Schizophrenia is characterized by positive and negative symptoms along with cognitive symptoms that include impairment in working memory (WM). WM is the storage of relevant information for short intervals of time to guide thoughts and actions. The neural correlate of WM is thought to be the persistent activity exhibited during the retention interval of WM tasks. Persistent activity is hypothesized to be mediated by the activation of NMDA receptors (NMDAR) within recurrent neuronal circuits. Consistent with this hypothesis, studies with healthy humans and monkeys have shown that the administration of the NMDAR antagonist ketamine induces memory-load dependent deficits in WM, along with increasing response time. In parallel to this, the pathophysiology of schizophrenia has been hypothesized to rest on the hypofunction of NMDAR. Previous studies in humans indicate that blockade of NMDAR induces schizophrenia-like symptoms. In addition, symptoms of schizophrenia patients are alleviated with sub-chronic treatments focusing on the activation of the NMDAR co-agonist site. Based on these observations, I tested the hypothesis that increasing the activation of NMDAR with co-agonist stimulation has beneficial effects on WM. D-serine (100mg/kg/day-6 weeks) was orally administered to two female macaque monkeys performing a visual sequential comparison task (VCST), which allows the manipulation of memory load. In this task, the monkeys had to identify the location of a colour change within an array of 2 to 5 coloured stimuli following a retention interval of 1 second. I hypothesized that sub-chronic treatment with D-serine produces a gradual improvement in the monkeys’ performance on the VSCT. Specifically, I predicted that the improvement would scale with memory load due to increased demands on WM resources at higher loads. Contrary to my hypothesis, D-serine produced minute changes in response accuracy, which were not memory load-dependent. Also, the response latency of the monkeys was found to increase, which is commonly observed following NMDAR antagonist treatments. These findings suggest that D-serine has a limited role in increasing the activation of NMDARs to improve WM per se. The beneficial effects reported by NMDAR co-agonists in schizophrenic patients could be a general reduction in cognitive symptoms, not specifically related to WM. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2013-10-01 17:45:20.643

Dans le présent travail, le rôle de la glie dans l’expression de la douleur cancéreuse et de la douleur neuropathique a été étudié de façon comparative. Le modèle animal de douleur cancéreuse a été obtenu par injection osseuse dans le tibia, chez la rate Sprague-Dawley, de cellules de carcinome mammaire de type MRMT-1. Le modèle de douleur neuropathique a été obtenu chez le rat Wistar par ligature des nerfs spinaux L5 et L6. Les données obtenues par l’analyse du comportement douloureux en réponse à la stimulation par des filaments de von Frey ont permis de quantifier l’allodynie et l’hyperalgésie mécaniques statiques. La douleur chronique, hors stimulation nociceptive, a été mesurée à l’aide d’un test d’impotence. Les agents pharmacologiques ont été administrés par voie intrapéritonéale ou par voie intrathécale, à l’aide d’un cathéter implanté de façon chronique. L’analyse des comportements nociceptifs après stimulation par filaments de von Frey montre que l’inhibition fonctionnelle transitoire de la glie spinale par le fluorocitrate est sans effet sur la douleur dans les deux modèles. Dans les deux modèles, l’expression des réponses douloureuses dépend de l’activation des récepteurs NMDA spinaux. L’administration par voie intrathécale d’une seule dose de D-aminoacide oxydase, qui dégrade la D-sérine, co-agoniste endogène du récepteur NMDA, réduit l’allodynie et l’hyperalgésie chez les rats neuropathiques et l’allodynie chez les rats cancéreux. Les effets d’un traitement chronique par le fluoroacétate chez les rats neuropathiques sont réversés par l’administration intrathécale de D-sérine. La D-sérine altère légèrement le seuil nociceptif chez les rats cancéreux. Aucun des agents pharmacologiques utilisés ne réverse la réduction d’appui du membre lésé chez les rats cancéreux ou neuropathiques. Ces résultats montrent que, chez le rat, la douleur neuropathique comme la douleur osseuse cancéreuse dépend de la co-activation des récepteurs NMDA spinaux par un de ses ligands endogènes, la D-sérine, mais que seule la douleur neuropathique requiert une glie spinale fonctionnelle. Ils suggèrent donc un rôle différentiel de la glie dans la physiopathologie de ces deux types de douleur chronique / The present work has investigated the role of glia upon pain symptoms in a well established peripheral neuropathic pain model and a bone cancer pain model. The neuropathic pain model was obtained by right L5-L6 spinal nerve ligation in male Wistar rats. Bone cancer pain was induced by injecting MRMT-1 rat mammary gland carcinoma cells into the right tibia of Sprague-Dawley female rats. Mechanical allodynia and hyperalgesia were quantified using von Frey hairs and ambulatory incapacitance using dynamic weight bearing. Drugs were administered either acutely or chronically using osmotic pumps, through intrathecal catheters chronically implanted in experimental animals. Using von Frey hair stimuli, we found that transient inhibition of glia metabolism by intrathecal injection of fluorocitrate was ineffective in both models. In both models, pain symptoms required spinal NMDA receptor activation. Intrathecal administration of a single dose of D-aminoacid oxidase, which degrades D-serine, a co-agonist of NMDA receptors, reduced mechanical allodynia and hyperalgesia in neuropathic rats and allodynia in cancer rats. The effect of chronic fluoroacetate in neuropathic rats was reversed by acutely administered intrathecal D-serine, which had only a slight effect in cancer rats. None of these compounds altered the functional disability shown by neuropathic or cancer animals and measured by the dynamic weight bearing apparatus. These results show that neuropathic pain and cancer pains depend upon D-serine co-activation of spinal NMDA receptors but only neuropathic pain requires functional spinal cord glia in the rat. Glia may thus play different roles in the development and maintenance of chronic pain in these two situations.

