The stressed hippocampus, synaptic plasticity and lost memories

Chronic stress-related behavioral and synaptic changes require caspase-3 activation in the ventral hippocampus of male mice

Although numerous studies have suggested that chronic stress is a major risk factor for major depressive disorder, the process by which stress causes depression is still not fully understood. Previously, we investigated glucocorticoids, which are stress response hormones that activate a synapse-weakening pathway. Therefore, we hypothesized that chronic stress may cause synaptic depression, which could reduce excitability related to emotions. Animals underwent chronic restraint stress (CRS), followed by basal synaptic transmission measurement in hippocampal slices to assess synaptic function. Drugs were infused into the ventral hippocampus via cannulation before behavioral tests, including forced swimming, tail suspension, and sucrose intake tests, which evaluated depressive-like behaviors and anhedonia. The field excitatory postsynaptic potentials (fEPSPs) are reduced by chronic restraint stress (CRS) in the ventral hippocampus. The ventral hippocampi of mice treated with CRS showed low levels of fEPSP after the forced swim test (FST). In the FST and tail suspension test, CRS-induced increases in immobility time were prevented by the acute inhibition of AMPAR internalization by Tat-GluA23y, which also prevented fEPSP reduction. Mice lacking caspase-3 exhibited resilience to CRS-induced increases in immobility time in the FST, as well as changes in the functionality of synaptic AMPAR. Finally, the caspase-3 inhibitor Z-DEVD-FMK rapidly blocked the CRS-induced increase in immobility time in the FST and the CRS-induced decrease in sucrose preference. These findings suggest that chronic stress-related behavioral changes may require caspase-3-dependent alterations in ventral hippocampal synapses.

mGluR5 in Pyramidal Neurons in the Hippocampus Mediates Chronic Stress-Induced Memory Deficits

BACKGROUND

Chronic stress causes variable profiles of physiological deficits, including mood disorders, sleep disorders, and memory deficits. However, the neural mechanisms and potential drug targets of chronic stress-induced memory deficit remain elusive.

AIMS

This study aimed to explore the function and regulatory mechanisms of metabotropic glutamate receptor 5 (mGluR5) in chronic stress-induced memory deficit and investigate the potential therapeutic target for stress-related memory deficit.

METHODS

Behavioral tests were used to assess the effects of chronic stress on memory. Electrophysiological recordings were conducted to examine the synaptic inputs after chronic stress. RNA sequencing was employed to achieve transcriptional alterations in the hippocampus after stress or mGluR5 knockdown. Enrichment analysis was performed to identify the downstream effector of chronic stress-induced memory deficits.

RESULTS

Chronic restraint stress (CRS) impairs hippocampal-dependent memory and electrophysiological recordings reveal that chronic stress impairs synaptic inputs. Subsequently, we observe that the mGluR5 level declines after CRS, which is an important molecule for learning and memory. mGluR5 knockdown induces memory deficits and impairs synaptic inputs. Enhancement of mGluR5 activity by CDPPB could restore chronic stress-induced memory deficits and rescue impaired synaptic inputs. Furthermore, we identify that pituitary adenylyl cyclase activating peptide (PACAP) is down-regulated after CRS and mGluR5 knockdown. PACAP application could restore the impaired inhibitory synaptic inputs after CRS.

CONCLUSIONS

These results illuminate that the mGluR5 mediates chronic stress-induced memory deficits, which may provide promising strategies for treating stress-related memory deficits.

Witness stress promotes age and sex-dependent behavioral and neurofunctional alterations in the amygdaloid complex and dorsal hippocampus in mice

Humans are frequently exposed to stress, with social stress being a predominant factor, either directly experienced or observed. Chronic stress is linked to psychiatric disorders such as depression and anxiety and induces morpho-functional changes in brain areas like the amygdaloid complex and dorsal hippocampus, which influence emotional responses. This study examined the impact of witness social defeat stress (WSDS) on depression-like behaviors and neural activation in Swiss-Webster mice, considering variables like sex and life stage. Two experiments were conducted: Experiment 1 assessed the effects of WSDS in adulthood (58-60 postnatal days [PND]) on behaviors such as coat state, nest building, novel object exploration, and body weight gain, as well as neuronal activation in the amygdaloid complex and dorsal hippocampus. Experiment 2 evaluated the long-term effects of early WSDS exposure (21 PND) on these same parameters, reassessing mice at 58-62 PND. Results showed sex-dependent behavioral changes, including altered novel object interaction, coat and nest quality, and decreased ΔFosB Protein Expression in the amygdaloid complex and hippocampus, with age and sex influencing the stress response. WSDS in adulthood produced smaller behavioral changes, with some signs of resilience particularly in females, while early exposure to this type of stress led to more pronounced effects. This study highlights the complexity of stress responses, suggesting that the intensity and timing of stress, along with sex, play critical roles in shaping behavioral outcomes.

Synurus deltoides Alleviates Anti-Depressive Like Behavior Dysfunction Induced by Chronic Unpredictable Mild Stress via Stress-Related CRF/TLR Pathway

This study was aimed at assessing the protective effect of the 80% ethanolic extract of Synurus deltoides (EESD) on chronic unpredictable mild stress (CUMS)-induced depressive-like behavior dysfunction. The bioactive compounds of S. deltoides were identified as quinic acid, chlorogenic acid, rutin, 1,3-dicaffeoylquinic acid, and dicaffeoylsuccinoylquinic acid. EESD and bioactive compounds in EESD significantly protected corticosterone-induced hippocampal cellular death and reactive oxygen species (ROS) contents compared to vitamin C in HT22 cells. By conducting the sucrose preference test, forced swimming test, open field test, and tail suspension test, EESD was found to significantly suppress depression-like behavior. EESD effectively reduced mitochondrial dysfunction by regulating cerebral ROS levels, mitochondrial membrane potential, and ATP contents. EESD showed a considerable regulatory effect by regulating serum stress hormones including corticosterone, norepinephrine, serotonin, 5-hydroxyindoleacetic acid, and melatonin. In addition, EESD significantly suppressed stress-related CRF pathway, inflammatory TLR pathway, and apoptotic signal in cerebral tissues. These results suggest that EESD might be a natural plant substance that improves CUMS-induced behavior abnormality by regulating inflammation and hormonal changes in brain tissue. In the future, additional clinical trials or efficacy evaluations of individual compounds of EESD will be needed to confirm the bioactivity ability and usability of EESD.

Key concepts, methods, findings, and questions about traumatic memories

This article is based on a Lifetime Achievement Award lecture delivered at the 40th Annual Meeting of the International Society for Traumatic Stress Studies in Boston (Massachusetts, United States) in September 2024. Understanding traumatic memory involves integrating clinical observations with a wide range of knowledge from philosophy, cognitive and social psychology, and neuroscience. I present definitions of traumatic memory; distinguish voluntary from involuntary forms, such as flashbacks; and introduce relevant concepts that can situate the clinical symptom within a wider framework. The distinction between flashbacks and standard episodic memory has important implications, and I discuss how the methods used to study traumatic memory can preserve it. Using this same perspective, I then review emerging evidence concerning the nature, neural underpinnings, and origin of traumatic memories. The final section reviews some significant unanswered questions for the future. These include the impact of traumatic memories on the experience of self and the implications of delayed onsets for postulating a family of posttraumatic stress disorders with different underlying mechanisms.

The regulation mechanism of perceived stress on cognitive function of patients with breast cancer undergoing chemotherapy: a multiple mediation analysis

AIM

Cancer-related cognitive impairment (CRCI) is one of the severe side effects affecting the quality of life of breast cancer (BC) patients. However, the mechanisms underlying CRCI are still unclear. The study aimed to examine the multiple mediating roles of resilience, social support, cortisol, and neutrophil-lymphocyte ratio (NLR) in the relationship between perceived stress and cognitive function.

DESIGN

The study was a descriptive, cross-sectional study.

METHODS

The study investigated 450 BC patients with chemotherapy in China. Convenience sampling was conducted from February to August 2023. The study used the Perceived Stress Scale, the Connor-Davidson Resilience Scale, the Social Support Rating Scale, the Functional Assessment of Cancer Therapy-Cognitive Function, the Montreal Cognitive Assessment, salivary cortisol, and NLR. SPSS 25.0 and AMOS 26.0 conducted bivariate correlations and multiple mediation analysis.

RESULTS

The correlations of magnitude variables ranged from no correlation to moderate level (r = - 0.002 to - 0.617). The multiple mediation path demonstrated that resilience and morning cortisol levels mediated the relationship between perceived stress and cognitive function, with a 95% confidence interval (CI) not including 0 for the direct, indirect, and total effects.

CONCLUSIONS

The study confirmed that when BC patients endure physical and psychological stress during diagnosis and treatment, individuals' resilience can buffer the stress on cognitive function. Morning salivary cortisol levels, as the product and indicator of the hypothalamic-pituitary-adrenal (HPA) axis function, may play a significant role in the effect of perceived stress on cognitive function while incapable of finding NLR as the marker of individuals' immune inflammatory response and social support play a role in this relationship. The study, based on a stress perspective, explored the regulatory mechanisms by which perceived stress affects cognitive function in patients undergoing chemotherapy for breast cancer, providing intervenable targets for subsequent improvement of patients' cognitive function.

