Using Transport to Map the Brain A major challenge in understanding how the brain processes information is defining the circuitry that links neurons into a functional distributed parallel processing network. Intracellular transport is a normal biological process that is experimentally exploited to define the anatomy of circuitry. Transport has recently been implicated in many neurological diseases, including neurodegeneration of Alzheimer's, Huntington's and Parkinson's disease and in Down's syndrome and in the optic tract in normal-pressure glaucoma. Recent ground-breaking work has demonstrated that Mn2+, a contrast agent for magnetic resonance imaging (MRI), is picked up and transported within neurons. Thus for the first time dynamics of transport (rates, directionality, trans-synaptic transmission) and changes in Mn2+distirbution, i.e. circuitry, over an animal's lifetime can now be studied with manganese-enhance MRI (MEMRI). Here three laboratories with complimentary expertise in molecular microscopy and neuropathology (Brown University), in small animal 5MRI imaging (Caltech), and in computational analysis (Center for Computational Biology (CCB) at UCLA, one of the centers of the National Centers for Biological Computing), are brought together to develop and apply this new technology and to train young scientists in its application. First we will investigate the biology of Mn2+ transport in the well-characterized visual system to learn about Mn2+ effects on electrical activity, its transport in axons, and the role of synaptic activity. Differences in transport rates will be analyzed using existing, modified and new software to extract meaningful data from multiple individuals. Second we will apply MEMRI to investigate the circuit between hippocampus and basal forebrain. Specific biological alterations in this circuit are implicated in cognitive impairment of both Alzheimer's disease (AD) and Down Syndrome (DS). We will inject Mn2+ together with traditional histologic tracers into precise locations in mouse mutant models, such as the Ts65Dn DS model, and APPswe and KLC-/- AD model. Living mice will be imaged by 5MRI at successive time points before and after injection. MR images will be align/warped using CCB software and statistically significant intensity changes determined on a voxel-by-voxel basis. Histological examination of brains post-mortem will verify injection sites, monitor injury, and assist in identifying individual neurons along the circuit. This project will result in progress in three areas: 1) Definitive understanding of the biologic basis of Mn2+ track tracing, a basis for all future MEMRI data analysis;2) Quantitative measurements of transport dynamics in the important hippocampal-forebrain memory circuit;and 3) Application and development of statistical mapping to mouse mutant models for comprehensive unbiased analysis of phenotypic alterations in circuitry over time. The technology developed here will prove useful for large-scale analysis of transgenic mice mutated in other genes affecting the brain anatomy and circuitry.
Mental retardation and senility may involve the same circuits within the brain: connections between the hippocampus and basal forebrain. Manganese enhanced magnetic resonance imaging (MEMRI) allows us to observe the anatomy and activity within this circuit in living brains. Here we propose to develop and apply this technology to map this important memory circuit in mouse models towards gaining an understanding of two frequently occurring diseases: Down syndrome and Alzheimer's disease.
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