The amyloid beta peptide (Aβ) plays an important role in Alzheimer’s disease (AD). Increasing evidence suggest that overactivation of extrasynaptic N-methyl-D-aspartate receptors (NMDARs) mediate Aβ-induced excitotoxicity. In serine racemase knockout (SRKO) mice with significantly depleted D-serine levels, Aβ-induced excitotoxicity is attenuated. Using SRKO mice, this thesis attempts to determine the effects of Aβ on synaptic and extrasynaptic NMDAR function, and how D-serine can alter these Aβ- mediated effects. In CA1 pyramidal neurons, Aβ significantly depresses evoked synaptic NMDAR excitatory postsynaptic currents (EPSCs), and this effect is even greater in SRKO mice. The same effect was also observed on isolated evoked extrasynaptic NMDAR currents. During synaptic NMDAR current recordings, Aβ potentiated the holding current in wild type (WT) mice, but not SRKO mice, suggesting an increase in extrasynaptic NMDAR activation in WT, but not in SRKO mice. SRKO mice attenuated Aβ-induced holding current shift and had reduced basal tonic NMDAR activation. These data, along with evidence from previous studies in the literature, suggest that low levels of D-serine can alter NMDAR function in the presence of Aβ. These findings provide insight for future experiments in exploring the importance of D-serine in AD.

No description available.

Yes / Incoherent neutron spectroscopy, in combination with dynamic light scattering, was used to investigate the effect of ligand binding on the center-of-mass self-diffusion and internal diffusive dynamics of Escherichia coli aspartate α-decarboxylase (ADC). The X-ray crystal structure of ADC in complex with the D-serine inhibitor was also determined, and molecular dynamics simulations were used to further probe the structural rearrangements that occur as a result of ligand binding. These experiments reveal that D-serine forms hydrogen bonds with some of the active site residues, that higher order oligomers of the ADC tetramer exist on ns–ms time-scales, and also show that ligand binding both affects the ADC internal diffusive dynamics and appears to further increase the size of the higher order oligomers. / TR acknowledges a PhD studentship jointly funded by the ILL and the Universität Hamburg (Federal Excellence Cluster Hamburg Centre for Ultrafast Imaging EXC 1074).

