The role of the locus coeruleus in the generation of pathological anxiety

Attentional Disengagement and the Locus Coeruleus - Norepinephrine System in Children With Autism Spectrum Disorder

Background

Differences in non-social attentional functions have been identified as among the earliest features that distinguish infants later diagnosed with autism spectrum disorder (ASD), and may contribute to the emergence of core ASD symptoms. Specifically, slowed attentional disengagement and difficulty reorienting attention have been found across the lifespan in those at risk for, or diagnosed with, ASD. Additionally, the locus coeruleus-norepinephrine (LC-NE) system, which plays a critical role in arousal regulation and selective attention, has been shown to function atypically in ASD. While activity of the LC-NE system is associated with attentional disengagement and reorienting in typically developing (TD) individuals, it has not been determined whether atypical LC-NE activity relates to attentional disengagement impairments observed in ASD.

Objective

To examine the relationship between resting pupil diameter (an indirect measure of tonic LC-NE activation) and attentional disengagement in children with ASD.

Methods

Participants were 21 school-aged children with ASD and 20 age- and IQ-matched TD children. The study consisted of three separate experiments: a resting eye-tracking task and visual and auditory gap-overlap paradigms. For the resting eye-tracking task, pupil diameter was monitored while participants fixated a central crosshair. In the gap-overlap paradigms, participants were instructed to fixate on a central stimulus and then move their eyes to peripherally presented visual or auditory targets. Saccadic reaction times (SRT), percentage of no-shift trials, and disengagement efficiency were measured.

Results

Children with ASD had significantly larger resting pupil size compared to their TD peers. The groups did not differ for overall SRT, nor were there differences in SRT for overlap and gap conditions between groups. However, the ASD group did evidence impairments in disengagement (larger step/gap effects, higher percentage of no-shift trials, and reduced disengagement efficiency) compared to their TD peers. Correlational analyses showed that slower, less efficient disengagement was associated with increased pupil diameter.

Conclusion

Consistent with prior reports, children with ASD show significantly larger resting pupil diameter, indicative of atypically elevated tonic LC-NE activity. Associations between pupil size and measures of attentional disengagement suggest that atypically increased tonic activation of the LC-NE system may be associated with poorer attentional disengagement in children with ASD.

Mental Resilience and Coping With Stress: A Comprehensive, Multi-level Model of Cognitive Processing, Decision Making, and Behavior

Aversive events can evoke strong emotions that trigger cerebral neuroactivity to facilitate behavioral and cognitive shifts to secure physiological stability. However, upon intense and/or chronic exposure to such events, the neural coping processes can be maladaptive and disrupt mental well-being. This maladaptation denotes a pivotal point when psychological stress occurs, which can trigger subconscious, "automatic" neuroreactivity as a defence mechanism to protect the individual from potential danger including overwhelming unpleasant feelings and disturbing or threatening thoughts.The outcomes of maladaptive neural activity are cognitive dysfunctions such as altered memory, decision making, and behavior that impose a risk for mental disorders. Although the neurocognitive phenomena associated with psychological stress are well documented, the complex neural activity and pathways related to stressor detection and stress coping have not been outlined in detail. Accordingly, we define acute and chronic stress-induced pathways, phases, and stages in relation to novel/unpredicted, uncontrollable, and ambiguous stressors. We offer a comprehensive model of the stress-induced alterations associated with multifaceted pathophysiology related to cognitive appraisal and executive functioning in stress.

Spinally projecting noradrenergic neurons of the locus coeruleus display resistance to AAV2retro-mediated transduction

BACKGROUND

The locus coeruleus (LC) is the principal source of noradrenaline (NA) in the central nervous system. Projection neurons in the ventral portion of the LC project to the spinal cord and are considered the main source of spinal NA. To understand the precise physiology of this pathway, it is important to have tools that allow specific genetic access to these descending projections. AAV2retro serotype vectors are a potential tool to transduce these neurons via their axon terminals in the spinal cord, and thereby limit the expression of genetic material to the spinal projections from the LC. Here, we assess the suitability of AAV2retro to target these neurons and investigate strategies to increase their labelling efficiency.

RESULTS

We show that the neurons in the LC that project to the spinal dorsal horn are largely resistant to transduction with AAV2retro serotype vectors. Compared to Cholera toxin B (CTb) tracing, AAV2retro.eGFP labelled far fewer neurons within the LC and surrounding regions, particularly within neurons that express tyrosine hydroxylase (TH), the rate-limiting enzyme for NA synthesis. We also show that the sensitivity for transduction of this projection can be increased using AAV2retro.eGFP.cre in ROSA26^tdTom reporter mice (23% increase), with a higher proportion of the newly revealed neurons expressing TH compared to those directly labelled with AAV2retro containing an eGFP expression sequence.

