History of chronic stress modifies acute stress-evoked fear memory and acoustic startle in male rats

Sex-specific threat responding and neuronal engagement in carbon dioxide associated fear and extinction: Noradrenergic involvement in female mice

Difficulty in appropriately responding to threats is a key feature of psychiatric disorders, especially fear-related conditions such as panic disorder (PD) and posttraumatic stress disorder (PTSD). Most prior work on threat and fear regulation involves exposure to external threatful cues. However, fear can also be triggered by aversive, within-the-body, sensations. This interoceptive signaling of fear is highly relevant to PD and PTSD but is not well understood, especially in the context of sex. Using female and male mice, the current study investigated fear-associated spontaneous and conditioned behaviors to carbon dioxide (CO2) inhalation, a potent interoceptive threat that induces fear and panic. We also investigated whether behavioral sensitivity to CO2 is associated with delayed PTSD-relevant behaviors. CO2 evoked heterogenous freezing behaviors in both male and female animals. However, active, rearing behavior was significantly reduced in CO2-exposed male but not female mice. Interestingly, behavioral sensitivity to CO2 was associated with compromised fear extinction, independent of sex. However, in comparison to CO2-exposed males, females elicited less freezing and higher rearing during extinction suggesting an engagement of active versus passive defensive coping. Persistent neuronal activation marker ΔFosB immuno-mapping revealed attenuated engagement of infralimbic-prefrontal areas in both sexes but higher activation of brain stem locus coeruleus (LC) area in females. Inter-regional co-activation mapping revealed sex-independent disruptions in the infralimbic-amygdala associations but altered LC associations only in CO2-exposed female mice. Lastly, dopamine β hydroxylase positive (DβH + ve) noradrenergic neuronal cell counts in the LC correlated with freezing and rearing behaviors during CO2 inhalation and extinction only in female but not male mice. Collectively, these data provide evidence for higher active defensive responding to interoceptive threat CO2-associated fear in females that may stem from increased recruitment of the brainstem noradrenergic system. Our findings reveal distinct contributory mechanisms that may promote sex differences in fear and panic associated pathologies.

Network analysis of the comorbidity between post-traumatic stress, depression and anxiety symptoms among frontline healthcare workers during the COVID-19 pandemic

Background

Coronavirus disease 2019 pandemic pointed out significant mental symptoms of frontline healthcare workers (HCWs).

Objective

We aimed to estimate the prevalence and comorbidity of post-traumatic stress symptoms (PTSS), depression and anxiety symptoms in HCWs from Fangcang shelter hospitals during the pandemic.

Design

Demographic information, post-traumatic stress disorder checklist for DSM-5 (PCL-5), Patient Health Questionnaire (PHQ-9) and Generalized Anxiety Disorder Questionnaire (GAD-7) were obtained online based on stratified random sampling design during April 2022, with 284 eligible responses.

Method

Hierarchical regression analyses were applied to investigate independent variables associated with psychological status outcomes (PHQ-9, GAD-7 and PCL-5), and the network analyses were applied to explore the comorbidity using all items of PCL-5, PHQ-9 and GAD-7.

Results

(1) 10.56%, 13.03% and 8.10% of HCWs reported PTSS, depression and anxiety symptoms. Fifty-three (18.66%) HCWs experienced at least one mental health disorder, among which 26.42-37.74% HCWs had comorbidity of two or three mental disorders; (2) several influence factors of mental health were identified, including medical professions, working hours, contacted patients (p < 0.05); (3) prominent bridge symptoms between PTSS and depression were sleep problems, suicide ideation, concentration difficulties and recklessness. Comorbidity between PTSS and anxiety was thought to mainly stem from negative affect, such as afraid, anxious, annoyed and worrying. Depressed mood and worry might be good targets during treatment of comorbidity of depression and anxiety.

Conclusion

Our data suggest mild level of PTSS, depression and anxiety symptoms among HCWs during the pandemic and might give novel insights into assessment and intervention of comorbidity.

