Behavioral profile of mice with impaired cognition in the elevated plus-maze due to a deficiency in neural cell adhesion molecule

Behavioral, biochemical, histopathological evaluation and gene expression of brain injury induced by nanoceria injected intranasal or intraperitoneal in mice

Background

Nanotechnology has shown a remarkable progress nevertheless, there is a growing concern about probable neurotoxic and neurodegenerative effects due to NPs exposure. Various toxicological and epidemiological studies reported that the brain is a main target for ultrafine particles. Brain inflammation is considered as a possible mechanism that can participate to neurotoxic and neurodegenerative effects. Whether nanoparticles (NPs) may produce neurotoxicity and promote neurodegenerative is largely unstudied. The present study was done to investigate whether intranasal and intra-peritoneal exposure to cerium oxide nanoparticles (CeO2NPs, nanoceria (NC)) could cause neurotoxicity and neurodegenerative changes in the brain tissue through conducting some behavioral tests, biochemical evaluation, histopathological examinations of brain hippocampus and gene expressions.

Method

Fifteen mice were separated into 3 equal groups. In group (I) "control group", mice were received distilled water orally and kept as a control group. Mice in the group (II) "NC I/P group" were injected i.p with cerium oxide nanoparticles at a dose of 40 mg/kg b.wt, twice weekly for 3 weeks. In group (III) "NC I/N group" mice were received nanoceria intranasally (40 mg/kg b.wt), twice weekly for 3 weeks.

Results

Exposure to nanceria resulted in oxidative damage in brain tissue, a significant increase in malondialdehyde (MDA) and acetylcholinestrase (AchE) levels, significant decrease in reduced glutathione (GSH) concentration, upregulation in the apoptosis-related genes (c-Jun: c-Jun N-terminal kinases (JNKs), c-Fos: Fos protooncogene, AP-1 transcription factor subunit, c-Myc: c-myelocytomatosis oncogene product or MYC protooncogene, bHLH transcription factor), locomotor and cognitive impairment in mice but the effect was more obvious when nanoceria adminstred intraperitoneally.

Conculsion

Nanoceria cause oxidative damage in brain tissue of mice when adminstred nanoceria intraperitoneally more than those received nanoceria intranasal.

Enhanced Cognition and Neurogenesis in miR-146b Deficient Mice

The miR-146 family consists of two microRNAs (miRNAs), miR-146a and miR-146b, which are both known to suppress a variety of immune responses. Here in this study, we show that miR-146b is abundantly expressed in neuronal cells, while miR-146a is mainly expressed in microglia and astroglia of adult mice. Accordingly, miR-146b deficient (Mir146b-/-) mice exhibited anxiety-like behaviors and enhanced cognition. Characterization of cellular composition of Mir146b-/- mice using flow cytometry revealed an increased number of neurons and a decreased abundancy of astroglia in the hippocampus and frontal cortex, whereas microglia abundancy remained unchanged. Immunohistochemistry showed a higher density of neurons in the frontal cortex of Mir146b-/- mice, enhanced hippocampal neurogenesis as evidenced by an increased proliferation, and survival of newly generated cells with enhanced maturation into neuronal phenotype. No microglial activation or signs of neuroinflammation were observed in Mir146b-/- mice. Further analysis demonstrated that miR-146b deficiency is associated with elevated expression of glial cell line-derived neurotrophic factor (Gdnf) mRNA in the hippocampus, which might be at least in part responsible for the observed neuronal expansion and the behavioral phenotype. This hypothesis is partially supported by the positive correlation between performance of mice in the object recognition test and Gdnf mRNA expression in Mir146b-/- mice. Together, these results show the distinct function of miR-146b in controlling behaviors and provide new insights in understanding cell-specific function of miR-146b in the neuronal and astroglial organization of the mouse brain.

