Stress-induced grey matter loss determined by MRI is primarily due to loss of dendrites and their synapses

Posttraumatic survivor guilt is associated with white matter microstructure alterations

BACKGROUND

Military veterans with posttraumatic stress disorder (PTSD) commonly experience posttraumatic guilt. Guilt over commission or omission evolves when responsibility is assumed for an unfortunate outcome (e.g., the death of a fellow combatant). Survivor guilt is a state of intense emotional distress experienced by the weight of knowing that one survived while others did not.

METHODS

This study of the Translational Research Center for TBI and Stress Disorders (TRACTS) analyzed structural and diffusion-weighted magnetic resonance imaging data from 132 male Iraq/Afghanistan veterans with PTSD. The Clinician-Administered PTSD Scale for DSM-IV (CAPS-IV) was employed to classify guilt. Thirty (22.7 %) veterans experienced guilt over acts of commission or omission, 34 (25.8 %) experienced survivor guilt, and 68 (51.5 %) had no posttraumatic guilt. White matter microstructure (fractional anisotropy, FA), cortical thickness, and cortical volume were compared between veterans with guilt over acts of commission or omission, veterans with survivor guilt, and veterans without guilt.

RESULTS

Veterans with survivor guilt had significantly lower white matter FA compared to veterans who did not experience guilt (p < .001), affecting several regions of major white matter fiber bundles. There were no significant differences in white matter FA, cortical thickness, or volumes between veterans with guilt over acts of commission or omission and veterans without guilt (p > .050).

LIMITATIONS

This cross-sectional study with exclusively male veterans precludes inferences of causality between the studied variables and generalizability to the larger veteran population that includes women.

CONCLUSION

Survivor guilt may be a particularly impactful form of posttraumatic guilt that requires specific treatment efforts targeting brain health.

Chronic activation of a negative engram induces behavioral and cellular abnormalities

Negative memories engage a brain and body-wide stress response in humans that can alter cognition and behavior. Prolonged stress responses induce maladaptive cellular, circuit, and systems-level changes that can lead to pathological brain states and corresponding disorders in which mood and memory are affected. However, it is unclear if repeated activation of cells processing negative memories induces similar phenotypes in mice. In this study, we used an activity-dependent tagging method to access neuronal ensembles and assess their molecular characteristics. Sequencing memory engrams in mice revealed that positive (male-to-female exposure) and negative (foot shock) cells upregulated genes linked to anti- and pro-inflammatory responses, respectively. To investigate the impact of persistent activation of negative engrams, we chemogenetically activated them in the ventral hippocampus over 3 months and conducted anxiety and memory-related tests. Negative engram activation increased anxiety behaviors in both 6- and 14-month-old mice, reduced spatial working memory in older mice, impaired fear extinction in younger mice, and heightened fear generalization in both age groups. Immunohistochemistry revealed changes in microglial and astrocytic structure and number in the hippocampus. In summary, repeated activation of negative memories induces lasting cellular and behavioral abnormalities in mice, offering insights into the negative effects of chronic negative thinking-like behaviors on human health.

Comparing the Efficacy of Two Cognitive Screening Tools in Identifying Gray and White Matter Brain Damage among Older Adults

Background

Ageing is associated with structural changes in brain regions and functional decline in cognitive domains. Noninvasive tools for identifying structural damage in the brains of older adults are relevant for early treatment.

Aims

This study aims to evaluate and compare the accuracy of the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA©) in identifying gray and white matter brain damage in older individuals with varying degrees of cognitive impairment.

Methods

Ninety older adults (62 women) with an average age of 69 ± 7 years were enrolled and categorized as having no cognitive impairment (NCI), mild cognitive impairment (MCI), or moderate cognitive impairment (MoCI). Magnetic resonance imaging (MRI) was utilized to assess the number, volume, and distribution of brain damage. The Fazekas and Scheltens scales were applied to the brain MRIs, and inferential statistics were employed to compare variables among the groups.

Results

Cognitive impairment was observed in 56.7% of the participants (95% confidence interval (CI): 46.4-66.4%), with thirty-six older adults (40%) classified as MCI and 15 (17%) as MoCI. Cognitive impairment and medial temporal lobe (MTL) atrophy were found to be associated (p=0.001), exhibiting higher mean volume scales of the MTL atrophied area in the MoCI group (p < 0.001). The MMSE accurately revealed MTL atrophy based on the Scheltens (p < 0.05) and Fazekas (p < 0.05) scales. At the same time, the MoCA accurately identified periventricular white matter (PWM) abnormalities according to the Fazekas scale (p < 0.05).

Conclusions

The MMSE and MoCA screening tools effectively identified gray and white matter brain damage in older adults with varying degrees of cognitive impairment. Lower MMSE scores are associated with MTL atrophy and lesions, and lower MoCA scores are related to PWM lesions. The concurrent use of MMSE and MoCA is recommended for assessing structural changes in distinct brain regions.

Socioeconomic Disparities in Hypothalamic-Pituitary-Adrenal Axis Regulation and Prefrontal Cortical Structure

Socioeconomic disadvantage during childhood predicts an increased risk for mental health problems across the life span. Socioeconomic disadvantage shapes multiple aspects of children's proximal environments and increases exposure to chronic stressors. Drawing from multiple literatures, we propose that childhood socioeconomic disadvantage may lead to adaptive changes in the regulation of stress response systems including the hypothalamic-pituitary-adrenal (HPA) axis. These changes, in turn, affect the development of prefrontal cortical (PFC) circuitry responsible for top-down control over cognitive and emotional processes. Translational findings indicate that chronic stress reduces dendritic complexity and spine density in the medial PFC and anterior cingulate cortex, in part through altered HPA axis regulation. Socioeconomic disadvantage has frequently been associated with reduced gray matter in the dorsolateral and ventrolateral PFC and anterior cingulate cortex and lower fractional anisotropy in the superior longitudinal fasciculus, cingulum bundle, and uncinate fasciculus during middle childhood and adolescence. Evidence of socioeconomic disparities in hair cortisol concentrations in children has accumulated, although null findings have been reported. Coupled with links between cortisol levels and reduced gray matter in the PFC and anterior cingulate cortex, these results support mechanistic roles for the HPA axis and these PFC circuits. Future longitudinal studies should simultaneously consider multiple dimensions of proximal factors, including cognitive stimulation, while focusing on epigenetic processes and genetic moderators to elucidate how socioeconomic context may influence the HPA axis and PFC circuitry involved in cognitive and emotional control. These findings, which point to modifiable factors, can be harnessed to inform policy and more effective prevention strategies.

Hippocampal subfield volumes predict treatment response to oral ketamine in people with suicidality

Ongoing stress results in hippocampal neuro-structural alterations which produce pathological consequences, including depression and suicidality. Ketamine may ameliorate stress related illnesses, including suicidality, via neuroplasticity processes. This novel study sought to determine whether oral ketamine treatment specifically affects hippocampal (whole and subfield) volumes in patients with chronic suicidality and MDD. It was hypothesised that oral ketamine treatment would differentially alter hippocampal volumes in trial participants categorised as ketamine responders, versus those who were non-responders. Twenty-eight participants received 6 single, weekly doses of oral ketamine (0.5-3 mg/kg) and underwent MRI scans at pre-ketamine (week 0), post-ketamine (week 6), and follow up (week 10). Hippocampal subfield volumes were extracted using the longitudinal pipeline in FreeSurfer. Participants were grouped according to ketamine response status and then compared in terms of grey matter volume (GMV) changes, among 10 hippocampal regions, over 6 and 10 weeks. Mixed ANOVAs were used to analyse interactions between time and group. Post treatment analysis revealed a significant main effect of group for three left hippocampal GMVs as well in the left and right whole hippocampus. Ketamine acute responders (Week 6) showed increased GMVs in both left and right whole hippocampus and in three subfields compared to acute non-responders, across all three timepoints, suggesting that pre-treatment increased hippocampal GMVs (particularly left hemisphere) may be predictive biomarkers of acute treatment response. Future studies should further investigate the potential of hippocampal volumes as a biomarker of ketamine treatment response.

Are sleep disturbances a cause or consequence of autism spectrum disorder?

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by core symptoms such as atypical social communication, stereotyped behaviors, and restricted interests. One of the comorbid symptoms of individuals with ASD is sleep disturbance. There are two major hypotheses regarding the neural mechanism underlying ASD, i.e., the excitation/inhibition (E/I) imbalance and the altered neuroplasticity hypotheses. However, the pathology of ASD remains unclear due to inconsistent research results. This paper argues that sleep is a confounding factor, thus, must be considered when examining the pathology of ASD because sleep plays an important role in modulating the E/I balance and neuroplasticity in the human brain. Investigation of the E/I balance and neuroplasticity during sleep might enhance our understanding of the neural mechanisms of ASD. It may also lead to the development of neurobiologically informed interventions to supplement existing psychosocial therapies.

