Polysialylated Form Of Neural Cell Adhesion Molecule Research Articles

Thiamine and benfotiamine counteract ultrasound-induced aggression, normalize AMPA receptor expression and plasticity markers, and reduce oxidative stress in mice

The negative societal impacts associated with the increasing prevalence of violence and aggression is increasing, and, with this rise, is the need to understand the molecular and cellular changes that underpin ultrasound-induced aggressive behavior. In mice, stress-induced aggression is known to alter AMPA receptor subunit expression, plasticity markers, and oxidative stress within the brain. Here, we induced aggression in BALB/c mice using chronic ultrasound exposure and examined the impact of the psychoactive anti-oxidant compounds thiamine (vitamin B1), and its derivative benfotiamine, on AMPA receptor subunit expression, established plasticity markers, and oxidative stress. The administration of thiamine or benfotiamine (200 mg/kg/day) in drinking water decreased aggressive behavior following 3-weeks of ultrasound exposure and benfotiamine, reduced floating behavior in the swim test. The vehicle-treated ultrasound-exposed mice exhibited increases in protein carbonyl and total glutathione, altered AMPA receptor subunits expression, and decreased expression of plasticity markers. These ultrasound-induced effects were ameliorated by thiamine and benfotiamine treatment; in particular both antioxidants were able to reverse ultrasound-induced changes in GluA1 and GluA2 subunit expression, and, within the prefrontal cortex, significantly reversed the changes in protein carbonyl and polysialylated form of neural cell adhesion molecule (PSA-NCAM) expression levels. Benfotiamine was usually more efficacious than thiamine. Thus, the thiamine compounds were able to counteract ultrasound-induced aggression, which was accompanied by the normalization of markers that have been showed to be associated with ultrasound-induced aggression. These commonly used, orally-active compounds may have considerable potential for use in the control of aggression within the community.This article is part of the Special Issue entitled ‘Current status of the neurobiology of aggression and impulsivity’.

G-CSF improves CUMS-induced depressive behaviors through downregulating Ras/ERK/MAPK signaling pathway

Neuronal plasticity in hippocampal neurons is closely related to memory, mood and behavior as well as in the development of depression. Granulocyte colony-stimulating factor (G-CSF) can promote neuronal plasticity and enhance motor skills. However, the function of G-CSF in depression remains poorly understood. In this study, we explored the biological role and potential molecular mechanism of G-CSF on depression-like behaviors. Our results showed that G-CSF was significantly downregulated in the hippocampus of chronic unexpected mild stress (CUMS) rats. Administration of G-CSF significantly reversed CUMS-induced depression-like behaviors in the open field test (OFT), sucrose preference test (SPT) and forced swimming test (FST). Moreover, G-CSF upregulated the expression of synaptic-associated proteins including polysialylated form of neural cell adhesion molecule (PSA-NCAM), synaptophysin (SYN), and postsynaptic density protein 95 (PSD-95) in the hippocampus and G-CSF significantly increased cell viability rate of hippocampal neurons in vitro. Further studies indicated that the renin-angiotensin system (Ras)/extracellular signal-regulated kinase (ERK)/p38 mitogen-activated protein kinase (MAPK) signaling pathways was involved in the regulation of G-CSF on depressive-like behaviors and neuronal plasticity in CUMS rats. Taken together, our results showed that G-CSF improves depression-like behaviors via inhibiting Ras/ERK/MAPK signaling pathways. Our study suggests that G-CSF may be a promising therapeutic strategy for the treatment of depression.

Characterization and isolation of immature neurons of the adult mouse piriform cortex.