From memory disorders to the development of depression: A system approach

In this review, a hypothesis explaining the origin and genesis of depression development from the perspective of a holistic functional system of behavioral control is proposed. The core of the functional system is the memory apparatus, on which all other key components of the behavioral control system (sensory information, motivation, reinforcement, and motor activity) are interlocked. In the organization of memory traces (engrams) there are two inputs, sensory and motivational, through which the stimulus-stimulus (S-S) and stimulus-motor (S-R) engrams are formed. These engrams are organized and actualized by means of forward and backward conditional connections between cortical representations of sensory information and motivational structures of the brain. Through feedback connections from reinforcing (emotional) input to the memory apparatus, the S-S and S-R engrams are consolidated or weakened depending on the strength of reward or negative events. Depression begins with a breakdown in memory mechanisms. These breakdowns are related to problems with the three mentioned memory inputs: sensory, motivational, and reinforcing (emotional). Disruptions in sensory and motivational input lead to an inability to form new memory engrams, their actualization and retrieval. This creates difficulty in solving current and past unresolved problems, eliciting more accumulation and increasing difficulties in their solving. Unresolved tasks lead to weakening of the reinforcing input, and further impairment of consolidation of the acting engrams. Another reason for the weakening of reinforcing input is excessive action of directly harmful events or constant chronic stress. The review presents the current literature and some data from our laboratory in favor of each memory input's contribution and their impact on the development of depression, when they are problematic.

Prenatal stress increases learning and memory deficits in offspring: A toxicological study on hippocampal neuronal damage in rats

BACKGROUND

Recent epidemiological studies have observed that prenatal stress induced learning and memory deficits in children, but the toxicological mechanisms remain unclear.

OBJECTIVES

We conducted a systematic study to explore the toxicological mechanisms of prenatal stress on learning and memory in offspring.

METHODS

We established a prenatal stress model by corticosterone (CORT) administration at different dose levels (0, 10, 40 mg/kg) from gestational days 14-21. First we assessed hippocampal damage in the offspring by the neuronal damage, synaptic damage, and neurotransmitter levels. We then detected learning and memory ability by Morris water maze test, and finally we analyzed biomarkers of oxidative stress and apoptosis to explore the potential mechanism.

RESULTS

Prenatal stress induced by CORT administration was indicated by decreased body weight, increased serum CORT and reduced food consumption (p < 0.05). With prenatal stress increasing, hippocampal damage in the offspring worsened, characterized by damaged neurons, decreased synaptic proteins, and reduced neurotransmitters. Learning and memory deficits were observed, including long escape latency and increased travel distance to find the platform in the Morris water maze test (p < 0.05).The potential toxicological mechanisms underlying the learning and memory impairments were indicated by biomarkers: decreased antioxidant enzymes (SOD and T-AOC), increased pro-inflammatory cytokines (IL-6) and apoptosis (p < 0.05).

CONCLUSION

Prenatal stress leads to hippocampus-dependent learning and memory impairments by neuron loss, synaptic injury, and reduced neurotransmitters. Our study implies that improving maternal well-being is helpful for the learning and memory development of the next generation.

Running Reverses Chronic Stress-Induced Changes in Serotonergic Modulation of Hippocampal Granule Cells and Altered Behavioural Responses

Chronic stress increases susceptibility to anxiety and depression disorders, recurrent and common psychiatric conditions. Current antidepressant medications have varying degrees of efficacy and often have multiple side effects limiting treatment adherence. Physical exercise has beneficial effects on stress-related mental disorders. However, the underlying mechanisms are unclear. Dentate gyrus granule cells (GCs) excitability may mediate stress resilience. Here, we expose young adult C57Bl6 mice to chronic restraint stress (CRS) for 14 days followed by 30 days of running treatment. Behavioural evaluation before and after treatment showed that the behavioural alterations elicited by CRS were mitigated by running. Next, we evaluated serotonergic modulation of GC excitability, as a potential mechanism underlying running-induced stress resilience. Electrophysiological recordings indicate that CRS alters serotonergic modulation of GC excitability. Utilising (S)-WAY 100135 and Tropisetron, antagonists of 5-HT1A and 5-HT3 receptors respectively, we show that running recovers 5-HT1A receptor activity lost by CRS. Additionally, running promotes the indirect modulation of GCs through 5-HT3 receptor activation. Thus, 5-HT1A and 5-HT3 receptors may be potential targets for the treatment of stress-related psychiatric disorders.

Missense mutation in the activation segment of the kinase CK2 models Okur-Chung neurodevelopmental disorder and alters the hippocampal glutamatergic synapse

Exome sequencing has enabled the identification of causative genes of monogenic forms of autism, amongst them, in 2016, CSNK2A1, the gene encoding the catalytic subunit of the kinase CK2, linking this kinase to Okur-Chung Neurodevelopmental Syndrome (OCNDS), a newly described neurodevelopmental condition with many symptoms resembling those of autism spectrum disorder. Thus far, no preclinical model of this condition exists. Here we describe a knock-in mouse model that harbors the K198R mutation in the activation segment of the α subunit of CK2. This region is a mutational hotspot, representing one-third of patients. These mice exhibit behavioral phenotypes that mirror patient symptoms. Homozygous knock-in mice die mid-gestation while heterozygous knock-in mice are born at half of the expected mendelian ratio and are smaller in weight and size than wildtype littermates. Heterozygous knock-in mice showed alterations in cognition and memory-assessing paradigms, enhanced stereotypies, altered circadian activity patterns, and nesting behavior. Phosphoproteome analysis from brain tissue revealed alterations in the phosphorylation status of major pre- and postsynaptic proteins of heterozygous knock-in mice. In congruence, we detect reduced synaptic maturation in hippocampal neurons and attenuated long-term potentiation in the hippocampus of knock-in mice. Taken together, heterozygous knock-in mice (CK2αK198R/+) exhibit significant face validity, presenting ASD-relevant phenotypes, synaptic deficits, and alterations in synaptic plasticity, all of which strongly validate this line as a mouse model of OCNDS.

Neural stem cell-specific deletion of Atg7 alleviates hippocampal dysfunction and neuronal alterations induced by chronic restraint stress

Adult hippocampal neurogenesis is inhibited by chronic psychological stress and impaired neurogenesis underlies stress-related psychological disorders. We previously reported that chronic restraint stress (CRS) evokes autophagic death of adult hippocampal neural stem cells (NSCs) while NSC-specific deletion of Atg7 prevents death of NSCs. Examination of cognitive ability and mood regulation next day of the termination of stress showed normal hippocampal function in mice deficient of Atg7. However, it was not investigated whether the preservation of NSC pool alleviates hippocampal neuronal alterations. Here, we show that CRS increased c-Fos-positive, activated neurons in the granule cell layer and decreased spine density of CA3 neurons in the hippocampus, and these hippocampal neuronal deficits were prevented by NSC-specific deletion of Atg7. Of note, our observation was conducted right after the termination of CRS. Therefore, our results suggest that the detrimental effects of stress on hippocampal neurons can be buffered by NSCs independent of neurogenesis and NSCs are essential to the hippocampal function both through the neurogenesis-dependent developmental process and by direct regulation of neural activation.

Variations of Aberrant Volume, Activity, and Network Connectivity of Hippocampus in Adolescent Male Rats Exposed to Juvenile Stress

BACKGROUND

Childhood is a crucial period for brain development, and short-term juvenile stress has demonstrated long-lasting effects on cognitive and cellular functions in the hippocampus. However, the influence of such stress on the brain's overall network remains unclear.

METHODS

In this study, we employed functional magnetic resonance imaging (fMRI) to explore the effects of transient wild stress on juvenile male rats. Pregnant rats were purchased and housed in a specific pathogen-free (SPF) environment, with pups separated by sex on postnatal day 21 (PD21). From PD27 to PD29, male rats were subjected to transient wild stress, which included forced swimming, elevated platform exposure, and restraint stress. Following stress exposure, all animals were carefully maintained and scanned at 42 days of age (PD42) using fMRI. Structural analysis was performed using voxel-based morphometry (VBM) to assess changes in gray matter volume, while functional activity was evaluated through regional homogeneity (ReHo) and voxel-wise functional connectivity.

RESULTS

The results showed significant reductions in gray matter volume in several brain regions in the stress group, including the periaqueductal gray (PAG), entorhinal cortex (Ent), and dentate gyrus (DG). In terms of functional activity, cortical regions, particularly the primary somatosensory areas, exhibited decreased activity, whereas increased activity was observed in the PAG, DG, and medulla. Furthermore, functional connectivity analysis revealed a significant reduction in connectivity between the DG and entorhinal cortex, while the DG-PAG connectivity was significantly enhanced.