Hippocampal BAIAP2 prevents chronic mild stress-induced depression-like behaviors in mice

Background

The pathogenesis of depression is closely related to changes in hippocampal synaptic plasticity; however, the underlying mechanism is still unclear. Brain-specific angiogenesis inhibitor 1-associated protein 2 (BAIAP2), a postsynaptic scaffold protein in excitatory synapses important for synaptic plasticity, is highly expressed in the hippocampus and has been implicated in several psychiatric disorders. However, the role of BAIAP2 in depression remains poorly understood.

Methods

In the present study, a mouse model of depression was established via exposure to chronic mild stress (CMS). An adeno-associated virus (AAV) vector expressing BAIAP2 was injected into the hippocampal brain region of mice and a BAIAP2 overexpression plasmid was transfected into HT22 cells to upregulate BAIAP2 expression. Depression- and anxiety-like behaviors and dendritic spine density were examined in mice using behavioral tests and Golgi staining, respectively. In vitro, hippocampal HT22 cells were treated with corticosterone (CORT) to simulate the stress state, and the effect of BAIAP2 on CORT-induced cell injury was explored. Reverse transcription-quantitative PCR and western blotting were employed to determine the expression levels of BAIAP2 and those of the synaptic plasticity-related proteins glutamate receptor ionotropic, AMPA 1 (GluA1), and synapsin 1 (SYN1).

Results

Mice exposed to CMS exhibited depression- and anxiety-like behaviors accompanied by decreased levels of BAIAP2 in the hippocampus. In vitro, the overexpression of BAIAP2 increased the survival rate of CORT-treated HT22 cells and upregulated the expression of GluA1 and SYN1. Consistent with the in vitro data, the AAV-mediated overexpression of BAIAP2 in the hippocampus of mice significantly inhibited CMS-induced depression-like behavior, concomitant with increases in dendritic spine density and the expression of GluA1 and SYN1 in hippocampal regions.

Conclusion

Our findings indicate that hippocampal BAIAP2 can prevent stress-induced depression-like behavior and may be a promising target for the treatment of depression or other stress-related diseases.

The synaptic hypothesis of schizophrenia version III: a master mechanism

The synaptic hypothesis of schizophrenia has been highly influential. However, new approaches mean there has been a step-change in the evidence available, and some tenets of earlier versions are not supported by recent findings. Here, we review normal synaptic development and evidence from structural and functional imaging and post-mortem studies that this is abnormal in people at risk and with schizophrenia. We then consider the mechanism that could underlie synaptic changes and update the hypothesis. Genome-wide association studies have identified a number of schizophrenia risk variants converging on pathways regulating synaptic elimination, formation and plasticity, including complement factors and microglial-mediated synaptic pruning. Induced pluripotent stem cell studies have demonstrated that patient-derived neurons show pre- and post-synaptic deficits, synaptic signalling alterations, and elevated, complement-dependent elimination of synaptic structures compared to control-derived lines. Preclinical data show that environmental risk factors linked to schizophrenia, such as stress and immune activation, can lead to synapse loss. Longitudinal MRI studies in patients, including in the prodrome, show divergent trajectories in grey matter volume and cortical thickness compared to controls, and PET imaging shows in vivo evidence for lower synaptic density in patients with schizophrenia. Based on this evidence, we propose version III of the synaptic hypothesis. This is a multi-hit model, whereby genetic and/or environmental risk factors render synapses vulnerable to excessive glia-mediated elimination triggered by stress during later neurodevelopment. We propose the loss of synapses disrupts pyramidal neuron function in the cortex to contribute to negative and cognitive symptoms and disinhibits projections to mesostriatal regions to contribute to dopamine overactivity and psychosis. It accounts for the typical onset of schizophrenia in adolescence/early adulthood, its major risk factors, and symptoms, and identifies potential synaptic, microglial and immune targets for treatment.

Neuroplasticity-Related Genes and Dopamine Receptors Associated with Regional Cortical Thickness Increase Following Electroconvulsive Therapy for Major Depressive Disorder

Electroconvulsive therapy (ECT) is an effective neuromodulatory therapy for major depressive disorder (MDD). Treatment is associated with regional changes in brain structure and function, indicating activation of neuroplastic processes. To investigate the underlying neurobiological mechanism of macroscopic reorganization following ECT, we longitudinally (before and after ECT in two centers) collected magnetic resonance images for 96 MDD patients. Similar patterns of cortical thickness (CT) changes following ECT were observed in two centers. These CT changes were spatially colocalized with a weighted combination of genes enriched for neuroplasticity-related ontology terms and pathways (e.g., synaptic pruning) as well as with a higher density of D2/3 dopamine receptors. A multiple linear regression model indicated that the region-specific gene expression and receptor density patterns explained 40% of the variance in CT changes after ECT. In conclusion, these findings suggested that dopamine signaling and neuroplasticity-related genes are associated with the ECT-induced morphological reorganization.

Microglia-dependent excessive synaptic pruning leads to cortical underconnectivity and behavioral abnormality following chronic social defeat stress in mice

Synapse loss in medial prefrontal cortex (mPFC) has been implicated in stress-related mood disorders, such as depression. However, the exact effect of synapse elimination in the depression and how it is triggered are largely unknown. Through repeated longitudinal imaging of mPFC in the living brain, we found both presynaptic and postsynaptic components were declined, together with the impairment of synapse remodeling and cross-synaptic signal transmission in the mPFC during chronic stress. Meanwhile, chronic stress also induced excessive microglia phagocytosis, leading to engulfment of excitatory synapses. Further investigation revealed that the elevated complement C3 during the stress acted as the tag of synapses to be eliminated by microglia. Besides, chronic stress induced a reduction of the connectivity between the mPFC and neighbor regions. C3 knockout mice displayed significant reduction of synaptic pruning and alleviation of disrupted functional connectivity in mPFC, resulting in more resilience to chronic stress. These results indicate that complement-mediated excessive microglia phagocytosis in adulthood induces synaptic dysfunction and cortical hypo-connectivity, leading to stress-related behavioral abnormality.

The times they are a-changin': a proposal on how brain flexibility goes beyond the obvious to include the concepts of "upward" and "downward" to neuroplasticity

Since the brain was found to be somehow flexible, plastic, researchers worldwide have been trying to comprehend its fundamentals to better understand the brain itself, make predictions, disentangle the neurobiology of brain diseases, and finally propose up-to-date treatments. Neuroplasticity is simple as a concept, but extremely complex when it comes to its mechanisms. This review aims to bring to light an aspect about neuroplasticity that is often not given enough attention as it should, the fact that the brain's ability to change would include its ability to disconnect synapses. So, neuronal shrinkage, decrease in spine density or dendritic complexity should be included within the concept of neuroplasticity as part of its mechanisms, not as an impairment of it. To that end, we extensively describe a variety of studies involving topics such as neurodevelopment, aging, stress, memory and homeostatic plasticity to highlight how the weakening and disconnection of synapses organically permeate the brain in so many ways as a good practice of its intrinsic physiology. Therefore, we propose to break down neuroplasticity into two sub-concepts, "upward neuroplasticity" for changes related to synaptic construction and "downward neuroplasticity" for changes related to synaptic deconstruction. With these sub-concepts, neuroplasticity could be better understood from a bigger landscape as a vector in which both directions could be taken for the brain to flexibly adapt to certain demands. Such a paradigm shift would allow a better understanding of the concept of neuroplasticity to avoid any data interpretation bias, once it makes clear that there is no morality with regard to the organic and physiological changes that involve dynamic biological systems as seen in the brain.

Seeking the Amygdala: Novel Use of Diffusion Tensor Imaging to Delineate the Basolateral Amygdala

The amygdaloid complex, including the basolateral nucleus (BLA), contributes crucially to emotional and cognitive brain functions, and is a major target of research in both humans and rodents. However, delineating structural amygdala plasticity in both normal and disease-related contexts using neuroimaging has been hampered by the difficulty of unequivocally identifying the boundaries of the BLA. This challenge is a result of the poor contrast between BLA and the surrounding gray matter, including other amygdala nuclei. Here, we describe a novel diffusion tensor imaging (DTI) approach to enhance contrast, enabling the optimal identification of BLA in the rodent brain from magnetic resonance (MR) images. We employed this methodology together with a slice-shifting approach to accurately measure BLA volumes. We then validated the results by direct comparison to both histological and cellular-identity (parvalbumin)-based conventional techniques for defining BLA in the same brains used for MRI. We also confirmed BLA connectivity targets using DTI-based tractography. The novel approach enables the accurate and reliable delineation of BLA. Because this nucleus is involved in and changed by developmental, degenerative and adaptive processes, the instruments provided here should be highly useful to a broad range of neuroimaging studies. Finally, the principles used here are readily applicable to numerous brain regions and across species.