Physiological studies indicate that the piriform or primary olfactory cortex of adult mammals exhibits a high degree of synaptic plasticity. Interestingly, a subpopulation of cells in the layer II of the adult piriform cortex expresses neurodevelopmental markers, such as the polysialylated form of neural cell adhesion molecule (PSA-NCAM) or doublecortin (DCX). This study analyzes the nature, origin, and potential function of these poorly understood cells in mice. As previously described in rats, most of the PSA-NCAM expressing cells in layer II could be morphologically classified as tangled cells and only a small proportion of larger cells could be considered semilunar-pyramidal transitional neurons. Most were also immunoreactive for DCX, confirming their immature nature. In agreement with this, detection of PSA-NCAM combined with that of different cell lineage-specific antigens revealed that most PSA-NCAM positive cells did not co-express markers of glial cells or mature neurons. Their time of origin was evaluated by birthdating experiments with halogenated nucleosides performed at different developmental stages and in adulthood. We found that virtually all cells in this paleocortical region, including PSA-NCAM-positive cells, are born during fetal development. In addition, proliferation analyses in adult mice revealed that very few cells were cycling in layer II of the piriform cortex and that none of them was PSA-NCAM-positive. Moreover, we have established conditions to isolate and culture these immature neurons in the adult piriform cortex layer II. We find that although they can survive under certain conditions, they do not proliferate in vitro either. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 748-763, 2016.

Withania somnifera Suppresses Tumor Growth of Intracranial Allograft of Glioma Cells.

Gliomas are the most frequent type of primary brain tumor in adults. Their highly proliferative nature, complex cellular composition, and ability to escape therapies have confronted investigators for years, hindering the advancement toward an effective treatment. Agents that are safe and can be administered as dietary supplements have always remained priority to be most feasible for cancer therapy. Withania somnifera (ashwagandha) is an essential ingredient of Ayurvedic preparations and is known to eliminate cancer cells derived from a variety of peripheral tissues. Although our previous studies have addressed the in vitro anti-proliferative and differentiation-inducing properties of ashwagandha on neuronal cell lines, in vivo studies validating the same are lacking. While exploring the mechanism of its action in vitro, we observed that the ashwagandha water extract (ASH-WEX) induced the G2/M phase blockade and caused the activation of multiple pro-apoptotic pathways, leading to suppression of cyclin D1, bcl-xl, and p-Akt, and reduced the expression of polysialylated form of neural cell adhesion molecule (PSA-NCAM) as well as the activity of matrix metalloproteinases. ASH-WEX reduced the intracranial tumor volumes in vivo and suppressed the tumor-promoting proteins p-nuclear factor kappa B (NF-κB), p-Akt, vascular endothelial growth factor (VEGF), heat shock protein 70 (HSP70), PSA-NCAM, and cyclin D1 in the rat model of orthotopic glioma allograft. Reduction in glial fibrillary acidic protein (GFAP) and upregulation of mortalin and neural cell adhesion molecule (NCAM) expression specifically in tumor-bearing tissue further indicated the anti-glioma efficacy of ASH-WEX in vivo. Combining this enhanced understanding of the molecular mechanisms of ASH-WEX in glioma with in vivo model system offers new opportunities to develop therapeutic strategy for safe, specific, and effective formulations for treating brain tumors.

Second generation anti-epileptic drugs adversely affect reproductive functions in young non-epileptic female rats

Reproductive endocrine disturbances are a major health concern in women with epilepsy due to their long term use of antiepileptic drugs (AEDs). Second generation AEDs such as topiramate (TPM) and gabapentin are frequently used for the treatment of epilepsy as well as migraine, bipolar disorder etc. Despite the widespread clinical complications, however the definitive mechanism(s) mediating the side effects of TPM and gabapentin remain obscure. The present study was aimed to evaluate the long term effects of TPM and gabapentin on reproductive functions in young female Wistar rats. Estrous cyclicity, ovarian histology as well as estradiol, LH, leptin and insulin hormones level were studied to elucidate the long-term effect of these AEDs monotherapy on reproductive functions in non-epileptic animals. Further to explore the effects on gonadotropin releasing hormone (GnRH) neuroendocrine plasticity, the expression of GnRH, gamma-amino butyric acid (GABA), glutamic acid decarboxylase (GAD), glial fibrilliary acidic protein (GFAP) and polysialylated form of neural cell adhesion molecule (PSA-NCAM) was studied in median eminence (ME) region of these animals by immunohistochemistry, Western blot hybridization and RT-PCR. Our results demonstrate that TPM and gabapentin treatment for 8 weeks cause reproductive dysfunction as ascertained by disturbed hormonal levels and estrous cyclicity as well as alterations in GABAergic system and GnRH neuronal–glial plasticity. Our findings suggest that treatment with TPM and gabapentin disrupts the complete hypothalamo-hypophyseal-gonadal axis (HPG) through GnRH pulse generator in hypothalamus.

