Harm avoidance, anxiety, and response to novelty in the adolescent S-100beta transgenic mouse: role of serotonin and relevance to Down syndrome

Sexual dimorphism in neurobehavioural phenotype and gut microbial composition upon long-term exposure to structural analogues of bisphenol-A

Bisphenol S (BPS) and Bisphenol F (BPF), the analogues of the legacy endocrine disrupting chemical, Bisphenol A (BPA) are ubiquitous in the environment and present in various consumer goods, and potentially neurotoxic. Here, we studied sex-specific responses of bisphenols on behavioural phenotypes, including their association with pro-inflammatory biomarkers and altered neurotransmitters levels, and the key gut microbial abundances. Neurobehavioural changes, using standard test battery, biochemical and molecular estimations for inflammatory cytokines, neurotransmitters, and oxido-nitrosative stress markers, gene expression analysis using qRT-PCR, H&E based histological investigations, gut permeability assays and Oxford Nanopore-based 16S-rRNA metagenomics sequencing for the gut microbial abundance estimations were performed. Bisphenol(s) exposure induces anxiety and depression-like behaviours, particularly in the male mice, with heightened pro-inflammatory cytokines levels and systemic endotoxemia, altered monoamine neurotransmitters levels/turnovers and hippocampal neuronal degeneration and inflammatory responses in the brain. They also increased gut permeability and altered microbial diversity, particularly in males. Present study provides evidence for sex-specific discrepancies in neurobehavioural phenotypes and gut microbiota, which necessitate a nuanced understanding of sex-dependent responses to bisphenols. The study contributes to ongoing discussions on the multifaceted implications of bisphenols exposure and underscores the need for tailored regulatory measures to mitigate potential health risks associated with them.

Genetics, molecular control and clinical relevance of habituation learning

Habituation is the most fundamental form of learning. As a firewall that protects our brain from sensory overload, it is indispensable for cognitive processes. Studies in humans and animal models provide increasing evidence that habituation is affected in autism and related monogenic neurodevelopmental disorders (NDDs). An integrated application of habituation assessment in NDDs and their animal models has unexploited potential for neuroscience and medical care. With the aim to gain mechanistic insights, we systematically retrieved genes that have been demonstrated in the literature to underlie habituation. We identified 258 evolutionarily conserved genes across species, describe the biological processes they converge on, and highlight regulatory pathways and drugs that may alleviate habituation deficits. We also summarize current habituation paradigms and extract the most decisive arguments that support the crucial role of habituation for cognition in health and disease. We conclude that habituation is a conserved, quantitative, cognition- and disease-relevant process that can connect preclinical and clinical work, and hence is a powerful tool to advance research, diagnostics, and treatment of NDDs.

Partial Monosomy 21 Mirrors Gene Expression of Trisomy 21 in a Patient-Derived Neuroepithelial Stem Cell Model

Induced pluripotent stem cells (iPSCs) from patients are an attractive disease model to study tissues with poor accessibility such as the brain. Using this approach, we and others have shown that trisomy 21 results in genome-wide transcriptional dysregulations. The effects of loss of genes on chromosome 21 is much less characterized. Here, we use patient-derived neural cells from an individual with neurodevelopmental delay and a ring chromosome 21 with two deletions spanning 3.8 Mb at the terminal end of 21q22.3, containing 60 protein-coding genes. To investigate the molecular perturbations of the partial monosomy on neural cells, we established patient-derived iPSCs from fibroblasts retaining the ring chromosome 21, and we then induced iPSCs into neuroepithelial stem cells. RNA-Seq analysis of NESCs with the ring chromosome revealed downregulation of 18 genes within the deleted region together with global transcriptomic dysregulations when compared to euploid NESCs. Since the deletions on chromosome 21 represent a genetic “contrary” to trisomy of the corresponding region, we further compared the dysregulated transcriptomic profile in with that of two NESC lines with trisomy 21. The analysis revealed opposed expression changes for 23 genes on chromosome 21 as well as 149 non-chromosome 21 genes. Taken together, our results bring insights into the effects on the global and chromosome 21 specific gene expression from a partial monosomy of chromosome 21qter during early neuronal differentiation.