CONCLUSIONS

These findings suggest that juvenile stress leads to profound alterations in both brain structure and function, potentially disrupting emotional regulation and memory processing by affecting the development and connectivity of key brain regions.

Cannabidiol/cannabidiolic acid-rich hemp (Cannabis sativa L.) extract attenuates cognitive impairments and glial activations in rats exposed to chronic stress

ETHNOPHARMACOLOGICAL RELEVANCE

Hemp (Cannabis sativa L.) is increasingly being recognized for its medicinal properties beside utilizing it for food, oil, and textile fibers. The high level of cannabidiol (CBD) content in hemp's flowers shows promising neuroprotective properties without causing psychotomimetic or addictive effects. Recently, products containing CBD and its precursor, cannabidiolic acid (CBDA), have been used to treat stress-related cognitive impairment. However, the therapeutic potential of hemp extract remains inadequately explored.

AIM OF THE STUDY

To investigate the effect of CBD/CBDA-rich hemp extract on learning and memory, neuroendocrine alterations, and hippocampal neuropathological changes in the chronic restraint stress model.

MATERIALS AND METHODS

Chronic restraint stress (CRS) was induced in male Wistar rats by immobilizing them in a restrainer for 6 h per day for 21 consecutive days. CBD/CBDA-rich hemp extract (10 and 30 mg/kg, intraperitoneal injection) was administered daily, 1 h before restraint. After the last day of CRS, behavioral tests for cognition were conducted using the Y-maze and object recognition tests. Serum corticosterone (CORT) levels were measured by ELISA. Histopathological changes, neuronal density, and the activation of microglia and astrocytes were visualized using cresyl violet and immunohistochemical staining.

RESULTS

A high dose of CBD/CBDA-rich hemp extract effectively ameliorated CRS-induced cognitive impairment and reversed HPA axis hyperactivity in CRS rats by reducing CORT levels and adrenal gland weight. Additionally, CBD/CBDA-rich hemp extract protected CRS-induced damage to hippocampal neurons. Further analysis showed that CBD/CBDA-rich hemp extract reduced specific markers of microglial activation (ionized calcium-binding adaptor molecule-1, Iba-1) and astrocytic structural protein (glial fibrillary acidic protein, GFAP) in CRS rats.

CONCLUSION

CBD/CBDA-rich hemp extracts remarkably reversed the stress-induced behavioral perturbations and hippocampal damage, suggesting its ameliorative effect on stress response.

Hunger Games: A Modern Battle Between Stress and Appetite

Stress, an evolutionarily adaptive mechanism, has become a pervasive challenge in modern life, significantly impacting feeding-relevant circuits that play a role in the development and pathogenesis of eating disorders (EDs). Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, disrupts specific neural circuits, and dysregulates key brain regions, including the hypothalamus, hippocampus, and lateral septum. These particular structures are interconnected and key in integrating stress and feeding signals, modulating hunger, satiety, cognition, and emotional coping behaviors. Here we discuss the interplay between genetic predispositions and environmental factors that may exacerbate ED vulnerability. We also highlight the most commonly used animal models to study the mechanisms driving EDs and recent rodent studies that emphasize the discovery of novel cellular and molecular mechanisms integrating stress and feeding signals within the hippocampus-lateral septum-hypothalamus axis. In this review, we discuss the role of gut microbiome, an emerging area of research in the field of EDs and unanswered questions that persist and hinder the scientific progress, such as why some individuals remain resilient to stress while others become at high risk for the development of EDs. We finally discuss the need for future research delineating the impact of specific stressors on neural circuits, clarifying the relevance and functionality of hippocampal-septal-hypothalamic connectivity, and investigating the role of key neuropeptides such as CRH, oxytocin, and GLP-1 in human ED pathogenesis. Emerging tools like single-cell sequencing and advanced human imaging could uncover cellular and circuit-level changes in brain areas relevant for feeding in ED patients. Ultimately, by integrating basic and clinical research, science offers promising avenues for developing personalized, mechanism-based treatments targeting maladaptive eating behavior for patients suffering from EDs.

Caffeic acid differentially modulates behavior and neurochemicals in chronic unpredictable mild stress and dexamethasone induced models of depression

In the present study authors studied the effect of caffeic acid (CA) in chronic unpredictable mild stress (CUMS) and dexamethasone (DEXA) model of depression. CUMS (21 days) and DEXA (1.5 mg/kg × 21 days) was used for the induction of depression and anxiety related behavior. Locomotor activity was determined using actophotometer. Depression related behavior was determined using tail suspension test (TST) and forced swim test (FST) whereas for the determination of anxiety related behavior elevated plus maze (EPM) test was used. Following behavioral studies, mice were sacrificed by decapitation method. Hippocampus was dissected and was used for the neurochemical assays including 5-HT (serotonin), glutamate, nitrite and gamma-aminobutyric acid (GABA). The results obtained suggested that the CA (25-100 mg/kg, i.p.) did not affect the activity count in CUMS exposed and DEXA treated mice. CA (50 mg/kg) evoked anxiogenic reactions in CUMS model by increasing the hippocampal nitrite and glutamate level while CA (50 mg/kg) exerted anxiolysis in DEXA model by reducing the level of 5-HT. In CUMS model, CA exerted antidepressant like effect by increasing the hippocampal nitric oxide (NO) level, in DEXA model CA exerted antidepressant like effect by reducing the hippocampal glutamate level. CA failed to reverse DEXA mediated nNOS inhibition and therefore decreases hippocampal glutamate level to exert antidepressant like effect. Thus, CA modulate anxiety and depression related neurobehavioral alterations in both CUMS and DEXA models.

Tell me why: the missing w in episodic memory's what, where, and when

Endel Tulving defined episodic memory as consisting of a spatiotemporal context. It enables us to recollect personal experiences of people, things, places, and situations. In other words, it is made up of what, where, and when components. However, this definition does not include arguably the most important aspect of episodic memory: the why. Understanding why we remember has important implications to better understand how our memory system works and as a potential target of intervention for memory impairment. The intrinsic and extrinsic factors related to why some experiences are better remembered than others have been widely investigated but largely independently studied. How these factors interact with one another to drive an event to become a lasting memory is still unknown. This review summarizes research examining the why of episodic memory, where we aim to uncover the factors that drive core features of our memory. We discuss the concept of episodic memory examining the what, where, and when, and how the why is essential to each of these key components of episodic memory. Furthermore, we discuss the neural mechanisms known to support our rich episodic memories and how a why signal may provide critical modulatory impact on neural activity and communication. Finally, we discuss the individual differences that may further drive why we remember certain experiences over others. A better understanding of these elements, and how we experience memory in daily life, can elucidate why we remember what we remember, providing important insight into the overarching goal of our memory system.

The Role of Genetic, Environmental, and Dietary Factors in Alzheimer's Disease: A Narrative Review

Alzheimer's disease (AD) is one of the most common and severe forms of dementia and neurodegenerative disease. As life expectancy increases in line with developments in medicine, the elderly population is projected to increase in the next few decades; therefore, an increase in the prevalence of some diseases, such as AD, is also expected. As a result, until a radical treatment becomes available, AD is expected to be more frequently recorded as one of the top causes of death worldwide. Given the current lack of a cure for AD, and the only treatments available being ones that alleviate major symptoms, the identification of contributing factors that influence disease incidence is crucial. In this context, genetic and/or epigenetic factors, mainly environmental, disease-related, dietary, or combinations/interactions of these factors, are assessed. In this review, we conducted a literature search focusing on environmental factors such as air pollution, toxic elements, pesticides, and infectious agents, as well as dietary factors including various diets, vitamin D deficiency, social factors (e.g., tobacco and alcohol use), and variables that are affected by both environmental and genetic factors, such as dietary behavior and gut microbiota. We also evaluated studies on the beneficial effects of antibiotics and diets, such as the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) and Mediterranean diets.

Exposure to Ambient Temperature and Functional Connectivity of Brain Resting-State Networks in Preadolescents

OBJECTIVE

Exposure to extreme temperatures has been linked to acute mental health events in young populations, but the underlying neural mechanisms are not well understood. Resting-state functional magnetic resonance imaging allows for the assessment of connectivity patterns in brain functional networks, which have been associated with mental health disorders. This study investigated the short-term effects of ambient temperature on functional connectivity of brain resting-state networks in preadolescents.

METHOD

The study was embedded in the Generation R Study, Rotterdam, the Netherlands. Daily mean temperature estimates at the residential addresses of participants were obtained from a high-resolution urban climate model (UrbClim). Resting-state functional connectivity data were assessed with brain magnetic resonance images of 2,229 children ages 9 to 12 years. Distributed lag nonlinear models were fitted to assess the cumulative effects of temperature during the week before the brain scan on within- and between-network connectivity of 15 resting-state networks.

RESULTS

Higher ambient temperature during the week before the imaging assessment was associated with lower functional connectivity within the medial parietal, salience, and hippocampus networks. The effect was highest the day before the brain scan and progressively decayed in the preceding days. Lower temperatures were not related to functional connectivity.

