Spectrum measurement of fast optical signal of neural activity in brain tissue and its theoretical origin
Functional brain imaging technologies have enabled recent advances in understanding human brain function. In particular, a noninvasive and fast optical technique will become one of the most promising tools for future studies. As a fundamental ex vivo study for the development of such a technique, this paper demonstrates the spectral measurement of fast optical changes associated with neural activity in bulk brain tissue. For this purpose, a high-speed confocal near-infrared spectrometer was built and used. The results verified that observed transient optical responses (tORs) are associated with neural activity by showing that the following: tORs were concurrent and correlated with local field potentials (LFPs); tORs disappeared following tetrodotoxin application; and tORs were reproducibly observed across preparations. In addition, the amplitude of tORs was statistically significantly larger in longer wavelengths (approximately 1200 nm). The time course of tORs, however, is quite different from that of LFPs. Since this difference implies that tORs may originate not directly from the electric potential variation but from other neurophysiological events accompanying excitation, this paper tested the hypothesis that tORs are attributed to transient cellular volume changes (tCVCs). With no previous dynamic equation to elucidate such different temporal dynamics of the optical responses, a novel mathematical neuron model to describe tCVCs was developed. This neuron model, along with finite-difference time-domain simulations, showed that tCVCs and tORs were similar in the temporal dynamics, order of magnitude, response direction, and detectability in the bulk tissue; thus supporting the hypothesis.

title: Dynamic light scattering optical coherence tomography.
abstract: We introduce an integration of dynamic light scattering (DLS) and optical coherence tomography (OCT) for high-resolution 3D imaging of heterogeneous diffusion and flow. DLS analyzes fluctuations in light scattered by particles to measure diffusion or flow of the particles, and OCT uses coherence gating to collect light only scattered from a small volume for high-resolution structural imaging. Therefore, the integration of DLS and OCT enables high-resolution 3D imaging of diffusion and flow. We derived a theory under the assumption that static and moving particles are mixed within the OCT resolution volume and the moving particles can exhibit either diffusive or translational motion. Based on this theory, we developed a fitting algorithm to estimate dynamic parameters including the axial and transverse velocities and the diffusion coefficient. We validated DLS-OCT measurements of diffusion and flow through numerical simulations and phantom experiments. As an example application, we performed DLS-OCT imaging of the living animal brain, resulting in 3D maps of the absolute and axial velocities, the diffusion coefficient, and the coefficient of determination.

title: Multiple-Capillary Measurement of RBC Speed, Flux, and Density with Optical Coherence Tomography
abstract: As capillaries exhibit heterogeneous and fluctuating dynamics even during baseline, a technique measuring red blood cell (RBC) speed and flux over many capillaries at the same time is needed. Here, we report that optical coherence tomography can capture individual RBC passage simultaneously over many capillaries located at different depths. Further, we demonstrate the ability to quantify RBC speed, flux, and linear density. This technique will provide a means to monitor microvascular flow dynamics over many capillaries at different depths at the same time.

title: Quantitative Imaging of Cerebral Blood Flow Velocity and Intracellular Motility using Dynamic Light Scattering–Optical Coherence Tomography
abstract: This paper describes a novel optical method for label-free quantitative imaging of cerebral blood flow (CBF) and intracellular motility (IM) in the rodent cerebral cortex. This method is based on a technique that integrates dynamic light scattering (DLS) and optical coherence tomography (OCT), named DLS–OCT. The technique measures both the axial and transverse velocities of CBF, whereas conventional Doppler OCT measures only the axial one. In addition, the technique produces a three-dimensional map of the diffusion coefficient quantifying nontranslational motions. In the DLS–OCT diffusion map, we observed high-diffusion spots, whose locations highly correspond to neuronal cell bodies and whose diffusion coefficient agreed with that of the motion of intracellular organelles reported in vitro in the literature. Therefore, the present method has enabled, for the first time to our knowledge, label-free imaging of the diffusion-like motion of intracellular organelles in vivo. As an example application, we used the method to monitor CBF and IM during a brief ischemic stroke, where we observed an induced persistent reduction in IM despite the recovery of CBF after stroke. This result supports that the IM measured in this study represent the cellular energy metabolism-related active motion of intracellular organelles rather than free diffusion of intracellular macromolecules.