Neuroimaging in schizophrenia: an overview of findings and their implications for synaptic changes

Over the last five decades, a large body of evidence has accrued for structural and metabolic brain alterations in schizophrenia. Here we provide an overview of these findings, focusing on measures that have traditionally been thought to reflect synaptic spine density or synaptic activity and that are relevant for understanding if there is lower synaptic density in the disorder. We conducted literature searches to identify meta-analyses or other relevant studies in patients with chronic or first-episode schizophrenia, or in people at high genetic or clinical risk for psychosis. We identified 18 meta-analyses including over 50,000 subjects in total, covering: structural MRI measures of gyrification index, grey matter volume, grey matter density and cortical thickness, neurite orientation dispersion and density imaging, PET imaging of regional glucose metabolism and magnetic resonance spectroscopy measures of N-acetylaspartate. We also review preclinical evidence on the relationship between ex vivo synaptic measures and structural MRI imaging, and PET imaging of synaptic protein 2A (SV2A). These studies show that schizophrenia is associated with lower grey matter volumes and cortical thickness, accelerated grey matter loss over time, abnormal gyrification patterns, and lower regional SV2A levels and metabolic markers in comparison to controls (effect sizes from ~ -0.11 to -1.0). Key regions affected include frontal, anterior cingulate and temporal cortices and the hippocampi. We identify several limitations for the interpretation of these findings in terms of understanding synaptic alterations. Nevertheless, taken with post-mortem findings, they suggest that schizophrenia is associated with lower synaptic density in some brain regions. However, there are several gaps in evidence, in particular whether SV2A findings generalise to other cohorts.

Rapid volumetric brain changes after acute psychosocial stress

Stress is an important trigger for brain plasticity: Acute stress can rapidly affect brain activity and functional connectivity, and chronic or pathological stress has been associated with structural brain changes. Measures of structural magnetic resonance imaging (MRI) can be modified by short-term motor learning or visual stimulation, suggesting that they also capture rapid brain changes. Here, we investigated volumetric brain changes (together with changes in T1 relaxation rate and cerebral blood flow) after acute stress in humans as well as their relation to psychophysiological stress measures. Sixty-seven healthy men (25.8±2.7 years) completed a standardized psychosocial laboratory stressor (Trier Social Stress Test) or a control version while blood, saliva, heart rate, and psychometrics were sampled. Structural MRI (T1 mapping / MP2RAGE sequence) at 3T was acquired 45 min before and 90 min after intervention onset. Grey matter volume (GMV) changes were analysed using voxel-based morphometry. Associations with endocrine, autonomic, and subjective stress measures were tested with linear models. We found significant group-by-time interactions in several brain clusters including anterior/mid-cingulate cortices and bilateral insula: GMV was increased in the stress group relative to the control group, in which several clusters showed a GMV decrease. We found a significant group-by-time interaction for cerebral blood flow, and a main effect of time for T1 values (longitudinal relaxation time). In addition, GMV changes were significantly associated with state anxiety and heart rate variability changes. Such rapid GMV changes assessed with VBM may be induced by local tissue adaptations to changes in energy demand following neural activity. Our findings suggest that endogenous brain changes are counteracted by acute psychosocial stress, which emphasizes the importance of considering homeodynamic processes and generally highlights the influence of stress on the brain.

Imaging synaptic density in depression

Major depressive disorder is a prevalent and heterogeneous disorder with treatment resistance in at least 50% of individuals. Most of the initial studies focused on the monoamine system; however, recently other mechanisms have come under investigation. Specific to the current issue, studies show synaptic involvement in depression. Other articles in this issue report on reductions in synaptic density, dendritic spines, boutons and glia associated with stress and depression. Importantly, it appears that some drugs (e.g., ketamine) may lead to rapid synaptic restoration or synaptogenesis. Direct evidence for this comes from preclinical work. However, neuroimaging studies, such as magnetic resonance imaging (MRI) and positron emission tomography (PET), have become useful in assessing these changes in vivo. Here, we describe the use of neuroimaging techniques in the evaluation of synaptic alterations associated with depression in humans, as well as measurement of synaptic restoration after administration of ketamine. Although more research is desired, use of these techniques widen our understanding of depression and move us further along the path to targeted and effective treatment for depression.

The gradient in gray matter thickness across auditory cortex and differential cortical thickness changes following perinatal deafness

In the absence of hearing during development, the brain adapts and repurposes what was destined to become auditory cortex. As cortical thickness is commonly used as a proxy to identify cortical regions that have undergone plastic changes, the purpose of this investigation was to compare cortical thickness patterns between hearing and deaf cats. In this study, normal hearing (n = 29) and deaf (n = 26) cats were scanned to examine cortical thickness in hearing controls, as well as differential changes in thickness as a consequence of deafness. In hearing cats, a gradient in cortical thickness was identified across auditory cortex in which it is thinner in more dorsal regions and thicker in more ventral regions. Compared with hearing controls, differential thickening and thinning was observed in specific regions of deaf auditory cortex. More dorsal regions were found to be bilaterally thicker in the deaf group, while more ventral regions in the left hemisphere were thinner. The location and nature of these changes creates a gradient along the dorsoventral axis, wherein dorsal auditory cortical fields are thicker, whereas more ventral fields are thinner in deaf animals compared with hearing controls.

Structural plasticity of motor cortices assessed by voxel-based morphometry and immunohistochemical analysis following internal capsular infarcts in macaque monkeys

Compensatory plastic changes in the remaining intact brain regions are supposedly involved in functional recovery following stroke. Previously, a compensatory increase in cortical activation occurred in the ventral premotor cortex (PMv), which contributed to the recovery of dexterous hand movement in a macaque model of unilateral internal capsular infarcts. Herein, we investigated the structural plastic changes underlying functional changes together with voxel-based morphometry (VBM) analysis of magnetic resonance imaging data and immunohistochemical analysis using SMI-32 antibody in a macaque model. Unilateral internal capsular infarcts were pharmacologically induced in 5 macaques, and another 5 macaques were used as intact controls for immunohistochemical analysis. Three months post infarcts, we observed significant increases in the gray matter volume (GMV) and the dendritic arborization of layer V pyramidal neurons in the contralesional rostral PMv (F5) as well as the primary motor cortex (M1). The histological analysis revealed shrinkage of neuronal soma and dendrites in the ipsilesional M1 and several premotor cortices, despite not always detecting GMV reduction by VBM analysis. In conclusion, compensatory structural changes occur in the contralesional F5 and M1 during motor recovery following internal capsular infarcts, and the dendritic growth of pyramidal neurons is partially correlated with GMV increase.

A combined use of silver pretreatment and impregnation with consequent Nissl staining for cortex and striatum architectonics study

Despite a rapid growth in the application of modern techniques for visualization studies in life sciences, the classical methods of histological examination are yet to be outdated. Herein, we introduce a new approach that involves combining silver nitrate pretreatment and impregnation with consequent Nissl (cresyl violet) staining for cortex and striatum architectonics study on the same microscopy slide. The developed approach of hybrid staining provides a high-quality visualization of cellular and subcellular structures, including impregnated neurons (about 10%), Nissl-stained neurons (all the remaining ones), and astrocytes, as well as chromatophilic substances, nucleoli, and neuropil in paraffin sections. We provide a comparative study of the neuronal architectonics in both the motor cortex and striatum based on the differences in their tinctorial properties. In addition to a comparative study of the neuronal architectonics in both the motor cortex and striatum, the traditional methods to stain the cortex (motor and piriform) and the striatum are considered. The proposed staining approach compiles the routine conventional methods for thin sections, expanding avenues for more advanced examination of neurons, blood–brain barrier components, and fibers both under normal and pathological conditions. One of the main hallmarks of our method is the ability to detect changes in the number of glial cells. The results of astrocyte visualization in the motor cortex obtained by the developed technique agree well with the alternative studies by glial fibrillary acidic protein (GFAP) immunohistochemical reaction. The presented approach of combined staining has great potential in current histological practice, in particular for the evaluation of several neurological disorders in clinical, pre-clinical, or neurobiological animal studies.

Differential grey matter structure in women with premenstrual dysphoric disorder: evidence from brain morphometry and data-driven classification

Premenstrual dysphoric disorder (PMDD) is a female-specific condition classified in the Diagnostic and Statical Manual-5th edition under depressive disorders. Alterations in grey matter volume, cortical thickness and folding metrics have been associated with a number of mood disorders, though little is known regarding brain morphological alterations in PMDD. Here, women with PMDD and healthy controls underwent magnetic resonance imaging (MRI) during the luteal phase of the menstrual cycle. Differences in grey matter structure between the groups were investigated by use of voxel- and surface-based morphometry. Machine learning and multivariate pattern analysis were performed to test whether MRI data could distinguish women with PMDD from healthy controls. Compared to controls, women with PMDD had smaller grey matter volume in ventral posterior cortices and the cerebellum (Cohen's d = 0.45-0.76). Region-of-interest analyses further indicated smaller volume in the right amygdala and putamen of women with PMDD (Cohen's d = 0.34-0.55). Likewise, thinner cortex was observed in women with PMDD compared to controls, particularly in the left hemisphere (Cohen's d = 0.20-0.74). Classification analyses showed that women with PMDD can be distinguished from controls based on grey matter morphology, with an accuracy up to 74%. In line with the hypothesis of an impaired top-down inhibitory circuit involving limbic structures in PMDD, the present findings point to PMDD-specific grey matter anatomy in regions of corticolimbic networks. Furthermore, the results include widespread cortical and cerebellar regions, suggesting the involvement of distinct networks in PMDD pathophysiology.