Deriving psychiatric symptom-based biomarkers from multivariate relationships between psychophysiological and biochemical measures

Identification of biomarkers for psychiatric disorders remains very challenging due to substantial symptom heterogeneity and diagnostic comorbidity, limiting the ability to map symptoms to underlying neurobiology. Dimensional symptom clusters, such as anhedonia, hyperarousal, etc., are complex and arise due to interactions of a multitude of complex biological relationships. The primary aim of the current investigation was to use multi-set canonical correlation analysis (mCCA) to derive biomarkers (biochemical, physiological) linked to dimensional symptoms across the anxiety and depressive spectrum. Active-duty service members (N = 2,592) completed standardized depression, anxiety and posttraumatic stress questionnaires and several psychophysiological and biochemical assays. Using this approach, we identified two phenotype associations between distinct physiological and biological phenotypes. One was characterized by symptoms of dysphoric arousal (anhedonia, anxiety, hypervigilance) which was associated with low blood pressure and startle reactivity. This finding is in line with previous studies suggesting blunted physiological reactivity is associated with subpopulations endorsing anxiety with comorbid depressive features. A second phenotype of anxious fatigue (high anxiety and reexperiencing/avoidance symptoms coupled with fatigue) was associated with elevated blood levels of norepinephrine and the inflammatory marker C-reactive protein in conjunction with high blood pressure. This second phenotype may describe populations in which inflammation and high sympathetic outflow might contribute to anxious fatigue. Overall, these findings support the growing consensus that distinct neuropsychiatric symptom patterns are associated with differential physiological and blood-based biological profiles and highlight the potential of mCCA to reveal important psychiatric symptom biomarkers from several psychophysiological and biochemical measures.

The influence of risk perception for COVID-19 pandemic on posttraumatic stress disorder in healthcare workers: A survey from four designated hospitals

The aim of current study was to investigate risk perception of COVID‐19 pandemic, sleep quality and time change of leisure activity and their correlations with posttraumatic stress disorder (PTSD) in healthcare workers (HCWs) from four designated hospitals in China. Medical staffs (n = 317) from three designated hospitals in Guangdong Province and one designated hospital in Guangxi Province were surveyed on their demographic information, sleep quality and time change of leisure activity, risk perception of pandemic and PTSD symptoms (by using PTSD checklist for DSM‐5 (PCL‐5)). Hierarchical regression and structural equation model (SEM) were used to examine the correlated factors of PTSD. The prevalence of high level of PTSD symptoms (PCL‐5 > =33, a probable diagnosis of PTSD) was 10.7%. Regression analysis found that risk perception (dread: β = 0.142, p < 0.01; familiarity: β = 0.203, p < 0.01), sleep quality (β = 0.250, p < 0.001), time change of leisure activity (β = −0.179, p < 0.01), were independently correlated with PTSD severity, which was further confirmed by SEM. Locations of COVID‐19‐related hazards were significant different in cognitive map of risk perception between groups with high and low levels of PTSD symptoms. Risk perception of COVID‐19 pandemic influenced PTSD symptoms in HCWs. Adequate time for leisure activity and good sleep quality protected some HCWs against PTSD symptoms under the influence of pandemic. More researches were warranted to understand the path from pre‐factors of risk perception to its psychological consequences among HCWs.

Turning the 'Tides on Neuropsychiatric Diseases: The Role of Peptides in the Prefrontal Cortex

Recent advancements in technology have enabled researchers to probe the brain with the greater region, cell, and receptor specificity. These developments have allowed for a more thorough understanding of how regulation of the neurophysiology within a region is essential for maintaining healthy brain function. Stress has been shown to alter the prefrontal cortex (PFC) functioning, and evidence links functional impairments in PFC brain activity with neuropsychiatric disorders. Moreover, a growing body of literature highlights the importance of neuropeptides in the PFC to modulate neural signaling and to influence behavior. The converging evidence outlined in this review indicates that neuropeptides in the PFC are specifically impacted by stress, and are found to be dysregulated in numerous stress-related neuropsychiatric disorders including substance use disorder, major depressive disorder (MDD), posttraumatic stress disorder, and schizophrenia. This review explores how neuropeptides in the PFC function to regulate the neural activity, and how genetic and environmental factors, such as stress, lead to dysregulation in neuropeptide systems, which may ultimately contribute to the pathology of neuropsychiatric diseases.

A probabilistic model of startle response reveals opposite effects of acute versus chronic Methylphenidate treatment

BACKGROUND

The startle response is considered as the major physio-behavioral indication of anxiety in health and disease conditions. However, due to different protocols of stimulation and measurement, the magnitude as well as the appearance of the startle response is inconsistent.

NEW METHOD

We postulate that the startle probability and not merely the amplitude may bare information that will form a consistent physiological measure of anxiety.

