Altered locus coeruleus-norepinephrine function following single prolonged stress

The locus coeruleus-dorsal hippocampal CA1 pathway is involved in depression-induced perioperative neurocognitive disorders in adult mice

BACKGROUND

Patients undergoing surgical anesthesia increasingly suffer from preoperative depression. Clinical studies have shown that depression is a risk factor for perioperative neurocognitive disorders (PNDs) in elder patients. However, the underlying mechanism, especially at the neural circuit level, remains poorly understood.

METHODS

Right carotid artery separation under sevoflurane and chronic social defeat stress (CSDS) in adult mice were used to establish surgical anesthesia and chronic depression models. Cognitive function was assessed by the Y maze and novel object recognition tests. A chemogenetic approach was used to modulate the locus coeruleus-dorsal hippocampal CA1 (LC-dCA1) circuit. Hippocampal synaptic alterations were evaluated by Golgi staining and whole-cell patch clamp recording.

RESULTS

We found that CSDS induced synaptic impairments in dorsal hippocampal CA1 pyramidal neurons and cognitive deficits in adult mice after surgery under sevoflurane. Chemogenetic activation of the LC-dCA1 pathway significantly alleviated the CSDS-induced synaptic impairments and cognitive dysfunction. On the contrary, inhibition of this pathway could mimic CSDS-induced deficits. Furthermore, we showed that dopamine played an important role in CSDS-induced PNDs in adult mice after surgery/sevoflurane.

CONCLUSION

Overall, our results have demonstrated a vital role for the LC-dCA1 pathway in CSDS-induced PNDs in adult mice undergoing surgery with sevoflurane anesthesia.

Linking individual variability in functional brain connectivity to polygenic risk in major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a highly heterogeneous disease, which brings great difficulties to clinical diagnosis and therapy. Its mechanism is still unknown. Prior neuroimaging studies mainly focused on mean differences between patients and healthy controls (HC), largely ignoring individual differences between patients.

METHODS

This study included 112 MDD patients and 93 HC subjects. Resting-state functional MRI data were obtained to examine the patterns of individual variability of brain functional connectivity (IVFC). The genetic risk of pathways including dopamine, 5-hydroxytryptamine (5-HT), norepinephrine (NE), hypothalamic-pituitary-adrenal (HPA) axis, and synaptic plasticity was assessed by multilocus genetic profile scores (MGPS), respectively.

RESULTS

The IVFC pattern of the MDD group was similar but higher than that in HCs. The inter-network functional connectivity in the default mode network contributed to altered IVFC in MDD. 5-HT, NE, and HPA pathway genes affected IVFC in MDD patients. The age of onset, duration, severity, and treatment response, were correlated with IVFC. IVFC in the left ventromedial prefrontal cortex had a mediating effect between MGPS of the 5-HT pathway and baseline depression severity.

LIMITATIONS

Environmental factors and differences in locations of functional areas across individuals were not taken into account.

CONCLUSIONS

This study found MDD patients had significantly different inter-individual functional connectivity variations than healthy people, and genetic risk might affect clinical manifestations through brain function heterogeneity.

Priorities for research on neuromodulatory subcortical systems in Alzheimer's disease: Position paper from the NSS PIA of ISTAART

The neuromodulatory subcortical system (NSS) nuclei are critical hubs for survival, hedonic tone, and homeostasis. Tau-associated NSS degeneration occurs early in Alzheimer's disease (AD) pathogenesis, long before the emergence of pathognomonic memory dysfunction and cortical lesions. Accumulating evidence supports the role of NSS dysfunction and degeneration in the behavioral and neuropsychiatric manifestations featured early in AD. Experimental studies even suggest that AD-associated NSS degeneration drives brain neuroinflammatory status and contributes to disease progression, including the exacerbation of cortical lesions. Given the important pathophysiologic and etiologic roles that involve the NSS in early AD stages, there is an urgent need to expand our understanding of the mechanisms underlying NSS vulnerability and more precisely detail the clinical progression of NSS changes in AD. Here, the NSS Professional Interest Area of the International Society to Advance Alzheimer's Research and Treatment highlights knowledge gaps about NSS within AD and provides recommendations for priorities specific to clinical research, biomarker development, modeling, and intervention. HIGHLIGHTS: Neuromodulatory nuclei degenerate in early Alzheimer's disease pathological stages. Alzheimer's pathophysiology is exacerbated by neuromodulatory nuclei degeneration. Neuromodulatory nuclei degeneration drives neuropsychiatric symptoms in dementia. Biomarkers of neuromodulatory integrity would be value-creating for dementia care. Neuromodulatory nuclei present strategic prospects for disease-modifying therapies.

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

RATIONALE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Anxious Personality Traits: Perspectives from Basic Emotions and Neurotransmitters

Objective: Recently, many emotional diseases, such as anxiety and depression, have prevailed, and it is expected that emotional disease will be the leading cause of social and economic burden in 2030. These emotional diseases may be due to certain personality traits, which could be the reasons for the development of mental illness. Personality theories have been constantly developed over the past hundreds of years, and different dimensions of personality traits corresponding to different physiological bases and emotional feelings have been proposed. However, personality may be the least studied area in psychology. Methods: In this paper, we will give a short review on the development of personality theories as well as dimensional emotional theory. Then, we will compare the similarities between the emotional dimension and personality dimension. Furthermore, we will also investigate the neural mechanisms of personality and emotions, focusing on neuromodulators for anxiety-related personality traits, in order to provide a clear relationship between different neurotransmitters and anxiety-related personality traits. Results: The results of our study suggest that the emotional dimension and personality dimension may be somewhat related, for example, the extrovert/introvert dimension of personality might be related to the hedonic dimension, which includes happiness/sadness, and the neurotic dimensions might be related to emotional arousal. In addition, our study found that personality traits are also related to basic emotions, for instance, people who are too self-centered are prone to feeling a mood of disgust or depression, while anger and fear correspond to unstable personality traits. The analysis suggested that the neural substrates of both personality and emotions might be described as follows: extroverted–joy–dopamine (DA); introverted–disgust–5-hydroxytryptamine (5-HT); unstable (neuroticism)–anger/fear–noradrenaline (NE); stable–calmness. Conclusions: The results of this study suggest that there is a correlation between personality traits and emotions, and both depend on monoamine neurotransmitters (dopamine, norepinephrine and serotonin). In addition, personality disorders can be interfered via the regulation of emotions and neurotransmitters. This paper opens up a whole new perspective for future research on personality traits and emotional diseases and has great clinical value and practical significance.

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

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

Variable Response of Norepinephrine Transporter to Traumatic Stress and Relationship to Hyperarousal

The noradrenergic systems play a key role in stress triggered disorders such as post-traumatic stress disorder (PTSD). We hypothesized that traumatic stress will alter expression of norepinephrine transporter (NET) in locus coeruleus (LC) and its target brain regions which could be related to hyperarousal. Male Sprague-Dawley rats were subjected to single prolonged stress (SPS) and several weeks later the LC was isolated. NET mRNA levels in LC, determined by RT-PCR, displayed variable response with high and low responsive subgroups. In different cohort, acoustic startle response (ASR) was measured 2 weeks after SPS and levels of NET mRNA and protein in LC determined. The high NET responsive subgroup had greater hyperarousal. Nevertheless, NET protein levels, as determined by western blots, were lower than unstressed controls in LC, ventral hippocampus and medial prefrontal cortex and displayed considerable variability. Hypermethylation of specific CpG region in promoter of SLC6A2 gene, encoding NET, was present in the low, but not high, NET mRNA responsive subgroup. Taken together, the results demonstrate variability in stress elicited changes in NET gene expression and involvement of epigenetic changes. This may underlie mechanisms of susceptibility and resilience to traumatic stress triggered neuropsychiatric symptoms, especially hyperarousal.

