Protective effect of Hsp70i against chronic social isolation stress in the rat hippocampus

Effects of topiramate on morphological and structural alterations of the anterior cingulate cortex in aggressive socially isolated mice

RATIONALE

Topiramate, an approved antiepileptic drug, was found effective in treating aggressive symptoms in humans and rodents. However, the effects and mechanisms of Topiramate on aggressive behavior are still unclear. Our previous study indicated that intraperitoneal administration of Topiramate successfully decreased aggression and reinforced sociability in socially aggressive mice, and increased cFos-expressing neurons in the anterior cingulate cortex (ACC). In addition to its pharmacological properties, previous studies have approved the neuroprotective effects of Topiramate. These suggest a potential effect of Topiramate on ACC's structure and function.

OBJECTIVES AND RESULTS

In the present study, we first investigated the structural characteristics of ACC in the social isolation-induced aggression paradigm. The results showed that hyper-aggressive behavior in socially aggressive mice was associated with several structural alterations in ACC: increased neuron death combined with decreased neuron density, increased damaged neuronal morphology and increased neuroinflammation markers. Based on these observations, we next investigated the potential neuroprotective effect of Topiramate against structural alterations of ACC observed in socially aggressive mice. Results indicated that intraperitoneal administration of Topiramate (30 mg/kg) decreased aggression and enhanced sociability without affecting locomotor activity. Interestingly, the anti-aggressive effect of Topiramate was associated with decreased neuronal death, ameliorated damaged neuronal morphology, and decreased reactive microglia markers in ACC.

CONCLUSIONS

Our results provide insights into the structural alterations of ACC in aggressive socially aggressive mice. Moreover, the present study suggested that the anti-aggressive effect of Topiramate could be related to its neuroprotective effects against the structural alterations of ACC.

Social isolation induces neuroinflammation and microglia overactivation, while dihydromyricetin prevents and improves them

BACKGROUND

Anxiety disorders are the most prevalent mental illnesses in the U.S. and are estimated to consume one-third of the country's mental health treatment cost. Although anxiolytic therapies are available, many patients still exhibit treatment resistance, relapse, or substantial side effects. Further, due to the COVID-19 pandemic and stay-at-home order, social isolation, fear of the pandemic, and unprecedented times, the incidence of anxiety has dramatically increased. Previously, we have demonstrated dihydromyricetin (DHM), the major bioactive flavonoid extracted from Ampelopsis grossedentata, exhibits anxiolytic properties in a mouse model of social isolation-induced anxiety. Because GABAergic transmission modulates the immune system in addition to the inhibitory signal transmission, we investigated the effects of short-term social isolation on the neuroimmune system.

METHODS

Eight-week-old male C57BL/6 mice were housed under absolute social isolation for 4 weeks. The anxiety-like behaviors after DHM treatment were examined using elevated plus-maze and open field behavioral tests. Gephyrin protein expression, microglial profile changes, NF-κB pathway activation, cytokine level, and serum corticosterone were measured.

RESULTS

Socially isolated mice showed increased anxiety levels, reduced exploratory behaviors, and reduced gephyrin levels. Also, a dynamic alteration in hippocampal microglia were detected illustrated as a decline in microglia number and overactivation as determined by significant morphological changes including decreases in lacunarity, perimeter, and cell size and increase in cell density. Moreover, social isolation induced an increase in serum corticosterone level and activation in NF-κB pathway. Notably, DHM treatment counteracted these changes.

CONCLUSION

The results suggest that social isolation contributes to neuroinflammation, while DHM has the ability to improve neuroinflammation induced by anxiety.

Social Isolation Induces Neuroinflammation And Microglia Overactivation, While Dihydromyricetin Prevents And Improves Them

Background:

Anxiety disorders are the most prevalent mental illnesses in the U.S. and are estimated to consume one-third of the country’s mental health treatment cost. Although anxiolytic therapies are available, many patients still exhibit treatment-resistance, relapse, or substantial side effects. Further, due to the COVID-19 pandemic and stay-at-home order, social isolation, fear of the pandemic, and unprecedented times, the incidence of anxiety has dramatically increased. Previously, we have demonstrated dihydromyricetin (DHM), the major bioactive flavonoid extracted from Ampelopsis grossedentata, exhibits anxiolytic properties in a mouse model of social isolation-induced anxiety. Because GABAergic transmission modulates the immune system in addition to the inhibitory signal transmission, we investigated the effects of short-term social isolation on the neuroimmune system.