CONCLUSION

These tracing studies identify limitations in AAV2retro-mediated retrograde transduction of a subset of projection neurons, specifically those that express NA and project to the spinal cord. This is likely to have implications for the study of NA-containing projections as well as other types of projection neuron in the central nervous system.

Fluoroquinolones-Associated Disability: It Is Not All in Your Head

Fluoroquinolones (FQs) are a broad class of antibiotics typically prescribed for bacterial infections, including infections for which their use is discouraged. The FDA has proposed the existence of a permanent disability (Fluoroquinolone Associated Disability; FQAD), which is yet to be formally recognized. Previous studies suggest that FQs act as selective GABAA receptor inhibitors, preventing the binding of GABA in the central nervous system. GABA is a key regulator of the vagus nerve, involved in the control of gastrointestinal (GI) function. Indeed, GABA is released from the Nucleus of the Tractus Solitarius (NTS) to the Dorsal Motor Nucleus of the vagus (DMV) to tonically regulate vagal activity. The purpose of this review is to summarize the current knowledge on FQs in the context of the vagus nerve and examine how these drugs could lead to dysregulated signaling to the GI tract. Since there is sufficient evidence to suggest that GABA transmission is hindered by FQs, it is reasonable to postulate that the vagal circuit could be compromised at the NTS-DMV synapse after FQ use, possibly leading to the development of permanent GI disorders in FQAD.

The neurobiology of human fear generalization: meta-analysis and working neural model

Fear generalization to stimuli resembling a conditioned danger-cue (CS+) is a fundamental dynamic of classical fear-conditioning. Despite the ubiquity of fear generalization in human experience and its known pathogenic contribution to clinical anxiety, neural investigations of human generalization have only recently begun. The present work provides the first meta-analysis of this growing literature to delineate brain substrates of conditioned fear-generalization and formulate a working neural model. Included studies (K = 6, N = 176) reported whole-brain fMRI results and applied generalization-gradient methodology to identify brain activations that gradually strengthen (positive generalization) or weaken (negative generalization) as presented stimuli increase in CS+ resemblance. Positive generalization was instantiated in cingulo-opercular, frontoparietal, striatal-thalamic, and midbrain regions (locus coeruleus, periaqueductal grey, ventral tegmental area), while negative generalization was implemented in default-mode network nodes (ventromedial prefrontal cortex, hippocampus, middle temporal gyrus, angular gyrus) and amygdala. Findings are integrated within an updated neural account of generalization centering on the hippocampus, its modulation by locus coeruleus and basolateral amygdala, and the excitation of threat- or safety-related loci by the hippocampus.

Is a Mask That Covers the Mouth and Nose Free from Undesirable Side Effects in Everyday Use and Free of Potential Hazards?

Many countries introduced the requirement to wear masks in public spaces for containing SARS-CoV-2 making it commonplace in 2020. Up until now, there has been no comprehensive investigation as to the adverse health effects masks can cause. The aim was to find, test, evaluate and compile scientifically proven related side effects of wearing masks. For a quantitative evaluation, 44 mostly experimental studies were referenced, and for a substantive evaluation, 65 publications were found. The literature revealed relevant adverse effects of masks in numerous disciplines. In this paper, we refer to the psychological and physical deterioration as well as multiple symptoms described because of their consistent, recurrent and uniform presentation from different disciplines as a Mask-Induced Exhaustion Syndrome (MIES). We objectified evaluation evidenced changes in respiratory physiology of mask wearers with significant correlation of O2 drop and fatigue (p < 0.05), a clustered co-occurrence of respiratory impairment and O2 drop (67%), N95 mask and CO2 rise (82%), N95 mask and O2 drop (72%), N95 mask and headache (60%), respiratory impairment and temperature rise (88%), but also temperature rise and moisture (100%) under the masks. Extended mask-wearing by the general population could lead to relevant effects and consequences in many medical fields.

Locus Coeruleus Malfunction Is Linked to Psychopathology in Prodromal Dementia With Lewy Bodies

Background: The locus coeruleus (LC) is a nucleus in the human brainstem with a variety of noradrenaline-driven functions involved in cognition, emotions, and perception. Dementia with Lewy bodies (DLB) constitutes a neurodegenerative disease involving deposits of alpha-synuclein, first appearing in the brainstem. The goal of this narrative review is to delineate the relationship between the expression of psychiatric symptoms as an early-onset of DLB and the degeneration of the LC's noradrenaline system.

Methods: We searched in PubMed for relevant articles concerning LC degeneration and psychiatric symptoms in prodromal DLB in this narrative review. We rely on the McKeith criteria for prodromal psychiatric DLB.

Results: We found four studies that document neuronal loss, deposits of Lewy bodies and other hints for neurodegeneration in the LC in patients with DLB. Furthermore, we reviewed theories and studies on how the degenerated noradrenaline LC system contributes to psychiatric DLB's phenotype. We hypothesized how anxiety, hallucinations, delusions, and depressive symptoms might occur in DLB patients due to degenerated noradrenergic neurons entailing consecutive altered noradrenergic transmission in the LC's projection areas.