CONCLUSION

Exposure to high ambient temperatures over a 7-day period was associated with lower within-network connectivity in preadolescents, suggesting impacts of heat on brain function. These findings raise new research questions on whether decreases in functional connectivity within the salience network may partially explain the association between high temperatures and suicide rates previously reported in the literature.

Deficiency of the palmitoyl acyltransferase ZDHHC7 modulates depression-like behaviour in female mice after a mild chronic stress paradigm

Chronic stress (CS) is a debilitating condition that negatively affects body and brain. In mice, CS effects range from changes in behaviour and brain microstructure down to the level of gene expression. These effects are partly mediated by sex and sex steroid hormones, which in turn are affected by the palmitoyl acyltransferase ZDHHC7. ZDHHC7 might modulate also the response to CS via palmitoylation of sex steroid hormone receptors and other proteins critical for neuronal structure and functions. Therefore, we aimed to investigate the role of ZDHHC7 in response to CS on different system levels in a mouse model of Zdhhc7-deficiency. Female and male Zdhhc7-knockout (KO) and -wildtype (WT) mice underwent a four-week-mild CS paradigm or non-stress control (C) condition. After C or CS, behaviours, hippocampal microstructures (via MRI-based diffusion tensor imaging) and brain gene expression profiles (via mRNA-seq transcriptomics) were investigated. Analyses focused on effects of genotype (KO vs. WT) or condition (C vs. CS) separately in both sexes. Our results revealed significant effects particularly in females. Female KOs displayed increased locomotion and reduced depression-like behaviour after CS (KO vs. WT, C vs. CS: pall < 0.05). Hippocampal fibres were reduced in female KOs after C (KO vs. WT: pall < 0.05) but in female WTs after CS (C vs. CS: pall < 0.05). Furthermore, female KOs showed increased cortistatin expression after CS (C vs. CS: mRNAseq and qPCR pall < 0.05). In sum, Zdhhc7-deficiency reduced depression-like behaviours, prevented hippocampal fibre reduction and upregulated cortistatin after CS. It seemed to be related to a sex-specific stress response and may reveal genetic factors of CS-resilience in female mice.

Bibliometric insights into astrocytic roles in depression and treatment

Objective

Depression is a mental disorder that significantly impairs both physical and mental health. Recent studies have shown that reactive astrogliosis have gained significant attention for their involvement in the pathophysiology of depression. However, there is no bibliometric analysis in this research field. This study aims to provide a comprehensive overview of the knowledge structure and research hotspots regarding the role of astrocytes in the mechanisms and treatment of depression through bibliometric analysis. The scope of the literature review encompasses both basic and clinical research.

Methods

Publications related to astrocytes in depression and treatment from 2014 to 2023 were searched in the Web of Science Core Collection (WoSCC) database. VOSviewer, CiteSpace, and the R package "bibliometrix" were used to conduct this bibliometric analysis.

Results

From 2014 to 2023, a total of 1,502 documents from 78 countries on astrocytes in depression and treatment were analyzed from 169 journals, with the most co-cited journals being the Journal of Neuroscience and PNAS. China Medical University was the most productive institution. The analysis identified key authors like Verkhratsky Alexei and Baoman Li, and major co-cited references by Rajkowska and Liddelow. Keywords such as "synaptic plasticity," "astrocytes," and "neuroinflammation" revealed research trends focusing on molecular mechanisms, gut microbiota, and inflammation.

Conclusion

This is the first bibliometric study to comprehensively summarize the research trends and advancements regarding astrocytes in depression and its treatment. Through this bibliometric analysis, we aim to enhance the understanding of the significance of astrocytes in depression research and provide new perspectives and insights for future investigations. We hope that this study will facilitate a broader integration of basic and clinical research, offering novel approaches for the treatment of depression.

Sex in aging matters: exercise and chronic stress differentially impact females and males across the lifespan

Assessing sex as a biological variable is critical to determining the influence of environmental and lifestyle risks and protective factors mediating behavior and neuroplasticity across the lifespan. We investigated sex differences in affective behavior, memory, and hippocampal neurogenesis following short- or long-term exposure to exercise or chronic mild stress in young and aged mice. Male and female mice were assigned control, running, or chronic stress rearing conditions for 1 month (young) or for 15 months (aged), then underwent a behavioral test battery to assess activity, affective behavior, and memory. Stress exposure into late-adulthood increased hyperactivity in both sexes, and enhanced anxiety-like and depressive-like behavior in aged female, but not male, mice. One month of stress or running had no differential effects on behavior in young males and females. Running increased survival of BrdU-labelled hippocampal cells in both young and aged mice, and enhanced spatial memory in aged mice. These findings highlight the importance of considering sex when determining how aging is differently impacted by modifiable lifestyle factors across the lifespan.

The Potential Role of Dopamine Pathways in the Pathophysiology of Depression: Current Advances and Future Aspects

Depression is a serious mental health disorder that impacts more than 350 million individuals globally. While the roles of serotonin and norepinephrine in depression have been extensively studied, the importance of dopaminergic pathways-essential for mood, cognition, motor control, and endocrine function-often gets overlooked. This review focuses on four major dopamine (DA) circuits: the mesolimbic (MLP), mesocortical (MCP), nigrostriatal (NSP), and thalamictuberoinfundibular pathways (TTFP), and their roles in depression. The MLP, which is key to reward processing, is linked to anhedonia, a primary depression symptom. The MCP, projecting to the prefrontal cortex, affects cognitive issues like impaired attention and decision-making. The NSP, mainly responsible for motor control, is related to psychomotor retardation in depression, while the TTFP manages neuroendocrine responses, which are often disrupted in stress-related depressive conditions. Current antidepressant treatments mainly target serotonin and norepinephrine systems but tend to be less effective for patients with DArgic dysfunction, leading to treatment resistance. This review underscores emerging evidence that suggests targeting DArgic pathways could improve treatment outcomes, especially for symptoms like anhedonia and cognitive deficits that conventional therapies often fail to address. Future research should aim to combine advancements in neuroimaging, optogenetics, and genetic studies to better map DArgic pathways and create personalized treatment plans. This review highlights the potential for new therapies that focus on DA systems, which could pave the way for more effective and tailored approaches to treating depression.

The Aggravating Role of Failing Neuropeptide Networks in the Development of Sporadic Alzheimer's Disease

Alzheimer's disease imposes an increasing burden on aging Western societies. The disorder most frequently appears in its sporadic form, which can be caused by environmental and polygenic factors or monogenic conditions of incomplete penetrance. According to the authors, in the majority of cases, Alzheimer's disease represents an aggravated form of the natural aging of the central nervous system. It can be characterized by the decreased elimination of amyloid β1-42 and the concomitant accumulation of degradation-resistant amyloid plaques. In the present paper, the dysfunction of neuropeptide regulators, which contributes to the pathophysiologic acceleration of senile dementia, is reviewed. However, in the present review, exclusively those neuropeptides or neuropeptide families are scrutinized, and the authors' investigations into their physiologic and pathophysiologic activities have made significant contributions to the literature. Therefore, the pathophysiologic role of orexins, neuromedins, RFamides, corticotrope-releasing hormone family, growth hormone-releasing hormone, gonadotropin-releasing hormone, ghrelin, apelin, and natriuretic peptides are discussed in detail. Finally, the therapeutic potential of neuropeptide antagonists and agonists in the inhibition of disease progression is discussed here.

Complex emotion processing and early life adversity in the Healthy Brain Network sample

OBJECTIVE

Early life adversity (ELA) has shown to have negative impacts on mental health. One possible mechanism is through alterations in neural emotion processing. We sought to characterize how multiple indices of ELA were related to naturalistic neural socio-emotional processing.

METHOD

In 521 5-15-year-old participants from the Healthy Brain Network Biobank, we identified scenes that elicited activation of the Default Mode Network (DMN), Ventral Attention Network (VAN), Cingulo-Opercular Network (CON) and amygdala, all of which are networks shown to be associated with ELA. We used linear regression to examine associations between activation and ELA: negative parenting, social status, financial insecurity, neighborhood disadvantage, negative experiences, and parent psychopathology.

RESULTS

We found DMN, VAN, CON and amygdala activation during sad/emotional, bonding, action, conflict, sad, or fearful scenes. Greater inconsistent discipline was associated with greater VAN activation during sad or emotional scenes.

CONCLUSION

Findings suggest that the DMN, VAN, CON networks and the amygdala support socio-emotional processing consistent with prior literature. Individuals who experienced inconsistent discipline may have greater sensitivity to parent-child separation signals. Since no other ELA-activation associations were found, it is possible that unpredictability may be more strongly associated with complex neural emotion processing than socio-economic status or negative life events.

