Early hippocampal volume loss as a marker of eventual memory deficits caused by repeated stress

Hippocampus and striatum show distinct contributions to longitudinal changes in value-based learning in middle childhood

The hippocampal-dependent memory system and striatal-dependent memory system modulate reinforcement learning depending on feedback timing in adults, but their contributions during development remain unclear. In a 2-year longitudinal study, 6-to-7-year-old children performed a reinforcement learning task in which they received feedback immediately or with a short delay following their response. Children's learning was found to be sensitive to feedback timing modulations in their reaction time and inverse temperature parameter, which quantifies value-guided decision-making. They showed longitudinal improvements towards more optimal value-based learning, and their hippocampal volume showed protracted maturation. Better delayed model-derived learning covaried with larger hippocampal volume longitudinally, in line with the adult literature. In contrast, a larger striatal volume in children was associated with both better immediate and delayed model-derived learning longitudinally. These findings show, for the first time, an early hippocampal contribution to the dynamic development of reinforcement learning in middle childhood, with neurally less differentiated and more cooperative memory systems than in adults.

Long-term administration of omeprazole in mice: a study of behavior, inflammatory, and oxidative stress alterations with focus on central nervous system

Chronic use of omeprazole has been linked to central effects alongside with the global concern of increasing appearance of neuropsychiatric disorders. This study aimed to identifying behavioral, inflammatory, and oxidative stress alterations after long-term administration of omeprazole. C57BL/6 mice were divided in groups: OME and Sham, each received either solutions of omeprazole or vehicle, administered for 28 days by gavage. Results observed in the omeprazole-treated mice: Decrease in the crossing parameter in the open field, no change in the motor performance assessed by rotarod, an immobility time reduction in the forced swimming test, improved percentage of correct alternances in the Ymaze and an exploration time of the novel object reduction in the novel object recognition. Furthermore, a reduced weight gain and hippocampal weight were observed. There was an increase in the cytokine IL1-β levels in both prefrontal cortex (PFC) and serum, whereas TNF-α increased only in the PFC. Nitrite levels increased in the hippocampus (HP) and PFC, while malondialdehyde (MDA) and glutathione (GSH) levels decreased. These findings suggest that omeprazole improves depressive-like behavior and working memory, likely through the increase in nitrite and reduction in MDA levels in PFC and HP, whereas, the impairment of the recognition memory is more likely to be related to the reduced hippocampal weight. The diminished weight gain might be associated with the IL-1β increased levels in the peripheral blood. Altogether, omeprazole showed to have the potential to impact at central level and inflammatory and oxidative parameters might exert a role between it.

Emotional- and cognitive-like responses induced by social defeat stress in male mice are modulated by the BNST, amygdala, and hippocampus

Introduction

Chronic exposure to social defeat stress (SDS) has been used to investigate the neurobiology of depressive- and anxiety-like responses and mnemonic processes. We hypothesized that these affective, emotional, and cognitive consequences induced by SDS are regulated via glutamatergic neurons located in the bed nucleus of the stria terminalis (BNST), amygdaloid complex, and hippocampus in mice.

Methods

Here, we investigated the influence of chronic SDS on (i) the avoidance behavior assessed in the social interaction test, (ii) the anxiety-like behavior (e.g., elevated plus-maze, and open field tests) (iii) depressive-like behaviors (e.g., coat state, sucrose splash, nesting building, and novel object exploration tests), (iv) the short-term memory (object recognition test), (v) ΔFosB, CaMKII as well as ΔFosB + CaMKII labeling in neurons located in the BNST, amygdaloid complex, dorsal (dHPC) and the ventral (vHPC) hippocampus.

Results

The main results showed that the exposure of mice to SDS (a) increased defensive and anxiety-like behaviors and led to memory impairment without eliciting clear depressive-like or anhedonic effects; (b) increased ΔFosB + CaMKII labeling in BNST and amygdala, suggesting that both areas are strongly involved in the modulation of this type of stress; and produced opposite effects on neuronal activation in the vHPC and dHPC, i.e., increasing and decreasing, respectively, ΔFosB labeling. The effects of SDS on the hippocampus suggest that the vHPC is likely related to the increase of defensive- and anxiety-related behaviors, whereas the dHPC seems to modulate the memory impairment.

Discussion

Present findings add to a growing body of evidence indicating the involvement of glutamatergic neurotransmission in the circuits that modulate emotional and cognitive consequences induced by social defeat stress.

Boophone disticha attenuates five day repeated forced swim-induced stress and adult hippocampal neurogenesis impairment in male Balb/c mice

Depression is one of the most common neuropsychiatric disorders and is associated with dysfunction of the neuroendocrine system and alterations in specific brain proteins. Boophone disticha (BD) is an indigenous psychoactive bulb that belongs to the Amaryllidacae family, which is widely used in Southern Africa to treat depression, with scientific evidence of potent antidepressant-like effects. The present study examined the antidepressant effects of BD and its mechanisms of action by measuring some behavioural parameters in the elevated plus maze, brain content of corticosterone, brain derived neurotropic factor (BDNF), and neuroblast differentiation in the hippocampus of Balb/c mice exposed to the five day repeated forced swim stress (5d-RFSS). Male Balb/c mice were subjected to the 5d-RFSS protocol to induce depressive-like behaviour (decreased swimming, increased floating, decreased open arm entry, decreased time spent in the open arms and decreased head dips in the elevated plus maze test) and treated with distilled water, fluoxetine and BD. BD treatment (10 mg/kg/p.o for 3 weeks) significantly attenuated the 5d-RFSS-induced behavioural abnormalities and the elevated serum corticosterone levels observed in stressed mice. Additionally, 5d-RFSS exposure significantly decreased the number of neuroblasts in the hippocampus and BDNF levels in the brain of Balb/c mice, while fluoxetine and BD treatment attenuated these changes. The antidepressant effects of BD were comparable to those of fluoxetine, but unlike fluoxetine, BD did not show any anxiogenic effects, suggesting better pharmacological functions. In conclusion, our study shows that BD exerted antidepressant-like effects in 5d-RFSS mice, mediated in part by normalizing brain corticosterone and BDNF levels.

