Using a line-scanning method during functional magnetic resonance imaging (fMRI) we obtain high temporal (50 ms) and spatial (50 μm) resolution information along the cortical thickness, and show that the laminar position of fMRI onset coincides with distinct neural inputs t in therat somatosensory and motor cortices. This laminar specific fMRI onset allowed the identification of the neural inputs underlying ipsilateral fMRI activation in the barrel cortex due to peripheral denervation-induced plasticity.
Summary Experience-dependent plasticity in the adult brain has clinical potential for functional rehabilitation following central and peripheral nerve injuries. Here, plasticity induced by unilateral infraorbital (IO) nerve resection in four week-old rats was mapped using MRI and synaptic mechanisms were elucidated by slice electrophysiology. Functional MRI demonstrates a cortical potentiation compared to thalamus two weeks after IO nerve resection. Tracing thalamocortical (TC) projections with manganese-enhanced MRI revealed circuit changes in the spared layer 4 (L4) barrel cortex. Brain slice electrophysiology revealed TC input strengthening onto L4 stellate cells due to an increase in postsynaptic strength and the number of functional synapses. This work shows that the TC input is a site for robust plasticity after the end of the previously defined critical period for this input. Thus, TC inputs may represent a major site for adult plasticity in contrast to the consensus that adult plasticity mainly occurs at cortico-cortical connections.
Purpose:To assess the feasibility of imaging deep-lying internal organs at high spatial resolution by imaging kidney glomeruli in a rodent model with use of a newly developed, wireless amplified nuclear magnetic resonance (MR) detector. Materials and Methods:This study was approved by the Animal Care and Use Committee at the National Institutes of Health/National Institute of Neurologic Disorder and Stroke. As a preclinical demonstration of this new detection technology, five different millimeter-scale wireless amplified nuclear MR detectors configured as double frequency resonators were chronically implanted on the medial surface of the kidney in five Sprague-Dawley rats for MR imaging at 11.7 T. Among these rats, two were administered gadopentetate dimeglumine to visualize renal tubules on T1-weighted gradient-refocused echo (GRE) images, two were administered cationized ferritin to visualize glomeruli on T2*-weighted GRE images, and the remaining rat was administered both gadopentetate dimeglumine and cationized ferritin to visualize the interleaved pattern of renal tubules and glomeruli. The image intensity in each pixel was compared with the local tissue signal intensity average to identify regions of hyper-or hypointensity. Results:T1-weighted images with 70-mm in-plane resolution and 200-mm section thickness were obtained within 3.2 minutes to image renal tubules, and T2*-weighted images of the same resolution were obtained within 5.8 minutes to image the glomeruli. Hyperintensity from gadopentetate dimeglumine enabled visualization of renal tubules, and hypointensity from cationic ferritin enabled visualization of the glomeruli. Conclusion:High-spatial-resolution images have been obtained to observe kidney microstructures in vivo with a wireless amplified nuclear MR detector.q RSNA, 2013 Supplemental material: http://radiology.rsna.org/lookup /suppl
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