Reduced expression of PSA-NCAM in the hippocampus and piriform cortex of the R6/1 and R6/2 mouse models of Huntington's disease

Neuroplastic alterations in cannabinoid receptors type 1 (CB1) in animal models of epileptic seizures

Currently, there is an urgent need to better comprehend neuroplastic alterations in cannabinoid receptors type 1 (CB1) and to understand the biological meaning of these alterations in epileptic disorders. The present study reviewed neuroplastic changes in CB1 distribution, expression, and functionality in animal models of epileptic seizures. Neuroplastic alterations in CB1 were consistently observed in chemical, genetic, electrical, and febrile seizure models. Most studies assessed changes in hippocampal and cortical CB1, while thalamic, hypothalamic, and brainstem nuclei were rarely investigated. Additionally, the relationship between CB1 alteration and the control of brain excitability through modulation of specific neuronal networks, such as striatonigral, nigrotectal and thalamocortical pathways, and inhibitory projections to hippocampal pyramidal neurons, were all presented and discussed in the present review. Neuroplastic alterations in CB1 detected in animal models of epilepsy may reflect two different scenarios: (1) endogenous adaptations aimed to control neuronal hyperexcitability in epilepsy or (2) pathological alterations that facilitate neuronal hyperexcitability. Additionally, a better comprehension of neuroplastic and functional alterations in CB1 can improve pharmacological therapies for epilepsies and their comorbidities.

Early life stress and brain plasticity: from molecular alterations to aberrant memory and behavior

Early life stress (ELS) is one of the most critical factors that could modify brain plasticity, memory and learning abilities, behavioral reactions, and emotional response in adulthood leading to development of different mental disorders. Prenatal and early postnatal periods appear to be the most sensitive periods of brain development in mammals, thereby action of various factors at these stages of brain development might result in neurodegeneration, memory impairment, and mood disorders at later periods of life. Deciphering the processes underlying aberrant neurogenesis, synaptogenesis, and cerebral angiogenesis as well as deeper understanding the effects of ELS on brain development will provide novel approaches to prevent or to cure psychiatric and neurological deficits caused by stressful conditions at the earliest stages of ontogenesis. Neuropeptide oxytocin serves as an amnesic, anti-stress, pro-angiogenic, and neurogenesis-controlling molecule contributing to dramatic changes in brain plasticity in ELS. In the current review, we summarize recent data on molecular mechanisms of ELS-driven changes in brain plasticity with the particular focus on oxytocin-mediated effects on neurogenesis and angiogenesis, memory establishment, and forgetting.

Polysialylation and disease

Polysialic acid (polySia, PSA) is a unique constituent of the glycocalyx on the surface of bacterial and vertebrate cells. In vertebrates, its biosynthesis is highly regulated, not only in quantity and quality, but also in time and location, which allows polySia to be involved in various important biological phenomena. Therefore, impairments in the expression and structure of polySia sometimes relate to diseases, such as schizophrenia, bipolar disorder, and cancer. Some bacteria express polySia as a tool for protecting themselves from the host immune system during invasion. PolySia is proven to be a biosafe material; polySia, as well as polySia-recognizing molecules, are key therapeutic agents. This review first comprehensive outlines the occurrence, features, biosynthesis, and functions of polySia and subsequently focuses on the related diseases.

Early deficits in olfaction are associated with structural and molecular alterations in the olfactory system of a Huntington disease mouse model

Olfactory dysfunction and altered neurogenesis are observed in several neurodegenerative disorders including Huntington disease (HD). These deficits occur early and correlate with a decline in global cognitive performance, depression and structural abnormalities of the olfactory system including the olfactory epithelium, bulb and cortices. However, the role of olfactory system dysfunction in the pathogenesis of HD remains poorly understood and the mechanisms underlying this dysfunction are unknown. We show that deficits in odour identification, discrimination and memory occur in HD individuals. Assessment of the olfactory system in an HD murine model demonstrates structural abnormalities in the olfactory bulb (OB) and piriform cortex, the primary cortical recipient of OB projections. Furthermore, a decrease in piriform neuronal counts and altered expression levels of neuronal nuclei and tyrosine hydroxylase in the OB are observed in the YAC128 HD model. Similar to the human HD condition, olfactory dysfunction is an early phenotype in the YAC128 mice and concurrent with caspase activation in the murine HD OB. These data provide a link between the structural olfactory brain region atrophy and olfactory dysfunction in HD and suggest that cell proliferation and cell death pathways are compromised and may contribute to the olfactory deficits in HD.

