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 couple of years 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 and myelin in auditory cortex can be detected both in fixed specimens and in vivo. This work has been performed at 3T and is limited by signal to noise. Over the next year we hope to make a new 7T human MRI function to increase resolution by a factor of two over the 3T so that myeloarchitecture can be performed in individuals. 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 couple of years, 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. To test if the fMRI is detecting laminar communication, specific protocols that rely on well known inhibitory circuits are being developed. In addition, we have developed techniques that allow robust whole brain fMRI in rodents at very hgih magnetic field strengths (11.7T). These technqiues will be used to study simple behavioral paradigms. 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 couple of years 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. Future work will use manganese to study changes in brain anatomy and connections elicited by simple behavioral changes and interventions known to give rise to plasticity in the brain. Finally, our work on bioenergetics remains focused on the role of creatine kinase in cellular energy metabolism. Recent work has demonstrated that there is coupling of creatine kinase and cellular calcium handling. Calcium handling is one of the most energetic demanding tasks for cells and we have shown that loss of creatine kinase alters calcium handling in the heart. Future studies will explore the mechanism and the physiological consequences of these changes. This work relies on the combination of non-invasive imaging to analyse specific genetic changes made in mice.
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