]FPEB from aryl-chloro precursor and validation for clinical application

The radioligand [18F]FPEB, used for PET imaging of the brain's metabotropic glutamate receptor subtype 5 (mGluR5), undergoes a thorough validation process to ensure its safety, efficacy, and quality for clinical use. The process starts by optimizing the synthesis of [18F]FPEB to achieve high radiochemical yield and purity. This study focuses on optimizing the radiolabeling process using an aryl-chloro precursor and validating the GMP production for clinical applications. Fully automated radiolabeling was achieved via one-step nucleophilic substitution reaction. [18F]FPEB was produced and isolated in high radioactivity and radiochemical purity. Throughout the validation process, thorough quality control measures are implemented. Radiopharmaceutical batch release criteria are established, including testing for physical appearance, filter integrity, pH, radiochemical purity, molar activity, radiochemical identity, chemical impurity, structural identity, stability, residual solvent, sterility, and endotoxin levels. In conclusion, the validation of [18F]FPEB involved a comprehensive process of synthesis optimization, quality control, which ensure the safety, efficacy, and quality of [18F]FPEB, enabling its reliable use in clinical PET. Here, we successfully radiolabeled and validated [18F]FPEB using aryl-chloro precursor according to GMP production for clinical application.

A Neuroanatomic and Pathophysiologic Framework for Novel Pharmacological Approaches to the Treatment of Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a debilitating disorder inflicting high degrees of symptomatic and socioeconomic burdens. The development of PTSD results from a cascade of events with contributions from multiple processes and the underlying pathophysiology is complex, involving neurotransmitters, neurocircuitry, and neuroanatomical pathways. Presently, only two medications are US FDA-approved for the treatment of PTSD, both selective serotonin reuptake inhibitors (SSRIs). However, the complex underlying pathophysiology suggests a number of alternative pathways and mechanisms that may be targets for potential drug development. Indeed, investigations and drug development are proceeding in a number of these alternative, non-serotonergic pathways in an effort to improve the management of PTSD. In this manuscript, the authors introduce novel and emerging treatments for PTSD, including drugs in various stages of development and clinical testing (BI 1358894, BNC-210, PRAX-114, JZP-150, LU AG06466, NYV-783, PH-94B, SRX246, TNX-102), established agents and known compounds being investigated for their utility in PTSD (brexpiprazole, cannabidiol, doxasoin, ganaxolone, intranasal neuropeptide Y, intranasal oxytocin, tianeptine oxalate, verucerfont), and emerging psychedelic interventions (ketamine, MDMA-assisted psychotherapy, psilocybin-assisted psychotherapy), with an aim to examine and integrate these agents into the underlying pathophysiological frameworks of trauma-related disorders.

Inflammation in Posttraumatic Stress Disorder: Dysregulation or Recalibration?

Despite ample experimental data indicating a role of inflammatory mediators in the behavioral and neurobiological manifestations elicited by exposure to physical and psychologic stressors, causative associations between systemic low-grade inflammation and central nervous system inflammatory processes in posttraumatic stress disorder (PTSD) patients remain largely conceptual. As in other stress-related disorders, pro-inflammatory activity may play an equivocal role in PTSD pathophysiology, one that renders indiscriminate employment of anti-inflammatory agents of questionable relevance. In fact, as several pieces of preclinical and clinical research convergingly suggest, timely and targeted potentiation rather than inhibition of inflammatory responses may actually be beneficial in patients who are characterized by suppressed microglia function in the face of systemic low-grade inflammation. The deleterious impact of chronic stress-associated inflammation on the systemic level may, thus, need to be held in context with the - often not readily apparent - adaptive payoffs of low-grade inflammation at the tissue level.

Preliminary Study of White Matter Abnormalities and Associations With the Metabotropic Glutamate Receptor 5 to Distinguish Bipolar and Major Depressive Disorders

Background

Understanding distinct neurobiological mechanisms underlying bipolar disorder (BD) and major depressive disorder (MDD) is crucial for accurate diagnosis and the discovery of novel and more effective targeted treatments. Previous diffusion-weighted MRI studies have suggested some common frontotemporal corticolimbic system white matter (WM) abnormalities across the disorders. However, critical to the development of more precise diagnosis and treatment is identifying distinguishing abnormalities. Promising candidates include more prominent frontotemporal WM abnormalities observed in BD in the uncinate fasciculus (UF) that have been associated with frontal-amygdala functional dysconnectivity, and with suicide that is especially high in BD. Prior work also showed differentiation in metabotropic glutamate receptor 5 (mGlu5) abnormalities in BD versus MDD, which could be a mechanism affected in the frontotemporal system. However, associations between WM and mGlu5 have not been examined previously as a differentiator of BD. Using a multimodal neuroimaging approach, we examined WM integrity alterations in the disorders and their associations with mGluR5 levels.

Methods

Individuals with BD (N = 21), MDD (N = 10), and HC (N = 25) participated in structural and diffusion-weighted MRI scanning, and imaging with [18F]FPEB PET for quantification of mGlu5 availability. Whole-brain analyses were used to assess corticolimbic WM matter fractional anisotropy (FA) across BD and MDD relative to HC; abnormalities were tested for associations with mGlu5 availability.

Results

FA corticolimbic reductions were observed in both disorders and altered UF WM integrity was observed only in BD. In BD, lower UF FA was associated with lower amygdala mGlu5 availability (p < .05).

Conclusions

These novel preliminary findings suggest important associations between lower UF FA and lower amygdala mGlu5 levels that could represent a disorder-specific neural mechanism in which mGluR5 is associated with the frontotemporal dysconnectivity of the disorder.

Single-Cell Sequencing Technology and Its Application in the Study of Central Nervous System Diseases

The mammalian central nervous system consists of a large number of cells, which contain not only different types of neurons, but also a large number of glial cells, such as astrocytes, oligodendrocytes, and microglia. These cells are capable of performing highly refined electrophysiological activities and providing the brain with functions such as nutritional support, information transmission and pathogen defense. The diversity of cell types and individual differences between cells have brought inspiration to the study of the mechanism of central nervous system diseases. In order to explore the role of different cells, a new technology, single-cell sequencing technology has emerged to perform specific analysis of high-throughput cell populations, and has been continuously developed. Single-cell sequencing technology can accurately analyze single-cell expression in mixed-cell populations and collect cells from different spatial locations, time stages and types. By using single-cell sequencing technology to compare gene expression profiles of normal and diseased cells, it is possible to discover cell subsets associated with specific diseases and their associated genes. Therefore, scientists can understand the development process, related functions and disease state of the nervous system from an unprecedented depth. In conclusion, single-cell sequencing technology provides a powerful technology for the discovery of novel therapeutic targets for central nervous system diseases.

"NO" Time in Fear Response: Possible Implication of Nitric-Oxide-Related Mechanisms in PTSD

Post-traumatic stress disorder (PTSD) is a psychiatric condition characterized by persistent fear responses and altered neurotransmitter functioning due to traumatic experiences. Stress predominantly affects glutamate, a neurotransmitter crucial for synaptic plasticity and memory formation. Activation of the N-Methyl-D-Aspartate glutamate receptors (NMDAR) can trigger the formation of a complex comprising postsynaptic density protein-95 (PSD95), the neuronal nitric oxide synthase (nNOS), and its adaptor protein (NOS1AP). This complex is pivotal in activating nNOS and nitric oxide (NO) production, which, in turn, activates downstream pathways that modulate neuronal signaling, including synaptic plasticity/transmission, inflammation, and cell death. The involvement of nNOS and NOS1AP in the susceptibility of PTSD and its comorbidities has been widely shown. Therefore, understanding the interplay between stress, fear, and NO is essential for comprehending the maintenance and progression of PTSD, since NO is involved in fear acquisition and extinction processes. Moreover, NO induces post-translational modifications (PTMs), including S-nitrosylation and nitration, which alter protein function and structure for intracellular signaling. Although evidence suggests that NO influences synaptic plasticity and memory processing, the specific role of PTMs in the pathophysiology of PTSD remains unclear. This review highlights pathways modulated by NO that could be relevant to stress and PTSD.

Alterations of BDNF, mGluR5, Homer1a, p11 and excitatory/inhibitory balance in corticolimbic brain regions of suicide decedents

BACKGROUND

Developing biological based approaches for preventing suicide has become a priority. In recent years, there has been a surge in studies investigating the role of the glutamatergic system in suicide, although it remains unclear.