The Role of Hypothalamic Pathology for Non-Motor Features of Huntington's Disease

 Huntington’s disease (HD) is a fatal genetic neurodegenerative disorder. It has mainly been considered a movement disorder with cognitive symptoms and these features have been associated with pathology of the striatum and cerebral cortex. Importantly, individuals with the mutant huntingtin gene suffer from a spectrum of non-motor features often decades before the motor disorder manifests. These symptoms and signs include a range of psychiatric symptoms, sleep problems and metabolic changes with weight loss particularly in later stages. A higher body mass index at diagnosis is associated with slower disease progression. The common psychiatric symptom of apathy progresses with the disease. The fact that non-motor features are present early in the disease and that they show an association to disease progression suggest that unravelling the underlying neurobiological mechanisms may uncover novel targets for early disease intervention and better symptomatic treatment. The hypothalamus and the limbic system are important brain regions that regulate emotion, social cognition, sleep and metabolism. A number of studies using neuroimaging, postmortem human tissue and genetic manipulation in animal models of the disease has collectively shown that the hypothalamus and the limbic system are affected in HD. These findings include the loss of neuropeptide-expressing neurons such as orexin (hypocretin), oxytocin, vasopressin, somatostatin and VIP, and increased levels of SIRT1 in distinct nuclei of the hypothalamus. This review provides a summary of the results obtained so far and highlights the potential importance of these changes for the understanding of non-motor features in HD.

FGF2 and dual agonist of NCAM and FGF receptor 1, Enreptin, rescue neurite outgrowth loss in hippocampal neurons expressing mutated huntingtin proteins

In the present study, we developed an in vitro model of Huntington disease (HD) by transfecting primary rat hippocampal neurons with plasmids coding for m-htt exon 1 with different number of CAG repeats (18, 50 and 115) and demonstrated the influence of the length of polyQ sequence on neurite elongation. We found that exogenously applied FGF2 significantly rescued the m-htt-induced loss of neurite outgrowth. Moreover, the Enreptin peptide, an FGFR1 and NCAM dual agonist, had a similar neuritogenic effect to FGF2 in clinically relevant m-htt 50Q-expressing neurons. This study has developed an in vitro model of primary hippocampal neurons transfected with m-htt-coding vectors that is a powerful tool to study m-htt-related effects on neuronal placticity.

Animal models of olfactory dysfunction in neurodegenerative diseases

Olfactory dysfunction seems to occur earlier than classic motor and cognitive symptoms in many neurodegenerative diseases, including Parkinson's disease (PD) and Alzheimer's disease (AD). Thus, the use of the olfactory system as a clinical marker for neurodegenerative diseases is helpful in the characterization of prodromal stages of these diseases, early diagnostic strategies, differential diagnosis, and, potentially, prediction of treatment success. The use of genetic and neurotoxin animal models has contributed to the understanding of the mechanisms underlying olfactory dysfunction in a number of neurodegenerative diseases. In this chapter, we provide an overview of behavioral and neurochemical alterations observed in animal models of different neurodegenerative diseases (such as genetic and Aβ infusion models for AD and neurotoxins and genetic models of PD), in which olfactory dysfunction has been described.

Inhibition of DREAM-ATF6 interaction delays onset of cognition deficit in a mouse model of Huntington's disease

The transcriptional repressor DREAM (downstream regulatory element antagonist modulator) is a multifunctional neuronal calcium sensor (NCS) that controls Ca²⁺ and protein homeostasis through gene regulation and protein-protein interactions. Downregulation of DREAM is part of an endogenous neuroprotective mechanism that improves ATF6 (activating transcription factor 6) processing, neuronal survival in the striatum, and motor coordination in R6/2 mice, a model of Huntington’s disease (HD). Whether modulation of DREAM activity can also ameliorate cognition deficits in HD mice has not been studied. Moreover, it is not known whether DREAM downregulation in HD is unique, or also occurs for other NCS family members. Using the novel object recognition test, we show that chronic administration of the DREAM-binding molecule repaglinide, or induced DREAM haplodeficiency delays onset of cognitive impairment in R6/1 mice, another HD model. The mechanism involves a notable rise in the levels of transcriptionally active ATF6 protein in the hippocampus after repaglinide administration. In addition, we show that reduction in DREAM protein in the hippocampus of HD patients was not accompanied by downregulation of other NCS family members. Our results indicate that DREAM inhibition markedly improves ATF6 processing in the hippocampus and that it might contribute to a delay in memory decline in HD mice. The mechanism of neuroprotection through DREAM silencing in HD does not apply to other NCS family members.