Buspirone for the Treatment of Generalized Anxiety Disorder in Down Syndrome: 3 Cases

OBJECTIVE

Reports on the pharmacologic treatment of anxiety, including generalized anxiety disorder (GAD), in individuals with Down syndrome (DS) are lacking.

METHODS

We present the case histories of 1 adolescent and 2 young adults with DS and the treatment course of comorbid GAD with buspirone.

RESULTS

Treatment with buspirone was safe and well-tolerated and resulted in sustained improvement in symptoms of anxiety for a minimum of 2 years in all 3 cases.

CONCLUSION

Buspirone's generally benign adverse effect profile makes it well suited for treating anxiety in individuals with DS in light of their common medical comorbidities.

Beneficial effects of intravenous dexmedetomidine on cognitive function and cerebral injury following a carotid endarterectomy

The present study aimed to investigate the effects of dexmedetomidine (DEX) on cognition following a carotid endarterectomy (CEA). In addition, the neuroprotective effects of DEX against ischemia-reperfusion injury during CEA were analyzed. Patients due to undergo elective CEA under general anesthesia were randomly assigned to either the DEX-treated group (group D; n=25) or the control group (group C; n=25). Patients in group D were treated with 0.3 µg/kg DEX pre-CEA, followed by 0.3 µg/kg/h DEX intraoperatively up to 30 min prior to the completion of surgery, and the patients in group C received an equal volume of normal saline. Cognitive function was assessed prior to CEA (T0), and at 24, 48, and 72 h, 7 days and 1 month post-surgery (T1-5, respectively), using the Mini-Mental State Examination (MMSE). Blood samples were drawn from the ipsilateral jugular bulb of all patients at 20 min prior to anesthesia (t0), and at 10 min following tracheal intubation, 15 min following clamping and unclamping of the carotid artery, and at 6 and 24 h postoperatively (t1-5, respectively). The protein expression levels of markers of cerebral ischemia and injury, namely S100 calcium-binding protein B (S100B) and neuron-specific enolase (NSE), and the concentration of the oxidative stress marker malondialdehyde (MDA), were analyzed. Patients in group D exhibited elevated MMSE scores at T2 and T3 post-CEA, as compared with group C. Furthermore, the protein expression level of S100B and the concentration of MDA in the jugular bulb of group D patients were markedly decreased compared with those in group C at t3-5 and t3, respectively. The results of the present study suggested that DEX was able to enhance the recovery of cognition following CEA, and this was associated with decreased cerebral damage and antioxidative effects.

Neurotransmitters and Novelty: A Systematic Review

Our brains are highly responsive to novelty. However, how novelty is processed in the brain, and what neurotransmitter systems play a role therein, remains elusive. Here, we systematically review studies on human participants that have looked at the neuromodulatory basis of novelty detection and processing. While theoretical models and studies on nonhuman animals have pointed to a role of the dopaminergic, cholinergic, noradrenergic and serotonergic systems, the human literature has focused almost exclusively on the first two. Dopamine was found to affect electrophysiological responses to novelty early in time after stimulus presentation, but evidence on its effects on later processing was found to be contradictory: While neuropharmacological studies mostly yielded null effects, gene studies did point to an important role for dopamine. Acetylcholine seems to dampen novelty signals in the medial temporal lobe, but boost them in frontal cortex. Findings on 5-HT (serotonin) were found to be mostly contradictory. Two large gaps were identified in the literature. First, few studies have looked at neuromodulatory influences on behavioral effects of novelty. Second, no study has looked at the involvement of the noradrenergic system in novelty processing.