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.

Association between stressful life events and grey matter volume in the medial prefrontal cortex: A 2-year longitudinal study

Stressful life events (SLEs) in adulthood are a risk factor for various disorders such as depression, cancer or infections. Part of this risk is mediated through pathways altering brain physiology and structure. There is a lack of longitudinal studies examining associations between SLEs and brain structural changes. High-resolution structural magnetic resonance imaging data of 212 healthy subjects were acquired at baseline and after 2 years. Voxel-based morphometry was used to identify associations between SLEs using the Life Events Questionnaire and grey matter volume (GMV) changes during the 2-year period in an ROI approach. Furthermore, we assessed adverse childhood experiences as a possible moderator of SLEs-GMV change associations. SLEs were negatively associated with GMV changes in the left medial prefrontal cortex. This association was stronger when subjects had experienced adverse childhood experiences. The medial prefrontal cortex has previously been associated with stress-related disorders. The present findings represent a potential neural basis of the diathesis-stress model of various disorders.

Astrocytes in Post-traumatic Stress Disorder

Although posttraumatic stress disorder (PTSD) is on the rise, traumatic events and their consequences are often hidden or minimized by patients for reasons linked to PTSD itself. Traumatic experiences can be broadly classified into mental stress (MS) and traumatic brain injury (TBI), but the cellular mechanisms of MS- or TBI-induced PTSD remain unknown. Recent evidence has shown that the morphological remodeling of astrocytes accompanies and arguably contributes to fearful memories and stress-related disorders. In this review, we summarize the roles of astrocytes in the pathogenesis of MS-PTSD and TBI-PTSD. Astrocytes synthesize and secrete neurotrophic, pro- and anti-inflammatory factors and regulate the microenvironment of the nervous tissue through metabolic pathways, ionostatic control, and homeostatic clearance of neurotransmitters. Stress or trauma-associated impairment of these vital astrocytic functions contribute to the pathophysiological evolution of PTSD and may present therapeutic targets.

The Neurobiological Effects of Electroconvulsive Therapy Studied Through Magnetic Resonance: What Have We Learned, and Where Do We Go?

Electroconvulsive therapy (ECT) is an established treatment choice for severe, treatment-resistant depression, yet its mechanisms of action remain elusive. Magnetic resonance imaging (MRI) of the human brain before and after treatment has been crucial to aid our comprehension of the ECT neurobiological effects. However, to date, a majority of MRI studies have been underpowered and have used heterogeneous patient samples as well as different methodological approaches, altogether causing mixed results and poor clinical translation. Hence, an association between MRI markers and therapeutic response remains to be established. Recently, the availability of large datasets through a global collaboration has provided the statistical power needed to characterize whole-brain structural and functional brain changes after ECT. In addition, MRI technological developments allow new aspects of brain function and structure to be investigated. Finally, more recent studies have also investigated immediate and long-term effects of ECT, which may aid in the separation of the therapeutically relevant effects from epiphenomena. The goal of this review is to outline MRI studies (T1, diffusion-weighted imaging, proton magnetic resonance spectroscopy) of ECT in depression to advance our understanding of the ECT neurobiological effects. Based on the reviewed literature, we suggest a model whereby the neurobiological effects can be understood within a framework of disruption, neuroplasticity, and rewiring of neural circuits. An improved characterization of the neurobiological effects of ECT may increase our understanding of ECT's therapeutic effects, ultimately leading to improved patient care.

lncRNA Neat1 regulates neuronal dysfunction post sepsis via stabilization of hemoglobin subunit beta

Sepsis-associated encephalopathy (SAE) is characterized by acute and diffuse brain dysfunction and correlates with long-term cognitive impairments with no targeted therapy. We used a mouse model of sepsis-related cognitive impairment to examine the role of lncRNA nuclear enriched abundant transcript 1 (Neat1) in SAE. We observed that Neat1 expression was increased in neuronal cells from septic mice and that it directly interacts with hemoglobin subunit beta (Hbb), preventing its degradation. The Neat1/Hbb axis suppressed postsynaptic density protein 95 (PSD-95) levels and decreased dendritic spine density. Neat1 knockout mice exhibited decreased Hbb levels, which resulted in increased PSD-95 levels, increased neuronal dendritic spine density, and decreased anxiety and memory impairment. Neat1 silencing via the antisense oligonucleotide GapmeR ameliorated anxiety-like behavior and cognitive impairment post-sepsis. In conclusion, we uncovered a previously unknown mechanism of the Neat1/Hbb axis in regulating neuronal dysfunction, which may lead to a novel treatment strategy for SAE.

Differential associations of regional cerebellar volume with gait speed and working memory

The relationship between gait speed and working memory is well-understood in older adults. However, it remains to be determined whether this relationship also exists in younger adults; and there is little known regarding the possible neural mechanism underlying the association between gait speed and working memory. The aims of this study are to determine if there is: (1) an association between gait speed and working memory performance; and (2) a mediating role of cerebellar subregion volume in the correlation between gait speed and working memory in healthy younger adults. 1054 younger adults (28.7 ± 3.6 years) from the Human Connectome Project were included in the analyses. A four-meter gait test was used to assess gait speed. The 2-back task was used to measure working memory performance [accuracy and response time (RT)]. T1-weighted structural MRI data (obtained using Siemens 3 T MRI scanner) was used to assess cerebellar subregion volumes. Linear regression and mediation analysis were used to examine the relationships between the variables after controlling for age, sex, and education. There was no association between gait speed and 2-back working memory performance in younger adults. Greater Crus I and whole cerebellar volumes were associated with better 2-back working memory accuracy. Greater VIIIa volume was associated with faster gait speed. Greater Crus 1 and VIIIa volumes were also associated with higher fluid cognition. The present study suggests that specific subregions of the cerebellar volumes are distinctively associated with gait speed and working memory performance in healthy younger adults.

Mitochondrial transplantation improves anxiety- and depression-like behaviors in aged stress-exposed rats

Impaired mitochondrial function and abnormalities in the tryptophan (Trp)-kynurenine (Kyn) pathway are linked to age-related mood disorders. This study investigated the effect of intracerebroventricular (ICV) injection of the mitochondria isolated from young rat brain on depression-like behaviors of aged rats subjected to chronic mild stress (CMS). Aged (22 months old) male rats were randomly assigned into four groups: Aged, Aged + Mit, Aged + CMS, and Aged + CMS + Mit. Anxiety- and depression-like behaviors were assessed using elevated plus maze (EPM), open field test (OFT), forced swimming test (FST), and sucrose preference test (SPT). Mitochondrial membrane potential (MMP), ATP levels, indoleamine 2, 3-dioxygenase (IDO) levels, and Kyn metabolites were measured in the prefrontal cortex (PFC). Golgi Cox staining was used to investigate the neuronal morphology. Mitotherapy decreased immobility time and anhedonia in the FST; increased open arm time and entries in the EPM; decreased grooming and increased rearing, center time, and the entrance in the OFT. Mitotherapy also reduced IDO and Kyn metabolites, restored MMP and ATP production, and enhanced dendritic length and spine density in the PFC. Overall, mitotherapy improved anxiety-and depression-like behaviors in aged rats and it could be considered as a new therapeutic strategy for age-related depressive disorders.