The Neurobiology of Infant Attachment-Trauma and Disruption of Parent-Infant Interactions

Current clinical literature and supporting animal literature have shown that repeated and profound early-life adversity, especially when experienced within the caregiver-infant dyad, disrupts the trajectory of brain development to induce later-life expression of maladaptive behavior and pathology. What is less well understood is the immediate impact of repeated adversity during early life with the caregiver, especially since attachment to the caregiver occurs regardless of the quality of care the infant received including experiences of trauma. The focus of the present manuscript is to review the current literature on infant trauma within attachment, with an emphasis on animal research to define mechanisms and translate developmental child research. Across species, the effects of repeated trauma with the attachment figure, are subtle in early life, but the presence of acute stress can uncover some pathology, as was highlighted by Bowlby and Ainsworth in the 1950s. Through rodent neurobehavioral literature we discuss the important role of repeated elevations in stress hormone corticosterone (CORT) in infancy, especially if paired with the mother (not when pups are alone) as targeting the amygdala and causal in infant pathology. We also show that following induced alterations, at baseline infants appear stable, although acute stress hormone elevation uncovers pathology in brain circuits important in emotion, social behavior, and fear. We suggest that a comprehensive understanding of the role of stress hormones during infant typical development and elevated CORT disruption of this typical development will provide insight into age-specific identification of trauma effects, as well as a better understanding of early markers of later-life pathology.

Perceived stress associations with hippocampal-dependent behavior and hippocampal subfield volume

Background

Individual differences in stress appraisals influence trajectories of risk and resilience following exposure to chronic and acute stressors. Smaller hippocampal volume may contribute to elevated stress appraisals via deficient pattern separation, a process depending on dentate gyrus (DG)/CA3 hippocampal subfields. Here, we investigated links between perceived stress, DG/CA3 volume, and behavioral pattern separation to test hypothesized mechanisms underlying stress-related psychopathology.

Methods

We collected the Perceived Stress Scale (PSS) and ratings of subjective stress reactivity during the Trier Social Stress Test (TSST) from 71 adult community participants. We obtained high-resolution T2 MRI scans and used Automatic Segmentation of Hippocampal Subfields to estimate DG/CA3 volume in 56 of these participants. Participants completed the mnemonic similarity task, which provides a behavioral index of pattern separation. Analyses investigated associations between perceived stress, DG/CA3 volume, and behavioral pattern separation, controlling for age, gender, hemisphere, and intracranial volume.

Results

Greater PSS scores and TSST subjective stress reactivity were each independently related to poorer behavioral pattern separation, together accounting for 15% of variance in behavioral performance in a simultaneous regression. Contrary to hypotheses, DG/CA3 volume was not associated with either stress measure, although exploratory analyses suggested a link between hippocampal volume asymmetry and PSS scores.

Conclusions

We observed novel associations between laboratory and questionnaire measures of perceived stress and a behavioral assay of pattern separation. Additional work is needed to clarify the involvement of the hippocampus in this stress-behavior relationship and determine the relevance of behavioral pattern separation for stress-related disorders.

Stress Elicits Contrasting Effects on Rac1-Cofilin Signaling in the Hippocampus and Amygdala

There is accumulating evidence for contrasting patterns of stress-induced morphological and physiological plasticity in glutamatergic synapses of the hippocampus and amygdala. The same chronic stress that leads to the formation of dendritic spines in the basolateral amygdala (BLA) of rats, leads to a loss of spines in the hippocampus. However, the molecular underpinnings of these divergent effects of stress on dendritic spines are not well understood. Since the activity of the Rho GTPase Rac1 and the actin-depolymerizing factor cofilin are known to play a pivotal role in spine morphogenesis, we investigated if alterations in this signaling pathway reflect the differential effects of stress on spine plasticity in the hippocampus and amygdala. A day after the end of chronic immobilization stress (2 h/day for 10 days), we found a reduction in the activity of Rac1, as well as its effector p21-activated kinase 1 (PAK1), in the rat hippocampus. These changes, in turn, decreased cofilin phosphorylation alongside a reduction in the levels of profilin isoforms. In striking contrast, the same chronic stress increased Rac1, PAK1 activity, cofilin phosphorylation, and profilin levels in the BLA, which is consistent with enhanced actin polymerization leading to spinogenesis in the BLA. In the hippocampus, on the other hand, the same stress caused the opposite changes, the functional consequences of which would be actin depolymerization leading to the elimination of spines. Together, these findings reveal a role for brain-region specific differences in the dysregulation of Rac1-to-cofilin signaling in the effects of repeated stress on two brain areas that are implicated in the emotional and cognitive symptoms of stress-related psychiatric disorders.

Riluzole prevents stress-induced spine plasticity in the hippocampus but mimics it in the amygdala

Stress elicits divergent patterns of structural plasticity in the amygdala and hippocampus. Despite these contrasting effects, at least one of the immediate consequences of stress – elevated levels of extracellular glutamate – is similar in both brain areas. This raises the possibility that the contrasting effects of stress on neuronal plasticity is shaped by differences in astrocytic glutamate clearance in these two brain areas. Although astrocytes play a key role in glutamate reuptake, past analyses of, and interventions against, stress-induced plasticity have focused largely on neurons. Hence, we tested the impact of riluzole, which potentiates glutamate clearance by astrocytic glutamate transporters, on principal neurons and astrocytes in the basal amygdala (BA) and hippocampal area CA1. Chronic immobilization stress reduced spine-density on CA1 pyramidal neurons of male rats. Riluzole, administered in the drinking water during chronic stress, prevented this decrease; but, the drug by itself had no effect. In contrast, the same chronic stress enhanced spine-density on BA principal neurons, and this effect, unlike area CA1, was not reversed by riluzole. Strikingly, riluzole treatment alone also caused spinogenesis in the BA. Thus, the same riluzole treatment that prevented the effect of stress on spines in the hippocampus, mimicked its effect in the amygdala. Further, chronic stress and riluzole alone decreased the neuropil volume occupied by astrocytes in both the BA and CA1 area. Riluzole treatment in stressed animals, however, did not reverse or further add to this reduction in either region. Thus, while the effects on astrocytes were similar, neuronal changes were distinct between the two areas following stress, riluzole and the two together. Therefore, similar to the impact of repeated stress, pharmacological potentiation of glutamate clearance, with or without stress, also leads to differential effects on dendritic spines in principal neurons of the amygdala and hippocampus. This highlights differences in the astrocytic glutamate reuptake machinery that are likely to have important functional consequences for stress-induced dysfunction, and its reversal, in two brain areas implicated in stress-related psychiatric disorders.

Altered small-world property of a dynamic metabolic network in murine left hippocampus after exposure to acute stress

The acute stress response is a natural and fundamental reaction that balances the physiological conditions of the brain. To maintain homeostasis in the brain, the response is based on changes over time in hormones and neurotransmitters, which are related to resilience and can adapt successfully to acute stress. This increases the need for dynamic analysis over time, and new approaches to examine the relationship between metabolites have emerged. This study investigates whether the constructed metabolic network is a realistic or a random network and is affected by acute stress. While the metabolic network in the control group met the criteria for small-worldness at all time points, the metabolic network in the stress group did not at some time points, and the small-worldness had resilience after the fifth time point. The backbone metabolic network only met the criteria for small-worldness in the control group. Additionally, creatine had lower local efficiency in the stress group than the control group, and for the backbone metabolic network, creatine and glutamate were lower and higher in the stress group than the control group, respectively. These findings provide evidence of metabolic imbalance that may be a pre-stage of alterations to brain structure due to acute stress.