Avicularin Attenuates Memory Impairment in Rats with Amyloid Beta-Induced Alzheimer's Disease

Amyloid-beta-induced Alzheimer's disease (AD) and its further complications are well-established models in preclinical studies and demonstrated by many researchers. Intracerebroventricular injection of Aβ produces brain malfunction, including neurodegeneration and memory impairment. Avicularin is a bioactive flavonoid that has been found to prevent oxidative stress and proinflammatory cytokines. Alzheimer's disease treatment may benefit from inhibiting amyloid-beta and its related complications. Hence, by considering multiple actions of avicularin, including antioxidant and anti-inflammatory, we demonstrated the neuroprotective action of avicularin against amyloid beta-induced neurotoxicity. Aβ_1-42 (1 µg/µl) was dissolved in phosphate buffer solution (pH7.4) and incubated at 37 °C for 3 days to induce aggregation. A single intracerebroventricular (i.c.v.) injection of the Aβ_1-42 was given to the animals utilizing stereotaxic equipment. Avicularin was dissolved in 0.5% sodium carboxymethyl cellulose (CMC), and treatment was given to the animals for 21 days at a dose of (25, 50, and 100 mg/kg, p.o.) after Aβ_1-42 peptide (i.c.v.) injection. Several behavioral studies, acetylcholinesterase activity, oxidative stress, TNFα, IL-6, IL-1β, and expression of BDNF and amyloid-beta were measured. Avicularin treatment (50 and 100 mg/kg) showed cognition enhancement activity in behavioral studies and could reverse the effects of amyloid beta-induced inflammatory response and excessive oxidative stress. Furthermore, the findings reveal that avicularin can halt AD progression by targeting BDNF and amyloid-beta levels in the brain, suggesting that avicularin could be used for Alzheimer's disease treatment.

Development of Synergy-Based Combination for Learning and Memory Using in vitro, in vivo and TLC-MS-Bioautographic Studies

The present study is aimed at developing a synergistic combination to enhance learning and memory in Alzheimer’s patients with the help of eight common medicinal plants used in the AYUSH system. Aqueous and hydroalcoholic extracts of eight medicinal plants from the AYUSH system of medicine were prepared. These were subjected to in vitro anticholinesterase activity, to find out the combination index of synergistic combination. The synergistic combination and their individual extracts were subjected to total phenol, flavonoid and antioxidant activity estimation. Further, in vivo neurobehavioral studies in rats were carried out followed by TLC-MS-bioautographic identification of bioactive metabolites. Out of the sixteen extracts, aqueous extracts of Withania somnifera (L.) Dunal (WSA) and Myristica fragrans (L.) Dunal (MFA) were selected for the development of synergistic combination based on their IC₅₀ value in vitro anticholinesterase assay. The synergistic combination inhibited the anticholinesterase activity significantly as compared to the individual extracts of WSA and MFA. The synergistic combination also showed more phenolic and flavonoid contents with potential antioxidant activity. The TLC-bioautography showed four white spots in WSA, signifying sitoindosides VII, VIII, quercetin, isopelletierine and Withanolide S as AChE inhibitory compounds while showing five white spots of anti-cholinesterase active metabolites identified as eugenol, methyl eugenol, myristic acid, galbacin and β-sitosterol in MFA. The observation of neurocognitive behavior in amnesia induced subjects manifested that both the synergistic combinations showed comparable results to that of standard piracetam, though the synergistic combination containing a higher concentration of WSA showed more appreciable results in ameliorating dementia in rats. The study suggests that the synergy based combination successfully enhanced memory and learning by abating free radical and acetylcholine levels, and increased learning and memory in rats, providing a strong rationale for its use in the treatment of dementia and Alzheimer’s disease.

Development of depression-like behavior and altered hippocampal neurogenesis in a mouse model of chronic neuropathic pain

Chronic-pain patients often suffer from depression. In rodent models of neuropathic pain, animals develop depression-like and anxiety behaviors, indicating a relationship between chronic pain and affective disorders. However, the underlying neurobiological mechanisms linking chronic pain and depression are not yet fully understood. Neurogenesis in the hippocampus is a fundamental process related to brain plasticity. Reduced neurogenesis has been associated with the development of mood disorders and cognitive impairments. The current study aims to elucidate the underlying long-term changes in brain plasticity induced by neuropathic pain in mice at a time point when depression-like behavior has already developed. Furthermore, our focus is set on alterations in neurogenesis in the hippocampus. We found that manifestation of anxiety- and depressive-like behavior as well as cognitive impairment co-occur with decreased survival of newly generated cells but not with impaired proliferative activity or reduced number of immature neurons in the dentate gyrus area of the hippocampus. Moreover, we detected an impairment of differentiation of newly generated cells into mature calbindin-positive neurons, accompanied with a shift towards increased differentiation into astroglial cells. These findings indicate that a reduction in mature functional neurons, rather than reduced proliferation or neuronal progenitor cells, are the long-term changes in hippocampal plasticity that manifest in neuropathic pain conditions after depression-like behavior has developed.