Lower synaptic density is associated with psychiatric and cognitive alterations in obesity

Obesity is a serious medical condition that often co-occurs with stress-related psychiatric disorders. It is recognized that the brain plays a key role in the (patho)physiology of obesity and that there is a bidirectional relationship between obesity and psychopathology, yet molecular mechanisms altered in obesity have not been fully elucidated. Thus, we investigated relationships between obesity and synaptic density in vivo using the radioligand [11C]UCB-J (which binds to synaptic glycoprotein SV2A) and positron emission tomography in individuals with obesity, and with or without stress-related psychiatric disorders. Regions of interest were the dorsolateral prefrontal cortex, orbitofrontal cortex, ventromedial, amygdala, hippocampus, and cerebellum. Forty individuals with a body mass index (BMI) ≥ 25 kg/m2 (overweight/obese), with (n = 28) or without (n = 12) psychiatric diagnosis, were compared to 30 age- and sex-matched normal weight individuals (BMI < 25), with (n = 14) or without (n = 16) psychiatric diagnosis. Overall, significantly lower synaptic density was observed in overweight/obese relative to normal weight participants (ηp2 = 0.193, F = 2.35, p = 0.042). Importantly, in participants with stress-related psychiatric diagnoses, we found BMI to be negatively correlated with synaptic density in all regions of interest (p ≤ 0.03), but no such relationship observed for mentally healthy controls (p ≥ 0.68). In the stress-related psychiatric groups, dorsolateral prefrontal cortex synaptic density was negatively associated with measures of worry (r = -0.46, p = 0.01), tension/anxiety (r = -0.38, p = 0.04), fatigue (r = -0.44, p = 0.02), and attentional difficulties (r = -0.44, p = 0.02). In summary, the findings of this novel in vivo experiment suggest compounding effects of obesity and stress-related psychopathology on the brain and the associated symptomatology that may impact functioning. This offers a novel biological mechanism for the relationship between overweight/obesity and stress-related psychiatric disorders that may guide future intervention development efforts.

A Novel Estimation Method for the Counting of Dendritic Spines

BACKGROUND

Since Cajal's visualisations of the synaptic spine, this feature of the neuron has been of interest to neuroscientists and has been investigated usually in reference to degeneration or proliferation of dendrites and their neurons. Synaptic spine measurement often forms a critical element of any study investigating neuronal morphology. However, the way researchers have counted spines hasn't changed for almost a century. Some of the currently used legacy methods fail to accommodate obscured pisnes or factor-in visibility differences between histological stains.

NEW METHOD

Here we investigate the neuronal dendrite and its synaptic spines, and reveal that using confocal or bright-field technologies may in fact obfuscate spine counts. A mathematical model is developed for the distribution of synaptic spines within the rat, that should, by nature of the formula and the impartiality of probability quotients, be applied to estimate the number of synaptic spines across any length of dendrite that has protrusions within any species.

RESULTS

Using this estimation method, we show that, depending on the method of image capture, there are in fact more spines present than typically counted on lengths of dendrite, something that may have biased morphological studies in the past.

COMPARISON WITH EXISTING METHODS

This new estimation method has been collapsed down into an easy-to-use free website. With input of only four fields, we provide the researcher with a more accurate estimation of the amount of spines on a length of dendrite. This was made possible by fluorescing a Golgi stain and comparing two-photon, bright-field and confocal images.

CONCLUSIONS

An easy web-based resource has been made available to use this new method for spine calculation. Using this method improves the validity of spine measurement and provides a means to review previously published work.

Structural correlates of trauma-induced hyperarousal in mice

Post-traumatic stress disorder (PTSD) is a chronic disease caused by traumatic incidents. Numerous studies have revealed grey matter volume differences in affected individuals. The nature of the disease renders it difficult to distinguish between a priori versus a posteriori changes. To overcome this difficulty, we studied the consequences of a traumatic event on brain morphology in mice before and 4 weeks after exposure to brief foot shocks (or sham treatment), and correlated morphology with symptoms of hyperarousal. In the latter context, we assessed hyperarousal upon confrontation with acoustic, visual, or composite (acoustic/visual/tactile) threats and integrated the individual readouts into a single Hyperarousal Score using logistic regression analysis. MRI scans with subsequent whole-brain deformation-based morphometry (DBM) analysis revealed a volume decrease of the dorsal hippocampus and an increase of the reticular nucleus in shocked mice when compared to non-shocked controls. Using the Hyperarousal Score as regressor for the post-exposure MRI measurement, we observed negative correlations with several brain structures including the dorsal hippocampus. If the development of changes with respect to the basal MRI was considered, reduction in globus pallidus volume reflected hyperarousal severity. Our findings demonstrate that a brief traumatic incident can cause volume changes in defined brain structures and suggest the globus pallidus as an important hub for the control of fear responses to threatening stimuli of different sensory modalities.

Impact of Pharmacological and Non-Pharmacological Modulators on Dendritic Spines Structure and Functions in Brain

Dendritic spines are small, thin, hair-like protrusions found on the dendritic processes of neurons. They serve as independent compartments providing large amplitudes of Ca²⁺ signals to achieve synaptic plasticity, provide sites for newer synapses, facilitate learning and memory. One of the common and severe complication of neurodegenerative disease is cognitive impairment, which is said to be closely associated with spine pathologies viz., decreased in spine density, spine length, spine volume, spine size etc. Many treatments targeting neurological diseases have shown to improve the spine structure and distribution. However, concise data on the various modulators of dendritic spines are imperative and a need of the hour. Hence, in this review we made an attempt to consolidate the effects of various pharmacological (cholinergic, glutamatergic, GABAergic, serotonergic, adrenergic, and dopaminergic agents) and non-pharmacological modulators (dietary interventions, enriched environment, yoga and meditation) on dendritic spines structure and functions. These data suggest that both the pharmacological and non-pharmacological modulators produced significant improvement in dendritic spine structure and functions and in turn reversing the pathologies underlying neurodegeneration. Intriguingly, the non-pharmacological approaches have shown to improve intellectual performances both in preclinical and clinical platforms, but still more technology-based evidence needs to be studied. Thus, we conclude that a combination of pharmacological and non-pharmacological intervention may restore cognitive performance synergistically via improving dendritic spine number and functions in various neurological disorders.

Electroacupuncture Ameliorates Depression-Like Behaviour in Rats by Enhancing Synaptic Plasticity via the GluN2B/CaMKII/CREB Signalling Pathway

Background

Hippocampal synaptic plasticity during the pathological process of depression has received increasing attention. Hippocampal neuron atrophy and the reduction in synaptic density induced by chronic stress are important pathological mechanisms of depression. Electroacupuncture (EA) exerts beneficial effects on depression, but the mechanism is unclear. This study explored the effect of EA on synaptic plasticity and the potential mechanism.

Methods

Forty-eight SD rats were randomly divided into the control, chronic unpredictable mild stress (CUMS), EA, and fluoxetine (FLX) groups, and each group consisted of 12 rats. The sucrose preference test, open field test, and forced swimming test were used for the evaluation of depression-like behaviour, and Golgi and Nissl staining were used for the assessment of synaptic plasticity. Western blotting and immunofluorescence were conducted to detect proteins related to synaptic plasticity and to determine their effects on signalling pathways.

Results

We found that CUMS led to depression-like behaviours, including a reduced preference for sucrose, a prolonged immobility time, and reduced exploration activity. The dendritic spine densities and neuron numbers and the protein levels of MAP-2, PSD-95, and SYN were decreased in the hippocampi of rats with CUMS-induced depression, and these trends were reversed by EA. The molecular mechanism regulating this plasticity may involve the GluN2B/CaMKII/CREB signalling pathway.

Conclusion

These results suggest that EA can improve depression-like behaviour and hippocampal plasticity induced by CUMS, and the mechanism may be related to the GluN2B/CaMKII/CREB pathway.

Young Plasma Induces Antidepressant-Like Effects in Aged Rats Subjected to Chronic Mild Stress by Suppressing Indoleamine 2,3-Dioxygenase Enzyme and Kynurenine Pathway in the Prefrontal Cortex

Pathophysiology of depression in elderlies is linked to aging-associated increase in indoleamine 2,3-dioxygenase (IDO) levels and activity and kynurenine (Kyn) metabolites. Moreover, these aging-induced changes may alter the brain's responses to stress. Growing evidence suggested that young plasma can positively affect brain dysfunctions in old age. The present study aimed to investigate whether the antidepressant effects of young plasma administration in aged rats subjected to chronic unpredictable mild stress (CUMS) and underlying mechanisms, focusing on the prefrontal cortex (PFC). Young (3 months old) and aged (22 months old) male rats were divided into five groups; young control, aged control, aged rats subjected to CUMS (A + CUMS), aged rats subjected to CUMS and treated with young plasma (A + CUMS + YP), and aged rats subjected to CUMS and treated with old plasma (A + CUMS + OP). Plasma was injected (1 ml, intravenously) three times per week for four weeks. Young plasma significantly improved CUMS-induced depressive-like behaviors, evidenced by the increased sucrose consumption ratio in the sucrose preference test and the reduced immobility time in the forced swimming test. Furthermore, young plasma markedly reduced the levels of interferon-gamma (IFN-γ), IDO, Kyn, and Kyn to tryptophan (Kyn/Trp) ratio in PFC tissue. Expression levels of the serotonin transporter and growth-associated protein (GAP)-43 were also significantly increased after chronic administration of young plasma. These findings provide evidence for the antidepressant effect of young plasma in old age; however, whether it improves depressive behaviors or faster recovery from stress-induced deficits is required to be elucidated.