RESULTS

To examine the proof-of-concept of our suggested probability model, we evaluated the effects of acute (single) versus chronic (14 days) MPH administration on both startle amplitude and probability. We found that both acute and chronic MPH administration has yielded similar effects on startle amplitude. However, acute MPH increased the startle's probability while chronic MPH decreased it. Next, we evaluated the effects of acute versus chronic stress on the startle's parameters and found a complementary effect. Explicitly, acute stress increased the startle's probability while chronic stress increased the startle amplitude. In contrast, enriched environment had no significant effects. Finally, to further validate the probability measure, we show that Midazolam had significant anxiolytic effects. In the second part, we investigated the acoustic startle response parameters (e.g. background noise and pulse duration), to better understand the interplay between these parameters and the startle amplitude versus probability.

CONCLUSIONS

We show that the probabilistic element of the startle response does not only point to deeper physiologic relationships but may also serve as "hidden variables" congruent but not entirely identical to the commonly researched amplitude of the startle response.

Recruitment of central angiotensin II type 1 receptor associated neurocircuits in carbon dioxide associated fear

Individuals with fear-associated conditions such as panic disorder (PD) and posttraumatic stress disorder (PTSD) display increased emotional responses to interoceptive triggers, such as CO₂ inhalation, that signal a threat to physiological homeostasis. Currently, effector systems and mechanisms underlying homeostatic modulation of fear memory are not well understood. In this regard, the renin angiotensin system (RAS), particularly the angiotensin receptor type 1 (AT1R), a primary homeostatic regulatory target, has gained attention. RAS polymorphisms have been reported in PD and PTSD, and recent studies report AT1R-mediated modulation of fear extinction. However, contribution of AT1Rs in fear evoked by the interoceptive threat of CO₂ has not been investigated. Using pharmacological, behavioral, and AT1R/ACE gene transcription analyses, we assessed central AT1R recruitment in CO₂-associated fear. CO₂ inhalation led to significant AT1R and ACE mRNA upregulation in homeostatic regulatory regions, subfornical organ (SFO) and paraventricular nucleus (PVN), in a temporal manner. Intracerebroventricular infusion of selective AT1R antagonist, losartan, significantly attenuated freezing during CO₂ inhalation, and during re-exposure to CO₂ context, suggestive of AT1R modulation of contextual fear. Regional Fos mapping in losartan-treated mice post-behavior revealed significantly attenuated labeling in areas regulating defensive behavior, contextual fear, and threat responding; such as, the bed nucleus of stria terminalis, dorsal periaqueductal gray, hypothalamic nuclei, hippocampus, and prefrontal areas such as the prelimbic, infralimbic, and anterior cingulate cortices. Sub-regions of the amygdala did not show CO₂-associated AT1R regulation or altered Fos labeling. Collectively, our data suggests central AT1R recruitment in modulation of fear behaviors associated with CO₂ inhalation via engagement of neurocircuits regulating homeostasis and defensive behaviors. Our data provides mechanistic insights into the interoceptive regulation of fear, relevant to fear related disorders such as PD and PTSD.

Animal models of PTSD: a challenge to be met

Recent years have seen increased interest in psychopathologies related to trauma exposure. Specifically, there has been a growing awareness to posttraumatic stress disorder (PTSD) in part due to terrorism, climate change-associated natural disasters, the global refugee crisis, and increased violence in overpopulated urban areas. However, notwithstanding the increased awareness to the disorder, the increasing number of patients, and the devastating impact on the lives of patients and their families, the efficacy of available treatments remains limited and highly unsatisfactory. A major scientific effort is therefore devoted to unravel the neural mechanisms underlying PTSD with the aim of paving the way to developing novel or improved treatment approaches and drugs to treat PTSD. One of the major scientific tools used to gain insight into understanding physiological and neuronal mechanisms underlying diseases and for treatment development is the use of animal models of human diseases. While much progress has been made using these models in understanding mechanisms of conditioned fear and fear memory, the gained knowledge has not yet led to better treatment options for PTSD patients. This poor translational outcome has already led some scientists and pharmaceutical companies, who do not in general hold opinions against animal models, to propose that those models should be abandoned. Here, we critically examine aspects of animal models of PTSD that may have contributed to the relative lack of translatability, including the focus on the exposure to trauma, overlooking individual and sex differences, and the contribution of risk factors. Based on findings from recent years, we propose research-based modifications that we believe are required in order to overcome some of the shortcomings of previous practice. These modifications include the usage of animal models of PTSD which incorporate risk factors and of the behavioral profiling analysis of individuals in a sample. These modifications are aimed to address factors such as individual predisposition and resilience, thus taking into consideration the fact that only a fraction of individuals exposed to trauma develop PTSD. We suggest that with an appropriate shift of practice, animal models are not only a valuable tool to enhance our understanding of fear and memory processes, but could serve as effective platforms for understanding PTSD, for PTSD drug development and drug testing.

