Resilience to chronic stress is mediated by hippocampal brain-derived neurotrophic factor

Experiences of Second-Grade Primary School Children and Their Teachers in a Mind-Body Activity Program: A Descriptive Qualitative Study

OBJECTIVES

This study explored the experiences of second-grade children and their teachers who participated in a mind-body program to understand its impact on their development.

METHODS

A qualitative descriptive study was conducted. Student data were collected through seven focus groups, and semi-structured interviews were conducted with tutors in December 2021. Data analysis was performed following COREQ guidelines.

RESULTS

Three themes were generated: (1) competitiveness and restlessness in children: something needs to be done; (2) seeds sown and fruits harvested; and (3) it is necessary to advance from the occasional to the structural. Participants reported positive changes in areas of their development such as self-regulation, relaxation, attention capacity, and stress reduction. Improvements in interpersonal relationships and social skills were also observed.

CONCLUSIONS

These improvements in emotional well-being and social skills highlight the importance of this type of intervention in the school environment.

New insights into individual differences in response to chronic unpredictable mild stress (CUMS) in rats with respect to hippocampal BDNF and GSK3-β expression levels

Preclinical and clinical studies have shown a wide-range of individual differences in response to stressors or novel environments which can affect the susceptibility to develop abnormal behaviors and neuropsychiatric disorders. Both vulnerability and resiliency have been observed in animals and humans experiencing stressful events. Chronic unpredictable mild stress (CUMS) is a rodent depression model consisting of various stressors. This protocol leads to depressive- and anhedonic-like behaviors in rodents. The present study aimed to evaluate potential individual differences in response to CUMS in rats, with respect to the expression level of brain-derived neurotrophic factor (BDNF) and glycogen synthase kinases 3-beta (GSK3-β) (proteins involved in the modulation of mood, neuroplasticity, and cognition) in the hippocampus. CUMS was performed for four consecutive weeks. Depressive-like behavior, locomotor activity, anxiety-like behavior, and pain threshold were also evaluated using forced swim test (FST), open field test (OFT), and the hot plate (HP), respectively. Real-time PCR was used to evaluate BDNF and GSK3-β expression levels. The results showed that CUMS rats can be classified as two clusters: affected and non-affected (depressed and non-depressed). Affected rats showed depressive- and anxiety-like behaviors, decreased locomotor activity, and increased pain threshold. However, non-affected rats were similar to controls. In addition, there was a downregulation of BDNF and upregulation of GSK3-β in affected rats. Spearman correlation analysis also showed a relationship between BDNF and GSK3-β expression levels with individual differences. In conclusion, the present study showed that BDNF and GSK3-β may be involved in individual differences in CUMS rats.

Serum brain-derived neurotrophic factor in relation to craving and duration of abstinence in patients with heroin dependence-A case-control study

BACKGROUND AND OBJECTIVES

Addiction is a chronic disorder that comes with emotional and financial burdens. Several neurobiological factors were correlated to opiate-use disorder which is brain-derived neurotrophic factor (BDNF). BDNF has been found to be involved in long-term potentiation of synaptic strength, a mechanism that is thought to motivate both natural adaption mechanisms as well as the development of addictive behavior. In this study, we aimed to address the relation between BDNF serum level and heroin craving and the effect of duration of abstinence on them.

METHODS

A case study was conducted on 80 subjects from Kasr Al-Ainy Psychiatry and Addiction Treatment Hospital with a history of heroin dependence and were divided into two groups: Group A had 40 active heroin-dependent subjects while in Group B, 40 subjects with 1-year heroin abstinence. Severity of addiction was assessed by the addiction severity index, heroin craving was measured by Brief Substance Craving Scale and serum BDNF level was investigated using an enzyme-linked immunosorbent assay.

RESULTS

The findings show that active heroin users had significantly higher serum BDNF which is associated with high heroin craving in comparison to the abstinent group.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

This study revealed a significant positive correlation between serum BDNF levels and craving in active heroin users versus 1-year abstinent subjects. It is the first study to address the relationship between craving and serum BDNF level in a 1-year abstinent participants. These findings help to determine the brain alterations associated with illness and recovery in heroin dependence.

Neurobiology and systems biology of stress resilience

Stress resilience is the phenomenon that some people maintain their mental health despite exposure to adversity or show only temporary impairments followed by quick recovery. Resilience research attempts to unravel the factors and mechanisms that make resilience possible and to harness its insights for the development of preventative interventions in individuals at risk for acquiring stress-related dysfunctions. Biological resilience research has been lagging behind the psychological and social sciences but has seen a massive surge in recent years. At the same time, progress in this field has been hampered by methodological challenges related to finding suitable operationalizations and study designs, replicating findings, and modeling resilience in animals. We embed a review of behavioral, neuroimaging, neurobiological, and systems biological findings in adults in a critical methods discussion. We find preliminary evidence that hippocampus-based pattern separation and prefrontal-based cognitive control functions protect against the development of pathological fears in the aftermath of singular, event-type stressors [as found in fear-related disorders, including simpler forms of posttraumatic stress disorder (PTSD)] by facilitating the perception of safety. Reward system-based pursuit and savoring of positive reinforcers appear to protect against the development of more generalized dysfunctions of the anxious-depressive spectrum resulting from more severe or longer-lasting stressors (as in depression, generalized or comorbid anxiety, or severe PTSD). Links between preserved functioning of these neural systems under stress and neuroplasticity, immunoregulation, gut microbiome composition, and integrity of the gut barrier and the blood-brain barrier are beginning to emerge. On this basis, avenues for biological interventions are pointed out.

A TrkB cleavage fragment in hippocampus promotes Depressive-Like behavior in mice

Decreased hippocampal tropomyosin receptor kinase B (TrkB) level is implicated in the pathophysiology of stress-induced mood disorder and cognitive decline. However, how TrkB is modified and mediates behavioral responses to chronic stress remains largely unknown. Here the effects and mechanisms of TrkB cleavage by asparagine endopeptidase (AEP) were examined on a preclinical murine model of chronic restraint stress (CRS)-induced depression. CRS activated IL-1β-C/EBPβ-AEP pathway in mice hippocampus, accompanied by elevated TrkB 1-486 fragment generated by AEP. Specifi.c overexpression or suppression of AEP-TrkB axis in hippocampal CaMKIIα-positive cells aggravated or relieved depressive-like behaviors, respectively. Mechanistically, in addition to facilitating AMPARs internalization, TrkB 1-486 interacted with peroxisome proliferator-activated receptor-δ (PPAR-δ) and sequestered it in cytoplasm, repressing PPAR-δ-mediated transactivation and mitochondrial function. Moreover, co-administration of 7,8-dihydroxyflavone and a peptide disrupting the binding of TrkB 1-486 with PPAR-δ attenuated depression-like symptoms not only in CRS animals, but also in Alzheimer's disease and aged mice. These findings reveal a novel role for TrkB cleavage in promoting depressive-like phenotype.

Effects of melancholic features on positive and negative suicidal ideation in patients with treatment-resistant depression and strong suicidal ideation receiving low-dose ketamine infusion

The role of melancholic features on the antisuicidal effect of 0.5 mg/kg ketamine infusion has remained unclear in patients with treatment-resistant depression (TRD) and strong suicidal ideation (SI). Whether ketamine diminishes suicidal ideation in patients with TRD-SI was also unknown. We enrolled 84 patients with TRD-SI, including 27 with melancholic features and 57 without, and then randomly administered a single infusion of 0.5 mg/kg ketamine or 0.045 mg/kg midazolam. The clinician-rated Montgomery-Åsberg Depression Rating Scale (MADRS) item 10, Columbia Suicide Severity Rating Scale-Ideation Severity Subscale (CSSRS-ISS), and self-reported Positive and Negative Suicide Ideation Inventory (PANSI) were used to assess suicidal symptoms from baseline to day 7. Generalized estimating equation models showed that only patients without melancholic features (MADRS item 10: infusion group effect, p = 0.017; CSSRS-ISS: infusion group × time effect, p = 0.008; PANSI-negative suicidal ideation: infusion group effect, p = 0.028) benefited from the antisuicidal effect of low-dose ketamine. The PANSI-positive ideation scores were higher in the ketamine group than in the midazolam group (p = 0.038) for patients with melancholic features. Additional studies are necessary to clarify the neuromechanisms underlying the ketamine-related positive effect against SI and antisuicidal effects among patients with TRD-SI. Additional studies are necessary to clarify the neuromechanisms underlying the ketamine-related positive effect against SI and antisuicidal effects among patients with TRD-SI.