METHODS

We evaluated changes in the gene expression of the metabotropic glutamate receptor 5 (mGluR5) and its scaffolding proteins Homer1a and p11 in the dorsolateral prefrontal cortex (DLPFC), amygdala (AMY), and hippocampus (HIP) of 28 suicide decedents (S) (with no clinical psychiatric history or treatment with anxiolytics or antidepressants) and 26 controls (C) by real-time PCR (qPCR). Indeed, we measured BDNF gene expression and VGluT1 and VGAT immunoreactivities in the HIP by qPCR and immunohistochemistry, respectively. Cases and controls matched for age (C: 48.6 ± 11.6 years; S: 46.9 ± 14.5 years) and postmortem interval (PMI; C: 20.1 ± 13h; S: 16.9 ± 5h).

RESULTS

In DLPFC, S had lower p11 gene expression levels, but no differences were found in mGluR5 or Homer1a. In the AMY and HIP, mGluR5 and Homer1a were increased, p11 and BDNF were reduced. In the HIP, there were less VGAT-ir and more VGluT1-ir.

LIMITATIONS

Future studies are necessary to evaluate protein levels, and determine the cell types and potential compensatory mechanisms in a larger sample including S diagnosed with psychiatric disorders, females and different ethnicities.

CONCLUSIONS

This study identified significant alterations in mGluR5, Homer1a, p11, BDNF and excitatory/inhibitory balance in corticolimbic brain areas of S. These results further characterize the biological basis of suicide, contributing to the identification of potential biomarkers for suicide prevention.

Progress in the application of molecular imaging in psychiatric disorders

Psychiatric disorders have always attracted a lot of attention from researchers due to the difficulties in their diagnoses and treatments. Molecular imaging, as an emerging technology, has played an important role in the researchers of various diseases. In recent years, molecular imaging techniques including magnetic resonance spectroscopy, nuclear medicine imaging, and fluorescence imaging have been widely used in the study of psychiatric disorders. This review will briefly summarize the progression of molecular imaging in psychiatric disorders.

Unveiling the Secrets of the Stressed Hippocampus: Exploring Proteomic Changes and Neurobiology of Posttraumatic Stress Disorder

Intense stress, especially traumatic stress, can trigger disabling responses and in some cases even lead to the development of posttraumatic stress disorder (PTSD). PTSD is heterogeneous, accompanied by a range of distress symptoms and treatment-resistant disorders that may be associated with a number of other psychopathologies. PTSD is a very heterogeneous disorder with different subtypes that depend on, among other factors, the type of stressor that provokes it. However, the neurobiological mechanisms are poorly understood. The study of early stress responses may hint at the way PTSD develops and improve the understanding of the neurobiological mechanisms involved in its onset, opening the opportunity for possible preventive treatments. Proteomics is a promising strategy for characterizing these early mechanisms underlying the development of PTSD. The aim of the work was to understand how exposure to acute and intense stress using water immersion restraint stress (WIRS), which could be reminiscent of natural disaster, may induce several PTSD-associated symptoms and changes in the hippocampal proteomic profile. The results showed that exposure to WIRS induced behavioural symptoms and corticosterone levels reminiscent of PTSD. Moreover, the expression profiles of hippocampal proteins at 1 h and 24 h after stress were deregulated in favour of increased inflammation and reduced neuroplasticity, which was validated by histological studies and cytokine determination. Taken together, these results suggest that neuroplastic and inflammatory dysregulation may be a therapeutic target for the treatment of post-traumatic stress disorders.

Emphasizing the Crosstalk Between Inflammatory and Neural Signaling in Post-traumatic Stress Disorder (PTSD)

Post-traumatic stress disorder (PTSD) is a chronic incapacitating condition with recurrent experience of trauma-related memories, negative mood, altered cognition, and hypervigilance. Agglomeration of preclinical and clinical evidence in recent years specified that alterations in neural networks favor certain characteristics of PTSD. Besides the disruption of hypothalamus-pituitary-axis (HPA) axis, intensified immune status with elevated pro-inflammatory cytokines and arachidonic metabolites of COX-2 such as PGE2 creates a putative scenario in worsening the neurobehavioral facet of PTSD. This review aims to link the Diagnostic and Statistical Manual of mental disorders (DSM-V) symptomology to major neural mechanisms that are supposed to underpin the transition from acute stress reactions to the development of PTSD. Also, to demonstrate how these intertwined processes can be applied to probable early intervention strategies followed by a description of the evidence supporting the proposed mechanisms. Hence in this review, several neural network mechanisms were postulated concerning the HPA axis, COX-2, PGE2, NLRP3, and sirtuins to unravel possible complex neuroinflammatory mechanisms that are obscured in PTSD condition.

Differences in Quantification of the Metabotropic Glutamate Receptor 5 Across Bipolar Disorder and Major Depressive Disorder

BACKGROUND

Understanding the neurobiology underlying bipolar disorder (BD) versus major depressive disorder (MDD) is crucial for accurate diagnosis and for driving the discovery of novel treatments. A promising target is the metabotropic glutamate receptor 5 (mGluR5), a modulator of glutamate transmission associated with synaptic plasticity. We measured mGluR5 availability in individuals with MDD and BD for the first time using positron emission tomography.

METHODS

Individuals with BD (n = 17 depressed; n = 10 euthymic) or MDD (n = 17) and healthy control (HC) individuals (n = 18) underwent imaging with [18F]FPEB positron emission tomography to quantify mGluR5 availability in regions of the prefrontal cortex, which was compared across groups and assessed in relation to depressive symptoms and cognitive function.

RESULTS

Prefrontal cortex mGluR5 availability was significantly different across groups (F6,116 = 2.18, p = .050). Specifically, mGluR5 was lower in BD versus MDD and HC groups, with no difference between MDD and HC groups. Furthermore, after dividing the BD group, mGluR5 was lower in both BD-depression and BD-euthymia groups versus both MDD and HC groups across regions of interest. Interestingly, lower dorsolateral prefrontal cortex mGluR5 was associated with worse depression in MDD (r = -0.67, p = .005) but not in BD. Significant negative correlations were observed between mGluR5 and working memory in MDD and BD-depression groups.

CONCLUSIONS

This work suggests that mGluR5 could be helpful in distinguishing BD and MDD as a possible treatment target for depressive symptoms in MDD and for cognitive alterations in both disorders. Further work is needed to confirm differentiating roles for mGluR5 in BD and MDD and to probe modulation of mGluR5 as a preventive/treatment strategy.

Associations of psychiatric disease and ageing with FKBP5 expression converge on superficial layer neurons of the neocortex

Identification and characterisation of novel targets for treatment is a priority in the field of psychiatry. FKBP5 is a gene with decades of evidence suggesting its pathogenic role in a subset of psychiatric patients, with potential to be leveraged as a therapeutic target for these individuals. While it is widely reported that FKBP5/FKBP51 mRNA/protein (FKBP5/1) expression is impacted by psychiatric disease state, risk genotype and age, it is not known in which cell types and sub-anatomical areas of the human brain this occurs. This knowledge is critical to propel FKBP5/1-targeted treatment development. Here, we performed an extensive, large-scale postmortem study (n = 1024) of FKBP5/1, examining neocortical areas (BA9, BA11 and ventral BA24/BA24a) derived from subjects that lived with schizophrenia, major depression or bipolar disorder. With an extensive battery of RNA (bulk RNA sequencing, single-nucleus RNA sequencing, microarray, qPCR, RNAscope) and protein (immunoblot, immunohistochemistry) analysis approaches, we thoroughly investigated the effects of disease state, ageing and genotype on cortical FKBP5/1 expression including in a cell type-specific manner. We identified consistently heightened FKBP5/1 levels in psychopathology and with age, but not genotype, with these effects strongest in schizophrenia. Using single-nucleus RNA sequencing (snRNAseq; BA9 and BA11) and targeted histology (BA9, BA24a), we established that these disease and ageing effects on FKBP5/1 expression were most pronounced in excitatory superficial layer neurons of the neocortex, and this effect appeared to be consistent in both the granular and agranular areas examined. We then found that this increase in FKBP5 levels may impact on synaptic plasticity, as FKBP5 gex levels strongly and inversely correlated with dendritic mushroom spine density and brain-derived neurotrophic factor (BDNF) levels in superficial layer neurons in BA11. These findings pinpoint a novel cellular and molecular mechanism that has potential to open a new avenue of FKBP51 drug development to treat cognitive symptoms in psychiatric disorders.