title: Motion correction for phase-resolved dynamic optical coherence tomography imaging of rodent cerebral cortex
abstract: Cardiac and respiratory motions in animals are the primary source of image quality degradation in dynamic imaging studies, especially when using phase-resolved imaging modalities such as spectral-domain optical coherence tomography (SD-OCT), whose phase signal is very sensitive to movements of the sample. This study demonstrates a method with which to compensate for motion artifacts in dynamic SD-OCT imaging of the rodent cerebral cortex. We observed that respiratory and cardiac motions mainly caused, respectively, bulk image shifts (BISs) and global phase fluctuations (GPFs). A cross-correlation maximization-based shift correction algorithm was effective in suppressing BISs, while GPFs were significantly reduced by removing axial and lateral global phase variations. In addition, a non-origin-centered GPF correction algorithm was examined. Several combinations of these algorithms were tested to find an optimized approach that improved image stability from 0.5 to 0.8 in terms of the cross-correlation over 4 s of dynamic imaging, and reduced phase noise by two orders of magnitude in ~8% voxels.

title: Sensitivity of MRI resonance frequency to the orientation of brain tissue microstructure
abstract: Recent advances in high-field (≥7 T) MRI have made it possible to study the fine structure of the human brain at the level of fiber bundles and cortical layers. In particular, techniques aimed at detecting MRI resonance frequency shifts originating from local variation in magnetic susceptibility and other sources have greatly improved the visualization of these structures. A recent theoretical study [He X, Yablonskiy DA (2009) Proc Natl Acad Sci USA 106:13558–13563] suggests that MRI resonance frequency may report not only on tissue composition, but also on microscopic compartmentalization of susceptibility inclusions and their orientation relative to the magnetic field. The proposed sensitivity to tissue structure may greatly expand the information available with conventional MRI techniques. To investigate this possibility, we studied postmortem tissue samples from human corpus callosum with an experimental design that allowed separation of microstructural effects from confounding macrostructural effects. The results show that MRI resonance frequency does depend on microstructural orientation. Furthermore, the spatial distribution of the resonance frequency shift suggests an origin related to anisotropic susceptibility effects rather than microscopic compartmentalization. This anisotropy, which has been shown to depend on molecular ordering, may provide valuable information about tissue molecular structure.

title: Sprouting of dopamine terminals and altered dopamine release and uptake in Parkinsonian dyskinaesia.
abstract: Failed storage capacity, leading to pulsatile delivery of dopamine (DA) in the striatum, is used to explain the emergence of 'wearing off' and dyskinaesia in Parkinson's disease. In this study, we show that surviving DA neurons in 6-OHDA lesioned rats sprout to re-innervate the striatum, and maintain terminal density until approximately 60% of neurons are lost. We demonstrate that DA terminal density correlates with baseline striatal DA concentration ([DA]). Electrochemical and synaptosome studies in 6-OHDA lesioned rats and primates suggest that impaired striatal DA re-uptake and increased DA release from medial forebrain bundle fibres contribute to maintaining striatal DA levels. In lesioned rats where terminal density fell by 60% or more, L-DOPA administration increased striatal DA levels markedly. The striatal [DA] produced by L-DOPA directly correlated with the extent of dyskinaesia, suggesting that dyskinaesia was related to high striatal [DA]. While sprouting and decreased dopamine uptake transporter function would be expected to contribute to the marked increase in L-DOPA induced [DA], the increased [DA] was most marked when DAergic fibres were >60% denervated, suggesting that other release sites, such as serotonergic fibres might be contributing. In conclusion, the extent of dyskinaesia was directly proportional to the extent of DA terminal denervation and levels of extra-synaptic striatal DA. We propose that sprouting of DA terminals and decreased dopamine uptake transporter function prevent the appearance of Parkinsonian symptoms until about 60% loss of nigral neurons, but also contribute to dysregulated striatal DA release that is responsible for the emergence of dyskinaesia and 'wearing off'.