Protective effects of tetramethylpyrazine on dysfunction of the locus coeruleus in rats exposed to single prolonged stress by anti-ER stress mechanism

Post-traumatic stress disorder (PTSD) is a serious stress-related neuropsychiatric disorder caused by major traumatic events. Abnormal activity of the locus coeruleus (LC)-noradrenergic system is related to the development of PTSD-like symptoms. Our previous studies have indicated that endoplasmic reticulum (ER) stress induced neuronal apoptosis of LC in rats with PTSD. The purpose of this study was to further investigate the role of ER stress pathways in LC neuronal dysfunction and elucidate the effect of the bioactive component tetramethylpyrazine (TMP) against ER stress response. We used an acute exposure to single prolonged stress (SPS) to model PTSD in rats. There were higher norepinephrine (NE) levels in the brain, increased tyrosine hydroxylase expression in LC, and enhanced anxiety-like behaviors in rats exposed to SPS, which were observed by enzyme-linked immunosorbent assay, western blot analysis and elevated plus maze test, respectively. In addition, the three major pathways of ER stress were activated by SPS exposure, which may be involved in the dysregulation of the LC-noradrenergic system of rats with PTSD. Furthermore, we found that TMP administration significantly suppressed the increased responsiveness of LC-noradrenergic system, effectively reduced the anxiety response of SPS rats, and selectively attenuated the activation of pro-apoptotic ER stress pathways. The results suggest that TMP was efficient in improving the LC-NE dysfunction induced by excessive ER stress. TMP exhibited a significant neuroprotective effect and potential therapeutics on PTSD-like symptoms.

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

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

Real-world stress resilience is associated with the responsivity of the locus coeruleus

Individuals may show different responses to stressful events. Here, we investigate the neurobiological basis of stress resilience, by showing that neural responsitivity of the noradrenergic locus coeruleus (LC-NE) and associated pupil responses are related to the subsequent change in measures of anxiety and depression in response to prolonged real-life stress. We acquired fMRI and pupillometry data during an emotional-conflict task in medical residents before they underwent stressful emergency-room internships known to be a risk factor for anxiety and depression. The LC-NE conflict response and its functional coupling with the amygdala was associated with stress-related symptom changes in response to the internship. A similar relationship was found for pupil-dilation, a potential marker of LC-NE firing. Our results provide insights into the noradrenergic basis of conflict generation, adaptation and stress resilience.

Locus coeruleus anchors a trisynaptic circuit controlling fear-induced suppression of feeding

The circuit mechanisms underlying fear-induced suppression of feeding are poorly understood. To help fill this gap, mice were fear conditioned, and the resulting changes in synaptic connectivity among the locus coeruleus (LC), the parabrachial nucleus (PBN), and the central nucleus of amygdala (CeA)-all of which are implicated in fear and feeding-were studied. LC neurons co-released noradrenaline and glutamate to excite PBN neurons and suppress feeding. LC neurons also suppressed inhibitory input to PBN neurons by inducing heterosynaptic, endocannabinoid-dependent, long-term depression of CeA synapses. Blocking or knocking down endocannabinoid receptors in CeA neurons prevented fear-induced depression of CeA synaptic transmission and fear-induced suppression of feeding. Altogether, these studies demonstrate that LC neurons play a pivotal role in modulating the circuitry that underlies fear-induced suppression of feeding, pointing to new ways of alleviating stress-induced eating disorders.

The role of glutamate transporter-1 in firing activity of locus coeruleus neurons and nociception in rats

Locus coeruleus (LC) is considered to be the main source of norepinephrine in the central nervous system (CNS) and plays important role in relieving pain in the body. Changes in the activity of synaptic excitatory amino acid transporters (EAATs) would be an applicable way to regulate synaptic transmission in the LC. In the present study, we examined the role of astrocytic glutamate transporter-1 (GLT1) in the firing activity of LC neurons and the sensation of pain in rats. Male Wistar rats were divided into three control (CNT), ceftriaxone (CFT) and dihydrokainic acid (DHK) groups. Animals were given intraperitoneal injections for nine consecutive days after which the electrophysiological and behavioral experiments were performed to determine the single-unit activity of LC neurons and pain sensation. Results of this study revealed that CFT as a well-known up-regulator of GLT1 expression decreases the latency of pain sensation in rats but inhibition of GLT1 activity by DHK showed no significant effects. Furthermore, the results obtained by single-unit recording from LC showed a significant decrease in evoked response in CFT group compared to the CNT group. Therefore, this study suggests that GLT1 might be considered as a potential therapeutic target for pain modulation in the future.

Autophagy status as a gateway for stress-induced catecholamine interplay in neurodegeneration

The catecholamine-containing brainstem nuclei locus coeruleus (LC) and ventral tegmental area (VTA) are critically involved in stress responses. Alterations of catecholamine systems during chronic stress may contribute to neurodegeneration, including cognitive decline. Stress-related catecholamine alterations, while contributing to anxiety and depression, might accelerate neuronal degeneration by increasing the formation of toxic dopamine and norepinephrine by-products. These, in turn, may impair proteostasis within a variety of cortical and subcortical areas. In particular, the molecular events governing neurotransmission, neuroplasticity, and proteostasis within LC and VTA affect a variety of brain areas. Therefore, we focus on alterations of autophagy machinery in these nuclei as a relevant trigger in this chain of events. In fact, these catecholamine-containing areas are mostly prone to autophagy-dependent neurodegeneration. Thus, we propose a dynamic hypothesis according to which stress-induced autophagy alterations within the LC-VTA network foster a cascade towards early neurodegeneration within these nuclei.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Sex and the noradrenergic system

The central noradrenergic system comprises multiple brainstem nuclei whose cells synthesize and release the catecholamine transmitter norepinephrine (NE). The largest of these nuclei is the pontine locus coeruleus (LC), which innervates the vast majority of the forebrain. NE interacts with a number of pre- and postsynaptically expressed G protein-coupled receptors to affect a wide array of functions, including sensory signal processing, waking and arousal, stress responsiveness, mood, attention, and memory. Given the myriad functions ascribed to the locus coeruleus-noradrenergic (LC-NE) system, it is unsurprising that it is implicated in many disease states, including various mood, cognitive, neuropsychiatric, and neurodegenerative diseases. The LC-NE system is also notably sexually dimorphic with regard to its morphologic and anatomical features as well as how it responds to the peptide transmitter corticotropin releasing hormone (CRH), a major mediator of the central stress response. The sex-biased morphology and signaling that is observed in the LC could then be considered a potential contributor to the differential prevalence of various diseases between men and women. This chapter summarizes the primary differences between the male and female LC, based primarily on preclinical observations and how these disparities may relate to differential diagnoses of several diseases between men and women.