Photoperiodic variations of the polysialylated form of neural cell adhesion molecule within the hypothalamus and related reproductive output in the ewe

Cellular mechanisms induced by melatonin to synchronise seasonal reproduction in several species, including sheep, remain unclear. We sought to evaluate the scale and physiological significance of neural plasticity in order to explain the delay between the change of duration of melatonin secretion and the change of reproductive status following a transition from long days (LD, 16 h light/24 h) to short days (SD, 8 h light/24 h) and from SD to LD. Using Western blots in ovariectomised oestradiol-replaced ewes, we evaluated the content of the polysialylated form of neural cell adhesion molecule (PSA-NCAM), a plasticity marker, in the hypothalamus. From day 15 following a transition to SD, most hypothalamic areas showed a decrease of PSA-NCAM level that was particularly significant in the preoptic area (POA). Following a transition to LD, PSA-NCAM content increased at day 15 in most regions except in the premammillary hypothalamic area (PMH) in which a significant decrease was noted. The functional importance of PSA-NCAM variations for seasonal reproduction was assessed for the PMH and POA. PSA-NCAM was degraded by stereotaxic injections of endoneuraminidase N and luteinising hormone (LH) secretion was recorded in treated and control ewes. Degradation of PSA-NCAM in the PMH in SD-treated ewes failed to produce a significant effect on LH secretion, whereas a similar treatment in the POA before a transition to SD delayed activation of the gonadotroph axis in two-thirds of the ewes. Our results suggest that the photoperiod controls variations of the hypothalamic content of a plasticity marker and that these might be important for the regulation of seasonal reproduction, particularly in the POA.

The Role of Dentate Gyrus Neurogenesis in Neuropsychiatric Disorders

The Role of Dentate Gyrus Neurogenesis in Neuropsychiatric Disorders

Neural cell adhesion molecule and its polysialic acid moiety exhibit opposing and linked effects on neuropathic hyperalgesia

Spinal lamina II, where nociceptive C-fibers terminate, expresses high amounts of the polysialylated form of neural cell adhesion molecule (PSA-NCAM). While enzymatic removal of the PSA moiety from NCAM did not affect normal sensitivity to thermal stimuli, it exacerbated nerve injury-induced neuropathic hyperalgesia. The genetic removal of the NCAM core protein also did not alter thermal sensitivity. However in the presence of a peripheral nerve injury, NCAM-null mutants exhibited a complete suppression of thermal hyperalgesia. This strong NCAM mutant phenotype appears to involve the long form of NCAM's cytoplasmic domain, in that it is duplicated by selective genetic deletion of the NCAM-180 isoform. PSA appears therefore to provide a mechanism for modulation of chronic sensory overload, by means of attenuation of the activity of the NCAM-180 isoform, which reduces nociceptive transmission.

The intimate relationship of gonadotropin‐releasing hormone neurons with the polysialylated neural cell adhesion molecule revisited across development and adult plasticity

The neurohormone gonadotropin-releasing hormone (GnRH) is critical for all the aspects of reproductive life in vertebrates. GnRH is secreted by a small number of neurons dispersed within the preoptic-hypothalamic region. These neurons are derived from the embryonic olfactory pit. They then migrate along olfactory, vomeronasal and terminal nerves to their final destination. Classical approaches to study the regulation of GnRH secretion during the reproductive cycle have focused on the various neuronal inputs on GnRH neurons and their regulation by ovarian steroids. However, it is well known that steroids will change the microenvironment of neuronal networks and can induce plasticity and functional changes. In this review, we will focus on the intimate relationship of developing and adult GnRH neurons with the polysialylated form of neural cell adhesion molecule (PSA-NCAM), a major molecular actor in the morphogenesis and adult plasticity of the nervous system. We will first recapitulate the spatiotemporal relationship between PSA-NCAM and migrating GnRH neurons during embryogenesis of various vertebrate species and discuss its importance for GnRH neuron development as shown by various loss of function studies. In the adult, we will review the relationships between PSA-NCAM and GnRH neurons across various physiological states, and open the discussion to the use of new model systems that can help to unravel the function and mechanism of action of PSA-NCAM on GnRH neuronal network activity and GnRH release.

