This project will test the hypothesis that schizophrenia is associated with NMDA hypofunction by examining in-vivo brain data acquired through the combined use of proton magnetic resonance spectroscopy (MRS) and BOLD functional magnetic resonance imaging (fMRI). We propose to measure proton metabolite concentrations, including N-acetyl-aspartate (NAA) and N-acetyl-aspartyl-glutamate (NAAG), in temporal and prefrontal cortical regions in schizophrenic patients and healthy controls. MRS data will be acquired on a 4T scanner with newly developed methods that provide improved resolution of peaks and signal components within the proton spectrum, thus improving interpretability of NAA measurements, as well as extending MRS capabilities to include quantification of NAAG. The quantification of these metabolites is relevant for the main hypothesis of the center grant as work from our group has reported reduced NAA in temporal cortex bilaterally. Further, NAAG has been implicated in NMDA hypofunction. At present in-vivo measurements of these metabolites, have not been concurrently characterized in schizophrenia. Moreover, it has been shown that NMDA receptors in the hippocampus are essential for spatial learning and that pharmacological blockade of NMDA receptors impairs spatial navigation. Therefore, as an exploratory endpoint, we propose to acquire fMRI data on a 3Tscanner during the completion of a virtual analogue of a spatial navigation task, the water maze, to assess spatial memory performance. We will also acquire fMRI data during a transitive inference task to assess relational memory, and during a facial recall challenge, tasks previously shown to be mediated by the hippocampus. Finally, in collaboration with Dr. Don Goff (Clinical Trials Section), we will enroll 60 schizophrenic patients into a placebo-controlled trial of D-serine, an agonist at the glycine site on the NMDA receptor. Patients will be imaged with the MRS/fMRI protocols described above to examine the effects of D-serine treatment on spatial and relational memory performance, BOLD activation and NAA and NAAG concentrations.
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