Review: Early life piglet experiences and impacts on immediate and longer-term adaptability

Pigs in production systems are routinely exposed to challenging situations including abrupt weaning, painful husbandry procedures, intense contact with stockpeople, and exposure to novel social and physical environments. The resilience of pigs to these stressors has implications for animal welfare and productivity and can be affected by early life experiences. In rodents and primates, early experiences with stressors that the animal can adequately cope with confers future stress adaptability, leading to less abnormal behaviour, lower behavioural and physiological responses to stressors, and faster recovery after stress exposure. Early experiences that can affect the ability of pigs to overcome challenge include interactions with the dam, conspecifics, humans, and the overall complexity of the environment. Farrowing crates limit the sow's ability to show maternal behaviour towards piglets, and negatively affect piglet social behaviour during lactation, with less play and more manipulation of pen mates in crates than in large pens. Rearing in pens has been proposed to improve the ability of pigs to cope with routine stressors, but the evidence for this is conflicting. The early housing environment can affect general fearfulness and fear of humans, and surprisingly, most studies have shown fear responses to be greater in pigs reared pens than in crates. Given the potential for fear to affect animal welfare and productivity, more detailed research on early housing effects is needed. While there is limited evidence that early housing influences fear in the longer term, human contact early in life appears to have a more profound and sustained effect, with regular positive human interaction early in life having an enduring effect on reducing pigs' fear of humans. The practicality of positive human-pig interaction in a commercial environment needs to be examined further, but only a small amount of positive human contact early in life can improve the resilience of pigs to routine husbandry stressors. Early social experience with non-littermates reduces stress at weaning and mixing, while early weaning before 3-4 weeks of age increases abnormal behaviours. Environmental enrichment, such as foraging substrates and increased floor space, reduces abnormal behaviour in piglets, but housing in an enriched environment early in life and subsequently in a non-enriched environment can increase abnormal behaviour if these environments are dramatically different. Although the later environment can modify the influence of the early environment, overall, early life experiences can be important in shaping how pigs cope with stress in both an immediate and longer-term capacity.

Early human contact and housing for pigs - part 3: ability to cope with the environment

Early experiences can have long-term impacts on stress adaptability. This paper is the last of three in a series on early experiences and stress in pigs, and reports on the effects of early human contact and housing on the ability of pigs to cope with their general environment. Using a 2 × 2 factorial design, 48 litters of pigs were reared in either a farrowing crate (FC) or a loose farrowing pen (LP; PigSAFE pen) which was larger, more physically complex and allowed the sow to move freely. Piglets were provided with either routine contact from stockpeople (C), or routine contact plus regular opportunities for positive human contact (+HC) involving 5 min of scratching, patting and stroking imposed to the litter 5 days/week from 0 to 4 weeks of age. At 4 weeks of age (preweaning), C piglets that were reared in FC had considerably lower concentrations of serum brain-derived neurotrophic factor (BDNF) than piglets from the other treatment combinations. Compared to C pigs, +HC pigs had fewer injuries at 4 weeks of age. There were no clear effects of human contact on BDNF concentrations or injuries after weaning, or on basal cortisol or immunoglobulin-A concentrations, behavioural time budgets, tear staining, growth, or piglet survival. Compared to FC piglets, LP piglets showed more play behaviour and interactions with the dam and less repetitive nosing towards pen mates during lactation. There was no evidence that early housing affected pigs' behavioural time budgets or physiology after weaning. Tear staining severity was greater in LP piglets at 4 weeks of age, but this may have been associated with the higher growth rates of LP piglets preweaning. There was no effect of lactation housing on growth after weaning. Preweaning piglet mortality was higher in the loose system. The findings on BDNF concentrations, injuries and play behaviour suggest improved welfare during the treatment period in +HC and LP piglets compared to C and FC piglets, respectively. These results together with those from the other papers in this series indicate that positive human interaction early in life promotes stress adaptability in pigs. Furthermore, while the farrowing crate environment deprives piglets of opportunities for play behaviour and sow interaction, there was no evidence that rearing in crates negatively affected pig welfare or stress resilience after weaning. Whether these findings are specific to the two housing systems studied here, or can be generalised to other housing designs, warrants further research.

Zebrafish Model in Illuminating the Complexities of Post-Traumatic Stress Disorders: A Unique Research Tool

Post-traumatic stress disorder (PTSD) is a debilitating psychological condition that may develop in certain individuals following exposure to life-threatening or traumatic events. Distressing symptoms, including flashbacks, are characterized by disrupted stress responses, fear, anxiety, avoidance tendencies, and disturbances in sleep patterns. The enduring effects of PTSD can profoundly impact personal and familial relationships, as well as social, medical, and financial stability. The prevalence of PTSD varies among different populations and is influenced by the nature of the traumatic event. Recently, zebrafish have emerged as a valuable model organism in studying various conditions and disorders. Zebrafish display robust behavioral patterns that can be effectively quantified using advanced video-tracking tools. Due to their relatively simple nervous system compared to humans, zebrafish are particularly well suited for behavioral investigations. These unique characteristics make zebrafish an appealing model for exploring the underlying molecular and genetic mechanisms that govern behavior, thus offering a powerful comparative platform for gaining deeper insights into PTSD. This review article aims to provide updates on the pathophysiology of PTSD and the genetic responses associated with psychological stress. Additionally, it highlights the significance of zebrafish behavior as a valuable tool for comprehending PTSD better. By leveraging zebrafish as a model organism, researchers can potentially uncover novel therapeutic interventions for the treatment of PTSD and contribute to a more comprehensive understanding of this complex condition.

In silico analysis of the Val66Met mutation in BDNF protein: implications for psychological stress

The brain-derived neurotrophic factor (BDNF) involves stress regulation and psychiatric disorders. The Val66Met polymorphism in the BDNF gene has been linked to altered protein function and susceptibility to stress-related conditions. This in silico analysis aimed to predict and analyze the consequences of the Val66Met mutation in the BDNF gene of stressed individuals. Computational techniques, including ab initio, comparative, and I-TASSER modeling, were used to evaluate the functional and stability effects of the Val66Met mutation in BDNF. The accuracy and reliability of the models were validated. Sequence alignment and secondary structure analysis compared amino acid residues and structural components. The phylogenetic analysis assessed the conservation of the mutation site. Functional and stability prediction analyses provided mixed results, suggesting potential effects on protein function and stability. Structural models revealed the importance of BDNF in key biological processes. Sequence alignment analysis showed the conservation of amino acid residues across species. Secondary structure analysis indicated minor differences between the wild-type and mutant forms. Phylogenetic analysis supported the evolutionary conservation of the mutation site. This computational study suggests that the Val66Met mutation in BDNF may have implications for protein stability, structural conformation, and function. Further experimental validation is needed to confirm these findings and elucidate the precise effects of this mutation on stress-related disorders.

Chemogenetic activation of CRF neurons as a model of chronic stress produces sex-specific physiological and behavioral effects

Trauma and chronic stress exposure are the strongest predictors of lifetime neuropsychiatric disease presentation. These disorders often have significant sex biases, with females having higher incidences of affective disorders such as major depression, anxiety, and PTSD. Understanding the mechanisms by which stress exposure heightens disease vulnerability is essential for developing novel interventions. Current rodent stress models consist of a battery of sensory, homeostatic, and psychological stressors that are ultimately integrated by corticotropin-releasing factor (CRF) neurons to trigger corticosteroid release. These stress paradigms, however, often differ between research groups in the type, timing, and duration of stressors utilized. These inconsistencies, along with the variability of individual animals' perception and response to each stressor, present challenges for reproducibility and translational relevance. Here, we hypothesized that a more direct approach using chemogenetic activation of CRF neurons would recapitulate the effects of traditional stress paradigms and provide a high-throughput method for examining stress-relevant phenotypes. Using a transgenic approach to express the Gq-coupled Designer Receptor Exclusively Activated by Designer Drugs (DREADD) receptor hM3Dq in CRF-neurons, we found that the DREADD ligand clozapine-N-oxide (CNO) produced an acute and robust activation of the hypothalamic-pituitary-adrenal (HPA) axis, as predicted. Interestingly, chronic treatment with this method of direct CRF activation uncovered a novel sex-specific dissociation of glucocorticoid levels with stress-related outcomes. Despite hM3Dq-expressing females producing greater corticosterone levels in response to CNO than males, hM3Dq-expressing males showed significant typical physiological stress sensitivity with reductions in body and thymus weights. hM3Dq-expressing females while resistant to the physiological effects of chronic CRF activation, showed significant increases in baseline and fear-conditioned freezing behaviors. These data establish a novel mouse model for interrogating stress-relevant phenotypes and highlight sex-specific stress circuitry distinct for physiological and limbic control that may underlie disease risk.

Stress-related cellular pathophysiology as a crosstalk risk factor for neurocognitive and psychiatric disorders

In this narrative review, we examine biological processes linking psychological stress and cognition, with a focus on how psychological stress can activate multiple neurobiological mechanisms that drive cognitive decline and behavioral change. First, we describe the general neurobiology of the stress response to define neurocognitive stress reactivity. Second, we review aspects of epigenetic regulation, synaptic transmission, sex hormones, photoperiodic plasticity, and psychoneuroimmunological processes that can contribute to cognitive decline and neuropsychiatric conditions. Third, we explain mechanistic processes linking the stress response and neuropathology. Fourth, we discuss molecular nuances such as an interplay between kinases and proteins, as well as differential role of sex hormones, that can increase vulnerability to cognitive and emotional dysregulation following stress. Finally, we explicate several testable hypotheses for stress, neurocognitive, and neuropsychiatric research. Together, this work highlights how stress processes alter neurophysiology on multiple levels to increase individuals' risk for neurocognitive and psychiatric disorders, and points toward novel therapeutic targets for mitigating these effects. The resulting models can thus advance dementia and mental health research, and translational neuroscience, with an eye toward clinical application in cognitive and behavioral neurology, and psychiatry.