Cortical Synaptic Reorganization Under Chronic Arsenic Exposure

There is solid epidemiological evidence that arsenic exposure leads to cognitive impairment, while experimental work supports the hypothesis that it also contributes to neurodegeneration. Energy deficit, oxidative stress, demyelination, and defective neurotransmission are demonstrated arsenic effects, but it remains unclear whether synaptic structure is also affected. Employing both a triple-transgenic Alzheimer's disease model and Wistar rats, the cortical microstructure and synapses were analyzed under chronic arsenic exposure. Male animals were studied at 2 and 4 months of age, after exposure to 3 ppm sodium arsenite in drinking water during gestation, lactation, and postnatal development. Through nuclear magnetic resonance, diffusion-weighted images were acquired and anisotropy (integrity; FA) and apparent diffusion coefficient (dispersion degree; ADC) metrics were derived. Postsynaptic density protein and synaptophysin were analyzed by means of immunoblot and immunohistochemistry, while dendritic spine density and morphology of cortical pyramidal neurons were quantified after Golgi staining. A structural reorganization of the cortex was evidenced through high-ADC and low-FA values in the exposed group. Similar changes in synaptic protein levels in the 2 models suggest a decreased synaptic connectivity at 4 months of age. An abnormal dendritic arborization was observed at 4 months of age, after increased spine density at 2 months. These findings demonstrate alterations of cortical synaptic connectivity and microstructure associated to arsenic exposure appearing in young rodents and adults, and these subtle and non-adaptive plastic changes in dendritic spines and in synaptic markers may further progress to the degeneration observed at older ages.

The effect of the PARK16 rs11240572 variant on brain structure in Parkinson's disease

Increasing evidence suggests that genetic factors play a key role in the development of Parkinson's disease (PD). The variant rs11240572 in the PARK16 gene locus is strongly associated with PD. However, its effect on the pathogenesis of PD is yet to be clarified. The objective of the study was to explore the effect of the PARK16 rs11240572 variant on brain structure in PD patients. A total of 51 PD patients were enrolled in the study and genotyped for the rs11240572 variant. Clinical assessments and MRI scans were conducted across all participants. Voxel-based morphometry (VBM) was used to investigate gray matter volume (GMV) of the whole brain between these two groups. Correlation analysis was performed to identify the relationships between GMV and clinical features. There were 17 rs11240572-A variant carriers and 34 non-carriers, with no significant demographic differences between these two groups. Compared with non-carriers, rs11240572-A carriers showed increased GMV in the left caudate nucleus and putamen, but decreased GMV in the left superior temporal gyrus and supramarginal gyrus. In non-carriers, left basal ganglia GMV was positively correlated with UPDRS III (r = 0.365, p = 0.034) and bradykinesia (r = 0.352, p = 0.042), but negatively correlated with MMSE (r =  - 0.344, p = 0.047), while in carriers negative correlation between basal ganglia GMV and MMSE was also observed (r =  - 0.666, p = 0.004). Moreover, the GMV of left temporoparietal cortex was positively associated with cognitive function in both groups (carriers, r = 0.692, p = 0.002; non-carriers, r = 0.879, p < 0.001). When reducing the sample size of non-carriers to the level of the carrier sample, similar correlations were observed in both groups. Our study showed that the PARK16 rs11240572 variant affects the brain structure of patients with PD, especially in the basal ganglia and temporoparietal cortex. This indicated that this variant might play an important role in the pathogenesis of PD.

Brainstem Pain-Modulation Circuitry and Its Plasticity in Neuropathic Pain: Insights From Human Brain Imaging Investigations

Acute pain serves as a protective mechanism that alerts us to potential tissue damage and drives a behavioural response that removes us from danger. The neural circuitry critical for mounting this behavioural response is situated within the brainstem and is also crucial for producing analgesic and hyperalgesic responses. In particular, the periaqueductal grey, rostral ventromedial medulla, locus coeruleus and subnucleus reticularis dorsalis are important structures that directly or indirectly modulate nociceptive transmission at the primary nociceptive synapse. Substantial evidence from experimental animal studies suggests that plasticity within this system contributes to the initiation and/or maintenance of chronic neuropathic pain, and may even predispose individuals to developing chronic pain. Indeed, overwhelming evidence indicates that plasticity within this circuitry favours pro-nociception at the primary synapse in neuropathic pain conditions, a process that ultimately contributes to a hyperalgesic state. Although experimental animal investigations have been crucial in our understanding of the anatomy and function of the brainstem pain-modulation circuitry, it is vital to understand this system in acute and chronic pain states in humans so that more effective treatments can be developed. Recent functional MRI studies have identified a key role of this system during various analgesic and hyperalgesic responses including placebo analgesia, offset analgesia, attentional analgesia, conditioned pain modulation, central sensitisation and temporal summation. Moreover, recent MRI investigations have begun to explore brainstem pain-modulation circuitry plasticity in chronic neuropathic pain conditions and have identified altered grey matter volumes and functioning throughout the circuitry. Considering the findings from animal investigations, it is likely that these changes reflect a shift towards pro-nociception that ultimately contributes to the maintenance of neuropathic pain. The purpose of this review is to provide an overview of the human brain imaging investigations that have improved our understanding of the pain-modulation system in acute pain states and in neuropathic conditions. Our interpretation of the findings from these studies is often guided by the existing body of experimental animal literature, in addition to evidence from psychophysical investigations. Overall, understanding the plasticity of this system in human neuropathic pain conditions alongside the existing experimental animal literature will ultimately improve treatment options.

Repeated cocaine exposure prior to fear conditioning induces persistency of PTSD-like symptoms and enhancement of hippocampal and amygdala cell density in male rats

Pre- and post-trauma drug use can interfere with recovery from post-traumatic stress disorder (PTSD). However, the biological underpinnings of this interference are poorly understood. Here we examined the effect of pre-fear conditioning cocaine self-administration on PTSD-like symptoms in male rats, and defined impairment of fear extinction as difficulty to recover from PTSD. We also examined cell density changes in brain regions suspected of being involved in resistance to PTSD recovery. Before footshock stress testing, rats were trained to self-administer cocaine during 20 consecutive days, after which they were exposed to footshocks, while other rats continued to self-administer cocaine until the end of the experiment. Upon assessment of three PTSD-like symptoms (fear during situational reminders, anxiety-like behavior, and impairment of recognition memory) and fear extinction learning and memory, changes in cell density were measured in the medial prefrontal cortex, hippocampus, and amygdala. Results show that pre-footshock cocaine exposure did not affect fear during situational reminders. Fear conditioning did not lead to an increase in cocaine consumption. However, in footshock stressed rats, cocaine induced a reduction of anxiety-like behavior, an aggravation of recognition memory decline, and an impairment of extinction memory. These behavioral alterations were associated with increased cell density in the hippocampal CA1, CA2, and CA3 regions and basolateral amygdala, but not in the medial prefrontal cortex. Our findings suggest that enhancement of cell density in the hippocampus and amygdala may be changes associated with drug use, interfering with PTSD recovery.

Emerging role of glutamate in the pathophysiology and therapeutics of Gulf War illness

Gulf War illness (GWI) is a chronic and multi-symptomatic disorder affecting veterans who served in the Gulf War. The commonly reported symptoms in GWI veterans include mood problems, cognitive impairment, muscle and joint pain, migraine/headache, chronic fatigue, gastrointestinal complaints, skin rashes, and respiratory problems. Neuroimaging studies have revealed significant brain structure alterations in GWI veterans, including subcortical atrophy, decreased volume of the hippocampus, reduced total grey and white matter, and increased brain white matter axial diffusivity. These brain changes may contribute to or increase the severities of the GWI-related symptoms. Epidemiological studies have revealed that neurotoxic exposures and stress may be significant contributors to the development of GWI. However, the mechanism underlying how the exposure and stress could contribute to the multi-symptomatic disorder of GWI remains unclear. We and others have demonstrated that rodent models exposed to GW-related agents and stress exhibited higher extracellular glutamate levels, as well as impaired structure and function of glutamatergic synapses. Restoration of the glutamatergic synapses ameliorated the GWI-related pathological and behavioral deficits. Moreover, recent studies showed that a low-glutamate diet reduced multiple symptoms in GWI veterans, suggesting an important role of the glutamatergic system in GWI. Currently, growing evidence has indicated that abnormal glutamate neurotransmission may contribute to the GWI symptoms. This review summarizes the potential roles of glutamate dyshomeostasis and dysfunction of the glutamatergic system in linking the initial cause to the multi-symptomatic outcomes in GWI and suggests the glutamatergic system as a therapeutic target for GWI.