Methods:

Eight-week-old male C57BL/6 mice were housed under absolute social isolation for 4 weeks. The anxiety like behaviors after DHM treatment were examined using elevated plus maze and open field behavioral tests. Gephyrin protein expression, microglial profile changes, NF-κB pathway activation, cytokine level, and serum corticosterone were measured.

Results:

Socially isolated mice showed increased anxiety levels, reduced exploratory behaviors, and reduced gephyrin levels. Also, a dynamic alteration in hippocampal microglia were detected illustrated as a decline in microglia number and overactivation as determined by significant morphological changes including decreases in lacunarity, perimeter, and cell size and increase in cell density. Moreover, social isolation also induced an increase in serum corticosterone level and activation in NF-κB pathway. Notably, DHM treatment counteracted these changes.

Conclusion:

The results suggest that social isolation contributes to neuroinflammation, while DHM has the ability to restore neuroinflammatory changes induced by anxiety.

Duration of Social Isolation Affects Production of Nitric Oxide in the Rat Brain

Social isolation deprives rodents of social interactions that are critical for normal development of brain and behavior. Several studies have indicated that postweaning isolation rearing may affect nitric oxide (NO) production. The aim of this study was to compare selected behavioral and biochemical changes related to NO production in the brain of rats reared in social isolation for different duration. At the age of 21 days, male Sprague Dawley rats were randomly assigned into four groups reared in isolation or socially for 10 or 29 weeks. At the end of the rearing, open-field and prepulse inhibition (PPI) tests were carried out. Furthermore, in several brain areas we assessed NO synthase (NOS) activity, protein expression of nNOS and iNOS isoforms and the concentration of conjugated dienes (CD), a marker of oxidative damage and lipid peroxidation. Social isolation for 10 weeks resulted in a significant decrease in PPI, which was accompanied by a decrease in NOS activity in the cerebral cortex and the cerebellum, an increase in iNOS in the hippocampus and an increase in CD concentration in cortex homogenate. On the other hand, a 29 week isolation had an opposite effect on NOS activity, which increased in the cerebral cortex and the cerebellum in animals reared in social isolation, accompanied by a decrease in CD concentration. The decrease in NOS activity after 10 weeks of isolation might have been caused by chronic stress induced by social isolation, which has been documented in previous studies. The increased oxidative state might result in the depleted NO bioavailability, as NO reacts with superoxide radical creating peroxynitrite. After 29 weeks of isolation, this loss of NO might be compensated by the subsequent increase in NOS activity.

Social isolation causes downregulation of immune and stress response genes and behavioural changes in a social insect

Humans and other social mammals experience isolation from their group as stressful, triggering behavioural and physiological anomalies that reduce fitness. While social isolation has been intensely studied in social mammals, it is less clear how social insects, which evolved sociality independently, respond to isolation. Here we examined whether the typical mammalian responses to social isolation, e.g., an impaired ability to interact socially and immune suppression are also found in social insects. We studied the consequences of social isolation on behaviour and brain gene expression in the ant Temnothorax nylanderi. Following isolation, workers interacted moderately less with adult nestmates, increased the duration of brood contact, and reduced the time spent self-grooming, an important sanitary behaviour. Our brain transcriptome analysis revealed that only a few behaviour-related genes had altered their expression with isolation time. Rather, many genes linked to immune system functioning and stress response had been downregulated. This probably sensitizes isolated individuals to various stressors, in particular because isolated workers exhibit reduced sanitary behaviour. We provide evidence of the diverse consequences of social isolation in social insects, some of which resemble those found in social mammals, suggesting a general link between social well-being, stress tolerance, and immune competence in social animals.

Molecular correlates of mitochondrial dysfunctions in major depression: Evidence from clinical and rodent studies

Major depressive disorder (MDD) is one of the most prevalent stress-related mental disorders worldwide. Several biological mechanisms underlying the pathophysiology of MDD have been proposed, including endocrine disturbances, neurotransmitter deficits, impaired neuronal plasticity, and more recently, mitochondrial dysfunctions. In this review, we provide an overview of relevant molecular correlates of mitochondrial dysfunction in MDD, based on findings from clinical studies and stress-induced rodent models. We also compare differences and similarities between the phenotypes of MDD patients and animal models. Our analysis of the literature reveals that both MDD and stress are associated, in humans and animals, with changes in mitochondrial biogenesis, redox imbalance, increased oxidative damages of cellular macromolecules, and apoptosis. Yet, a considerable amount of conflicting data exist and therefore, the translation of findings from clinical and preclinical research to novel therapies for MDD remains complex. Further studies are needed to advance our understanding of the molecular networks and biological mechanisms involving mitochondria in the pathophysiology of MDD.