Effect of intranasal administration of neuropeptide Y and single prolonged stress on food consumption and body weight in male rats

Emerging evidence indicates that intranasal delivery of neuropeptide Y (NPY) to the brain has therapeutic potential for management of stress-triggered neuropsychiatric disorders. Here we aimed to determine how intranasal administration of NPY, either before or immediately after, traumatic stress in single prolonged stress (SPS) rodent model of Post-traumatic stress disorder (PTSD) impacts food consumption and body weight. SPS stressors suppressed food consumption for at least two days in the vehicle-treated animals. When given prior to SPS stressors, intranasal NPY prevented the SPS-elicited reduction in food intake only for several hours afterwards. When given after the SPS stressors, under conditions shown to prevent behavioral and biochemical impairments, intranasal NPY had no effect on food intake. Although all groups showed circadian variation, the SPS-exposed rats ate less than unstressed animals during the dark (active) phase. Seven days after exposure to SPS stressors, there were no differences in food intake, although body weight was still lower than unstressed controls in all the experimental groups. Thus, traumatic stress has pronounced effect on food consumption during the rodent's active phase, and a prolonged effect on body weight. Single intranasal infusion of NPY, which was previously shown to prevent development of several PTSD associated behavioral and neuroendocrine impairments, did not elicit prolonged changes in stress triggered food consumption nor regulation of body weight.

Protagonist Role of Opioidergic System on Post-Traumatic Stress Disorder and Associated Pain

OBJECTIVE

Post-traumatic stress disorder (PTSD) and chronic pain often co-occur. Studies have shown an interaction between pain and PTSD. In this narrative review, we aim to support conducting comprehensive studies by describing PTSD, pain and determining whether opioidergic system, its agonist and antagonist manipulation could positively or negatively affect PTSD symptoms and concurrent pain.

METHODS

Term searches was done in Google Scholar, Scopus, ScienceDirect, Web of Science and PubMed databases as well as hand searching in key resource journals from 1979-2019.

RESULTS

There are a lot of contradictions and disputes when endogenous opioidergic system and opioidergic antagonist system are studied in PTSD patients. Exogenous morphine administration in PTSD patients can decrease the symptoms of PTSD but it doesn't have a pain reduction effect to an acceptable level. Beta-endorphin as an endogenous opioid is effective in pain reduction in the moment of events but after minutes to hours, the endorphins withdrawal syndrome leads to exaggerated intrusive thoughts and flashbacks of PTSD, which exacerbate the pain. It has also been shown that naloxone, as an opioidergic antagonist, can reduce or increase the PTSD symptoms and its associated pain.

CONCLUSION

Data suggest different roles of opioidergic system and their antagonist in pain control and mood in PTSD. However, further investigations need to be done in order to reveal the role of endogenous opioidergic system and opioidergic antagonist system as a mediator in PTSD patients suffering from acute or chronic pain.

Antidepressant-Like Effect of Terpineol in an Inflammatory Model of Depression: Involvement of the Cannabinoid System and D2 Dopamine Receptor

Depression has a multifactorial etiology that arises from environmental, psychological, genetic, and biological factors. Environmental stress and genetic factors acting through immunological and endocrine responses generate structural and functional changes in the brain, inducing neurogenesis and neurotransmission dysfunction. Terpineol, monoterpenoid alcohol, has shown immunomodulatory and neuroprotective effects, but there is no report about its antidepressant potential. Herein, we used a single lipopolysaccharide (LPS) injection to induce a depressive-like effect in the tail suspension test (TST) and the splash test (ST) for a preventive and therapeutic experimental schedule. Furthermore, we investigated the antidepressant-like mechanism of action of terpineol while using molecular and pharmacological approaches. Terpineol showed a coherent predicted binding mode mainly against CB1 and CB2 receptors and also against the D2 receptor during docking modeling analyses. The acute administration of terpineol produced the antidepressant-like effect, since it significantly reduced the immobility time in TST (100-200 mg/kg, p.o.) as compared to the control group. Moreover, terpineol showed an antidepressant-like effect in the preventive treatment that was blocked by a nonselective dopaminergic receptor antagonist (haloperidol), a selective dopamine D2 receptor antagonist (sulpiride), a selective CB1 cannabinoid receptor antagonist/inverse agonist (AM281), and a potent and selective CB2 cannabinoid receptor inverse agonist (AM630), but it was not blocked by a nonselective adenosine receptor antagonist (caffeine) or a β-adrenoceptor antagonist (propranolol). In summary, molecular docking suggests that CB1 and CB2 receptors are the most promising targets of terpineol action. Our data showed terpineol antidepressant-like modulation by CB1 and CB2 cannabinoid receptors and D2-dopaminergic receptors to further corroborate our molecular evidence.

Impaired Phasic Discharge of Locus Coeruleus Neurons Based on Persistent High Tonic Discharge-A New Hypothesis With Potential Implications for Neurodegenerative Diseases

The locus coeruleus (LC) is a small brainstem nucleus with widely distributed noradrenergic projections to the whole brain, and loss of LC neurons is a prominent feature of age-related neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). This article discusses the hypothesis that in early stages of neurodegenerative diseases, the discharge mode of LC neurons could be changed to a persistent high tonic discharge, which in turn might impair phasic discharge. Since phasic discharge of LC neurons is required for the release of high amounts of norepinephrine (NE) in the brain to promote anti-inflammatory and neuroprotective effects, persistent high tonic discharge of LC neurons could be a key factor in the progression of neurodegenerative diseases. Transcutaneous vagal stimulation (t-VNS), a non-invasive technique that potentially increases phasic discharge of LC neurons, could therefore provide a non-pharmacological treatment approach in specific disease stages. This article focuses on LC vulnerability in neurodegenerative diseases, discusses the hypothesis that a persistent high tonic discharge of LC neurons might affect neurodegenerative processes, and finally reflects on t-VNS as a potentially useful clinical tool in specific stages of AD and PD.

Autophagy-Based Hypothesis on the Role of Brain Catecholamine Response During Stress

Stressful events, similar to abused drugs, significantly affect the homeostatic balance of the catecholamine brain systems while activating compensation mechanisms to restore balance. In detail, norepinephrine (NE)- and dopamine (DA)-containing neurons within the locus coeruleus (LC) and ventral tegmental area (VTA), are readily and similarly activated by psychostimulants and stressful events involving neural processes related to perception, reward, cognitive evaluation, appraisal, and stress-dependent hormonal factors. Brain catecholamine response to stress results in time-dependent regulatory processes involving mesocorticolimbic circuits and networks, where LC-NE neurons respond more readily than VTA-DA neurons. LC-NE projections are dominant in controlling the forebrain DA-targeted areas, such as the nucleus accumbens (NAc) and medial pre-frontal cortex (mPFC). Heavy and persistent coping demand could lead to sustained LC-NE and VTA-DA neuronal activity, that, when persisting chronically, is supposed to alter LC-VTA synaptic connections. Increasing evidence has been provided indicating a role of autophagy in modulating DA neurotransmission and synaptic plasticity. This alters behavior, and emotional/cognitive experience in response to drug abuse and occasionally, to psychological stress. Thus, relevant information to address the role of stress and autophagy can be drawn from psychostimulants research. In the present mini-review we discuss the role of autophagy in brain catecholamine response to stress and its dysregulation. The findings here discussed suggest a crucial role of regulated autophagy in the response and adaptation of LC-NE and VTA-DA systems to stress.

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

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

Locus coeruleus-CA1 projections are involved in chronic depressive stress-induced hippocampal vulnerability to transient global ischaemia

Depression and transient ischaemic attack represent the common psychological and neurological diseases, respectively, and are tightly associated. However, studies of depression-affected ischaemic attack have been limited to epidemiological evidences, and the neural circuits underlying depression-modulated ischaemic injury remain unknown. Here, we find that chronic social defeat stress (CSDS) and chronic footshock stress (CFS) exacerbate CA1 neuron loss and spatial learning/memory impairment after a short transient global ischaemia (TGI) attack in mice. Whole-brain mapping of direct outputs of locus coeruleus (LC)-tyrosine hydroxylase (TH, Th:) positive neurons reveals that LC-CA1 projections are decreased in CSDS or CFS mice. Furthermore, using designer receptors exclusively activated by designer drugs (DREADDs)-based chemogenetic tools, we determine that Th:LC-CA1 circuit is necessary and sufficient for depression-induced aggravated outcomes of TGI. Collectively, we suggest that Th:LC-CA1 pathway plays a crucial role in depression-induced TGI vulnerability and offers a potential intervention for preventing depression-related transient ischaemic attack.