Structural Plastic Changes of Cortical Gray Matter Revealed by Voxel-Based Morphometry and Histological Analyses in a Monkey Model of Central Post-Stroke Pain

Central post-stroke pain (CPSP) is a chronic pain caused by stroke lesions of somatosensory pathways. Several brain imaging studies among patients with CPSP demonstrate that the pathophysiological mechanism underlying this condition is the maladaptive plasticity of pain-related brain regions. However, the temporal profile of the regional plastic changes, as suggested by brain imaging of CPSP patients, as well as their cellular basis, is unknown. To investigate these issues, we performed voxel-based morphometry (VBM) using T1-weighted magnetic resonance imaging and immunohistochemical analysis with our established CPSP monkey model. From 8 weeks after a hemorrhagic lesion to the unilateral ventral posterolateral nucleus of the thalamus, the monkeys exhibited significant behavioral changes that were interpreted as reflecting allodynia. The present VBM results revealed a decrease in gray matter volume in the pain-related areas after several weeks following the lesion. Furthermore, immunohistochemical staining in the ipsilesional posterior insular cortex (ipsi-PIC) and secondary somatosensory cortex (ipsi-SII), where the significant reduction in gray matter volume was observed in the VBM result, displayed a significant reduction in both excitatory and inhibitory synaptic terminals compared to intact monkeys. Our results suggest that progressive changes in neuronal morphology, including synaptic loss in the ipsi-PIC/SII, are involved in theCPSP.

Reduced anterior cingulate cortex volume induced by chronic stress correlates with increased behavioral emotionality and decreased synaptic puncta density

Clinical and preclinical studies report that chronic stress induces behavioral deficits as well as volumetric and synaptic alterations in corticolimbic brain regions including the anterior cingulate cortex (ACC), amygdala (AMY), nucleus accumbens (NAc) and hippocampus (HPC). Here, we aimed to investigate the volumetric changes associated with chronic restraint stress (CRS) and link these changes to the CRS-induced behavioral and synaptic deficits. We first confirmed that CRS increases behavioral emotionality, defined as collective scoring of anxiety- and anhedonia-like behaviors. We then demonstrated that CRS induced a reduction of total brain volume which negatively correlated with behavioral emotionality. Region-specific analysis identified that only the ACC showed significant decrease in volume following CRS (p < 0.05). Reduced ACC correlated with increased behavioral emotionality (r = -0.56; p = 0.0003). Although not significantly altered by CRS, AMY and NAc (but not the HPC) volumes were negatively correlated with behavioral emotionality. Finally, using structural covariance network analysis to assess shared volumetric variances between the corticolimbic brain regions and associated structures, we found a progressive decreased ACC degree and increased AMY degree following CRS. At the cellular level, reduced ACC volume correlated with decreased PSD95 (but not VGLUT1) puncta density (r = 0.35, p < 0.05), which also correlated with increased behavioral emotionality (r = -0.44, p < 0.01), suggesting that altered synaptic strength is an underlying substrate of CRS volumetric and behavioral effects. Our results demonstrate that CRS effects on ACC volume and synaptic density are linked to behavioral emotionality and highlight key ACC structural and morphological alterations relevant to stress-related illnesses including mood and anxiety disorders.

Translating the immediate effects of S-Ketamine using hippocampal subfield analysis in healthy subjects-results of a randomized controlled trial

Antidepressant doses of ketamine rapidly facilitate synaptic plasticity and modify neuronal function within prefrontal and hippocampal circuits. However, most studies have demonstrated these effects in animal models and translational studies in humans are scarce. A recent animal study showed that ketamine restored dendritic spines in the hippocampal CA1 region within 1 h of administration. To translate these results to humans, this randomized, double-blind, placebo-controlled, crossover magnetic resonance imaging (MRI) study assessed ketamine's rapid neuroplastic effects on hippocampal subfield measurements in healthy volunteers. S-Ketamine vs. placebo data were analyzed, and data were also grouped by brain-derived neurotrophic factor (BDNF) genotype. Linear mixed models showed that overall hippocampal subfield volumes were significantly larger (p = 0.009) post ketamine than post placebo (LS means difference=0.008, standard error=0.003). Post-hoc tests did not attribute effects to specific subfields (all p > 0.05). Trend-wise volumetric increases were observed within the left hippocampal CA1 region (p = 0.076), and trend-wise volumetric reductions were obtained in the right hippocampal-amygdaloid transition region (HATA) (p = 0.067). Neither genotype nor a genotype-drug interaction significantly affected the results (all p > 0.7). The study provides evidence that ketamine has short-term effects on hippocampal subfield volumes in humans. The results translate previous findings from animal models of depression showing that ketamine has pro-neuroplastic effects on hippocampal structures and underscore the importance of the hippocampus as a key region in ketamine's mechanism of action.

Low-Dose Copper Exposure Exacerbates Depression-Like Behavior in ApoE4 Transgenic Mice

Depression is one of the most common neuropsychiatric disorders. Although the pathogenesis of depression is still unknown, environmental risk factors and genetics are implicated. Copper (Cu), a cofactor of multiple enzymes, is involved in regulating depression-related processes. Depressed patients carrying the apolipoprotein ε4 allele display more severe depressive symptoms, indicating that ApoE4 is closely associated with an increased risk of depression. The study explored the effect of low-dose Cu exposure and ApoE4 on depression-like behavior of mice and further investigates the possible mechanisms. The ApoE4 mice and wild-type (WT) mice were treated with 0.13 ppm CuCl₂ for 4 months. After the treatment, ApoE4 mice displayed obvious depression-like behavior compared with the WT mice, and Cu exposure further exacerbated the depression-like behavior of ApoE4 mice. There was no significant difference in anxiety behavior and memory behavior. Proteomic analysis revealed that the differentially expressed proteins between Cu-exposed and nonexposed ApoE4 mice were mainly involved in the Ras signaling pathway, protein export, axon guidance, serotonergic synapse, GABAergic synapse, and dopaminergic synapse. Among these differentially expressed proteins, immune response and synaptic function are highly correlated. Representative protein expression changes are quantified by western blot, showing consistent results as determined by proteomic analysis. Hippocampal astrocytes and microglia were increased in Cu-exposed ApoE4 mice, suggesting that neuroglial cells played an important role in the pathogenesis of depression. Taken together, our study demonstrated that Cu exposure exacerbates depression-like behavior of ApoE4 mice and the mechanisms may involve the dysregulation of synaptic function and immune response and overactivation of neuroinflammation.

Lifelong impact of extreme stress on the human brain: Holocaust survivors study

Background

We aimed to assess the lifelong impact of extreme stress on people who survived the Holocaust. We hypothesised that the impact of extreme trauma is detectable even after more than 70 years of an often complicated and stressful post-war life.

Methods

Psychological testing was performed on 44 Holocaust survivors (HS; median age 81.5 years; 29 women; 26 HS were under the age of 12 years in 1945) and 31 control participants without a personal or family history of the Holocaust (control group (CG); median 80 years; 17 women). Magnetic resonance imaging (MRI) using the 3T Siemens Prisma scanner was performed on 29 HS (median 79 years; 18 women) and 21 CG participants (median 80 years; 11 women). The MRI-tested subgroup that had been younger than 12 years old in 1945 was composed of 20 HS (median 79 years; 17 women) and 21 CG (median 80 years; 11 women).

Results

HS experienced significantly higher frequency of depression symptoms, posttraumatic stress symptoms, and posttraumatic growth, and lower levels of well-being. The MRI shows a lifelong neurobiological effect of extreme stress. The areas with reduced grey matter correspond to the map of the impact of stress on the brain structure: insula, anterior cingulate, ventromedial cortex including the subgenual cingulate/orbitofrontal cortex, temporal pole, prefrontal cortex, and angular gyrus. HS showed good adjustment to post-war life conditions.

Psychological growth may contribute to compensation for the psychological and neurobiological consequences of extreme stress.

The reduction of GM was significantly expressed also in the subgroup of participants who survived the Holocaust during their childhood.

Conclusion

The lifelong psychological and neurobiological changes in people who survived extreme stress were identified more than 70 years after the Holocaust. Extreme stress in childhood and young adulthood has an irreversible lifelong impact on the brain.

The effect of aging and chronic microglia activation on the morphology and numbers of the cerebellar Purkinje cells

Reduced cerebellar volume and motor dysfunction have previously been observed in the GFAP-IL6 murine model of chronic neuroinflammation. This study aims to extend these findings by investigating the effect of microglial activation and ageing on the total number of Purkinje cells and the morphology of their dendritic arborization. Through comparison of transgenic GFAP-IL6 mice and their wild-type counterparts at the ages of 12 and 24-months, we were able to investigate the effects of ageing and chronic microglial activation on Purkinje cells. Unbiased stereology was used to estimate the number of microglia in Iba1⁺ stained tissue and Purkinje cells in calbindin stained tissue. Morphological analyses were made using 3D reconstructions of images acquired from the Golgi-stained cerebellar tissue. We found that the total number of microglia increased by approximately 5 times in the cerebellum of GFAP-IL6 mice compared to their WT littermates. The number of Purkinje cells decreased by as much as 50 % in aged wild type mice and 83 % in aged GFAP-IL6 mice. The remaining Purkinje cells in these cohorts were found to have significant reductions in their total dendritic length and number of branching points, indicating how the complexity of the Purkinje cell dendritic arbor reduces through age and inflammation. GFAP-IL6 mice, when compared to WT mice, had higher levels of microglial activation and more profound neurodegenerative changes in the cerebellum. The presence of constitutive IL6 production, driving chronic neuroinflammation, may account for these neurodegenerative changes in GFAP-IL6 mice.