Comparative transcriptomics reveal conserved impacts of rearing density on immune response of two important aquaculture species

Infectious diseases represent an important barrier to sustainable aquaculture development. Rearing density can substantially impact fish productivity, health and welfare in aquaculture, including growth rates, behaviour and, crucially, immune activity. Given the current emphasis on aquaculture diversification, stress-related indicators broadly applicable across species are needed. Utilising an interspecific comparative transcriptomic (RNAseq) approach, we compared gill gene expression responses of Atlantic salmon (Salmo salar) and Nile tilapia (Oreochromis niloticus) to rearing density and Saprolegnia parasitica infection. Salmon reared at high-density showed increased expression of stress-related markers (e.g. c-fos and hsp70), and downregulation of innate immune genes. Upon pathogen challenge, only salmon reared at low density exhibited increased expression of inflammatory interleukins and lymphocyte-related genes. Tilapia immunity, in contrast, was impaired at low-density. Using overlapping gene ontology enrichment and gene ortholog analyses, we found that density-related stress similarly impacted salmon and tilapia in key immune pathways, altering the expression of genes vital to inflammatory and Th₁₇ responses to pathogen challenge. Given the challenges posed by ectoparasites and gill diseases in fish farms, this study underscores the importance of optimal rearing densities for immunocompetence, particularly for mucosal immunity. Our comparative transcriptomics analyses identified density stress impacted immune markers common across different fish taxa, providing key molecular targets with potential for monitoring and enhancing aquaculture resilience in a wide range of farmed species.

The effect of voluntary wheel running on the antioxidant status is dependent on sociability conditions

Voluntary wheel running is widely used as a physical activity (PA) model in rodents, but most studies investigate the beneficial effects of this intervention in socially isolated mice. Social isolation stress (SIS) is associated with vulnerability to oxidative stress and reduced mitochondrial activity. Thus, the aim of this study was to investigate the effects of free access to a running wheel for 21 days on the various markers of the cellular redox/antioxidant status as well as mitochondrial function of mice subjected to SIS or maintained in groups of 3 in the homecage. SIS increased thiobarbituric acid reactive substance (TBARS) levels in the cerebral cortex, and PA intervention was not able to reverse such alteration. PA reduced TBARS levels in the liver of grouped mice and gastrocnemius of socially isolated mice. PA increased nonprotein thiol (NPSH) levels in the cerebral cortex of grouped mice. Furthermore, socially isolated mice presented lower glutathione peroxidase (GPx) activity in the cerebellum and gastrocnemius, and glutathione reductase (GR) activity in the cerebral cortex and liver. By contrast, SIS induced higher GPx activity in the cerebral cortex and heart. PA reduced GPx (cerebral cortex) and GR (cerebral cortex and liver) activities of socially isolated mice. SIS caused higher activity of mitochondrial complexes I and II in the cerebral cortex, and the PA paradigm was not able to alter this effect. Interestingly, the PA produced antidepressant-like effect at both SIS and control groups. In conclusion, the results showed the influence of SIS for the effects of PA on the antioxidant status, but not on the mitochondrial function and emotionality.

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PA intervention produces antioxidant responses dependent on sociability conditions.

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SIS induces mitochondria function and antioxidant defense abnormalities.

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Running produces antidepressant-like behavior and does not change the ambulation.

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The distance travelled on the running wheel is correlated with immobility time in the TST.

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The lipoperoxidation index is negatively correlated with time spent on the running wheel.