The effects of trauma on brain and body: A unifying role for the midbrain periaqueductal gray

Post-traumatic stress disorder (PTSD), a diagnosis that may follow the experience of trauma, has multiple symptomatic phenotypes. Generally, individuals with PTSD display symptoms of hyperarousal and of hyperemotionality in the presence of fearful stimuli. A subset of individuals with PTSD; however, elicit dissociative symptomatology (i.e., depersonalization, derealization) in the wake of a perceived threat. This pattern of response characterizes the dissociative subtype of the disorder, which is often associated with emotional numbing and hypoarousal. Both symptomatic phenotypes exhibit attentional threat biases, where threat stimuli are processed preferentially leading to a hypervigilant state that is thought to promote defensive behaviors during threat processing. Accordingly, PTSD and its dissociative subtype are thought to differ in their proclivity to elicit active (i.e., fight, flight) versus passive (i.e., tonic immobility, emotional shutdown) defensive responses, which are characterized by the increased and the decreased expression of the sympathetic nervous system, respectively. Moreover, active and passive defenses are accompanied by primarily endocannabinoid- and opioid-mediated analgesics, respectively. Through critical review of the literature, we apply the defense cascade model to better understand the pathological presentation of defensive responses in PTSD with a focus on the functioning of lower-level midbrain and extended brainstem systems.

Neuroendocrine Regulation of Brain Cytokines After Psychological Stress

There is growing evidence that stress-induced brain cytokines are important in the etiology of depression and anxiety. Here, we review how the neuroendocrine responses to psychological stressors affect the immediate and long-term regulation of inflammatory cytokines within the brain and highlight how the regulation changes across time with repeated stress exposure. In doing so, we report on the percentage of studies in the literature that observed increases in either IL-1β, TNF-α, or IL-6 within the hypothalamus, hippocampus, or prefrontal cortex after either acute or chronic stress exposure. The key takeaway is that catecholamines and glucocorticoids play critical roles in the regulation of brain cytokines after psychological stress exposure. Central catecholamines stimulate the release of IL-1β from microglia, which is a key factor in the further activation of microglia and recruitment of monocytes into the brain. Meanwhile, the acute elevation of glucocorticoids inhibits the production of brain cytokines via two mechanisms: the suppression of noradrenergic locus coeruleus neurons and inhibition of the NFκB signaling pathway. However, glucocorticoids and peripheral catecholamines facilitate inflammatory responses to future stimuli by stimulating monocytes to leave the bone marrow, downregulating inhibitory receptors on microglia, and priming inflammatory responses mediated by peripheral monocytes or macrophages. The activation of microglia and the elevation of peripheral glucocorticoid and catecholamine levels are both necessary during times of stress exposure for the development of psychopathologies.

Current understanding of fear learning and memory in humans and animal models and the value of a linguistic approach for analyzing fear learning and memory in humans

Fear is an emotion that serves as a driving factor in how organisms move through the world. In this review, we discuss the current understandings of the subjective experience of fear and the related biological processes involved in fear learning and memory. We first provide an overview of fear learning and memory in humans and animal models, encompassing the neurocircuitry and molecular mechanisms, the influence of genetic and environmental factors, and how fear learning paradigms have contributed to treatments for fear-related disorders, such as posttraumatic stress disorder. Current treatments as well as novel strategies, such as targeting the perisynaptic environment and use of virtual reality, are addressed. We review research on the subjective experience of fear and the role of autobiographical memory in fear-related disorders. We also discuss the gaps in our understanding of fear learning and memory, and the degree of consensus in the field. Lastly, the development of linguistic tools for assessments and treatment of fear learning and memory disorders is discussed.

Single Prolonged Stress as a Prospective Model for Posttraumatic Stress Disorder in Females

Sex plays an important role in susceptibility to stress triggered disorders. Posttraumatic Stress disorder (PTSD), a debilitating psychiatric disorder developed after exposure to a traumatic event, is two times more prevalent in women than men. However, the vast majority of animal models of PTSD, including single prolonged stress (SPS), were performed mostly with males. Here, we evaluated SPS as an appropriate PTSD model for females in terms of anxiety, depressive symptoms and changes in gene expression in the noradrenergic system in the brain. In addition, we examined intranasal neuropeptide Y (NPY) as a possible treatment in females. Female rats were subjected to SPS and given either intranasal NPY or vehicle in two separate experiments. In the first experiment, stressed females were compared to unstressed controls on forced swim test (FST) and for levels of expression of several genes in the locus coeruleus (LC) 12 days after SPS exposure. Using a separate cohort of animals, experiment two examined stressed females and unstressed controls on the elevated plus maze (EPM) and LC gene expression 7 days after SPS stressors. SPS led to increased anxiety-like behavior on EPM and depressive-like behavior on FST. Following FST, the rats displayed elevated tyrosine hydroxylase (TH), CRHR1 and Y1R mRNA levels in the LC, consistent with increased activation of the noradrenergic system. The expression level of these mRNAs was unchanged following EPM, except Y1R. Intranasal NPY at the doses shown to be effective in males, did not prevent development of depressive or anxiety-like behavior or molecular changes in the LC. The results indicate that while SPS could be an appropriate PTSD model for females, sex differences, such as response to NPY, are important to consider.

Recent advances in the neurobiology of posttraumatic stress disorder: A review of possible mechanisms underlying an effective pharmacotherapy

Recent progress in the field of neurobiology supported by clinical evidence gradually reveals the mystery of human brain functioning. So far, many psychiatric disorders have been described in great detail, although there are still plenty of cases that are misunderstood. These include posttraumatic stress disorder (PTSD), which is a unique disease that combines a wide range of neurobiological changes, which involve disturbances of the hypothalamic-pituitary-adrenal gland axis, hyperactivation of the amygdala complex, and attenuation of some hippocampal and cortical functions. Such multiplicity results in differential symptomatology, including elevated anxiety, nightmares, fear retrieval episodes that may trigger delusions and hallucinations, sleep disturbances, and many others that strongly interfere with the quality of the patient's life. Because of widespread neurological changes and the disease manifestation, the pharmacotherapy of PTSD remains unclear and requires a multidimensional approach and involvement of polypharmacotherapy. Hopefully, more and more neuroscientists and clinicians will study PTSD, which will provide us with new information that would possibly accelerate establishment of well-tolerated and effective pharmacotherapy. In this review, we have focused on neurobiological changes regarding PTSD, addressing the most disturbed brain structures and neurotransmissions, as well as discussing in detail the recently taken and novel therapeutic paths.

Back to the Basics: Resting State Functional Connectivity of the Reticular Activation System in PTSD and its Dissociative Subtype

BACKGROUND

Brainstem and midbrain neuronal circuits that control innate, reflexive responses and arousal are increasingly recognized as central to the neurobiological framework of post-traumatic stress disorder (PTSD). The reticular activation system represents a fundamental neuronal circuit that plays a critical role not only in generating arousal but also in coordinating innate, reflexive responding. Accordingly, the present investigation aims to characterize the resting state functional connectivity of the reticular activation system in PTSD and its dissociative subtype.