In vivo imaging of brain glutamate defects in a knock-in mouse model of Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative disease characterized by motor, cognitive and psychiatric symptoms. Atrophy of the striatum has been proposed for several years as a biomarker to assess disease progression in HD gene carriers. However, it does not provide any information about the biological mechanisms linked to HD pathogenesis. Changes in brain metabolites have been also consistently seen in HD patients and animal models using Magnetic Resonance Spectroscopy (MRS), but metabolite measurements are generally limited to a single voxel. In this study, we used Chemical Exchange Saturation Transfer imaging of glutamate (gluCEST) in order to map glutamate distribution in the brain of a knock-in mouse model (Ki140CAG) with a precise anatomical resolution. We demonstrated that both heterozygous and homozygous mice with pathological CAG repeat expansion in gene encoding huntingtin exhibited an atrophy of the striatum and a significant alteration of their metabolic profile in the striatum as compared to wild type littermate controls. The striatal decrease was then confirmed by gluCEST imaging. Surprisingly, CEST imaging also revealed that the corpus callosum was the most affected structure in both genotype groups, suggesting that this structure could be highly vulnerable in HD. We evaluated for the first time gluCEST imaging as a potential biomarker of HD and demonstrated its potential for characterizing metabolic defects in neurodegenerative diseases in specific regions.

Changes in Dopamine Signalling Do Not Underlie Aberrant Hippocampal Plasticity in a Mouse Model of Huntington's Disease

Altered dopamine receptor labelling has been demonstrated in presymptomatic and symptomatic Huntington's disease (HD) gene carriers, indicating that alterations in dopaminergic signalling are an early event in HD. We have previously described early alterations in synaptic transmission and plasticity in both the cortex and hippocampus of the R6/1 mouse model of Huntington's disease. Deficits in cortical synaptic plasticity were associated with altered dopaminergic signalling and could be reversed by D1- or D2-like dopamine receptor activation. In light of these findings we here investigated whether defects in dopamine signalling could also contribute to the marked alteration in hippocampal synaptic function. To this end we performed dopamine receptor labelling and pharmacology in the R6/1 hippocampus and report a marked, age-dependent elevation of hippocampal D1 and D2 receptor labelling in R6/1 hippocampal subfields. Yet, pharmacological inhibition or activation of D1- or D2-like receptors did not modify the aberrant synaptic plasticity observed in R6/1 mice. These findings demonstrate that global perturbations to dopamine receptor expression do occur in HD transgenic mice, similarly in HD gene carriers and patients. However, the direction of change and the lack of effect of dopaminergic pharmacological agents on synaptic function demonstrate that the perturbations are heterogeneous and region-specific, a finding that may explain the mixed results of dopamine therapy in HD.

Distinctive PSA-NCAM and NCAM hallmarks in glutamate-induced dendritic atrophy and synaptic disassembly

Dendritic and synapse remodeling are forms of structural plasticity that play a critical role in normal hippocampal function. Neural cell adhesion molecule (NCAM) and its polysialylated form (PSA-NCAM) participate in neurite outgrowth and synapse formation and plasticity. However, it remains unclear whether they contribute to dendritic retraction and synaptic disassembly. Cultured hippocampal neurons exposed to glutamate (5 µM) showed a reduced MAP-2 (+) area in the absence of neuronal death 24 h after the insult. Concomitantly, synapse loss, revealed by decreased synaptophysin and post-synaptic density-95 cluster number and area, together with changes in NCAM and PSA-NCAM levels were found. Dendritic atrophy and PSA-NCAM reduction proved NMDA-receptor dependent. Live-imaging experiments evidenced dendritic atrophy 4 h after the insult; this effect was preceded by smaller NCAM clusters (1 h) and decreased surface and total PSA-NCAM levels (3 h). Simultaneously, total NCAM cluster number and area remained unchanged. The subsequent synapse disassembly (6 h) was accompanied by reductions in total NCAM cluster number and area. A PSA mimetic peptide prevented both the dendritic atrophy and the subsequent synaptic changes (6 h) but had no effect on the earliest synaptic remodeling (3 h). Thus, NCAM-synaptic reorganization and PSA-NCAM level decrease precede glutamate-induced dendritic atrophy, whereas the NCAM level reduction is a delayed event related to synapse loss. Consequently, distinctive stages in PSA-NCAM/NCAM balance seem to accompany glutamate-induced dendritic atrophy and synapse loss.

