In vivo magnetic resonance studies reveal neuroanatomical and neurochemical abnormalities in the serine racemase knockout mouse model of schizophrenia

- Serine racemase knockout (SR−/−) mice model phenotypes found in schizophrenia (Scz)
- We obtained the first in vivo MRI and MRS scans of SR−/− mice.
- SR−/− mice had enlarged ventricles and increased frontal cortex glutamate and GABA.
- SR−/− mice exhibit some MRI and MRS abnormalities observed in Scz.
- Imaging of SR−/− mice may lead to new diagnostic methods and treatments for Scz.

BackgroundDecreased availability of the N-methyl-d-aspartate receptor (NMDAR) co-agonist d-serine is thought to promote NMDAR hypofunction and contribute to the pathophysiology of schizophrenia, including neuroanatomical abnormalities, such as cortical atrophy and ventricular enlargement, and neurochemical abnormalities, such as aberrant glutamate and γ-aminobutyric acid (GABA) signaling. It is thought that these abnormalities directly relate to the negative symptoms and cognitive impairments that are hallmarks of the disorder. Because of the genetic complexity of schizophrenia, animal models of the disorder are extremely valuable for the study of genetically predisposing factors. Our laboratory developed a transgenic mouse model lacking serine racemase (SR), the synthetic enzyme of d-serine, polymorphisms of which are associated with schizophrenia. Null mutants (SR−/−) exhibit NMDAR hypofunction and cognitive impairments. We used 9.4 T magnetic resonance imaging (MRI) and proton spectroscopy (MRS) to compare in vivo brain structure and neurochemistry in wildtype (WT) and SR−/− mice.MethodsMice were anesthetized with isoflurane for MRI and MRS scans.ResultsCompared to WT controls, SR−/− mice exhibited 23% larger ventricular volumes (p < 0.05). Additionally, in a medial frontal cortex voxel (15 μl), SR−/− mice exhibited significantly higher glutamate/water (12%, t = 1.83, p < 0.05) and GABA/water (72%, t = 4.10, p < 0.001) ratios.ConclusionsCollectively, these data demonstrate in vivo neuroanatomical and neurochemical abnormalities in the SR−/− mouse comparable to those previously reported in humans with schizophrenia.