Pretreatment with 4-methylumbilliferon improves anxiety-like behaviors and memory impairment in stressed rats via modulation of neuronal cell death and oxidative stress

This work was done to investigate the ameliorating impact of 4-methylumbilliferon (4-MU) on spatial learning and memory dysfunction and restraint stress (STR)-induced anxiety-like behaviors in male Wistar rats and the underlying mechanisms. Thirty-two animals were assigned into 4 cohorts: control, 4-MU, STR, and STR+4-MU. Animals were exposed to STR for 4 h per day for 14 consecutive days or kept in normal conditions (healthy animals without exposure to stress). 4-MU (25 mg/kg) was intraperitoneally administered once daily to STR rats before restraint stress for 14 consecutive days. The behavioral tests were performed through Morris water maze tests and elevated-plus maze to examine learning/memory function, and anxiety levels, respectively. The levels of the antioxidant defense biomarkers (GPX, SOD) and MDA as an oxidant molecule in the brain tissues were measured using commercial ELISA kits. Neuronal loss or density of neurons was evaluated using Nissl staining. STR exposure could cause significant alterations in the levels of the antioxidant defense biomarkers (MDA, GPX, and SOD) in the prefrontal cortex and hippocampus, induce anxiety, and impair spatial learning and memory function. Treatment with 4-MU markedly reduced anxiety levels and improved spatial learning and memory dysfunction via restoring the antioxidant defense biomarkers to normal values and reducing MDA levels. Moreover, more intact cells with normal morphologies were detected in STR-induced animals treated with 4-MU. 4-MU could attenuate the STR-induced anxiety-like behaviors and spatial learning and memory dysfunction by reducing oxidative damage and neuronal loss in the prefrontal cortex and hippocampus region. Taken together, our findings provide new insights regarding the potential therapeutic effects of 4-MU against neurobehavioral disorders induced by STR.

Melatonin ameliorates chronic sleep deprivation against memory encoding vulnerability: Involvement of synapse regulation via the mitochondrial-dependent redox homeostasis-induced autophagy inhibition

Voluntary sleep curtailment is increasingly more rampant in modern society and compromises healthy cognition, including memory, to varying degrees. However, whether memory encoding is impaired after chronic sleep deprivation (CSD) and the underlying molecular mechanisms involved remain unclear. Here, using the mice, we tested the impact of CSD on the encoding abilities of social recognition-dependent memory and object recognition-dependent memory. We found that memory encoding was indeed vulnerable to CSD, while memory retrieval remained unaffected. The hippocampal neurons of mice with memory encoding deficits exhibited significant synapse damage and hyperactive autophagy, which dissipates during regular sleep cycles. This excessive autophagy appeared to be triggered by damage to mitochondrial DNA (mtDNA), resulting from oxidative stress within the mitochondria. The relief at the behavioral and molecular biological levels can be achieved with intraperitoneal injections of the antioxidant compound melatonin. Moreover, our in vitro experiments using HT-22 cells demonstrated that oxidative stress induced by hydrogen peroxide led to oxidative damage, including mtDNA damage, and activation of autophagy. Melatonin treatment effectively countered these effects, restoring redox homeostasis and reducing excessive autophagic activity. Notably, this protective effect was not observed when melatonin was administered as a pre-treatment. Together, our findings reveal the vulnerability of memory encoding during chronic sleep curtailment, which is caused by oxidative stress and consequent enhancement of autophagy, suggest a potential therapeutic strategy for addressing these effects following prolonged wakefulness through melatonin intervention, and reiterate the significance of adequate sleep for memory formation and retention.

Genetic patterning in hippocampus of rat undergoing impaired spatial memory induced by long-term heat stress

The organism's normal physiological function is greatly impacted in a febrile environment, leading to the manifestation of pathological conditions including elevated body temperature, dehydration, gastric bleeding, and spermatogenic dysfunction. Numerous lines of evidence indicate that heat stress significantly impacts the brain's structure and function. Previous studies have demonstrated that both animals and humans experience cognitive impairment as a result of exposure to high temperatures. However, there is a lack of research on the effects of prolonged exposure to high-temperature environments on learning and memory function, as well as the underlying molecular regulatory mechanisms. In this study, we examined the impact of long-term heat stress exposure on spatial memory function in rats and conducted transcriptome sequencing analysis of rat hippocampal tissues to identify the crucial molecular targets affected by prolonged heat stress exposure. It was found that the long-term heat stress impaired rats' spatial memory function due to the pathological damages and apoptosis of hippocampal neurons at the CA3 region, which is accompanied with the decrease of growth hormone level in peripheral blood. RNA sequencing analysis revealed the signaling pathways related to positive regulation of external stimulation response and innate immune response were dramatically affected by heat stress. Among the verified differentially expressed genes, the knockdown of Arhgap36 in neuronal cell line HT22 significantly enhances the cell apoptosis, suggesting the impaired spatial memory induced by long-term heat stress may at least partially be mediated by the dysregulation of Arhgap36 in hippocampal neurons. The uncovered relationship between molecular changes in the hippocampus and behavioral alterations induced by long-term heat stress may offer valuable insights for the development of therapeutic targets and protective drugs to enhance memory function in heat-exposed individuals.

Higher intensity exercise after encoding is more conducive to episodic memory retention than lower intensity exercise: A field study in endurance runners

An acute bout of exercise in the moments after learning benefits the retention of new memories. This finding can be explained, at least partly, through a consolidation account: exercise provides a physiological state that is conducive to the early stabilisation of labile new memories, which supports their retention and subsequent retrieval. The modification of consolidation through non-invasive exercise interventions offers great applied potential. However, it remains poorly understood whether effects of exercise translate from the laboratory to naturalistic settings and whether the intensity of exercise determines the effect in memory. To this end, adult endurance runners were recruited as participants and completed two study sessions spaced two weeks apart. In each session, participants were presented with a list of words and asked to recall them on three occasions: (i) immediately following their presentation, (ii) after a 30-minute retention interval, and (iii) after 24 hours. Crucially, the 30-minute retention interval comprised our experimental manipulation: higher intensity exercise (running) in the first session and lower intensity exercise (walking) in the second, both completed in a naturalistic setting around participants' existing physical activity training programmes. Exertion was recorded through heart rate and rate of perceived exertion data. Alertness, mood, and arousal ratings were also collected before and after the 30-minute retention interval. Immediate memory for the two wordlists was matched, but participants retained significantly more words after 30 minutes and 24 hours when encoding was followed by higher than lower intensity exercise. Exertion data revealed that participants experienced vigorous and light exercise in the higher and lower intensity conditions, respectively. Significant improvements in alertness, mood, and arousal were observed following both exercise conditions, but especially in the higher intensity condition. These outcomes reveal that experiencing higher intensity physical activity in the field is conducive to declarative memory retention, possibly because it encourages consolidation.

Influence of stress-specific interventions on biomarker levels and cognitive function in cancer patients: Systematic review and meta-analysis

PURPOSE

Cancer patients' psycho-physiological health is seriously affected by long-term exposure to stress. Many studies have explored the impact of stress-specific interventions on cancer patients' biomarker levels and cognitive functions. However, the current research findings are inconsistent, and their statistical power is limited by the small samples. Therefore, we conducted this meta-analysis to verify the effect of stress-specific interventions on cancer patients.

METHODS

The literature involved nine databases from the inception until January 13, 2024, extracted 19 randomized controlled trials (RCTs). Review Manager (RevMan) 5.4 software was used to perform a meta-analysis, and the revised Cochrane risk of bias tool (RoB2) was utilized for quality evaluation.

RESULTS

Nine RCTs were assessed as having a low risk of bias, and others had a moderate risk. The results showed that stress-specific interventions had beneficial effects on patients' subjective cognition but uncertain impacts on their executive function, tumour necrosis factor-α level, morning cortisol level, and no effect on cortisol at other times, interleukin (IL)-10, IL-8, IL-6, IL-1, and C-reactive protein.

CONCLUSION

More rigorous studies are required to elucidate the influence of stress-specific interventions on biomarker levels. The potential mechanism by which stress-specific interventions affect the cancer patient's cognitive function remains unclear.

Genetic and environmental influences on structural brain development from childhood to adolescence: A longitudinal twin study on cortical thickness, surface area, and subcortical volume

The human brain undergoes structural development from childhood to adolescence, with specific regions in the sensorimotor, social, and affective networks continuing to grow into adulthood. While genetic and environmental factors contribute to individual differences in these brain trajectories, the extent remains understudied. Our longitudinal study, utilizing up to three biennial MRI scans (n=485), aimed to assess the genetic and environmental effects on brain structure (age 7) and development (ages 7-14) in these regions. Heritability estimates varied across brain regions, with all regions showing genetic influence (ranging from 18 % to 59 %) with additional shared environmental factors affecting the primary motor cortex (30 %), somatosensory cortex (35 %), DLPFC (5 %), TPJ (17 %), STS (17 %), precuneus (10 %), hippocampus (22 %), amygdala (5 %), and nucleus accumbens (10 %). Surface area was more genetically driven (38 %) than cortical thickness (14 %). Longitudinal brain changes were primarily driven by genetics (ranging from 1 % to 29 %), though shared environment factors (additionally) influenced the somatosensory cortex (11 %), DLPFC (7 %), cerebellum (28 %), TPJ (16 %), STS (20 %), and hippocampus (17 %). These findings highlight the importance of further investigating brain-behavior associations and the influence of enriched and deprived environments from childhood to adolescence. Ultimately, our study can provide insights for interventions aimed at supporting children's development.