Novel ethological endophenotypes in a transgenic mouse model of Huntington's disease

Huntington's disease (HD) is an autosomal dominant, neurodegenerative disorder with a characteristic triad of cognitive, affective and motor symptoms. Transgenic HD mice show excellent construct and face validity for many of these symptoms, however the decline in some facets of every day activity in humans is difficult to model. One approach is the assessment of species-relevant behaviors. Here we described three ethologically appropriate tests in the mouse-olfactory sensitivity, nest-building and sexually-motivated vocalizations. In R6/1 HD mice, olfactory and nest-building tests were sensitive to early dysfunctions induced by the HD mutation. Male vocalization testing revealed a late-stage sexual disinterest in R6/1 HD mice compared to WT littermates. We show that essential, species-relevant functions are disrupted by the HD mutation. The development of integrative behavioral assays which more closely model 'activities of daily living' (ADL) will facilitate the testing of novel therapeutic interventions in animal models as well as their clinical translation.

Neurogenesis in neurological and psychiatric diseases and brain injury: from bench to bedside

Researchers who have uncovered the presence of stem cells in an adult's central nervous system have not only challenged the dogma that new neurons cannot be generated during adulthood, but also shed light on the etiology and disease mechanisms underlying many neurological and psychiatric disorders. Brain trauma, neurodegenerative diseases, and psychiatric disorders pose enormous burdens at both personal and societal levels. Although medications for these disorders are widely used, the treatment mechanisms underlying the illnesses remain largely elusive. In the past decade, an increasing amount of evidence indicate that adult neurogenesis (i.e. generating new CNS neurons during adulthood) may be involved in the pathology of different CNS disorders, and thus neurogenesis may be a potential target area for treatments. Although new neurons were shown to be a major player in mediating treatment efficacy of neurological and psychotropic drugs on cognitive functions, it is still debatable if the altered production of new neurons can cause the disorders. This review hence seeks to discuss pre and current clinical studies that demonstrate the functional impact adult neurogenesis have on neurological and psychiatric illnesses while examining the related underlying disease mechanisms.

Significance of the cell adhesion molecules and sialic acid in neurodegeneration

The central nervous system (CNS) is a complex and precise mechanism that controls the most highest functions of the body. All of them depend on the cellular and molecular interactions called by neurobiologists "cellular plasticity". The CNS is a flexible structure but its regeneration after damage is strongly limited. Better understanding of cellular and molecular basis of brain repair can open new way in the development of therapeutic tools for neurodegeneration. Among many molecules that participate in the formation of neuronal networks, neural cell adhesion molecule (NCAM) and its sialylated derivative seem to play crucial role in the life of brain. In particular, polysialylated cell adhesion molecule (PSA-NCAM) is proposed to participate in the neuroprotective response in neurodegeneration by reducing of AMPA/NMDA receptors sensitivity to glutamate and facilitating disconnection of cell-cell interactions. These mechanisms protect from excitotoxic damage and promote dendritic/spine re-growth. This review briefly focuses on the expression and role of PSA-NCAM in neurodegenerative diseases and its potential application in therapy.

The effect of PTZ-induced epileptic seizures on hippocampal expression of PSA-NCAM in offspring born to kindled rats

BACKGROUND

Maternal epileptic seizures during pregnancy can affect the hippocampal neurons in the offspring. The polysialylated neural cell adhesion molecule (PSA-NCAM), which is expressed in the developing central nervous system, may play important roles in neuronal migration, synaptogenesis, and axonal outgrowth. This study was designed to assess the effects of kindling either with or without maternal seizures on hippocampal PSA-NCAM expression in rat offspring.