METHODS

We investigated patterns of resting state functional connectivity of a central node of the reticular activation system, namely, the pedunculopontine nuclei, among individuals with PTSD (n = 77), its dissociative subtype (PTSD+DS; n = 48), and healthy controls (n = 51).

RESULTS

Participants with PTSD and PTSD+DS were characterized by within-group pedunculopontine nuclei resting state functional connectivity to brain regions involved in innate threat processing and arousal modulation (i.e., midbrain, amygdala, ventromedial prefrontal cortex). Critically, this pattern was most pronounced in individuals with PTSD+DS, as compared to both control and PTSD groups. As compared to participants with PTSD and controls, individuals with PTSD+DS showed enhanced pedunculopontine nuclei resting state functional connectivity to the amygdala and the parahippocampal gyrus as well as to the anterior cingulate and the ventromedial prefrontal cortex. No group differences emerged between PTSD and control groups. In individuals with PTSD+DS, state derealization/depersonalization was associated with reduced resting state functional connectivity between the left pedunculopontine nuclei and the anterior nucleus of the thalamus. Altered connectivity in these regions may restrict the thalamo-cortical transmission necessary to integrate internal and external signals at a cortical level and underlie, in part, experiences of depersonalization and derealization.

CONCLUSIONS

The present findings extend the current neurobiological model of PTSD and provide emerging evidence for the need to incorporate brainstem structures, including the reticular activation system, into current conceptualizations of PTSD and its dissociative subtype.

Age-related accumulation of toxic metals in the human locus ceruleus

Damage to the locus ceruleus has been implicated in the pathogenesis of a number of neurological conditions. Locus ceruleus neurons accumulate toxic metals such as mercury selectively, however, the presence of toxic metals in locus ceruleus neurons of people of different ages, and with a variety of disorders, is not known. To demonstrate at what age toxic metals are first detectable in the locus ceruleus, and to evaluate whether their presence is more common in certain clinicopathological conditions, we looked for these metals in 228 locus ceruleus samples. Samples were taken at coronial autopsies from individuals with a wide range of ages, pre-existing conditions and causes of death. Paraffin sections of pons containing the locus ceruleus were stained with silver nitrate autometallography, which indicates inorganic mercury, silver and bismuth within cells (termed autometallography-detected toxic metals, or AMG™). No locus ceruleus AMG neurons were seen in 38 individuals aged under 20 years. 47% of the 190 adults (ie, aged 20 years and over) had AMG locus ceruleus neurons. The proportion of adults with locus ceruleus AMG neurons increased during aging, except for a decreased proportion in the 90-plus years age group. No differences were found in the proportions of locus ceruleus AMG neurons between groups with different neurological, psychiatric, or other clinicopathological conditions, or among various causes of death. Elemental analysis with laser ablation-inductively coupled plasma-mass spectrometry was used to cross-validate the metals detected by AMG, by looking for silver, gold, bismuth, cadmium, chromium, iron, mercury, nickel, and lead in the locus ceruleus of ten individuals. This confirmed the presence of mercury in locus ceruleus samples containing AMG neurons, and showed cadmium, silver, lead, iron, and nickel in the locus ceruleus of some individuals. In conclusion, toxic metals stained by AMG (most likely inorganic mercury) appear in locus ceruleus neurons in early adult life. About half of adults in this study had locus ceruleus neurons containing inorganic mercury, and elemental analysis found a range of other toxic metals in the locus ceruleus. Locus ceruleus inorganic mercury increased during aging, except for a decrease in advanced age, but was not found more often in any single clinicopathological condition or cause of death.

Traumatic Stress Produces Distinct Activations of GABAergic and Glutamatergic Neurons in Amygdala

Posttraumatic stress disorder (PTSD) is an anxiety disorder characterized by intrusive recollections of a severe traumatic event and hyperarousal following exposure to the event. Human and animal studies have shown that the change of amygdala activity after traumatic stress may contribute to occurrences of some symptoms or behaviors of the patients or animals with PTSD. However, it is still unknown how the neuronal activation of different sub-regions in amygdala changes during the development of PTSD. In the present study, we used single prolonged stress (SPS) procedure to obtain the animal model of PTSD, and found that 1 day after SPS, there were normal anxiety behavior and extinction of fear memory in rats which were accompanied by a reduced proportion of activated glutamatergic neurons and increased proportion of activated GABAergic neurons in basolateral amygdala (BLA). About 10 days after SPS, we observed enhanced anxiety and impaired extinction of fear memory with increased activated both glutamatergic and GABAergic neurons in BLA and increased activated GABAergic neurons in central amygdala (CeA). These results indicate that during early and late phase after traumatic stress, distinct patterns of activation of glutamatergic neurons and GABAergic neurons are displayed in amygdala, which may be implicated in the development of PTSD.

A Comprehensive Overview on Stress Neurobiology: Basic Concepts and Clinical Implications

Stress is recognized as an important issue in basic and clinical neuroscience research, based upon the founding historical studies by Walter Canon and Hans Selye in the past century, when the concept of stress emerged in a biological and adaptive perspective. A lot of research after that period has expanded the knowledge in the stress field. Since then, it was discovered that the response to stressful stimuli is elaborated and triggered by the, now known, stress system, which integrates a wide diversity of brain structures that, collectively, are able to detect events and interpret them as real or potential threats. However, different types of stressors engage different brain networks, requiring a fine-tuned functional neuroanatomical processing. This integration of information from the stressor itself may result in a rapid activation of the Sympathetic-Adreno-Medullar (SAM) axis and the Hypothalamus-Pituitary-Adrenal (HPA) axis, the two major components involved in the stress response. The complexity of the stress response is not restricted to neuroanatomy or to SAM and HPA axes mediators, but also diverge according to timing and duration of stressor exposure, as well as its short- and/or long-term consequences. The identification of neuronal circuits of stress, as well as their interaction with mediator molecules over time is critical, not only for understanding the physiological stress responses, but also to understand their implications on mental health.

Persistent Stress-Induced Neuroplastic Changes in the Locus Coeruleus/Norepinephrine System

Neural plasticity plays a critical role in mediating short- and long-term brain responses to environmental stimuli. A major effector of plasticity throughout many regions of the brain is stress. Activation of the locus coeruleus (LC) is a critical step in mediating the neuroendocrine and behavioral limbs of the stress response. During stressor exposure, activation of the hypothalamic-pituitary-adrenal axis promotes release of corticotropin-releasing factor in LC, where its signaling promotes a number of physiological and cellular changes. While the acute effects of stress on LC physiology have been described, its long-term effects are less clear. This review will describe how stress changes LC neuronal physiology, function, and morphology from a genetic, cellular, and neuronal circuitry/transmission perspective. Specifically, we describe morphological changes of LC neurons in response to stressful stimuli and signal transduction pathways underlying them. Also, we will review changes in excitatory glutamatergic synaptic transmission in LC neurons and possible stress-induced modifications of AMPA receptors. This review will also address stress-related behavioral adaptations and specific noradrenergic receptors responsible for them. Finally, we summarize the results of several human studies which suggest a link between stress, altered LC function, and pathogenesis of posttraumatic stress disorder.