Effects of Aerobic Exercise on Executive and Memory Functions in Patients With Alzheimer's Disease: A Systematic Review

BACKGROUND

Alzheimer's disease threatens the health of older adults, particularly by disrupting executive and memory functions, and many studies have shown that aerobic exercise prevents and improves the symptoms associated with the disease.

OBJECTIVE

The objective was to systematically review the effects of aerobic exercise on executive and memory functions in patients with Alzheimer's disease and to determine the effect factors and mechanisms of the design of aerobic exercise intervention programs.

METHOD

Relevant literature was searched in three databases (PubMed, Web of Science, and EBSCO) from January 1, 2014 to March 1, 2023, using a subject-word search method. Data on 10 items, including author and country, were extracted from the literature after screening. The quality of the literature was evaluated using the Physiotherapy Evidence Database scale, and a systematic review was performed.

RESULTS

Twelve papers from seven countries were ultimately included, embodying 11 randomized controlled trials and one study with a repeated-measures design. The overall quality of the studies was good as 657 study participants, aged 45 years and older who had varying degrees of Alzheimer's disease and significant symptoms, were included. Aerobic exercise was found to have a significant positive impact on executive and memory functions in people with Alzheimer's disease.

CONCLUSION

The effects of aerobic exercise on aspects of executive function were mainly characterized by improvements in inhibitory control, working memory, and cognitive flexibility, whereas the effects on aspects of memory function were mainly characterized by improvements in logical memory, situational memory, and short-term memory.

Longitudinal study on hippocampal subfields and glucose metabolism in early psychosis

Altered hippocampal morphology and metabolic pathology, but also hippocampal circuit dysfunction, are established phenomena seen in psychotic disorders. Thus, we tested whether hippocampal subfield volume deficits link with deviations in glucose metabolism commonly seen in early psychosis, and whether the glucose parameters or subfield volumes change during follow-up period using one-year longitudinal study design of 78 first-episode psychosis patients (FEP), 48 clinical high-risk patients (CHR) and 83 controls (CTR). We also tested whether hippocampal morphology and glucose metabolism relate to clinical outcome. Hippocampus subfields were segmented with Freesurfer from 3T MRI images and parameters of glucose metabolism were determined in fasting plasma samples. Hippocampal subfield volumes were consistently lower in FEPs, and findings were more robust in non-affective psychoses, with strongest decreases in CA1, molecular layer and hippocampal tail, and in hippocampal tail of CHRs, compared to CTRs. These morphometric differences remained stable at one-year follow-up. Both non-diabetic CHRs and FEPs had worse glucose parameters compared to CTRs at baseline. We found that, insulin levels and insulin resistance increased during the follow-up period only in CHR, effect being largest in the CHRs converting to psychosis, independent of exposure to antipsychotics. The worsening of insulin resistance was associated with deterioration of function and symptoms in CHR. The smaller volume of hippocampal tail was associated with higher plasma insulin and insulin resistance in FEPs, at the one-year follow-up. Our longitudinal study supports the view that temporospatial hippocampal subfield volume deficits are stable near the onset of first psychosis, being more robust in non-affective psychoses, but less prominent in the CHR group. Specific subfield defects were related to worsening glucose metabolism during the progression of psychosis, suggesting that hippocampus is part of the circuits regulating aberrant glucose metabolism in early psychosis. Worsening of glucose metabolism in CHR group was associated with worse clinical outcome measures indicating a need for heightened clinical attention to metabolic problems already in CHR.

Apocynin Prevents Cigarette Smoke-Induced Anxiety-Like Behavior and Preserves Microglial Profiles in Male Mice

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death globally and is primarily caused by cigarette smoking (CS). Neurocognitive comorbidities such as anxiety and cognitive impairments are common among people with COPD. CS-induced lung inflammation and oxidative stress may "spill-over" into the systemic circulation, driving the onset of these comorbidities. We investigated whether a prophylactic treatment with the NADPH Oxidase 2 (NOX2) inhibitor, apocynin, could prevent CS-induced neurocognitive impairments. Adult male BALB/c mice were exposed to CS (9 cigarettes/day, 5 days/week) or room air (sham) for 8 weeks with co-administration of apocynin (5 mg/kg, intraperitoneal injection once daily) or vehicle (0.01% DMSO in saline). Following 7 weeks of CS exposure, mice underwent behavioral testing to assess recognition and spatial memory (novel object recognition and Y maze, respectively) and anxiety-like behaviors (open field and elevated plus maze). Mice were then euthanized, and blood, lungs, and brains were collected. Apocynin partially improved CS-induced lung neutrophilia and reversed systemic inflammation (C-reactive protein) and oxidative stress (malondialdehyde). Apocynin exerted an anxiolytic effect in CS-exposed mice, which was associated with restored microglial profiles within the amygdala and hippocampus. Thus, targeting oxidative stress using apocynin can alleviate anxiety-like behaviors and could represent a novel strategy for managing COPD-related anxiety disorders.

In vivo structural connectivity of the reward system along the hippocampal long axis

Recent work has identified a critical role for the hippocampus in reward-sensitive behaviors, including motivated memory, reinforcement learning, and decision-making. Animal histology and human functional neuroimaging have shown that brain regions involved in reward processing and motivation are more interconnected with the ventral/anterior hippocampus. However, direct evidence examining gradients of structural connectivity between reward regions and the hippocampus in humans is lacking. The present study used diffusion MRI (dMRI) and probabilistic tractography to quantify the structural connectivity of the hippocampus with key reward processing regions in vivo. Using a large sample of subjects (N = 628) from the human connectome dMRI data release, we found that connectivity profiles with the hippocampus varied widely between different regions of the reward circuit. While the dopaminergic midbrain (ventral tegmental area) showed stronger connectivity with the anterior versus posterior hippocampus, the ventromedial prefrontal cortex showed stronger connectivity with the posterior hippocampus. The limbic (ventral) striatum demonstrated a more homogeneous connectivity profile along the hippocampal long axis. This is the first study to generate a probabilistic atlas of the hippocampal structural connectivity with reward-related networks, which is essential to investigating how these circuits contribute to normative adaptive behavior and maladaptive behaviors in psychiatric illness. These findings describe nuanced structural connectivity that sets the foundation to better understand how the hippocampus influences reward-guided behavior in humans.

Breathing life into social emotional learning programs: A Bio-Psycho-Social approach to risk reduction and positive youth development

INTRODUCTION

Over one-third of US adolescents engage in health risk and problem behaviors. Additionally, significant percentages of problem-free youth aren't flourishing. Left unaddressed, the lifetime mental/physical health and financial burdens may be substantial. Social-Emotional Learning (SEL) and Positive Youth Development (PYD) programs have proliferated to address the drivers of adaptive versus risk behaviors. Research suggests SEL/PYD program outcomes can be improved by adding techniques that physiologically induce calmness, yet few studies exist.

METHODS

This randomized controlled trial of 79 urban eighth-graders examined a standardized bio-psycho-social program, SKY Schools, which incorporates a physiologically calming component: controlled yogic breathing.

RESULTS

Repeated-measures ANOVAs demonstrated that compared to controls, SKY graduates exhibited significant improvements in emotion regulation, planning and concentration, and distractibility. After 3 months, significant improvements were evidenced in emotion regulation, planning and concentration, identity formation, and aggressive normative beliefs.

CONCLUSION

SEL/PYD programs may benefit by incorporating biologically-calming techniques to enhance well-being and prevent risk/problem behaviors.

Acute Stress Effects on Statistical Learning and Episodic Memory

Stress is widely considered to negatively impact hippocampal function, thus impairing episodic memory. However, the hippocampus is not merely the seat of episodic memory. Rather, it also (via distinct circuitry) supports statistical learning. On the basis of rodent work suggesting that stress may impair the hippocampal pathway involved in episodic memory while sparing or enhancing the pathway involved in statistical learning, we developed a behavioral experiment to investigate the effects of acute stress on both episodic memory and statistical learning in humans. Participants were randomly assigned to one of three conditions: stress (socially evaluated cold pressor) immediately before learning, stress ∼15 min before learning, or no stress. In the learning task, participants viewed a series of trial-unique scenes (allowing for episodic encoding of each image) in which certain scene categories reliably followed one another (allowing for statistical learning of associations between paired categories). Memory was assessed 24 hr later to isolate stress effects on encoding/learning rather than retrieval. We found modest support for our hypothesis that acute stress can amplify statistical learning: Only participants stressed ∼15 min in advance exhibited reliable evidence of learning across multiple measures. Furthermore, stress-induced cortisol levels predicted statistical learning retention 24 hr later. In contrast, episodic memory did not differ by stress condition, although we did find preliminary evidence that acute stress promoted memory for statistically predictable information and attenuated competition between statistical and episodic encoding. Together, these findings provide initial insights into how stress may differentially modulate learning processes within the hippocampus.