METHODS

Forty timed-pregnant Wistar rats were divided into four groups: A) Kind+/Seiz+, pregnant kindled (induced two weeks prior to pregnancy) rats that received repeated intraperitoneal (i.p.) pentylenetetrazol, PTZ injections on gestational days (GD) 14-19; B) Kind-/Seiz+, pregnant non-kindled rats that received PTZ injections on GD14-GD19; C) Kind+/Seiz-, pregnant kindled rats that did not receive any PTZ injections; and D) Kind-/Seiz-, the sham controls. Following birth, the pups were sacrificed on PD1 and PD14, and PSA-NCAM expression and localization in neonates' hippocampi were analyzed by Western blots and immunohistochemistry.

RESULTS

Our data show a significant down regulation of hippocampal PSA-NCAM expression in the offspring of Kind+/Seiz+ (p = 0.001) and Kind-/Seiz+ (p = 0.001) groups compared to the sham control group. The PSA-NCAM immunoreactivity was markedly decreased in all parts of the hippocampus, especially in the CA3 region, in Kind+/Seiz+ (p = 0.007) and Kind-/Seiz+ (p = 0.007) group's newborns on both PD1 and 14.

CONCLUSION

Our findings demonstrate that maternal seizures but not kindling influence the expression of PSA-NCAM in the offspring's hippocampi, which may be considered as a factor for learning/memory and cognitive impairments reported in children born to epileptic mothers.

New scenarios for neuronal structural plasticity in non-neurogenic brain parenchyma: the case of cortical layer II immature neurons

The mammalian central nervous system, due to its interaction with the environment, must be endowed with plasticity. Conversely, the nervous tissue must be substantially static to ensure connectional invariability. Structural plasticity can be viewed as a compromise between these requirements. In adult mammals, brain structural plasticity is strongly reduced with respect to other animal groups in the phylogenetic tree. It persists under different forms, which mainly consist of remodeling of neuronal shape and connectivity, and, to a lesser extent, the production of new neurons. Adult neurogenesis is mainly restricted within two neurogenic niches, yet some gliogenic and neurogenic processes also occur in the so-called non-neurogenic tissue, starting from parenchymal progenitors. In this review we focus on a population of immature, non-newly generated neurons in layer II of the cerebral cortex, which were previously thought to be newly generated since they heavily express the polysialylated form of the neural cell adhesion molecule and doublecortin. These unusual neurons exhibit characteristics defining an additional type of structural plasticity, different from either synaptic plasticity or adult neurogenesis. Evidences concerning their morphology, antigenic features, ultrastructure, phenotype, origin, fate, and reaction to different kind of stimulations are gathered and analyzed. Their possible role is discussed in the context of an enriched complexity and heterogeneity of mammalian brain structural plasticity.

Morphometrical study of polysialylated neural cell adhesion molecule positive cells in rat pups hippocampus following induction of seizure during pregnancy

BACKGROUND

The polysialylated neural cell adhesion molecule (PSA-NCAM) is expressed in developing brain. Fetal brain damage is caused by different conditions such as seizure and hypoxia. The present study was designed to investigate the effect of maternal seizures on the number of PSA-NCAM positive cells in pup's hippocampus.

METHODS

Female Wistar rats were divided into four groups: (a) kindled rats which received PTZ (40 mg/kg, i.p.) during pregnancy from embryonic day 14-19 (E14-E19) every 48 h, (b) kindled rats which did not receive PTZ during pregnancy, (c) non-kindle, pregnant rats which received PTZ injection (40 mg/kg, i.p.) during pregnancy from E14 to E19 every 48 h, and (d) non-kindle, pregnant rats which received injection with an equal volume of normal saline as sham controls. At postnatal day 14 (PD14), rat pups were perfused, and their brain were fixed, embedded and coronal sections stained by immunohistochemistry method. The number of PSA-NCAM positive cells per unit area in the pup's hippocampus was counted.

RESULTS

The number of PSA-NCAM positive cells in the CA1, CA3, and DG fields of pup's hippocampus, which was obtained from mothers who experienced PTZ injection during pregnancy, was decreased approximately 2.6 (P = 0.001), 2 (P = 0.001), and 2.1 (P = 0.001) times compared with non-PTZ treated maternal groups, respectively.