Green Tea Catechins Trigger Immediate-Early Genes in the Hippocampus and Prevent Cognitive Decline and Lifespan Shortening

Senescence-accelerated mouse prone 10 (SAMP10) mice, after ingesting green tea catechins (GT-catechin, 60 mg/kg), were found to have suppressed aging-related decline in brain function. The dose dependence of brain function on GT-catechin indicated that intake of 1 mg/kg or more suppressed cognitive decline and a shortened lifespan. Mice that ingested 1 mg/kg GT-catechin had the longest median survival, but the dose was less effective at suppressing cognitive decline. The optimal dose for improving memory acquisition was 60 mg/kg, and memory retention was higher in mice that ingested 30 mg/kg or more. To elucidate the mechanism by which cognitive decline is suppressed by GT-catechin, changes in gene expression in the hippocampus of SAMP10 mice one month after ingesting GT-catechin were analyzed. The results show that the expression of immediate-early genes such as nuclear receptor subfamily 4 (Nr4a), FBJ osteosarcoma oncogene (Fos), early growth response 1 (Egr1), neuronal PAS domain protein 4 (Npas4), and cysteine-rich protein 61 (Cyr61) was significantly increased. These results suggest that GT-catechin suppresses age-related cognitive decline via increased expression of immediate-early genes that are involved in long-term changes in plasticity of synapses and neuronal circuits.

Chronic Isolation Stress Affects Subsequent Crowding Stress-Induced Brain Nitric Oxide Synthase (NOS) Isoforms and Hypothalamic-Pituitary-Adrenal (HPA) Axis Responses

The nitric oxide (NO) pathway in the brain is involved in response to psychosocial stressors. The aim of this study was to elucidate the role of nNOS and iNOS in the prefrontal cortex (PFC), hippocampus (HIP), and hypothalamus (HYPO) during social isolation stress (IS), social crowding stress (CS), and a combined IS + CS. In the PFC, 3 days of CS increased iNOS but not nNOS protein level. In the HIP and HYPO, the levels of nNOS and iNOS significantly increased after 3 days of CS. In the PFC, IS alone (11 days) enhanced iNOS protein level following 3 days of CS and increased nNOS level in the HIP and HYPO after 14 days of CS. By contrast, in the HIP, IS abolished the subsequent CS-induced increase in nNOS in the HIP and strongly elevated iNOS level after 7 days of CS. In the HYPO, prior IS inhibited nNOS protein level induced by subsequent CS for 3 days, but increased nNOS protein level after longer exposure times to CS. Isolation stress strongly upregulated plasma interleukin-1β (IL-1β) and adrenocorticotropic hormone (ACTH) levels while corticosterone (CORT) level declined. We show that the modulatory action of the NO pathway and ACTH/CORT adaptation to chronic social isolation stress is dependent on the brain structure and nature and duration of the stressor. Our results indicate that isolation is a robust natural stressor in social animals; it enhances the NO pathway in the PFC and abolishes subsequent social CS-induced NOS responses in the HIP and HYPO.

Depression and sterile inflammation: Essential role of danger associated molecular patterns

Stress is a major risk factor for psychiatric disorder including major depressive disorder (MDD) and can induce inflammation, which is known to be dysregulated in depression. Several clinical and pre-clinical studies have demonstrated a strong association between depressive symptoms and the expression of factors that increase inflammation. Conversely, administration of anti-inflammatory agents has been shown to ameliorate depressive symptoms, demonstrating the importance of inflammation as a mediator of depression. Although it is clear that inflammation plays a role in the pathophysiology of depression, the mechanism by which inflammation is activated in mood disorders remains unclear. To address this issue, studies have investigated the role of pattern recognition receptor (PRR) activation in stress-induced inflammation and mood disorders. However, the identification of the endogenous factors, referred to as danger-associated molecular patterns (DAMP) that activate these receptors remains understudied. Here we review the role of DAMPs in depression and highlight the clinical evidence for elevation of DAMP signaling in MDD patients and in pre-clinical animal stress models of depression.

Neurobiology and consequences of social isolation stress in animal model-A comprehensive review