Conclusions: LC degeneration in prodromal DLB might cause psychiatric symptoms as the first and non-motor manifestation of DLB, as the LC is affected earlier by degeneration than are dopaminergic structures such as the substantia nigra, which are impaired later in the disease course.

Effects of norepinephrine on colonic tight junction protein expression during heat stress

Stress induced by changes in the internal or external environment in humans and animals leads to intestinal epithelial damage, in a manner that is associated with impaired intestinal barrier function. However, the role of the stress hormone norepinephrine (NE) in impairments in barrier function remains poorly understood. In the present study, a rat heat-exposed model was used to observe changes in the tight junction proteins Occludin and zonula occludens-1 (ZO-1), in addition to those in protease-activated receptor 2 (PAR-2) and transient receptor potential ankyrin 1 channel (TRPA1) in colon. The levels of plasma NE were detected using an ELISA kit. Different concentrations of NE were used to culture the human colon cell line Caco-2 for 6 and 24 h to investigate the cell viability using Cell Counting Kit-8 assay, whilst the expression levels of Occludin, ZO-1, PAR-2 and TRPA1 were examined using western blotting and immunofluorescence in Caco-2 cells and immunohistrochemistry in rat colon tissues. Although there was no clear histological damage to the rat colonic mucosa, there were decreased expression levels of tight junction proteins Occludin and ZO-1 after heat exposure. In addition, PAR-2 expression was increased by heat exposure. It was found that TRPA1 expression was concentrated to the luminal surface of the colon in the heat exposed group compared with that in the control group. After the administration of increasing concentrations of NE for 6 h, treatment did not affect cell viability. Furthermore, after application of NE for 24 h, cell viability gradually increased as the NE concentration was elevated from 10 to 100 µM. However, no significant increase in viability was observed when the cells were treated with 120 and 160 µM NE. Occludin expression was decreased when 10 µM NE was applied for 6 or 24 h. By contrast, 60 µM NE significantly downregulated Occludin expression in the 6 h group, but caused an insignificant decrease in the 24 h group. It was found that ZO-1 expression was upregulated after treatment with 10 µM NE for 6 h, whilst downregulation was observed after treatment with 10 µM NE for 24 h. PAR-2 protein expression was increased after application of NE for both 6 and 24 h, but not after treatment with 60 µM NE. In addition, TRPA1 expression was not affected by the treatment of NE, but increased positive staining was observed on the luminal side of the mucosa, which appeared to be concentrated in the cells of the luminal side in the rat colon after heat exposure. Collectively, the present results suggested that expression of tight junction proteins Occludin and ZO-1, in addition to that of PAR-2, can be regulated by NE, which may contribute to impairments in barrier function observed during heat stress.

Alterations in reward network functional connectivity are associated with increased food addiction in obese individuals

Functional neuroimaging studies in obesity have identified alterations in the connectivity within the reward network leading to decreased homeostatic control of ingestive behavior. However, the neural mechanisms underlying sex differences in the prevalence of food addiction in obesity is unknown. The aim of the study was to identify functional connectivity alterations associated with: (1) Food addiction, (2) Sex- differences in food addiction, (3) Ingestive behaviors. 150 participants (females: N = 103, males: N = 47; food addiction: N = 40, no food addiction: N = 110) with high BMI ≥ 25 kg/m2 underwent functional resting state MRIs. Participants were administered the Yale Food Addiction Scale (YFAS), to determine diagnostic criteria for food addiction (YFAS Symptom Count ≥ 3 with clinically significant impairment or distress), and completed ingestive behavior questionnaires. Connectivity differences were analyzed using a general linear model in the CONN Toolbox and images were segmented using the Schaefer 400, Harvard-Oxford Subcortical, and Ascending Arousal Network atlases. Significant connectivities and clinical variables were correlated. Statistical significance was corrected for multiple comparisons at q < .05. (1) Individuals with food addiction had greater connectivity between brainstem regions and the orbital frontal gyrus compared to individuals with no food addiction. (2) Females with food addiction had greater connectivity in the salience and emotional regulation networks and lowered connectivity between the default mode network and central executive network compared to males with food addiction. (3) Increased connectivity between regions of the reward network was positively associated with scores on the General Food Cravings Questionnaire-Trait, indicative of greater food cravings in individuals with food addiction. Individuals with food addiction showed greater connectivity between regions of the reward network suggesting dysregulation of the dopaminergic pathway. Additionally, greater connectivity in the locus coeruleus could indicate that the maladaptive food behaviors displayed by individuals with food addiction serve as a coping mechanism in response to pathological anxiety and stress. Sex differences in functional connectivity suggest that females with food addiction engage more in emotional overeating and less cognitive control and homeostatic processing compared to males. These mechanistic pathways may have clinical implications for understanding the sex-dependent variability in response to diet interventions.