CONCLUSIONS

Our study showed that maternal seizures reduced the number of neurons and also PSA-NCAM positive cells per unit area in the offspring hippocampus that it may cause impairment in hippocampal functions.

Neurogenesis in the R6/2 mouse model of Huntington's disease is impaired at the level of NeuroD1

Adult neurogenesis is impaired in the hippocampus of transgenic R6 mouse models of Huntington's disease (HD). The phenotypes of R6 transgenic mice mimic several symptoms and signs of the disease (Li et al., 2005). They exhibit neurological and endocrine changes resembling some symptoms seen in humans. The reduction in neurogenesis is only apparent in the dentate gyrus as the number of newborn neurons in the subventricular zone, and olfactory bulb, is normal in R6 mice. The mechanism(s) underlying the reduction in hippocampal neurogenesis is still not fully understood. Here we show that the number of neuroblasts, but not granule neuron progenitors, is greatly reduced in 11-week old transgenic mice compared with wild-type (WT) controls. We demonstrate that NeuroD1 expression is reduced in the hippocampus. This is coupled to a decreased expression of downstream markers doublecortin and calretinin in maturing neurons. Taken together, our results suggest that mutant huntingtin (Htt) causes alterations of proteins expression in hippocampal progenitors, which might contribute to cognitive deficits in Huntington's disease.

Age-dependent effect of prenatal stress on hippocampal cell proliferation in female rats

Stressors occurring during pregnancy can alter the developmental trajectory of offspring and lead to, among other deleterious effects, cognitive deficits and hyperactivity of the hypothalamo-pituitary-adrenal axis. A recent feature of the prenatal stress (PS) model is its reported influence on structural plasticity in hippocampal formation, which sustains both cognitive functions and stress responsiveness. Indeed, we and others have previously reported that males exposed to stress in utero are characterized by a decrease in hippocampal cell proliferation, and consequently neurogenesis, from adolescence to senescence. Recent studies in females submitted to PS have reported conflicting results, ranging from no effect to a decrease in cell proliferation. We hypothesized that changes in cell proliferation in PS female rats are age dependent. To address this issue, we examined the impact of PS on hippocampal cell proliferation in juvenile, young, middle-aged and old females. As hypothesized, we found an age-dependent effect of PS in female rats as cell proliferation was significantly decreased only when animals reached senescence, a time when adrenal gland weight also increased. These data suggest that the deleterious effects of PS on hippocampal cell proliferation in females are either specific to senescence or masked during adulthood by protective factors.

DCX and PSA-NCAM expression identifies a population of neurons preferentially distributed in associative areas of different pallial derivatives and vertebrate species

In adult rodents, doublecortin (DCX) and polysialylated neural cell adhesion molecule (PSA-NCAM) expression is mostly restricted to newly generated neurons. These molecules have also been described in prenatally generated cells of the piriform cortex and, to a lesser extent, neocortex (NC) of the rat. In addition, PSA-NCAM+ cells have been identified in several telencephalic regions of the lizard. Here, through immunohistochemistry and 3-dimensional reconstruction, we have investigated distribution, morphology, and phenotype of DCX/PSA-NCAM-expressing cells in the pallium of different mammals and in lizard. In all species, a population of nonnewly-generated pallial DCX+/PSA-NCAM+ cells shows common morphological and phenotypic characteristics, including expression of Tbr-1, a transcription factor expressed in pallial projection neurons, and preferential distribution in associative areas. In the guinea pig and rabbit, DCX+/PSA-NCAM+ elements are also abundant in the NC, particularly in areas implicated in nonspatial learning and memory networks. In reptiles, DCX+/PSA-NCAM+ cells are located in the lateral and medial cortex and dorsal ventricular ridge but not in the dorsal cortex. These data support the fact that coexpression of DCX+/PSA-NCAM+/Tbr-1+ in the adult brain identifies evolutionary conserved cell populations shared by different pallial derivatives including the mammalian NC.