Neurodevelopment and phenotype-modulating functions of S100B protein: a pilot study

The importance of certain neurotrophic proteins found in maternal blood and milk for breastfed infants has remained ambiguous. This study was conducted to present evidence of the impact of an induced deficit of active S100B protein on neonate development. Newborn mice from two groups of mothers, immunized or sham-immunized against S100B, were subjected to various behavioral tests, and the development of their morphological characteristics was recorded from birth until weaning. Morphological problems, including weight gain and fur coating, a delay in the maturation of neurobehavioral systems and a deficit in neuromotor functions, including visual abilities, somato-sensory and posture reactions, muscular strength, locomotion, and fear/orienting processes, were observed in pups of immunized mothers. The S100B protein of external or internal origin in infants may be considered to be a specific factor that determines neuro- and morphological development and a risk-avoidance ('homeward-bent' or fearful) phenotype. The suppression of activity of the S100B protein results in a slower neonatal development and the formation of a risk-tolerant (fearless) phenotype of the offspring. This study thus considers the mechanism of neuroplastic regulation on the extent of sensation-seeking or risk-taking (homeless-like or fearless) and sensation- or risk-avoidance (home-bound or fearful) features in individual phenotypes.

Neurotransmitter-based strategies for the treatment of cognitive dysfunction in Down syndrome

Down syndrome (DS) is a multisystem disorder affecting the cardiovascular, respiratory, gastrointestinal, neurological, hematopoietic, and musculoskeletal systems and is characterized by significant cognitive disability and a possible common pathogenic mechanism with Alzheimer's disease. During the last decade, numerous studies have supported the notion that the triplication of specific genes on human chromosome 21 plays a significant role in cognitive dysfunction in DS. Here we reviewed studies in trisomic mouse models and humans, including children and adults with DS. In order to identify groups of genes that contribute to cognitive disability in DS, multiple mouse models of DS with segmental trisomy have been generated. Over-expression of these particular genes in DS can lead to dysfunction of several neurotransmitter systems. Therapeutic strategies for DS have either focused on normalizing the expression of triplicated genes with important roles in DS or restoring the function of these systems. Indeed, our extensive review of studies on the pathogenesis of DS suggests that one plausible strategy for the treatment of cognitive dysfunction is to target the cholinergic, serotonergic, GABA-ergic, glutamatergic, and norepinephrinergic system. However, a fundamental strategy for treatment of cognitive dysfunction in DS would include reducing to normal levels the expression of specific triplicated genes in affected systems before the onset of neurodegeneration.

Chronic fluoxetine treatment changes S100B expression during postnatal rat brain development

BACKGROUND

Fluoxetine, a selective serotonin reuptake inhibitor, is approved for treatment of childhood depression. In rats, fluoxetine influences neuronal development, but it is unclear whether it also influences glia development. S100B is a glia-derived calcium-binding protein, which may influence the development of serotonergic fibers and, vice versa, serotonin may influence the expression of S100B.

OBJECTIVES

The purpose of this study was to investigate whether fluoxetine treatment influences the expression of S100B during postnatal development, and whether potential changes are regionally dependent upon the time frame of drug administration.

METHODS

S100B gene expression and S100B protein expression in three different brain regions (frontal cortex, hippocampus, and striatum) were studied by real-time polymerase chain reaction (PCR) and immunohistochemistry, respectively. First, a short-term effect, 24 hours after a 14 day fluoxetine treatment (5 mg/kg/bw s.c.) of rats either from postnatal day (PD) 1 to 15, 21 to 35, or 50 to 64, was investigated. Then, the same treatment was used to analyze S100B gene and protein levels at PD 90 (long-term effect).

RESULTS

At PD 90, a significant increase of gene and protein expression was observed in all regions if rats were treated during PDs 21-35, whereas treatment during other periods had no long-term effects. A short-term effect 24 hours after fluoxetine treatment was found for almost all development stages and regions, demonstrated by a significant increase of S100B.

CONCLUSIONS

These results support recent research indicating a highly drug-sensitive period (i.e., periadolescence) of rat brain development. Therefore, further clinical studies should be performed to clarify whether such a sensitive period also exists in children.

