Caroline Magnain

Age-Related Decline in Oligodendrogenesis Retards White Matter Repair in Mice

Background and Purpose— Aging is one of the major risk factors for white matter injury in cerebrovascular disease. However, the effects of age on the mechanisms of injury/repair in white matter remain to be fully elucidated. Here, we ask whether, compared with young brains, white matter regions in older brains may be more vulnerable in part because of decreased rates of compensatory oligodendrogenesis after injury. Methods— A mouse model of prolonged cerebral hypoperfusion was prepared by bilateral common carotid artery stenosis in 2-month and 8-month-old mice. Matching in vitro studies were performed by subjecting oligodendrocyte precursor cells to sublethal 7-day CoCl2 treatment to induce chemical hypoxic stress. Results— Baseline myelin density in the corpus callosum was similar in 2-month and 8-month-old mice. But after induction of prolonged cerebral hypoperfusion, older mice showed more severe white matter injury together with worse deficits in working memory. The numbers of newborn oligodendrocytes and their precursors were increased by cerebral hypoperfusion in young mice, whereas these endogenous responses were significantly dampened in older mice. Defects in cyclic AMP response element-binding protein signaling may be involved because activating cyclic AMP response element-binding protein with the type-III phosphodiesterase inhibitor cilostazol in older mice restored the differentiation of oligodendrocyte precursor cells, alleviated myelin loss, and improved cognitive dysfunction during cerebral hypoperfusion. Cell culture systems confirmed that cilostazol promoted the differentiation of oligodendrocyte precursor cells. Conclusions— An age-related decline in cyclic AMP response element-binding protein–mediated oligodendrogenesis may compromise endogenous white matter repair mechanisms, and therefore, drugs that activate cyclic AMP response element-binding protein signaling provide a potential therapeutic approach for treating white matter injury in aging brains.

Blockface histology with optical coherence tomography: A comparison with Nissl staining

Spectral domain optical coherence tomography (SD-OCT) is a high resolution imaging technique that generates excellent contrast based on intrinsic optical properties of the tissue, such as neurons and fibers. The SD-OCT data acquisition is performed directly on the tissue block, diminishing the need for cutting, mounting and staining. We utilized SD-OCT to visualize the laminar structure of the isocortex and compared cortical cytoarchitecture with the gold standard Nissl staining, both qualitatively and quantitatively. In histological processing, distortions routinely affect registration to the blockface image and prevent accurate 3D reconstruction of regions of tissue. We compared blockface registration to SD-OCT and Nissl, respectively, and found that SD-OCT-blockface registration was significantly more accurate than Nissl-blockface registration. Two independent observers manually labeled cortical laminae (e.g. III, IV and V) in SD-OCT images and Nissl stained sections. Our results show that OCT images exhibit sufficient contrast in the cortex to reliably differentiate the cortical layers. Furthermore, the modalities were compared with regard to cortical laminar organization and showed good agreement. Taken together, these SD-OCT results suggest that SD-OCT contains information comparable to standard histological stains such as Nissl in terms of distinguishing cortical layers and architectonic areas. Given these data, we propose that SD-OCT can be used to reliably generate 3D reconstructions of multiple cubic centimeters of cortex that can be used to accurately and semi-automatically perform standard histological analyses.

Optical coherence tomography visualizes neurons in human entorhinal cortex.

Abstract. The cytoarchitecture of the human brain is of great interest in diverse fields: neuroanatomy, neurology, neuroscience, and neuropathology. Traditional histology is a method that has been historically used to assess cell and fiber content in the ex vivo human brain. However, this technique suffers from significant distortions. We used a previously demonstrated optical coherence microscopy technique to image individual neurons in several square millimeters of en-face tissue blocks from layer II of the human entorhinal cortex, over 50  μm in depth. The same slices were then sectioned and stained for Nissl substance. We registered the optical coherence tomography (OCT) images with the corresponding Nissl stained slices using a nonlinear transformation. The neurons were then segmented in both images and we quantified the overlap. We show that OCT images contain information about neurons that is comparable to what can be obtained from Nissl staining, and thus can be used to assess the cytoarchitecture of the ex vivo human brain with minimal distortion. With the future integration of a vibratome into the OCT imaging rig, this technique can be scaled up to obtain undistorted volumetric data of centimeter cube tissue blocks in the near term, and entire human hemispheres in the future.

Holographic laser Doppler ophthalmoscopy.

We report laser Doppler ophthalmoscopic fundus imaging in the rat eye with near-IR heterodyne holography. Sequential sampling of the beat of the reflected radiation against a frequency-shifted optical local oscillator is made onto an array detector. Wide-field maps of fluctuation spectra in the 10 Hz to 25 kHz band exhibit angiographic contrasts in the retinal vascular tree without requirement of an exogenous marker.

Skin color modeling using the radiative transfer equation solved by the auxiliary function method

The auxiliary function method is an efficient technique for solving the radiative tranfer equation without adding any assumption and was applied until now only for theoretical stratified media. The first application (to our knowledge) of the method to a real case, the human skin, is presented. This makes it possible to validate the method by comparing model results with experimental reflectance spectra of real skin. An excellent agreement is obtained for a multilayer model of the skin made of 22 sublayers and taking into account the anisotropic phase function of the scatterers. Thus there is the opportunity to develop interest in such models by quantitatively evaluating the influence of the parameters commonly used in the literature that modify skin color, such as the concentration of the scatterers and the thickness of each sublayer.