Influence of Mild Chronic Stress and Social Isolation on Acute Ozone-Induced Alterations in Stress Biomarkers and Brain-Region-Specific Gene Expression in Male Wistar-Kyoto Rats

Individuals with psychosocial stress often experience an exaggerated response to air pollutants. Ozone (O3) exposure has been associated with the activation of the neuroendocrine stress-response system. We hypothesized that preexistent mild chronic stress plus social isolation (CS), or social isolation (SI) alone, would exacerbate the acute effects of O3 exposure on the circulating adrenal-derived stress hormones, and the expression of the genes regulating glucocorticoid stress signaling via an altered stress adaptation in a brain-region-specific manner. Male Wistar-Kyoto rats (5 weeks old) were socially isolated, plus were subjected to either CS (noise, confinement, fear, uncomfortable living, hectic activity, and single housing), SI (single housing only, restricted handling and no enrichment) or no stress (NS; double housing, frequent handling and enrichment provided) for 8 weeks. The rats were then exposed to either air or O3 (0.8 ppm for 4 h), and the samples were collected immediately after. The indicators of sympathetic and hypothalamic-pituitary axis (HPA) activation (i.e., epinephrine, corticosterone, and lymphopenia) increased with O3 exposure, but there were no effects from CS or SI, except for the depletion of serum BDNF. CS and SI revealed small changes in brain-region-specific glucocorticoid-signaling-associated markers of gene expression in the air-exposed rats (hypothalamic Nr3c1, Nr3c2 Hsp90aa1, Hspa4 and Cnr1 inhibition in SI; hippocampal HSP90aa1 increase in SI; and inhibition of the bed nucleus of the stria terminalis (BNST) Cnr1 in CS). Gene expression across all brain regions was altered by O3, reflective of glucocorticoid signaling effects, such as Fkbp5 in NS, CS and SI. The SI effects on Fkbp5 were greatest for SI in BNST. O3 increased Cnr2 expression in the hypothalamus and olfactory bulbs of the NS and SI groups. O3, in all stress conditions, generally inhibited the expression of Nr3c1 in all brain regions, Nr3c2 in the hippocampus and hypothalamus and Bdnf in the hippocampus. SI, in general, showed slightly greater O3-induced changes when compared to NS and CS. Serum metabolomics revealed increased sphingomyelins in the air-exposed SI and O3-exposed NS, with underlying SI dampening some of the O3-induced changes. These results suggest a potential link between preexistent SI and acute O3-induced increases in the circulating adrenal-derived stress hormones and brain-region-specific gene expression changes in glucocorticoid signaling, which may partly underlie the stress dynamic in those with long-term SI.

Reduction of BDNF Levels and Biphasic Changes in Glutamate Release in the Prefrontal Cortex Correlate with Susceptibility to Chronic Stress-Induced Anhedonia

Chronic stress has been considered to induce depressive symptoms, such as anhedonia, particularly in susceptible individuals. Synaptic plasticity in the prefrontal cortex (PFC) is closely associated with susceptibility or resilience to chronic stress-induced anhedonia. However, effects of chronic stress with different durations on the neurobiological mechanisms that underlie susceptibility to anhedonia remain unclear. The present study investigated effects of chronic mild stress (CMS) for 14, 21, and 35 d on anhedonia-like behavior and glutamate synapses in the PFC. We found that brain-derived neurotrophic factor (BDNF) levels in the PFC significantly decreased only in anhedonia-susceptible rats that were exposed to CMS for 14, 21, and 35 d. Additionally, 14 d of CMS increased prefrontal glutamate release, and 35 d of CMS decreased glutamate release, in addition to reducing synaptic proteins and spine density in the PFC. Moreover, we found that anhedonia-like behavior in a subset of rats spontaneously decreased, accompanied by the restoration of BDNF levels and glutamate release, on day 21 of CMS. Ketamine treatment restored the reduction of BDNF levels and biphasic changes in glutamate release that were induced by CMS. Our findings revealed a progressive reduction of synaptic plasticity and biphasic changes in glutamate release in the PFC during CMS. Reductions of BDNF levels may be key neurobiological markers of susceptibility to stress-induced anhedonia.

Co-exposure to Toluene and Noise Made Synergistic and Antagonistic Effects on Some Neurotoxic Parameters in New Zealand White Rabbits

Introduction

Numerous physical and chemical agents can induce destructive effects on the brain tissue. Noise and toluene, which are some of these harmful agents, have significant adverse effects on the brain tissue. This work aimed to investigate the neurotoxic changes induced by co-exposure to toluene and noise.

Methods

A total of 24 male white New Zealand rabbits were randomly segregated into four groups, including toluene exposure, noise exposure, co-exposure to noise and toluene, and control. This in vivo study tested the neurotoxic effects of exposure to 1000 ppm toluene and 100 dB noise during two weeks (8 h/day). The serum levels of brain-derived neurotrophic factor-α (BDNF-α), malondialdehyde (MDA), glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase and total antioxidant capacity (TAC) values in the brain tissue were measured. Moreover, hematoxylin and eosin (H&E) staining was utilized for brain pathological analysis.

Results

Exposure to noise increased TAC values in the cerebral cortex. Co-exposure to toluene and noise increased the serum levels of BDNF-α. Nevertheless, exposure to noise decreased the levels of BDNF-α in serum. On the other hand, histopathological examinations using H&E staining exhibited that different signs of inflammation, such as lymphocyte infiltration, pyknosis, vacuolization, and chromatolysis were induced by exposure to noise and toluene in the cerebellum, hippocampus, and frontal section in the brain tissue. In addition, simultaneous exposure to toluene and noise induced antagonistic and synergistic changes in some neurotoxic parameters.

Conclusion

Exposure to noise and toluene, which caused inflammation in the brain tissue cells, could be a noticeable risk factor for the neurological system.

Highlights

Exposure to noise increased total antioxidant capacity.Exposure to toluene decreased brain-derived neurotrophic factor-α.Exposure to noise decreased brain-derived neurotrophic factor-α.Co-exposure to noise and toluene increased brain-derived neurotrophic factor-α.Noise and toluene induced some histopathological effects on the brain tissue.

Plain Language Summary

The brain tissue can be adversely affected by various agents, including noise and toluene. This study aimed to examine the effects of simultaneous exposure to noise and toluene on the nervous system. Twenty-four healthy male white New Zealand rabbits were randomly divided into four groups: control, noise, toluene, and simultaneous exposure to noise and toluene. The study involved a two-week in-vivo experiment, subjecting the rabbits to 100 dB noise and 1000 ppm toluene for eight hours per day. This study showed that exposure to noise and toluene changed different parameters relating to the neurological system. Furthermore, noise and toluene induced some adverse effects on the brain tissue. This study suggested that exposure to noise and toluene can lead to harmful effects on the brain tissue, posing a significant risk to the neurological system.

Post-stroke depression: epigenetic and epitranscriptomic modifications and their interplay with gut microbiota

Epigenetic and epitranscriptomic modifications that regulate physiological processes of an organism at the DNA and RNA levels, respectively, are novel therapeutic candidates for various neurological diseases. Gut microbiota and its metabolites are known to modulate DNA methylation and histone modifications (epigenetics), as well as RNA methylation especially N6-methyladenosine (epitranscriptomics). As gut microbiota as well as these modifications are highly dynamic across the lifespan of an organism, they are implicated in the pathogenesis of stroke and depression. The lack of specific therapeutic interventions for managing post-stroke depression emphasizes the need to identify novel molecular targets. This review highlights the interaction between the gut microbiota and epigenetic/epitranscriptomic pathways and their interplay in modulating candidate genes that are involved in post-stroke depression. This review further focuses on the three candidates, including brain-derived neurotrophic factor, ten-eleven translocation family proteins, and fat mass and obesity-associated protein based on their prevalence and pathoetiologic role in post-stroke depression.

Supplementation with Vitamin D3 Protects against Mitochondrial Dysfunction and Loss of BDNF-Mediated Akt Activity in the Hippocampus during Long-Term Dexamethasone Treatment in Rats

Dexamethasone (DEXA) is a commonly used steroid drug with immunosuppressive and analgesic properties. Unfortunately, long-term exposure to DEXA severely impairs brain function. This study aimed to investigate the effects of vitamin D3 supplementation during chronic DEXA treatment on neurogenesis, mitochondrial energy metabolism, protein levels involved in the BDNF-mediated Akt activity, and specific receptors in the hippocampus. We found reduced serum concentrations of 25-hydroxyvitamin D3 (25(OH)D3), downregulated proBDNF and pAkt, dysregulated glucocorticosteroid and mineralocorticoid receptors, impaired mitochondrial biogenesis, and dysfunctional mitochondria energy metabolism in the DEXA-treated group. In contrast, supplementation with vitamin D3 restored the 25(OH)D3 concentration to a value close to that of the control group. There was an elevation in neurotrophic factor protein level, along with augmented activity of pAkt and increased citrate synthase activity in the hippocampus after vitamin D3 administration in long-term DEXA-treated rats. Our findings demonstrate that vitamin D3 supplementation plays a protective role in the hippocampus and partially mitigates the deleterious effects of long-term DEXA administration. The association between serum 25(OH)D3 concentration and BDNF level in the hippocampus indicates the importance of applying vitamin D3 supplementation to prevent and treat pathological conditions.