Inhibition of mGluR5 alters BDNF/TrkB and GLT-1 expression in the prefrontal cortex and hippocampus and ameliorates PTSD-like behavior in rats

RATIONALE AND OBJECTIVE

Post-traumatic stress disorder (PTSD) is a prevalent and debilitating psychiatric disorder. However, its specific etiological mechanism remains unclear. Previous studies have shown that traumatic stress changes metabotropic glutamate receptor 5 (mGluR5) expression in the hippocampus (HIP) and prefrontal cortex (PFC). More importantly, mGluR5 expression is often accompanied by alterations in brain-derived neurotrophic factor (BDNF). Furthermore, BDNF/tropomyosin-associated kinase B (TrkB) signaling plays multiple roles, including roles in neuroplasticity and antidepressant activity, by regulating glutamate transporter-1 (GLT-1) expression. This study aims to explore the effects of inhibiting mGluR5 on PTSD-like behaviors and BDNF, TrkB, and GLT-1 expression in the HIP and PFC of inevitable foot shock (IFS)-treated rats.

METHODS

Seven-day IFS was used to establish a PTSD rat model, and 2-methyl-6-(phenylethynyl)-pyridine (MPEP) (10 mg/kg, intraperitoneal injection) was used to inhibit the activity of mGluR5 during IFS in rats. After modeling, behavioral changes and mGluR5, BDNF, TrkB, and GLT-1 expression in the PFC and HIP were examined.

RESULTS

First, the IFS procedure induced PTSD-like behavior. Second, IFS increased the expression of mGluR5 and decreased BDNF, TrkB, and GLT-1 expression in the PFC and HIP. Third, the mGluR5 antagonist blocked the above behavioral and molecular alterations.

CONCLUSIONS

mGluR5 was involved in IFS-induced PTSD-like behavior by changing BDNF, TrkB, and GLT-1 expression.

Transcriptome profiles associated with resilience and susceptibility to single prolonged stress in the locus coeruleus and nucleus accumbens in male sprague-dawley rats

Although most people are subjected to traumatic stress at least once in their lifetime, only a subset develop long-lasting, stress-triggered neuropsychiatric disorders, such as PTSD. Here we examined different transcriptome profiles within the locus coeruleus (LC) and nucleus accumbens (NAc) that may contribute to stress susceptibility. Sprague Dawley male rats were exposed to the single prolonged stress (SPS) model for PTSD. Two weeks later they were tested for their anxiety/avoidance behavior on the Elevated Plus Maze (EPM) and were divided into high and low anxiety-like subgroups. RNA (n = 5 per group) was subsequently isolated from LC and NAc and subjected to RNAseq. Transcriptome analysis was used to identify differentially-expressed genes (DEGs) which differed by at least 50 % with significance of 0.01. The LC had more than six times the number of DEGs than the NAc. Only one DEG was regulated similarly in both locations. Many of the DEGs in the LC were associated with morphological changes, including regulation of actin cytoskeleton, growth factor activity, regulation of cell size, brain development and memory, with KEGG pathway of regulation of actin cytoskeleton. The DEGs in the NAc were primarily related to DNA repair and synthesis, and differential regulation of cytokine production. The analysis identified MTPN (myotrophin) and NR3C1 (glucocorticoid receptor) as important upstream regulators of stress susceptibility in the LC. Overall the study provides new insight into molecular pathways in the LC and NAc that are associated with anxiety-like behavior triggered by stress susceptibility or resilience.

Examining sex differences in responses to footshock stress and the role of the metabotropic glutamate receptor 5: an [18F]FPEB and positron emission tomography study in rats

Clinical investigations suggest involvement of the metabotropic glutamate receptor 5 (mGluR5) in the pathophysiology of fear learning that underlies trauma-related disorders. Here, we utilized a 4-day fear learning paradigm combined with positron emission tomography (PET) to examine the relationship between mGluR5 availability and differences in the response of rats to repeated footshock exposure (FE). Specifically, on day 1, male (n = 16) and female (n = 12) rats received 15 footshocks and were compared with control rats who did not receive footshocks (n = 7 male; n = 4 female). FE rats were classified as low responders (LR) or high responders (HR) based on freezing to the context the following day (day 2). PET with [18F]FPEB was used to calculate regional mGluR5 binding potential (BPND) at two timepoints: prior to FE (i.e., baseline), and post-behavioral testing. Additionally, we used an unbiased proteomics approach to assess group and sex differences in prefrontal cortex (PFC) protein expression. Post-behavioral testing we observed decreased BPND in LR females, but increased BPND in HR males relative to baseline. Further, individuals displaying the greatest freezing during the FE context memory test had the largest increases in PFC BPND. Males and females displayed unique post-test molecular profiles: in males, the greatest differences were between FE and CON, including upregulation of mGluR5 and related molecular networks in FE, whereas the greatest differences among females were between the LR and HR groups. These findings suggest greater mGluR5 availability increases following footshock exposure may be related to greater contextual fear memory. Results additionally reveal sex differences in the molecular response to footshock, including differential involvement of mGluR5-related molecular networks.

Metabotropic glutamate receptor function and regulation of sleep-wake cycles

Metabotropic glutamate (mGlu) receptors are the most abundant family of G-protein coupled receptors and are widely expressed throughout the central nervous system (CNS). Alterations in glutamate homeostasis, including dysregulations in mGlu receptor function, have been indicated as key contributors to multiple CNS disorders. Fluctuations in mGlu receptor expression and function also occur across diurnal sleep-wake cycles. Sleep disturbances including insomnia are frequently comorbid with neuropsychiatric, neurodevelopmental, and neurodegenerative conditions. These often precede behavioral symptoms and/or correlate with symptom severity and relapse. Chronic sleep disturbances may also be a consequence of primary symptom progression and can exacerbate neurodegeneration in disorders including Alzheimer's disease (AD). Thus, there is a bidirectional relationship between sleep disturbances and CNS disorders; disrupted sleep may serve as both a cause and a consequence of the disorder. Importantly, comorbid sleep disturbances are rarely a direct target of primary pharmacological treatments for neuropsychiatric disorders even though improving sleep can positively impact other symptom clusters. This chapter details known roles of mGlu receptor subtypes in both sleep-wake regulation and CNS disorders focusing on schizophrenia, major depressive disorder, post-traumatic stress disorder, AD, and substance use disorder (cocaine and opioid). In this chapter, preclinical electrophysiological, genetic, and pharmacological studies are described, and, when possible, human genetic, imaging, and post-mortem studies are also discussed. In addition to reviewing the important relationships between sleep, mGlu receptors, and CNS disorders, this chapter highlights the development of selective mGlu receptor ligands that hold promise for improving both primary symptoms and sleep disturbances.

Examining mGlu5 Receptor Availability as a Predictor of Vulnerability to PTSD: An [18F]FPEB and PET Study in Male and Female Rats

Background

Females are twice as likely to experience post-traumatic stress disorder (PTSD) than males, yet specific factors contributing to this greater risk are not fully understood. Our clinical and recent preclinical findings suggest a role for the metabotropic glutamate receptor 5 (mGlu5) in PTSD and differential involvement between males and females.

Methods

Here, we further investigate whether mGlu5 receptor availability may contribute to individual and sex differences in PTSD susceptibility by quantifying receptor availability using the mGlu5 receptor-specific radiotracer, [18F]FPEB, and positron emission tomography in male (n = 16) and female (n = 16) rats before and after traumatic footshock exposure (FE) and assessment of stress-enhanced fear learning (SEFL) susceptibility, as compared with no-shock controls (CON; n = 7 male; n = 8 female).

Results

Overall, FE rats displayed greater fear generalization as compared with CON (p < .001). Further, greater mGlu5 receptor availability at baseline (p = .003) and post-test (p = .005) was significantly associated with expression of the SEFL phenotype. Notably, FE female rats displayed a shift to more passive coping (ie, freezing), and displayed greater SEFL susceptibility (p = .01), and had lower baseline mGlu5 availability (p = .03) relative to their FE male rat counterparts.