Integrated Epigenetics, Transcriptomics, and Metabolomics to Analyze the Mechanisms of Benzo[a]pyrene Neurotoxicity in the Hippocampus

Benzo[a]pyrene (B[a]P) is a common environmental pollutant that is neurotoxic to mammals, which can cause changes to hippocampal function and result in cognitive disorders. The mechanisms of B[a]P-induced impairments are complex .To date there have been no studies on the association of epigenetic, transcriptomic, and metabolomic changes with neurotoxicity after B[a]P exposure. In the present study, we investigated the global effect of B[a]P on DNA methylation patterns, noncoding RNAs (ncRNAs) expression, coding RNAs expression, and metabolites in the rat hippocampus. Male Sprague Dawley rats (SD rats) received daily gavage of B[a]P (2.0 mg/kg body weight [BW]) or corn oil for 7 weeks. Learning and memory ability was analyzed using the Morris water maze (MWM) test and change to cellular ultrastructure in the hippocampus was analyzed using electron microscope observation. Integrated analysis of epigenetics, transcriptomics, and metabolomics was conducted to investigate the effect of B[a]P exposure on the signaling and metabolic pathways. Our results suggest that B[a]P could lead to learning and memory deficits, likely as a result of epigenetic and transcriptomic changes that further affected the expression of CACNA1C, Tpo, etc. The changes in expression ultimately affecting LTP, tyrosine metabolism, and other important metabolic pathways.

Effects of the drug combination memantine and melatonin on impaired memory and brain neuronal deficits in an amyloid-predominant mouse model of Alzheimer's disease

Objectives

Alzheimer's disease (AD) is a neurodegenerative disorder with no cure. Limited treatment options available today do not offer solutions to slow or stop any of the suspected causes. The current medications used for the symptomatic treatment of AD include memantine and acetylcholine esterase inhibitors. Some studies suggest that melatonin could also be used in AD patients due to its sleep-improving properties.

Methods

In this study, we evaluated whether a combination of memantine with melatonin, administered for 32 days in drinking water, was more effective than either drug alone with respect to Aβ aggregates, neuroinflammation and cognition in the double transgenic APP/PS1 (5xFAD) mouse model of AD.

Key findings

In this study, chronic administration of memantine with melatonin improved episodic memory in the object recognition test and reduced the number of amyloid aggregates and reactive microgliosis in the brains of 5xFAD mice. Although administration of memantine or melatonin alone also reduced the number of amyloid aggregates and inflammation in brain, this study shows a clear benefit of the drug combination, which had a significantly stronger effect in this amyloid-dominant mouse model of AD.

Conclusion

Our data suggest considerable potential for the use of memantine with melatonin in patients with AD.

Cognitive and emotional alterations in App knock-in mouse models of Aβ amyloidosis

Background

Alzheimer’s disease (AD), the most common cause of dementia, is characterized by the progressive deposition of amyloid-β (Aβ) peptides and neurofibrillary tangles. Mouse models of Aβ amyloidosis generated by knock-in (KI) of a humanized Aβ sequence provide distinct advantages over traditional transgenic models that rely on overexpression of amyloid precursor protein (APP). In App-KI mice, three familial AD-associated mutations were introduced into the endogenous mouse App locus to recapitulate Aβ pathology observed in AD: the Swedish (NL) mutation, which elevates total Aβ production; the Beyreuther/Iberian (F) mutation, which increases the Aβ42/Aβ40 ratio; and the Arctic (G) mutation, which promotes Aβ aggregation. App^NL-G-F mice harbor all three mutations and develop progressive Aβ amyloidosis and neuroinflammatory response in broader brain areas, whereas App^NL mice carrying only the Swedish mutation exhibit no overt AD-related pathological changes. To identify behavioral alterations associated with Aβ pathology, we assessed emotional and cognitive domains of App^NL-G-F and App^NL mice at different time points, using the elevated plus maze, contextual fear conditioning, and Barnes maze tasks.