The impact of stress on the hippocampal spatial code

Hippocampal function is severely compromised by prolonged, uncontrollable stress. However, how stress alters neural representations of our surroundings and events that occur within them remains less clear. We review hippocampal place cell studies that examine how spatial coding is affected by acute and chronic stress, as well as by stress accompanying fear conditioning. Emerging data suggest that chronic stress disrupts the acuity and specificity of CA1 spatial coding, both in familiar and novel contexts, and alters hippocampal oscillations. By contrast, acute stress may have a facilitatory impact on spatial representations. These findings encourage a fresh look at the documented stress-induced changes in hippocampal anatomy and in vitro excitability, and offer a new perspective on the links between stress and memory.

Cross-species Association Between Telomere Length and Glucocorticoid Exposure

CONTEXT

Chronic exposure to glucocorticoids (GCs) or stress increases the risk of medical disorders, including cardiovascular and neuropsychiatric disorders. GCs contribute to accelerated aging; however, while the link between chronic GC exposure and disease onset is well established, the underpinning mechanisms are not clear.

OBJECTIVE

We explored the potential nexus between GCs or stress exposure and telomere length.

METHODS

In addition to rats exposed to 3 weeks of chronic stress, an iatrogenic mouse model of Cushing syndrome (CS), and a mouse neuronal cell line, we studied 32 patients with CS and age-matched controls and another cohort of 75 healthy humans.

RESULTS

(1) Exposure to stress in rats was associated with a 54.5% (P = 0.036) reduction in telomere length in T cells. Genomic DNA (gDNA) extracted from the dentate gyrus of stressed and unstressed rats showed 43.2% reduction in telomere length (P = 0.006). (2) Mice exposed to corticosterone had a 61.4% reduction in telomere length in blood gDNA (P = 5.75 × 10-5) and 58.8% reduction in telomere length in the dentate gyrus (P = 0.002). (3) We observed a 40.8% reduction in the telomere length in patients with active CS compared to healthy controls (P = 0.006). There was a 17.8% reduction in telomere length in cured CS patients, which was not different from that of healthy controls (P = 0.08). For both cured and active CS, telomere length correlated significantly with duration of hypercortisolism (R2 = 0.22, P = 0.007). (4) There was a 27.6% reduction in telomere length between low and high tertiles in bedtime cortisol levels of healthy participants (P = 0.019).

CONCLUSION

Our findings demonstrate that exposure to stress and/or GCs is associated with shortened telomeres, which may be partially reversible.

Long-term changes in neuroimaging markers, cognitive function and psychiatric symptoms in an experimental model of Gulf War Illness

AIMS

Gulf War Illness (GWI) is a multi-symptom disease with debilitating cognitive and emotional impairments in veterans. GWI, like epilepsy, is caused by chemical neurotoxicity and manifests from disturbances in neuronal excitability. However, the mechanisms underlying such devastating neurological and psychiatric symptoms remain unclear. Here we investigated the long-term changes in neural behavior and brain structural abnormalities in a rat model of GWI. GWI is linked to exposure to GWI-related organophosphate chemicals (pyridostigmine bromide or PB and insecticide DEET, permethrin) during the stressful Gulf war.

METHODS

To mimic GWI, we generated an experimental GWI prototype in rats by daily exposure to GWI-related chemicals with restraint stress (GWIR-CS) for 4 weeks. Changes in MRI scan and cognitive function were assessed at 5- and 10- months post-exposure.

KEY FINDINGS

In MRI scans, rats displayed significant increases in lateral ventricle T2 relaxation times at both 5- and 10-months after GWIR-CS, indicating alterations in the cerebrospinal fluid (CSF) density. Furthermore, at 10 months, there were significant decreases in the volumes of the hippocampus and thalamus and an increase in the lateral ventricle volume. At both time points, they exhibited impairments in multiple neurobehavioral tests, confirming substantial deficits in memory and mood function. GWI-CS rats also displayed aggressive behavior and a marked decrease in social interaction and forced swimming, indicating depression.

CONCLUSIONS

These results confirm that chronic GWIR-CS exposure led to cognitive and psychiatric symptoms with concurrent neuroimaging abnormalities in CSF, with morphological neural lesions, demonstrating the role of divergent etiological mechanisms in GWI and its comorbidities.

Methylomic and transcriptomic predictors of one-month exposure to cortisol in healthy individuals

Allostatic load (AL) refers to the cumulative "wear and tear" on an organism throughout its lifetime. One of the primary contributing factors to AL is prolonged exposure to stress or its primary catabolic agent cortisol. Chronic exposure to stress or cortisol is associated with numerous diseases, including cardiovascular disease, metabolic disorders, and psychiatric disorders. Therefore, a molecular marker capable of integrating a past history of cortisol exposure would be of great utility for assessing disease risk. To this end, we recruited 87 healthy males and females of European ancestry between 18 and 60 years old, extracted genomic DNA and RNA from leukocytes, and implemented a gene-centric DNA enrichment method coupled with bisulfite sequencing and RNA-Seq of total RNA for the determination of genome-wide methylation and gene transcription, respectively. Sequencing data were analyzed against awakening and bedtime cortisol data to identify differentially methylated regions (DMRs) and CpGs (DMCs) and differentially expressed genes (DEGs). Six candidate DMCs (p_unadjusted < 0.005) and nine DEGs (p_unadjusted < 0.0005) were used to construct a prediction model that could capture past 30+ days of both bedtime and awakening cortisol levels. Utilizing a cross-validation approach, we obtained a regression coefficient of R² = 0.308 for predicting continuous awakening cortisol and an area under the curve (AUC) = 0.753 for dichotomous (high vs. low tertile) awakening cortisol, and R² = 0.224 and AUC = 0.723 for continuous and dichotomous bedtime cortisol levels, respectively. To our knowledge, the current study represents the first attempt to identify genome-wide predictors of cortisol exposure that utilizes both methylation and transcription targets. The utility of our approach needs to be replicated in an independent cohort of samples for which similar cortisol metrics are available.