The brain is a vital organ, susceptible to alterations under genetic influences and environmental experiences. Social isolation (SI) acts as a stressor which results in alterations in reactivity to stress, social behavior, function of neurochemical and neuroendocrine system, physiological, anatomical and behavioral changes in both animal and humans. During early stages of life, acute or chronic SIS has been proposed to show signs and symptoms of psychiatric and neurological disorders such as anxiety, depression, schizophrenia, epilepsy and memory loss. Exposure to social isolation stress induces a variety of endocrinological changes including the activation of hypothalamic-pituitary-adrenal (HPA) axis, culminating in the release of glucocorticoids (GCs), release of catecholamines, activation of the sympatho-adrenomedullary system, release of Oxytocin and vasopressin. In several regions of the central nervous system (CNS), SIS alters the level of neurotransmitter such as dopamine, serotonin, gamma aminobutyric acid (GABA), glutamate, nitrergic system and adrenaline as well as leads to alteration in receptor sensitivity of N-methyl-D-aspartate (NMDA) and opioid system. A change in the function of oxidative and nitrosative stress (O&NS) mediated mitochondrial dysfunction, inflammatory factors, neurotrophins and neurotrophicfactors (NTFs), early growth response transcription factor genes (Egr) and C-Fos expression are also involved as a pathophysiological consequences of SIS which induce neurological and psychiatric disorders.

Altered Behavior in Mice Socially Isolated During Adolescence Corresponds With Immature Dendritic Spine Morphology and Impaired Plasticity in the Prefrontal Cortex

Mice socially isolated during adolescence exhibit behaviors of anxiety, depression and impaired social interaction. Although these behaviors are well documented, very little is known about the associated neurobiological changes that accompany these behaviors. It has been hypothesized that social isolation during adolescence alters the development of the prefrontal cortex, based on similar behavioral abnormalities observed in isolated mice and those with disruption of this structure. To establish relationships between behavior and underlying neurobiological changes in the prefrontal cortex, Thy-1-GFP mice were isolated from weaning until adulthood and compared to group-housed littermates regarding behavior, electrophysiological activity and dendritic morphology. Results indicate an immaturity of dendritic spines in single housed animals, with dendritic spines appearing smaller and thinner. Single housed mice additionally show impaired plasticity through measures of long-term potentiation. Together these findings suggest an altered development and impairment of the prefrontal cortex of these animals underlying their behavioral characteristics.

Regulators of glucocorticoid receptor function in an animal model of depression and obesity

Obesity is a disease that often co-occurs with depression, and some evidence indicates that chronic stress in the perinatal period, in association with overactive glucocorticoids, can cause permanent changes that increase the risk of the development of both depression and obesity later in life. However, the mechanism responsible for the overly potent action of glucocorticoids in both depression and obesity is not known. The aim of the present study was to determine the expression of glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) and the factors that affect GR function (FKBP51, Bag-1 and HSP70) in a prenatal stress animal model of depression, a model of obesity and a model of both depression and obesity. Prenatal stress but not high-fat diet (HFD) was found to decrease the GR concentration in the frontal cortex. The level of the Bag-1M (46 kDa) isoform was also decreased in this structure but only in prenatal-stressed animals that did not show depression-like behaviour in the Porsolt test and were fed the standard diet (STD). In the model of depression employed here, decreases in MR expression and GR co-chaperone (FKBP51) levels in the hippocampus were also observed, and HFD intensified the prenatal stress-induced changes in MR expression. The obtained results indicated that prenatal stress affected the expression of GRs, MRs and their co-chaperones in the brain, but its effects were different in the frontal cortex and hippocampus. The decrease in MR density in the hippocampus and increased plasma insulin level seemed to be the most significant changes observed in the model of the co-occurrence of depression and obesity, which could limit the neuroprotective effects associated with the activation of MR and be a marker of peripheral insulin resistance, respectively. This article is protected by copyright. All rights reserved.

The effect of chronic tianeptine administration on the brain mitochondria: direct links with an animal model of depression

A growing body of evidence has focused on the impact of mitochondrial disturbances in the development of depression, but little data exist regarding the effects of chronic administration of antidepressant drugs on the brain's mitochondrial protein profile. The aim of this study was to investigate the impact of chronic treatment with an atypical antidepressant drug-tianeptine-on the mitochondria-enriched subproteome profile in the hippocampus and the frontal cortex of 3-month-old male rats following a prenatal stress procedure. Rats that were exposed to a prenatal stress procedure displayed depressive- and anxiety-like disturbances based on the elevated plus-maze and Porsolt tests. Moreover, two-dimensional electrophoresis coupled with mass spectrometry showed structure-dependent mitoproteome changes in brains of prenatally stressed rats after chronic tianeptine administration. A component of 2-oxoglutarate and succinate flavoprotein subunit dehydrogenases, isocitrate subunit alpha, was upregulated in the hippocampus. In the frontal cortex, there was a striking increase in the expression of glutamate dehydrogenase and cytochrome bc1 complex subunit 2. These findings suggest that mitochondria are underappreciated targets for therapeutic interventions, and mitochondrial function may be crucial for the effective treatment of stress-related diseases.