Results

Assessments of emotional domains revealed that, in comparison with wild-type (WT) C57BL/6J mice, App^{NL-G-F/NL-G-F} mice exhibited anxiolytic-like behavior that was detectable from 6 months of age. By contrast, App^NL/NL mice exhibited anxiogenic-like behavior from 15 months of age. In the contextual fear conditioning task, both App^NL/NL and App^{NL-G-F/NL-G-F} mice exhibited intact learning and memory up to 15–18 months of age, whereas App^{NL-G-F/NL-G-F} mice exhibited hyper-reactivity to painful stimuli. In the Barnes maze task, App^{NL-G-F/NL-G-F} mice exhibited a subtle decline in spatial learning ability at 8 months of age, but retained normal memory functions.

Conclusion

App^NL/NL and App^{NL-G-F/NL-G-F} mice exhibit behavioral changes associated with non-cognitive, emotional domains before the onset of definitive cognitive deficits. Our observations consistently indicate that App^{NL-G-F/NL-G-F} mice represent a model for preclinical AD. These mice are useful for the study of AD prevention rather than treatment after neurodegeneration.

Electronic supplementary material

The online version of this article (10.1186/s12868-018-0446-8) contains supplementary material, which is available to authorized users.

Species-conserved SYNGAP1 phenotypes associated with neurodevelopmental disorders

SYNGAP1 loss-of-function variants are causally associated with intellectual disability, severe epilepsy, autism spectrum disorder and schizophrenia. While there are hundreds of genetic risk factors for neurodevelopmental disorders (NDDs), this gene is somewhat unique because of the frequency and penetrance of loss-of-function variants found in patients combined with the range of brain disorders associated with SYNGAP1 pathogenicity. These clinical findings indicate that SYNGAP1 regulates fundamental neurodevelopmental processes that are necessary for brain development. Here, we describe four phenotypic domains that are controlled by Syngap1 expression across vertebrate species. Two domains, the maturation of cognitive functions and maintenance of excitatory-inhibitory balance, are defined exclusively through a review of the current literature. Two additional domains are defined by integrating the current literature with new data indicating that SYNGAP1/Syngap1 regulates innate survival behaviors and brain structure. These four phenotypic domains are commonly disrupted in NDDs, suggesting that a deeper understanding of developmental Syngap1 functions will be generalizable to other NDDs of known or unknown etiology. Therefore, we discuss the known molecular and cellular functions of Syngap1 and consider how these functions may contribute to the emergence of disease-relevant phenotypes. Finally, we identify major unexplored areas of Syngap1 neurobiology and discuss how a deeper understanding of this gene may uncover general principles of NDD pathobiology.

Disturbances of systemic and hippocampal insulin sensitivity in macrophage migration inhibitory factor (MIF) knockout male mice lead to behavioral changes associated with decreased PSA-NCAM levels

Macrophage migration inhibitory factor (MIF) is a multifunctional cytokine well known for its role in inflammation enhancement. However, a growing body of evidence is emerging on its role in energy metabolism in insulin sensitive tissues such as hippocampus, a brain region implicated in cognition, learning and memory. We hypothesized that genetic deletion of MIF may result in the specific behavioral changes, which may be linked tо impairments in brain or systemic insulin sensitivity by possible changes of the hippocampal synaptic plasticity. To assess memory, exploratory behavior and anxiety, three behavioral tests were applied on Mif gene-deficient (MIF^-/-) and "wild type" C57BL/6J mice (WT). The parameters of systemic and hippocampal insulin sensitivity were also determined. The impact of MIF deficiency on hippocampal plasticity was evaluated by analyzing the level of synaptosomal polysialylated-neural cell adhesion molecule (PSA-NCAM) plasticity marker and mRNA levels of different neurotrophic factors. The results showed that MIF^-/- mice exhibit emphasized anxiety-like behaviors, as well as impaired recognition memory, which may be hippocampus-dependent. This behavioral phenotype was associated with impaired systemic insulin sensitivity and attenuated hippocampal insulin sensitivity, characterized by increased inhibitory Ser³⁰⁷ phosphorylation of insulin receptor substrate 1 (IRS1). Finally, MIF^-/- mice displayed a decreased hippocampal PSA-NCAM level and unchanged Bdnf, NT-3, NT-4 and Igf-1 mRNA levels. The results suggest that the lack of MIF leads to disturbances of systemic and hippocampal insulin sensitivity, which are possibly responsible for memory deficits and anxiety, most likely through decreased PSA-NCAM-mediated neuroplasticity rather than through neurotrophic factors.