Sex-Dependent Effects of Chronic Restraint Stress on Mood-Related Behaviours and Neurochemistry in Mice

Anxiety and depressive disorders are closely associated; however, the pathophysiology of these disorders remains poorly understood. Further exploration of the mechanisms involved in anxiety and depression such as the stress response may provide new knowledge that will contribute to our understanding of these disorders. Fifty-eight 8-12-week-old C57BL6 mice were separated into experimental groups by sex as follows: male controls (n = 14), male restraint stress (n = 14), female controls (n = 15) and female restraint stress (n = 15). These mice were taken through a 4-week randomised chronic restraint stress protocol, and their behaviour, as well as tryptophan metabolism and synaptic proteins, were measured in the prefrontal cortex and hippocampus. Adrenal catecholamine regulation was also measured. The female mice showed greater anxiety-like behaviour than their male counterparts. Tryptophan metabolism was unaffected by stress, but some basal sex characteristics were noted. Synaptic proteins were reduced in the hippocampus in stressed females but increased in the prefrontal cortex of all female mice. These changes were not found in any males. Finally, the stressed female mice showed increased catecholamine biosynthesis capability, but this effect was not found in males. Future studies in animal models should consider these sex differences when evaluating mechanisms related to chronic stress and depression.

The Melanocortin System: A Promising Target for the Development of New Antidepressant Drugs

Major depression is one of the most prevalent mental disorders, causing significant human suffering and socioeconomic loss. Since conventional antidepressants are not sufficiently effective, there is an urgent need to develop new antidepressant medications. Despite marked advances in the neurobiology of depression, the etiology and pathophysiology of this disease remain poorly understood. Classical and newer hypotheses of depression suggest that an imbalance of brain monoamines, dysregulation of the hypothalamic-pituitary-adrenal axis (HPAA) and immune system, or impaired hippocampal neurogenesis and neurotrophic factors pathways are cause of depression. It is assumed that conventional antidepressants improve these closely related disturbances. The purpose of this review was to discuss the possibility of affecting these disturbances by targeting the melanocortin system, which includes adrenocorticotropic hormone-activated receptors and their peptide ligands (melanocortins). The melanocortin system is involved in the regulation of various processes in the brain and periphery. Melanocortins, including peripherally administered non-corticotropic agonists, regulate HPAA activity, exhibit anti-inflammatory effects, stimulate the levels of neurotrophic factors, and enhance hippocampal neurogenesis and neurotransmission. Therefore, endogenous melanocortins and their analogs are able to complexly affect the functioning of those body’s systems that are closely related to depression and the effects of antidepressants, thereby demonstrating a promising antidepressant potential.

Chronic mild stress induces differential depression-like symptoms and c-Fos and 5HT1A protein levels in high-anxiety female Long Evans rats

Depression and anxiety disorders overlap in clinical populations, suggesting common mechanisms that may be further investigated in reliable animal models. We used filial 8 female Long-Evans rats bred for high (HAn; n = 19) and low anxiety (LAn)-like behavior (n = 21) to assess forced swim test mobility strategies and chronic mild stress (CMS)-induced depression-like symptoms. We measured (1) weight, (2) fur piloerection, (3) sweet food consumption, (4) grooming behavior, and (5) circulating estradiol (E2). One month after CMS terminated and following a terminal forced swim test, brains were processed for immunohistochemistry targeting c-Fos and serotonin 1 A receptor (5-HT1AR) protein in the paraventricular nucleus (PVN) of the hypothalamus. HAn female rats showed increased anxiety-like behavior (i.e., lower open to closed arm ratios, increased closed arm entries), more swimming (i.e., mobility), and less floating (i.e., immobility) behavior in the forced swim test. Overall, HAn females weighed less than their LAn counterparts. After chronic mild stress, HAn lines displayed even greater mobility and consumed fewer Froot Loops™. Fur and grooming analyses indicated no significant differences in mean counts across experimental groups. One month after CMS, cycling E2 concentrations (pg/ml) did not differ between HAn and LAn animals. Elevated c-Fos and 5-HT1AR expression were observed in the PVN, where HAn CMS rats expressed the most c-Fos and 5-HT1AR immunoreactivity. In summary, outbred HAn rats show robust anxiety-like behavior, exhibit more mobility in the forced swim test, and are more sensitive to chronic mild stress-induced grooming and decline in palatable food ingestion.

The sex-dependent response to psychosocial stress and ischaemic heart disease

Stress is an important risk factor for modern chronic diseases, with distinct influences in males and females. The sex specificity of the mammalian stress response contributes to the sex-dependent development and impacts of coronary artery disease (CAD). Compared to men, women appear to have greater susceptibility to chronic forms of psychosocial stress, extending beyond an increased incidence of mood disorders to include a 2- to 4-fold higher risk of stress-dependent myocardial infarction in women, and up to 10-fold higher risk of Takotsubo syndrome-a stress-dependent coronary-myocardial disorder most prevalent in post-menopausal women. Sex differences arise at all levels of the stress response: from initial perception of stress to behavioural, cognitive, and affective responses and longer-term disease outcomes. These fundamental differences involve interactions between chromosomal and gonadal determinants, (mal)adaptive epigenetic modulation across the lifespan (particularly in early life), and the extrinsic influences of socio-cultural, economic, and environmental factors. Pre-clinical investigations of biological mechanisms support distinct early life programming and a heightened corticolimbic-noradrenaline-neuroinflammatory reactivity in females vs. males, among implicated determinants of the chronic stress response. Unravelling the intrinsic molecular, cellular and systems biological basis of these differences, and their interactions with external lifestyle/socio-cultural determinants, can guide preventative and therapeutic strategies to better target coronary heart disease in a tailored sex-specific manner.

The hippocampus in stress susceptibility and resilience: Reviewing molecular and functional markers

Understanding the individual variability that comes with the likelihood of developing stress-related psychopathologies is of paramount importance when addressing mechanisms of their neurobiology. This article focuses on the hippocampus as a region that is highly influenced by chronic stress exposure and that has strong ties to the development of related disorders, such as depression and post-traumatic stress disorder. We first outline three commonly used animal models that have been used to separate animals into susceptible and resilient cohorts. Next, we review molecular and functional hippocampal markers of susceptibility and resilience. We propose that the hippocampus plays a crucial role in the differences in the processing and storage of stress-related information in animals with different stress susceptibilities. These hippocampal markers not only help us attain a more comprehensive understanding of the various facets of stress-related pathophysiology, but also could be targeted for the development of new treatments.

Activity-Dependent Induction of Younger Biological Phenotypes

In several mammalian species, including humans, complex stimulation patterns such as cognitive and physical exercise lead to improvements in organ function, organism health and performance, as well as possibly longer lifespans. A framework is introduced here in which activity-dependent transcriptional programs, induced by these environmental stimuli, move somatic cells such as neurons and muscle cells toward a state that resembles younger cells to allow remodeling and adaptation of the organism. This cellular adaptation program targets several process classes that are heavily implicated in aging, such as mitochondrial metabolism, cell-cell communication, and epigenetic information processing, and leads to functional improvements in these areas. The activity-dependent gene program (ADGP) can be seen as a natural, endogenous cellular reprogramming mechanism that provides deep insight into the principles of inducible improvements in cell and organism function and can guide the development of therapeutic approaches for longevity. Here, these ADGPs are analyzed, exemplary critical molecular nexus points such as cAMP response element-binding protein, myocyte enhancer factor 2, serum response factor, and c-Fos are identified, and it is explored how one may leverage them to prevent, attenuate, and reverse human aging-related decline of body function.

Stress, mental disorder and ketamine as a novel, rapid acting treatment

The experience of stress is often utilised in models of emerging mental illness and neurobiological systems are implicated as the intermediary link between the experience of psychological stress and the development of a mental disorder. Chronic stress and prolonged glucocorticoid exposure have potent effects on neuronal architecture particularly in regions that modulate the hypothalamic-pituitary-adrenal (HPA) axis and are commonly associated with psychiatric disorders. This review provides an overview of stress modulating neurobiological and neurochemical systems which underpin stress-related structural and functional brain changes. These changes are thought to contribute not only to the development of disorders, but also to the treatment resistance and chronicity seen in some of our most challenging mental disorders. Reports to date suggest that stress-related psychopathology is the aetiological mechanism of these disorders and thus we review the rapid acting antidepressant ketamine as an effective emerging treatment. Ketamine, an N-methyl D-aspartate (NMDA) receptor antagonist, is shown to induce a robust treatment effect in mental disorders via enhanced synaptic strength and connectivity in key brain regions. Whilst ketamine's glutamatergic effect has been previously examined, we further consider ketamine's capacity to modulate the HPA axis and associated pathways.

Early-life maternal deprivation affects the mother-offspring relationship in domestic pigs, as well as the neuroendocrine development and coping behavior of piglets

Early-life adversity may have programming effects on the psychological and physiological development of offspring. Domestic pigs (Sus scrofa) are an excellent model species for studying these effects because of their many physiological similarities to humans. Piglets from 10 sows were subjected to daily 2-h maternal deprivation on postnatal days (PND) 2–15 alone (DA) or in a group of littermates (DG). Control piglets (C) from 10 sows stayed with their mothers. Mother-offspring interaction, milk oxytocin, and cortisol were analyzed. An open-field/novel-object (OF/NO) test was performed with piglets on PNDs 16 and 40. Plasma cortisol and immune parameters were determined on PND 5 and 16. Two piglets from each group and sow were sacrificed on PND 20 and stress-related gene expression in the limbic system and prefrontal cortex (PFC), as well as splenic lymphocyte proliferative abilities, were examined. The milk cortisol of sows increased during the first separation of mother and offspring on the second day of lactation, whereas milk oxytocin did not change. The increase in cortisol by the OF/NO test on PND 16 was greater in C piglets than in DA and DG ones. DA piglets showed less agitated behavior than DG and C piglets in the OF/NO test at PND 16, but appeared more fearful. On PND 40, DA piglets showed more arousal than DG and C piglets in the OF/NO test. Neither plasma IgA nor N/L ratios in blood nor mitogen-induced proliferation of spleen lymphocytes were affected by deprivation. We found a higher mRNA expression of CRHR1 in the hypothalamus and a higher expression of MR in the hippocampus in DA piglets than in DG ones. The expression of GR, MR, and CRHR1 genes in the PFC was reduced by maternal deprivation, however, the expression of arginine vasopressin and oxytocin receptors was not affected. Repeated maternal deprivation induces sustained effects on stress reactivity and behavior of domestic piglets. Some of these effects were buffered by the presence of littermates. In addition, we found sex-specific differences in behavior and gene expression.