Observing Plasticity of the Auditory System: Volumetric Decreases Along with Increased Functional Connectivity in Aspiring Professional Musicians

Playing music relies on several sensory systems and the motor system, and poses strong demands on control processes, hence, offering an excellent model to study how experience can mold brain structure and function. Although most studies on neural correlates of music expertise rely on cross-sectional comparisons, here we compared within-person changes over time in aspiring professionals intensely preparing for an entrance exam at a University of the Arts to skilled amateur musicians not preparing for a music exam. In the group of aspiring professionals, we observed gray-matter volume decrements in left planum polare, posterior insula, and left inferior frontal orbital gyrus over a period of about 6 months that were absent among the amateur musicians. At the same time, the left planum polare, the largest cluster of structural change, showed increasing functional connectivity with left and right auditory cortex, left precentral gyrus, left supplementary motor cortex, left and right postcentral gyrus, and left cingulate cortex, all regions previously identified to relate to music expertise. In line with the expansion-renormalization pattern of brain plasticity (Wenger et al., 2017a. Expansion and renormalization of human brain structure during skill acquisition. Trends Cogn Sci. 21:930-939.), the aspiring professionals might have been in the selection and refinement period of plastic change.

How stress physically re-shapes the brain: Impact on brain cell shapes, numbers and connections in psychiatric disorders

Severe stress is among the most robust risk factors for the development of psychiatric disorders. Imaging studies indicate that life stress is integral to shaping the human brain, especially regions involved in processing the stress response. Although this is likely underpinned by changes to the cytoarchitecture of cellular networks in the brain, we are yet to clearly understand how these define a role for stress in human psychopathology. In this review, we consolidate evidence of macro-structural morphometric changes and the cellular mechanisms that likely underlie them. Focusing on stress-sensitive regions of the brain, we illustrate how stress throughout life may lead to persistent remodelling of the both neurons and glia in cellular networks and how these may lead to psychopathology. We support that greater translation of cellular alterations to human cohorts will support parsing the psychological sequalae of severe stress and improve our understanding of how stress shapes the human brain. This will remain a critical step for improving treatment interventions and prevention outcomes.

Gray matter volume of rostral anterior cingulate cortex predicts rapid antidepressant response to ketamine

Ketamine was recently approved for treatment resistant depression. However, despite its therapeutic potential, about 50% of patients do not show improvement under this therapy. In this prospective two-site study, we investigated baseline brain structural predictors for rapid symptom improvement after a single subanesthetic ketamine infusion. Furthermore, given the preclinical evidence and findings from a pilot study in a clinical population that ketamine induces rapid neuroplasticity, we performed an exploratory investigation of macroscopic changes 24 h post-treatment. T1-weighted MRI brain images from 33 depressed patients were acquired before and 24 h after a single ketamine infusion and analyzed using voxel-based morphometry (VBM). Additionally, we performed a region of interest (ROI)-based analysis of structures that have previously been shown to play a role in the antidepressant effects of ketamine: bilateral hippocampus, nucleus accumbens, anterior cingulate cortex, and thalamus. A whole-brain regression analysis showed that greater baseline volume of the bilateral rostral anterior cingulate cortex (rACC) significantly predicts rapid symptom reduction. The right ACC showed the same association in the ROI analysis, while the other regions yielded no significant results. Exploratory follow-up analyses revealed no volumetric changes 24 h after treatment. This is the first study reporting an association between pretreatment gray matter volume of the bilateral rACC and the rapid antidepressant effects of ketamine. Results are in line with previous investigations, which highlighted the potential of the rACC as a biomarker for response prediction to different antidepressant treatments. Ketamine-induced volumetric changes may be seen at later time points.

Stress Resilience is Associated with Hippocampal Synaptoprotection in the Female Rat Learned Helplessness Paradigm

The synaptogenic hypothesis of major depressive disorder implies that preventing the onset of depressive-like behavior also prevents the loss of hippocampal spine synapses. By applying the psychoactive drugs, diazepam and fluoxetine, we investigated whether blocking the development of helpless behavior by promoting stress resilience in the rat learned helplessness paradigm is associated with a synaptoprotective action in the hippocampus. Adult ovariectomized and intact female Sprague-Dawley rats (n = 297) were treated with either diazepam, fluoxetine, or vehicle, exposed to inescapable footshocks or sham stress, and tested in an active escape task to assess helpless behavior. Escape-evoked corticosterone secretion, as well as remodeling of hippocampal spine synapses at a timepoint representing the onset of escape testing were also analyzed. In ovariectomized females, treatment with diazepam prior to stress exposure prevented helpless behavior, blocked the loss of hippocampal spine synapses, and muted the corticosterone surge evoked by escape testing. Although fluoxetine stimulated escape performance and hippocampal synaptogenesis under non-stressed conditions, almost all responses to fluoxetine were abolished following exposure to inescapable stress. Only a much higher dose of fluoxetine was capable of partly reproducing the strong protective actions of diazepam. Importantly, these protective actions were retained in the presence of ovarian hormones. Our findings indicate that stress resilience is associated with the preservation of spine synapses in the hippocampus, raising the possibility that, besides synaptogenesis, hippocampal synaptoprotection is also implicated in antidepressant therapy.

Microglial deletion and inhibition alleviate behavior of post-traumatic stress disorder in mice

Background

Alteration of immune status in the central nervous system (CNS) has been implicated in the development of post-traumatic stress disorder (PTSD). However, the nature of overall changes in brain immunocyte landscape in PTSD condition remains unclear.

Methods

We constructed a mouse PTSD model by electric foot-shocks followed by contextual reminders and verified the PTSD-related symptoms by behavior test (including contextual freezing test, open-field test, and elevated plus maze test). We examined the immunocyte panorama in the brains of the naïve or PTSD mice by using single-cell mass cytometry. Microglia number and morphological changes in the hippocampus, prefrontal cortex, and amygdala were analyzed by histopathological methods. The gene expression changes of those microglia were detected by quantitative real-time PCR. Genetic/pharmacological depletion of microglia or minocycline treatment before foot-shocks exposure was performed to study the role of microglia in PTSD development and progress.

Results

We found microglia are the major brain immune cells that respond to PTSD. The number of microglia and ratio of microglia to immunocytes was significantly increased on the fifth day of foot-shock exposure. Furthermore, morphological analysis and gene expression profiling revealed temporal patterns of microglial activation in the hippocampus of the PTSD brains. Importantly, we found that genetic/pharmacological depletion of microglia or minocycline treatment before foot-shock exposure alleviated PTSD-associated anxiety and contextual fear.

Conclusion

Our results demonstrated a critical role for microglial activation in PTSD development and a potential therapeutic strategy for the clinical treatment of PTSD in the form of microglial inhibition.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02069-9.

The Antidepressant Effects of Resveratrol are Accompanied by the Attenuation of Dendrite/Dendritic Spine Loss and the Upregulation of BDNF/p-cofilin1 Levels in Chronic Restraint Mice

Depression afflicts more than 300 million people worldwide, but there is currently no universally effective drug in clinical practice. In this study, chronic restraint stress (CRS)-induced mice depression model was used to study the antidepressant effects of resveratrol and its mechanism. Our results showed that resveratrol significantly attenuated depression-like behavior in mice. Consistent with behavioral changes, resveratrol significantly attenuated CRS-induced reduction in the density of dendrites and dendritic spines in both hippocampus and medial prefrontal cortex (mPFC). Meanwhile, in hippocampus and mPFC, resveratrol consistently alleviated CRS-induced cofilin1 activation by increasing its ser3 phosphorylation. In addition, cofilin1 immunofluorescence distribution in neuronal inner peri-membrane in controls, and cofilin1 diffusely distribution in the cytoplasm in CRS group were common in hippocampus. However, the distribution of cofilin1 in mPFC was reversed. Pearson's correlation analysis revealed that there was a significant positive correlation found between the sucrose consumption in sucrose preference test and the dendrite density in multiple sub-regions of hippocampus and mPFC, and a significant negative correlation between the immobility time in tail suspension test and the dendrite/dendritic spine density in several different areas of hippocampus and mPFC. P-cofilin1 was significantly positively correlated with the overall dendritic spine density in mPFC as well as with the overall dendrite density or BDNF in the hippocampus. Our results suggest that the BDNF/cofilin1 pathway, in which cofilin1 may be activated in a brain-specific manner, was involved in resveratrol's attenuating the dendrite and dendritic spine loss and behavioral abnormality.