Vagally mediated gastric effects of brain stem α2-adrenoceptor activation in stressed rats

Chronic stress exerts vagally dependent effects to disrupt gastric motility; previous studies have shown that, among other nuclei, A2 neurons are involved in mediating these effects. Several studies have also shown robust in vitro and in vivo effects of α2-adrenoceptor agonists on vagal motoneurons. We have demonstrated previously that brainstem vagal neurocircuits undergo remodeling following acute stress; however, the effects following brief periods of chronic stress have not been investigated. Our aim, therefore, was to test the hypothesis that different types of chronic stress influence gastric tone and motility by inducing plasticity in the response of vagal neurocircuits to α2-adrenoreceptor agonists. In rats that underwent 5 days of either homotypic or heterotypic stress loading, we applied the α2-adrenoceptor agonist, UK14304, either by in vitro brainstem perfusion to examine its ability to modulate GABAergic synaptic inputs to vagal motoneurons or in vivo brainstem microinjection to observe actions to modulate antral tone and motility. In neurons from naïve rats, GABAergic currents were unresponsive to exogenous application of UK14304. In contrast, GABAergic currents were inhibited by UK14304 in all neurons from homotypic and, in a subpopulation of neurons, heterotypic stressed rats. In control rats, UK14304 microinjection inhibited gastric tone and motility via withdrawal of vagal cholinergic tone; in heterotypic stressed rats, the larger inhibition of antrum tone was due to a concomitant activation of peripheral nonadrenergic, noncholinergic pathways. These data suggest that stress induces plasticity in brainstem vagal neurocircuits, leading to an upregulation of α2-mediated responses. NEW & NOTEWORTHY Catecholaminergic neurons of the A2 area play a relevant role in stress-related dysfunction of the gastric antrum. Brief periods of chronic stress load induce plastic changes in the actions of adrenoceptors on vagal brainstem neurocircuits.

Noradrenergic Modulation of Fear Conditioning and Extinction

The locus coeruleus norepinephrine (LC-NE) system plays a broad role in learning and memory. Here we begin with an overview of the LC-NE system. We then consider how both direct and indirect manipulations of the LC-NE system affect cued and contextual aversive learning and memory. We propose that NE dynamically modulates Pavlovian conditioning and extinction, either promoting or impairing learning aversive processes under different levels of behavioral arousal. We suggest that under high levels of stress (e.g., during/soon after fear conditioning) the locus coeruleus (LC) promotes cued fear learning by enhancing amygdala function while simultaneously blunting prefrontal function. Under low levels of arousal, the LC promotes PFC function to promote downstream inhibition of the amygdala and foster the extinction of cued fear. Thus, LC-NE action on the medial prefrontal cortex (mPFC) might be described by an inverted-U function such that it can either enhance or hinder learning depending on arousal states. In addition, LC-NE seems to be particularly important for the acquisition, consolidation and extinction of contextual fear memories. This may be due to dense adrenoceptor expression in the hippocampus (HPC) which encodes contextual information, and the ability of NE to regulate long-term potentiation (LTP). Moreover, recent work reveals that the diversity of LC-NE functions in aversive learning and memory are mediated by functionally heterogeneous populations of LC neurons that are defined by their projection targets. Hence, LC-NE function in learning and memory is determined by projection-specific neuromodulation that accompanies various states of behavioral arousal.

Oleuropein reduces anxiety-like responses by activating of serotonergic and neuropeptide Y (NPY)-ergic systems in a rat model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a stress-related mental disorder caused by traumatic experiences. This psychopathological response to traumatic stressors induces anxiety in rats. Oleuropein (OLE), a major compound in olive leaves, reportedly possesses several pharmacological properties, including anti-cancer, anti-diabetic, and anti-atherosclerotic and neuropsychiatric activities. However, the anxiolytic-like effects of OLE and its mechanism of action in PTSD are unclear. The present study used several behavioral tests to examine the effects of OLE on symptoms of anxiety in rats after a single prolonged stress (SPS) exposure by inhibiting the hypothalamic-pituitary-adrenal axis. Male Sprague Dawley rats received OLE (10, 50 and 70 mg/kg, i.p., once daily) for 14 days after SPS exposure. Daily OLE (70 mg/kg) administration significantly increased the number and duration of open arm visits in the elevated plus maze (EPM) test, reduced the anxiety index and grooming behavior in the EPM test, and increased the time spent and number of central zone crossings in the open field test. OLE also blocked the SPS-induced decrease in hippocampal serotonin and neuropeptide Y expression in hippocampus. These findings suggest that OLE has anxiolytic-like effects on behavioral and biochemical symptoms similar to those observed in patients with PTSD.

Locus Coeruleus Activity Mediates Hyperresponsiveness in Posttraumatic Stress Disorder

BACKGROUND

Patients with posttraumatic stress disorder (PTSD) are hyperresponsive to unexpected or potentially threatening environmental stimuli. Research in lower animals and humans suggests that sensitization of the locus coeruleus-norepinephrine system may underlie behavioral and autonomic hyperresponsiveness in PTSD. However, direct evidence linking locus coeruleus system hyperactivity to PTSD hyperresponsiveness is sparse.

METHODS

Psychophysiological recording and functional magnetic resonance imaging were used during passive listening to brief, 95-dB sound pressure level, white noise bursts presented intermittently to determine whether behavioral and autonomic hyperresponsiveness to sudden sounds in PTSD is associated with locus coeruleus hyperresponsiveness.

RESULTS

Participants with PTSD (n = 28) showed more eye-blink reflexes and larger heart rate, skin conductance, and pupil area responses to loud sounds (multivariate p = .007) compared with trauma-exposed participants without PTSD (n = 26). PTSD participants exhibited larger responses in locus coeruleus (t = 2.60, region of interest familywise error corrected), intraparietal sulcus, caudal dorsal premotor cortex, and cerebellar lobule VI (t ≥ 4.18, whole-brain familywise error corrected). Caudal dorsal premotor cortex activity was associated with both psychophysiological response magnitude and levels of exaggerated startle responses in daily life in PTSD participants (t ≥ 4.39, whole-brain familywise error corrected).

CONCLUSIONS

Behavioral and autonomic hyperresponsiveness in PTSD may arise from a hyperactive alerting/orienting system in which processes related to attention and motor preparation localized to lateral premotor cortex, intraparietal sulcus, and posterior superior cerebellar cortex are modulated by atypically high phasic noradrenergic influences originating in the locus coeruleus.

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

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

Molecular mechanism of noradrenaline during the stress-induced major depressive disorder

Chronic stress-induced depression is a common hallmark of many psychiatric disorders with high morbidity rate. Stress-induced dysregulation of noradrenergic system has been implicated in the pathogenesis of depression. Lack of monoamine in the brain has been believed to be the main causative factor behind pathophysiology of major depressive disorder (MDD) and several antidepressants functions by increasing the monoamine level at the synapses in the brain. However, it is undetermined whether the noradrenergic receptor stimulation is critical for the therapeutic effect of antidepressant. Contrary to noradrenergic receptor stimulation, it has been suggested that the desensitization of β-adrenoceptor is involved in the therapeutic effect of antidepressant. In addition, enhanced noradrenaline (NA) release is central response to stress and thought to be a risk factor for the development of MDD. Moreover, fast acting antidepressant suppresses the hyperactivation of noradrenergic neurons in locus coeruleus (LC). However, it is unclear how they alter the firing activity of LC neurons. These inconsistent reports about antidepressant effect of NA-reuptake inhibitors (NRIs) and enhanced release of NA as a stress response complicate our understanding about the pathophysiology of MDD. In this review, we will discuss the role of NA in pathophysiology of stress and the mechanism of therapeutic effect of NA in MDD. We will also discuss the possible contributions of each subtype of noradrenergic receptors on LC neurons, hypothalamic-pituitary-adrenal axis (HPA-axis) and brain derived neurotrophic factor-induced hippocampal neurogenesis during stress and therapeutic effect of NRIs in MDD.