The Fibrinolytic System in Peripartum Depression

The relationship between depression and reduced fibrinolytic activity reflects the role of tissue plasminogen activator and plasmin in brain remodeling underlying resilience, depression remission, and reward processing, rather than the dissolution of fibrin clots. Individuals who experience depression demonstrate hippocampal and prefrontal cortex atrophy, as well as impaired neuronal connectivity. Brain-derived neurotrophic factor (BDNF), synthesized as a precursor that is activated through cleavage by tissue plasminogen activator and plasmin, influences adult neurogenesis and neuronal plasticity in the hippocampus and prefrontal cortex. Depression is associated with decreased brain levels of BDNF, due to reduced activity of tissue plasminogen activator and plasmin. Tissue plasminogen activator and plasmin also mediate the release of dopamine, a neurotransmitter implicated in motivation and reward. Peripartum depression defines a depressive episode that occurs during pregnancy or in the first month after delivery, reinforcing the concept that postpartum depression may be a continuum of antenatal depression. This article describes the fibrinolytic status in the healthy brain, in stress and depression, emphasizing the links between biological markers of depression and defective fibrinolysis. It also discusses the association between hypofibrinolysis and risk factors for perinatal depression, including polycystic ovary syndrome, early miscarriage, preeclampsia, stressful life events, sedentariness, eating habits, gestational and type 2 diabetes, and antithyroid peroxidase antibodies. In addition, it reviews the evidence that antidepressant medications and interventions as diverse as placebo, psychotherapy, massage, video game playing, regular exercise, dietary modifications, omega 3 fatty acid supplementation, neurohormones, and cigarette smoking may reduce depression by restoring the fibrinolytic activity. Last, it suggests new directions for research.

Benzoresorcinol induces developmental neurotoxicity and injures exploratory, learning and memorizing abilities in zebrafish

Benzophenones (BPs) are a class of UV absorber commonly used in skin care products like sunscreens. With its wide range of application, its environmental and human hazards have received much attention in recent days. Previous studies on the toxicity of BPs mainly focused on its endocrine-disrupting effects, but there are limited studies on its neurodevelopment and neurotoxicity. Herein, using the zebrafish model we studied the neurodevelopmental- and neuro-toxicity of benzophenone 1 (BP1) (0.8, 1.0, 1.2, 1.6, and 2.4 μg/mL). As a result, BP1 led to an increase of embryo mortality, a decrease in hatching rate, and an increase in the rate of developmental abnormalities in a concentration-dependent manner. BP1 also caused developmental defects in the central nervous system (CNS) and dopaminergic (DA) neurons. Accordingly, BP1 injured larval zebrafish general locomotion and response to stimuli in light/dark challenge. In adult zebrafish, BP1 exposure (1, 10, 100, 1000 μg/L) caused inhibition of learning and memory abilities in the T-maze tests, and inhibited exploratory behavior and activity in the novel tank diving tests. Further, transcription levels of genes related to neurotoxicity, neurodevelopment, and anxiety revealed that BP1 may affect the development and function of the myelin sheath, inducing structural and functional defects of CNS, manifested as abnormal behaviors such as anxiety. Hence, the current study revealed the neurodevelopmental toxicity and neurotoxicity of BP1, expanded our knowledge about the toxic effects of BP1 on organisms, posing a possible threat to the environment and human health.

Elevated BICD2 DNA methylation in blood of major depressive disorder patients and reduction of depressive-like behaviors in hippocampal Bicd2-knockdown mice

Major depressive disorder (MDD) is a prevalent and devastating mental illness. To date, the diagnosis of MDD is largely dependent on clinical interviews and questionnaires and still lacks a reliable biomarker. DNA methylation has a stable and reversible nature and is likely associated with the course and therapeutic efficacy of complex diseases, which may play an important role in the etiology of a disease. Here, we identified and validated a DNA methylation biomarker for MDD from four independent cohorts of the Chinese Han population. First, we integrated the analysis of the DNA methylation microarray (n = 80) and RNA expression microarray data (n = 40) and identified BICD2 as the top-ranked gene. In the replication phase, we employed the Sequenom MassARRAY method to confirm the DNA hypermethylation change in a large sample size (n = 1,346) and used the methylation-sensitive restriction enzymes and a quantitative PCR approach (MSE-qPCR) and qPCR method to confirm the correlation between DNA hypermethylation and mRNA down-regulation of BICD2 (n = 60). The results were replicated in the peripheral blood of mice with depressive-like behaviors, while in the hippocampus of mice, Bicd2 showed DNA hypomethylation and mRNA/protein up-regulation. Hippocampal Bicd2 knockdown demonstrates antidepressant action in the chronic unpredictable mild stress (CUMS) mouse model of depression, which may be mediated by increased BDNF expression. Our study identified a potential DNA methylation biomarker and investigated its functional implications, which could be exploited to improve the diagnosis and treatment of MDD.

Uncovering the Underlying Mechanisms of Ketamine as a Novel Antidepressant

Major depressive disorder (MDD) is a devastating psychiatric disorder which exacts enormous personal and social-economic burdens. Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, has been discovered to exert rapid and sustained antidepressant-like actions on MDD patients and animal models. However, the dissociation and psychotomimetic propensities of ketamine have limited its use for psychiatric indications. Here, we review recently proposed mechanistic hypotheses regarding how ketamine exerts antidepressant-like actions. Ketamine may potentiate α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR)-mediated transmission in pyramidal neurons by disinhibition and/or blockade of spontaneous NMDAR-mediated neurotransmission. Ketamine may also activate neuroplasticity- and synaptogenesis-relevant signaling pathways, which may converge on key components like brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) and mechanistic target of rapamycin (mTOR). These processes may subsequently rebalance the excitatory/inhibitory transmission and restore neural network integrity that is compromised in depression. Understanding the mechanisms underpinning ketamine’s antidepressant-like actions at cellular and neural circuit level will drive the development of safe and effective pharmacological interventions for the treatment of MDD.

Convergent neural correlates of prenatal exposure to air pollution and behavioral phenotypes of risk for internalizing and externalizing problems: Potential biological and cognitive pathways

Humans are ubiquitously exposed to neurotoxicants in air pollution, causing increased risk for psychiatric outcomes. Effects of prenatal exposure to air pollution on early emerging behavioral phenotypes that increase risk of psychopathology remain understudied. We review animal models that represent analogues of human behavioral phenotypes that are risk markers for internalizing and externalizing problems (behavioral inhibition, behavioral exuberance, irritability), and identify commonalities among the neural mechanisms underlying these behavioral phenotypes and the neural targets of three types of air pollutants (polycyclic aromatic hydrocarbons, traffic-related air pollutants, fine particulate matter < 2.5 µm). We conclude that prenatal exposure to air pollutants increases risk for behavioral inhibition and irritability through distinct mechanisms, including altered dopaminergic signaling and hippocampal morphology, neuroinflammation, and decreased brain-derived neurotrophic factor expression. Future studies should investigate these effects in human longitudinal studies incorporating complex exposure measurement methods, neuroimaging, and behavioral characterization of temperament phenotypes and neurocognitive processing to facilitate efforts aimed at improving long-lasting developmental benefits for children, particularly those living in areas with high levels of exposure.

Resilience to Stress: Lessons from Rodents about Nature versus Nurture

Individual differences in human temperament influence how we respond to stress and can confer vulnerability (or resilience) to emotional disorders. For example, high levels of behavioral inhibition in children predict increased risk of mood and anxiety disorders in later life. The biological underpinnings of temperament are unknown, although improved understanding can offer insight into the pathogenesis of emotional disorders. Our laboratory has used a rat model of temperamental differences to study neurodevelopmental factors that lead to a highly inhibited, stress vulnerable phenotype. Selective breeding for high versus low behavioral response to novelty created two rat strains that exhibit dramatic behavior differences over multiple domains relevant to emotional disorders. Low novelty responder (bLR) rats exhibit high levels of behavioral inhibition, passive stress coping, anhedonia, decreased sociability and vulnerability to chronic stress compared to high novelty responders (bHRs). On the other hand, bHRs exhibit high levels of behavioral dis-inhibition, active coping, and aggression. This review article summarizes our work with the bHR/bLR model showing the developmental emergence of the bHR/bLR phenotypes, the role the environment plays in shaping it, and the involvement of epigenetic processes such as DNA methylation that mediate differences in emotionality and stress reactivity.

Prenatal Exposure to Air Pollution and Early Life Stress Effects on Hippocampal Subregional Volumes and Associations with Visual-Spatial Reasoning

Background

Children from economically distressed families and neighborhoods are at risk for stress and pollution exposure and potential neurotoxic sequelae. We examine dimensions of early-life stress affecting hippocampal volumes, how prenatal exposure to air pollution might magnify these effects, and associations between hippocampal volumes and visuospatial reasoning.