Lack of association between PSA-NCAM expression and migration in the rostral migratory stream of a Huntington's disease transgenic mouse model

Huntington's disease is a neurodegenerative autosomal disorder characterized by selective loss of striatal and cortical neurons. The mammalian brain subventricular zone contains a population of neural precursors involved in postnatal neurogenesis. These newly generated cells migrate from the subventricular zone along the rostral migratory stream and differentiate into mature olfactory bulb neurons throughout adulthood. The establishment of this pathway depends upon a variety of molecules, including polysialylated neural cell adhesion molecule (PSA-NCAM). We used a murine model of Huntington's disease, the R6/2 transgenic mouse, and in vivo bromodeoxyuridine administration to label cells undergoing proliferation and to follow their migration along the rostral migratory stream. Bromodeoxyuridine labeling did not show any significant increase in proliferation of progenitor cells in symptomatic R6/2 mice, but migration of neuroblasts along the rostral migratory stream was significantly diminished. The decrease in neuroblast migration was not due to an alteration in the expression of PSA-NCAM along the rostral migratory stream since immunohistochemical analysis showed no significant differences between R6/2 and wild type mice. In addition, we used Fluoro-Jade C to evaluate apoptosis and demonstrated that the number of apoptotic cells in the rostral migratory stream is similar in affected and wild type animals, suggesting that cell death is not responsible for the differences observed in neuroblast migration. We conclude that in R6/2 mice, progenitor cells have an impaired migration in their route to the olfactory bulb, with accumulation of cells in the caudal rostral migratory stream that does not result from changes in PSA-NCAM expression and/or cell death.

Doublecortin-expressing cells are present in layer II across the adult guinea pig cerebral cortex: partial colocalization with mature interneuron markers

Doublecortin-immunoreactive (DCX+) cells were detected across the allo- and neo-cortical regions in the adult guinea pig cerebrum, localized to layer II specifically at its border with layer I. The density of labeled cells declined with age, whereas no apparent apoptotic activity was detectable over the cortex including layer II. DCX+ cells varied in somal size, labeling intensity, nuclear appearance, and complexity of processes. These cells were often arranged in clusters with cells of similar morphology sometimes packed tightly together. They exhibited complete colocalization with polysialylated neural cell adhesion molecule (PSA-NCAM) and neuron-specific type III beta-tubulin (TuJ1). Medium to large-sized DCX+ cells had well-developed neuritic processes, and expressed neuron-specific nuclear protein (NeuN). Large mature-looking cells with weak DCX reactivity invariably displayed heavy NeuN reactivity, implicating a transitional stage of these labeled cells. These "transitional" cells also consistently exhibited weak reactivity for gamma-aminobutyric acid (GABA), glutamate decarboxylase (GAD67), beta-nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) and neuronal nitric oxide synthase (nNOS), suggestive of them being young GABAergic/nitrinergic interneurons. Our data indicate that DCX+ cells exist widely in the adult guinea pig cerebral cortex, with a predominant localization in upper layer II. The morphological variation and differential expression of neuronal markers in these cells implicate that they might be developing neurons, and that they are probably differentiating into GABAergic interneurons. This population of cells might be involved in interneuron plasticity in the adult mammalian cerebral cortex.

Deficiency of neural cell adhesion molecule or its polysialylation modulates pharmacological effects of the AMPA receptor antagonist NBQX

The neural cell adhesion molecule NCAM and its dynamically regulated posttranslational modification polysialic acid (PSA) are major determinants of cellular interactions during ontogeny. While NCAM in the absence of PSA stabilizes cell-cell interactions, the attachment of the large and polyanionic PSA negatively influences cell adhesion and promotes plasticity. Disease-associated changes in the polysialylation state of NCAM raise the question whether the PSA-NCAM system can affect CNS pharmacology. Here we investigated the pharmacological effects of the competitive AMPA antagonist NBQX in genetic mouse models either lacking NCAM and PSA (female NCAM knockout mice) or being drastically reduced in the level of PSA expression (female ST8SiaIV knockout mice). Studies were carried out with the respective wildtype littermate controls. In mice lacking NCAM and PSA, NBQX-induced ataxia proved to be more intense as compared with wild-type mice. On both mutant backgrounds, NBQX significantly elevated seizure thresholds during i.v. infusion of the chemoconvulsant pentylenetetrazole. In summary, the data demonstrate that the PSA-NCAM system impacts AMPA receptor pharmacology under in vivo conditions. The fact that comparable effects were observed in NCAM- and ST8SiaIV-knockout mice indicates that this impact is not due to a stabilizing effect of NCAM in the absence of PSA. Thus, disease-related changes in the polysialylation of NCAM are likely to be associated with effects on the efficacy and tolerability of AMPA receptor antagonists.