Reduced locomotor activity and exploratory behavior in CC chemokine receptor 4 deficient mice

Chemokines and their receptors are key regulators of immune cell trafficking and activation. Recent findings suggest that they may also play pathophysiological roles in psychiatric diseases like depression and anxiety disorders. The CC chemokine receptor 4 (CCR4) and its two ligands, CCL17 and CCL22, are functionally involved in neuroinflammation as well as anti-infectious and autoimmune responses. However, their influence on behavior remains unknown. Here we characterized the functional role of the CCR4-CCL17 chemokine-receptor axis in the modulation of anxiety-related behavior, locomotor activity, and object exploration and recognition. Additionally, we investigated social exploration of CCR4 and CCL17 knockout mice and wild type (WT) controls. CCR4 knockout (CCR4(-/-)) mice exhibited fewer anxiety-related behaviors in the elevated plus-maze, diminished locomotor activity, exploratory behavior, and social exploration, while their recognition memory was not affected. In contrast, CCL17 deficient mice did not show an altered behavior compared to WT mice regarding locomotor activity, anxiety-related behavior, social exploration, and object recognition memory. In the dark-light and object recognition tests, CCL17(-/-) mice even covered longer distances than WT mice. These data demonstrate a mechanistic or developmental role of CCR4 in the regulation of locomotor and exploratory behaviors, whereas the ligand CCL17 appears not to be involved in the behaviors measured here. Thus, either CCL17 and the alternative ligand CCL22 may be redundant, or CCL22 is the main activator of CCR4 in these processes. Taken together, these findings contribute to the growing evidence regarding the involvement of chemokines and their receptors in the regulation of behavior.

Anxiety as a neurodevelopmental disorder in a neuronal subpopulation: Evidence from gene expression data

The relationship between genes and anxious behavior, is nor linear nor monotonic. To address this problem, we analyzed with a meta-analytic method the literature data of the behavior of knockout mice, retrieving 33 genes whose deletion was accompanied by increased anxious behavior, 34 genes related to decreased anxious behavior and 48 genes not involved in anxiety. We correlated the anxious behavior resulting from the deletion of these genes to their brain expression, using the Allen Brain Atlas and Gene Expression Omnibus (GEO) database. The main finding is that the genes accompanied, after deletion, by a modification of the anxious behavior, have lower expression in the cerebral cortex, the amygdala and the ventral striatum. The lower expression level was putatively due to their selective presence in a neuronal subpopulation. This difference was replicated also using a database of human gene expression, further showing that the differential expression pertained, in humans, a temporal window of young postnatal age (4 months up to 4 years) but was not evident at fetal or adult human stages. Finally, using gene enrichment analysis we also show that presynaptic genes are involved in the emergence of anxiety and postsynaptic genes in the reduction of anxiety after gene deletion.

Effects of Npas4 deficiency on anxiety, depression-like, cognition and sociability behaviour

The transcription factor neuronal PAS domain-containing protein 4 (Npas4), which regulates the formation of inhibitory synapses on excitatory neurons, has been suggested as a candidate gene for neurological and psychiatric conditions such as bipolar depression, autism spectrum and cognitive disorders. A mouse model of Npas4 deficiency has been developed to investigate any role in these disorders. Behavioural characterisation of Npas4(-/-), Npas4(+/-) and Npas4(+/+) mice has been conducted using the open field, elevated zero maze (EZM), Y-maze, sociability test and forced swim test (FST) to investigate a range of behaviours. Npas4(-/-) mice spent more time in the open arm of the EZM than other genotypes, suggesting decreased anxiety-like behaviour. Npas4(+/-) mice, however, were more immobile in the FST than other genotypes, suggesting increased depression-like behaviour, and also showed impaired spatial recognition memory in the Y-maze. There were no differences between genotype in social behaviour. These results suggest that differential levels of Npas4 expression in the brain may regulate anxiety, depression and cognition related disorders.