Methods

Fifty-three Hispanic/Latinx and/or Black children of ages 7 to 9 years were recruited from a longitudinal birth cohort for magnetic resonance imaging and cognitive assessment. Exposure to airborne polycyclic aromatic hydrocarbons was measured during the third trimester of pregnancy. Maternal report of psychosocial stress was collected at child age 5 and served as measures of early-life stress. Whole hippocampus and subfield volumes were extracted using FreeSurfer. Wechsler performance IQ measured visuospatial reasoning.

Results

Maternal perceived stress associated with smaller right hippocampal volume among their children (B = −0.57, t₃₄ = −3.05, 95% CI, −0.95 to −0.19). Prenatal polycyclic aromatic hydrocarbon moderated the association between maternal perceived stress and right CA1, CA3, and CA4/dentate gyrus volumes (B ≥ 0.68, t₃₃ ≥ 2.17) such that higher prenatal polycyclic aromatic hydrocarbon exposure magnified negative associations between stress and volume, whereas this was buffered at lower exposure. Right CA3 and CA4/dentate gyrus volumes (B ≥ 0.35, t₃₃ > 2.16) were associated with greater performance IQ.

Conclusions

Prenatal and early-life exposures to chemical and social stressors are likely compounding. Socioeconomic deprivation and disparities increase risk of these exposures that exert critical neurobiological effects. Developing deeper understandings of these complex interactions will facilitate more focused public health strategies to protect and foster the development of children at greatest risk of mental and physical effects associated with poverty.

Integrative Brain Dynamics in Childhood Bullying Victimization: Cognitive and Emotional Convergence Associated With Stress Psychopathology

Bullying victimization is a form of psychological stress that is associated with poor outcomes in the areas of mental health and learning. Although the emotional maladjustment and memory impairment following interpersonal stress are well documented, the mechanisms of complex cerebral dysfunctions have neither been outlined nor studied in depth in the context of childhood bullying victimization. As a contribution to the cross-disciplinary field of developmental psychology and neuroscience, we review the neuropathophysiology of early life stress, as well as general psychological stress to synthesize the data and clarify the versatile dynamics within neuronal networks linked to bullying victimization. The stress-induced neuropsychological cascade and associated cerebral networks with a focus on cognitive and emotional convergence are described. The main findings are that stress-evoked neuroendocrine reactivity relates to neuromodulation and limbic dysregulation that hinder emotion processing and executive functioning such as semantic cognition, cognitive flexibility, and learning. Developmental aspects and interacting neural mechanisms linked to distressed cognitive and emotional processing are pinpointed and potential theory-of-mind nuances in targets of bullying are presented. The results show that childhood stress psychopathology is associated with a complex interplay where the major role belongs to, but is not limited to, the amygdala, fusiform gyrus, insula, striatum, and prefrontal cortex. This interplay contributes to the sensitivity toward facial expressions, poor cognitive reasoning, and distress that affect behavioral modulation and emotion regulation. We integrate the data on major brain dynamics in stress neuroactivity that can be associated with childhood psychopathology to help inform future studies that are focused on the treatment and prevention of psychiatric disorders and learning problems in bullied children and adolescents.

Resilience to the effects of social stress on vulnerability to developing drug addiction

We review the still scarce but growing literature on resilience to the effects of social stress on the rewarding properties of drugs of abuse. We define the concept of resilience and how it is applied to the field of drug addiction research. We also describe the internal and external protective factors associated with resilience, such as individual behavioral traits and social support. We then explain the physiological response to stress and how it is modulated by resilience factors. In the subsequent section, we describe the animal models commonly used in the study of resilience to social stress, and we focus on the effects of chronic social defeat (SD), a kind of stress induced by repeated experience of defeat in an agonistic encounter, on different animal behaviors (depression- and anxiety-like behavior, cognitive impairment and addiction-like symptoms). We then summarize the current knowledge on the neurobiological substrates of resilience derived from studies of resilience to the effects of chronic SD stress on depression- and anxiety-related behaviors in rodents. Finally, we focus on the limited studies carried out to explore resilience to the effects of SD stress on the rewarding properties of drugs of abuse, describing the current state of knowledge and suggesting future research directions.

Sex-Specific Behavioral Response to Early Adolescent Stress in the Genetically More Stress-Reactive Wistar Kyoto More Immobile, and Its Nearly Isogenic Wistar Kyoto Less Immobile Control Strain

Genetic predisposition and environmental stress are known etiologies of stress-related psychiatric disorders. Environmental stress during adolescence is assumed to be particularly detrimental for adult affective behaviors. To investigate how genetic stress-reactivity differences modify the effects of stress during adolescence on adult affective behaviors we employed two inbred strains with differing stress reactivity. The Wistar Kyoto More Immobile (WMI) rat strain show increased stress-reactivity and despair-like behaviors as well as passive coping compared to the nearly isogenic control strain, the Wistar Kyoto Less Immobile (WLI). Males and females of these strains were exposed to contextual fear conditioning (CFC) during early adolescence (EA), between 32 and 34 postnatal days (PND), and were tested for the consequences of this mild EA stress in adulthood. Early adolescent stress significantly decreased anxiety-like behavior, measured in the open field test (OFT) and increased social interaction and recognition in adult males of both strains compared to controls. In contrast, no significant effects of EA stress were observed in adult females in these behaviors. Both males and females of the genetically less stress-reactive WLI strain showed significantly increased immobility in the forced swim test (FST) after EA stress compared to controls. In contrast, immobility was significantly attenuated by EA stress in adult WMI females compared to controls. Transcriptomic changes of the glucocorticoid receptor (Nr3c1, GR) and the brain-derived neurotrophic factor (Bdnf) illuminate primarily strain and stress-dependent changes, respectively, in the prefrontal cortex and hippocampus of adults. These results suggest that contrary to expectations, limited adolescent stress is beneficial to males thru decreasing anxiety and enhancing social behaviors, and to the stress more-reactive WMI females by way of decreasing passive coping.

Chronic mild stress paradigm as a rat model of depression: facts, artifacts, and future perspectives

RATIONALE

The chronic mild stress (CMS) paradigm was first described almost 40 years ago and has become a widely used model in the search for antidepressant drugs for major depression disorder (MDD). It has resulted in the publication of almost 1700 studies in rats alone. Under the original CMS procedure, the expression of an anhedonic response, a key symptom of depression, was seen as an essential feature of both the model and a depressive state. The prolonged exposure of rodents to unpredictable/uncontrollable mild stressors leads to a reduction in the intake of palatable liquids, behavioral despair, locomotor inhibition, anxiety-like changes, and vegetative (somatic) abnormalities. Many of the CMS studies do not report these patterns of behaviors, and they often fail to include consistent molecular, neuroanatomical, and physiological phenotypes of CMS-exposed animals.

OBJECTIVES

To critically review the CMS studies in rats so that conceptual and methodological flaws can be avoided in future studies.

RESULTS

Analysis of the literature supports the validity of the CMS model and its impact on the field. However, further improvements could be achieved by (i) the stratification of animals into 'resilient' and 'susceptible' cohorts within the CMS animals, (ii) the use of more refined protocols in the sucrose test to mitigate physiological and physical artifacts, and (iii) the systematic evaluation of the non-specific effects of CMS and implementation of appropriate adjustments within the behavioral tests.

CONCLUSIONS

We propose methodological revisions and the use of more advanced behavioral tests to refine the rat CMS paradigm, which offers a valuable tool for developing new antidepressant medications.

Hippocampal-Prefrontal Connectivity Prior to the COVID-19 Pandemic Predicts Stress Reactivity

BACKGROUND

By adolescence, foundational cognitive and affective neurobehavioral processes specialize based on environmental demands, such as stress, to determine the basis of adult trajectories. The ongoing COVID-19 pandemic has increased stress for everyone, particularly adolescents who face unique stressors such as restrictions in socialization and education. However, variability in brain processes supporting stress reactivity is not well understood. Here, we leverage pre-pandemic brain development studies to identify how maturity of prefrontal connectivity with the amygdala and hippocampus (HPC) is associated with response to COVID-19. We hypothesized that age-related changes in connectivity of affective and cognitive brain systems may underlie the emotional response of adolescents during the pandemic.

METHODS

In this study, 10- to 31-year-old participants (n = 111) completed resting-state functional magnetic resonance imaging scans prior to the pandemic and then completed a questionnaire 9 months into the pandemic measuring worry, COVID-related stress, sadness, perceived stress, and positive affect. Associations between pairwise functional connectivity of HPC/amygdala subregions with prefrontal cortex subdivisions and affective reactivity during the pandemic were examined.

RESULTS

Regression analyses indicated that both worry and COVID-19-related stress increased with age (false discovery rate-corrected p < .05). Furthermore, greater connectivity between the anterior ventromedial prefrontal cortex and posterior HPC was associated with greater worry and COVID-19-related stress (p < .05 corrected), which was primarily driven by individuals younger than 18 years.

CONCLUSIONS

Taken together, our results indicate that increases in stress reactivity to the COVID-19 pandemic across the transition to adulthood are driven by maturation of posterior HPC-ventromedial prefrontal cortex coupling, which integrates stress response and emotional memory processing.

Do Neurotrophins Connect Neurological Disorders and Heart Diseases?