Relationship between polysialylated neural cell adhesion molecule and β-endorphin- or gonadotropin releasing hormone-containing neurons during activation of the gonadotrope axis in short daylength in the ewe

Morphological plasticity has been demonstrated between breeding and anestrous seasons in the ewe hypothalamus, particularly for the gonadotropin-releasing hormone (GnRH) system. We sought to determine the impact of a photoperiodic transition, from long days (LD, 16 h light/24 h) to short days (SD; 8 h light/24 h), on the association between a marker of cerebral plasticity, the polysialylated form of neural cell adhesion molecule (PSA-NCAM), and two diencephalic populations: the GnRH and β-endorphin (β-END) neurons, the latter being potent inhibitors of GnRH neuronal activity. We also estimated the number of contacts on GnRH neurons after the passage to SD, using synaptophysin as a marker for synaptic buttons. Those parameters were evaluated in ovariectomized estradiol-replaced ewes using double immunocytochemistry and confocal microscopy at different times after the transition to SD: day 0 (D0), D30, D45, D60 and D112. Luteinizing hormone (LH) secretion was recorded throughout the experiment. High LH levels were observed only at D112. Significantly more PSA-NCAM was found in the GnRH neuron perimeters in the D112 group than in the other groups. This increase was not associated with any change in the number of synaptophysin-immunoreactive contacts on GnRH neurons. The β-END peri-neuronal space was affected negatively by the transition to SD: the percentage of PSA-NCAM on β-END neurons decreased between D45 and D112 in the posterior two thirds of the arcuate nucleus (ARC). These results suggest that photoperiod may reorganize cell interactions in different hypothalamic areas, ultimately reactivating GnRH neurons, in our model of ovariectomized-estradiol replaced ewes.

Removal of Polysialic Acid Triggers Dispersion of Subventricularly Derived Neuroblasts into SurroundingCNS Tissues

Cells generated in the subventricular zone give rise to neuroblasts that migrate to the olfactory bulb (OB) along the rostral migratory stream (RMS). The polysialylated form of neural cell adhesion molecule (PSA-NCAM) is expressed by these cells, and has been shown to both promote their migration and suppress differentiation induced by NCAM. In the present study, enzymatic removal of PSA from these neuroblasts using PSA-specific endoneuraminidase has been found not only to disrupt the tangential migration and cellular organization of the RMS, but also to cause a massive dispersion of BrdU (5-bromo-2'-deoxyuridine)-labeled neuroblasts into surrounding brain regions, including cortex and striatum. These dispersed cells are capable of differentiation, some into mature neurons, and could potentially be of value in the repair of CNS injury. Although the removal of PSA by genetic deletion of NCAM also results in a smaller OB and a swollen RMS, the cells do not escape the RMS in large numbers. These findings suggest that the presence of NCAM without PSA plays a role in the dispersion process, possibly by inducing a new pattern of migration associated with NCAM-dependent differentiation.

Olanzapine, but not haloperidol, enhances PSA-NCAM immunoreactivity in rat prefrontal cortex

Repeated antipsychotic treatment may produce adaptive changes ranging from cytoarchitectural rearrangements to synaptic modifications that might contribute to clinical improvement. We performed a prolonged treatment (2 wk) with the first-generation antipsychotic (FGA) haloperidol (1 mg/kg) and the second-generation antipsychotic (SGA) olanzapine (2 mg/kg twice daily) and analysed the expression of the polysialylated form of neural cell adhesion molecule (PSA-NCAM) in rat hippocampus and prefrontal cortex via immunohistochemistry. We found a regional- and drug-selective increase of PSA-NCAM expression in prefrontal cortex of olanzapine-treated rats with no effects in hippocampus; conversely, haloperidol did not produce a change in either brain region. Our findings reveal a possible role for PSA-NCAM in the mechanism of action of the SGA olanzapine adding complexity as well as specificity to the molecular changes set in motion by this drug.