Dysregulation of aversive signaling pathways: a novel circuit endophenotype for pain and anxiety disorders

Aversive experiences activate dedicated neural instructive pathways which trigger memory formation and change behavior. The strength of these aversive memories and the degree to which they alter behavior is proportional to the intensity of the aversive experience. Dysregulation of aversive learning circuits can lead to psychiatric pathology. Here we review recent findings elucidating aversive instructive signaling circuits for fear conditioning. We then examine how chronic pain as well as stress and anxiety disrupt these circuits and the implications this has for understanding and treating psychiatric disease. Together this review synthesizes current work on aversive instructive signaling circuits in health and disease and suggests a novel circuit based framework for understanding pain and anxiety syndromes.

Neural indicators of interpersonal anger as cause and consequence of combat training stress symptoms

BACKGROUND

Angry outbursts are an important feature of various stress-related disorders, and commonly lead to aggression towards other people. Findings regarding interpersonal anger have linked the ventromedial prefrontal cortex (vmPFC) to anger regulation and the locus coeruleus (LC) to aggression. Both regions were previously associated with traumatic and chronic stress symptoms, yet it is unclear if their functionality represents a consequence of, or possibly also a cause for, stress symptoms. Here we investigated the relationship between the neural trajectory of these indicators of anger and the development and manifestation of stress symptoms.

METHOD

A total of 46 males (29 soldiers, 17 civilians) participated in a prospective functional magnetic resonance imaging experiment in which they played a modified interpersonal anger-provoking Ultimatum Game (UG) at two-points. Soldiers were tested at the beginning and end of combat training, while civilians were tested at the beginning and end of civil service. We assumed that combat training would induce chronic stress and result in increased stress symptoms.

RESULTS

Soldiers showed an increase in stress symptoms following combat training while civilians showed no such change following civil service. All participants were angered by the modified UG irrespective of time point. Higher post-combat training stress symptoms were associated with lower pre-combat training vmPFC activation and with higher activation increase in the LC between pre- and post-combat training.

CONCLUSIONS

Results suggest that during anger-provoking social interactions, flawed vmPFC functionality may serve as a causal risk factor for the development of stress symptoms, and heightened reactivity of the LC possibly reflects a consequence of stress-inducing combat training. These findings provide potential neural targets for therapeutic intervention and inoculation for stress-related psychopathological manifestations of anger.

Altered miRNA expression network in locus coeruleus of depressed suicide subjects

Norepinephrine (NE) is produced primarily by neurons in the locus coeruleus (LC). Retrograde and ultrastructural examinations reveal that the core of the LC and its surrounding region receives afferent projections from several brain areas which provide multiple neurochemical inputs to the LC with changes in LC neuronal firing, making it a highly coordinated event. Although NE and mediated signaling systems have been studied in relation to suicide and psychiatric disorders that increase the risk of suicide including depression, less is known about the corresponding changes in molecular network within LC. In this study, we examined miRNA networks in the LC of depressed suicide completers and healthy controls. Expression array revealed differential regulation of 13 miRNAs. Interaction between altered miRNAs and target genes showed dense interconnected molecular network. Functional clustering of predicated target genes yielded stress induced disorders that collectively showed the complex nature of suicidal behavior. In addition, 25 miRNAs were pairwise correlated specifically in the depressed suicide group, but not in the control group. Altogether, our study revealed for the first time the involvement of LC based dysregulated miRNA network in disrupting cellular pathways associated with suicidal behavior.

Loud Noise Exposure Produces DNA, Neurotransmitter and Morphological Damage within Specific Brain Areas

Exposure to loud noise is a major environmental threat to public health. Loud noise exposure, apart from affecting the inner ear, is deleterious for cardiovascular, endocrine and nervous systems and it is associated with neuropsychiatric disorders. In this study we investigated DNA, neurotransmitters and immune-histochemical alterations induced by exposure to loud noise in three major brain areas (cerebellum, hippocampus, striatum) of Wistar rats. Rats were exposed to loud noise (100 dBA) for 12 h. The effects of noise on DNA integrity in all three brain areas were evaluated by using Comet assay. In parallel studies, brain monoamine levels and morphology of nigrostriatal pathways, hippocampus and cerebellum were analyzed at different time intervals (24 h and 7 days) after noise exposure. Loud noise produced a sudden increase in DNA damage in all the brain areas under investigation. Monoamine levels detected at 7 days following exposure were differently affected depending on the specific brain area. Namely, striatal but not hippocampal dopamine (DA) significantly decreased, whereas hippocampal and cerebellar noradrenaline (NA) was significantly reduced. This is in line with pathological findings within striatum and hippocampus consisting of a decrease in striatal tyrosine hydroxylase (TH) combined with increased Bax and glial fibrillary acidic protein (GFAP). Loud noise exposure lasting 12 h causes immediate DNA, and long-lasting neurotransmitter and immune-histochemical alterations within specific brain areas of the rat. These alterations may suggest an anatomical and functional link to explain the neurobiology of diseases which prevail in human subjects exposed to environmental noise.

Activation of Extracellular Signal-Regulated Kinases (ERK 1/2) in the Locus Coeruleus Contributes to Pain-Related Anxiety in Arthritic Male Rats

BACKGROUND

There is increasing evidence suggesting that the Locus Coeruleus plays a role in pain-related anxiety. Indeed, we previously found that prolonged arthritis produces anxiety-like behavior in rats, along with enhanced expression of phosphorylated extracellular signal-regulated kinase 1/2 (a marker of plasticity) in the Locus Coeruleus. However, it is unknown how this effect correlates with the electrophysiological activity of Locus Coeruleus neurons or pain-related anxiety.

METHODS

Using the complete Freund's adjuvant model of monoarthritis in male Sprague-Dawley rats, we studied the behavioral attributes of pain and anxiety as well as Locus Coeruleus electrophysiology in vivo 1 (MA1W) and 4 weeks (MA4W) after disease induction.

RESULTS

The manifestation of anxiety in MA4W was accompanied by dampened tonic Locus Coeruleus activity, which was coupled to an exacerbated evoked Locus Coeruleus response to noxious stimulation of the inflamed and healthy paw. When a mitogen-activating extracellular kinase inhibitor was administered to the contralateral Locus Coeruleus of MA4W, the phosphorylated extracellular signal-regulated kinase 1/2 levels in the Locus Coeruleus were restored and the exaggerated evoked response was blocked, reversing the anxiogenic-like behavior while pain hypersensitivity remained unaltered.

CONCLUSION

As phosphorylated extracellular signal-regulated kinase 1/2 blockade in the Locus Coeruleus relieved anxiety and counteracted altered LC function, we propose that phosphorylated extracellular signal-regulated kinase 1/2 activation in the Locus Coeruleus plays a crucial role in pain-related anxiety.

Post-Traumatic Stress Disorder: The Relationship Between the Fear Response and Chronic Stress

Post-traumatic stress disorder (PTSD) is a disabling psychiatric condition that can develop following a physical, psychological, or sexual trauma. Despite the growing body of literature examining the psychological and biological factors involved in PTSD psychopathology, specific biomarkers that may improve diagnosis and treatment of PTSD have yet to be identified and validated. This challenge may be attributed to the diverse array of symptoms that individuals with the disorder manifest. Examining the interrelated stress and fear systems allows for a more comprehensive study of these symptoms, and through this approach, which aligns with the research domain criteria (RDoC) framework, neural and psychophysiological measures of PTSD have emerged. In this review, we discuss PTSD neurobiology and treatment within the context of fear and stress network interactions and elucidate the advantages of using an RDoC approach to better understand PTSD with fear conditioning and extinction paradigms.