Pain relief reverses hippocampal abnormalities in trigeminal neuralgia

Chronic pain patients frequently report memory and concentration difficulties. Objective testing in this population points to poor performance on memory and cognitive tests, and increased comorbid anxiety and depression. Recent evidence has suggested convergence between chronic pain and memory deficits onto the hippocampus. The hippocampus consists of heterogenous subfields involved in memory consolidation, behavior regulation, and stress modulation. Despite significant studies outlining hippocampal changes in human and chronic pain animal models, the effect of pain relief on hippocampal abnormalities remains unknown. Trigeminal neuralgia (TN) is a chronic neuropathic pain disorder which is highly amenable to surgical interventions, providing a unique opportunity to investigate the effect of pain relief. This study investigates the effect of pain relief on hippocampal subfields in TN. Anatomical MR images of 61 TN patients were examined before and 6 months after surgery. Treatment responders (n=47) reported 95% pain relief, whereas non-responders (n=14) reported 40% change in pain on average. At baseline, patients had smaller hippocampal volumes, compared to controls. After surgery, responders' hippocampal volumes normalized, largely driven by CA2/3, CA4 and dentate gyrus, which are involved in memory consolidation and neurogenesis. We propose that hippocampal atrophy in TN is pain-driven and successful treatment normalizes such abnormalities.

Differential Impact of Acute and Chronic Stress on CA1 Spatial Coding and Gamma Oscillations

Chronic and acute stress differentially affect behavior as well as the structural integrity of the hippocampus, a key brain region involved in cognition and memory. However, it remains unclear if and how the facilitatory effects of acute stress on hippocampal information coding are disrupted as the stress becomes chronic. To examine this, we compared the impact of acute and chronic stress on neural activity in the CA1 subregion of male mice subjected to a chronic immobilization stress (CIS) paradigm. We observed that following first exposure to stress (acute stress), the spatial information encoded in the hippocampus sharpened, and the neurons became increasingly tuned to the underlying theta oscillations in the local field potential (LFP). However, following repeated exposure to the same stress (chronic stress), spatial tuning was poorer and the power of both the slow-gamma (30–50 Hz) and fast-gamma (55–90 Hz) oscillations, which correlate with excitatory inputs into the region, decreased. These results support the idea that acute and chronic stress differentially affect neural computations carried out by hippocampal circuits and suggest that acute stress may improve cognitive processing.

Early maternal deprivation impairs learning and memory and alters hippocampal gene expression in adult male rats

Maternal deprivation (MD) in early life severely disrupts hippocampal development, leading to persistent cognitive and behavior deficits. The current study uncovered that early MD (P1-P21) impaired spatial learning and memory capacity detected by Morris water maze (MWM) tests from juvenile (P31) to adult (P81) rats compared to age-matched controls. And the protein expression in hippocampus were detected by two-dimensional gel electrophoresis (2-DE) before MWM, respectively. Protein changes in hippocampal were examined to identify the molecular pathways underlying MD-induced hippocampal dysfunction. There were 11 differentially expressed proteins analyzed between adult MD and control male rats, while the 8 proteins were then identified by UPLC-ESI-Q-TOF-MS. Gene Ontology (GO) annotations of the identified proteins were related to neuronal and glial cytoskeletal dynamics, membrane signaling, stress responses, biosynthesis, and metabolism. The different expression proteins spectrin alpha chain, non-erythrocytic 1 (Sptan1), ATP-citrate synthase (Acly), and heat shock protein 90-alpha (Hsp90aa1) have been verified by western blot analysis, and their expression levels showed consistent with 2-DE analysis. In addition, glial fibrillary acidic protein (GFAP) was also found reduced in adult hippocampus of MD rats. This study identifies candidate proteins encompassing a range of functional categories that may contribute to persistent learning and memory deficits due to early life MD.

Estrogen attenuates physical and psychological stress-induced cognitive impairments in ovariectomized rats

INTRODUCTION

Women are more vulnerable to stress-related disorders than men, which is counterintuitive as female sex hormones, especially estrogen, have been shown to be protective against stress disorders.

METHODS

In this study, we investigated whether two different models of stress act differently on ovariectomized (OVX) rats and the impact of estrogen on physical or psychological stress-induced impairments in cognitive-behaviors. Adult female Wistar rats at 21-22 weeks of age were utilized for this investigation. Sham and OVX rats were subjected to physical and psychological stress for 1 hr/day for 7 days, and cognitive performance was assessed using morris water maze (MWM) and passive avoidance (PA) tests. The open field and elevated plus maze tests (EPM) evaluated exploratory and anxiety-like behaviors.

RESULTS

In sham and OVX rats, both physical and psychological stressors were associated with an increase in EPM-determined anxiety-like behavior. OVX rats exhibited decreased explorative behavior in comparison with nonstressed sham rats (p < .05). Both physical stress and psychological stress resulted in disrupted spatial cognition as assayed in the MWM (p < .05) and impaired learning and memory as determined by the PA test when the OVX and sham groups were compared with the nonstressed sham group. Estrogen increased explorative behavior, learning and memory (p < .05), and decreased anxiety-like behavior compared with vehicle in OVX rats exposed to either type of stressor.

CONCLUSIONS

When taken together, estrogen and both stressors had opposite effects on memory, anxiety, and PA performance in a rat model of menopause, which has important implications for potential protective effects of estrogen in postmenopausal women exposed to chronic stress.

Stress enhances hippocampal neuronal synchrony and alters ripple-spike interaction

Adverse effects of chronic stress include anxiety, depression, and memory deficits. Some of these stress-induced behavioural deficits are mediated by impaired hippocampal function. Much of our current understanding about how stress affects the hippocampus has been derived from post-mortem analyses of brain slices at fixed time points. Consequently, neural signatures of an ongoing stressful experiences in the intact brain of awake animals and their links to later hippocampal dysfunction remain poorly understood. Further, no information is available on the impact of stress on sharp-wave ripples (SPW-Rs), high frequency oscillation transients crucial for memory consolidation. Here, we used in vivo tetrode recordings to analyze the dynamic impact of 10 days of immobilization stress on neural activity in area CA1 of mice. While there was a net decrease in pyramidal cell activity in stressed animals, a greater fraction of CA1 spikes occurred specifically during sharp-wave ripples, resulting in an increase in neuronal synchrony. After repeated stress some of these alterations were visible during rest even in the absence of stress. These findings offer new insights into stress-induced changes in ripple-spike interactions and mechanisms through which chronic stress may interfere with subsequent information processing.

Associations between Chewing Difficulty, Subjective Cognitive Decline, and Related Functional Difficulties among Older People without Dementia: Focus on Body Mass Index

OBJECTIVE

This study aimed to determine whether chewing difficulty is associated with subjective cognitive decline (SCD) and related functional difficulties by body mass index.