Lithium attenuates the proconvulsant effect of adolescent social isolation stress via involvement of the nitrergic system

In this study, we tested whether acute administration of lithium mitigates the deleterious effect of adolescent social isolation stress (SIS) on seizure susceptibility. In comparison with socially conditioned (SC) mice, isolated conditioned (IC) mice exhibited an increase in seizure susceptibility to pentylenetetrazole. Acute administration of lithium (10mg/kg) reversed the proconvulsant effect of SIS in IC mice, but this effect was not observed in SC mice. Coadministration of subthreshold doses of lithium (3mg/kg) with nitric oxide synthase (NOS) inhibitors reversed the effect of SIS on seizure susceptibility and decreased hippocampal nitrite levels in IC animals. In addition, a subthreshold dose of a nitric oxide precursor reduced the protective effect of lithium on seizure susceptibility and increased nitrite levels in the hippocampus of IC mice. These results suggest that lithium exerts a protective influence against the proconvulsant effect of adolescent SIS via a nitrergic system that includes activation of neuronal NOS in the hippocampus.

Integrating neuroimmune systems in the neurobiology of depression

Data from clinical and preclinical studies indicate that immune dysregulation, specifically of inflammatory processes, is associated with symptoms of major depressive disorder (MDD). In particular, increased levels of circulating pro-inflammatory cytokines and concomitant activation of brain-resident microglia can lead to depressive behavioural symptoms. Repeated exposure to psychological stress has a profound impact on peripheral immune responses and perturbs the function of brain microglia, which may contribute to neurobiological changes underlying MDD. Here, we review these findings and discuss ongoing studies examining neuroimmune mechanisms that influence neuronal activity as well as synaptic plasticity. Interventions targeting immune-related cellular and molecular pathways may benefit subsets of MDD patients with immune dysregulation.

Oxidative and nitrosative stress pathways in the brain of socially isolated adult male rats demonstrating depressive- and anxiety-like symptoms

Various stressors may disrupt the redox homeostasis of an organism by causing oxidative and nitrosative stress that may activate stressor-specific pathways and provoke specific responses. Chronic social isolation (CSIS) represents a mild chronic stress that evokes a variety of neurobehavioral changes in rats similar to those observed in people with psychiatric disorders, including depression. Most rodent studies have focused on the effect of social isolation during weaning or adolescence, while its effect in adult rats has not been extensively examined. In this review, we discuss the current knowledge regarding the involvement of oxidative/nitrosative stress pathways in the prefrontal cortex and hippocampus of adult male rats exposed to CSIS, focusing on hypothalamic-pituitary-adrenocortical (HPA) axis activity, behavior parameters, antioxidative defense systems, stress signaling mediated by nuclear factor-kappa B (NF-κB), and mitochondria-related proapoptotic signaling. Although increased concentrations of corticosterone (CORT) have been shown to induce oxidative and nitrosative stress, we suggest a mechanism underlying the glucocorticoid paradox whereby a state of oxidative/nitrosative stress may exist under basal CORT levels. This review also highlights the differential susceptibility of prefrontal cortex and hippocampus to oxidative stress following CSIS and suggests a possible cellular pathway of stress tolerance that preserves the hippocampus from molecular damage and apoptosis. The differential regulation of the transcriptional factor NF-κB, and the enzymes inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) following CSIS may be one functional difference between the response of the prefrontal cortex and hippocampus, thus identifying potentially relevant targets for antidepressant treatment.