Conclusion

Results are consistent with clinical findings of higher mGlu5 receptor availability in PTSD, and add to growing evidence implicating these receptors in the pathophysiology of PTSD and sex-differences in susceptibility for this disorder.

Biological embedding of early trauma: the role of higher prefrontal synaptic strength

Background: Early trauma predicts poor psychological and physical health. Glutamatergic synaptic processes offer one avenue for understanding this relationship, given glutamate's abundance and involvement in reward and stress sensitivity, emotion, and learning. Trauma-induced glutamatergic excitotoxicity may alter neuroplasticity and approach/avoidance tendencies, increasing risk for psychiatric disorders. Studies examine upstream or downstream effects instead of glutamatergic synaptic processes in vivo, limiting understanding of how trauma affects the brain.Objective: In a pilot study using a previously published data set, we examine associations between early trauma and a proposed measure of synaptic strength in vivo in one of the largest human samples to undergo Carbon-13 (13C MRS) magnetic resonance spectroscopy. Participants were 18 healthy controls and 16 patients with PTSD (male and female).Method: Energy per cycle (EPC), which represents the ratio of neuronal oxidative energy production to glutamate neurotransmitter cycling, was generated as a putative measure of glutamatergic synaptic strength.Results: Results revealed that early trauma was positively correlated with EPC in individuals with PTSD, but not in healthy controls. Increased synaptic strength was associated with reduced behavioural inhibition, and EPC showed stronger associations between reward responsivity and early trauma for those with higher EPC.Conclusion: In the largest known human sample to undergo 13C MRS, we show that early trauma is positively correlated with EPC, a direct measure of synaptic strength. Our study findings have implications for pharmacological treatments thought to impact synaptic plasticity, such as ketamine and psilocybin.

The metabotropic glutamate receptor 5 as a biomarker for psychiatric disorders

The role of glutamate system in the etiology and pathophysiology of psychiatric disorders has gained considerable attention in the past two decades, including dysregulation of the metabotropic glutamatergic receptor subtype 5 (mGlu5). Thus, mGlu5 may represent a promising therapeutic target for psychiatric conditions, particularly stress-related disorders. Here, we describe mGlu5 findings in mood disorders, anxiety, and trauma disorders, as well as substance use (specifically nicotine, cannabis, and alcohol use). We highlight insights gained from positron emission tomography (PET) studies, where possible, and discuss findings from treatment trials, when available, to explore the role of mGlu5 in these psychiatric disorders. Through the research evidence reviewed in this chapter, we make the argument that, not only is dysregulation of mGlu5 evident in numerous psychiatric disorders, potentially functioning as a disease "biomarker," the normalization of glutamate neurotransmission via changes in mGlu5 expression and/or modulation of mGlu5 signaling may be a needed component in treating some psychiatric disorders or symptoms. Finally, we hope to demonstrate the utility of PET as an important tool for investigating mGlu5 in disease mechanisms and treatment response.

Nicotine Use and Metabotropic Glutamate Receptor 5 in Individuals With Major Depressive and Posttraumatic Stress Disorders

Metabotropic glutamate receptor 5 (mGluR5) dysregulation has been implicated in the pathophysiology of many psychiatric disorders, as well as nicotine use and dependence. We used positron emission tomography with [18F]FPEB to measure mGluR5 availability in vivo in 6 groups: (1) nicotine users (NUs) without other psychiatric comorbidities (n = 23); (2) comparison controls (CCs) without nicotine use or psychiatric comorbidities (n = 38); (3) major depressive disorder subjects with concurrent nicotine use (MDD-NU; n = 19); (4) MDD subjects without concurrent nicotine use (MDD-CC; n = 20); (5) posttraumatic stress disorder subjects with concurrent nicotine use (PTSD-NU; n = 17); and (6) PTSD subjects without concurrent nicotine use (PTSD-CC; n = 16). The goal of the study was to test the hypothesis that mGluR5 availability in key corticolimbic regions of interest (ROIs) is different in NU with versus without comorbid psychiatric disorders (ROI: dorsolateral prefrontal cortex [dlPFC], orbitofrontal cortex [OFC], ventromedial prefrontal cortex [vmPFC], anterior cingulate cortex [ACC], amygdala, hippocampus). We found that NU had 11%-13% lower mGluR5 availability in OFC, vmPFC, dlPFC, and ACC as compared with CC, while PTSD-NU had 9%-11% higher mGluR5 availability in OFC, dlPFC, and ACC compared with PTSD. Furthermore, relationships between mGluR5 availability and psychiatric symptoms varied as a function of psychiatric diagnosis among NUs. NU showed a negative correlation between mGluR5 and smoking cravings and urges (r's = -0.58 to -0.70, p's = 0.011 - 0.047), while PTSD-NU had the reverse relationship (r's = 0.60-0.71, p's = 0.013-0.035 in ACC, vmPFC, and dlPFC). These findings have substantial implications for our understanding of glutamate homeostasis in psychiatric subgroups and for identifying key neural phenotypes among NU. mGluR5 is a potential treatment target for precision medicine in individuals with nicotine use.

Prophylactic Efficacy of Riluzole against Anxiety- and Depressive-Like Behaviors in Two Rodent Stress Models

Introduction

Chronic stress-related illnesses such as major depressive disorder and post-traumatic stress disorder share symptomatology, including anxiety, anhedonia, and helplessness. Across disorders, neurotoxic dysregulated glutamate (Glu) signaling may underlie symptom emergence. Current first-line antidepressant drugs, which do not directly target Glu signaling, fail to provide adequate benefit for many patients and are associated with high relapse rates. Riluzole modulates glutamatergic neurotransmission by increasing metabolic cycling and modulating signal transduction. Clinical studies exploring riluzole's efficacy in stress-related disorders have provided varied results. However, the utility of riluzole for treating specific symptom dimensions or as a prophylactic treatment has not been comprehensively assessed.

Methods

We investigated whether chronic prophylactic riluzole (∼12-15 mg/kg/day p.o.) could prevent the emergence of behavioral deficits induced by unpredictable chronic mild stress (UCMS) in mice. We assessed (i) anxiety-like behavior using the elevated-plus maze, open-field test, and novelty-suppressed feeding, (ii) mixed anxiety/anhedonia-like behavior in the novelty-induced hypophagia test, and (iii) anhedonia-like behavior using the sucrose consumption test. Z-scoring summarized changes across tests measuring similar dimensions. In a separate learned helplessness (LH) cohort, we investigated whether chronic prophylactic riluzole treatment could block the development of helplessness-like behavior.

Results

UCMS induced an elevation in anhedonia-like behavior and overall behavioral emotionality that was blocked by prophylactic riluzole. In the LH cohort, prophylactic riluzole blocked the development of helplessness-like behavior.

Discussion/Conclusion

This study supports the utility of riluzole as a prophylactic medication for preventing anhedonia and helplessness symptoms associated with stress-related disorders.

Control of Theta Oscillatory Activity Underlying Fear Expression by mGlu5 Receptors

Metabotropic glutamate 5 receptors (mGlu₅) are thought to play an important role in mediating emotional information processing. In particular, negative allosteric modulators (NAMs) of mGlu₅ have received a lot of attention as potential novel treatments for several neuropsychiatric diseases, including anxiety-related disorders. The aim of this study was to assess the influence of pre- and post-training mGlu₅ inactivation in cued fear conditioned mice on neuronal oscillatory activity during fear retrieval. For this study we used the recently developed mGlu₅ NAM Alloswicth-1 administered systemically. Injection of Alloswicth-1 before, but not after, fear conditioning resulted in a significant decrease in freezing upon fear retrieval. Mice injected with Alloswicth-1 pre-training were also implanted with recording microelectrodes into both the medial prefrontal cortex (mPFC) and ventral hippocampus (vHPC). The recordings revealed a reduction in theta rhythmic activity (4-12 Hz) in both the mPFC and vHPC during fear retrieval. These results indicate that inhibition of mGlu₅ signaling alters local oscillatory activity in principal components of the fear brain network underlying a reduced response to a predicted threat.

Functional and structural brain abnormalities in posttraumatic stress disorder: A multimodal meta-analysis of neuroimaging studies

BACKGROUND

Numerous resting-state functional and structural studies have revealed that many brain regions are involved in the pathogenesis of posttraumatic stress disorder (PTSD), but their findings have been inconsistent. Moreover, there has no study explored the functional and structural alterations across languages in PTSD.