DESIGN

A population-based cross-sectional study.

SETTING AND PARTICIPANTS

A nationwide sample of 54,004 individuals aged ≥65 years from the 2018 Korea Community Health Survey.

MEASUREMENTS

SCD and SCD-related functional difficulties were measured using the cognitive decline module of the Behavioral Risk Factor Surveillance System. Chewing difficulty was assessed based on a self-report questionnaire from an oral health-related behaviors interview survey. BMI was calculated from objective values by measuring height and weight through a physical meter.

RESULTS

Among the 54,004 individuals, the prevalence of SCD in underweight, overweight, and obesity group was 33.6% (n = 806), 30.3% (n = 9,691), and 28.7% (n=5,632) respectively. Chewing difficulty was associated with SCD and SCD-related functional difficulties. This association was more pronounced in underweight (BMI: <18.5 kg/m2) people [underweight: (odds ratio [OR] = 1.68, 95% confidence interval [CI] 1.48-1.92); normal weight: OR = 1.13, 95% CI 1.04-1.22; obese: OR = 1.15, 95% CI 1.05-1.27]. Similar trends were demonstrated for SCD-related functional difficulties (underweight: OR = 1.53, 95% CI 1.17-2.01; normal weight: OR = 1.36, 95% CI 1.15-1.63; obese: OR = 1.50, 95% CI 1.22-1.86).

CONCLUSIONS

Chewing difficulty was associated with SCD and SCD-related functional difficulties in older people. Our results suggest that underweight status may play roles in the associations between chewing difficulty and SCD and SCD-related functional difficulties.

Magnetic resonance imaging analysis of long-term neuropathology after exposure to the nerve agent soman: correlation with histopathology and neurological dysfunction

Nerve agents (NAs) produce acute and long-term brain injury and dysfunction, as evident from the Japan and Syria incidents. Magnetic resonance imaging (MRI) is a versatile technique to examine such chronic anatomical, functional, and neuronal damage in the brain. The objective of this study was to investigate long-term structural and neuronal lesion abnormalities in rats exposed to acute soman intoxication. T2-weighted MRI images of 10 control and 17 soman-exposed rats were acquired using a Siemens MRI system at 90 days after soman exposure. Quantification of brain tissue volumes and T2 signal intensity was conducted using the Inveon Research Workplace software and the extent of damage was correlated with histopathology and cognitive function. Soman-exposed rats showed drastic hippocampal atrophy with neuronal loss and reduced hippocampal volume (HV), indicating severe damage, but had similar T2 relaxation times to the control group, suggesting limited scarring and fluid density changes despite the volume decrease. Conversely, soman-exposed rats displayed significant increases in lateral ventricle volumes and T2 times, signifying strong cerebrospinal fluid expansion in compensation for tissue atrophy. The total brain volume, thalamic volume, and thalamic T2 time were similar in both groups, however, suggesting that some brain regions remained more intact long-term after soman intoxication. The MRI neuronal lesions were positively correlated with the histological markers of neurodegeneration and neuroinflammation 90 days after soman exposure. The predominant MRI hippocampal atrophy (25%) was highly consistent with massive reduction (35%) of neuronal nuclear antigen-positive (NeuN+ ) principal neurons and parvalbumin-positive (PV+ ) inhibitory interneurons within this brain region. The HV was significantly correlated with both inflammatory markers of GFAP+ astrogliosis and IBA1+ microgliosis. The reduced HV was also directly correlated with significant memory deficits in the soman-exposed cohort, confirming a possible neurobiological basis for neurological dysfunction. Together, these findings provide powerful insight on long-term region-specific neurodegenerative patterns after soman exposure and demonstrate the feasibility of in vivo neuroimaging to monitor neuropathology, predict the risk of neurological deficits, and evaluate response to medical countermeasures for NAs.

Children's family income is associated with cognitive function and volume of anterior not posterior hippocampus

Children from lower income backgrounds tend to have poorer memory and language abilities than their wealthier peers. It has been proposed that these cognitive gaps reflect the effects of income-related stress on hippocampal structure, but the empirical evidence for this relationship has not been clear. Here, we examine how family income gaps in cognition relate to the anterior hippocampus, given its high sensitivity to stress, versus the posterior hippocampus. We find that anterior (but not posterior) hippocampal volumes positively correlate with family income up to an annual income of ~$75,000. Income-related differences in the anterior (but not posterior) hippocampus also predicted the strength of the gaps in memory and language. These findings add anatomical specificity to current theories by suggesting a stronger relationship between family income and anterior than posterior hippocampal volumes and offer a potential mechanism through which children from different income homes differ cognitively.

Association of Neighborhood-Level Disadvantage With Cerebral and Hippocampal Volume

Importance

Identifying risk factors for brain atrophy during the aging process can help direct new preventive approaches for dementia and cognitive decline. The association of neighborhood socioeconomic disadvantage with brain volume in this context is not well known.

Objective

To test whether neighborhood-level socioeconomic disadvantage is associated with decreased brain volume in a cognitively unimpaired population enriched for Alzheimer disease risk.

Design, Setting, and Participants

This study, conducted from January 6, 2010, to January 17, 2019, at an academic research neuroimaging center, used cross-sectional data on 951 participants from 2 large, ongoing cohort studies of Alzheimer disease (Wisconsin Registry for Alzheimer's Prevention and Wisconsin Alzheimer's Disease Research Center clinical cohort). Participants were cognitively unimpaired based on National Institute on Aging-Alzheimer's Association workgroup diagnostic criteria for mild cognitive impairment and Alzheimer disease, confirmed through a consensus diagnosis panel. The cohort was enriched for Alzheimer disease risk based on family history of dementia. Statistical analysis was performed from April 3 to September 27, 2019.

Main Outcomes and Measures

The Area Deprivation Index, a geospatially determined index of neighborhood-level disadvantage, and cardiovascular disease risk indices were calculated for each participant. Linear regression models were fitted to test associations between relative neighborhood-level disadvantage (highest 20% based on state of residence) and hippocampal and total brain tissue volume, as assessed by magnetic resonance imaging.

Results

In the primary analysis of 951 participants (637 women [67.0%]; mean [SD] age, 63.9 [8.1] years), living in the 20% most disadvantaged neighborhoods was associated with 4.1% lower hippocampal volume (β = -317.44; 95% CI, -543.32 to -91.56; P = .006) and 2.0% lower total brain tissue volume (β = -20 959.67; 95% CI, -37 611.92 to -4307.43; P = .01), after controlling for intracranial volume, individual-level educational attainment, age, and sex. Robust propensity score-matched analyses determined that this association was not due to racial/ethnic or demographic characteristics. Cardiovascular risk score, examined in a subsample of 893 participants, mediated this association for total brain tissue but not for hippocampal volume.