Effects of S100B on Serotonergic Plasticity and Neuroinflammation in the Hippocampus in Down Syndrome and Alzheimer's Disease: Studies in an S100B Overexpressing Mouse Model

S100B promotes development and maturation in the mammalian brain. However, prolonged or extensive exposure can lead to neurodegeneration. Two important functions of S100B in this regard, are its role in the development and plasticity of the serotonergic neurotransmitter system, and its role in the cascade of glial changes associated with neuroinflammation. Both of these processes are therefore accelerated towards degeneration in disease processes wherein S100B is increased, notably, Alzheimer's disease (AD) and Down syndrome (DS). In order to study the role of S100B in this context, we have examined S100B overexpressing transgenic mice. Similar to AD and DS, the transgenic animals show a profound change in serotonin innervation. By 28 weeks of age, there is a significant loss of terminals in the hippocampus. Similarly, the transgenic animals show neuroinflammatory changes analogous with AD and DS. These include decreased numbers of mature, stable astroglial cells, increased numbers of activated microglial cells and increased microglial expression of the cell surface receptor RAGE. Eventually, the S100B transgenic animals show neurodegeneration and the appearance of hyperphosphorylated tau structures, as seen in late stage DS and AD. The role of S100B in these conditions is discussed.

The S100B/RAGE Axis in Alzheimer's Disease

Increasing evidence suggests that the small EF-hand calcium-binding protein S100B plays an important role in Alzheimer's disease. Among other evidences are the increased levels of both S100B and its receptor, the Receptor for Advanced Glycation Endproducts (RAGEs) in the AD diseased brain. The regulation of RAGE signaling by S100B is complex and probably involves other ligands including the amyloid beta peptide (Aβ), the Advanced Glycation Endproducts (AGEs), or transtheyretin. In this paper we discuss the current literature regarding the role of S100B/RAGE activation in Alzheimer's disease.

Antibodies to S100 proteins have anxiolytic-like activity at ultra-low doses in the adult rat

S100 proteins are small calcium-binding proteins interacting with numerous intra- and extra cellular targets involved in diverse physiological functions. In particular, S100 proteins may be involved in the regulation of anxiety-related behaviour. In the present study, the effects of affinity-purified antibodies to S100 proteins administered orally at ultra-low doses were evaluated in pre-clinical tests for anxiolytic-like activity in the adult rat. In the Vogel conflict test in the rat, antibodies to S100 proteins increased punished drinking (anti-conflict effect) at 5 and 7.5 mL kg−1, but not at 2.5 or 10 mL kg−1. Antibodies to S100 proteins increased the percentage of entries into the open arms of an elevated plus-maze at 10 mL kg−1, but not at lower doses. Taken together, these results indicate the presence of anxiolytic-like activity for antibodies to S100 proteins over the dose range 5–10 mL kg−1 in the adult rat.

Vitamin E increases S100B-mediated microglial activation in an S100B-overexpressing mouse model of pathological aging

S100B is a calcium-binding protein released by astroglial cells of the brain capable of producing numerous extracellular effects. Although the direct molecular mechanism remains unknown, these effects can be trophic including differentiation, growth, recovery, and survival of neurons when the S100B protein is mainly oxidized and neurotoxic including apoptosis and neuroinflammatory processes marked by microglial activation when in a reduced state. S100B and its receptor RAGE (receptor for advanced glycation end products) have been found to be increased in Alzheimer's disease, Down syndrome, with tissue trauma and ischemia. In the current study, we examined the binding of the S100B receptor (RAGE) on microglial cells and the developmental effects of the antioxidant vitamin E on microglial activation and the upregulation of RAGE in an S100B over-expressing mouse model of pathological aging. We report that RAGE is co-localized on activated microglial cells and vitamin E induced dramatic increases in microglial activation as well as total microglial relative optical density that was accompanied by upregulation of the RAGE receptor, particularly in the CA1 region of the hippocampus. Our findings suggest further investigation into the potential role of vitamin E in reducing the oxidation state of the S100B protein and its influence on neuroinflammatory processes marked by microglial activation in vivo.