Transcriptional regulation of PSA-NCAM mediated neuron–glial plasticity in the adult hypothalamus

Gonadotropin releasing hormone (GnRH)-secreting neurons in mammal's project principally to the median eminence-arcuate (ME-ARC) region where they make contact with basal lamina and open into the pericapillary space of the primary hypophyseal portal plexus. In the present study we report the expression of polysialylated form of neural cell adhesion molecule (PSA-NCAM) on the cell bodies of GnRH-secreting neurons and on glial cells in the medial preoptic area (mPOA) of the hypothalamus in both the proestrous and diestrous phases of cycling rats, using dual immunohistofluorescent staining. Regulation of PSA-NCAM occurs via regulation of PSA biosynthesis by the polysialyltransferase enzyme (PST-1). Therefore, we studied the expression of PST mRNA and GnRH in GnRH-releasing cell bodies by combining fluorescent in situ hybridization with immunohistofluorescence, and expression of PST mRNA in the mPOA using northern blotting. We observed dynamic upregulation of PSA-NCAM on GnRH cell bodies in the proestrous phase, accompanied by enhanced expression of PST-1 mRNA. The present results indicate that PSA-NCAM has a permissive role in the structural remodeling of GnRH neurons. Enhanced expression of mRNA encoding PST-1 in the proestrous phase indicates that the biosynthesis of PSA and, thus, PSA-NCAM is regulated at the transcriptional level.

Valproic Acid Alters GnRH-GABA Interactions in Cycling Female Rats

SUMMARY OF THE AIMS: Women with epilepsy using antiepileptic drug valproic acid (VPA) often suffer from reproductive endocrine disorders, menstrual disorders and polycystic ovaries. Valproic acid exerts anticonvulsive effects via gamma amino butyric acid (GABA) neurotransmitter system, which also acts as a neurochemical regulator of gonadotropin-releasing hormone (GnRH) neurons and suggests possibility of valproic acid mediated interruption in gonadotropin releasing hormone pulse generator in hypothalamus. The aim of this study was to investigate the effects of valproic acid treatment on the expression of gonadotropin releasing hormone, gamma amino butyric acid and polysialylated form of neural cell adhesion molecule (PSA-NCAM) a marker of neuronal plasticity in the median preoptic area (mPOA) and median eminence-arcuate (ME-ARC) region having GnRH neuron cell bodies and axon terminals, respectively. Three-month-old virgin Wistar strain female rats received VPA (i.p.) at a dose of 300 mg/kg once a day for 12 weeks; control group received an equivalent volume of vehicle. GnRH, GABA and PSA-NCAM expressions were studied by immunohistofluorescence technique from mPOA and ME-ARC region of hypothalamus. Ovarian histology was also studied using Mayer's Haematoxylin-Eosin staining method. GnRH and PSA-NCAM staining was much higher in mPOA and ME-ARC region from vehicle treated control proestrous rats, whereas VPA treatment significantly enhanced GABA expression, and reduced both GnRH and PSA-NCAM expression. Mayer's Haematoxylin-Eosin staining of mid-ovarian sections revealed significantly higher number of ovarian follicular cysts in VPA treated rats. Our findings of alterations in GnRH and GABA expression and GnRH neuronal plasticity marker PSA-NCAM as well as changes in ovarian histology suggest that treatment with VPA disrupts hypothalamo-hypophyseal-gonadal axis (HPG) at the level of GnRH pulse generator in hypothalamus.

Polysialylation Increases Lateral Diffusion of Neural Cell Adhesion Molecule in the Cell Membrane

Polysialic acid (PSA) is a polymer of N-acetylneuraminic acid residues added post-translationally to the membrane-bound neural cell adhesion molecule (NCAM). The large excluded volume created by PSA polymer is thought to facilitate cell migration by decreasing cell adhesion. Here we used live cell imaging (spot fluorescence recovery after photobleaching and fluorescence correlation spectroscopy) combined with biochemical approaches in an attempt to uncover a link between cell motility and the impact of polysialylation on NCAM dynamics. We show that PSA regulates specifically NCAM lateral diffusion and this is dependent on the integrity of the cytoskeleton. However, whereas the glial-derivative neurotrophic factor chemotactic effect is dependent on PSA, the molecular dynamics of PSA-NCAM is not directly affected by glial-derivative neurotrophic factor. These findings reveal a new intrinsic mechanism by which polysialylation regulates NCAM dynamics and thereby a biological function like cell migration.