Conclusions and Relevance

For cognitively unimpaired individuals, living in the most disadvantaged neighborhoods was associated with significantly lower cerebral volumes, after controlling for maximal premorbid (total intracranial) volume. This finding suggests an association of community socioeconomic context, distinct from individual-level socioeconomic status, with brain volume during aging. Cardiovascular risk mediated this association for total brain tissue volume but not for hippocampal volume, suggesting that neighborhood-level disadvantage may be associated with these 2 outcomes via distinct biological pathways.

Chronic Mild Stress Modified Epigenetic Mechanisms Leading to Accelerated Senescence and Impaired Cognitive Performance in Mice

Cognitive and behavioural disturbances are a growing public healthcare issue for the modern society, as stressful lifestyle is becoming more and more common. Besides, several pieces of evidence state that environment is crucial in the development of several diseases as well as compromising healthy aging. Therefore, it is important to study the effects of stress on cognition and its relationship with aging. To address these queries, Chronic Mild Stress (CMS) paradigm was used in the senescence-accelerated mouse prone 8 (SAMP8) and resistant 1 (SAMR1). On one hand, we determined the changes produced in the three main epigenetic marks after 4 weeks of CMS treatment, such as a reduction in histone posttranslational modifications and DNA methylation, and up-regulation or down-regulation of several miRNA involved in different cellular processes in mice. In addition, CMS treatment induced reactive oxygen species (ROS) damage accumulation and loss of antioxidant defence mechanisms, as well as inflammatory signalling activation through NF-κB pathway and astrogliosis markers, like Gfap. Remarkably, CMS altered mTORC1 signalling in both strains, decreasing autophagy only in SAMR1 mice. We found a decrease in glycogen synthase kinase 3 β (GSK-3β) inactivation, hyperphosphorylation of Tau and an increase in sAPPβ protein levels in mice under CMS. Moreover, reduction in the non-amyloidogenic secretase ADAM10 protein levels was found in SAMR1 CMS group. Consequently, detrimental effects on behaviour and cognitive performance were detected in CMS treated mice, affecting mainly SAMR1 mice, promoting a turning to SAMP8 phenotype. In conclusion, CMS is a feasible intervention to understand the influence of stress on epigenetic mechanisms underlying cognition and accelerating senescence.

Chronic unpredictable intermittent restraint stress disrupts spatial memory in male, but not female rats

Chronic stress leads to sex-dependent outcomes on spatial memory by producing deficits in males, but not in females. Recently it was reported that compared to daily restraint, intermittent restraint (IR) produced more robust stress and anxiety responses in male rats. Whether IR would be sufficiently robust to impair hippocampal-dependent spatial memory in both male and female rats was investigated. IR involved mixing restraint with non-restraint days over weeks before assessing spatial memory and anxiety profile on the radial arm water maze, object placement, novel object recognition, Y-maze, open field and novelty suppressed feeding. Experiments 1 and 2 used Sprague-Dawley male rats only and determined that IR for 6 h/d (IR6), but not 2 h/d, impaired spatial memory and that task order was important. In experiment 3, IR6 was extended for 6wks before spatial memory testing commenced using both sexes. Unexpectedly, an extended IR6 paradigm failed to impair spatial memory in either sex, suggesting that by 6wks IR6 may have become predictable. In experiment 4, an unpredictable IR (UIR) paradigm was implemented, in which restraint duration (30 or 60-min) combined with orbital shaking, time of day, and the days off from UIR were varied. UIR impaired spatial memory in males, but not in females. Together with other reports, these findings support the interpretation that chronic stress negatively impairs hippocampal-dependent function in males, but not in females. We interpret these findings to show that females are more resilient to chronic stress than are males as it pertains to spatial ability.

Oxytocin and Stress: Neural Mechanisms, Stress-Related Disorders, and Therapeutic Approaches

Clinical reports show that oxytocin (OT) is related to stress-related disorders such as depression, anxiety disorder, and post-traumatic stress disorder. Two key structures in the brain should be paid special attention with regard to stress regulation, namely, the hypothalamus and the hippocampus. The former is the region for central command for most, if not all, of the major endocrine systems, and the latter takes a key position in the regulation of mood and anxiety. There are extensive neural projections between the two structures, and both are functionally intertwined. The hypothalamus projects OTergic neurons to the hippocampus, and the latter possesses high levels of OT receptors. The hippocampus also regulates the secretion of glucocorticoids, a major group of stress hormones. Excessive levels of glucocorticoids in chronic stress cause atrophy of the hippocampus, whereas OT has been shown to protect hippocampal neurons from the toxic effects of glucocorticoids. In this article, we discuss how neural and endocrine mechanisms interplay in stress regulation, with an emphasis on the role of OT, as well as its therapeutic potential in the treatment of stress-related disorders.

Sex differences in the effects of acute stress on cerebral glucose metabolism: A microPET study

Stress has been considered as a risk factor for the development and aggravation of several diseases. The hypothalamic-pituitary-adrenal axis (HPA) is one of the main actors for the stress response and homeostasis maintenance. Positron emission tomography (PET) has been used to evaluate neuronal activity and to study brain regions that may be related to the HPA axis response. Since neuroimaging is an important tool in detecting neuroendocrine-related changes, we used fluorodeoxyglucose-18 (¹⁸F-FDG) and positron emission microtomography (microPET) to evaluate sexual differences in the glucose brain metabolism after 10, 30 and 40 min of acute stress in Balb/c mice. We also investigated the effects of restraint stress in blood, liver and adrenal gland ¹⁸F-FDG biodistribution using a gamma counter. A decreased glucose uptake in the whole brain in both females and males was found. Additionally, there were time and sex-dependent alterations in the ¹⁸F-FDG uptake after restraint stress in specific brain regions, indicating that males could be more vulnerable to the short-term effects of acute stress. According to the gamma counter biodistribution, only females showed a significant decreased glucose uptake in the blood, liver and right adrenal after restraint stress. In addition, in comparisons between the sexes, males showed a decreased glucose uptake in the whole brain and in several brain regions compared to females. In conclusion, exposure to acute restraint stress resulted in significant decreased glucose metabolism in the brain, with particular effects in different regions and organs in a sex-specific manner.

Validation of hippocampal biomarkers of cumulative affective experience

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Recent knowledge on hippocampal structural plasticity is reviewed.

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This knowledge is harnessed to develop biomarkers of cumulative experience.

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Hippocampal plasticity is shown to have construct, content and criterion validity in mammals.

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The biomarkers require further validation to be used in birds and fish.