Binding of S100 proteins to RAGE: an update

The Receptor for Advanced Glycation Endproducts (RAGE) is a multi-ligand receptor of the immunoglobulin family. RAGE interacts with structurally different ligands probably through the oligomerization of the receptor on the cell surface. However, the exact mechanism is unknown. Among RAGE ligands are members of the S100 protein family. S100 proteins are small calcium binding proteins with high structural homology. Several members of the family have been shown to interact with RAGE in vitro or in cell-based assays. Interestingly, many RAGE ligands appear to interact with distinct domains of the extracellular portion of RAGE and to trigger various cellular effects. In this review, we summarize the modes of S100 protein-RAGE interaction with regard to their cellular functions.

Mental retardation in Down syndrome: From gene dosage imbalance to molecular and cellular mechanisms

Down syndrome (DS), the most frequent genetic disorder leading to mental retardation (MR), is caused by three copies of human chromosome 21 (HC21). Trisomic and transgenic mouse models for DS allow genetic dissection of DS neurological and cognitive disorders in view to identify genes responsible for these phenotypes. The effects of the gene dosage imbalance on DS phenotypes are explained by two hypotheses: the "gene dosage effect" hypothesis claims that a DS critical region, containing a subset of dosage-sensitive genes, determines DS phenotypes, and the "amplified developmental instability" hypothesis holds that HC21 trisomy determines general alteration in developmental homeostasis. Transcriptome and expression studies showed different up- or down-expression levels of genes located on HC21 and the other disomic chromosomes. HC21 genes, characterized by their overexpression in brain regions affected in DS patients and by their contribution to neurological and cognitive defects when overexpressed in mouse models, are proposed herein as good candidates for MR. In this article, we propose a new molecular and cellular mechanism explaining MR pathogenesis in DS. In this model, gene dosage imbalance effects on transcriptional variations are described considering the nature of gene products and their functional relationships. These transcriptional variations may affect different aspects of neuronal differentiation and metabolism and finally, determine the brain neuropathologies and mental retardation in DS.

Neonatal serotonin depletion alters behavioral responses to spatial change and novelty

Multiple brain disorders that show serotonergic imbalances have a developmental onset. Experimental models indicate a role for serotonin as a morphogen in brain development. To selectively study the effects of serotonin depletions on cortical structural development and subsequent behavior, we developed a mouse model in which a serotonin neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), is injected into the medial forebrain bundle (mfb) on the day of birth. Littermates with saline injections into the mfb and age matched mice served as controls. This study characterized the extent and duration of serotonergic denervation after the selective neonatal lesion and investigated effects on exploratory behavior, spatial learning and anxiety in mice of both sexes. We report significant decreases in the serotonergic (5-HT) innervation to cortex and hippocampus, but not to subcortical forebrain structures in 5,7-DHT-lesioned mice. The depletion of 5-HT fibers in cortical areas was long lasting in lesioned mice but autoradiographic binding to high affinity 5-HT transporters was only transiently reduced. Male but not female lesioned mice reduced their exploration significantly in response to spatial rearrangement and object novelty, suggesting increased anxiety in response to change but normal spatial cognition. Our data show that developmental disruptions in the serotonergic innervation of cortex and hippocampus are sufficient to induce permanent, sex specific, behavioral alterations. These results may have significant implications for understanding brain disorders presenting with cortical morphogenetic abnormalities and altered serotonin neurotransmission, such as autism, schizophrenia and affective disorders.

