The overall goal of this work is to develop functional magnetic resonance imaging (MRI) and optical imaging techniques that allow non-invasive assessment of brain and heart function. A secondary goal is to combine molecular genetics with non-invasive imaging to understand cellular energetics and the role of the enzyme creatine kinase. MRI technqiues are having a broad impact on understanding brain. Anatomical based MRI has been very useful for separating gray and white matter and detecting numerous brain disorders. There is little evidence for detecting cortical heterogeniety such as layers or boundaries between specific functional areas. Over the past year we have demonstrated that high resolution MRI with pixel dimensions less than 500 microns can robustly detect cortical heterogeniety. The thick myelin stripe that defines layer 4 in visual cortical area V1 can be detected by MRI both in fixed specimens and in vivo. Myelination in other areas of the brain have been detected in vitro. Over the next year we hope to be able to fully delineate the V1 stripe as well as detect myelin in other cortical regions in vivo. These results have great potential for extending the power of MRI and enable quantitative measurement of functional areas. This approach of acquiring high resolution MRI is being extended to study hippocampus. In addition to anatomical techniques we have been using functional and molecular MRI techniques to define cortical architecture. Over the past year, we have completed studies in the rodent brain that acquired very high temporal and spatial resolution functional MRI to monitor changes in hemodynamics during forepaw stimulation. The results clearly indicate that specific layers in the mammalian cortex can be defined. This opens the possibility of studying the specific route of communication from different cortical regions during plasticity and learning. In the coming year we will perform experiments to prove that the pattern of fMRI activation we detect reflects neuronal signalling. To expand the useful MRI tools available to study the brain, we have continued to develop the use of manganese ion as a molecular MRI contrast agent. Previously we have shown that manganese ion can sensitize MRI to assess calcium influx and to trace neuronal connections in vivo. Over the past year we have demonstrated that manganese enhanced MRI can distinguish cortical layers using two approaches. First, a systemic dose of manganese enters brain and gives MRI contrast specific for layers. Over the next year we will assign the specific layers being detected. Another way to detect layers is to use the track tracing properties of manganese ion. For example, an injection into thalamus leads to enhancment of the input layer 4 of somatosensory cortex. Manganese is a useful molecular imaging agent for other organs in addition to brain, such as heart. We have demonstrated that manganese accumulation can be detected by MRI and is proportional to calcium influx rate during different inotropic states. Results indicate that manganese can distinguish ischemic areas. Finally, we have an exciting finding that the mitochondrial isoform of creatine kinase can inhibit liver regeneration without damaging existing cells. This opens up possibilities for efficient replacement of liver with exogenous cells. Over the past year we have demonstrated that the inhibition in growth by creatine kinase depends on anesthetic and may require both mitochondrial creatine kinase and an activator of cytochrome p450. In addition, we have begun to transplant liver cells into mice where cretine kinase has inhibited regeneration to see if we can replace the liver using transplanted cells.
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