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.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/19050 |
| Date | 18 February 2010 |
| Creators | Labrie, Viviane |
| Contributors | Roder, John C. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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