Neurotrophins (NTs) are one of the most characterized neurotrophic factor family members and consist of four members in mammals. Growing evidence suggests that there is a complex inter- and bi-directional relationship between central nervous system (CNS) disorders and cardiac dysfunction, so-called "brain-heart axis". Recent studies suggest that CNS disorders, including neurodegenerative diseases, stroke, and depression, affect cardiovascular function via various mechanisms, such as hypothalamic-pituitary-adrenal axis augmentation. Although this brain-heart axis has been well studied in humans and mice, the involvement of NT signaling in the axis has not been fully investigated. In the first half of this review, we emphasize the importance of NTs not only in the nervous system, but also in the cardiovascular system from the embryonic stage to the adult state. In the second half, we discuss the involvement of NTs in the pathogenesis of cardiovascular diseases, and then examine whether an alteration in NTs could serve as the mediator between neurological disorders and heart dysfunction. The further investigation we propose herein could contribute to finding direct evidence for the involvement of NTs in the axis and new treatment for cardiovascular diseases.

The coupling of RACK1 with the beta isoform of the glucocorticoid receptor promotes resilience to chronic stress exposure

Several intracellular pathways that contribute to the adaptation or maladaptation to environmental challenges mediate the vulnerability and resilience to chronic stress. The activity of the hypothalamic-pituitary-adrenal (HPA) axis is fundamental for the proper maintenance of brain processes, and it is related to the functionality of the isoform alfa and beta of the glucocorticoid receptor (Gr), the primary regulator of HPA axis. Among the downstream effectors of the axis, the scaffolding protein RACK1 covers an important role in regulating synaptic activity and mediates the transcription of the neurotrophin Bdnf. Hence, by employing the chronic mild stress (CMS) paradigm, we studied the role of the Grβ-RACK1-Bdnf signaling in the different susceptibility to chronic stress exposure. We found that resilience to two weeks of CMS is paralleled by the activation of this pathway in the ventral hippocampus, the hippocampal subregion involved in the modulation of stress response. Moreover, the results we obtained in vitro by exposing SH-SY5Y cells to cortisol support the data we found in vivo. The results obtained add novel critical information about the link among Gr, RACK1 and Bdnf and the resilience to chronic stress, suggesting novel targets for the treatment of stress-related disorders, including depression.

Brain derived neurotrophic factor deficiency exacerbates inflammation-induced anhedonia in mice

Brain-derived neurotrophic factor (BDNF) is implicated in the pathology of major depression and influences the inflammatory response. Prolonged immune system activation can cause depression symptoms, and individuals with low BDNF expression may be vulnerable to inflammation-induced depression. We tested the hypothesis that BDNF deficient mice are vulnerable to the induction of depressive-like behavior following peripheral immune challenge. BDNF heterozygous (BDNF+/-) or wild-type (BDNF+/+) littermate mice were injected intraperitoneally (i.p.) with endotoxin (lipopolysaccharide, LPS) to trigger an acute pro-inflammatory response. After resolution of the acute sickness response, central expression of inflammatory genes, kynurenine metabolites, and depressive-like behaviors across multiple dimensions (symptoms) were measured. BDNF+/- mice displayed an exaggerated neuroinflammatory response following peripheral immune challenge. Pro-inflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor α (TNFα) and interleukin-6 (IL-6) were overexpressed in BDNF+/- mice relative to BDNF+/+ littermate control mice. While behavioral despair and anxiety-like behavior was not different between genotypes, LPS-induced anhedonia-like behavior was significantly more pronounced in BDNF+/- mice relative to BDNF+/+ mice. The kynurenine pathway mediates the many depressive-like behavioral effects of peripheral LPS, and similar to pro-inflammatory cytokine gene expression, indoleamine 2,3-dioxygenase (IDO) expression and kynurenine metabolism was exaggerated in BDNF+/- mice. Genetic BDNF deficiency results in a dysregulated neuroinflammatory and metabolic response to peripheral immune challenge and in a specific vulnerability to the development of inflammation-induced anhedonia.

The Effects of Intermittent Fasting on Brain and Cognitive Function

The importance of diet and the gut-brain axis for brain health and cognitive function is increasingly acknowledged. Dietary interventions are tested for their potential to prevent and/or treat brain disorders. Intermittent fasting (IF), the abstinence or strong limitation of calories for 12 to 48 h, alternated with periods of regular food intake, has shown promising results on neurobiological health in animal models. In this review article, we discuss the potential benefits of IF on cognitive function and the possible effects on the prevention and progress of brain-related disorders in animals and humans. We do so by summarizing the effects of IF which through metabolic, cellular, and circadian mechanisms lead to anatomical and functional changes in the brain. Our review shows that there is no clear evidence of a positive short-term effect of IF on cognition in healthy subjects. Clinical studies show benefits of IF for epilepsy, Alzheimer’s disease, and multiple sclerosis on disease symptoms and progress. Findings from animal studies show mechanisms by which Parkinson’s disease, ischemic stroke, autism spectrum disorder, and mood and anxiety disorders could benefit from IF. Future research should disentangle whether positive effects of IF hold true regardless of age or the presence of obesity. Moreover, variations in fasting patterns, total caloric intake, and intake of specific nutrients may be relevant components of IF success. Longitudinal studies and randomized clinical trials (RCTs) will provide a window into the long-term effects of IF on the development and progress of brain-related diseases.

Altered white matter microstructural organization in posttraumatic stress disorder across 3047 adults: results from the PGC-ENIGMA PTSD consortium

A growing number of studies have examined alterations in white matter organization in people with posttraumatic stress disorder (PTSD) using diffusion MRI (dMRI), but the results have been mixed which may be partially due to relatively small sample sizes among studies. Altered structural connectivity may be both a neurobiological vulnerability for, and a result of, PTSD. In an effort to find reliable effects, we present a multi-cohort analysis of dMRI metrics across 3047 individuals from 28 cohorts currently participating in the PGC-ENIGMA PTSD working group (a joint partnership between the Psychiatric Genomics Consortium and the Enhancing NeuroImaging Genetics through Meta-Analysis consortium). Comparing regional white matter metrics across the full brain in 1426 individuals with PTSD and 1621 controls (2174 males/873 females) between ages 18-83, 92% of whom were trauma-exposed, we report associations between PTSD and disrupted white matter organization measured by lower fractional anisotropy (FA) in the tapetum region of the corpus callosum (Cohen's d = -0.11, p = 0.0055). The tapetum connects the left and right hippocampus, for which structure and function have been consistently implicated in PTSD. Results were consistent even after accounting for the effects of multiple potentially confounding variables: childhood trauma exposure, comorbid depression, history of traumatic brain injury, current alcohol abuse or dependence, and current use of psychotropic medications. Our results show that PTSD may be associated with alterations in the broader hippocampal network.

Association between hippocampal structure and serum Brain-Derived Neurotrophic Factor (BDNF) in healthy adults: A registered report

The hippocampus is a highly plastic brain structure supporting functions central to human cognition. Morphological changes in the hippocampus have been implicated in development, aging, as well as in a broad range of neurological and psychiatric disorders. A growing body of research suggests that hippocampal plasticity is closely linked to the actions of brain-derived neurotrophic factor (BDNF). However, evidence on the relationship between hippocampal volume (HCV) and peripheral BDNF levels is scarce and limited to elderly and patient populations. Further, despite evidence that BDNF expression differs throughout the hippocampus and is implicated in adult neurogenesis specifically in the dentate gyrus, no study has so far related peripheral BDNF levels to the volumes of individual hippocampal subfields. Besides its clinical implications, BDNF-facilitated hippocampal plasticity plays an important role in regulating cognitive and affective processes. In the current registered report, we investigated how serum BDNF (sBDNF) levels relate to volumes of the hippocampal formation and its subfields in a large sample of healthy adults (N = 279, 160 f) with a broad age range (20-55 years, mean 40.5) recruited in the context of the ReSource Project. We related HCV to basal sBDNF and, in a subsample (n = 103, 57 f), to acute stress-reactive change in sBDNF. We further tested the role of age as a moderator of both associations. Contrary to our hypotheses, neither basal sBDNF levels nor stress-reactive sBDNF change were associated with total HCV or volume of the dentate gyrus/cornu ammonis 4 (DG/CA4) subfield. We also found no evidence for a moderating effect of age on any of these associations. Our null results provide a first point of reference on the relationship between sBDNF and HCV in healthy mid-age, in contrast to patient or aging populations. We suggest that sBDNF levels have limited predictive value for morphological differences of the hippocampal structure when notable challenge to its neuronal integrity or to neurotrophic capacity is absent.

Chronic stress and Alzheimer's disease: the interplay between the hypothalamic-pituitary-adrenal axis, genetics and microglia

Chronic psychosocial stress is increasingly being recognised as a risk factor for sporadic Alzheimer's disease (AD). The hypothalamic-pituitary-adrenal axis (HPA axis) is the major stress response pathway in the body and tightly regulates the production of cortisol, a glucocorticoid hormone. Dysregulation of the HPA axis and increased levels of cortisol are commonly found in AD patients and make a major contribution to the disease process. The underlying mechanisms remain poorly understood. In addition, within the general population there are interindividual differences in sensitivities to glucocorticoid and stress responses, which are thought to be due to a combination of genetic and environmental factors. These differences could ultimately impact an individuals' risk of AD. The purpose of this review is first to summarise the literature describing environmental and genetic factors that can impact an individual's HPA axis reactivity and function and ultimately AD risk. Secondly, we propose a mechanism by which genetic factors that influence HPA axis reactivity may also impact inflammation, a key driver of neurodegeneration. We hypothesize that these factors can mediate glucocorticoid priming of the immune cells of the brain, microglia, to become pro-inflammatory and promote a neurotoxic environment resulting in neurodegeneration. Understanding the underlying molecular mechanisms and identifying these genetic factors has implications for evaluating stress-related risk/progression to neurodegeneration, informing the success of interventions based on stress management and potential risks associated with the common use of glucocorticoids.

