Ultrasound and MR Imaging of Mouse Brain Development.

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Genetically-engineered mice are currently being developed for in vivo studies of brain development and a wide range of neurodevelopmental diseases. Indeed, defined mutant mice have been critical for identifying the affected genetic pathways and addressing the underlying cellular and molecular basis of developmental brain diseases. Lacking in these efforts have been effective in vivo imaging methods that can be used to study mouse models of neurodevelopmental disorders, especially during early postnatal stages when disease is first manifested, and the greatest changes in brain structure and function are likely to occur. A major challenge is therefore to develop and validate in vivo imaging techniques that can detect and monitor early changes in brain structure and function in the developing mouse brain. We have established quantitative, in vivo manganese (Mn)-enhanced MRI (MEMRI) approaches for analyzing the early postnatal mouse brain, showing that MEMRI provides an exquisitely sensitive method for revealing multiple nuclei and axonal tracts in the early postnatal mouse brain. Results from our laboratory and others have already proven the utility of MEMRI for assessing neural activity and connectivity. These new findings now point to the potential of MEMRI for in vivo detection and quantitative analysis of functional circuits in the developing mouse brain. We have also discovered that the Divalent Metal Transporter, DMT1 can be utilized as an effective reporter gene for MEMRI. We now propose to develop and test a combination of DMT1 expression with MEMRI to provide a precise in vivo approach to analyze functional connectivity in the mouse brain, starting from critical neonatal stages when the circuitry is first established. We will test this new imaging technology in mice with mutations in the mid-hindbrain (MHB) genes engrailed (En1 and En2) and Fgf17, which have morphological and functional cerebellum and midbrain phenotypes. Recent evidence also suggests that both En and Fgf17 mutant mice have defects in MHB circuitry. We will therefore use DMT1-MEMRI to study MHB circuitry in these mice during the critical postnatal period of brain development. The specific aims of the project are: 1) Determine the normal stage-dependent MEMRI intensities in defined nuclei in wildtype (WT), En and Fgf17 mutant mice; 2) Utilize DMT1 to genetically label defined nuclei for MEMRI analysis of midbrain and cerebellar circuits; and 3) Analyze differences in functional circuitry between WT, En and Fgf17 mouse mutants using DMT1-MEMRI. This research has high potential to establish an innovative, genetically-controlled form of MEMRI for in vivo analysis of circuits in the developing mouse brain, providing critical new tools for analyzing mouse models of a wide variety of neurodevelopmental disorders, including cerebellum hypoplasia syndromes (e.g., Joubert and Dandy-Walker syndromes), autism spectrum disorders, and schizophrenia.