METHODS

A meta-analysis of whole-brain on the amplitude of low-frequency fluctuation (ALFF) and voxel-based morphometry (VBM) studies that explored alterations in the spontaneous functional brain activity and grey matter volume (GMV) in PTSD patients across languages by using the Seed-based d Mapping with Permutation of Subject Images (SDM-PSI) software.

RESULTS

A total of 15 studies (19 datasets) comprising 577 PTSD patients and 499 HCs for ALFF, and 27 studies (31 datasets) comprising 539 PTSD patients and 693 HCs for VBM were included. Overall, PTSD patients across languages displayed decreased ALFF in the in the left amygdala. For VBM meta-analysis, PTSD patients across languages displayed reduced GMV in the bilateral anterior cingulate cortex/medial prefrontal cortex (ACC/mPFC), striatum, insula, superior temporal gyrus, left postcentral gyrus, and occipital gyrus.

CONCLUSIONS

The multimodal meta-analysis suggest that PTSD patients showed similar pattern of aberrant resting-state functional brain activity and structure mainly in the amygdala, suggesting that structural deficits might underlie alterations in function. In addition, some regions exhibited only structural abnormalities in PTSD, including the ACC/mPFC, striatum, insula, primary visual, auditory and sensorimotor cortices. Moreover, consistent alterations in PTSD patients across languages may draw attention to the disparity in multi-cultural considerations in psychiatric research and further understanding the neurophysiopathology of PTSD.

Clinical, environmental, and molecular factors associated to the occurrence and persistence of posttraumatic stress disorder after an earthquake

Post-traumatic stress disorder (PTSD) is a common and disabling condition with high incidence after an earthquake. The objective of the present study was to identify risk factors associated with the occurrence and persistence of PTSD. Individuals (18-65 years old) who experienced the earthquake of September 19th, 2017, attended the National Institute of Psychiatry (INPRFM) between October and November 2017 (baseline n = 68). Participants were followed 4-6 (first follow-up, n = 40) and 7-9 (second follow-up n = 41) months after the earthquake. Delay returning to normal activities, a negative emotional valence to a previous earthquake, comorbidity with depression, history of childhood maltreatment, and low expression of Glucocorticoid Receptor (GR) were associated with PTSD in the basal assessment. The earthquake-related variable associated with the persistence of PTSD at the second follow-up was that the earthquake had directly affected the participants, either because they were evicted, had damage to their homes, or suffered some injury. Comorbidity with dysthymia, history of childhood maltreatment, and higher severity of PTSD in the basal assessment were associated with persistent PTSD in the second follow-up. The lower expression of the FK506 binding protein 5 (FKBP5) in participants with persistent PTSD in the second follow-up was better explained by childhood physical abuse than with PTSD severity. These findings suggest that acute exposure to earthquake-related stressful situations is relevant for the initial risk of PTSD, while potential long-term stressful conditions are associated with its persistence. Likewise, molecular markers associated with hypothalamus-pituitary-adrenal-axis dysregulation were differentially associated with PTSD diagnosis at the different assessment times.

Enhancing Endocannabinoid Signaling via β-Catenin in the Nucleus Accumbens Attenuates PTSD- and Depression-like Behavior of Male Rats

Inhibition of fatty acid amide hydrolase (FAAH), which increases anandamide levels, has been suggested as a potential treatment for stress-related conditions. We examined whether the stress-preventing effects of the FAAH inhibitor URB597 on behavior are mediated via β-catenin in the nucleus accumbens (NAc). Male rats were exposed to the shock and reminders model of PTSD and then treated with URB597 (0.4 mg/kg; i.p.). They were tested for anxiety- (freezing, startle response), depression-like behaviors (despair, social preference, anhedonia), and memory function (T-maze, social recognition). We also tested the involvement of the CB1 receptor (CB1r), β-catenin, and metabotropic glutamate receptor subtype 5 (mGluR5) proteins. URB597 prevented the shock- and reminders-induced increase in anxiety- and depressive-like behaviors, as well as the impaired memory via the CB1r-dependent mechanism. In the NAc, viral-mediated β-catenin overexpression restored the behavior of rats exposed to stress and normalized the alterations in protein levels in the NAc and the prefrontal cortex. Importantly, when NAc β-catenin levels were downregulated by viral-mediated gene transfer, the therapeutic-like effects of URB597 were blocked. We suggest a potentially novel mechanism for the therapeutic-like effects of FAAH inhibition that is dependent on β-catenin activation in the NAc in a PTSD rat model.

Central and Peripheral Immune Dysregulation in Posttraumatic Stress Disorder: Convergent Multi-Omics Evidence

Posttraumatic stress disorder (PTSD) is a chronic and multifactorial disorder with a prevalence ranging between 6–10% in the general population and ~35% in individuals with high lifetime trauma exposure. Growing evidence indicates that the immune system may contribute to the etiology of PTSD, suggesting the inflammatory dysregulation as a hallmark feature of PTSD. However, the potential interplay between the central and peripheral immune system, as well as the biological mechanisms underlying this dysregulation remain poorly understood. The activation of the HPA axis after trauma exposure and the subsequent activation of the inflammatory system mediated by glucocorticoids is the most common mechanism that orchestrates an exacerbated immunological response in PTSD. Recent high-throughput analyses in peripheral and brain tissue from both humans with and animal models of PTSD have found that changes in gene regulation via epigenetic alterations may participate in the impaired inflammatory signaling in PTSD. The goal of this review is to assess the role of the inflammatory system in PTSD across tissue and species, with a particular focus on the genomics, transcriptomics, epigenomics, and proteomics domains. We conducted an integrative multi-omics approach identifying TNF (Tumor Necrosis Factor) signaling, interleukins, chemokines, Toll-like receptors and glucocorticoids among the common dysregulated pathways in both central and peripheral immune systems in PTSD and propose potential novel drug targets for PTSD treatment.

Stress-related cognitive style is related to volumetric change of the hippocampus and FK506 binding protein 5 polymorphism in post-traumatic stress disorder

BACKGROUND

Patients with post-traumatic stress disorder (PTSD) show a different stress-related cognitive style compared with healthy controls (HC). The FK506 binding protein 5 gene (FKBP5), one of the PTSD known risk factors, is involved in the stress response through the hypothalamic-pituitary-adrenal axis and brain volumetric alterations. The present study aimed to uncover the neural correlates of stress-related cognitive styles through the analysis of the regional brain volumes and FKBP5 genotype in patients with PTSD compared with HC.

METHODS

In this study, 51 patients with PTSD and 94 HC were assessed for stress-related cognitive styles, PTSD symptoms severity, and genotype of FKBP5 single nucleotide polymorphisms, and underwent T1-weighted structural magnetic resonance imaging. Diagnosis-by-genotype interaction for regional brain volumes was examined in 16 brain regions of interest.

RESULTS

Patients with PTSD showed significantly higher levels of catastrophizing, ruminative response, and repression, and reduced distress aversion and positive reappraisal compared with HC (p < 0.001). Significant diagnosis-by-genotype interactions for regional brain volumes were observed for bilateral hippocampi and left frontal operculum. A significant positive correlation between the severity of the repression and left hippocampal volume was found in a subgroup of patients with PTSD with FKBP5 rs3800373 (AA genotype) or rs1360780 (CC genotype).

CONCLUSIONS

The present study showed the influences of FKBP5 genotype on the distorted cognitive styles in PTSD by measuring the volumetric alteration of hippocampal regions, providing a possible role of the hippocampus and left frontal operculum as significant neurobiological correlates of PTSD.

Prefrontal Glutamate Neurotransmission in PTSD: A Novel Approach to Estimate Synaptic Strength in Vivo in Humans

Background

Trauma and chronic stress are believed to induce and exacerbate psychopathology by disrupting glutamate synaptic strength. However, in vivo in human methods to estimate synaptic strength are limited. In this study, we established a novel putative biomarker of glutamatergic synaptic strength, termed energy-per-cycle (EPC). Then, we used EPC to investigate the role of prefrontal neurotransmission in trauma-related psychopathology.

Methods

Healthy controls (n = 18) and patients with posttraumatic stress (PTSD; n = 16) completed ¹³C-acetate magnetic resonance spectroscopy (MRS) scans to estimate prefrontal EPC, which is the ratio of neuronal energetic needs per glutamate neurotransmission cycle (V_TCA/V_Cycle).