Central Sensitization-Related Symptoms and Influencing Factors on Health-Related Quality of Life among Frail Older Adults in Senior Day Care Centers: A Cross-Sectional Study

The recent increase in the number of frail older adults has led to increased attention being paid to care services in communities such as senior day care centers. Maintaining health-related quality of life (HRQOL) in frail older adults is important for managing long-term care. The purpose of this study was to comprehensively explore the impact of physical, mental, and cognitive factors, particularly central sensitization-related symptoms (CSSs), on the HRQOL among frail older adults in senior day care centers. HRQOL, physical, mental, and cognitive factors, and severity of CSSs were comprehensively measured using validated methods. Correlation and multiple regression analyses were used to examine factors affecting HRQOL among frail older adults in senior day care centers. The results showed that the timed up and go test significantly affected the HRQOL among frail older adults at senior day care centers. Additionally, knee extension muscle strength, number of pain sites, depressive tendencies, and CSS severity showed a significant negative correlation with HRQOL but were not significant influencing factors. This suggests that functional mobility assessments and approaches are important for maintaining and improving the HRQOL in frail older adults at senior day care centers.

Divergent effects of sex on hippocampal subfield alterations in drug-naive patients with major depressive disorder

BACKGROUND

The hippocampus is a crucial brain structure in etiological models of major depressive disorder (MDD). It remains unclear whether sex differences in the incidence and symptoms of MDD are related to differential illness-associated brain alterations, including alterations in the hippocampus. This study investigated divergent the effects of sex on hippocampal subfield alterations in drug-naive patients with MDD.

METHODS

High-resolution structural MR images were obtained from 144 drug-naive individuals with MDD early in their illness course and 135 age- and sex-matched healthy controls (HCs). Hippocampal subfields were segmented using FreeSurfer software and analyzed in terms of both histological subfields (CA1-4, dentate gyrus, etc.) and more integrative larger functional subregions (head, body and tail).

RESULTS

We observed a significant overall reduction in hippocampal volume in MDD patients, with deficits more prominent deficits in the posterior hippocampus. Differences in anatomic alterations between male and female patients were observed in the CA1-head, presubiculum-body and fimbria in the left hemisphere. Exploratory analyses revealed different patterns of clinical and memory function correlations with histological subfields and functional subregions between male and female patients primarily in the hippocampal head and body.

LIMITATIONS

This cross-sectional study cannot clarify the causality of hippocampal alterations or their association with illness risk or onset.

CONCLUSIONS

These findings represent the first reported sex-specific alterations in hippocampal histological subfields in patients with MDD early in the illness course prior to treatment. Sex-specific hippocampal alterations may contribute to diverse sex differences in the clinical presentation of MDD.

Hippocampus diffusivity abnormalities in classical trigeminal neuralgia

Introduction

Patients with chronic pain frequently report cognitive symptoms that affect memory and attention, which are functions attributed to the hippocampus. Trigeminal neuralgia (TN) is a chronic neuropathic pain disorder characterized by paroxysmal attacks of unilateral orofacial pain. Given the stereotypical nature of TN pain and lack of negative symptoms including sensory loss, TN provides a unique model to investigate the hippocampal implications of chronic pain. Recent evidence demonstrated that TN is associated with macrostructural hippocampal abnormalities indicated by reduced subfield volumes; however, there is a paucity in our understanding of hippocampal microstructural abnormalities associated with TN.

Objectives

To explore diffusivity metrics within the hippocampus, along with its functional and structural subfields, in patients with TN.

Methods

To examine hippocampal microstructure, we utilized diffusion tensor imaging in 31 patients with TN and 21 controls. T1-weighted magnetic resonance images were segmented into hippocampal subfields and registered into diffusion-weighted imaging space. Fractional anisotropy (FA) and mean diffusivity were extracted for hippocampal subfields and longitudinal axis segmentations.

Results

Patients with TN demonstrated reduced FA in bilateral whole hippocampi and hippocampal body and contralateral subregions CA2/3 and CA4, indicating microstructural hippocampal abnormalities. Notably, patients with TN showed significant correlation between age and hippocampal FA, while controls did not exhibit this correlation. These effects were driven chiefly by female patients with TN.

Conclusion

This study demonstrates that TN is associated with microstructural hippocampal abnormalities, which may precede and potentially be temporally linked to volumetric hippocampal alterations demonstrated previously. These findings provide further evidence for the role of the hippocampus in chronic pain and suggest the potential for targeted interventions to mitigate cognitive symptoms in patients with chronic pain.

Visual EMDR stimulation mitigates acute varied stress effects on morphology of hippocampal neurons in male Wistar rats

Introduction

Stress is a pervasive health concern known to induce physiological changes, particularly impacting the vulnerable hippocampus and the morphological integrity of its main residing cells, the hippocampal neurons. Eye Movement Desensitization and Reprocessing (EMDR), initially developed to alleviate emotional distress, has emerged as a potential therapeutic/preventive intervention for other stress-related disorders. This study aimed to investigate the impact of Acute Variable Stress (AVS) on hippocampal neurons and the potential protective effects of EMDR.

Methods

Rats were exposed to diverse stressors for 7 days, followed by dendritic morphology assessment of hippocampal neurons using Golgi-Cox staining.

Results

AVS resulted in significant dendritic atrophy, evidenced by reduced dendritic branches and length. In contrast, rats receiving EMDR treatment alongside stress exposure exhibited preserved dendritic morphology comparable to controls, suggesting EMDR's protective role against stressinduced dendritic remodeling.

Conclusions

These findings highlight the potential of EMDR as a neuroprotective intervention in mitigating stress-related hippocampal alterations.

Post-retrieval stress impairs subsequent memory depending on hippocampal memory trace reinstatement during reactivation

Upon retrieval, memories can become susceptible to meaningful events, such as stress. Post-retrieval memory changes may be attributed to an alteration of the original memory trace during reactivation-dependent reconsolidation or, alternatively, to the modification of retrieval-related memory traces that impact future remembering. Hence, how post-retrieval memory changes emerge in the human brain is unknown. In a 3-day functional magnetic resonance imaging study, we show that post-retrieval stress impairs subsequent memory depending on the strength of neural reinstatement of the original memory trace during reactivation, driven by the hippocampus and its cross-talk with neocortical representation areas. Comparison of neural patterns during immediate and final memory testing further revealed that successful retrieval was linked to pattern-dissimilarity in controls, suggesting the use of a different trace, whereas stressed participants relied on the original memory representation. These representation changes were again dependent on neocortical reinstatement during reactivation. Our findings show disruptive stress effects on the consolidation of retrieval-related memory traces that support future remembering.

Integrating and fragmenting memories under stress and alcohol

Stress can powerfully influence the way we form memories, particularly the extent to which they are integrated or situated within an underlying spatiotemporal and broader knowledge architecture. These different representations in turn have significant consequences for the way we use these memories to guide later behavior. Puzzlingly, although stress has historically been argued to promote fragmentation, leading to disjoint memory representations, more recent work suggests that stress can also facilitate memory binding and integration. Understanding the circumstances under which stress fosters integration will be key to resolving this discrepancy and unpacking the mechanisms by which stress can shape later behavior. Here, we examine memory integration at multiple levels: linking together the content of an individual experience, threading associations between related but distinct events, and binding an experience into a pre-existing schema or sense of causal structure. We discuss neural and cognitive mechanisms underlying each form of integration as well as findings regarding how stress, aversive learning, and negative affect can modulate each. In this analysis, we uncover that stress can indeed promote each level of integration. We also show how memory integration may apply to understanding effects of alcohol, highlighting extant clinical and preclinical findings and opportunities for further investigation. Finally, we consider the implications of integration and fragmentation for later memory-guided behavior, and the importance of understanding which type of memory representation is potentiated in order to design appropriate interventions.

Neuronal plasticity in hippocampal neurons due to chronic mild stress and after stress removal in postnatal chicks

The avian dorsomedial surface of the cerebral hemisphere is occupied by the hippocampal complex (HCC), which plays an important role in learning, memory, cognitive functions, and regulating instinctive behavior patterns. The objective of the study was to evaluate the effect of chronic mild stress (CMS) in 4, 6, and 8 weeks and after chronic stress removal (CSR) in 6 and 8 weeks, on neuronal plasticity in HCC neurons of chicks through the Golgi-Cox technique. Further, behavioral study and open field test were conducted to test of exploration or of anxiety. The study revealed that the length of CMS and CSR groups shows a similar pattern as in nonstressed (NS) chicks, while weight shows nonsignificant decrease due to CMS as compared to NS and after CSR. The behavioral test depicts that the CMS group took more time to reach the food as compared to the NS and CSR groups. Due to CMS, the dendritic field of multipolar neurons shows significant decrease in 4 weeks, but in 6- and 8-week-old chicks, the multipolar, pyramidal, and stellate neurons depict significant decrease, whereas after CSR all neurons show significant increase in 8-week-old chicks. In 4- and 8-week-old chicks, all neurons depict significant decrease in their spine number, whereas in 6 weeks only multipolar neurons show significant decrease, but after CSR significant increase in 8-week-old chicks was observed. The study revealed that HCC shows continuous neuronal plasticity, which plays a significant role in normalizing and re-establishing the homeostasis in animals to survive.