Skin color modeling using the radiative transfer equation solved by the auxiliary function method: inverse problem

In a previous article [J. Opt. Soc. Am. A 24, 2196 (2007)] we have modeled skin color using the radiative transfer equation, solved by the auxiliary function method. Three main parameters have been determined as being predominant in the diversity of skin color: the concentrations of melanosomes and of red blood cells and the oxygen saturation of blood. From the reflectance spectrum measured on real Caucasian skin, these parameters are now evaluated by minimizing the standard deviation on the adjusted wavelength range between the experimental spectrum and simulated spectra gathered in a database.

UV-fluorescence spectroscopy for identification of varnishes in works of art: influence of the underlayer on the emission spectrum

The identification of varnishes may be essential for the choice of the appropriate solvent during their removal by restorers. This recognition is obtained by UV-fluorescence emission spectroscopy with a quasi-monochromatic UVexcitation. A new portable instrument has been developed in order to implement non-destructive, contactless and in situ measurements, providing results in real time. The method is applied to the analysis of a real ancient painting. The resin-based varnish, the recipe and the state of degradation of the varnish are deduced in different locations of the painting by comparison with a database of reference varnishes. Moreover, spectral data are compared with the Fluorescence Lifetime Imaging (FLIM) analysis, performed on the same painting. Different areas containing the same varnish can then be localized on the whole painting. These results show that both UV-fluorescence methods are complementary for rapid and in situ analysis of varnishes of an entire work of art. Nevertheless, the paint layer beneath the varnish modifies the varnish fluorescence spectrum thus complicating its recognition. Indeed, the possible fluorescence of the binder of the paint layer or its reflectance spectrum must be taken into account. A systematic experimental study on fresh and aged model samples made of different varnishes, pigments and binders is presented in this work. It shows that UV-fluorescence emission spectra and diffuse reflectance spectra must be coupled to extract the fluorescence of the single varnish. Both spectra can be recorded by the presented instrument. A new theoretical approach is summarized in order to explain this phenomenon.

Contribution of surface state characterization to studies of works of art

This paper has two purposes. The first one underlines that qualitative and quantitative studies of surface states lead to relevant information for analyzing works of art, with lots of potential for art history, restorers, and curators. The discrimination between different artistic techniques and the influence of a varnish on the leveling of paint surfaces are presented. The second purpose is the comparison between different nondestructive optical topographic methods, i.e., goniophotometry, optical coherence topography, and confocal microscopy, according to their accuracy, their discriminatory ability, their practicability inside a museum, and the size limits of the studied objects.

as-PSOCT: Volumetric microscopic imaging of human brain architecture and connectivity

ABSTRACT Polarization sensitive optical coherence tomography (PSOCT) with serial sectioning has enabled the investigation of 3D structures in mouse and human brain tissue samples. By using intrinsic optical properties of back‐scattering and birefringence, PSOCT reliably images cytoarchitecture, myeloarchitecture and fiber orientations. In this study, we developed a fully automatic serial sectioning polarization sensitive optical coherence tomography (as‐PSOCT) system to enable volumetric reconstruction of human brain samples with unprecedented sample size and resolution. The 3.5 &mgr;m in‐plane resolution and 50 &mgr;m through‐plane voxel size allow inspection of cortical layers that are a single‐cell in width, as well as small crossing fibers. We show the abilities of as‐PSOCT in quantifying layer thicknesses of the cerebellar cortex and creating microscopic tractography of intricate fiber networks in the subcortical nuclei and internal capsule regions, all based on volumetric reconstructions. as‐PSOCT provides a viable tool for studying quantitative cytoarchitecture and myeloarchitecture and mapping connectivity with microscopic resolution in the human brain.

Characterizing the optical properties of human brain tissue with high numerical aperture optical coherence tomography

Quantification of tissue optical properties with optical coherence tomography (OCT) has proven to be useful in evaluating structural characteristics and pathological changes. Previous studies primarily used an exponential model to analyze low numerical aperture (NA) OCT measurements and obtain the total attenuation coefficient for biological tissue. In this study, we develop a systematic method that includes the confocal parameter for modeling the depth profiles of high NA OCT, when the confocal parameter cannot be ignored. This approach enables us to quantify tissue optical properties with higher lateral resolution. The model parameter predictions for the scattering coefficients were tested with calibrated microsphere phantoms. The application of the model to human brain tissue demonstrates that the scattering and back-scattering coefficients each provide unique information, allowing us to differentially identify laminar structures in primary visual cortex and distinguish various nuclei in the midbrain. The combination of the two optical properties greatly enhances the power of OCT to distinguish intricate structures in the human brain beyond what is achievable with measured OCT intensity information alone, and therefore has the potential to enable objective evaluation of normal brain structure as well as pathological conditions in brain diseases. These results represent a promising step for enabling the quantification of tissue optical properties from high NA OCT.