title: Population structure of and mycotoxin production by Fusarium graminearum from maize in South Korea.
abstract: Fusarium graminearum (Gibberella zeae) is an important pathogen of wheat, maize, barley, and rice in South Korea, and harvested grain often is contaminated with trichothecenes such as deoxynivalenol and nivalenol. In this study, we examined 568 isolates of F. graminearum collected from maize at eight locations in South Korea. We used amplified fragment length polymorphisms (AFLPs) to identify four lineages (2, 3, 6, and 7); lineage 7 was the most common (75%), followed by lineage 6 (12%), lineage 3 (12%), and lineage 2 (1%). The genetic identity among populations was high (>0.98), and the effective migration rate between locations was higher than that between lineages. Female fertility varied by lineage: all lineage 7 isolates were fertile, while 70%, 26%, and 14% of the isolates in lineages 6, 3, and 2, respectively, were fertile. All lineage 3 and lineage 7 isolates produced deoxynivalenol, whereas most lineage 2 and 6 isolates produced nivalenol. Genotypic diversity in lineage 3 and lineage 6 populations is similar to that found in previously described Korean rice populations, but genotypic diversity in lineage 7 is much lower, even though similar levels of gene flow occur between lineage 7 populations. We conclude that lineage 7 was relatively recently introduced into South Korea, perhaps accompanying imported maize seeds.

title: Development of near-infrared fluorophore (NIRF)-labeled activity-based probes for in vivo imaging of legumain.
abstract: Asparaginyl endopeptidase, or legumain, is a lysosomal cysteine protease that was originally identified in plants and later found to be involved in antigen presentation in higher eukaryotes. Legumain is also up-regulated in a number of human cancers, and recent studies suggest that it may play important functional roles in the process of tumorigenesis. However, detailed functional studies in relevant animal models of human disease have been hindered by the lack of suitably selective small molecule inhibitors and imaging reagents. Here we present the design, optimization, and in vivo application of fluorescently labeled activity-based probes (ABPs) for legumain. We demonstrate that optimized aza-peptidyl Asn epoxides are highly selective and potent inhibitors that can be readily converted into near-infrared fluorophore-labeled ABPs for whole body, noninvasive imaging applications. We show that these probes specifically label legumain in various normal tissues as well as in solid tumors when applied in vivo. Interestingly, addition of cell-penetrating peptides to the probes enhanced cellular uptake but resulted in increased cross-reactivity toward other lysosomal proteases as the result of their accumulation in lysosomes. Overall, we find that aza-peptidyl Asn ABPs are valuable new tools for the future study of legumain function in more complex models of human disease.

title: Heritable Imprinting Defect Caused by Epigenetic Abnormalities in Mouse Spermatogonial Stem Cells1
abstract: Male germ cells undergo dynamic epigenetic reprogramming during fetal development, eventually establishing spermatogonial stem cells (SSCs) that can convert into pluripotent stem cells. However, little is known about the developmental potential of fetal germ cells and how they mature into SSCs. We developed a culture system for fetal germ cells that proliferate for long periods of time. Male germ cells from embryos 12.5–18.5 days postcoitum could expand by glial cell line-derived neurotrophic factor, a self-renewal factor for SSCs. These cells did not form teratomas, but repopulated seminiferous tubules and produced spermatogenesis, exhibiting spermatogonia potential. However, the offspring from cultured cells showed growth abnormalities and were defective in genomic imprinting. The imprinting defect persisted in both the male and female germlines for at least four generations. Moreover, germ cells in the offspring showed abnormal histone modifications and DNA methylation patterns. These results indicate that fetal germ cells have a limited ability to become pluripotent cells and lose the ability to undergo epigenetic reprogramming by in vitro culture.