NMDA receptor antagonists attenuate the proconvulsant effect of juvenile social isolation in male mice

Experiencing psychosocial stress in early life, such as social isolation stress (SIS), is known to have negative enduring effects on the development of the brain and behavior. In addition to anxiety and depressive-like behaviors, we previously showed that juvenile SIS increases susceptibility to pentylenetetrazole (PTZ)-induced seizures in mice through enhancing the nitrergic system activity in the hippocampus. In this study, we investigated the possible involvement of N-methyl-D-aspartate (NMDA) receptors in proconvulsant effects of juvenile SIS. Applying 4 weeks of SIS to juvenile male mice at postnatal day 21-23, we observed an increased susceptibility to PTZ as well as anxiety and depressive-like behaviors in adult mice. Intraperitoneal (i.p.) administration of NMDA receptor antagonists, MK-801 (0.05 mg/kg) and ketamine (0.5mg/kg), reversed the proconvulsant effects of SIS in Isolated (and not social) housed animals. Co-administration of non-effective doses of nitric oxide synthase (NOS) inhibitors, 7NI (25mg/kg) and L-NAME (10mg/kg), with NMDA receptor antagonists, MK-801 (0.01 mg/kg) and ketamine (0.1mg/kg) attenuated the proconvulsant effects of juvenile SIS only in isolated housed mice. Also, using real time RT-PCR, we showed that hippocampal upregulation of NR2B subunit of NMDA receptor may play a critical role in proconvulsant effects of juvenile SIS by dysregulation of NMDA/NO pathway. In conclusion, results of present study revealed that experiencing SIS during adolescence predisposes the co-occurrence of seizure disorders with psychiatric comorbidities and also, alteration of NMDA receptor structure and function in hippocampus plays a role in proconvulsant effects of juvenile SIS through enhancing the NMDA/NO pathway.

Involvement of the nitrergic system in the proconvulsant effect of social isolation stress in male mice

Social isolation stress (SIS) in adolescence is accompanied by neurobehavioral disturbances and pathophysiological changes in certain regions of the CNS such as the hippocampus. In this study, we tested whether SIS impacts seizure susceptibility in postnatal male mice due to a role of hippocampal nitric oxide (NO). To do this, we used the pentylenetetrazole (PTZ) model of clonic seizures, open-field test, hole-board test, forced swimming test, and plasma corticosterone assay. We aimed to evaluate if 4 weeks of SIS is capable of decreasing seizure threshold along with altering affective and neuroendocrine responses in isolated conditioned (IC) animals in comparison with socially conditioned (SC) animals. In addition, we applied subeffective doses of NO precursor L-arginine (25, 50, and 100mg/kg) and NOS inhibitors 7-NI (15 and 40 mg/kg), aminoguanidine (50 and 100mg/kg), and L-NAME (10 and 15 mg/kg) to both IC and SC groups prior to the determination of seizure threshold. Injection of a single dose of all mentioned drugs did not induce changes in seizure threshold of SC mice. On the other hand, L-NAME and 7-NI, but not aminoguanidine, modulated the proconvulsant effect of SIS, while L-arginine augmented the latter effect. We also measured the hippocampal nitrite levels after the administration of the aforementioned drugs. Social isolation stress increased the nitrite levels in comparison with those in SC mice, whereas 7-NI and L-NAME, unlike aminoguanidine, mitigated the effect of SIS. Additionally, L-arginine boosted the effects of SIS on nitrite production. In summary, we showed that SIS enhanced seizure susceptibility in the PTZ model of clonic seizures through the activation of the nitrergic system in the hippocampus. Also, we proved that nNOS, but not iNOS, accounts for these changes following SIS.

Involvement of heat shock proteins in gluten-sensitive enteropathy

Gluten-sensitive enteropathy, also known as coeliac disease (CD), is an autoimmune disorder occurring in genetically susceptible individuals that damages the small intestine and interferes with the absorption of other nutrients. As it is triggered by dietary gluten and related prolamins present in wheat, rye and barley, the accepted treatment for CD is a strict gluten-free diet. However, a complete exclusion of gluten-containing cereals from the diet is often difficult, and new therapeutic strategies are urgently needed. A class of proteins that have already emerged as drug targets for other autoimmune diseases are the heat shock proteins (HSPs), which are highly conserved stress-induced chaperones that protect cells against harmful extracellular factors. HSPs are expressed in several tissues, including the gastrointestinal tract, and their levels are significantly increased under stress circumstances. HSPs exert immunomodulatory effects, and also play a crucial role in the maintenance of epithelial cell structure and function, as they are responsible for adequate protein folding, influence the degradation of proteins and cell repair processes after damage, and modulate cell signalling, cell proliferation and apoptosis. The present review discusses the involvement of HSPs in the pathophysiology of CD. Furthermore, HSPs may represent a useful therapeutic target for the treatment of CD due to the cytoprotective, immunomodulatory, and anti-apoptotic effects in the intestinal mucosal barrier.