Results

Patients with PTSD were found to have 28% reduction in prefrontal EPC (t = 3.0; df = 32, P = .005). There was no effect of sex on EPC, but age was negatively associated with prefrontal EPC across groups (r = -0.46, n = 34, P = .006). Controlling for age did not affect the study results.

Conclusion

The feasibility and utility of estimating prefrontal EPC using ¹³C-acetate MRS were established. Patients with PTSD were found to have reduced prefrontal glutamatergic synaptic strength. These findings suggest that reduced glutamatergic synaptic strength may contribute to the pathophysiology of PTSD and could be targeted by new treatments.

Mineralocorticoid receptor and glucocorticoid receptor work alone and together in cell-type-specific manner: Implications for resilience prediction and targeted therapy

‘You can't roll the clock back and reverse the effects of experiences' Bruce McEwen used to say when explaining how allostasis labels the adaptive process. Here we will for once roll the clock back to the times that the science of the glucocorticoid hormone was honored with a Nobel prize and highlight the discovery of their receptors in the hippocampus as inroad to its current status as master regulator in control of stress coping and adaptation. Glucocorticoids operate in concert with numerous neurotransmitters, neuropeptides, and other hormones with the aim to facilitate processing of information in the neurocircuitry of stress, from anticipation and perception of a novel experience to behavioral adaptation and memory storage. This action, exerted by the glucocorticoids, is guided by two complementary receptor systems, mineralocorticoid receptors (MR) and glucocorticoid receptors (GR), that need to be balanced for a healthy stress response pattern. Here we discuss the cellular, neuroendocrine, and behavioral studies underlying the MR:GR balance concept, highlight the relevance of hypothalamic-pituitary-adrenal (HPA) -axis patterns and note the limited understanding yet of sexual dimorphism in glucocorticoid actions. We conclude with the prospect that (i) genetically and epigenetically regulated receptor variants dictate cell-type-specific transcriptome signatures of stress-related neuropsychiatric symptoms and (ii) selective receptor modulators are becoming available for more targeted treatment. These two new developments may help to ‘restart the clock’ with the prospect to support resilience.

The effects of predator odor (TMT) exposure and mGlu3 NAM pretreatment on behavioral and NMDA receptor adaptations in the brain

A stressor can trigger lasting adaptations that contribute to neuropsychiatric disorders. Predator odor (TMT) exposure is an innate stressor that may activate the metabotropic glutamate receptor 3 (mGlu3) to produce stress adaptations. To evaluate functional involvement, the mGlu3 negative allosteric modulator (NAM, VU6010572; 3 mg/kg, i.p.) was administered before TMT exposure in male, Long Evans rats. Two weeks after, rats underwent context re-exposure, elevated zero maze (ZM), and acoustic startle (ASR) behavioral tests, followed by RT-PCR gene expression in the insular cortex and bed nucleus of the stria terminalis (BNST) to evaluate lasting behavioral and molecular adaptations from the stressor. Rats displayed stress-reactive behaviors in response to TMT exposure that were not affected by VU6010572. Freezing and hyperactivity were observed during the context re-exposure, and mGlu3-NAM pretreatment during stressor prevented the context freezing response. TMT exposure did not affect ZM or ASR measures, but VU6010572 increased time spent in the open arms of the ZM and ASR habituation regardless of stressor treatment. In the insular cortex, TMT exposure increased expression of mGlu (Grm3, Grm5) and NMDA (GriN2A, GriN2B, GriN2C, GriN3A, GriN3B) receptor transcripts, and mGlu3-NAM pretreatment blocked GriN3B upregulation. In the BNST, TMT exposure increased expression of GriN2B and GriN3B in vehicle-treated rats, but decreased expression in the mGlu3-NAM group. Similar to the insular cortex, mGlu3-NAM reversed the stressor-induced upregulation of GriN3B in the BNST. mGlu3-NAM also upregulated GriN2A, GriN2B, GriN3B and Grm2 in the control group, but not the TMT group. Together, these data implicate mGlu3 receptor signaling in some lasting adaptations of predator odor stressor and anxiolytic-like effects.

Flights and Perchings of the BrainMind: A Temporospatial Approach to Psychotherapy

This article introduces a process-oriented approach for improving present moment conceptualization in psychotherapy that is in alignment with neuroscience: the Temporospatial movements of mind (TSMM) model. We elaborate on seven temporal movements that describe the moment-to-moment morphogenesis of emotional feelings and thoughts from inception to maturity. Temporal refers to the passage of time through which feelings and thoughts develop, and electromagnetic activity, that among other responsibilities, bind information across time. Spatial dynamics extend from an undifferentiated to three dimensional experiences of emotional and cognitive processes. Neurophysiologically, spatial refers to structures within the brain and their varying interactions with one another. This article culminates in the development of an atheoretical temporospatial grid that may help clinicians conceptualize where patients are in their cognitive and emotional development to further guide technique.

Differential Role of mGluR5 in Cognitive Processes in Posttraumatic Stress Disorder and Major Depression

Background

A robust literature supports the role of the metabotropic glutamate receptor type 5 (mGluR5) in cognitive functioning. mGluR5 is also implicated in the pathophysiology of posttraumatic stress disorder (PTSD) and major depressive disorder (MDD), which are characterized by cognitive alterations. However, the relationship between mGluR5 and cognition in MDD and PTSD has not yet been directly investigated. To address this gap, we examined the relationship between in vivo mGluR5 availability and cognition in PTSD, MDD, and matched healthy adults (HA).

Methods

Individuals with PTSD (N = 28) and MDD (N = 21), and HA (N = 28) were matched for age, gender, and smoking status. Participants completed 18F-FPEB positron emission tomography (PET) scan, psychiatric and cognitive assessments.

Results

Across models examining the relationship between mGluR5 availability and different domains of cognition across diagnostic groups, only the interaction of diagnosis*attention was significant (F 4,64 = 3.011, P = .024). Higher mGluR5 availability was associated with poorer attention in PTSD in 4 frontolimbic regions of interests (ROI's: OFC (r = -.441, P = .016), vmPFC (r = -.408, P = .028), dlPFC (r = -.421, P = .023), hippocampus (r = -.422, P = .025). By contrast, mGluR5 availability in the MDD group was positively related to Attention (ATTN) in the OFC (r = .590, P = .006), vmPFC (r = .653, P = .002), and dlPFC (r = .620, P = .004). Findings in the hippocampus for MDD followed the same pattern but did not survive correction for multiple comparisons (r = .480, P = .036). ATTN and mGluR5 availability were not significantly related in the HA group. Of note, in MANOVA analyses group*ATTN interaction results in the OFC did not survive multiple comparisons (P = .046). All other findings survived correction for multiple comparisons and remained significant when covarying for potential confounds (eg, depressed mood).

Conclusions

We observed a significant relationship between frontolimbic mGluR5 availability and performance on tests of attention in individuals with MDD and PTSD. This finding aligns with animal work showing dysregulation in mGluR5 in cognitive functioning, and differed as a function of diagnosis. Results suggest interventions targeting mGluR5 may help bolster cognitive difficulties, highlighting the importance of employing different mGluR5 directed treatment strategies in MDD and PTSD.

Sleep and anxiety: From mechanisms to interventions

Anxiety is the most common mental health problem worldwide. Epidemiological studies show that sleep disturbances, particularly insomnia, affect ∼50% of individuals with anxiety, and that insufficient sleep can instigate or further exacerbate it. This review outlines brain mechanisms underlying sleep and anxiety, by addressing recent human functional/structural imaging studies on brain networks underlying the anxiogenic impact of sleep loss, and the beneficial effect of sleep on these brain networks. We discuss recent developments from human molecular imaging studies that highlight the role of specific brain neurotransmitter mechanisms, such as the adenosinergic receptor system, on anxiety, arousal, and sleep. This review further discusses frontline sleep interventions aimed at enhancing sleep in individuals experiencing anxiety, such as nonbenzodiazepines/antidepressants, lifestyle and sleep interventions and cognitive behavioral therapy for insomnia. Notwithstanding therapeutic success, up to ∼30% of individuals with anxiety can be nonresponsive to frontline treatments. Thus, we address novel non-invasive brain stimulation techniques that can enhance electroencephalographic slow waves, and might help alleviate sleep and anxiety symptoms. Collectively, these findings contribute to an emerging biological framework that elucidates the interrelationship between sleep and anxiety, and highlight the prospect of slow wave sleep as a potential therapeutic target for reducing anxiety.