D-serine metabolism is implicated in schizophrenia pathophysiology. This is based on reduced D-serine levels in the disorder, its ameliorative effects therapeutically and the potential genetic contributions of its metabolic enzymes, D-amino acid oxidase (DAO) and serine racemase (SRR). D-serine is a gliotransmitter and the N-methyl D-aspartate receptor (NMDAR) co-agonist. Thus, altered D-serine metabolism may contribute to NMDAR hypofunction in schizophrenia. The research in this thesis was designed to investigate D-serine metabolic enzymes further through studying their distribution, their expression in schizophrenia and their effect on NMDARs. The regional and cellular distribution of DAO and SRR in rodent and human brain were investigated using immunohistochemistry. Both enzymes were found within frontal cortex, hippocampus and cerebellum. In rodent frontal cortex, SRR expression was neuronal suggesting D-serine is not always glia-derived. In the human this was not the case, highlighting possible species differences. DAO in the rodent and human cortex was robustly detected, challenging previous views. In rodent cerebellum, both enzymes were neuronal and glial and in human, predominantly glial. In schizophrenia, DAO and SRR expression were investigated using western blotting and real-time PCR. DAO expression was elevated in the cerebellum in the disorder, without an accompanying change in SRR. In the dorso-lateral prefrontal cortex (DPFC), DAO and SRR mRNAs were unchanged in schizophrenia but SRR protein was significantly increased. The elevation in DPFC SRR protein was not replicated however in a second study. To investigate the effects of D-serine metabolic enzymes on NMDARs, an in vitro model of altered SRR expression was developed, but its use hindered through technical complications. The data detailed demonstrate new findings of DAO and SRR’s distributions in the brain and highlight novel potential roles for these enzymes. In addition, the data provide some paradoxical findings including DAO’s cortical expression. The investigations in schizophrenia lend to robust demonstrations of DAO’s elevated cerebellar expression in the disorder. However, its roles therein and that of DAO and SRR on NMDAR function remain unclear.

La D-sérine, co-agoniste endogène du récepteur N-Méthyl D-Aspartate, est impliquée à la fois dans des fonctions physiologiques telles que l'apprentissage et le vieillissement et dans des pathologies psychiatriques et neurodégénératives comme la schizophrénie ou la sclérose latérale amyotrophique. Ce travail de thèse est composé de deux parties. Premièrement, je me suis intéressée aux mécanismes de régulation de la D-sérine extracellulaire. A l'aide de biocapteurs enzymatiques développés au laboratoire, nous avons évalué, in vivo, la diffusion de la D-sérine à travers la barrière hématoencéphalique et estimé sa concentration dans différents compartiments. Nous avons aussi montré que la recapture de la D-sérine est assurée par les transporteurs de type ASC et que sa dégradation est effectuée par la D-amino acide oxydase dans le cervelet et par la sérine racémase dans le cortex. Deuxièmement, j'ai étudié l'implication de la D-sérine dans le status épilepticus, un modèle présentant une forte excitotoxicité avérée. Nous avons tout d'abord développé une méthode de comptage automatique pour quantifier précisément la mort neuronale. Puis nous avons enregistré les concentrations de D-sérine et de glutamate extracellulaires lors du status épilepticus et nous avons montré que ces deux transmetteurs ont leur concentration augmentée dans le cortex piriforme/amygdale, zones fortement touchées par l'excitotoxicité. En revanche dans le cortex où il n'y a pas de perte neuronale excitotoxique, leur concentration reste inchangée. Mieux comprendre la régulation de la D-sérine et son rôle pathologique est essentiel pour développer et adapter des traitements / D-serine, an endogenous agonist of the N-methyl-D aspartate receptor, is implicated both in physiological functions like learning, aging and in psychiatric and neurodegenerative diseases like schizophrenia and amyotrophic lateral sclerosis. This thesis work is composed of two parts. First, I studied the mechanisms regulating D-serine extracellular concentration in the brain. With biosensors developed in the laboratory, we evaluated D-serine diffusion across the blood brain barrier and estimated its concentration in different compartments in vivo. We have shown that D-serine reuptake is mediated by ASC transporters and that its degradation relies on D-amino Acid oxidase in the cerebellum and on serine racemase in the cortex. Second, I have study the implication of D-serine in neuronal lesions produced by status epilepticus, a pathological model in which excitotoxicity is demonstrated. We have developed an automatic software to determine the density of neurons in a brain slice and identify the brain regions with most neuronal lesions following status epilepticus. We have then recorded the extracellular D-serine and glutamate concentration during status epilepticus and demonstrated that the concentration of both transmitters is increased in piriform cortex/amygdala, area corresponding to extended excitotoxic neuronal death. However, in the cortex, an area without excitotoxic neuronal death, D-serine and glutamate concentration are constant. Understanding D-serine regulation and its pathological implication is essential to develop new treatment for protecting the neuronal tissue against excitotoxic insult