Pathologies involving the S100 proteins and RAGE

The S100 proteins are exclusively expressed in vertebrates and are the largest subgroup within the superfamily of EF-hand Ca2(+)-binding proteins Generally, S100 proteins are organized as tight homodimers (some as heterodimers). Each subunit is composed of a C-terminal, 'canonical' EF-hand, common to all EF-hand proteins, and a N-terminal, 'pseudo' EF-hand, characteristic of S100 proteins. Upon Ca2(+)-binding, the C-terminal EF-hand undergoes a large conformational change resulting in the exposure of a hydrophobic surface responsible for target binding A unique feature of this protein family is that some members are secreted from cells upon stimulation, exerting cytokine- and chemokine-like extracellular activities via the Receptor for Advanced Glycation Endproducts, RAGE. Recently, larger assemblies of some S100 proteins (hexamers, tetramers, octamers) have been also observed and are suggested to be the active extracellular species required for receptor binding and activation through receptor multimerization Most S100 genes are located in a gene cluster on human chromosome 1q21, a region frequently rearranged in human cancer The functional diversification of S100 proteins is achieved by their specific cell- and tissue-expression patterns, structural variations, different metal ion binding properties (Ca2+, Zn2+ and Cu2+) as well as their ability to form homo-, hetero- and oligomeric assemblies Here, we review the most recent developments focussing on the biological functions of the S100 proteins and we discuss the presently available S100-specific mouse models and their possible use as human disease models In addition, the S100-RAGE interaction and the activation of various cellular pathways will be discussed. Finally, the close association of S100 proteins with cardiomyopathy, cancer, inflammation and brain diseases is summarized as well as their use in diagnosis and their potential as drug targets to improve therapies in the future.

Mouse Models of Cognitive Disorders in Trisomy 21: A Review

Trisomy 21 (TRS21) is the most frequent genetic cause of mental retardation. Although the presence of an extra copy of HSA21 is known to be at the origin of the syndrome, we do not know which 225 HSA21 genes have an effect on cognitive processes. Mouse models of TRS21 have been developed using syntenies between HSA21 and MMU16, MMU10 and MMU17. Available mouse models carry extra fragments of MMU16 or of HSA21 that cover all of HSA21 (chimeric HSA21) or MMU16 (Ts16); some carry large parts of MMU16 (Ts65Dn, Ts1Cje, Ms1Cje), while others have reduced contiguous fragments covering the D21S17-ETS2 region or single transfected genes. This offers a nest design strategy for deciphering cognitive (learning, memory and exploration) and associated brain abnormalities involving each of these chromosomal regions. This review confirms the crucial but not exclusive contribution of the D21S17-ETS2 region encompassing 16 genes to cognitive disorders.

Mouse models of autism spectrum disorders: The challenge for behavioral genetics

Autism is a severe neurodevelopmental disorder, which typically emerges early in childhood. The core symptoms of autism include deficits in social interaction, impaired communication, and aberrant repetitive behavior, including self-injury. Despite the strong genetic component for the disease, most cases of autism have not been linked to mutations in a specific gene, and the etiology of the disorder has yet to be established. At the present time, there is no generally accepted therapeutic strategy to treat the core symptoms of autism, and there remains a critical need for appropriate animal models and relevant behavioral assays to promote the understanding and treatment of the clinical syndrome. Challenges for the development of valid mouse models include complex genetic interactions underlying the high heritability of the disease in humans, diagnosis based on deficits in social interaction and communication, and the lack of confirmatory neuropathological markers to provide validation for genetic models of the disorder. Research focusing on genes that mediate social behavior in mice may help identify neural circuitry essential for normal social interaction, and lead to novel genetic animal models of the autism behavioral phenotype.

S100 proteins in mouse and man: from evolution to function and pathology (including an update of the nomenclature)

The S100 protein family is the largest subgroup within the superfamily of proteins carrying the Ca2+-binding EF-hand motif. Despite their small molecular size and their conserved functional domain of two distinct EF-hands, S100 proteins developed a plethora of tissue-specific intra- and extracellular functions. Accordingly, various diseases such as cardiomyopathies, neurodegenerative and inflammatory disorders, and cancer are associated with altered S100 protein levels. Here, we review the different S100 protein functions and related diseases from an evolutionary point of view. We analyzed the structural variations, which are the basis of functional diversification, as well as the genomic organization of the S100 family in human and compared it with the S100 repertoires in mouse and rat. S100 genes and proteins are highly conserved between the different mammalian species. Moreover, we identified evolutionary related subgroups of S100 proteins within the three species, which share functional similarity and form subclusters on the genomic level. The available S100-specific mouse models are summarized and the consequences of our results are discussed with regard to the use of genetically engineered mice as human disease models. An update of the S100 nomenclature is included, because some of the recently identified S100 genes and pseudogenes had to be renamed.