Potential roles of NCAM/PSA-NCAM proteins in depression and the mechanism of action of antidepressant drugs

Recently, it has been proposed that abnormalities in neuronal structural plasticity may underlie the pathogenesis of major depression, resulting in changes in the volume of specific brain regions, including the hippocampus (HIP), the prefrontal cortex (PC), and the amygdala (AMY), as well as the morphology of individual neurons in these brain regions. In the present survey, we compile the data regarding the involvement of the neural cell adhesion molecule (NCAM) protein and its polysialylated form (PSA-NCAM) in the pathogenesis of depression and the mechanism of action of antidepressant drugs (ADDs). Elevated expression of PSA-NCAM may reflect neuroplastic changes, whereas decreased expression implies a rigidification of neuronal morphology and an impedance of dynamic changes in synaptic structure. Special emphasis is placed on the clinical data, genetic models, and the effects of ADDs on NCAM/PSA-NCAM expression in the brain regions in which these proteins are constitutively expressed and neurogenesis is not a major factor; this emphasis is necessary to prevent cell proliferation and neurogenesis from obscuring the issue of brain plasticity.

Effects of chemokine receptor signalling on cognition-like, emotion-like and sociability behaviours of CCR6 and CCR7 knockout mice

Inflammation is regarded as an important mechanism of neuropsychiatric disorders. Chemokines, which are a part of the immune system, have effects on various aspects of brain function, but little is known about their effects on behaviour. We have compared the cognition-like behaviour (learning and spatial memory) of CCR6(-/-) and CCR7(-/-) mice with wild type (WT) C57BL/6 mice, in the Barnes maze, as well as a range of other behaviours, including exploratory, anxiety and depression-like behaviour, using a battery of tests. Levels of cytokines TNF-α, IL-1β and IL-6 were also measured. In the Barnes maze, CCR7(-/-) mice were shown to take longer to learn the location of the escape box on the 1st of 4 days of training. In the behavioural battery, CCR6(-/-) mice showed higher locomotor activity and lower anxiety in the open field test, and a lack of preference for social novelty in a sociability test. CCR7(-/-) mice behaved much like WT mice, although showed higher anxiety in Elevated Zero Maze. While baseline saccharin preference in a 2-bottle choice test, a test for anhedonia depression-like behaviour, was equal in all strains at baseline, weekly tests showed that both CCR6(-/-) and CCR7(-/-) mice developed a decreased preference for saccharin compared to WT over time. There were no differences between strains in any of the cytokines measured. These results suggest that chemokine receptors may play a role in cognition and learning behaviour, as well as anxiety and other behaviours, although the biological mechanisms are still unclear.

Partial reduction in neural cell adhesion molecule (NCAM) in heterozygous mice induces depression-related behaviour without cognitive impairment

The neural cell adhesion molecule (NCAM) plays an important role in brain plasticity. Using mice deficient in all isoforms of NCAM we have previously demonstrated that constitutive deficiency in the NCAM gene (NCAM-/-) resulted in cognitive impairment, anhedonic behaviour and a reduced ability to cope with stress. This was accompanied by reduced basal phosphorylation of the fibroblast growth factor receptor 1 (FGFR1) and reduced phosphorylation of calcium-calmodulin kinase (CaMK) II and IV and cAMP response element binding protein (CREB). The present study was aimed to investigate how partial deficiency in NCAM in mice (NCAM+/-) affected phenotype. We found that NCAM+/- mice showed a longer period of immobility in the tail suspension test, increased latency to feed in the novelty-suppressed feeding test and reduced preference for sucrose in sucrose preference test. Both NCAM+/- and NCAM-/- mice showed reduced extinction of contextual fear. In contrast to NCAM-/- mice, NCAM+/- mice did not demonstrate memory impairment in either object recognition or contextual fear conditioning tests. Levels of phosphorylated FGFR1 in the hippocampus and prefrontal/frontal cortex of NCAM+/- mice were partially reduced and no changes in the phosphorylation of CaMKII, CaMKIV or CREB in the hippocampus were found. We conclude that a constitutive partial reduction in NCAM proteins results in a behavioural phenotype related to depression without impairment in cognitive functions, also affecting the level of FGFR1 phosphorylation without major alterations in CaMKII and CaMKIV intracellular signalling. Partial reduction in FGFR1 phosphorylation might explain the observed behavioural phenotype in NCAM+/- mice.