Reduced activity of the N-methyl-D-aspartate receptor (NMDAR) has been implicated in the pathophysiology of schizophrenia. The NMDAR contains a glycine site on the NR1 subunit that may be a promising therapeutic target for psychiatric illness. Recently, D-serine has been discovered to be a high-affinity endogenous activator of the NMDAR glycine site. Levels of D-serine in the brain are controlled by its synthesis enzyme serine racemase (Srr) and its catabolic enzyme D-amino acid oxidase (DAO). This work investigates the NMDAR glycine site, D-serine, and D-serine-regulatory enzymes Srr and DAO in the pathophysiology and treatment of symptomatology relevant to schizophrenia and other psychiatric disorders. Pharmacological and genetic mouse models were used to alter glycine site function and D-serine availability. Behavioral responses in these models were assessed. Administration of exogenous D-serine and the glycine transporter 1 (GlyT-1) inhibitor ALX-5407 improved performance of C57BL/6J mice in behavioral tests examining prepulse inhibition (PPI) or latent inhibition (LI). These compounds also reversed impairments induced by the NMDAR antagonist MK-801, and produced similar beneficial effects to the classical atypical antipsychotic clozapine. Mice carrying a point mutation that leads to diminished NMDAR glycine site function demonstrated abnormally persistent LI and deficits in social approach and spatial recognition that were reversible by D-serine or clozapine administration. Similarly, mutant mice that lacked Srr function and had a severe reduction in D-serine displayed impairments in sociability, PPI, spatial recognition and memory. Behavioral deficits in mice without Srr were exacerbated by MK-801 and rescued by treatment with D-serine or clozapine. A genetically-induced loss of DAO function in mice resulted in the elevation of brain D-serine levels, and produced improvements in spatial reversal memory and extinction of a learned response in the Morris water maze, consistent with the effects of exogenous D-serine application in wild-type mice. Thus, deficiencies in NMDAR glycine site function and D-serine availability produce behavioral disturbances that are relevant to the negative and cognitive symptoms of schizophrenia. Activation of the NMDAR glycine site by D-serine, GlyT-1 inhibition, or diminished DAO activity may be beneficial for the treatment of schizophrenia and other psychopathologies involving cognitive dysfunction and persistent repetitive behaviors.