Potential of PSA-NCAM in neuron-glial plasticity in the adult hypothalamus: Role of noradrenergic and GABAergic neurotransmitters

The present study was designed to establish the dynamic regulation of polysialylated form of neural cell adhesion molecule (PSA-NCAM) expression by neurotransmitters controlling gonadotropin releasing hormone (GnRH) secretion. The expression of PSA-NCAM and glial fibrillary acidic protein (GFAP) on GnRH cell bodies and axon terminals in the medial preoptic area (mPOA) and median eminence-arcuate (ME-ARC) region of hypothalamus was studied in the proestrous phase of cycling rats treated with α-adrenergic receptor blocker phenoxybenzamine (PBZ) and γ-aminobutyric acid (GABA) by using dual immunohistofluorescent staining and Western blot hybridization. To further elucidate whether activity mediated regulation of PSA-NCAM in GnRH neuron is via regulation of PSA biosynthesis by polysialytransferase (PST) enzyme, the expression of PST-1 enzyme was studied by using fluorescent in situ hybridization (FISH). Both GnRH and PSA-NCAM immunostaining was much higher in the mPOA and ME-ARC region from proestrous phase rats, whereas, PBZ and GABA treatments significantly reduced their expression, GFAP-ir and its content were increased in the PBZ and GABA treated proestrous rats. Taken together, our observations add to the growing evidence that PSA-NCAM plays permissive role for neuronal-glial remodeling and further suggest a functional link between activity dependent structural remodeling in GnRH neurons. Further, enhanced mRNA expression of PST suggests that the biosynthesis of PSA on NCAM is regulated at the transcriptional level.

Methylphenidate Administration to Juvenile Rats Alters Brain Areas Involved in Cognition, Motivated Behaviors, Appetite, and Stress

Thousands of children receive methylphenidate (MPH; Ritalin) for attention deficit/hyperactivity disorder (ADHD), yet the long-term neurochemical consequences of MPH treatment are unknown. To mimic clinical Ritalin treatment in children, male rats were injected with MPH (5 mg/kg) or vehicle twice daily from postnatal day 7 (PND7)-PND35. At the end of administration (PND35) or in adulthood (PND135), brain sections from littermate pairs were immunocytochemically labeled for neurotransmitters and cytological markers in 16 regions implicated in MPH effects and/or ADHD etiology. At PND35, the medial prefrontal cortex (mPFC) of rats given MPH showed 55% greater immunoreactivity (-ir) for the catecholamine marker tyrosine hydroxylase (TH), 60% more Nissl-stained cells, and 40% less norepinephrine transporter (NET)-ir density. In hippocampal dentate gyrus, MPH-receiving rats showed a 51% decrease in NET-ir density and a 61% expanded distribution of the new-cell marker PSA-NCAM (polysialylated form of neural cell adhesion molecule). In medial striatum, TH-ir decreased by 21%, and in hypothalamus neuropeptide Y-ir increased by 10% in MPH-exposed rats. At PND135, MPH-exposed rats exhibited decreased anxiety in the elevated plus-maze and a trend for decreased TH-ir in the mPFC. Neither PND35 nor PND135 rats showed major structural differences with MPH exposure. These findings suggest that developmental exposure to high therapeutic doses of MPH has short-term effects on select neurotransmitters in brain regions involved in motivated behaviors, cognition, appetite, and stress. Although the observed neuroanatomical changes largely resolve with time, chronic modulation of young brains with MPH may exert effects on brain neurochemistry that modify some behaviors even in adulthood.