Scientific rationale of Indian AYUSH Ministry advisory for COVID-19 prevention, prophylaxis, and immunomodulation

The current outbreak of COVID-19 is caused by the SARS-CoV-2 virus that has affected > 210 countries. Various steps are taken by different countries to tackle the current war-like health situation. In India, the Ministry of AYUSH released a self-care advisory for immunomodulation measures during the COVID-19 and this review article discusses the detailed scientific rationale associated with this advisory. Authors have spotted and presented in-depth insight of advisory in terms of immunomodulatory, antiviral, antibacterial, co-morbidity associated actions, and their probable mechanism of action. Immunomodulatory actions of advised herbs with no significant adverse drug reaction/toxicity strongly support the extension of advisory for COVID-19 prevention, prophylaxis, mitigations, and rehabilitation capacities. This advisory also emphasized Dhyana (meditation) and Yogasanas as a holistic approach in enhancing immunity, mental health, and quality of life. The present review may open-up new meadows for research and can provide better conceptual leads for future researches in immunomodulation, antiviral-development, psychoneuroimmunology, especially for COVID-19.

Protocol for the Pregnancy During the COVID-19 Pandemic (PdP) Study: A Longitudinal Cohort Study of Mental Health Among Pregnant Canadians During the COVID-19 Pandemic and Developmental Outcomes in Their Children

BACKGROUND

The COVID-19 pandemic and countermeasures implemented by governments around the world have led to dramatically increased symptoms of depression and anxiety. Pregnant individuals may be particularly vulnerable to the negative psychological effects of COVID-19 public health measures because they represent a demographic that is most affected by disasters and because pregnancy itself entails significant life changes that require major psychosocial and emotional adjustments.

OBJECTIVE

The PdP study was designed to investigate the associations among exposure to objective hardship caused by the pandemic, perceived stress and psychological distress in pregnant individuals, and developmental outcomes in their offspring.

METHODS

The PdP study comprises a prospective longitudinal cohort of individuals who were pregnant at enrollment, with repeated follow-ups during pregnancy and the postpartum period. Participants were eligible if they were pregnant, ≥17 years old, at ≤35 weeks of gestation at study enrollment, living in Canada, and able to read and write in English or French. At enrollment, participants completed an initial survey that assessed demographic and socioeconomic characteristics, previous pregnancies and births, prepregnancy health, health conditions during pregnancy, medications, psychological distress, social support, and hardships experienced because of the COVID-19 pandemic (eg, lost employment or a loved one dying). For the first three months following the initial survey, participants received a monthly email link to complete a follow-up survey that asked about their experiences since the previous survey. After three months, follow-up surveys were sent every other month to reduce participant burden. For each of these surveys, participants were first asked if they were still pregnant and then routed either to the next prenatal survey or to the delivery survey. In the postpartum period, surveys were sent at 3, 6, and 12 months of infant age to assess maternal stress, psychological distress, and infant development.

RESULTS

Participant recruitment via social media (Facebook and Instagram) began on April 5, 2020, and is ongoing. As of April 2021, more than 11,000 individuals have started the initial survey. Follow-up data collection is ongoing.

CONCLUSIONS

This longitudinal investigation seeks to elucidate the associations among hardships, maternal psychological distress, child development during the COVID-19 pandemic, and risk and resilience factors that amplify or ameliorate these associations. The findings of this study are intended to generate knowledge about the psychological consequences of pandemics on pregnant individuals and point toward prevention and intervention targets.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/25407.

Harnessing the Neurobiology of Resilience to Protect the Mental Well-Being of Healthcare Workers During the COVID-19 Pandemic

Healthcare workers are at a high risk of psychological morbidity in the face of the COVID-19 pandemic. However, there is significant variability in the impact of this crisis on individual healthcare workers, which can be best explained through an appreciation of the construct of resilience. Broadly speaking, resilience refers to the ability to successfully adapt to stressful or traumatic events, and thus plays a key role in determining mental health outcomes following exposure to such events. A proper understanding of resilience is vital in enabling a shift from a reactive to a proactive approach for protecting and promoting the mental well-being of healthcare workers. Research in the past decade has identified six areas that provide promising leads in understanding the biological basis of individual variations in resilience. These are: (1) the key role played by the monoamines noradrenaline and serotonin, (2) the centrality of the hypothalamic-pituitary-adrenal axis in influencing stress vulnerability and resilience, (3) the intimate links between the immune system and stress sensitivity, (4) the role of epigenetic modulation of gene expression in influencing the stress response, (5) the role played by certain neuropeptides as a natural “brake” mechanism in the face of stress, and (6) the neurobiological mechanisms by which environmental factors, such as exercise, diet, and social support, influence resilience to subsequent life events. Though much of this research is still in its early stages, it has already provided valuable information on which strategies – including dietary changes, lifestyle modification, environmental modification, psychosocial interventions, and even pharmacological treatments – may prove to be useful in fostering resilience in individuals and groups. This paper examines the above evidence more closely, with a specific focus on the challenges faced by healthcare workers during the COVID-19 pandemic, and provides suggestions regarding how it may be translated into real-world interventions, as well as how the more tentative hypotheses advanced in this field may be tested during this critical period.

Experience and activity-dependent control of glucocorticoid receptors during the stress response in large-scale brain networks

The diversity of actions of the glucocorticoid stress hormones among individuals and within organs, tissues and cells is shaped by age, gender, genetics, metabolism, and the quantity of exposure. However, such factors cannot explain the heterogeneity of responses in the brain within cells of the same lineage, or similar tissue environment, or in the same individual. Here, we argue that the stress response is continuously updated by synchronized neural activity on large-scale brain networks. This occurs at the molecular, cellular and behavioral levels by crosstalk communication between activity-dependent and glucocorticoid signaling pathways, which updates the diversity of responses based on prior experience. Such a Bayesian process determines adaptation to the demands of the body and external world. We propose a framework for understanding how the diversity of glucocorticoid actions throughout brain networks is essential for supporting optimal health, while its disruption may contribute to the pathophysiology of stress-related disorders, such as major depression, and resistance to therapeutic treatments.

Activation of BDNF by transcription factor Nrf2 contributes to antidepressant-like actions in rodents

The transcription factor erythroid 2-related factor 2 (Nrf2) and brain-derived neurotrophic factor (BDNF) play a key role in depression. However, the molecular mechanisms underlying the crosstalk between Nrf2 and BDNF in depression remain unclear. We examined whether Nrf2 regulates the transcription of Bdnf by binding to its exon I promoter. Furthermore, the role of Nrf2 and BDNF in the brain regions from mice with depression-like phenotypes was examined. Nrf2 regulated the transcription of Bdnf by binding to its exon I promoter. Activation of Nrf2 by sulforaphane (SFN) showed fast-acting antidepressant-like effects in mice by activating BDNF as well as by inhibiting the expression of its transcriptional repressors (HDAC2, mSin3A, and MeCP2) and revising abnormal synaptic transmission. In contrast, SFN did not affect the protein expression of BDNF and its transcriptional repressor proteins in the medial prefrontal cortex (mPFC) and hippocampus, nor did it reduce depression-like behaviors and abnormal synaptic transmission in Nrf2 knockout mice. In the mouse model of chronic social defeat stress (CSDS), protein levels of Nrf2 and BDNF in the mPFC and hippocampus were lower than those of control and CSDS-resilient mice. In contrast, the protein levels of BDNF transcriptional repressors in the CSDS-susceptible mice were higher than those of control and CSDS-resilient mice. These data suggest that Nrf2 activation increases the expression of Bdnf and decreases the expression of its transcriptional repressors, which result in fast-acting antidepressant-like actions. Furthermore, abnormalities in crosstalk between Nrf2 and BDNF may contribute to the resilience versus susceptibility of mice against CSDS.

Neurosteroids and Neurotrophic Factors: What Is Their Promise as Biomarkers for Major Depression and PTSD?

Even though major depressive disorder (MDD) and post-traumatic stress disorder (PTSD) are among the most prevalent and incapacitating mental illnesses in the world, their diagnosis still relies solely on the characterization of subjective symptoms (many of which are shared by multiple disorders) self-reported by patients. Thus, the need for objective measures that aid in the detection of and differentiation between psychiatric disorders becomes urgent. In this paper, we explore the potential of neurosteroids and neurotrophic proteins as biomarkers for MDD and PTSD. Circulating levels of the GABAergic neuroactive steroid, allopregnanolone, are diminished in MDD and PTSD patients, which corroborates the finding of depleted neurosteroid levels observed in animal models of these disorders. The neurotrophic protein, brain-derived neurotropic factor (BDNF), is also reduced in the periphery and in the brain of MDD patients and depressed-like animals that express lower neurosteroid levels. Although the role of BDNF in PTSD psychopathology seems less clear and merits more research, we propose a causal link between allopregnanolone levels and BDNF expression that could function as a biomarker axis for the diagnosis of both MDD and PTSD.