Real-time in vivo two-photon imaging study reveals decreased cerebro-vascular volume and increased blood-brain barrier permeability in chronically stressed mice

Chronic stress disrupts brain homeostasis and adversely affects the cerebro-vascular system. Even though the effects of chronic stress on brain system have been extensively studied, there are few in vivo dynamic studies on the effects of chronic stress on the cerebro-vascular system. In this study, the effects of chronic stress on cerebral vasculature and BBB permeability were studied using in vivo two-photon (2p) microscopic imaging with an injection of fluorescence-conjugated dextran. Our real-time 2p imaging results showed that chronic stress reduced the vessel diameter and reconstructed vascular volume, regardless of vessel type and branching order. BBB permeability was investigated with two different size of tracers. Stressed animals exhibited a greater BBB permeability to 40-kDa dextran, but not to 70-kDa dextran, which is suggestive of weakened vascular integrity following stress. Molecular analysis revealed significantly higher VEGFa mRNA expression and a reduction in claudin-5. In summary, chronic stress decreases the size of cerebral vessels and increases BBB permeability. These results may suggest that the sustained decrease in cerebro-vascular volume due to chronic stress leads to a hypoxic condition that causes molecular changes such as VEGF and claudin-5, which eventually impairs the function of BBB.

Enhanced fear and altered neuronal activation in forebrain limbic regions of CX3CR1-deficient mice

Mounting evidence supports immune dysfunction in psychiatric conditions such as post-traumatic stress disorder (PTSD). The association of immunomodulatory mechanisms with PTSD-relevant behavior and physiology is not well understood. Communication between neurons and microglia, resident immune cells of the central nervous system, is crucial for optimal regulation of behavior and physiology. In this regard, the fractalkine CX3CL1, secreted from neurons and its target, the microglial CX3CR1 receptor represent a primary neuron-microglia inter-regulatory system important for synaptic plasticity and function. The current study investigated the impact of CX3CR1 deficiency on behaviors relevant to PTSD, such as fear acquisition and memory, acoustic startle response and anxiety-like behavior. Morphological analysis of microglia and neuronal activation within PTSD-relevant forebrain nuclei regulating stress and fear behaviors was also conducted. CX3CR1-deficient (CX3CR1-/-) mice elicited increased fear acquisition as well as reinstatement of fear as compared to wild type (CX3CR1+/+) mice. Conditioned fear and extinction were not significantly different between genotypes. No significant differences were observed in unconditioned acoustic startle response between genotypes. CX3CR1-/- mice showed reduced anxiety-like behaviors as compared with CX3CR1+/+ mice. Morphological assessment of microglia showed region-selective effects of CX3CR1 deficiency, primarily within hypothalamic and cortical areas. Lastly, CX3CR1-/- mice elicited elevated neuronal activity in the PVN and the ventral tegmental-interpeduncular area following reinstatement of fear. Collectively, our data suggest that impaired CX3CR1 function may evoke region-selective alterations in forebrain circuits regulating stress, anxiety and fear, impacting behaviors relevant to disorders such as PTSD.

Neuropeptide Y (NPY) and posttraumatic stress disorder (PTSD): A translational update

Posttraumatic stress disorder (PTSD) is a trauma-evoked syndrome, with variable prevalence within the human population due to individual differences in coping and resiliency. In this review, we discuss evidence supporting the relevance of neuropeptide Y (NPY), a stress regulatory transmitter in PTSD. We consolidate findings from preclinical, clinical, and translational studies of NPY that are of relevance to PTSD with an attempt to provide a current update of this area of research. NPY is abundantly expressed in forebrain limbic and brainstem areas that regulate stress and emotional behaviors. Studies in rodents demonstrate a role for NPY in stress responses, anxiety, fear, and autonomic regulation, all relevant to PTSD symptomology. Genetic studies support an association of NPY polymorphisms with stress coping and affect. Importantly, cerebrospinal fluid (CSF) measurements in combat veterans provide direct evidence of NPY association with PTSD diagnosis and symptomology. In addition, NPY involvement in pain, depression, addiction, and metabolism may be relevant to comorbidities associated with PTSD. Collectively, the literature supports the relevance of NPY to PTSD pathophysiology, although knowledge gaps remain. The NPY system is an attractive target in terms of understanding the physiological basis of PTSD as well as treatment of the disorder.