Activation of the subventricular zone in multiple sclerosis: Evidence for early glial progenitors

In multiple sclerosis (MS), oligodendrocyte and myelin destruction lead to demyelination with subsequent axonal loss. Experimental demyelination in rodents has highlighted the activation of the subventricular zone (SVZ) and the involvement of progenitor cells expressing the polysialylated form of neural cell adhesion molecule (PSA-NCAM) in the repair process. In this article, we studied the distribution of early PSA-NCAM(+) progenitors in the SVZ and MS lesions in human postmortem brains. Compared with controls, MS SVZ showed a 2- to 3-fold increase in cell density and proliferation, which correlated with enhanced numbers of PSA-NCAM(+) and glial fibrillary acidic protein-positive (GFAP(+)) cells. PSA-NCAM(+) progenitors mainly were Sox9(+), and a few expressed Sox10 and Olig2, markers of oligodendroglial specification. PSA-NCAM(+) progenitors expressing Sox10 and Olig2 also were detected in demyelinated MS lesions. In active and chronic active lesions, the number of PSA-NCAM(+) progenitors was 8-fold higher compared with chronic silent lesions, shadow plaques, and normal-appearing white matter. In active and chronic active lesions, PSA-NCAM(+) progenitors were more frequent in periventricular lesions (30-50%) than in lesions remote from the ventricular wall. These data indicate that, as in rodents, activation of gliogenesis in the SVZ occurs in MS and suggest the mobilization of SVZ-derived early glial progenitors to periventricular lesions, where they could give rise to oligodendrocyte precursors. These early glial progenitors could be a potential target for therapeutic strategies designed to promote myelin repair in MS.

Neuronal-glial plasticity in gonadotropin-releasing hormone release in adult female rats: role of the polysialylated form of the neural cell adhesion molecule

The gonadotropin-releasing hormone (GnRH) neurosecretory system undergoes marked structural and functional changes during the ovarian cycle. The aim of this study was to examine the neuroanatomical relationship between GnRH neurons and a polysialylated form of neural cell adhesion molecule (PSA-NCAM), a known marker of neuronal plasticity. Using immunohistofluorescent dual labeling, we determined that axon terminals of GnRH in the median arcuate nucleus (ME-ARC) region of the hypothalamus in the proestrous phase of the estrous cycle were intimately associated with PSA-NCAM. To further examine whether PSA-NCAM expression associated with GnRH neuron terminals varies in conjugation with cyclic changes in ovarian steroid hormone levels, we examined GnRH and PSA-NCAM dual expression in ovariectomized (OVX) and estrogen-progesterone-primed OVX (EBP-OVX) rats. The expression of PSA-NCAM immunoreactivity associated with the GnRH neurons in the proestrous phase and EBP-OVX rats was significantly higher than during the diestrous phase and in OVX rats where GnRH secretion declines. We further examined whether the structural changes in GnRH axon terminals in the ME-ARC region are also associated with glial plasticity. By extension and retraction of the glial processes, the GnRH neuron terminals in the ME-ARC region could undergo dynamic plastic changes that control GnRH release during the proestrous phase. PSA-NCAM expression was also seen on glial cells in the ME-ARC region. The close association between PSA-NCAM on GnRH and glial cells in the ME-ARC region of the hypothalamus in the rat showed dynamic structural changes in GnRH neuron terminals during the estrous cycle. These observations suggested that PSA-NCAM may act as a molecular substrate to promote neuroplastic changes in the GnRH neurosecretory system.

Direct Evidence That Neural Cell Adhesion Molecule (NCAM) Polysialylation Increases Intermembrane Repulsion and Abrogates Adhesion

Molecular force measurements quantified the impact of polysialylation on the adhesive properties both of membrane-bound neural cell adhesion molecule (NCAM) and of other proteins on the same membrane. These results show quantitatively that NCAM polysialylation increases the range and magnitude of intermembrane repulsion. The repulsion is sufficient to overwhelm both homophilic NCAM and cadherin attraction at physiological ionic strength, and it abrogates the protein-mediated intermembrane adhesion. The steric repulsion is ionic strength dependent and decreases substantially at high monovalent salt concentrations with a concomitant increase in the intermembrane attraction. The magnitude of the repulsion also depends on the amount of polysialic acid (PSA) on the membranes, and the PSA-dependent attenuation of cadherin adhesion increases with increasing PSA-NCAM:cadherin ratios. These findings agree qualitatively with independent reports based on cell adhesion studies and reveal the likely molecular mechanism by which NCAM polysialylation regulates cell adhesion and intermembrane space.