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We discuss some practical considerations to implement the biomarkers.

Progress in improving the welfare of captive animals has been hindered by a lack of objective indicators to assess the quality of lifetime experience, often called cumulative affective experience. Recent developments in stress biology and psychiatry have shed new light on the role of the mammalian hippocampus in affective processes. Here we review these findings and argue that structural hippocampal biomarkers demonstrate criterion, construct and content validity as indicators of cumulative affective experience in mammals. We also briefly review emerging findings in birds and fish, which have promising implications for applying the hippocampal approach to these taxa, but require further validation. We hope that this review will motivate welfare researchers and neuroscientists to explore the potential of hippocampal biomarkers of cumulative affective experience.

Systemic administration of a fibroblast growth factor receptor 1 agonist rescues the cognitive deficit in aged socially isolated rats

Social isolation predominantly occurs in elderly people and it is strongly associated with cognitive decline. However, the mechanisms that produce isolation-related cognitive dysfunction during aging remain unclear. Here, we evaluated the cognitive, electrophysiological, and morphological effects of short- (4 weeks) and long-term (12 weeks) social isolation in aged male Wistar rats. Long-term but not short-term social isolation increased the plasma corticosterone levels and impaired spatial memory in the Morris water maze. Moreover, isolated animals displayed dampened hippocampal long-term potentiation in vivo, both in the dentate gyrus (DG) and CA1, as well as a specific reduction in the volume of the stratum oriens and spine density in CA1. Interestingly, social isolation induced a transient increase in hippocampal basic fibroblast growth factor (FGF2), whereas fibroblast growth factor receptor 1 (FGFR1) levels only increased after long-term isolation. Importantly, subchronic systemic administration of FGL, a synthetic peptide that activates FGFR1, rescued spatial memory in long-term isolated rats. These findings provide new insights into the neurobiological mechanisms underlying the detrimental effects on memory of chronic social isolation in the aged.

Stress Elicits Contrasting Effects on the Structure and Number of Astrocytes in the Amygdala versus Hippocampus

Stress causes divergent patterns of structural and physiological plasticity in the hippocampus versus amygdala. However, a majority of earlier studies focused primarily on neurons. Despite growing evidence for the importance of glia in health and disease, relatively little is known about how stress affects astrocytes. Further, previous work focused on hippocampal astrocytes. Hence, we examined the impact of chronic immobilization stress (2 h/d, 10 d), on the number and structure of astrocytes in the rat hippocampus and amygdala. We observed a reduction in the number of glial fibrillary acidic protein (GFAP)-positive astrocytes in the basal amygdala (BA), 1 d after the end of 10 d of chronic stress. Detailed morphometric analysis of individual dye-filled astrocytes also revealed a decrease in the neuropil volume occupied by these astrocytes in the BA, alongside a reduction in the volume fraction of fine astrocytic protrusions rather than larger dendrite-like processes. By contrast, the same chronic stress had no effect on the number or morphology of astrocytes in hippocampal area CA3. We also confirmed previous reports that chronic stress triggers dendritic hypertrophy in dye-filled BA principal neurons that were located adjacent to astrocytes that had undergone atrophy. Thus, building on earlier evidence for contrasting patterns of stress-induced plasticity in neurons across brain areas, our findings offer new evidence that the same stress can also elicit divergent morphological effects in astrocytes in the hippocampus versus the amygdala.

DNA methylation and sex-specific expression of FKBP5 as correlates of one-month bedtime cortisol levels in healthy individuals

Chronic exposure to cortisol is associated with cardiovascular, metabolic, and psychiatric disorders. Although cortisol can be readily measured from peripheral sources such as blood, urine, or saliva, multiple samplings spanning several days to weeks are necessary to reliably assess chronic cortisol exposure levels (referred to as cortisol load). Although cortisol levels in hair have been proposed as a measure of cortisol load, measurement is cumbersome and many people are not candidates due to short hair length and use of hair dyes. To date, there are no blood biomarkers that capture cortisol load. To identify a blood biomarker capable of integrating one-month cortisol exposure levels, 75 healthy participants provided 30+ days of awakening and bedtime saliva cortisol and completed psychosocial measures of anxiety, depression, and stress. Mean daily awakening and bedtime cortisol levels were then compared to CpG methylation levels, gene expression, and genotypes of the stress response gene FKBP5 obtained from blood drawn on the last day of the study. We found a correlation between FKBP5 methylation levels and mean 30+day awakening and bedtime cortisol levels (|r|≥0.32, p ≤ 0.006). We also observed a sex-specific correlation between bedtime cortisol levels and FKBP5 mRNA expression in female participants (r = 0.42, p = 0.005). Dividing the 30-day sampling period into four weekly bins showed that the correlations for both methylation and expression were not being driven by cortisol levels in the week preceding the blood draw. We also identified a female-specific association between FKBP5 mRNA expression and scores on the Beck Anxiety Inventory (r = 0.37, p = 0.013) and Beck Depression Inventory-II (r = 0.32, p = 0.033). Finally, DNA was genotyped at four SNPs, and variation in rs4713902 was shown to have an effect on FKBP5 expression under a codominant model (f = 3.41, p = 0.048) for females only. Our results suggest that blood FKBP5 DNA methylation and mRNA expression levels may be a useful marker for determining general or sex-specific 30-day cortisol load and justifies genome-wide approaches that can potentially identify additional cortisol markers with broader clinical utility.

Behavioral and structural adaptations to stress

Unpredictable aversive experiences, or stressors, lead to changes in depression- and anxiety-related behavior and to changes in hippocampal structure including decreases in adult neurogenesis, granule cell and pyramidal cell dendritic morphology, and volume. Here we review the relationship between these behavioral and structural changes and discuss the possibility that these changes may be largely adaptive. Specifically, we suggest that new neurons in the dentate gyrus enhance behavioral adaptability to changes in the environment, biasing behavior in novel situations based on previous experience with stress. Conversely, atrophy-like changes in the hippocampus and decreased adult neurogenesis following chronic stress may serve to limit stress responses and stabilize behavior during chronic stress.

Influences of photic stress on postsubicular head-directional processing

The stress response serves vital adaptive functions. However, acute stress episodes often negatively impact cognitive processing. Here, we aimed to elucidate whether stress detrimentally affects the head‐direction cells of the postsubiculum, which may in turn impair downstream spatial information processing. We recorded neurons in the rats’ postsubiculum during a pellet‐chasing task during baseline non‐stress conditions and after a 30‐min acute photic stress exposure. Based on their baseline firing rate, we identified a subpopulation of head‐direction cells that drastically decreased its firing rate as a response to stress while preserving their head directionality. The remaining population of head‐direction cells as well as other neurons recorded in the postsubiculum were unaffected. The observed altered activity in the subpopulation might be the basis for spatial processing deficits observed following acute stress episodes.