Dynamic alterations in the central glutamatergic status following food and glucose intake: in vivo multimodal assessments in humans and animal models

Fluctuations of neuronal activities in the brain may underlie relatively slow components of neurofunctional alterations, which can be modulated by food intake and related systemic metabolic statuses. Glutamatergic neurotransmission plays a major role in the regulation of excitatory tones in the central nervous system, although just how dietary elements contribute to the tuning of this system remains elusive. Here, we provide the first demonstration by bimodal positron emission tomography (PET) and magnetic resonance spectroscopy (MRS) that metabotropic glutamate receptor subtype 5 (mGluR5) ligand binding and glutamate levels in human brains are dynamically altered in a manner dependent on food intake and consequent changes in plasma glucose levels. The brain-wide modulations of central mGluR5 ligand binding and glutamate levels and profound neuronal activations following systemic glucose administration were further proven by PET, MRS, and intravital two-photon microscopy, respectively, in living rodents. The present findings consistently support the notion that food-associated glucose intake is mechanistically linked to glutamatergic tones in the brain, which are translationally accessible in vivo by bimodal PET and MRS measurements in both clinical and non-clinical settings.

Optogenetic manipulation of the prelimbic cortex during fear memory reconsolidation alters fear extinction in a preclinical model of comorbid PTSD/AUD

RATIONALE AND OBJECTIVE

Post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD) are disorders of learning and memory that often occur comorbidly. Exposure to trauma-related cues can increase alcohol intake in PTSD patients that are using alcohol to self-medicate. The recurrence of anxiety symptoms with subsequent alcohol use may initiate a destructive cycle where stress and alcohol exposure impair the function of the prefrontal cortex (PFC). While the incidence of these disorders has steadily increased, current therapies and treatments often lack efficacy. Thus, investigation into the underlying neurocircuitry responsible for the establishment and maintenance of these disorders is necessary to develop novel treatment targets.

METHODS

The present study examined the effects of ethanol exposure on the ability to create new learned associations around previously conditioned fear cues in a rat model. Animals were exposed to fear conditioning followed by chronic intermittent ethanol to translationally model trauma exposure followed by alcohol abuse. Optogenetics was used to inhibit the prelimbic (PrL) or infralimbic (IfL) cortex during fear memory reconsolidation, and fear behaviors were measured during subsequent extinction and spontaneous recovery tests. Results and conclusion Chronic ethanol exposure led to deficits in fear extinction learning and increased freezing during spontaneous recovery, both of which were prevented following inhibition of the PrL, but not the IfL, during memory reconsolidation. These results support the involvement of the PrL in fear learning and memory, and strongly suggest that the PrL could serve as a potential target for the treatment of the learning and memory deficits that occur following exposure to stress and alcohol.

Transcriptomics of the depressed and PTSD brain

Stress is the response of an organism to demands for change, yet excessive or chronic stress contributes to nearly all psychiatric disorders. The advent of high-throughput transcriptomic methods such as single cell RNA sequencing poses new opportunities to understand the neurobiology of stress, yet substantial barriers to understanding stress remain. Stress adaptation is an organismal survival mechanism conserved across all organisms, yet there is an infinity of potential stressful experiences. Unraveling shared and separate transcriptional programs for adapting to stressful experience remains a challenge, despite methodological and analytic advances. Here we review the state of the field focusing on the technologies used to study the transcriptome for the stress neurobiologist, and also attempt to identify central questions about the heterogeneity of stress for those applying transcriptomic approaches. We further explore how postmortem transcriptome studies aided by preclinical animal models are converging on common molecular pathways for adaptation to aversive experience. Finally, we discuss approaches to integrate large genomic datasets with human neuroimaging and other datasets.

Metabotropic Glutamate Receptor Trafficking and its Role in Drug-Induced Neurobehavioral Plasticity

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system that guides developmental and experience-dependent changes in many cellular substrates and brain circuits, through the process collectively referred to as neurobehavioral plasticity. Regulation of cell surface expression and membrane trafficking of glutamate receptors represents an important mechanism that assures optimal excitatory transmission, and at the same time, also allows for fine-tuning neuronal responses to glutamate. On the other hand, there is growing evidence implicating dysregulated glutamate receptor trafficking in the pathophysiology of several neuropsychiatric disorders. This review provides up-to-date information on the molecular determinants regulating trafficking and surface expression of metabotropic glutamate (mGlu) receptors in the rodent and human brain and discusses the role of mGluR trafficking in maladaptive synaptic plasticity produced by addictive drugs. As substantial evidence links glutamatergic dysfunction to the progression and the severity of drug addiction, advances in our understanding of mGluR trafficking may provide opportunities for the development of novel pharmacotherapies of addiction and other neuropsychiatric disorders.

Cannabidiol and the corticoraphe circuit in post-traumatic stress disorder

Post-Traumatic Stress Disorder (PTSD), characterized by re-experiencing, avoidance, negative affect, and impaired memory processing, may develop after traumatic events. PTSD is complicated by impaired plasticity and medial prefrontal cortex (mPFC) activity, hyperactivity of the amygdala, and impaired fear extinction. Cannabidiol (CBD) is a promising candidate for treatment due to its multimodal action that enhances plasticity and calms hyperexcitability. CBD’s mechanism in the mPFC of PTSD patients has been explored extensively, but literature on the mechanism in the dorsal raphe nucleus (DRN) is lacking. Following the PRISMA guidelines, we examined current literature regarding CBD in PTSD and overlapping symptomologies to propose a mechanism by which CBD treats PTSD via corticoraphe circuit. Acute CBD inhibits excess 5-HT release from DRN to amygdala and releases anandamide (AEA) onto amygdala inputs. By first reducing amygdala and DRN hyperactivity, CBD begins to ameliorate activity disparity between mPFC and amygdala. Chronic CBD recruits the mPFC, creating harmonious corticoraphe signaling. DRN releases enough 5-HT to ameliorate mPFC hypoactivity, while the mPFC continuously excites DRN 5-HT neurons via glutamate. Meanwhile, AEA regulates corticoraphe activity to stabilize signaling. AEA prevents DRN GABAergic interneurons from inhibiting 5-HT release so the DRN can assist the mPFC in overcoming its hypoactivity. DRN-mediated restoration of mPFC activity underlies CBD’s mechanism on fear extinction and learning of stress coping.

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CBD reduces PTSD symptoms via the DRN and corticoraphe circuit.

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Acute effects of CBD reduce DRN-amygdala excitatory signaling to lessen the activity disparity between amygdala and mPFC.

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Chronic CBD officially resolves mPFC hypoactivity by facilitating 5-HT release from DRN to mPFC.

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CBD-facilitated endocannabinoid signaling stabilizes DRN activity and restores mPFC inhibitory control.

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Chronically administered CBD acts via the corticoraphe circuit to favor fear extinction over fear memory reconsolidation.

Increased mGlu5 mRNA expression in BLA glutamate neurons facilitates resilience to the long-term effects of a single predator scent stress exposure

Post-traumatic stress disorder (PTSD) develops in a subset of individuals exposed to a trauma with core features being increased anxiety and impaired fear extinction. To model the heterogeneity of PTSD behavioral responses, we exposed male Sprague-Dawley rats to predator scent stress once for 10 min and then assessed anxiety-like behavior 7 days later using the elevated plus maze and acoustic startle response. Rats displaying anxiety-like behavior in both tasks were classified as stress Susceptible, and rats exhibiting behavior no different from un-exposed Controls were classified as stress Resilient. In Resilient rats, we previously found increased mRNA expression of mGlu5 in the amygdala and prefrontal cortex (PFC) and CB1 in the amygdala. Here, we performed fluorescent in situ hybridization (FISH) to determine the subregion and cell-type-specific expression of these genes in Resilient rats 3 weeks after TMT exposure. Resilient rats displayed increased mGlu5 mRNA expression in the basolateral amygdala (BLA) and the infralimbic and prelimbic regions of the PFC and increased BLA CB1 mRNA. These increases were limited to glutamatergic cells. To test the necessity of mGlu5 for attenuating TMT-conditioned contextual fear 3 weeks after TMT conditioning, intra-BLA infusions of the mGlu5 negative allosteric modulator MTEP were administered prior to context re-exposure. In TMT-exposed Resilient rats, but not Controls, MTEP increased freezing on the day of administration, which extinguished over two additional un-drugged sessions. These results suggest that increased mGlu5 expression in BLA glutamate neurons contributes to the behavioral flexibility observed in stress-Resilient animals by facilitating a capacity for extinguishing contextual fear associations.