Reduced activity of the N-methyl-D-aspartate receptor (NMDAR) has been implicated in the pathophysiology of schizophrenia. The NMDAR contains a glycine site on the NR1 subunit that may be a promising therapeutic target for psychiatric illness. Recently, D-serine has been discovered to be a high-affinity endogenous activator of the NMDAR glycine site. Levels of D-serine in the brain are controlled by its synthesis enzyme serine racemase (Srr) and its catabolic enzyme D-amino acid oxidase (DAO). This work investigates the NMDAR glycine site, D-serine, and D-serine-regulatory enzymes Srr and DAO in the pathophysiology and treatment of symptomatology relevant to schizophrenia and other psychiatric disorders. Pharmacological and genetic mouse models were used to alter glycine site function and D-serine availability. Behavioral responses in these models were assessed. Administration of exogenous D-serine and the glycine transporter 1 (GlyT-1) inhibitor ALX-5407 improved performance of C57BL/6J mice in behavioral tests examining prepulse inhibition (PPI) or latent inhibition (LI). These compounds also reversed impairments induced by the NMDAR antagonist MK-801, and produced similar beneficial effects to the classical atypical antipsychotic clozapine. Mice carrying a point mutation that leads to diminished NMDAR glycine site function demonstrated abnormally persistent LI and deficits in social approach and spatial recognition that were reversible by D-serine or clozapine administration. Similarly, mutant mice that lacked Srr function and had a severe reduction in D-serine displayed impairments in sociability, PPI, spatial recognition and memory. Behavioral deficits in mice without Srr were exacerbated by MK-801 and rescued by treatment with D-serine or clozapine. A genetically-induced loss of DAO function in mice resulted in the elevation of brain D-serine levels, and produced improvements in spatial reversal memory and extinction of a learned response in the Morris water maze, consistent with the effects of exogenous D-serine application in wild-type mice. Thus, deficiencies in NMDAR glycine site function and D-serine availability produce behavioral disturbances that are relevant to the negative and cognitive symptoms of schizophrenia. Activation of the NMDAR glycine site by D-serine, GlyT-1 inhibition, or diminished DAO activity may be beneficial for the treatment of schizophrenia and other psychopathologies involving cognitive dysfunction and persistent repetitive behaviors.

Les récepteurs N-méthyl-D-aspartate (NMDA) sont des récepteurs ionotropiques du glutamate jouant un rôle clé dans la plasticité synaptique et les fonctions cognitives. En conséquence, la perturbation de leur activité est impliquée dans de nombreux troubles neurologiques et psychiatriques tels que l'épilepsie et la schizophrénie. La particularité de ces récepteurs est qu'ils nécessitent pour être activés la liaison simultanée de leur agoniste, le glutamate, et d'un co-agoniste. La glycine fut le premier co-agoniste identifié mais plus récemment, de nombreuses études ont révélé que la D-sérine joue également ce rôle dans de nombreuses régions cérébrales, notamment dans l'hippocampe. Toutefois il restait à définir si les fonctions de ces deux co-agonistes étaient régulées au cours du développement ou si elles étaient spécifiques à certaines synapses. Dans la première partie de mon travail, j'ai montré que la D-sérine est le co-agoniste préférentiel des synapses SC-CA1 matures alors que la glycine est le co-agoniste préférentiel des synapses mPP-DG. De plus, le remplacement des récepteurs NMDA composés de sous-unités GluN2B par des récepteurs contenant GluN2A au cours du développement post-natal survient au même moment qu'un changement dans l'identité du co-agoniste préférentiel des synapses SC-CA1. Dans la seconde partie de mon travail, je me suis intéressée à la contribution de la D-sérine en conditions pathologiques sur un modèle murin d'épilepsie chimio-induite par la pilocarpine. J'ai ainsi montré l'implication de la D-sérine dans l'activité épileptique initiée par la pilocarpine. / N-methyl-D-aspartate (NMDA) receptors are glutamate-gated ionotropic receptors which play a crucial role in synaptic plasticity and cognitive functions. As a consequence, disturbance in their activity is correlated with a broad range of neurological and psychiatric disorders including epilepsy and schizophrenia. The major particularity of NMDA receptors is the requirement of simultaneous binding of their agonist, glutamate, and a co-agonist to be activated. Glycine was the first co-agonist identified but more recently several studies showed that D-serine is also playing this role in many brain areas including the hippocampus. Whether the identity of the co-agonist is synapse specific or developmentally regulated remains unexplored. In the first part of my work I showed that D-serine is the preferred co-agonist at SC-CA1 mature synapses while glycine is the preferred one at mPP-DG synapse. Moreover, we showed that during postnatal development, the replacement of GluN2B by GluN2A-containing NMDA receptors at SC-CA1 synapses parallels a change in the co-agonist identity from glycine to D-serine. In the second part of my work I investigated the contribution of D-serine in pathological conditions. By using a model of acute intoxication of pilocarpine, I demonstrated that D-serine is implicated in epileptiform activity initiated after pilocarpine perfusion.