Polysialylated NCAM and ephrinA/EphA regulate synaptic development of GABAergic interneurons in prefrontal cortex

A novel function for the neural cell adhesion molecule (NCAM) was identified in ephrinA/EphA-mediated repulsion as an important regulatory mechanism for development of GABAergic inhibitory synaptic connections in mouse prefrontal cortex. Deletion of NCAM, EphA3, or ephrinA2/3/5 in null mutant mice increased the numbers and size of perisomatic synapses between GABAergic basket interneurons and pyramidal cells in the developing cingulate cortex (layers II/III). A functional consequence of NCAM loss was increased amplitudes and faster kinetics of miniature inhibitory postsynaptic currents in NCAM null cingulate cortex. NCAM and EphA3 formed a molecular complex and colocalized with the inhibitory presynaptic marker vesicular GABA transporter (VGAT) in perisomatic puncta and neuropil in the cingulate cortex. EphrinA5 treatment promoted axon remodeling of enhanced green fluorescent protein-labeled basket interneurons in cortical slice cultures and induced growth cone collapse in wild-type but not NCAM null mutant neurons. NCAM modified with polysialic acid (PSA) was required to promote ephrinA5-induced axon remodeling of basket interneurons in cortical slices, likely by providing a permissive environment for ephrinA5/EphA3 signaling. These results reveal a new mechanism in which NCAM and ephrinAs/EphA3 coordinate to constrain GABAergic interneuronal arborization and perisomatic innervation, potentially contributing to excitatory/inhibitory balance in prefrontal cortical circuitry.

Transgenic mice overexpressing the extracellular domain of NCAM are impaired in working memory and cortical plasticity

The neural cell adhesion molecule, NCAM, is a pivotal regulator of neural development, with key roles in axonal and dendritic growth and synaptic plasticity. Alterations in NCAM expression or proteolytic cleavage have been linked to human neuropsychiatric disorders such as schizophrenia, bipolar disorder and Alzheimer's disease, and may contribute to cognitive dysfunction. We have generated mice overexpressing the NCAM extracellular (EC) proteolytic cleavage fragment which has been reported to be increased in schizophrenic versus normal brains. These mice show impaired GABAergic innervation and reduced number of apical dendritic spines on pyramidal neurons in the prefrontal cortex (PFC). Here, these NCAM-EC transgenic mice were subjected to behavioral tasks and electrophysiological measurements to determine the impact of structural abnormalities in the PFC on synaptic and cognitive functions. NCAM-EC mice exhibited impaired working memory in a delayed non-match-to-sample task, which requires PFC function, but showed no differences in anxiety, olfactory abilities, or sociability. Transgenic mice displayed impaired long- and short-term potentiation in the PFC but normal synaptic plasticity in the hippocampus, suggesting that the abnormal synaptic innervation in NCAM-EC mice impairs PFC plasticity and alters working memory. These findings may have implications for cognitive dysfunctions observed in neuropsychiatric disorders.

Decision-making performance is related to levels of anxiety and differential recruitment of frontostriatal areas in male rats

In humans, high levels of anxiety are associated with poor performance in the Iowa Gambling Task (IGT). The IGT measures decision-making under conditions of uncertainty. In this study, we investigated the association between anxiety and decision-making in rats. Rats were screened for anxiety on the elevated plus maze (EPM) and subsequently tested in a rat analogue of the IGT (r-IGT). We explored the role of frontostriatal areas related to r-IGT performance using c-fos immunohistochemistry following the last training-session. High levels of anxiety were associated with poor r-IGT performance: high anxious rats made fewer choices for the advantageous option and collected fewer sucrose pellets in the r-IGT than low anxious rats. Analysis of win-stay/lose-shift behaviour of choices for the advantageous option revealed that good performing-low anxious subjects showed an increase in win-stays and a decrease in lose-shifts across trial blocks while poor performing-high anxious subjects did not. Furthermore, decision-making performance and, indirectly, anxiety levels were related to neural activity in parts of the medial prefrontal cortex, that is prelimbic and infralimbic cortex, and in parts of the striatum, that is nucleus accumbens shell and core. These data suggest a similar frontostriatal circuitry underlying affective decision-making in humans and rats.