CPEB3-dowregulated Nr3c1 mRNA translation confers resilience to developing posttraumatic stress disorder-like behavior in fear-conditioned mice

Susceptibility or resilience to posttraumatic stress disorder (PTSD) depends on one's ability to appropriately adjust synaptic plasticity for coping with the traumatic experience. Activity-regulated mRNA translation synthesizes plasticity-related proteins to support long-term synaptic changes and memory. Hence, cytoplasmic polyadenylation element-binding protein 3-knockout (CPEB3-KO) mice, showing dysregulated translation-associated synaptic rigidity, may be susceptible to PTSD-like behavior. Here, using a context-dependent auditory fear conditioning and extinction paradigm, we found that CPEB3-KO mice exhibited traumatic intensity-dependent PTSD-like fear memory. A genome-wide screen of CPEB3-bound transcripts revealed that Nr3c1, encoding glucocorticoid receptor (GR), was translationally suppressed by CPEB3. Thus, CPEB3-KO neurons with elevated GR expression exhibited increased corticosterone-induced calcium influx and decreased mRNA and protein levels of brain-derived neurotrophic factor (Bdnf). Moreover, the reduced expression of BDNF was associated with increased GR level during fear extinction in CPEB3-KO hippocampi. Intracerebroventricular delivery of BDNF before extinction training mitigated spontaneous fear intrusion in CPEB3-KO mice during extinction recall. Analysis of two GEO datasets revealed decreased transcriptomic expression of CPEB3 but not NR3C1 in peripheral blood mononuclear cells of humans with PTSD. Collectively, this study reveals that CPEB3, as a potential PTSD-risk gene, downregulates Nr3c1 translation to maintain proper GR-BDNF signaling for fear extinction.

Loss of mGluR5 in D1 Receptor-Expressing Neurons Improves Stress Coping

The metabotropic glutamate receptor type 5 (mGluR5) has been proposed to play a crucial role in the selection and regulation of cognitive, affective, and emotional behaviors. However, the mechanisms by which these receptors mediate these effects remain largely unexplored. Here, we studied the role of mGluR5 located in D1 receptor-expressing (D1) neurons in the manifestation of different behavioral expressions. Mice with conditional knockout (cKO) of mGluR5 in D1 neurons (mGluR5^D1 cKO) and littermate controls displayed similar phenotypical profiles in relation to memory expression, anxiety, and social behaviors. However, mGluR5^D1 cKO mice presented different coping mechanisms in response to acute escapable or inescapable stress. mGluR5^D1 cKO mice adopted an enhanced active stress coping strategy upon exposure to escapable stress in the two-way active avoidance (TWA) task and a greater passive strategy upon exposure to inescapable stress in the forced swim test (FST). In summary, this work provides evidence for a functional integration of the dopaminergic and glutamatergic system to mediate control over internal states upon stress exposure and directly implicates D1 neurons and mGluR5 as crucial mediators of behavioral stress responses.

The Neurocircuitry of Posttraumatic Stress Disorder and Major Depression: Insights Into Overlapping and Distinct Circuit Dysfunction-A Tribute to Ron Duman

The neurocircuitry that contributes to the pathophysiology of posttraumatic stress disorder and major depressive disorder, psychiatric conditions that exhibit a high degree of comorbidity, likely involves both overlapping and unique structural and functional changes within multiple limbic brain regions. In this review, we discuss neurobiological alterations that are associated with posttraumatic stress disorder and major depressive disorder and highlight both similarities and differences that may exist between these disorders to argue for the existence of a shared neurobiology. We highlight the key contributions based on preclinical studies, emerging from the late Professor Ronald Duman's research, that have shaped our understanding of the neurocircuitry that contributes to both the etiopathology and treatment of major depressive disorder and posttraumatic stress disorder.

Stress and Its Impact on the Transcriptome

Exposure to stress during the course of a lifetime is inevitable in the animal kingdom. It is the response to stress, the valence of the exposure, and the developmental time point that largely determine the consequences to the initial and subsequent exposures. The versatility of transcriptomic methods to yield rich, high-resolution, information-laden datasets from entire brain regions to single cells makes it a powerful approach to investigate the effects of stress from several angles. Dysregulation of the transcriptome is now a phenotypic signature of many neuropsychiatric disorders. New insight has been gained from examining stress-induced changes in gene expression at a global scale. Human postmortem datasets from depression and posttraumatic stress disorder studies have identified major gene expression changes in the diseased brain, including sex-specific changes and marked differences in male and female molecular profiles for the same disorder. Extensions of this work into animal models have explored the impact of transcriptomic dysregulation on early-life stress, chronic stress, and transgenerational impact of stress. Here, we explore the findings of human postmortem genomic studies of neuropsychiatric disorders and comparable animal models through the lens of transcriptomic dysregulation and how these findings have contributed to our understanding of stress.

Neonatal maternal separation affects metabotropic glutamate receptor 5 expression and anxiety-related behavior of adult rats

Exposure to early life stress leads to long-term neurochemical and behavioral alterations. Stress-induced psychiatric disorders, such as depression, have recently been linked to dysregulation of glutamate signaling, mainly via its postsynaptic receptors. The role of metabotropic glutamate receptor 5 (mGluR5) in stress-induced psychopathology has been the target of several studies in humans. In rodents, blockade of mGluR5 produces antidepressant-like actions, whereas mice lacking mGluR5 exhibit altered anxiety-like behaviors and learning. In this study, we used well-known rodent models of early life stress based on mother-infant separation during the first 3 weeks of life in order to examine the effects of neonatal maternal separation on mGluR5 expression and on anxiety-related behavior in adulthood. We observed that brief (15 min) neonatal maternal separation, but not prolonged (3 h), induced increases in mGluR5 mRNA and protein expression levels in medial prefrontal cortex and mGluR5 protein levels in dorsal, but not ventral, hippocampus of adult rat brain. Behavioral testing using the open-field and the elevated-plus maze tasks showed that brief maternal separations resulted in increased exploratory and decreased anxiety-related behavior, whereas prolonged maternal separations resulted in increased anxiety-related behavior in adulthood. The data indicate that the long-lasting effects of neonatal mother-offspring separation on anxiety-like behavior and mGluR5 expression depend on the duration of maternal separation and suggest that the increased mGluR5 receptors in medial prefrontal cortex and hippocampus of adult rats exposed to brief neonatal maternal separations may underlie their heightened ability to cope with stress.

Comparative Analysis of Pathobiochemical Changes in Major Depression and Post-Traumatic Stress Disorder

Comparative analysis of available literature data on the pathogenetic neuroendocrine mechanisms of depression and post-traumatic stress disorder (PTSD) is provided in this review to identify their common features and differences. We discuss the multidirectional modifications of the activity of cortical and subcortical structures of the brain, levels of neurotransmitters and their receptors, and functions of the hypothalamic-pituitary-adrenocortical axis in depression and PTSD. The analysis shows that these disorders are examples of opposite failures in the system of adaptive stress response of the body to stressful psychotraumatic events. On this basis, it is concluded that the currently widespread use of similar approaches to treat these disorders is not justified, despite the significant similarity of their anxiety-depressive symptoms; development of differential therapeutic strategies is required.

Genomic factors underlying sex differences in trauma-related disorders

Post-traumatic stress disorder (PTSD) is a devastating illness with treatment that is effective in only approximately half of the population. This limited rate of response highlights the necessity for research into underlying individual biological mechanisms that mediate development and progression of this disease, allowing for identification of patient-specific treatments. PTSD has clear sex differences in both risk and symptom patterns. Thus, one approach is to characterize trauma-related changes between men and women who exhibit differences in treatment efficacy and response to trauma. Recent technological advances in sequencing have identified several genomic loci and transcriptional changes that are associated with post-trauma symptomatology. However, although the diagnosis of PTSD is more prevalent in women, the genetic factors underlying sex differences remain poorly understood. Here, we review recent work that highlights current understanding and limitations in the field of sex differences in PTSD and related symptomatology.