The firestorm within: A narrative review of extreme heat and wildfire smoke effects on brain health

Climate change is generating increased heatwaves and wildfires across much of the world. With these escalating environmental changes comes greater impacts on human health leading to increased numbers of people suffering from heat- and wildfire smoke-associated respiratory and cardiovascular impairment. One area of health impact of climate change that has received far less attention is the effects of extreme heat and wildfire smoke exposure on human brain health. As elevated temperatures, and wildfire-associated smoke, are increasingly experienced simultaneously over summer periods, understanding this combined impact is critical to management of human health especially in the elderly, and people with dementia, and other neurological disorders. Both extreme heat and wildfire smoke air pollution (especially particulate matter, PM) induce neuroinflammatory and cerebrovascular effects, oxidative stress, and cognitive impairment, however the combined effect of these impacts are not well understood. In this narrative review, a comprehensive examination of extreme heat and wildfire smoke impact on human brain health is presented, with a focus on how these factors contribute to cognitive impairment, and dementia, one of the leading health issues today. Also discussed is the potential impact of combined heat and wildfire smoke on brain health, and where future efforts should be applied to help advance knowledge in this rapidly growing and critical field of health research.

Effects of chronic social equality and inequality conditions on passive avoidance memory and PTSD-like behaviors in rats under chronic empathic stress

INTRODUCTION

Social inequality conditions induce aversion and affect brain functions and mood. This study investigated the effects of chronic social equality and inequality (CSE and CSI, respectively) conditions on passive avoidance memory and post-traumatic stress disorder (PTSD)-like behaviors in rats under chronic empathic stress.

METHODS

Rats were divided into different groups, including control, sham-observer, sham-demonstrator, observer, demonstrator, and co-demonstrator groups. Chronic stress (2 h/day) was administered to all stressed groups for 21 days. Fear learning, fear memory, memory consolidation, locomotor activity, and PTSD-like behaviors were evaluated using the passive avoidance test. Apart from the hippocampal weight, the correlations of memory and right hippocampal weight with serum corticosterone (CORT) levels were separately assessed for all experimental groups.

RESULTS

Latency was significantly higher in the demonstrator and sham-demonstrator groups compared to the control group. It was decreased significantly in other groups compared to the control group. Latency was also decreased in the observer and co-demonstrator groups compared to the demonstrator group. Moreover, the right hippocampal weight was significantly decreased in the demonstrator and sham-demonstrator groups compared to the control group. Pearson's correlation of memory and hippocampal weight with serum CORT levels supported the present findings.

CONCLUSION

Maladaptive fear responses occurred in demonstrators and sham-demonstrators. Also, extremely high levels of psychological stress, especially under CSI conditions (causing abnormal fear learning) led to heightened fear memory and PTSD-like behaviors. Right hippocampal atrophy confirmed the potential role of CSI conditions in promoting PTSD-like behaviors. Compared to inequality conditions, the abnormal fear memory was reduced under equality conditions.

The Influence of Noise Level on the Stress Response of Hospitalized Cats

The study aimed to investigate the impact of noise levels in the hospital environment on the stress experienced by hospitalized cats undergoing elective ovariohysterectomy surgery. A total of 33 domestic female cats were included in the study, divided into four groups: a control group (CG) and three experimental groups based on ward noise levels: G1 (Quiet, <60 dB), G2 (Medium, between 60 and 85 dB), and G3 (Noisy, >85 dB). Behavioral assessments, respiratory rate (RR), and plasma cortisol levels ([Cort]p) were measured as indicators of stress. A composite measure of stress, termed the final stress value (FSV), was calculated by summing scores across various behavioral categories. Data collection occurred at three time points: immediately following surgery (T1), and at 2 h (T2) and 3 h (T3) post-surgery. FSV and RR were assessed at all three time points (T1, T2, and T3), while [Cort]p levels were measured at T1 and T3. The study observed that the median values of FSV, RR, and [Cort]p tended to increase with both higher noise levels and longer exposure durations to noise. Significant differences in RR were found between group pairs G1G2 at T1 (|D| = 0.63 < cut-off = 0.98), and G2G3 at T2 (|D| = 0.69 < cut-off = 0.97). Regarding [Cort]p, significant differences were noted between the CGG1 group pair at T0 (p < 0.01), and T3 (p = 0.03). Furthermore, an excellent Spearman correlation coefficient (rho = 0.91) was found between FSV and RR, indicating that RR can serve as an effective tool for assessing stress levels in cats. The findings of this study provide valuable insights into the welfare of cats in a hospital environment and support the scientific validity of existing recommendations aimed at improving their well-being. Specifically, the study underscores the importance of minimizing noise levels in hospitals as a means to reduce stress in cats. This conclusion aligns with existing guidelines and recommendations for enhancing the welfare of hospitalized cats.

Heterogenous effect of early adulthood stress on cognitive aging and synaptic function in the dentate gyrus

Cognitive aging widely varies among individuals due to different stress experiences throughout the lifespan and vulnerability of neurocognitive mechanisms. To understand the heterogeneity of cognitive aging, we investigated the effect of early adulthood stress (EAS) on three different hippocampus-dependent memory tasks: the novel object recognition test (assessing recognition memory: RM), the paired association test (assessing episodic-like memory: EM), and trace fear conditioning (assessing trace memory: TM). Two-month-old rats were exposed to chronic mild stress for 6 weeks and underwent behavioral testing either 2 weeks or 20 months later. The results show that stress and aging impaired different types of memory tasks to varying degrees. RM is affected by combined effect of stress and aging. EM became less precise in EAS animals. TM, especially the contextual memory, showed impairment in aging although EAS attenuated the aging effect, perhaps due to its engagement in emotional memory systems. To further explore the neural underpinnings of these multi-faceted effects, we measured long-term potentiation (LTP), neural density, and synaptic density in the dentate gyrus (DG). Both stress and aging reduced LTP. Additionally, the synaptic density per neuron showed a further reduction in the stress aged group. In summary, EAS modulates different forms of memory functions perhaps due to their substantial or partial dependence on the functional integrity of the hippocampus. The current results suggest that lasting alterations in hippocampal circuits following EAS could potentially generate remote effects on individual variability in cognitive aging, as demonstrated by performance in multiple types of memory.

Investigating the impact of nutritional insufficiency on parahippocampal neurons in domestic chickens, Gallus gallus domesticus

Over time, scientists have been fascinated by the complex connections among nutrition, brain development, and behavior. It's been well understood that the brain's peak performance relies on having the right nutrients available. Thus, nutritional insufficiency, where an organism lacks vital nutrients crucial for optimal growth and function, can upset the body's balance, potentially triggering stress responses. However, our grasp of how the brain reacts to insufficient nutrition, particularly in avian species like domestic chickens, has shown inconsistencies in our understanding. Domestic chickens have frequently served as subjects for studying memory and learning, primarily focusing on the hippocampus-a region highly responsive to environmental changes. Yet, another critical brain region, the parahippocampal region, integral to memory and spatial cognition, had received relatively little attention concerning the consequences of inadequate nutrition and hydration. To address this knowledge gap, our study sought to investigate the impact of stress induced by nutritional insufficiency on the neuronal cells within the region parahippocampalis in two distinct age groups of domestic chickens, Gallus gallus domesticus: fifteen and thirty days old. We employed the Golgi-Cox-Impregnation technique to explore whether the structural characteristics of neuronal cells, specifically the dendritic spines, underwent changes under transient stressful conditions during these crucial developmental stages. The results were intriguing. Stress evidently induced observable alterations in the dendritic spines of the parahippocampal neuronal cells, with the extent of these changes being age-dependent. In fifteen-day-old chickens, stress prompted substantial modifications in the dendritic spines of parahippocampal multipolar and pyramidal neurons. In contrast, among thirty-day-old chickens, the response to stress was less comprehensive, with only specific parahippocampal multipolar neurons displaying such alterations. These findings underscored the influential role of stress in reshaping the structure of parahippocampal neurons and emphasized the importance of considering age when studying the impact of stress on the brain. Through this research, we aim to enhance our understanding of the intricate interplay between stress, brain structure, and the critical role of adequate nutrition, especially during pivotal developmental stages. Our future research objectives include a deeper investigation into the intracellular events including cellular and molecular mechanisms precipitating these changes and determining whether these alterations have downstream effects on crucial brain functions like learning and memory.