Parametric characterization of neural activity in the locus coeruleus in response to vagus nerve stimulation

Vagus nerve stimulation (VNS) has emerged as a therapy to treat a wide range of neurological disorders, including epilepsy, depression, stroke, and tinnitus. Activation of neurons in the locus coeruleus (LC) is believed to mediate many of the effects of VNS in the central nervous system. Despite the importance of the LC, there is a dearth of direct evidence characterizing neural activity in response to VNS. A detailed understanding of the brain activity evoked by VNS across a range of stimulation parameters may guide selection of stimulation regimens for therapeutic use. In this study, we recorded neural activity in the LC and the mesencephalic trigeminal nucleus (Me5) in response to VNS over a broad range of current amplitudes, pulse frequencies, train durations, inter-train intervals, and pulse widths. Brief 0.5s trains of VNS drive rapid, phasic firing of LC neurons at 0.1mA. Higher current intensities and longer pulse widths drive greater increases in LC firing rate. Varying the pulse frequency substantially affects the timing, but not the total amount, of phasic LC activity. VNS drives pulse-locked neural activity in the Me5 at current levels above 1.2mA. These results provide insight into VNS-evoked phasic neural activity in multiple neural structures and may be useful in guiding the selection of VNS parameters to enhance clinical efficacy.

fMRI functional connectivity of the periaqueductal gray in PTSD and its dissociative subtype

BACKGROUND

Posttraumatic stress disorder (PTSD) is associated with hyperarousal and active fight or flight defensive responses. By contrast, the dissociative subtype of PTSD, characterized by depersonalization and derealization symptoms, is frequently accompanied by additional passive or submissive defensive responses associated with autonomic blunting. Here, the periaqueductal gray (PAG) plays a central role in defensive responses, where the dorsolateral (DL-PAG) and ventrolateral PAG (VL-PAG) are thought to mediate active and passive defensive responses, respectively.

METHODS

We examined PAG subregion (dorsolateral and ventrolateral) resting-state functional connectivity in three groups: PTSD patients without the dissociative subtype (n = 60); PTSD patients with the dissociative subtype (n = 37); and healthy controls (n = 40) using a seed-based approach via PickAtlas and SPM12.

RESULTS

All PTSD patients showed extensive DL- and VL-PAG functional connectivity at rest with areas associated with emotional reactivity and defensive action as compared to controls (n = 40). Although all PTSD patients demonstrated DL-PAG functional connectivity with areas associated with initiation of active coping strategies and hyperarousal (e.g., dorsal anterior cingulate; anterior insula), only dissociative PTSD patients exhibited greater VL-PAG functional connectivity with brain regions linked to passive coping strategies and increased levels of depersonalization (e.g., temporoparietal junction; rolandic operculum).

CONCLUSIONS

These findings suggest greater defensive posturing in PTSD patients even at rest and demonstrate that those with the dissociative subtype show unique patterns of PAG functional connectivity when compared to those without the subtype. Taken together, these findings represent an important first step toward identifying neural and behavioral targets for therapeutic interventions that address defensive strategies in trauma-related disorders.

Neural circuits via which single prolonged stress exposure leads to fear extinction retention deficits

Single prolonged stress (SPS) has been used to examine mechanisms via which stress exposure leads to post-traumatic stress disorder symptoms. SPS induces fear extinction retention deficits, but neural circuits critical for mediating these deficits are unknown. To address this gap, we examined the effect of SPS on neural activity in brain regions critical for extinction retention (i.e., fear extinction circuit). These were the ventral hippocampus (vHipp), dorsal hippocampus (dHipp), basolateral amygdala (BLA), prelimbic cortex (PL), and infralimbic cortex (IL). SPS or control rats were fear conditioned then subjected to extinction training and testing. Subsets of rats were euthanized after extinction training, extinction testing, or immediate removal from the housing colony (baseline condition) to assay c-Fos levels (measure of neural activity) in respective brain region. SPS induced extinction retention deficits. During extinction training SPS disrupted enhanced IL neural activity and inhibited BLA neural activity. SPS also disrupted inhibited BLA and vHipp neural activity during extinction testing. Statistical analyses suggested that SPS disrupted functional connectivity within the dHipp during extinction training and increased functional connectivity between the BLA and vHipp during extinction testing. Our findings suggest that SPS induces extinction retention deficits by disrupting both excitatory and inhibitory changes in neural activity within the fear extinction circuit and inducing changes in functional connectivity within the Hipp and BLA.

Comorbid anxiety-like behavior and locus coeruleus impairment in diabetic peripheral neuropathy: A comparative study with the chronic constriction injury model

Anxiety frequently appears in patients with diabetic neuropathic pain, a highly prevalent clinical condition. However, the neurobiological mechanisms of this comorbidity are poorly known. Anxiogenic phenotype has been associated with alterations of the noradrenergic locus coeruleus (LC) after peripheral nerve entrapment. We have examined the sensorial (pain) and affective (anxiety) behaviors, and the LC activity in streptozotocin (STZ)-induced diabetic rats. A comparative study with the chronic constriction injury (CCI) model of sciatic nerve was also carried out. Diabetic nociceptive hypersensitivity was observed to appear gradually, reaching their maximum at fourth week. In contrast, CCI displayed a sharp decrease in their sensorial threshold at seventh day. In both models, anxiety-like phenotype was evident after four weeks but not earlier, coincident with the LC alterations. Indeed, STZ animals showed reduced LC firing activity, tyrosine hydroxylase, pCREB and noradrenaline transporter levels, contrary to observed in CCI animals. However, in both models, enhanced LC alpha2-adrenoceptor sensitivity was presented at this time point. This study demonstrated that diabetes induced anxiety-like behavior comorbid with LC impairment at long-term. However, the nociceptive sensitivity time-course, as well as the LC functions, showed distinct features compared to the CCI model, indicating that specific neuroplastic mechanisms are at play in every model.

Altered function in medial prefrontal cortex and nucleus accumbens links to stress-induced behavioral inflexibility

The medial prefrontal cortex (mPFC) and its output area, the nucleus accumbens (NAc), are implicated in mediating attentional set-shifting. Patients with posttraumatic stress disorder (PTSD) exhibit difficulties in the disengagement of attention from traumatic cues, which is associated with impairments in set-shifting ability. However, unknown is whether alterations in corticostriatal function underlie deficits in this behavioral flexibility in individuals with PTSD. An animal model of single prolonged stress (SPS) has been partially validated as a model for PTSD, in which SPS rats recapitulate the pathophysiological abnormalities and behavioral characteristics of PTSD. In the present study, we firstly found that exposure to SPS impaired the ability in the shift from visual-cue learning to place response discrimination in rats. Conversely, SPS induced no effect on a place-to-cue set-shifting performance. Based on SPS-impaired set-shifting model, we used Western blot and immunofluorescent approaches to clarify SPS-induced alternations in synaptic plasticity and neuronal activation in the mPFC and NAc. Rats that were subjected to SPS exhibited a large increase in pSer845-GluA1 and total GluA1 levels in the mPFC, while no significant change in the NAc. We further found that exposure to SPS significantly decreased c-Fos expression in the NAc core but not the shell after set-shifting behavior. Whereas, enhanced c-Fos expression was observed in prelimbic and infralimbic cortices. Collectively, these findings suggest that abnormal hyperactivity in the mPFC and dysfunction in the NAc core underlie long-term deficits in executive function after traumatic experience, which might play an important role in the development of PTSD symptoms.