Stress and Loss of Adult Neurogenesis Differentially Reduce Hippocampal Volume

BACKGROUND

Hippocampal volume loss is a hallmark of clinical depression. Chronic stress produces volume loss in the hippocampus in humans and atrophy of CA3 pyramidal cells and suppression of adult neurogenesis in rodents.

METHODS

To investigate the relationship between decreased adult neurogenesis and stress-induced changes in hippocampal structure and volume, we compared the effects of chronic unpredictable restraint stress and inhibition of neurogenesis in a rat pharmacogenetic model.

RESULTS

Chronic unpredictable restraint stress over 4 weeks decreased total hippocampal volume, reflecting loss of volume in all hippocampal subfields and in both dorsal and ventral hippocampus. In contrast, complete inhibition of adult neurogenesis for 4 weeks led to volume reduction only in the dentate gyrus. With prolonged inhibition of neurogenesis for 8 or 16 weeks, volume loss spread to the CA3 region, but not CA1. Combining stress and inhibition of adult neurogenesis did not have additive effects on the magnitude of volume loss but did produce a volume reduction throughout the hippocampus. One month of chronic unpredictable restraint stress and inhibition of adult neurogenesis led to atrophy of pyramidal cell apical dendrites in dorsal CA3 and to neuronal reorganization in ventral CA3. Stress also significantly affected granule cell dendrites.

CONCLUSIONS

The findings suggest that adult neurogenesis is required to maintain hippocampal volume but is not responsible for stress-induced volume loss.

Detection of volume alterations in hippocampal subfields of rats under chronic unpredictable mild stress using 7T MRI: A follow-up study

PURPOSE

To determine hippocampal subfields volume loss in depression, which was simulated by a rat chronic unpredictable mild stress (CUMS) model. As different cellular and molecular characteristics in hippocampal subfields, these subfields are regarded as differentially vulnerable to processes associated with stress.

MATERIALS AND METHODS

Twenty male Wistar rats were exposed to various stressors until the model was successfully established. The effects of physical exercise on recovery of hippocampal volume in depressed rats were simulated using the wheel running test (WRT). These rats hippocampal volumes were dynamically measured using T2 -weighted images (T2 WIs) at 7T structural magnetic resonance imaging (MRI).

RESULTS

After 4 weeks of CUMS (CUMS-4W), the behavioral tests showed that the rat model of depression was successfully established (P < 0.001). In this process, the bilateral CA1 volume was significantly atrophic after 2 weeks of CUMS (CUMS-2W) compared with controls (left: 21.09 ± 2.31 vs. 26.16 ± 3.83 mm3 , P < 0.001; right: 21.05 ± 2.36 vs. 26.12 ± 3.78 mm3 , P < 0.001), whereas the other subfields did not show a similar change (all P > 0.05). The volume of CA3, dentate gyrus (DG), and subiculum displayed atrophy after CUMS-4W (CA3: left:12.23 ± 1.10 mm3 , right: 12.20 ± 1.14 mm3 ; DG: left:8.16 ± 0.58 mm3 , right: 8.18 ± 0.92 mm3 ; subiculum: left: 4.30 ± 0.52 mm3 , right: 4.29 ± 0.44 mm3 ; all P < 0.05). The rats' (CUMS-4W) hippocampal DG volume was restored (left: 10.67 ± 1.60 mm3 , right: 10.71 ± 1.58 mm3 ), and the depression-like behaviors of these rats improved after WRT-4W (P < 0.05).

CONCLUSION

In general, volume loss was demonstrated in various rat hippocampal subfields during the development and recovery from depression, which were detected by ultrahigh-field MRI.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2017;46:1456-1463.

Fibroblast growth factor 22 is a novel modulator of depression through interleukin-1β

BACKGROUND AND AIMS

Emerging evidence shows that fibroblast growth factor 22 (FGF22) plays a critical role in the etiology of depression. However, the molecular mechanisms of FGF22 are not fully comprehended. Here, the effect of FGF22 in depression and its relationship with interleukin-1β (IL-1β) were investigated in clinical, animal, and cell experiments.

METHODS

Serum from depressive patients was collected, and the levels of FGF22 and IL-1β were analyzed by ELISA. The chronic unpredictable mild stress (CUMS) model was established, and primary hippocampal neuronal cells were cultured to examine changes in FGF22 and IL-1β levels in rat hippocampus.

RESULTS

The results revealed a negative correlation between serum FGF22 levels and serum IL-1β levels. The expression of IL-1β in the CUMS rat hippocampus decreased, and the apoptosis of hippocampal cells improved after the injection of lentiviral vector-mediated FGF22 (LV-FGF22). Further tests in primary hippocampal neuronal cells also showed a reduction in IL-1β and the cell apoptosis rate after treatment with FGF22.

CONCLUSION

In conclusion, the results revealed that FGF22 plays a role in alleviating depression, which may be mediated by reduced expression of IL-1β.

The BDNF Val66Met polymorphism is associated with structural neuroanatomical differences in young children

The brain-derived neurotrophic factor (BDNF) Val⁶⁶Met single nucleotide polymorphism (SNP) has been associated with individual differences in brain structure and function, and cognition. Research on BDNF's influence on brain and cognition has largely been limited to adults, and little is known about the association of this gene, and specifically the Val⁶⁶Met polymorphism, with developing brain structure and emerging cognitive functions in children. We performed a targeted genetic association analysis on cortical thickness, surface area, and subcortical volume in 78 children (ages 6-10) who were Val homozygotes (homozygous Val/Val carriers) or Met carriers (Val/Met, Met/Met) for the Val⁶⁶Met locus using Atlas-based brain segmentation. We observed greater cortical thickness for Val homozygotes in regions supporting declarative memory systems (anterior temporal pole/entorhinal cortex), consistent with adult findings. Met carriers had greater surface area in the prefrontal and parietal cortices and greater cortical thickness in lateral occipital/parietal cortex in contrast to prior adult findings that may relate to performance on cognitive tasks supported by these regions in Met carriers. Finally, we found larger right hippocampal volume in Met carriers, although inconsistent with adult findings (generally reports larger volumes for Val homozygotes), is consistent with a recent finding in children. Gene expression levels vary across different brain regions and across development and our findings highlight the need to consider this developmental change in explorations of BDNF-brain relationships. The impact of the BDNF Val⁶⁶Met polymorphism on the structure of the developing brain therefore reflects regionally-specific developmental changes in BDNF expression and cortical maturation trajectories.